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YATS – Yet Another Tiny Simulator User's Manual for Version 0.3

1. For both strings it is possible to write the word NoExt This specifies the input with out extension input name equals object name mux AliasInput NoExt gt I 10 I 10 is reachable via the pure multiplexer name snk AliasInput Data gt NoExt snk is reachable via snk Data too YATS Yet Another Tiny Simulator User s Manual for Version 0 3 11 The command AliasInput does not perform any checks whether the given original input name exists Thus errors are detected lateron during connection setup Recursive aliasing is not supported 5 0 Statistical Evaluation Simulation Control 5 1 Calculation of Confidence Intervals Confidence intervals can be calculated using the object class ConfidObj Such an object is defined like a normal network object but it does not have network object functional ity Commands to add measured values to a dynamic array managed by the object and to ask for statistics and confidence interval bounds are provided Older macro based versions to calculate confidence intervals can be found in Section 11 5 on page 51 Declaration ConfidObj conf LEVEL 0 99 LEVEL optional level of confidence Default 0 95 For other values see below If LEVEL is not given then also the has to be left out For LEVEL the values 0 9 0 95 0 975 and 0 99 are supported The object has to be defined before the first simu lation run Si
2. 7 0 Available Network Object Classes 7 1 Sources 7 1 1 CBR Source Declaration CBRquelle src DELTA 5 VCI 1 OUT line DELTA cell distance integer VCI VC number of generated cells OUT input name of the succeeding object Exported variables src gt Count Returns the number of sent cells Commands src gt ResCount Resets the cell counter src Restart Sets a new cell phase random Output data type Cell 7 1 2 Bernoulli Source Declaration GEOquelle src ED 4 5 VCI 1 OUT line ED mean of the geometrically distributed cell distance double VCI VC number of generated cells OUT input name of the succeeding object Exported variables src Count number of sent cells Commands src ResCount Resets the cell counter YATS Yet Another Tiny Simulator User s Manual for Version 0 3 14 Output data type Cell 7 1 3 Source with Arbitrarily Distributed Cell Distances Declaration DistSrc src DIST dist VCI 1 OUT line DIST name of the distribution object providing the distribution VCI VC number of generated cells OUT input name of the succeeding object Function The source uses the distribution table of a distribution object which has to be declared in advance Distribution object Section 7 2 on page 17 Exported variables src Count number of sent cells Commands src ResCount Resets the cell counter Output data type Cell 7 1 4 ON OFF Source with Geometrical
3. Returns the emperical variance of the values collected so far ConfBase refObj refMean refWidth Calculates mean and half interval width as Confid Example include MACROS Var i nruns nruns 9 define the object abc ConfObj abc 0 95 nruns do the measurements YATS Yet Another Tiny Simulator User s Manual for Version 0 3 52 for i 1 to nruns ConfAdd ref abc i i is our measurement print results print ConfLo ref abc Nt ConfMean ref abc Nt ConfUp ref abc n YATS Yet Another Tiny Simulator User s Manual for Version 0 3 53
4. Yet Another Tiny Simulator User s Manual for Version 0 3 32 FRTT in the given version can not be determined during connection setup it has to be given explicitly The ABR source needs a data source implementing the start stop protocol e g Gmdp Stop see Section 9 3 on page 44 Otherwise error messages are generated upon input buffer overflow The exact internal behaviour of the source timer actions are documented in the source code file abrsrc c Exported Variables The following variables are exported for use with commands or measurement devices e src CountData number of data cells sent int e Ssrc CountRMCTI number of in rate RM cells sent int e src CountRMCO number of out of rate RM cells sent int e src QLen current input queue length int e Src IAT current IAT int changes permanently due to non interger cell spacing e Src ACR current ACR double Data types Atsrc src Start andsrc Stop cells are expected At sr c BRMC RM cells are expected 7 10 2 ABR Multiplexer Declaration AbrMux mux NINP 10 MAXVCI 100 BUFFCBR 200 BUFFABR 10000 BUFFRMCO 1000 HI THRESH 7000 LO THRESH 5000 TBE 2000 AI 30 CBRI 100 ZOL 12 5 LINKCR 2 2e5 TARGUTIL 0 9 DYNFAIRSHARE BINMODE OUTBRMC dmx OUTDATA line NINP number of inputs int MAXVCI largest VCI number possible int BUFFCBR buffer size for non ABR traffic int BUFFABR overall buffer for ABR traffic int BUFFRMCO optional ma
5. DELTA distance between two generated frames time slots LEN length of one frame bytes StartTime optional when to start to send see below default DELTA EndTime optional when to stop to send time slot default virtually infinite BYTES with wich byte stop to send default virtually infinite CONNID optional layer 4 connection ID of the generated frames default 0 OUT where to send frames generated Function This object class can be used to model bulk data transfer for TCP see Section 7 11 1 on page 35 Every DELTA th time slot a frame of length LEN is sent The object rec ognizes the start stop protocol Section 9 3 on page 44 the control input for this pur pose is src gt CTRL If StartTime is given and greater than zero the object begins to send at this instant In case StartTime is set to zero then the object begins to send between time slot 0 and 500 000 random choice equally distributed Output data type Frame 7 11 4 TCP Application Arbitrary Frame Distances The object class Data2F rame converts each incoming data item e g cell into a frame with constant length Hence it is possible to use the variety of cell sources for the generation of frames Declaration Data2Frame d2f FLEN 20 CONNID 10 OUT tss FLEN length of generated frames int CONNID optional layer 4 identifier default 0 OUT where to send frames In order to connect this object to a TCP sender or a
6. san error n exit 1 getX lit id s gt Count macro resX id command Reset lit id s gt ResCount MacroShell X ARGS lit81 MACRO defX string 81 CMD Reset MACRO resX no parameters no return value CMDV Get int MACRO getX integer parameter returns a value bla gt Reset print bla gt Get 1 bla Get 1 n bla gt Get 2 we should see our error message YATS Yet Another Tiny Simulator User s Manual for Version 0 3 50 11 3 2 NULL Value for Identifier Arguments For the definition of sub models with optional outputs like for a measurement device the following might be useful Default arguments of type lit identifier can have the default vale 0 This leads to an empty identifier The normally applied cast to string then results in the empty string which in turn can be tested by the macro Example macro hh id oo fy if oo Meas2 lit id MAXCTD 10 MAXIAT 10 else Meas2 lit id MAXCTD 10 MAXIAT 10 OUT lit o0 MacroShell HH ARGS lit81 OUT 1it 2 default 0 MACRO hh string 81 string 2 print HH hl OUT snk Senke snk HH h2 no succeeding object 11 4 Regarding Global Variables The following restrictions apply e When a global variable is defined then it is checked that currently no other variable macro or object with the same name is defined in any surrounding bl
7. whereas the normal print uses the stdout stream with fflush stdout at the end of each print statement print fdl fd2 generates the out put for all file descriptors in the list statement statement Block the is part of the statement like in C When the block is left then all var iables and macros defined inside are deleted This does not hold for globals see Section 11 4 on page 51 macro ID listOfFormalParameters block Definition of a macro The formal parameters if any are local to the block block statements The parameter names are separated by commas For examples see file MACROS and Section 4 1 on page 8 Note macro names cannot be over riden when entering a new block variables can however Nevertheless a macro is local to a block and is deleted when the block is left macroID expression Assignment of the macro return value rather like in PASCAL Inside of the macro body this assignment can be done arbitrarily often The macro returns the value from the last assignment If no such assignment is processed then the macro cannot be used in expressions error message otherwise macroID listOfExpressions V YATS Yet Another Tiny Simulator User s Manual for Version 0 3 3 Macro call The expressions in the list are the actual parameters they are seperated by commas The number of actual
8. BUFF 1000 TARGBUFF 500 HI THRESH 800 LO THRESH 600 AI 100 LINKCR 2 2e5 TARGUTIL 0 9 OUTBRMC line OUTDATA aal5 BUFF output buffer size int ATTENTION see below TARGBUFF optional buffer occupation at which to decrease ER default BUFF 2 HI THRESH optional turn congestion indication on int default BUFF LO THRESH optional turn congestion indication off int default HI THRESH AI optional measurement interval for output rate measurement default 30 LINKCR optional output link cell rate cells per second double default 353207 55 TARGUTIL optional ER reduction factor see below Default 1 0 OUTBRMC where to send backward RM cells OUTDATA where to send data cells Function AbrSrc implements an ABR sink which also can act as virtual sink The sink function is very simple RM cells are reflected towards the SES DIR bit set BN bit cleared Data cells are passed to the next object ATTENTION Also if the next object never stops the ABR sink the BUFF value limits the TBE value negotiated during connection setup So set BUFF high enough in any case Backpressure The binary feedback is performed as in the ABR multiplexer described If the current output buffer occupation reaches TARGBUFF due to stop send caused by the data sink or next ABR control loop ER is reduced to TARGUTIL times the current output link rate The latter one is measured over AI time slots For the start stop protocol see Section 9 3 on
9. DELTA 10000 FILE abr pos Meter mq VAL abrmuxl QLenABR TITLE Queue Len in muxabr1 WIN 200 200 400 200 MODE AbsMode NVALS 1000 MAXVAL 10000 DELTA 100 UPDATE 100 Meter mqz VAL abrmux1 2 TITLE Z in muxabrl WIN 200 200 400 200 MODE AbsMode NVALS 1000 MAXVAL 5 DELTA 100 UPDATE 100 Meter mqnabr VAL abrmux1 CRNABR TITLE CRNABR in muxabr1 WIN 200 200 400 200 MODE AbsMode NVALS 1000 MAXVAL 4e5 DELTA 100 UPDATE 100 Meter mqabr VAL abrmux1 CRABR TITLE CRABR in muxabr1 WIN 200 200 400 200 MODE AbsMode NVALS 1000 MAXVAL 4e5 DELTA 100 UPDATE 100 Meter ml VAL abrsrc 1 gt ACR TITLE ACR abrsrc 1 YATS Yet Another Tiny Simulator User s Manual for Version 0 3 47 WIN 700 200 400 200 MODE AbsMode NVALS 1000 AXVAL 10000 DELTA 100 UPDATE 100 eter mlir VAL abrsrc 1 CountData TITLE data abrsrc 1 WIN 700 200 400 200 MODE TA 1000 iffMode NVALS 100 DATE 10 CI TITLE RMCI abrsrc 1 i Oo ll o D U eter mlirm VAL abrsrc 1 gt Count WIN 700 200 400 200 MO U R O U AXVAL 100 DEL JE Uc iral ll Ho eens Fh rh AXVAL 100 DELTA 1000 DATE 10 eter mlor VAL abrsrc 1 CountRMCO TITLE RMCO abrsrc 1 WIN 700 200 400 200 MODE DiffMode NVALS
10. If MAXCID has been given then the translation table can be filled using com mand SetVCI On input and output the start stop protocol see Section 9 3 on page 44 is supported The data input is aals gt Data the control input is aals Start Commands YATS Yet Another Tiny Simulator User s Manual for Version 0 3 27 aals ResetStat Resets all statisitcs counter aals gt SetVCI cid voci Write translation table connection ID cid is converted in VCI vci Exported Variables For use in commands and with display devices the following variables are exported aals QLen current input queue length aals CellCount number of cells sent aals SDUCount number of AAL SDUS sent aals DelCount number of incoming data items dropped since start stop not recognized Input Data Type Data on inputs gt Data and gt Start Output Data Types OUTDATA AALSCell OUTCTRL Data 7 8 2 AAL 5 Receiver Declaration AAL5Rec aalr OUT tcpr OUT where to send reconstructed data items Function Data items segmented by the corresponding AAL 5 sender are reassembled Cell and SDU losses are detected using sequence numbers The incomming frame is embedded into the first cell of the burst generated by the sender Additionally the first cell carries the SDU sequence number All cells contain a cell sequence number therefore the receiver can detect cell loss and flushes its input cell queue w
11. Section 7 1 6 on page 16 The distribution must not have a nonzero probability for the r v value zero There is a couple of versions to specify the distribution Distribution dist FILE xyz YATS Yet Another Tiny Simulator User s Manual for Version 0 3 17 In the given ASCII file each line contains the r v value integer greater than zero ascending order and the associated probability double The values are delimited by white space R v values with probability zero can be omitted A marks the rest of a line as comment Distribution dist TABLE 1 0 5 2 0 5 The probabilities are directly given in the input text Distribution dist DISTRIB x x min to x max 1 0 1 x max x min Calculation of the distribution from a formula The variable x has to be defined in advance the formula can be an arbitrary double expression In case of very long distributions the repeated interpretative evaluation can become slow Distribution dist GEOMETRIC E 4 5 Gemetrical distribution with the given mean The distribution is shifted by one i e P X 0 0 Distribution dist BINOMIAL N 20 P 0 5 Binomial distribution with parameters n and p The distribution is shifted by one i e P X20 20 7 3 Multiplexer 7 3 1 Standard Multiplexer Arrival First Declaration Multiplexer mux NINP 10 BUFF 50 MAXVCI 50 OUT sink NINP number of inputs integ
12. a segment of half of the receiver s buffer size is sent always Nagle s algorithm according to RFC 1122 section 4 2 3 4 See remarks to SWS Karn s algorithm no RTT measurement during retransmissions e Fast retransmission and recovery RTT measurement with time stamp option according to RFC 1323 After connection setup both TCP sender and receiver know the identity of the peer object The identifiers are written in each frame sent data and ACK frames Thus checks can be performed whether an arriving frame stems from the peer object or whether it has arrived due to erroneous routing problem in large network configura tions Error messages are launched in this case Remarks The object DOES NOT YET IMPLEMENT the zero windo probe if an acknowledge ment packet reopening the receiver window is lost then the connection stops for ever To model the socket interface input t cps Data in a useful way the sending object already has to split available data into pieces of e g 4096 bytes This is necessary since the start stop protocol does not yet allow a partial reject of a received data item YATS Yet Another Tiny Simulator User s Manual for Version 0 3 36 Exported Variables An object exports the following variables for use with commands or measurement devices tcps NXT data sequence number next to send bytes tcps UNA first unacknowledged data sequence number bytes tcps gt RTT
13. estimated round trip time in ticks tcps RTTreal real measured in the simulator round trip time in time slots tcps gt RTOcalc retransmission timeout value most recently calculated from RTT tcps WND receiver window size currently seen bytes tcps WND MIN tcps WND MAX min an max WND tcps CWND current congestion widow size bytes tcps gt INPQ tcps INPOQ LEN current input queue length bytes tcps INPO MAX LEN max INPOQ LEN tcps PRCOQ LEN current processing queue length queue models PROCTIM tcps gt PRCQ_MAX_LEN max PRCQ_LEN tcps REXMTO number of retransmission timeouts tcps RECEIVED BYTES number of bytes received from the application tcps XMITTED BYTES total number of bytes sent with headers and retransm tcps XMITTED USER BYTES the same but without headers tcps XMITTED SEGMENTS overall number of packets sent tcps REXMITTED BYTES total number of retransmitted bytes headers included tcps REXMITTED SEGMENTS number of packets retransmitted tcps RECEIVED ACKS number of received ack packets tcps REX PERC current percentage of retransmissions Commands The command t cps ResetsStat resets the following variables INPQ MAX LEN PRCQ MAX LEN REXMTO RECEIVED BYTES XMITTED BYTES XMITTED USER BYTES XMITTED SEGMENTS REXMITTED BYTES REXMITTED SEGMENTS RECEIVED ACKS REX PERC Data types Input tcps gt Data Frame Input tcps Start Data Input teps gt Ack TCPAcknowle
14. ACTIVE optional serve output queue only every ACTIVE th time slot OUT where to send cells Function Multiplexer with Departure First strategy Inputs are served in random order The out put queue is served only during each ACTIVE th time slot in case ACTIVE is given Remark Lax Model The model is simple a queue comprises both the real queue places and the server place A deomon at multiplexer output scans the queue during each ACTIVE th time slot and sends a data item if available Thus some data may stay in the server for less then ACTIVE time slots For more sophisticated models see multiplexers in Section 7 4 on page 22 Exported Variables and Commands like for Multiplexer see Section 7 3 1 on page 18 7 3 3 Multiplexer with Lower Output Rate Arrival First MuxAF mux NINP 10 BUFF 100 MAXVCI 100 ACTIVE 4 OUT line Declaration function and commands as for MuxDF The server strategy is Arrival First Remark Lax Model The model is simple a queue comprises both the real queue places and the server place A deomon at multiplexer output scans the queue during each ACTIVE th time slot and sends a data item if available Thus some data may stay in the server for less then ACTIVE time slots For more sophisticated models see multiplexers in Section 7 4 on page 22 7 3 4 Multiplexer with Arbitrarily Distributed Serving Time Declaration MuxDist mux NINP 10 BUFF 50 MAXVCI 100 DIST serv dist OUT
15. Filsrc src FILE trace bin REPEAT 10 START 20 WAIT 100000 VCI 1 OUT line FILE name of the file containing the inter arrival times see below REPEAT number of trace repetitions Can be omitted then the file is read once START start with the START th entry in the trace file WAIT wait WAIT time slots before sending first cell Can be omitted VCI VC number of generated cells OUT input name of the succeeding object Function The object reads the inter arrival times from the given trace file The stored IAT values are in binary format unsigned integer In case of entries with IAT zero the source fails The parameters REPEAT START and WAIT are optional Exported variables src Count number of sent cells Commands src ResCount Resets the cell counter Output data type Cell 7 1 9 Source Sending a Directly Given Cell Sequence Declaration ListSrc src N 3 DELTA 10 10000 5 VCI 1 OUT line N number of cells int DELTA inter departure times first cell sent at the first DELTA int VCI VCI number of cells generated int OUT where to send cells Exported variables Src Count number of sent cells Commands Src ResCount Resets the cell counter Output data type Cell 7 2 Definition of Distributions A distribution object generates a r n transformation table from a given distribution This table can be imported by other objects see e g DistSrc Section 7 1 3 on page 15 and GMDPquelle
16. Hn 43 9 1 Used Data Object Classes Derivation Relations sese 43 9 2 Data Object Embedding otro ri e t P ete 44 9 3 Start Stop Protocol nee eie ee toe eres POP Ere A a inner ER 44 EXaInpleSad uon adii d tee EU RE utate eria a UV MIS 44 10 1 Complete Simulation Series with Confidence Intervals 44 10 2 ABR Multiplexer Graphical Online Displays eseeee 46 Some Further NOES vs dou aeri tci uer danas pL orbi Vu AREE Mit Stra dress 48 11 1 Regarding References iere e n eta eene ete een 48 112 a Regarding Literals senn Reno Ree abes 49 11 3 Regarding Macro Shells 52 nce ette tette teer ipe dede e etes 49 11 3 1 Commands to Macro Shell Objects seseeeee 49 YATS Yet Another Tiny Simulator User s Manual for Version 0 3 11 3 2 NULL Value for Identifier Arguments sese 51 11 4 Regarding Global Variables eese eee 51 11 5 Regarding Confidence Intervals seen 51 bl BastcMAcos sese onPRO ecd nutu 51 11 5 2 More Convenient Evaluation of Confidence Intervals 52 YATS Yet Another Tiny Simulator User s Manual for Version 0 3 iii 1 0 Introduction YATS is a small discrete time simulation tool tailored for investigations of ATM net works The tool is grown up during 1995 1996 at the chair for telecommunications
17. VCI 1 OUT demux TYPE data item type VCI if given can be omitted only data items on this VCI are checked OUT input name of the succeeding object Function The object ensures that all passing data items are of the specified class or of a class which is derived from the given one Violating data items cause an error message Fur thermore data items are accepted only in the early slot phase and receiving more than one item per time slot causes an error message No commands 7 12 3 Dummy Connection Object When using e g loops to describe networks structures then sometimes some names do not fit at all into the rule which is given for the whole loop To translate names this dummy object is usefull It really does nothing than forwarding an incomming data item to its output DummyObj dmy OUT line YATS Yet Another Tiny Simulator User s Manual for Version 0 3 40 7 12 4 A Class Implementing Non Local Variables Variables are local to the enclosing block It is therefore not possible to create auxiliary variables with macros Since objects are not local to the block of definition a special object class may solve some problems ValArray arr LEN 10 This defines an object containing an array of double values The values can be written with arr gt Set index value where index is an integer between 0 and LEN 1 The values can be read with arr Get index 8 0 Graphical Online Displays 8 1 Interactive Cont
18. displays can be defined These objects ask network objects for exporting addresses of variables to be displayed and process and display the values on their own This ensures that the complexity of network objects is independent of the possibilities for measurement and online display example input file var i nsrc load sent declaration of variables nsrc 10 load 0 95 10 Bernoulli sources for i 1 to nsrc GEOquelle src i ED nsrc double load VCI i OUT mux gt I i a multiplexer with buffer size 20 Multiplexer mux NINP nsrc BUFF 20 OUT sink the sink Senke sink simulate 100000 time slots Sim Run SLOTS 100000 print results sent 0 for i 1 to nsrc sent sent src i Count print cells sent sent Mn print CLR in mux mux Losses 1 nsrc double sent NAnfes end of example More complex examples using also macros can be found in Section 10 0 on page 44 3 0 Syntax of the Input Language 3 1 Statements Statements are e classID declaration Definition of a network object The syntax of the definition is determined by the net work object class implementation e objectID command Command to an network object The syntax of the command is determined by the network object class implementation e var listOfIDsWithOptionalInit YATS Yet Another Tiny Simulator User s Manual for Ve
19. for Cells and Frames 30 7 9 3 Updating Time Stamps eese enne 32 710 ABR ATM Forum TM 4 0 sees nennen enne nre ennt 32 TAO Ts ABR SOUT E niere etr er PERRO RR E NE ese IRE 32 7 02 ABR Multiplexer iie ete eter hots eas ER tie Cs 33 TIO ABR SIDE rone eR prO RR ERU REED HERE 35 7 11 TCP Connecti ri ro Rent rRNA E GE e ERREUR PANES ERKEUR 35 Jp TCR Sender sarrerei oeras DERE REED Db DERE 35 3112 TOP RGCOIV6r sch ete rere Petty ec om ri eei 37 7 11 3 TCP Application Constant Frame Distances eee 39 7 11 4 TCP Application Arbitrary Frame Distances sees 39 7 12 Miscellaneous mte eap darn 40 TIZI Signalling source nii mettez eee i Ries 40 7 12 2 Data type and timing checks 20 eee cee ceceeeeeeceeeeeeceseeeeeeseeeaecneecaeenaes 40 7 12 3 Dummy Connection Object esssesesseeeeeeeeeee enne enenne 40 7 12 4 A Class Implementing Non Local Variables sssss 4l Graphical Online Dis player ossa nen be ote p o sca eme aiuta 4 8 1 Interactive Control Window sees eene ener nennen nete ennnr ene 41 8 2 Sliding Time History of a Value esee eerte ener enne 41 8 3 Histogram of a Distribution eren enne enne 42 8 4 Production of a Distribution from Samples of a Value esses 43 Data Object C Iasses eom seti ive a nre ou Ges ng Hines aegre qu d na Peu Pa
20. macro calls The class MacroShell provides a better interface for the macro It allows to define whole sub models implemented by macros like normal network objects For larger sub models it might be worthwhile to write such an interface which provides typed arguments and also allows for optional arguments with default values see Section 4 2 on page 10 It is also possible to translate commands directed to a macro shell object into macro calls see Section 11 3 1 on page 49 The definition of macro endsys remains the same Interface MacroShell EndSys Arguments 1 amp 4 are identifiers keyword lit argument 2 is double argument 3 is integer The given keywords are expected none for arg 1 ARGS lit81 LOAD double 2 DELAY int 3 OUT 1it 4 arguments 1 amp 4 are casted to strings MACRO endsys string 81 2 3 string 4 var i for i L to 10 EndSys src i LOAD 0 05 DELAY i OUT mux gt I Multiplexer mux NINP 10 BUFF 100 OUT snk Senke snk Sim gt Run SLOTS 500 print sre li 9scounb wns H i YATS Yet Another Tiny Simulator User s Manual for Version 0 3 9 4 2 Macro Shells Macros are useful to define sub models in a modular model description but the code applying these macros becomes less readable see Section 4 1 on page 8 The object class MacroShell provides a better interface to the macro implementation allowing a read a
21. note here The possible inclusion of input name extensions is based on two facts Firstly lit does only check that its argument does not contain white space or the special character 001 which is essential for references Thus in principle all fency identifiers can be generated Secondly the routine used by network objects when evaluating names of their succeeding objects is based on the same piece of code also implementing the lax lit transformation kernel id c parse id An important consequence of this by chance possibility is that it unfortunately does not work for commands and exported variables There the whole thing has to be split ted into two parts e g Senke sink does NOT work syntax error print lit sink Count An works fine print lit sink lit Count An 11 3 Regarding Macro Shells 11 3 1 Commands to Macro Shell Objects Together with the instantiation of a macro shell an object can be created and com mands can be directed later on to the interface object These commands are mapped into macro calls This is only possible if 1 the macro shell has at least one argument and 2 the first argument is of type lit identifier The actual value of this argument is taken as name of the generated interface object YATS Yet Another Tiny Simulator User s Manual for Version 0 3 49 It is then possible to include a list of command specifications in
22. one The decision about serving order is made as follows A global variable Spacing Time it is common for all VCs always contains the Virtual Time of the last cell which has left the multiplexer This Virtual Time has been assigned to the cell when it was entering the sort queue the preceeding cell of this VC just had been served or the VC recently had not been present in the sort queue The Virtual Time is always set to the current Spacing Time plus the inverse mean cell rate of the new cell s connection registered at the multiplexer The sort queue serves cells in the order corresponding to their Virtual Times The effect of the algorithm is that a cell entering the sort queue can overtake other cells if its inverse mean cell rate is low enough compared to the other connections already waiting in the queue In the current implementation the sort queue does not really hold cells but only refers to the corresponding VC queues A cell is dequeued from a VC queue in the instance it has to be sent and the Virtual Time is assigned to the whole associated VC queue Thus possibly one additional buffer place might be needed in each VC queue com pared to the original algorithm Exported Variables additional to Multiplexer see Section 7 3 1 on page 18 mux gt QLenVCl vc current queue length of this VC Commands additional to Multiplexer see Section 7 3 1 on page 18 mux gt SetPar vci invCellRate BufSiz The
23. or if possible the generation by a template In the second case above i the variable has to be defined in advance and is counted from 1 to NOUT In the third case i a list of ranges can be specified A range is given in the form i to k the first range has to start with 1 the last has to end with NOUT A range with one member can be written short only the one number all ranges in the list are seperated by commas If a cell with unassigned VCI is received an error message is generated No commands Input data type Cell 7 6 Sinks Delay Line 7 6 1 Sink Declaration Senke snk Exported variables YATS Yet Another Tiny Simulator User s Manual for Version 0 3 24 snk Count number of arrived cells Commands snk ResCount Resets the counter Input data type Data 7 6 2 Sink Writing IATs to a Trace File Declaration SinkTrace snk FILE iat dat All functions as Senke see Section 7 6 1 on page 24 additionally the inter arrival times are written to the given file ASCII format one IAT per line 7 6 3 Delay Line Declaration Leitung line DELAY 100 OUT meas DELAY delay of the line integer in time slots OUT input name of the succeeding object No commands Input data type Data 7 7 Shaping Policing 7 7 1 Peak Rate Shaper with Integer Cell Spacing Declaration Shaper shap DELTA 10 BUFF 100 OUT line DELTA cell spacing enforced by the shaper time slots i
24. page 44 the source has an input src gt Start Exported Variables An object exports the following variables for use with commands or measurement devices e sink Qlen current output queue length int sink Loss number of lost cells output buffer int sink CountData number of ABR data cells passed int e sink CountRMCI number of in rate RM cells reflected int e sink CountRMCO number of out of rate RM cells reflected int e sink CROut current output cell rate double Data Types Input sink expects Cell and RMCell at s ink Start Data is accepted 7 11 TCP Connections 7 11 1 TCP Sender Declaration YATS Yet Another Tiny Simulator User s Manual for Version 0 3 35 TCPIPsend tcps BUF int BSTART int MTU lt int gt TS lt 0 1 gt NAGLE lt 0 1 gt FRETR lt 0 1 gt BITRATE lt double gt PROCTIM lt double gt TICK double RTOMIN lt double gt OQWM lt int gt LOGRETR lt 0 1 gt REC lt object gt OUTDATA object input OUTCTRL object input BUF input buffer size bytes BSTART optional buffer occupation where to wake up sender default BUF 4096 MTU optional maximum output frame size bytes default 9180 bytes TS optional time stamp option RFC1323 on off default on NAGLE optional Nagle s algorithm RFC1122 on off default on FRETR optional fast retransmission and recovery on off default on BITRATE optional ATM la
25. sink YATS Yet Another Tiny Simulator User s Manual for Version 0 3 19 NINP number of inputs integer BUFF buffer size cells integer MAXVCI optional largest VC number for loss count default NINP DIST name of the distribution object defining service time distribution OUT input name of the succeeding object Function Multiplexer with Departure First strategy Inputs are served in random order The time spent in the server at queue output is distributed according to the specified distribution Distribution object Section 7 2 on page 17 Exported Variables and Commands like for Multiplexer see Section 7 3 1 on page 18 7 3 5 Multiplexer with Early Packet Discard Scheme Declaration MuxEPD mux NINP lt int gt BUFF int MAXVCI lt int gt THRESH lt int gt OUT lt object input gt NINP number of inputs BUFF buffer size in cells MAXVCI optional maximum VC number default NINP THRESH buffer occupation at which to begin to discard bursts OUT where to send cells Function The object implements an early packed discard strategy for all connections sending data type AALSCell see Section 9 1 on page 43 on VCI 0 to MAXVCI burst dura tions are kept track off With each beginning of a burst the current buffer occupation is compared to THRESH If this mark is reached then all cells of the burst are dropped Bursts which began successfully but nevertheless lost a cell due to background traf
26. the macro shell defi nitions The specifications are separated by commas each element beginning with key word CMD or CMDV CMD defines a command wich cannot be used in expressions The corresponding macro does not need to return a value With CMDV commands with return value are defined and the corresponding macro has to return a value syn tax error message otherwise The syntax of a command specification is as follows CMD CMDV cmdName cmdArgs MACRO macroName If the command name cmdName has no parameter then the part cmdArgs with brackets has to be skipped Parameters are specified using the type keywords int double or string Keywords and default values as for the macro shell itself are not supported The parameter specifications are separated by commas The macro name macroName has to expect nShell nCmd arguments where nShell is the number of arguments of the shell and nCmd is the number of command parameters The first nShell values passed to the macro are the values used for the instantiation of the macro shell They are followed by the nCmd values used in the command statement or expres sion Example macro defX id definition macro Senke lit id s do NOT use lit id this is used as name of the interface object macro getX id n command Get int if n 1 only to demo sth print 2 ad
27. 0 ROUTE 2 abrmx abrsnk AUTOCONN OUTCTRL src Start OUTDATA line BUFF input buffer size int BSTART buffer occupation at which to start again the data source int LINKCR optional output link cell rate cells per second double default 353207 55 MCR minimum cell rate cells per second double PCR peak cell rate cells per second double FRTT fixed round tripp time micro seconds double ROUTE ABR routing members see below AUTOCONN optional if given connection establishment with first incomming cell OUTCTRL control input of the data source start stop protocol OUTDATA ABR cell output Function The class AbrSrc implements the reference source behaviour of ATM Forum TM 4 0 All parameters not specified are set to the default values given in TM 4 0 The source possesses four inputs e input src data input e input src BRMC input for backward RM cells e input src Start an incomming cell causes connection establishment e input src Stop an incomming cell causes connection release If the output link rate LINKCR is not given then it is set to the equivalent of 149 76 Mbps The ROUTE contains first the number of ABR members and then the members itself These objects are contacted in the given order at first cell arrival in case AUTOCONN is given or at request for connection establishment on input src gt Start In both cases a connection with the VCI of the incomming cell is established Since YATS
28. 1 0 2 0 3 0 4 0 5 0 6 0 7 0 YATS Yet Another Tiny Simulator User s Manual for Version 0 3 Matthias Baumann Dresden University of Technology Communications Laboratory EntrOOUe HOT oos edema age is ed tool totes o ect eS ep eek 1 General Remarks Example Input File eene 1 Syntax of the Input Langage oie eode to oerte Ce R te ares eo eR tees hr eee 2 3 1 Statements sues eene etna Un HU d DU pet 2 3 2 Iden tiets thie sac ERI teet nette hi nia ted 4 3 3 Variables Expressions and Built In Functions eese 5 3 4 Include Files System Interface seen 7 3 5 References Literals 2 oec tiere tete t Eee SETS ERE xe ree egeo 7 Modular Description of Complex Network Structures 8 4 1 Commented Example pete qu tte e te rd pae ers 8 4 2 Macro Shell vice n ctore ete eet rie i metere atur e v Ere Re NR 10 4 3 Input Name Aliasing and Dummy Objects sesesseseeeneen 11 Statistical Evaluation Simulation Control eee 12 5 1 Calculation of Confidence Intervals sss 12 52 Batch Means Procedure eee trecenti rei iriser 13 Commands to the Simulation Kernel doeet pee bt ete e ea ep inde 13 Available Network Object Classes 25 2 25 22 5 0 rodents age Or tend pue ur vetus 14 7 1 SOULCES E T E E A E dettes tees 14 7 1 1 GEIRE IONI KE E aso E E E E OR phum 14 7 1 2 Bernoulli
29. 100 AXVAL 100 DELTA 1000 UPDATE 10 eter m2 VAL abrsrc nsrc ACR TITLE ACR abrsrc string nsrc WIN 700 500 400 200 MODE AbsMode NVALS 1000 MAXVAL 10000 DELTA 100 UPDATE 100 BOK KKK KKK KK KK KR IK kCKCkCk KOC k kCk ck kck ck kck ck ck kck ck kck ck ckckck ck ck ck ke ke e kx K Simulation run of 1 million time slots Sim gt Run SLOTS int 1e6 ouptut some statistics print load in abrmux1 msloadi Count 1e6 Mn var 1 1290 for i 0 to nsre 1 1 1 abrmuxl LossData i print loss in abrmuxl 1 n print departures from abrsrc 1 abrsrc 1 CountData n print arrivals in datasink 1 datasink 1 Count Mn print data arrivals in abrsink 1 abrsink 1 CountData n print RMCI arrivals in abrsink 1 abrsink 1 CountRMCI Mn print RMCO arrivals in abrsink 1 abrsink 1 CountRMCO n print arrivals in datasink nsrc 2 datasink nsrc 2 Count Mn print arrivals in datasink nsrc datasink nsrc Count Mn end of YATS input file 11 0 Some Further Notes 11 1 Regarding References 1 For variables and macros a reference is bound to the home block of the entity unique ID for each block instance e g in a loop The reference therefore becomes invalid in case the block has been already left when resolving the reference which results in
30. 2 0 General Remarks Example Input File The input file contains a series of statements which can represent network object decla rations and commands Statements beginning with a network object class identifier are interpreted as an object declaration The parser creates an appropriate object and calls its initialisation method which then reads the parameters For classes with outputs the names of the succeeding objects are given in the statement This defines the network structure Simulation control and result analysis are realized by commands to the defined objects Sim is the predefined simulation kernel object All statements beginning with an object identifier are recognized as a command They are converted into a message to the object which again can read parameters from the input text The result analysis strategy is as follows All objects understand simple commands to return the content of counters and other values collected during a simulation run These values are passed into the kernel Therefore commands can be used in mathe YATS Yet Another Tiny Simulator User s Manual for Version 0 3 1 matical expressions Since the input language comprises macros it is possible to define libraries for statistical evaluations Output to the standard output normally redirected to a file is implemented by a print statement which gives full flexibility for output for matting Additionally measurement devices with graphical online
31. Dresden University of Technology The development was partly supported by the ACTS project AC 049 EXPERT An event scheduler a symbol manager and a scanner parser front end constitute the kernel of the system Basic network elements like different source types de multi plexers delay lines measurement devices and graphical online displays are provided The system uses a simple script language for the problem description and is written itself in C The program expects the name of an input file yats inputFile It contains a description of the model configuration and commands to the simulation kernel like simulate 1 million time slots and to the model objects like return losses in a multiplexer Model description simulation control and result analysis are eased by variables loops and macros Objects communicate with other ones and with the simulation kernel by unified methods On the web YATS is available via http www ifn et tu dresden de TK yats yats html Many thanks go to the following people who have implemented parts of the software were involved in debugging or made proposals for improvements e Alfonso Santos TID Spain e Andreas Teresiak TUD e Axel Buksnowitz TUD eGunnar L we TUD eSven Forner TUD e Torsten M ller TUD e Wouter Ooghe SUG Belgium A trace of the version development can be found in the ASCII file yats HISTORY of the distribution Here all differences between versions are listed
32. OUTCTRL gmdp i gt Start OUTDATA linefw i delay forward Leitung linefw i DELAY i 10 OUT abrmuxl I i delay backward YATS Yet Another Tiny Simulator User s Manual for Version 0 3 46 Leitung linebw i DELAY i 10 OUT abrsrc i BRMC ABR sink AbrSink abrsink i BUFF 1000 OUTBRMC snkmux gt I i OUTDATA datasink i Senke datasink i ie background source and sink A uncomment next two lines to turn on background traffic 7 MMBPquelle bgsrc EB 3000 ES 3000 ED 1 3 VCI nsrc 1 OUT abrmuxi I nsrc 1 Senke abrsink nsrc 1 background sink d forward direction E AbrMux abrmuxl NINP nsrc l MAXVCI nsrc 1 BUFFCBR 100 BUFFABR 100000 HI THRESH 5000 LO THRESH 4000 TBE 1000 AI 100 TARGUTIL 0 95 OUTBRMC srcdmx1 OUTDATA msloadl Meas2 msloadl MAXCTD 100 MAXIAT 100 OUT demux1 Demultiplexer demuxl MAXVCI nsrc 1 NOUT nsrctl OUT i abrsink i for i 1 to nsretl Signal demuxl i i i backward direction x Multiplexer snkmux NINP nsrc BUFF 100 OUT abrmux1l gt BRMC Demultiplexer srcdmx1 MAXVCI nsrc 1 NOUT nsrc OUT i linebw i for i 1 to nsrc Signal srcdmxl i i i ROKR KKK KKK Kk Ck KK KK RK I IK I k KCkCk kokck kckck ck kck ck kck ck ckck ck ckck ck ke ke e kx Graphics place the windows with first call positions are stored B in the file abr pos mur Control POS 50 50
33. Source naro AT ed c ES 14 7 1 3 Source with Arbitrarily Distributed Cell Distances 15 7 1 8 ON OFF Source with Geometrically Distributed Phase Durations 15 7 1 5 MMBP Source ON OFF sss ener ennt 15 7 1 6 GMDPB SOoUurte i aas essc coe an a eru UO ERE 16 7 1 7 GmdpsStop a Source Following the Start Stop Protocol 16 7 1 8 Source Reading IATs from a Trace File sese 17 7 1 9 Source Sending a Directly Given Cell Sequence ssss 17 7 2 Definition of Distributions cccccccesseceessseceeececeseecessececseaececesaeeesseeecesaeeeensaeens 17 7 3 M ltiplexets 52s ated aie eonmpOI Sep aetates 18 7 3 1 Standard Multiplexer Arrival First esee 18 7 3 Multiplexer with Lower Output Rate Departure First 19 7 3 3 Multiplexer with Lower Output Rate Arrival First 19 7 3 4 Multiplexer with Arbitrarily Distributed Serving Time 19 7 3 5 Multiplexer with Early Packet Discard Scheme ss 20 7 3 6 Multiplexer with Weighted Fair Queueing Strategy 20 7 3 7 Multiplexer with Input Buffers essen 21 7 4 Multiplexers with Pure Event Triggered Scheduling ssssss 22 7 4 1 MuxAsyncDF Asynchronous Output Departure Fir
34. according to RFC 1323 is supported A delayed acknowledgement is registered with every packet received in sequence Immediate ACKs are sent e if an out of sequence packet arrives e if the receiver window closes to zero ifazero window probe is received and ifthe right window edge shifts by at least one maximum sized segment or half of the total receiver buffer size After connection setup both TCP sender and receiver know the identity of the peer object The identifiers are written in each frame sent data and ACK frames Thus checks can be performed whether an arriving frame stems from the peer object or whether it has arrived due to erroneous routing problem in large network configura tions Error messages are launched in this case Remark RFC 1122 section 4 2 3 2 recommends to send an ACK for at least each second full sized segment This currently is only realised indirectly via the immediate ACK launched by the subsequent window update In case the receiver has been stopped by the successor this algortihm will fail no window update will occur as long as the receiver remains stopped Exported Variables An object exports the following variables for use with commands or measurement devices tcpr THROUGHPUT mean throughtput since first packet sent by sender bit s tcpr SDU DELAY mean TCP packet delay slots tcpr RESQ LEN current length of the resequencing queue packets tcpr gt RESQ_ MAX LEN max RESQ LEN
35. an error message Variables with the same identifier but used in different blocks can be differentiated due to the block information contained in a reference generated by ref 2 Although references eventually are normal strings they only should be assigned to variables but never be processed To avoid unintended mistakes references twice contain the character 001 which of course is not a protection against abuse YATS Yet Another Tiny Simulator User s Manual for Version 0 3 48 3 The null reference is e g if r deref r 1 4 When recognizing the following rule then references should be really save Avoid to declare in the same block arrays which only differ in the index ranges The next example probably will not behave as intended Instead of causing an error mes sage a 10 will be accessed by the macro We would get an error message how ever if the second array declaration and the macro call would be placed in a new block macro mac x deref x 10 1 var i r for i 1 to 5 var alil creates a 1 a 5 r ref a 1 intention reference to a 1 a 5 for i 10 to 15 var a i this extends the scope of r mac r will cause a 10 1 11 2 Regarding Literals As has been shown in the example of Section 4 1 on page 8 the string argument of lit may contain input name extensions built upon gt This is very useful but somewhat dirty therefore a
36. ation As for MuxDF see Section 7 3 2 on page 16 MuxSyncDF mux NINP 10 BUFF 100 MAXVCI 100 SERVICE 4 OUT line Function Synchronous Output Departure First specification see Section 7 4 on page 22 YATS Yet Another Tiny Simulator User s Manual for Version 0 3 23 Exported Variables and Commands As for Multiplexer see Section 7 3 1 on page 15 7 4 4 MuxSyncAF Synchronous Output Arrival First Declaration As for MuxDF see Section 7 3 2 on page 16 MuxSyncAF mux NINP 10 BUFF 100 MAXVCI 100 SERVICE 4 OUT line Function Synchronous Output Arrival First specification see Section 7 4 on page 22 Exported Variables and Commands As for Multiplexer see Section 7 3 1 on page 15 7 5 Demultiplexer Declaration Demultiplexer demux MAXVCI 100 NOUT 3 OUT sink 1 sink 2 sink 3 or Demultiplexer OUT i sink i or Demultiplexer OUT i 1 to 2 sx i gt Start 3 snk i MAXVCTI dimension of the routing table VCI range from 0 to MAXVCI NOUT number of outputs integer OUT input names of succeeding objects three possibilities see below Function Incomming cells are forwarded to the output which corresponds to the VCIs of the cells The routing table can be written with Signal demux vciOld vciNew outpNum see Signal object There are three possibilities to specify the names of the succeeding objects a complete list
37. command sets the connection specific WFQ parameters for VC vci The invers cells rate has to be integer mean cell spacing in time slots as well as the buffer size in cells Input data type Cell 7 3 7 Multiplexer with Input Buffers Declaration MuxInpBuf mx NINP 10 BUF 100 BSTART 90 BYTEFACT 0 3 SERVICE 1 RELAX 3 OUTCTRL i src ij Start OUT snk NINP int number of inputs BUF int buffer size per input counting in data objects BSTART optional int Turns on start stop protocol at inputs Buffer size at which to start again a stopped sender Default no start stop at inputs BYTEFACT double number of simulation time steps needed to serve one byte Specify either BY TEFACT or SERVICE See below SERVICE int number of time steps needed to serve one data object See below RELAX optional int Length of a relaxation period introduced between after each finished service in simulation time steps Default 0 OUTCTRL optional only if BSTART has been given Control inputs for start stop protocol Names can be specified using the same constructs as for YATS Yet Another Tiny Simulator User s Manual for Version 0 3 21 output names of demultiplexers see Section 7 5 on page 24 OUT where to connect multiplexer output network object inupt name Function A multiplexer with following features Input buffers same size per input The input buffer size counts in data objects e Start stop p
38. correlation measures flag set to zero if target conditions are met One otherwise 6 0 Commands to the Simulation Kernel Sim Run SLOTS slots DOTS dots Simulates the network for SLOTS time slots If DOTS is given and larger than zero then a dot is printed to standard output approximately after every DOTS th time slot Approximately means that the dots are only printed together with each time slot with SimulationTime modulo TIME_LEN 0 TIME_LEN is a constant defined in the source file defs h it defines the static length of the calendar queue used by the scheduler By default TIME LEN equals 1000 it might be useful to change it to a prime number Sim ResetTime YATS Yet Another Tiny Simulator User s Manual for Version 0 3 13 Reset simulation time The activation time of all events registered at the kernel is diminished by the current time This command is used to avoid an overflow of the simulation clock in case of very long runs for simple models this can happen after two hours e Sim gt SetRand seed The central r n generator is set to the seed value This is only usefull before defining any objects since some objects call the r n generator e g for the initial event regis tration By default the generator is initialized with the system time e Sim EchoInput The input text include files excluded is printed to standard output every line is marked with a hash mark
39. dge Output OUTDATA TCPIPFrame Output OUTCTRL Data 7 11 2 TCP Receiver Declaration TCPIPrec tcpr WND lt int gt PROCTIM lt double gt ACKDEL lt double gt IACKDEL lt double gt OUTDATA lt object input gt OUTACK lt object input gt WND receiver buffer size including resequencing queue bytes PROCTIM optional processing time per received packet msec default 0 3msec ACKDEL optional delay of delayed acknowledgmts msec default 200 msec IACKDEL optional delay of immediate acks msec default PROCTIM msecs OUTDATA where to send received data OUTACK where to send acknowledgement frames Function YATS Yet Another Tiny Simulator User s Manual for Version 0 3 37 The object implements the TCP receiver functionality TCP IP packets are expected at the input t cpr gt Data The object can be stopped by the succeeding network object which stops eventually the window update process of the receiver start stop protocol input tcpr Start During connection setup the object is informed by the peer sender about ATM bit rate to translate seconds into slots the time stamp option and the maximum segment size The sender in turn is provided with the maximum win dow size In case turned on by the peer sender the time stamp option
40. e related only to the ABR buffer During congestion indication the CI bit is set in forward and backward direction For the integration of non ABR the current non ABR load is measured interval CBRI time slots default AT The fair and VC share values of the ERICA algorithm then are computed as follows For the fair share the difference of target rate LINKCR times TARGUTIL and current non ABR rate is divided by the number of ABR con nections It is set to zero in case no ABR bandwidth available The z value for the VC share is the ratio of current ABR input rate measured over AI time slots and the dif ference between target and non ABR input rate Z is set to 1000 in case no ABR band with available or to ZOL if specified in the definition statement The current rate of a connection is taken from the CCR of forward RM cells the current ER of a connection is included in both forward and backward RM cells If DYNFAIRSHARE is given then the fair share computation is based on the number of connections which have sent during the last AI interval no averaging with previous values is performed Without DY NFAIRSHARE the fair share results from the number of established connections regardless wether actually sending or not In BINMODE no ER feedback is filled into RM cells Therefore the multiplexer behaves like a device with only binary feedback During connection setup initialized by the ABR source only a check of the sum of the curr
41. e shaping device ShapCtrl Section 7 7 3 on page 26 TCP IP will be next candi date 10 0 Examples 10 1 Complete Simulation Series with Confidence Intervals In the following an example producing a curve of the cell loss probability in a multi plexer over the buffer length is given Confidence intervals for the measurements are calculated and the produced output file can be visualized directly by gnuplot YATS Yet Another Tiny Simulator User s Manual for Version 0 3 44 The parameters of a simulation model can be changed by deriving values from environ ment variables These can be set by appropriate shell scripts The sript below sets the variable BLEN to 10 20 100 and calls YATS for each value bin sh BLEN 10 while SBLEN le 100 do export BLEN yats y in 1 gt gt y out 2 gt gt y err BLEN expr SBLEN 10 done end of shell script BLEN is recognized in the following simulator input file y in It performs a warm up and 10 runs for each value A confidence interval 95 96 is computed and results are written to standard output which has been redirected by the shell script finclude MACROS load macro library var i nruns nsrc blen slots blen int env BLEN read environment variable for buffer length convert to int slots int 5e6 length of one simulation run nruns 10 perform 10 simulation runs for i 1 to nruns var ploss i an array to store results of r
42. eading default keyword The expression or identifier de Va1 has to match the type given for the parameter For an exception NULL identifier see Section 11 3 2 on page 51 If during later instantiation an optional parameter is missing expected key word not found then the default value is passed to the macro The delimiter following the corresponding argList entry then is not expected thus directly continuing with the next argument The parameter list par List specifies the macro parameters delimited by commas A macro parameter declaration can comprise a cast operator specifying that the value shall be casted before it is passed to the macro Arguments declared as string can be transformed to lit the signes are stripped off lit can be changed to string simply add the signes to the identifier read Other casts currently are not foreseen To summarise a macro parameter in the list parList is defined as follows posNo again has to count upwards starting with 1 fx Sane qocltepeugte k AC F ae eNor T PNE Y The optional part marked with commandSpecs allows to generate an object and translate commands to this object into macro calls This is described in Section 11 3 1 on page 49 If the final print is given optional then the generated macro call is printed to stdout before the macro actually is executed Inserted default values are highlighted by com YATS Yet Another Tiny Simu
43. ed from the source of the data object or YATS Yet Another Tiny Simulator User s Manual for Version 0 3 30 from the last setting of the time stamps see Section 7 9 3 on page 32 In case min max is added to CTD then a complete distribution between min and max is collected The specification of CTDDIV div optional only if complete distribution collected says that all measured values are diveded by div before they are counted in the distribution Note however that the mean and extreme values commands MeanCTD MinCTD MaxCTD are not influenced by this down scaling The parame ters IAT and IATDIV follow the same rules The VCP or CONNID min max specifies the range of channel IDs over which the measurements are performed If nei ther of both is given then the range is 0 0 If ERANGE is given optional then an error message is generated if a data object with out of range ID arrives Otherwise only the global counter Count is incremented Commands ms ResStats Resets all CTD and IAT statistics and all counters no return value ms ResCount Resets the global counter Count no return value Exported Variables For use in commands and with display devices the following arrays are exported ms Count overall number of arrivals int ms Counts i number of arrivals for this index int ms CTD i tim counter for cell transfer delay time t im scaled by CTDDIV i
44. eference to the array of values nval number of values The expected array indices are 1 to nval refMean where to write estimate of mean value reference refWidth where to write interval width reference The interval extends from mean width to mean width Confid95 ref Vals nval refMean refLo refUp Resembles Confid but the level of confidence is fixed to 95 per cent Instead of the interval width its lower and upper bounds are returned references refLo and refUp 11 5 2 More Convenient Evaluation of Confidence Intervals For the following macro class it is not necessary to define auxiliary arrays which sometimes make the input file rather messy ConfObj name level maxNvals This defines an auxiliary array object see Section 7 12 4 on page 41 with the given name string The level of confidence is passed in level double maxNvals inte ger specifies the maximum number of observations which can be stored in the array Example ConfObj cce 0 95 20 7 object ccc defined ConfAdd refObj value This adds value double to the object referenced in refObj Example ConfAdd ref ccc x x is a measured value ConfMean refObj ConfMean returns the mean value as double of the values collected so far Example mean ConfMean ref ccc ConfLo refObj Returns the lower bound of the confidence interval ConfUp refObj Returns the upper bound of the confidence interval ConfVar refObj
45. embled concurrently This eases the definition of AAL end systems over which more than one higher layer connection is set up Otherwise the streams had to be demultiplexed and for each connection an AALSRec object would be necessary Commands aal gt ResetStat Resets all statistics counters Exported Variables For use in commands and with display devices the following arrays are exported The parameter vc is the ATM connection 1 MAXVCI aal QLen vc current cell queue length aal CellLoss vc number of cells lost aal CellCount vc number of cells received aal gt SDULoss vc number of SDUs lost aal SDUCount vc number of SDUs succesfully transmitted aal DelayMean vc mean SDU delay from sending first cell until receiving the last 7 9 CTD and IAT Measurements 7 9 1 Measurement Device Declaration Meas2 ms MAXCTD 100 MAXIAT 100 VCI 1 OUT line MAXCTD largest cell transfer delay which can be measured MAXIAT largest cell inter arrival time which can be measured VCI if given can be omitted only cells on this VC are recognized YATS Yet Another Tiny Simulator User s Manual for Version 0 3 29 OUT input name of the succeeding object can be omitted Function The object generates statistics over cell transfer delays and inter arrival times If no OUT is given it acts as sink The VCI can also be omitted Remark The device fails at Sim gt ResetTime Exported Variab
46. ent MCRs against the target rate is performed The current non ABR load is not taken into account For computing the initial cell rate also the ERICA algorithm is used CCR is set to MCR in this case The multiplexer has NINP 1 inputs e mux gt I i mux gt I NINP forward data inputs e mux BRMC input for backward RM cells Exported Variables An object exports the following variables for use with commands or measurement devices mux gt QLenNABR current non ABR queue length int ux gt QLenABR current ABR queue length all kinds of ABR cells int ux QLenABRData current ABR data cell queue length int ux gt QLenRMCTI current in rate RM cell queue length int ux QLenRMCO current out of rate RM cell queue length int ux LossData vci no number of cells lost on this VC non ABR or ABR ta int ux LossRMCI vci no number of in rate RM cells lost on this VC int ux LossRMCO vci no number of out of rate RM cells lost on this VC int ux CRNABR current non ABR input cell rate double ux CRABR current ABR input cell rate all kinds of cells double e mux gt Z current z value ERICA algorithm double Data types e 2333838838 5 e zo zx YATS Yet Another Tiny Simulator User s Manual for Version 0 3 34 The inputs mux gt I x expect Cell and RMCell on mux BRMC RMCell is expected 7 10 3 ABR Sink Declaration AbrSink sink
47. er BUFF buffer size cells integer MAXVCI optional max VC number default NINP OUT input name of the succeeding object Function Multiplexer with server strategy Arrival First inputs are served in random order Losses are counted per input and per VC The per VC registration is only performed for cell like data items and in the VCI range 0 MAXVCI The input names are nameOfObject gt I inputNumber where inputNumber ranges from 1 to NINP Remark Bug The implementation is fast but the sojourn time in the mutliplexer is exactly one time slot too long The network object class MuxAF Section 7 3 3 on page 19 implements the correct sojourn time Exported variables mux Loss i or mux LossInp i loss at input i mux LossVCI i loss at VCI i mux LossTot total loss mux QLen current queue length actually system occupation Commands YATS Yet Another Tiny Simulator User s Manual for Version 0 3 18 mux Losses i k or mux LossesInp i k Returns sum of losses on inputs i to k mux gt LossesVCI i k Returns sum of losses on VCs i to k mux ResLoss Resets all loss counters Input data type Data 7 3 2 Multiplexer with Lower Output Rate Departure First Declaration MuxDF mux NINP 10 BUFF 100 MAXVCI 100 ACTIVE 4 OUT line NINP number of inputs int BUFF number of buffer places int MAXVCI optional max VC number default NINP
48. fic or too high threshold are also dropped til the end Connections with out of range VCI and non AALSCell data items are multiplexed following the normal way using the same common buffer Remark The last cell of a dropped frame is not passed If THRESH has been set appropriately then this should not be a problem frames are either forwarded or dropped completely Otherwise it could be a problem Therefore it is planed to add a flag which turns on for warding of last cell the default should remain as it is Exported Variables and Commands like for Multiplexer see Section 7 3 1 on page 18 7 3 6 Multiplexer with Weighted Fair Queueing Strategy Declaration MuxWFQ mux NINP lt int gt MAXVCI int OUT lt object input NINP number of inputs MAXVCI optional largest VC number possible default NINP OUT where to send cells Function The weighted fair queueing algorithm according to J W Roberts is implemented The connection specific parameters buffer size and inverse of the mean cell rate are set by YATS Yet Another Tiny Simulator User s Manual for Version 0 3 20 the command mux SetPar see below An incomming cell causes an error message in case its VCI has not yet been initialized with SetPar WEO Algorithm Per VC an input queue is maintained A sort queue at the output manages the order in which to serve cells from the VC queues It holds the front cell from each VC queue provided there is
49. ger table lookup and costs not more than 5 96 speed but gives maximum flexibility Net work objects processing e g class Data do not complain about receiving Cell In con trast a Data item incomming at the backward RM cell input of an ABR source causes an error message 9 2 Data Object Embedding The specification of the Data object class defines a mechanism to embedd data objects into other objects This allows to implement protocol layers which are transpar ent for the next higher layer The first example will be the implementation of AAL5 connections which can tunnel arbitrary data objects provided they implement the methods for embedding 9 3 Start Stop Protocol Sometimes a loss free transmission of data objects between network objects is neces sary e g for the communication between higher protocol layers The data receiver should be able to stop and start the data sender depending on its internal state or even the state of the succeeding network object For this purpose the start stop protocol has been defined As a side effect of delivering the data item the sender is informed whether the receiver can accept more data If not then the sender has to stop It is informed by the receiver via an extra input often called Start that more data can be sent The protocol currently is used by ABR objects Section 7 10 on page 32 the source GmdpStop Section 7 1 7 on page 16 AAL 5 objects Section 7 8 on page 27 and th
50. hanges in the window positions You then can specify the appropriate CORR values Remarks The object is activated during the early slot phase and it registers at the event scheduler like every other object Therefore it is unspecified which other events destined for the current time slot have been activated already and which not Graphical online dis plays however normally register for the late slot phase Thus they may display an old value By choosing appropriate sample distances it can be ensured that they are syn chronized with each other when stopping the simulator 8 2 Sliding Time History of a Value Declaration YATS Yet Another Tiny Simulator User s Manual for Version 0 3 41 Meter meter VAL src Count TITLE Cell Rate in src WIN 100 100 400 200 MODE DiffMode NVALS 200 MAXVAL 100 DELTA 100 UPDATE 10 VAL object and variable name to be displayed TITLE window title can be omitted then the object name is used WIN xPos yPos width height integer MODE DiffMode or AbsMode see below NVALS number of displayed values history length integer MAXVAL values are normalized to MAX VAL DELTA number of time slots between two samples integer UPDATE the window is updated only with every UPDATE th sample can be omit ted Function The object specified by VAL is asked for the address of the given variable Its contents then is read during every DELTA th time slot The time history compr
51. hen detecting cell loss The last cell is marked with PT 1 and a field of this cell repeats the cell sequence number of the first cell of the burst The receiver checks whether the first cell in the input queue bears this sequence number If yes then the frame has been transmitted succesfully and it can be extracted from the first cell Otherwise all cells in the queue are dropped Thanks to the SDU sequence number the number of lost SDU also can be detected Commands aalr ResetStat Resets all statisitcs counter Exported Variables For use in commands and with display devices the following variables are exported aalr QLen current input queue length aalr CellCount number of cells received aalr SDUCount number of AAL SDUS successfully transmitted aalr CellLoss number of cells lost YATS Yet Another Tiny Simulator User s Manual for Version 0 3 28 aalr gt SDULoss number of AAL SDUs lost aalr DelayMean Mean SDU transfer delay measured from sending first until receiving last cell of SDU Input Data Type AALSCell Output Data Type The output data type is the type which has been encapsulated by the corresponding AAL 5 sender 7 8 3 AAL 5 Receiver with Concurrent Reassembly Declaration AAL5RecMult aal MAXVCI 100 OUT tcp MAXVCTI int largest VCI number OUT where to send packets Function The function is the same as for AAL5Rec Section 7 8 2 on page 28 but multiple frames can be reass
52. ises NVALS samples the full window height corresponds to MAXVAL The mode AbsMode dis plays the samples itself DiffMode displays the differences between subsequent sam ples If UPDATE is given can be omitted then the window is updated only with every UPDATE th sample On a mouse click on the window area a file name to store the current history content ASCII format is asked for Remarks The object registers at the event scheduler for the late slot phase Therefore values modified during the late phase can not be displayed exactly with a resolution of one time slot To enable the display of variables the data source has to implement the export method see object methods 8 3 Histogram of a Distribution Declaration Histogram histo VALS meas gt IAT TITLE IAT Distribution WIN 100 100 400 200 MAXFREQ 0 2 DELTA 100 VALS object and array name to be displayed TITLE window title can be omitted then the object name is used WIN xPos yPos width height integer MAXFREQ normalisation corresponds to the window height double can be omit ted DELTA number of time slots between two samples integer Function The object specified by VALS is asked for address and dimension of the given array The contents of the array is interpreted as a distribution the values are divided by the sum of them Sampling and display are performed during each DELTA th time slot If MAXFREQ is not specified then the d
53. isplay normalisation is done automatically the window height corresponds to the largest frequency times 1 25 On a mouse click on the window area a file name to store the current distribution con tent ASCII format is asked for Remarks See remarks for the Meter object YATS Yet Another Tiny Simulator User s Manual for Version 0 3 42 8 4 Production of a Distribution from Samples of a Value Declaration Histo2 histo VAL mux gt QLen TITLE Queue Length Distrib WIN 100 100 400 200 NVALS 52 MAXFREQ 0 2 DELTA 1 UPDATE 1000 VAL value from which to produce the distribution TITLE window title can be omitted then the object name is used WIN xPos yPos width height integer NVALS length of the distribution Value range 0 NVALS 1 MAXFREQ normalisation corresponds to the window height double can be omit ted DELTA number of time slots between two samples integer can be omitted UPDATE the window is updated only with every UPDATE th sample can be omit ted Function The object specified by VAL is asked for the address of the given variable Its contents then is read during every DELTA th time slot The produced distribution comprises NVALS values If UPDATE is given can be omitted then the window is updated only with every UPDATE th sample If MAXFREQ is not specified then the display nor malisation is done automatically the window height corresponds to the largest fre q
54. l the conditions are met To obtain observation results and report on procedure progress two user provided macros are applied references refObs and refLog Once BatchMeans has been called it entirely controls the simulation progress repeatedly calling the two specified macros It returns when the simulation goal has been reached Macro parameters are level level of confidence values see macro Confid prec relative target width of confidence interval upBound mean mean maxcorr upper bound of correlation measures Additionally to the confidence interval correlations between collected batch values are considered Measurements are continued as long as the coefficient of correlation between batch values exceeds this bound nbat number of batches to be used batsiz initial number of observations per batch This number is doubled with each iteration step refObs reference to a macro which performs an observation The macro has to prepare reset counters etc and perform a measurement The value of interest is expected as macro return value No arguments are passed to this macro refLog reference to a macro which is called to report on procedure progress It is invoked upon completion of an iteration as follows deref refLog cnt mean width cl c2 flag cnt number of observations already made mean current estimate of mean value width current absolute width of confidence interval upBound mean C1 c2 current
55. lator User s Manual for Version 0 3 10 ments In case the print is followed by an integer expression with then logging is performed only if the expression is non zero Example this macro actually should define our sub model macro sub nam a b only echo parameters print sub nam nam a a b b Mn the macro shell MacroShell Sub ARGS litQ1 first arg identifier no keyword delimiter D int 2 default 1 optional integer arg keyword D default value 1 LD double 3 mantadory double arg keyword LD MACRO sub call the macro sub string 1 convert identifier to string 2 3 pass arguments 2 and 3 directly print log the generated macro call apply the shell var i for i 1 to 2 Sub s i D i LD i for i 3 to 4 Sub s i LD i default value 1 for D Another example can be found in Section 4 1 on page 8 4 3 Input Name Aliasing and Dummy Objects Sometimes non matching input names of different network objects lead to description problems Then it is possible first to include dummy nodes see Section 7 12 3 on page 40 Secondly all network object classes derived from the generic class ino pro vide the following command objName AliasInput aliasInputNameAsString gt origInputNameAsString mux AliasInput I 12 gt I 10 I 10 is reachable via the name I 12 too
56. les ms Count number of arrived cells ms CTD time cell counter for this transfer delay ms CTIDover number of CTD values larger than CTDMAX ms IAT time counter for this inter arrival time ms IATover number of IAT values larger than IATMAX Commands ms ResCount Resets the counter ms ResDists Resets all counters The following commands are provided for convenience they could be realized in the input file or by macros too They only evaluate the stored distributions values up to MAXCTD and MAXIAT ms MeanlAT ms MeanCTD Return mean values of the recorded distributions ms MinIlAT ms MinCTD ms MaxIlAT ms MaxCID Return the minimum and maximum IAT and CTD values with counters larger than zero only inside of the specified MAX borders Input data type Data if no VCI given Cell otherwise 7 9 2 More Complex Measurement Device for Cells and Frames Declaration full version Meas3 ms CTD min max CTDDIV 10 IAT min max ATDIV 10 VCI min max ERANGE OUT sink Function All parameters are optional but one parameter has to be given at least If OUT is omit ted the the object acts as sink The device expects cells if VCP is given Frames can be measured if the word VCP is replaced by CONNID If the keyword CTD is given then mean values and extreme values min max of the transfer delays are measured either measur
57. ly Distributed Phase Durations Declaration BSquelle src EX 10 ES 100 DELTA 10 VCI 1 OUT line EX mean number of cells per burst double ES mean duration of the silence phase in time slots double DELTA cell distance in the ON state in time slots integer VCI VC number of generated cells OUT input name of the succeeding object Exported variables src Count number of sent cells Commands src ResCount Resets the cell counter Output data type Cell 7 1 5 MMBP Source ON OFF Declaration MMBPquelle src EB 100 ES 100 ED 10 VCI 1 OUT line EB mean duration of the ON state in time slots double ES mean duration of the OFF state in time slots double ED mean of the geometrically distributed cell distance double VCI VC number of generated cells OUT input name of the succeeding object Exported variables YATS Yet Another Tiny Simulator User s Manual for Version 0 3 15 Src Count number of sent cells Commands Src ResCount Resets the cell counter Output data type Cell 7 1 6 GMDP Source Declaration GMDPquelle src NSTAT 2 DELTA 2 3 EX 10 20 TRANS 0 1 1 0 VCI 1 OUT line or GMDPquelle src NSTAT 2 DELTA 2 3 DIST d1 d2 TRANS 0 1 1 0 VCI 1 OUT line NSTAT number of states integer DELTA cell distances integer for zero cell rate see below EX mean numbers of cells per state geom distributed double for zero cell rate
58. m Run is performed Commands conf Add double Adds a value to the internal array no return value conf Len Returns number of values collected so far int conf gt Val int Returns a specific value 1 Len double conf Flush Flushs all values Len 0 no return value conf Mean Returns the mean of the values collected so far double conf Var Returns the empirical variance of the values collected so far double conf Lo Returns the lower bound of the current confidence interval based on the values collected so far double conf Up Returns the upper bound of the current confidence interval based on the values collected so far double conf Width Returns the width upper bound mean of the current confidence interval based on the values collected so far double conf Lo double conf Up double conf Width double These versions return the values if the level of confidence equals the value of the additional parameters YATS Yet Another Tiny Simulator User s Manual for Version 0 3 12 5 2 Batch Means Procedure This macro is part of the macro file MACROS in src examples BatchMeans level prec maxcorr nbat batsiz refObs refLog Implements the algorithm of the so called batch means procedure For given level of confidence and relative target width of the confidence interval according to Student s t distribution observations are performed unti
59. mean Nt lo Nt up Xm end of YATS input file After having run the shell script gnuplot can vizualize the curve The following com mands have to be given gnuplot gnuplot set log y gnuplot plot y out with errorbars A simpler possibility to calculate confidence intervalls is described in Section 5 1 on page 12 For the macro version used here see Section 11 5 1 on page 51 10 2 ABR Multiplexer Graphical Online Displays The following input file defines an ABR multipxer loaded by 200 ABR sources and an optional background source Between ABR sources and multiplexer different delay lines are placed both in forward and backward direction The data sources always want to send with the full rate they are stopped by the ABR sources via the start stop proto col To turn on the background traffic uncomment the backround source below The graphical displays have to be placed on the screen with the first run initially most of them overlap The new positions are stored in the file abr pos see Control object below ABR example for YATS var i nsrc nsrc 200 of ABR sources BORK KKK KK KK KK KK I OR KK OK KK ke x kx model description for i 1 to nsrc data source GmdpStop gmdp i NSTAT 2 DELTA 1 1 EX 10 50 TRANS 0 1 1 0 VCI i OUT abrsrc i ABR source AbrSrc abrsrc i BUFF 5 BSTART 2 MCR 0 PCR 100000 FRTT 100 ROUTE 2 abrmuxl abrsink i AUTOCONN
60. n input queue capacity BUFF data items and a server Data items are fed into the server whenever the device is free They then are forwarded SERVICE time steps later The server therefore emulates a slower output line with asynchronous cycles If a data item reaches an empty multiplexer then it is immediately placed in the server from where it is forwarded SERVICE steps later A data item approaching a non empty system has to wait in the queue Synchronous Operation The multiplexer consists of an input queue capacity BUFF data items and a server Data items are fed into and taken from the server only at time steps with SimTime modulo SERVICE 0 The server therefore emulates a slower output line with syn chronous cycles YATS Yet Another Tiny Simulator User s Manual for Version 0 3 22 If a data item reaches an empty multiplexer with the first time step of an output cycle then it is immediately placed in the server from where it is forwarded SERVICE steps later If a data item reaches an empty multiplexer but not with beginning of the first step of an output cycle then it has to wait for service until start of next cycle while remaining in the queue Then it is put into the server from where it is forwarded after another SERVICE time steps A data item approaching a non empty system has to wait in the queue Departure First DF relates to events taking place during the same simulation time step If the server complete
61. nd feel like for direct network object declarations Keywords typed and optional parameters with default values are supported New identifiers can be written down as identifiers without signs they can be converted to strings by the interface object MacroShell shellID ARGS E argList MACRO macID parList commandSpecs print intExpr p The argument list argList specifies keywords argument types and default values for optional arguments It is built as list of entries the entries being separated by the same delimiters which are expected lateron during instantiation As delimiters cur rently only and are available The end of the list is marked by the closing bracket Y A list entry has the following syntax keyWord typeName posNo default defVal J The entry may begin with an optional keyword given as raw word followed by a sign Next a type name t ypeName has to follow It specifies the type of the argument Possible are int double string and lit The type lit says that a raw identifier is expected The required then is complemented by the integer position number which has to increase one by one starting with 1 Arguments with keyword only these can be marked as optional by specifying a default value This is done in brackets with l
62. nother Tiny Simulator User s Manual for Version 0 3 5 Operators priorities like in C are LEER r gt g The op is only applicable on integer operands The op also concatenates strings e le Ngee NS lt gt a Comparisons yield the values 0 and 1 integer The ops and are applicable on strings e eee OII Logical AND and OR yield 0 and 1 integer e expression VLE e TET Nat Negation yields 0 and 1 unary and e int expression double expression string expression Explicite type casts see above Operands in expressions can be e constant The type results from the way of writing see above e variableID Only initialised variables are allowed otherwise syntax error message e objectID command Commands to network objects can return a value The command method of the object decides whether the command returns a value e macroID listOfExpressions Macros can return a value A test is performed whether a return value has been specified e env stringExpression Reads an environment variable and returns its value as string In case the variable does not exist the empty string is returned Built in mathematical functions e pow expressionl expression2 Returns expression to the power of expression2 Integer and double expression
63. nother object relying on the Start Stop protocol an interface object has to be placed between frame source and TCP input This interface TermStartStop has not been integrated into Data2F rame since it is useful also for other purposes When the predecessor continues to send if the sucessor has stopped the interface then simply the input buffer overflows But the interface behaves according to the Start Stop protocol at its output The object has a control input tss Start YATS Yet Another Tiny Simulator User s Manual for Version 0 3 39 Declaration TermStartStop tss BUF 100 OUT tcpipsend gt Data BUF input buffer size in frames int OUT where to send frames Commands tss Count is the number of lost data items tss gt ResCount resets this counter 7 12 Miscellaneous 7 12 1 Signalling source This is more a command since no object is generated The routing table of the speci fied object is written Declaration Signal demux oldVCI newVCI outpNo Example Signal demux 1 2 1 7 8 2 Cells with VCI 1 are passed to output 1 the VCI is changed to 2 Cells with VCI 7 are passed to output 2 the VCI is changed to 8 The number of signalling messages specified with one Signal statement is arbitrarily Since the signalling is performed instantly the destination object has to be defined in advance 7 12 2 Data type and timing checks For purposes of debugging TypeCheck tc TYPE RMCell
64. nt ms IAT i tim counter for inter arrival time t im scaled by IATDIV int ms CTDover i overflow counter for CTD distribution int ms CTDunder i underflow counter for CTD distribution int ms IATover i overflow counter for IAT distribution int ms IATunder i underflow counter for IAT distribution int ms MeanCTID i current cumulative mean CTD value double Is updated on the fly with each arrival Note the difference to the command of Meas2 Section 7 9 1 on page 29 ms MaxCTD i largest encountered CTD int Same notes as for MeanCTD ms MinCTD 1 smallest encountered CTD int Same noteas for MeanCTD ms MeanIlAT i current cumulative mean IAT value double Same Note as for MeanCTD ms MaxIAT i largest encountered IAT int Same note as for MeanCTD ms MinIlAT i smallest encountered IAT int Same note as for MeanCTD YATS Yet Another Tiny Simulator User s Manual for Version 0 3 31 Input Data Type Cell if VCI given Frame if CONNID given Data if neither of both given 7 9 3 Updating Time Stamps Declaration TimeStamp ts VCI 1 OUT line Function Updates time stamps in all data items or only on the given VC VCI can be omitted Input data type Data if no VCI given Cell otherwise 7 10 ABR ATM Forum TM 4 0 7 10 1 ABR Source Declaration AbrSrc src BUFF 100 BSTART 50 LINKCR 2 2e5 MCR 200 PCR 1000 FRTT 100
65. nteger BUFF shaper buffer size cells integer OUT input name of the succeeding object Remark In case of BUFF 0 a hard spacing is performed Exported Variables shap gt QLen current queue length shap Count number of lost cells Command shap gt ResCount Resets the loss counter Input data type Data YATS Yet Another Tiny Simulator User s Manual for Version 0 3 25 7 7 2 Peak Rate Shaper with Arbitrary Cell Spacing Declaration Shaper2 shap DELTA 3 5 BUFF 100 OUT line DELTA effective cell spacing enforced by the shaper time slots double BUFF shaper buffer size cells integer OUT input name of the succeeding object Function The shaper works with 2 spacing values The ratio of both yields the effective cell rate In case of BUFF 0 a hard spacing is performed Exported Variables Command Data Types like for Shaper Section 7 7 1 on page 25 7 7 3 Shaper Using the Start Stop Protocol Declaration ShapCtrl shap DELTA 10 BUFF 100 BSTART 10 OUTCTRL src Start OUTDATA line DELTA cell spacing enforced by the shaper time slots integer BUFF shaper buffer size cells integer BSTART buffer occupation at which the sender is waked up again OUTCTRL control input name of the preceeding object OUTDATA input name of the succeeding object Function This class is similar to the Shaper class The object tries however to control its pre ceeding object by the Start Stop pr
66. obal variables are defined using the keyword global They are not local to the cur rent block but are viewable from everywhere Globals are never deleted A number of restricitons is bound to global variables see Section 11 4 on page 51 Variable types are interger double and string Variables are not declared with a certain type but bear the type resulting from the last assignment After declaration they have a special type which ensures that they cannot be used in expressions Constants have the following types xyz gt string 123 gt integer 1 23 gt double le 3 gt double Type casts With string expr int expr and double expr types can be translated The conversion double gt int performs rounding instead of truncation In case of casting string to int or double no white spaces are allowed in the string Arrays of variables can be defined as follows var i auxiliary variable for i 1 to 10 var x i defines x 1 to x 10 It is essential that the var statement is not encapsulated by a block since variables are only local to a block Arrays with more dimensions are possible strings can serve as indices For an example see Section 10 1 on page 44 Note Actually an element of an array is a variable on its own the name comprising the indices too Very large arrays therefore should be avoided speed memory space YATS Yet A
67. ock Once a global has been defined the name never can be used again This also holds for normal variables which cannot overlaod global variables as they can do with normal local ones Globals therefore only should be used if really necessary 11 5 Regarding Confidence Intervals The library MACROS directory yats examples comprises the following macros for statistical evaluation and simulation control The newer version based on an object class is described in Section 5 1 on page 12 the old macro based versions are given here 11 5 1 Basic Macros MeanVar Confid Q and Confid95 require that the user defines the necessary arrays More convenient macros are described in Section 11 5 2 on page 52 MeanVar refVals nval refMean refVar Calculates empirical mean and variance of an array of values Parameters are refVals reference to the array of values nval number of values The expected array indices are 1 to nval refMean where to write the empirical mean reference YATS Yet Another Tiny Simulator User s Manual for Version 0 3 51 refVar where to write the empirical variance reference Confid level refVals nval refMean ref Width Calculates the confidence interval from an array of values and to a specified level of confidence using quantiles of Student s t distribution The parameters are level level of confidence possible values are 0 9 0 95 0 975 and 0 99 refVals r
68. on 3 5 on page 7 the syntax for identifiers can be summarised as follows id stdId standard form also with lit dereflId somewhat restricted version with deref construct stdId comprises a kind of aggregate identifiers stdid baseld stdId intExpr normal integer index stdId stringExpr strings can form indices YATS Yet Another Tiny Simulator User s Manual for Version 0 3 4 stdId baseld aggregated ID baseld simplelIdentifier a normal word like al beginning with a letter lit stringExpr stringExpr may contain all except white space A deref construct only may stand at the beginning and it only may be expanded with indices number of exepected indices follows from the ref statement derefld deref refStringExpr refStringExpr has been generated by ref dereflId intExpr f normal index derefId stringExpr strings can serve as indices 3 3 Variables Expressions and Built In Functions The language is block oriented block statements This means that variables except globals and macros declared inside of a block are deleted when the block is left On the other hand variables defined outside of the block and having the same name appear again with their old value when the block is left Objects however are viewable for ever and will never be released Gl
69. otocol see Section 9 3 on page 44 The data sender is stopped if the buffer is full It is started again at a buffer occupation of BSTART Up to now the only corresponding object class is GmdpStop see under Sources Both are used for the test of new classes Exported Variables Command Data Types like for Shaper Section 7 7 1 on page 25 7 7 4 Leaky Bucket Policing Function Declaration LeakyBucket lb INC 10 DEC 5 SIZE 20 VCI 1 OUT line INC bucket increment with each incomming cell integer DEC bucket decrement with each time slot integer SIZE bucket size integer VCI if given can be omitted then only this VC is subject to policing OUT input name of the succeeding object Function With each time slot the bucket size is decremented by DEC until zero Upon receipt of a cell it is tested whether the increment would result in an overflow If yes then the cell is discarded no bucket increment If no then the increment is performed and the cell is passed In case no VCI is given all cells are subject to policing A histogram about bucket sizes seen by arriving good cells is maintained It can be displayed and used in commands Remark YATS Yet Another Tiny Simulator User s Manual for Version 0 3 26 The algortihm does not coincide with the continuous time algorithm given by ATM Forum TM 4 0 There the cell passes and the increment is performed when the bucket contents is not g
70. parameters is checked against the number of for mal parameters e system stringExpression Starts a shell with the command specified by the string e exit intExpression Leave YATS with the given exit status e el No op Control structures are e if expression statement else statement The else branch is optional e for variableID intExpression to intExpression statement PASCAL like loop the variable is counted from the first to the second int value e while expression statement The statement is executed until the expression evaluates to zero e foreach variableID listOfExpressions statement The statement is executed for each value values separated by commas given in the brackets e switch intExpression case listOfIntExpressions statement case listOfIntExpressions statement default statement y For each case branch a list of values can be specified seperated by The default branch is optional 3 2 Identifiers All identifiers for variables macros and for network objects can be formed using indi ces and aggregation with An example for an identifier with both integer indices and aggregation is a 1 b 2 String expressions also can serve as indices e g var a X Including references and literals see Secti
71. reater than the limit before incrementing Exported Variables lb Count number of lost cells lb LbSize current bucket size lb LbStat i number of arriving cells which have seen bucket size i The size is the size before increment Commands lb ResCount Resets the counter lb ResLbStat Resets LbStat counters Input data type Data if no VCI given Cell otherwise 7 8 AAL 5 Connections 7 8 1 AAL 5 Sender Declaration AAL5Send aals VCI 1 BUF 100 BSTART 20 OUTDATA line OUTCTRL src AAL5Send aals COPYCID BUF 100 BSTART 20 OUTDATA line OUTCTRL src AAL5Send aals MAXCID 100 BUF 100 BSTART 20 OUTDATA line OUTCTRL src VCI VC number of cells generated int COPYCID given use the connection ID of the current frame as VCI MAXCID establish a translation table connection ID gt VCI table length BUF input buffer size int BSTART input buffer occupation at which to wake up stopped data sender int OUTDATA where to send cells OUTCTRL control input of preceeding network object Function The object implements the AALS sender functionality Incoming data items which have to provide the interface for data item embedding Section 9 2 on page 44 are transformed into sequences of ATM cells The ATM cells contain sequence numbers for both cells and AAL SDUS This allows the receiver to detect cell losses Thus only uncorrupted AAL SDUS are extracted from transmitted cells and delivered to the data receiver
72. rol Window Declaration Control POS 50 50 DELTA 100 SLEEP 100000 FILE xx pos CORR 3 20 POS screen position of the control window integer DELTA number of time slots between to activations integer SLEEP time enforced between 2 activations micro seconds integer FILE optional file where positions and dimensions of graphical objects are stored CORR optional correction of window shift caused by window manager frames Function The object generates a window entitled YATS which displays the current simulation time and the current state running stopped The initial state is stopped Mouse clicks on the window area toggle between the states Window update and test on mouse events are performed with every DELTA th time slot If SLEEP is given it can be omitted then a pause is generated after each window update if the time expired since the last update is smaller than the specified one If the optional FILE is given then all changes of window dimensions and postions are stored in this file These stored values lateron override the specifications of the normal input text ATTENTION The position file only effects objects which are defined after the Control window definition The CORR parameter default 5 30 according to Solaris 2 5 DCE manager corrects the window shift caused by the window manager s window frames If window posi tions move between two calls of YATS then look into the position file and observe c
73. rotocol at output see Section 9 3 on page 44 The corresponding con trol input is mx gt Start e Optional start stop protocol Section 9 3 on page 44 at inputs If BSTART has been given then this is turned on and OUTCTRL with the specification of the control inputs of the preceding objects is expected e Service time constant or depending on data object size If BYTEFACT has been given then the service of a data objects takes BY TEFACT LenOfDataObject sim ulation time steps rounded to integer at least 1 If SERVICE is specified then each service takes this number of time steps Optional relaxation period between two services Turned on with RELAX Exported Variables mx gt Loss i Number of data objects lost at input i int mx QLen i Current queue length at input 1 in data objects int Command mx ResLosses Reset all loss counters No return value 7 4 Multiplexers with Pure Event Triggered Scheduling The following multiplexers are sometimes a bit slower than their counterparts which apply a combination of event and time triggered scheduling Section 7 3 on page 18 The combined approach has advantages if the output line operates at full speed But if e g one output ATM time slot corresponds to 10 simulation time steps then the pure event triggered scheduling becomes faster This also holds in case of very low traffic loads Asynchronous Operation The multiplexer consists of a
74. rsion 0 3 2 Definition of variables Variables can be defined everywhere They are viewable until the block end The entries in the list are seperated by commas An entry can simply comprise an identifier see Section 3 2 on page 4 or it may have the form ID expression initialisation global listOfIDsWithOptionalInit Declaration of global variables These variables are not local to the current block but are viewable from everywhere The syntax otherwise is the same as for normal variables This can be used to create e g global arrays as routing tables from inside of a macro Due to name space polution globals should be used with care For restrictions see Section 11 4 on page 51 variableID expression Assignment to a variable eprint expression expression V Print the expressions in the list to the standard output Formatting depends on the expression value integer value sign only if negative double exponential representation 1 10 digits string contents print intExpr V intExpr exprLbist y Some shells e g sh and bash allow to redirect arbitrary file descriptors e g aProgram 3 gt aFile print fd generates output to file descriptor fd If fd is not writable e g since it has not been redirected by a shell an error message is launched The output of print fd is unbuffered direct usage of write 2
75. s a service then first the next data item is taken from the queue if any and then new arrivals are queued Arrival First AF relates to events taking place during the same simulation time step If the server becomes available to begin a service then first new arrivals are queued and then the next data item if any is transfered from the queue to the server When combined with synchronous output operation this also holds for the case where the data item is transferred from the queue to the server with beginning of a new output cycle since the item did not arrive with cycle start the transfer occurs after having queued the current arrivals 7 4 4 MuxAsyncDF Asynchronous Output Departure First Declaration As for MuxDF see Section 7 3 2 on page 19 MuxAsyncDF mux NINP 10 BUFF 100 MAXVCI 100 SERVICE 4 OUT line Function Asynchronous Output Departure First specification see Section 7 4 on page 22 Exported Variables and Commands As for Multiplexer see Section 7 3 1 on page 18 7 4 2 MuxAsyncAF Asynchronous Output Arrival First Declaration As for MuxDF see Section 7 3 2 on page 16 MuxAsyncAF mux NINP 10 BUFF 100 MAXVCI 100 SERVICE 4 OUT line Function Asynchronous Output Arrival First specification see Section 7 4 on page 22 Exported Variables and Commands As for Multiplexer see Section 7 3 1 on page 15 7 4 3 MuxSyncDF Synchronous Output Departure First Declar
76. s are allowed the return type is always double e exp expression Returns e to the power of expression Integer and double expression allowed the return type is always double e log expression YATS Yet Another Tiny Simulator User s Manual for Version 0 3 6 Returns the natural logarithm Like exp e sqrt expression Returns the square root Like exp e dgandi Xxx gi Returns an integer random number equally distributed in 0 32767 3 4 Include Files System Interface Include file include fileName The rest of the input line is skipped also the start of a comment The directive has to be written immediatly at the beginning of a line Include files can be nested System interface e system stringExpression Starts a shell with the given command e exit intExpression Leave YATS with the given exit status e env stringExpression Reads an environment variable and returns its value as string In case the variable does not exist the empty string is returned Env can be applied in normal expressions The most common application is to read and convert an environment variable specifying a parameter value e g see also Section 10 1 on page 44 buf int env BUF generates a syntax error if BUF not set Multiplexer mx NINP 10 BUFF buf OUT sink 3 5 References Literals References The construc
77. see below DIST objects providing distributions of cells per state for zero cell rate see below TRANS matrix of transition probabilities row by row double VCI VC number of generated cells OUT input name of the succeeding object Function The object class provides a GMDP source with geometrically if EX is given or with arbitrarily DIST is given distributed sojourn times In the latter case the distributions are imported from Distribution objects Section 7 2 on page 17 wich have to be defined in advance To define states with zero cell rate define a DELTA value of zero The EX entry then specifies the mean duration of this silence state the DIST entry gives the distribution of the duration Exported variables src Count number of sent cells Commands src ResCount Resets the cell counter Output data type Cell 7 1 7 GmdpStop a Source Following the Start Stop Protocol The source recognizes start and stop messages see Section 9 3 on page 44 sent by the succeeding object Therefore it possesses an input src gt Start Declaration and com mands do not differ from GMDPquelle Up to now the only corresponding object class is ShapCtrl see Section 7 7 3 on page 26 Both are used for the test of new classes Oct 5 1996 Now also the ABR source is a candidate for GmdpStop YATS Yet Another Tiny Simulator User s Manual for Version 0 3 16 7 1 8 Source Reading IATs from a Trace File Declaration
78. st 23 YATS Yet Another Tiny Simulator User s Manual for Version 0 3 8 0 9 0 10 0 11 0 7 4 MuxAsyncAF Asynchronous Output Arrival First ss 23 7 4 5 MuxSyncDF Synchronous Output Departure First 23 7 4 4 MuxSyncAF Synchronous Output Arrival First eee eres 24 7 5 bemultiplexer tori mt RO RESERR IRR RE EO pd eie 24 7 6 Sinks 7 Delay Line ian am ien ere e eben ente 24 7 6 1 SIDE R EENE E ebd eus 24 7 6 2 Sink Writing IATs to a Trace File sess 25 7 6 3 Delay Line iiec ea ere per E EO preis 25 7 7 Shaping Pohicmg ues et ae ip reper iem eo ete adios 25 TE Peak Rate Shaper with Integer Cell Spacing ssssss 25 7 71 2 Peak Rate Shaper with Arbitrary Cell Spacing sess 26 7 7 3 Shaper Using the Start Stop Protocol sese 26 7 74 Leaky Bucket Policing Function essere 26 7 8 AALS CONMECUOMNS ve ee eee rep e septs ipee ote tec ee e ei 27 7 8 AAL Sender unn eave ae ERE OU ener eae 27 TEZ NATe S RECEVER used ette ERR ERE lens RE cantons 28 7 8 3 AAL 5 Receiver with Concurrent Reassembly sess 29 7 9 CTD and IAT Measurements Seeerei ereet eene entente nnne tenen netten nene 29 7 9 1 Measurement Device cenie er enne ener nnne nene 29 7 9 3 More Complex Measurement Device
79. tcpr PRCOQ LEN current length of the processing queue packets tcpr gt PRCQ_MAX_LEN max PRCQ_LEN tcpr gt ACK_CNT number of ACKs sent tcpr WND current window size bytes not yet necessarily advertised tcpr ARRIVED SEGMENTS total number of arrived packets tcpr ARRIVED BYTES total number of arrived bytes without headers tcpr ARRIVED VALID BYTES bytes arrived in the advertised window between nxt and nxt wnd tcpr USER PACKETS number of packets sent to the successor tcpr USER BYTES number of bytes forwarded to the successor tcpr OUT OF ORDER SEGMENTS number of packets received out of order tcpr OUT OF ORDER BYTES bytes received out of order without headers Commands The command t cpr ResetStat resets the following variables ARRIVED SEGMENTS ARRIVED BYTES ARRIVED VALID BYTES USER PACKETS USER BYTES PRCQ MAX LEN RESQ MAX LEN YATS Yet Another Tiny Simulator User s Manual for Version 0 3 38 OUT OF ORDER SEGMENTS OUT OF ORDER BYTES ACK CNT THROUGHPUT SDU DELAY Data types Input tepr gt Data TCPIPFrame Input tcpr gt Start Data Output OUTDATA Frame Output OUTACK TCPAcknowledge 7 11 3 TCP Application Constant Frame Distances Declaration CBRFrame src DELTA lt int gt LEN lt int gt StartTime lt int gt EndTime lt int gt BYTES lt int gt CONNID lt int gt OUT lt object input gt
80. ther notes in Section 11 2 on page 49 4 0 Modular Description of Complex Network Structures 4 1 Commented Example Some kind of hierarchical system description can be achieved using macros literals and string manipulation The gain in clarity of course depends on the complexity of the sub models Macros can be used to define sub models since network objects are not local to the current block They continue to exist and are never deleted The following example macro defines a simple end system consisting of a source and a delay line YATS Yet Another Tiny Simulator User s Manual for Version 0 3 8 Name and nxt are string arguments which are converted into identifiers using lit see Section 3 5 on page 7 macro endsys name load delay nxt CBRquelle lit name S DELTA int 1 0 load VCI 1 OUT lit name L Leitung lit name L DELAY delay OUT lit nxt To connect the end systems to a multiplexer some string manipulation can be used string i converts i into a string which can be concatenated with the rest macro idx bas i this macro is defined in MACROS idx bas string i var i for i 1 to 10 endsys idx src i 0 05 i idx mux gt I i Multiplexer mux NINP 10 BUFF 100 OUT snk Senke snk Sim gt Run SLOTS 500 print srcec 1 S gt Count An This first version has the disadvantage of less readable code due to the idx
81. ts below provide replacements for real pointers to scalars and arrays They allow to create and use references to variables macros and network objects as well as to arrays of these entity classes e ref entityID y Returns a reference to the given single entity which nevertheless may be part of an array The generated reference actually is a string encrypting the ID and additional block information It should only be assigned to variables but never be manipu lated e ref baseID validExampleIndices Returns a reference to an array of entities BaseID is the identifier without the indi ces which shall be added when resolving the reference ValidExampleIndices are used to construct a complete valid identifier necessary to bind the reference to the home block of the entity provides savety see Section 11 1 on page 48 The YATS Yet Another Tiny Simulator User s Manual for Version 0 3 7 generated reference actually is a string encrypting the ID and additional block and index information It should only be assigned to variables but never be manipu lated e deref scalarRef deref arrayRef indices Deref resolves the given reference The number of indices supplied is checked against the number declared in the corresponding ref expression If the entity is a macro parameters are appended as usual e g deref mRef x For net
82. uency times 1 25 On a mouse click on the window area a file name to store the current distribution con tent ASCII format is asked for Exported Variables histo Dist i frequency counter of value i Commands histo gt ResDist Resets all counters Remarks See remarks for the Meter object 9 0 Data Object Classes 9 1 Used Data Object Classes Derivation Relations Different network object classes communicate via different data object classes Cur rently the following data classes are defined 1 Data Base class Only contains a time stamp generation time Contains a hook to embed other data objects 2 Cell ATM cell derived from Data Contains a VCI number 3 RMCell ABR ressource management cell derived from Cell Contains RM data YATS Yet Another Tiny Simulator User s Manual for Version 0 3 43 4 AALSCell Cell with payload carrying cell and AAL SDU sequence numbers Derived from Cell Normally is used to embed other data objetcs 5 Frame Data frame only containing a length indicator used for TCP Section 7 11 on page 35 Derived from Data 6 TCPIPFrame PDU of TCP connections Section 7 11 on page 35 Derived from Frame 7 TCPAcknowledge PDU of TCP carrying acknowledgement information Derived from Frame The check whether the data item received by a network object is the same as expected or derived from it is performed at run time The mechanism is implemented as inte
83. uns BOK KKK KKK KK KK KK I KR I OR kokck ckckck ck kck ck ckck ck kck ke ke e x kx model description nsrc 60 number of sources for i 1 to nsrc nsrc Ethernet like sources BSquelle src i EX 32 ES 2720 DELTA 15 VCI i OUT mux gt I i Multiplexer mux NINP nsrc BUFF blen OUT sink Senke sink ROKK RK KKK Kk Ck KK KK RK I KC Kk KC KOC k KOC OR kokok ko kok ko kk k ko ke ke ke ke x e e x x t warm up nruns simulation runs Sim gt Run SLOTS slots one run for warm up for i 1 to nruns var k sent mux gt ResLoss reset loss counters in mux for k 1 to nsrc src k ResCount reset departure counters Sim gt Run SLOTS slots simulate the model sent 0 0 force sent to be a double value for k 1 to nsrc add departure counters sent sent src k Count ploss i mux Losses 1 nsrc sent store the result YATS Yet Another Tiny Simulator User s Manual for Version 0 3 45 BOK KKK KKK Kk Ck KK KK IK kCKCK kCKCkCk KCkCk kCk ck kck ck kckck ck kck ck kck ck ckck ck kck ck ke ke e kx calculate confidence interval output result The macro Confid95 is defined in the file MACROS It expects the reference to the array containing values its length and the references to the variables where to store results F F x var mean lo up Confid95 ref ploss 1 nruns ref mean ref lo ref up print blen Nt
84. work objects extensions also follow the normal rules e g deref objRef index command Example see also Section 5 0 on page 12 and Section 10 1 on page 44 var Xe yil yL2Zly rl 23 x 1 y 2 2 rl ref x reference to x r2 ref y 1 reference to y 1 and y 2 print deref rl1 2 Mn yields output 3 print deref r2 2 2 n yields output 4 deref r1 0 assignment to x For an exact syntax definition of identifiers comprising ref constructs see Section 3 2 on page 4 additional remarks are found in Section 11 1 on page 48 Literals Generally references should be used wherever possible since they provide some degree of savety see Section 11 1 on page 48 References always can be used if an entity already defined is referred to When writing e g macros which shall create com pound network objects like an entire switch then problems may arise The following identifier substitution will be usefull e lit stringExpr The effect is the same as it would be for deref st ringExpr except that stringExpr can be created arbitrarily Additionally the restrictions of deref only index expansion do not apply Thus lit can be used to flexibly generate new identifi ers For an exact syntax definition of identifiers comprising lit constructs see Section 3 2 on page 4 For applications see Section 4 1 on page 8 Please pay also attention to the fur
85. x number of out of rate cells to be stored int default BUFFABR HI THRESH optional turn congestion indication on int default BUFFABR LO THRESH optional turn congestion indication off int default HI THRESH TBE transient buffer exposure for connection negotiation int AT measurement interval for ABR traffic time slots int CBRI optional measurement interval for non ABR traffic time slots int default AI ZOL optional z value in case no ABR bandwidth available default 1000 LINKCR optional output link cell rate cells per second double default 353207 55 TARGUTIL target link utilisation double DYNFAIRSHARE optional use number of active connections for calculations see below BINMODE optional no ER feedback is written into RM cells pure CI bit mode OUTBRMC where to send backward RM cells OUTDATA multiplexer output Function YATS Yet Another Tiny Simulator User s Manual for Version 0 3 33 The AbrMux is an ABR multiplexer with ERICA and binary CI bit feed back and backward RM cell processing ABR and non ABR traffic use different buffers All ABR traffic virtually shares one buffer but the amount of out of rate RM cells can be limited The multiplexer serves cells in the following order 1 non ABR cells 2 in rate RM cells 3 out of rate RM cells 4 ABR data cells Thus RM cells overtake ABR data cells The binary feedback watermarks ar
86. yer bit rate Mbit s default 149 76 Mbit s PROCTIM optional processing time per sent packet msec default 0 3msec TICK optional length of TCP clock tick msec default 5 00msec RTOMIN optional minimum retransm timeout msec default 1500msec OQWM optional maximum output queue length packets default 2 packets LOGRETR optinal print retransmission messages on off default off REC name of the peer TCP receiver object OUTDATA where to send TCP frames OUTCTRL control input of the preceeding network object Function The object implements the TCP sender functionality The IP part only is reflected by 20 bytes IP overhead in each packet generated On the input t cps Data frames con taining a length indicator are expected On this input a network object following the start stop protocol see Section 9 3 on page 44 is expected it is stopped in case the input buffer is full The frames are segmented and appropriate TCP IP frames are gen erated The TCP sender also can be stopped by its succeeding network object start stop protocol the start input is tcps Start The input expecting the acknowl edgement packets is tcps gt Ack The following algorithms are implemented by the object class e Slow start and congestion avoidance e Silly window syndrome SWS avoidance according to RFC 1122 section 4 2 3 4 The implementation differs slightly condition 3 in this section is not subject to Nagle s algorithm i e

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YATS – Yet Another Tiny Simulator User's Manual for Version 0.3