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SNMP Application for the MINT Router (Walkstation II project)

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1. Figure 16 The message exchange during one cycle of the power control for the MS transmitter The manger asks the BS how strong the signal received from the MS is RSS Received Signal Strength It computes the Designated Signal Strength DSS i e the signal strength at which the MS MINT should send Then it asks the MS to adapt the DSS The execution of the power control loop in realtime is critical So far the manager program which runs on a SUN SPARC workstation pretending to manage one BS mobile MINT relationship The corresponding agents also execute on workstations If the signal strength of N mobile MINTS in a cell has to be controlled the message exchange diagram of figure Fig ure 16 will be modified to one Get Bulk Request from the manager to the BS MINT in order to read the received signal strength on the N radio links At the reception of the reply the management process will send a set DSS request to all the active mobile MINTs which need to adjust their signal strength The Get Bulk Response will actually inform the manager about the state of a radio link active or idle and about new mobile MINTs for which a power control session must be set up 3 4 The Implementation 3 4 1 The Agent For the time until the device driver is available the MIB variables are all contained in a structure which is a straightforward translation of the ASN 1 SMI definition into C types Extensions to the CMU agent were necessary to support th
2. SNMP Application for the MINT Router Figure 2 The main elements of the wireless LAN are the Mobile INTernet MINT Router and a Spread spectrum Radio Transceiver The MINTs run a special Network Layer Protocol which is an extended version of the Internet Protocol ZP with mobility support It is important to note the symmetric relationship between the Base Station BS and the Mobile Station MS i e each MS has basically the same equipment as a BS The wireless LAN which is being developed is a cellular system based on spread spectrum technology section 2 3 Neighbour cells use different virtual channels In order to provide a seamless access to the network Mobile Stations MS which change cells will be subjected to handover For each cell there is a Base Station BS which provides the access to the wired Network and thus to the Internet These features resemble existing cellular systems However the framework of the Walkstation II project differs in one point very strongly from them The system does not have the typical top down hierarchy which we see in GSM or DECT In these systems a BS controls the allocation of the radio resources in a cell or keeps at least track of them From this point of view the KTH system more closely resembles an ethernet than a cellular mobile telephone communication system The radio chan nel is a shared media which can be utilized by any station whenever it is free to send ethernet like Frames
3. rg LAN as IENE LELEI LAN MH MINT 2 MH MINT 1 P e o Figure 13 A possible NM configuration which corresponds to the top down structure of a traditional mobile communication system Although it looks quite simple in this scheme it is more difficult to realize than the current approach Figure 14 One reason is the limited processing power of the BS MINTS controlling the cell managers The question is now which different kinds of processes we need and on which machines they should execute As we saw in section 2 2 a MINT has basically the same capabil ities for running UNIX programs as a small SUN Microsystems workstation On the other hand it is possible to implement dual role SNMP entities 1 which have at the same time a manager role and an agent role So a possible solution to the problem would be that a Base Station BS MINT runs such a dual role entity with a manager communicating with the Agents at the Mobile Stations MS MINT and an Agent serving the queries from the top level Manager Figure 13 This approach which is inspired by the top down hierarchy of traditional mobile communication systems is not suitable for the Walk station II management for several reasons As we stated in section 2 1 the relationship between BS MINTSs and MS MINTs is basically symmetric at least in hardware and thus the managed objects in a page 26 SNMP Application for the MINT Router BS MINT and in an MS MINT are mostly the same
4. with the path specification to the subdi rectory in which the tcl module is installed on your system You can now generate the executable shell code the by typing make in the corresponding subdirectory Don t worry about warnings like cmu parse ce 433 warning do subtree was declared implicitly extern and later static User s manual Before running the browser it is important to specify the MIB file which should be parsed by setting the environment variable MIBFILE This is done by typing the following command in e g in an xterm setenv MIBFILE Mib Subdir my MIB txt Where Mib Subdir is the subdirectory where the MIB file is located and my MIB txt is its filename The customized version of the Tcl shell called br wish for browser window shell can now be launched by typing page 42 SNMP Application for the MINT Router br wish in the xterm The br wish code automatically starts the MIB parser and displays parser errors in the xterm An empty new window appears on the screen and the br wish prompts for interactive com mands in the old xterm The set of supported commands consists of the standard Tcl and Tk com mands 8 and on the commands specific to the MIB browser application After running br wish only the C programmed commands are available Table 1 gives a short description each of them From now on the MIB resides in a memory buffer until the user quits the shell by
5. Furthermore running a manager process needs more processing power than running an agent process The processing load will increase when more MSs are being served in a cell Running a dual entity on a BS MINT could easily overburden it with management processing and prevent it from doing its actual job the routing Figure 14 shows the configuration which we chose for the Walkstation II NM In this approach the cell manager executes at a workstation connected to the fixed network This structure takes into account the symmetry of the relationship between BS MINTs and MS MINTs Another advantage of this approach is that we can manage with one enterprise specific MIB and one type of Agent process for all the MINTs This is an important aspect of the software development In the rest of this section we only consider cell management Due to lack of time it was not possible to work on the implementation of the top level management Top MS 5 LAN bs S TMA aN LAN MH MINT 2 o o A Figure 14 The current configuration of the MN system of the Walkstation II project The management processes running at the Management Stations MS 1 and MS 2 control one cell each and report to a global management process which controls the whole system All the MINTs run the same type of Agent supporting one universal MINT MIB 3 3 2 The MIB Having fixed the configuration of the NM processes we now need to look at the
6. The packets are routed correctly towards the host on the Home LAN The inverse is not possible as the MH s traditional IP address implies that it is located on his home LAN In the Walkstation II project the Mobil IP protocol 13 14 which is described hereafter is used to overcome this kind of problem It was already implemented and tested in an earlier project at Columbia University 15 The specification of Mobile IP is currently an Internet Draft 11 It has the goal of specifying protocol enhancements that allow transparent routing of IP datagrams to Mobile Nodes in the Internet 11 Mobile IP fulfils the following requirements A Mobile Node using its Home Address shall be able to communicate with other nodes after having been disconnected from the Internet and then reconnected at a different point of attachment A Mobile Node shall continue to be capable of communicating directly with existing nodes that do not implement the mobility functions described in this document 11 From the second statement follows that no protocol enhancements are required in hosts or routers that are not serving any of the mobility functions Similarly no additional protocols are needed by a router that is not acting as a Home Agent or a Foreign Agent to route datagrams to or from a Mobile Node 11 Mobile IP is mainly based on three different types of entities The Mobile Host MH the Home Agent HA and the Foreign Agent
7. number of samples which is carefully chosen by the implementor Variance of the rtVrss The average of the received signal strength RSS Bit Error Rate rtBer The Bit Error Rate which is measured in the communi BER cation with the remote MINT Router Frame Error Rate rtFer The Frame Error Rate which is measured in the com FER munication with the remote MINT Router Last Received rtRecTstamp The Time Stamp of the last received packet from the Time Stamp remote entity Last Sent Time rtSentTstamp The Time Stamp of the packet which was last sent to Stamp the remote entity address for each When considering single radio links we still notice that they have some features in common The agent should be able to handle information about a radio channel in general Furthermore it is desirable that a MINT can listen to several radio channels This is essential for handover procedures Therefore the channel data is also contained in a conceptual table This channel table is referred to as chTable in the page 29 SNMP Application for the MINT Router MINT MIB module Each radio channel which is known to a MINT is represented by a row entry Table 4 Fields of a row in the Channel Table MIB Object Field Name Label Description Channel Identity The integer identity of the channel The value of this field corresponds to the one of the field rtCh annelld for the actual users of the channel Spreading Code chSpreadCode The Spr
8. CMOL Protocols Mac Graw Hill 1992 Heinz Gerd Hegering Sebastian Abeck Integriertes Netz und Systemmanagement Addison Wesley 1993 Fred Halsall Data Communications Computer Networks and Open Systems Addison Wesley 3rd edition 1992 Andrew S Tanenbaum Modern Operating Systems Prentice Hall International Editions 1992 Maurice J Bach The Design of the UNIX Operating System Prentice Hall 1986 Douglas E Comer David L Stevens Internetworking With TCP IP Volume II Prentice Hall 1991 Anders Klemets Gerald Q Maguire Frank Reichert Mark T Smith MINT A Mobile Internet Router First IEEE International Symposium on Global Data Networking 1993 Bruce Tuch An Engineer s Summary of an ISM Band Wireless LAN NCR Systems Engineering Utrecht 1991 Frank Reichert Integration of Mobile Communication into Fixed Networks Proceedings of NORDUnet 93 Helsinki Network Working Group IP Mobility Support Internet Draft May 1994 Daniel Kerek Hannu Tenhunen Gerald Maguire Jr Frank Reichert Direct Sequece COMA Technology and its Application to Future Portable Multimedia Communication Systems IEEE ISSSTA 794 Third International Symposium on Spread Spectrum Techniques amp Applications John Ioannidis and Gerald Q Maguire Jr The Design and Implementation of a Mobile Internetworking Architecture In USENIX Winter 1993 Technical Conference pages 491 502 USENIX Association J
9. IDENTIFIER enterprises 933 myFirst OBJECT IDENTIFIER KTH 1 myFirstInt OBJECT TYPE SYNTAX INTEGER ACCESS read write STATUS optional DESCRIPTION The first integer variable for testing myFirst 1 myFirstString OBJECT TYPE SYNTAX DisplayString ACCESS read write STATUS optional DESCRIPTION The first string variable for testing myFirst 2 END Add in file cmu snmp2 agent snmp_vars c the definition of a new subtree of variables in our case it consists of an integer valued and a string valued leaf object these are the values of the magic number define MYFIRSTINT 0 define MYFIRSTSTRING 1 struct variable is defined in snmp_vars h struct variable myFirst_variables MYFIRSTINT INTEGER RWRITE var_myFirst 1 1 MYFIRSTSTRING STRING RWRITE var_myFirst 1 2 i var_myFirst is a pointer to a function which is able to access the actual values of the conceptual var iables It is a generic function for all the variables which are grouped under the same subtree The magic number MYFIRSTINT and MYFIRSTSTRING is an integer which will be passed as a parame ter to the function var_myFirst It will allow the function to decide which variable of the subtree should be grabbed page 52 SNMP Application for the MINT Router C The CMU SNMP software development package How to support a new variable on the Agent side The MIB is not an actual database Let us
10. Managers can control clusters of machines or even subnetworks They report to the higher level Managers by filtering out the detailed information which is not of concern from a global point of view When specifying the actual Manager and Agent processes in this section we will see that the spatial considerations of section 2 5 are valid to some extent for the description of the two NM levels They still need refinement if we look at the functional blocks inside the Manager and Agent tasks Due to the cellular structure of our system it is suitble to control single cells at a lower NM level and the whole system at a higher level The advantages of this approach are obvious e If the cells are managed independantly the system remains still avaible even if a break down of a single cell occurs page 25 SNMP Application for the MINT Router e The cell is likely to be the unit by which the communication system is extended The cell manage ment is the corresponding unit by which the NM can be scaled e The cell management can take care of the functionalities which have hard real time requirements e g the power control of the mobile transmitters e From a project management point of view it will be possible to run and control a single test cell before the whole system is installed So far we have decided to run a dedicated management process for each cell and one global manager Manager Top ms Y A BS MINT 1 ES
11. OBJECT TYPE SYNTAX DisplayString SIZE 0 255 ACCESS read only STATUS mandatory DESCRIPTION A textual string containing information n ifEntry 2 iffype OBJECT TYPE SYNTAX INTEGER other 1 none of the following regular 1822 2 ethernet csmacd 6 iso88023 csmacd 7 iso88024 tokenBus 8 The type of interface Figure 1c ACCESS read only STATUS mandatory DESCRIPTION ifEnty3 Figure 1 b Figure 17 Three times the same MIB segment a The ASN 1 SMI definition b the graphical MIB tree how it is often shown in literature c a screen dump of the browser which emerged from the work on the SNMP application for the Walkstation II project at the TS Lab of KTH page 41 SNMP Application for the MINT Router Tel and Tk Tcl and Tk 8 provide together a programming system for developing and using Graphical User Inter faces GUI Tcl stands for Tool command language It is a simple scripting language for controlling and extending applications It provides generic programming facilities that are useful for a variety of applications such as variables loops and procedures Furthermore Tcl is embeddable its interpreter is implemented as a library of C procedures that can be incorporated into applications and each applica tion can extend the core Tcl features with additional commands specific to that application One of the most useful extensions to Tcl is Tk It is a toolkit fo
12. all Internet standards SNMP is defined in a so called Requests for Comments RFC RFC 1155 Structure of Management Information SMI RFC 1157 Simple Network Management Protocol SNMP RFC 1212 Concise MIB definitions RFC 1213 Management Information Base MIB I After some time the customers started to ask for more security and less traffic overhead due to NM In 199 it was time for version 2 of SNMP which is often referred to as SVMPv2 To improve security SNMPv2 adds two mechanisms to the framework one for authentication and one for data encryption To help improve performance a new message type is supported which allows the manager to retrieve page 19 SNMP Application for the MINT Router contiguous blocks of information from an Agent with one request Whereas in version 1 one request for each variable was necessary Furthermore version 2 defines a message type which is used in a com munication between managers SNMPv2 is defined in RFC 1441 Introduction to SNMPv2 RFC 1442 SMI for SNMPv2 RFC 1443 Textual Conventions RFC 1444 Conformance Statements for SNMPv2 RFC 1445 Security Protocols for SNMPv2 RFC 1446 Security Protocols RFC 1447 Party MIB for SNMPv2 RFC 1448 Protocol Operations for SNMPv2 RFC 1449 Transport Mappings for SNMPv2 RFC 1450 MIB for SNMPv2 RFC 1451 Manager to Manager MIB RFC 1452 Coexistence between SNMPv1 and SNMP
13. as it is also done when everything is OK Generating interrupts when something needs to be done is optimal with regard page 18 SNMP Application for the MINT Router to data traffic Its main disadvantage is that it is hard for the manager to distinguish important interrupts from harmless ones By assigning different priorities to types of interrupt things usually get very com plex as this priority order depends strongly on the scenario Therefore many Network managers prefer the polling approach except for serious events In these cases the Agents have to become active and send a message to the Manager without being queried e g system failure and system start up These interrupt like messages are known as notifications in the OSI framework and as Traps in the Internet Framework Some differences between the mentionned standard protocols There are still many differences between the different NM approaches The rules for defining OSI man aged objects resemble much to the ones applied by modern Object Oriented Programming Languages E g they include inheritance which is not used by SNMP SNMP does not even distinguish between attributes and objects but rather treats attributes like objects 2 As the IEEE framework includes part of the OSI documents in its standards it is very similar to the OSI framework There are also major dif ferences in the methods which apply to objects A quite fundamental gap between OSI and Internet NM is
14. be in the format 1 3 6 1 2 1 2 and can be fed as parameter to the function ReFormat described below page 43 SNMP Application for the MINT Router Table 6 The C programmed Commands Example for the syntax Description ReFormat 1 3 6 1 2 1 2 The output of this function will be in the format also ReFormatiId 1 3 6 1 2 1 2 and can be fed as a parameter to the command ObjGold described in Table 1 This is also the Old format required by the interactive CMU test pro grams walky Display a tree depth first starting at the current node Read the depth and the width for the walk in the corre sponding input widgets lt click with the left Display the Old of the current node in the format mouse button into a 1 3 6 1 2 1 2 widget representing a node gt lt click with the middle Start a new walk from that node with the depth and width mouse button into a specified in the corresponding input widgets widget representing a node gt The Implementation of the MIB browser The implementation of the MIB browser consisted of three parts find and isolate the needed functions of the CMU software development package program in C some specific Tcl commands and link them together with the basic set of Tcl commands to a new executable Tcl Shell code program a shell script file which defines at a higher level additional Tcl commands Concerning the first part we can state that
15. devices which do not support the TCP IP protocol suite e g repeaters An SNMP Agent executing on another machine can take care of such an agent and report its state to the Manager This is known as a Proxy relationship page 20 SNMP Application for the MINT Router The Management Information Base MIB A Management Information Base MIB is supposed to specify the object resources which are sup ported by a given SNMP application The objects of an SNMP MIB are represented in a tree structure which resembles to a file system in a computer Figure 10 MIBs are written using a set of rules called Structure of Management Information SMI which is defined in the RFCs 1155 and 1442 SMI is based on ASN 1 notation but adds further conventions to it by restricting strongly the number of supported ASN 1 types and adding some ASN 1 macros to define objects textual conventions which is similar to ASN 1 subtyping etc The resulting text file contain ing a MIB turns out to be barely readable For this reason it is desirable to have a browser tool for look ing at MIBs Appendix A contains a description of the browser tool which was developed by the author while at the TS Lab Many of the SNMP managed Internet nodes have a common set of basic features for instance the specification of their communications interfaces or the protocols they use The corresponding object resources are known as the standard MIB specified by Working Groups of the Inte
16. optional DESCRIPTION The Average taken over the Frame Error Rate column rtFer in the rtTable chEntry 7 chTotPower OBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS optional DESCRIPTION The total power in the channel dBm chEntry 8 chNumbMh OBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS optional DESCRIPTION The number of MINT routers using the channel i e number of rows in the rtTable with the same value in the column rtChannellId chEntry 9 END page 51 SNMP Application for the MINT Router C The CMU SNMP software development package How to support a new variable on the Agent side The MIB is not an actual database Let us recall that in SNMP the notion variable stands for a pair formed of an object together with its instance A MIB only defines objects which are handled by an agent but it does not say how exactly the values are accessed This section describes how the CMU code must be extended to support a simple integer typed variable Goal We want to support simple i e non tabular instances of two objects The actual value will reside as a C variable in memory A manager process will be allowed to apply get and set commands to it The variable are defined as follows in the MIB this is a complete MIB module which can be compiled MINT MIB DEFINITIONS BEGIN enterprises OBJECT IDENTIFIER iso org 3 dod 6 internet 1 private 4 1 KTH OBJECT
17. see in section 3 3 what implications this has to the NM in the Walkstation II project The functional dimension The ISO Management Framework distinguishes 5 different functional areas in this dimension During the configuration the parameters in the different nodes of a network are set in a suitable way to inter connect the stations The fault management is in charge of keeping the availability of the network as high as possible It detects isolates and tries to repair faults The performance management tries to con trol and improve the characteristics of the available network e g response time throughput An important role of the accounting management is charging the user for the obtained services The secu rity management provides for data protection and prevents the abuse of network resources A more detailed information of the functional dimension is given in 3 Top level Mangement Process Managed Network Figure 8 Management Applications are often structured into independent management subsystems each controlled by its own Management Process which reports to a Management Process with a more global view The subsidiary processes filter out detail information which of no concern to the global Manager They can be distributed over the network or run on the same management station representing virtual subsystems System Management Network Management Integrated Network Management In the past a dif
18. set of managed objects page 27 SNMP Application for the MINT Router in a MINT The MIB which is supported by a MINT consists of two parts The standard MIB which must be supported by all conforming SNMP managed entities and the MINT specific enterprise MIB Let us consider each in turn The standard MIB The standard MIB is defined in RFC 1213 Its full label is MIB II It defines object groups i e sub trees in the MIB structure concerning the system 1 e the managed machine the physical interfaces and the protocols ip icmp tcp udp The MIB II definitions can be found in the file mib txt which is included in the CMU package This MIB moudule is supported by the sample agent of the CMU software development package As the MINTs use rather Mobile IP than IP as network layer protocol the MIB II needs to be completed by some mobileIP group in MINT MIB module This part has not been realized yet Table 2 Some object groups of the standard MIB II Group label Description system Mainly textual information about the managed system which tells a human manager were the machine is located building floor room who is responsi ble for it phone etc interfaces Description of the machine s physical interfaces Besides the general proper ties the of the interface e g type bitrate and its current state e g number of discarded packet since last reboot this group contains a pointer to an inter
19. the files parse c and mib c with very few modifications and their include files of the CMU library are essential The implementation of the extended Tcl command set in C was is most tricky for beginners It is con tained in the file tcl_browser c Each command is defined in two parts The actual implementa tion of the function using a prescribed header format 8 and a call to the Tcl C function Tcl CreateCommand which adds the command to an interpreter and tags a command name to it Concerning the third part all the definitions are in the Tcl shell script file browser tk The core pro cedure in this file is called walk It is a recursive function which goes depth first through the tree structure of the memory buffer until the specified depth and width are reached It creates and binds all the button widgets which represent the nodes Bugs and proposed improvements There is no miracle bugs still exist in the code Furthermore some not so sophisticated things could be added in order to improve the MIB browser Some parts of the file parse c should be revised Due to lack of time it was not possible yet to do this Therefore the browser has to cope with these problems Just to mention two among them e Some statements which are SMI conform can not be parsed In such a case the program still dis plays a message which states on which line the error occurred A practical way of overcoming this kind of problems is comparing this line
20. the radio interface as a whole but we have to consider the radio links separately The link specific information is contained in the Router Table which page 28 SNMP Application for the MINT Router is referred to as rtTable in the module MIB module MINT MIB see Appendix C Its fields are explained in Table 3 Each remote MINT router which can be received and reached has an entry to this table The first field Local MAC Address needs a short explanation The hardware of the MINTs may be extended by more radio interfaces in the future and thus it will be necessary to specify the MAC Table 3 Fields of a row in the Router Table Field Name MIB Object Label Description Local MAC rtLocLinkAddress The Ethernet Address of the local radio LAN interface Address which must be used to reach the remote MINT Router Especially BS MINTs can have serveral interfaces Remote MAC rtRemLinkAddress The Ethernet Address of the remote MINT Address Channel Identity rtChannelld A pointer to a row in the Channel Table describing the channel on which the remote entity is received Designate Signal rtDss The transmitted signal strength to which the local radio Strength device has to be set when communicating with the remote entity Received Signal rtRss The signal strength with which the last incoming frame Strength RSS from the remote entity was received Average RSS rtErss The average of the received signal strength taken over a
21. typing exit All manipulations Table 5 The C programmed Commands ObjGoId Set the current position in the MIB buffer to the specified fl 36 ak el 2 Object Identifier Displays the Object label for success in our example interfaces ObjGoLabel interfaces Set the current position in the MIB buffer to the specified Object Label Object labels must be unique If they aren t this command goes to first found ObjChild 1 Set the current position to the n th child of the current node in the MIB buffer This does usually not correspond to the n th child in the MIB definition Obj Parent Set the current position to the current node s parent Obj Label Display the label of the current node The output of this command can be fed as a parameter to the function ObjGoLabel Obj SubId Display the subidentifier e g 2 for interfaces which follow will refer to this buffer and not to the MIB file If the MIB file is changed br wish must be quitted by typing exit and started again The user can now run the tcl shell script file browser tk which contains the second part of the command set specific to the browser This is done like in some other shell languages by typing source browser tk The Tcl command set is now further extended by the commands shown in Table 2 Table 6 The C programmed Commands Example for the syntax Description ObjId Display the Object Identifier of the current node The out put will
22. 2 etc page 54
23. 5 SNMP Application for the MINT Router 2 The Walkstation IT Project The Walkstation II project is being conducted at the Royal Institute of Technology Its purpose is to cre ate a wireless LAN with access to the Internet This chapter gives an overview on the Walkstation II project The first subsection shows the planned system from a global point of view The following three sections describe shortly its main functional blocks These are the Mobile INTernet Router MINT the Radio Transceiver an the Mobile IP Protocol The last section of this chapter states the requirements for the Network Management Application 2 1 The system In the Walkstation II project the software and hardware for communication and mobility support is located in a separate device the MINT implied byFigure 1 This approach has some major advan tages The MINT can be designed in a way that it is compatible with many different types of Mobile Hosts MH and the operating system of the MH does not have to undergo any modifications Further more the mobility does not cause additional computational load on the MH The wireless communica tion devices for the mobile host and for the base station are MINTs which are identical in hardware The actual asymmetry is in software in the implementation of the network layer protocol Mobile IP see section 2 4 This protocol allows the user to change LANs yet still being reachable via a tempo rary network address page 6
24. Agent which actions it must apply to the managed devices The Agent and the Management Process have both knowledge about the Management Information Base MIB which contains the object resources which are handled by an Application control messages to the Agent which executes at the managed entity and takes locally the correspond ing measures The information about the managed objects is contained in the Management Information Base MIB which is known by both the Manger and the Agent The three approaches to NM are all fairly object oriented In computer sciecne object oriented stands for an approach to software analy sis in which a computer program is based on a framework of elements objects which are described by attributes information and methods actions A MIB contains typically objects describing the state of a whole system hardware devices physical interfaces and programs in particular communica tion protocols Polling versus Interrupts As in any control system the question about polling or interrupt is important in NM Should a control process regularly send messages to a managed system in order to check its state polling or should the managed system notify the control process of special events interrupt The advantage of polling is that the manager can always distinguish the importance of different tasks and schedule them according to their priority On the other hand polling might cause more unnecessary data traffic
25. FA The Mobile Host which is attached to a new unknown subnetwork gets in touch with the FA by any means Either the foreign agents advertises its presence in its local subnetwork or the Mobile Host looks for it by sending out request messages After this the MH regis ters at its new location i e it gets a temporary IP address the so called Care Of Address To do so the MH contacts the FA which does the registration at the HA The HA has now knowledge about the MH s current location and is ready to forward the packets to its destination This forwarding is done by encapsulating the IP packets which are destined to the MH s constant network address into an IP packet with its Care Of Address as destination The encapsulated packet is finally decapsulated and page 10 SNMP Application for the MINT Router delivered to the MH by the FA There is variant to this scheme which manages without the concept of Foreign Agents In that case the registration is done directly by a message exchange between the MH and the HA and the MH is in charge of decapsulating the forwarded packets However the HA remains the entity which keeps track of the MH s location The draft also treats security issues but the description of the authentication scheme that is used is beyond the scope of this overview The reader is referred to 11 for more detail encapsulation decapsulation Figure 5 Mobile IP solves the problem of Figure 4 The Mobi
26. For example if a walk with depth 3 is done then at each node the last three children are taken into account rather than the first three This is not what one would normally expect A smarter version of the recursive shell script function walk in the file browser tk could help page 45 SNMP Application for the MINT Router B The MINT MIB module MINT MIB DEFINITIONS BEGIN IMPORTS TruthValue DisplayString TestAndIncr TimeStamp PhysAddress RowStatus FROM SNMPv2 TC KTH OBJECT IDENTIFIER enterprises 933 myFirst OBJECT IDENTIFIER KTH 1 The mint group defines the data structures which are needed to control the radio device associated with a MINT router mint OBJECT IDENTIFIER KTH 2 The myFirst group gives two examples of the definition of objects with simple instances myFirstInt OBJECT TYPE SYNTAX INTEGER ACCESS read write STATUS optional DESCRIPTION The first integer variable for testing myFirst 1 myFirstString OBJECT TYPE SYNTAX DisplayString ACCESS read write STATUS optional DESCRIPTION The first string variable for testing myFirst 2 The rt router subgroup defines data which are specific to a MINT Router Note that this kind of data is stored by both a Mobile Host MH and a Base Station BS associated MINT Router rt OBJECT IDENTIFIER mint 1 rtTable OBJECT TYPE SYNTAX SEQUENCE OF RtEntry ACCESS not accessible STATUS optio
27. GER chEVrss Average of rtVrss INTEGER chEBer Average of rtBer INTEGER chEFer Average of rtFer INTEGER chTotPower Total received Power INTEGER chNumbMh Number of users in the channel INTEGER chId OBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS optional DESCRIPTION Row index of the channel This value is identical to the rtChannelId which points here chEntry 1 chRowStatus OBJECT TYPE SYNTAX RowStatus MAX ACCESS read create STATUS optional DESCRIPTION The status of a conceptual row in the Channel Table chEntry 2 chSpreadCode OBJECT TYPE SYNTAX BIT STRING ACCESS read write STATUS optional DESCRIPTION page 50 SNMP Application for the MINT Router The Spreading Code used in this channel chEntry 3 chEErss OBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS optional DESCRIPTION The Average taken over the column Average Received Signal Strength rtErss in the rtTable chEntry 4 chEVrss OBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS optional DESCRIPTION The Average taken over the column Variance of the Received Signal Strength rtVrss in the rtTable chEntry 5 chEBer OBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS optional DESCRIPTION The Average taken over the Bit Error Rate column rtBer of the rtTable chEntry 6 chEFer OBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS
28. Mellon University CMU was chosen as SNMP implementation for the Walkstation II project It includes the C code of a sample Agent which supports the object resources defined in the standard MIB II This MIB is com mon to all the conformly managed Internet nodes It defines objects about the managed system and the state of its physical interfaces It also contains objects for the most common protocols of the TCP IP suite which are used by the managed machine This part of the agent s code remains to be ported to the MINT hardware Since the management information defined in the MIB II is often not sufficient to describe a managed Internet node The SNMP framework povides means for defining MIBs which are specific to the man aged node For the MINT router we needed to define objects concerning the state of a radio device The enterprise specific MIB which was created completes the standard MIB by a group of objects describ ing a radio channel and a group of objects describing the state of a radio link The new MIB can be parsed and instances of its objects can be retreived from the modified CMU agent So far all the actual variables are defined as C structures even those which will ultimately be accessed through the radio device driver On the manager side particular attention was paid to the control mechanism the strength of the trans mitted signal This part of the requirements for the network management application is hard to fulfill because o
29. Multiple events are awaited by an ordinary select call with a specified set of file descriptors A list of all the UNIX sockets which are bound to SNMP sessions with outstanding requests can be obtained by acall to the SNMP library function snmp_select_info This function returns as soon as a packet or an interrupt is received The packet can then be retrieved from the appropriate socket by a call to the function snmp_read The code of the manager is aranged in different C files in the subdirectory cmu snmp2 wstat_ manag The file BS MINT mang c contains all the definitions necessary for handling a the power con trol seesion with a BS The file MS MINT manag c contains all the definitions needed in the context of page 34 SNMP Application for the MINT Router a power control session with a mobile MINT page 35 SNMP Application for the MINT Router 4 Summary and Conclusion The organization of network management at different levels helps to control different subnetworks in an independant way This approach leads to a structure of the network management in the Walkstation II porject at two levels a global level and a cell level The global level which wil have a monitoring function over the whole system and allow for configuring the system in a suitable way has been planned but not yet implemented Parts of the cell level management have been realized and tested on workstations which have a similar processing power similar to the MINT route
30. SNMP Application for the MINT Router AYES KUNGLTEKNISKA H GSKOLAN G KONST E a NY See SNMP Application for the MINT Router Walkstation II project Markus Oelhafen EURECOM Institute June 1994 The Royal Institute of Technology Institut EURECOM Departement of Teleinformatics TSlab BP 193 Electrum 204 F 06904 Sophia Antipolis Cedex S 164 40 KISTA FRANCE Sweden page 1 SNMP Application for the MINT Router SNMP Application for the MINT Router Walkstation II project Markus Oelhafen EURECOM Institute Ecole Nationale Sup rieure des T l communications de Supervisors Paris Telecom University of Paris January June 1994 Prof Gerald Q Maguire The Royal Institute of Technology Departement of Teleinformatics TSlab Electrum 204 S 164 40 KISTA Sweden Prof Pierre Humblet Institut EURECOM CICA BP 194 F 06904 SOPHIA ANTIPOLIS C dex page 2 SNMP Application for the MINT Router Acknowledgements I would like to express my gratitude to a number of people who have helped me during my work at KTH Special thanks go to the head of the Teleinformatics Department of the Royal Institute of Technology KTH Professor Bj rn Pehrson who accepted me as a thesis student in the Telcommuncation Systems Laboratory TSlab group My work at KTH was financially supported by Ellemtel Utvecklings AB Thanks go to this enterprise Much credit for this Master Thesis should go to my superviso
31. Technology Netherlands 17 Unlike the other implementations it uses the multi tasking facilities of the UNIX Operating System The SNMP Protocol Machine SPM is one task which communicates by means of interprocess communi cation with the management application Multiple applications may use the same 17 SPM This can be interesting especially for large multilayered NM applications Figure 7 3 3 The Design of the SNMP Application This section describes the architecture of the SNMP Application for the Walkstation II project It does not consider details of the implementation using the CMU software development package It actually shows the NM framework of a system which should meet the requirements for NM stated in 2 5 for the mobile communication system sections 2 1 2 4 using SNMP section 3 2 This section has four subsections Section 3 3 1 shows how the NM functionalities can be classified into blocks From these considerations will follow the Information which is present at the entiities 3 3 2 and the functional blocks of the Agent 3 3 3 and the Manager 3 3 4 3 3 1 The different NM functionalities at two levels In section 2 5 we looked at NM requirements in space and in time In space we distinguished require ments for station management cell management and system management In section 3 1 Figure 7 we saw that it is ofen desirable to organize the management functionalities at diffent levels Let us recall that subsidiary
32. This chapter Network Management NM is structured into different sections Section 3 1 treats gen eral issues of NM Besides the goals and the evolution of Network Management it contains considera tions about how to classify the different tasks of Network Management and an overview on three common management protocols Section 3 2 gives an introduction to the Simple Network Management Protocol SNMP It includes the architectural framework the underlying protocol suite and the imple mentations of the protocol which are available on the Internet Section 3 3 introduces the general struc ture of the SNMP Application for the Walkstation II Project Section 3 4 contains issues concerning the actual implementation This section is completed by rather technical details in the Appendix Functional dimension Performance Fault Configuration Components Planing Realisation Operation System Application Enterprise Time dimension Scenario dimension Figure 7 The issues of the wide Network Management field can be classified into three dimensions The scenario the time and the functional dimension 3 1 Overview on Network Management Management of a communication system has always been a field where technical economical and political decisions had to be taken Needless to say that the solution to a problem is often requires com promises between different interests rather than being optimal from one point of view Sin
33. and it is released immediately after that section 2 2 For instance it is possible for an MS to page 7 SNMP Application for the MINT Router send data directly to another MS within the same cell without utilizing the BS The Base Station is needed to route data packets to and from the fixed network and to and from other cells Therefore the approach of the Walkstation II project is somehow a synthesis of a wireless data network which does packet routing and the location update facilities of a cellular radio system We will see in section 3 3 how these considerations influence the framework of the network management 2 2 The Mobile INTernet MINT Router The MINT resembles a host computer Figure 3 Besides the Central Processing Unit CPU it has cru ci jma _ _ t Ram Radio Rom DUAL PORT RAM SLIP PPP Network Host MH MINT ETHERNET DUAL PORT RAM Network MH MINT l Parallel et SG SS eS S E SSS E SS SS E Ser SS Figure 3 Basic components of a MINT Integrated Circuits containing ROM and RAM The MACH Kernel which was ported by Anders Klemets at the TS Lab allows to run an emulator of the a UNIX operating system and thus UNIX soft ware The computational power of the MINT is roughly 10 MIPS i e comparable with a SUN Micro systems SLC It is also equipped with multiple communication interfaces This is to provide compatibility with many different types of hosts as we
34. anuary 1993 J Ioannidis and G Q Maguire Jr The Design and Implementation of a Mobile Internetworking Architecture USENIX Winter 1993 Technical Conference pages 491 502 USENIX Association January 1993 John Ioannidis Dan Duchamp and G Q Maguire Jr IP based Protocols for Mobile Internetworking SIGCOMM 91 Conference Communications Architectures and Protocols pages 235 245 Association for Computing Machinery September 1991 D Duchamp S Feiner and G Q Maguire Jr Software Technology for Wireless Mobile Computing JEEE Network 5 6 12 18 November 1991 David T Perkins Understanding SNMP MIBs copyright and distribution by D Perkins July 1992 Marshall T Rose The Simple Times The Quarterly Newsletter of SNMP Technology February 1994 page 38 SNMP Application for the MINT Router Appendix A The MIB Browser The MIB browser was released to the Internet in June 1994 It is available via anonymous FTP on the server it kth se or tristan electrum kth se in the file pub snmp MIB browser tar Z By the end of June echos were received from people who were successfully using the tool The content of this appendix was released as a README ps file annex to the program MIBs are written using a framework called Structure of Management Information SMI which is defined in the RFCs 1155 and 1442 SMI is based on the Abstract Syntax Notation one ASN 1 but adds further conventions to it by restricting stron
35. ation specific issues Some of the implementations are freely available on the Internet Most of them are released by universities which do research in the NM domain Unfortu nately most providers of public domain software put little effort into writing manuals for their code This is also true for the SNMP development packages Three of these software development packages were installed on the computer system of the Telecommunication System Lab in order to check whether they were suitable for the needs of the current NM application No experiments were made with commercial software The SMP Development Kit was created by the Massachusetts Institute of Technology MIT the CMU SNMP2 by the Carnegie Mellon University CMU and the ISODE SNMPv2 by Marshall T Rose from Dover Beach Consulting Inc Using the programming libraries often turns out be troublesome The installation of the SNMP Development Kit MIT is rather straightforward but it is poorly docu mented and its library code is not commented at all Furthermore it does not support version 2 of SNMP ISODE SNMPv2 was hard to install on the local system in the TS lab This is due to the fact that it is probably the most complete package and thus very complex A general rule for installing soft ware is that the uncompiled source code of a module takes three times less disk space than the result ing executable programs About 40 of the impressive 53 MBytes of source code which m
36. ce there are people with different backgrounds working in this field there are also different ways of classifying the Network Management NM issues However the content of this report is limited to the technical aspects of NM Figure 7 shows the three dimensional approach proposed in 3 which considers the functional dimension the time dimension and the scenario dimension The time dimension The time dimension takes into account the different stages of a NM system s life cycle A system is planned then realised and finally runs Each of these phases brings up its particular issues This report will mainly treat points of planning and realisation page 14 SNMP Application for the MINT Router The scenario dimension The nature of the managed system or subsystem influences strongly the management task E g if sin gle components are controlled most of the management actions are likely to be invoked automatically If a whole subnetwork is managed there might be more human interactions required Figure 7 shows how the NM task for complex systems is often subdivided into different layers At a lower level there may be Management Processes which control several network nodes or even components of nodes They report only the significant information to a higher level process which has the overview on the network The various Management Processes may be distributed over the network or run all at the same machine as virtual subsystems We will
37. e Stations BS and the Mobile Stations MS use the same virtual channel CH n to communicate within a cell MINTs can still listen to channels which they are not using The Figure shows only the information known by BS 1 and MS 2 BS 1 listens to channel CH 1 and has knowledge about MS 1 and MS 2 MS 2 listens to CH 1 and CH 2 and thus has knowledge about MS1 MS 3 and MS2 It is important to note that the structure of the Management Information Base at a MS is identical with the one present at a BS 3 3 3 The Agent Since the MIBs for the BS MINT and mobile MINT are identical both agent processes are of the same nature too An SNMP agent process is usually run as a daemon i e a server like background process The development of the agent can also be considered in two parts one concerning the standard MIB and one concerning the enterprise specific MINT MIB moudule The standard MIB II support An agent which supports the object resources of the standard MIB II is included in the CMU software package It could be installed on a Sun Microsystems SLC UNIX machine which has approximately the same processing power as a MINT The realisation of the corresponding part for the MINT agent consists of porting the code of the current CMU agent to the MINT hardware In the frame of the cur rent NM system for the Walkstation II project some experience was made with the crossdevelopment environment described in the first intermediate report in the Appendi
38. e new set of variables The reader who is interested in these practical details is referred to the Appendix B Recently the prototype of a device driver called radionet which provides the same interface as the future radio device driver was developed by Pascal Guerin in the TS group of KTH It can be launched page 33 SNMP Application for the MINT Router on a SUN Microsystems workstation Its principle is that the device driver and the SNMP agent have each a table with an entry for each radio link and with the following fields struct MHPARAM char ether 6 ethernet address of the mobile host char ip 4 IP address of the mobile host char RSS Received Signal Strength RSS char ARSS Average of the RSS between two polls char DSS Designated Signal Strength DSS short key Spread Spectrum Key 13 bits long and padded with zeros char flag tells if one of the previous fields has been updated MobileTab length of struct MHPARAM is 16 bytes Unfortunately it has not been possible anymore to integrate the radionet driver into the agent which executes at a workstation 3 4 2 The Manager The CMU software development package contains a set of sample manager programs which allow to generate Get or Set Request PDUs They use a synchronous request scheme i e the manager remains blocked on a given request until either a response is received or the request times out Figure 16 shows that this is no
39. eading Code which is being used by the entities accessing the channel Average of the Average RSS val ues chEErss The average taken of the values in the column rtErss of the Router Table Average of the Variance of the RSS Average of the BER Average of the FER Total power in the channel Number of Users in a Channel chEVrss chEBer chEFer chTotPower chNumbMh The average of the values in the column rtVrss of the Router Table The average of the values in the column 7tBer of the Router Table The average of the values in the column rtFer of the Router Table The total energy measured in the channel The number of MINT Routers which are using the channel including the Base Station Eventually there is a relation between the router table and the channel table as every link has an asso ciated radio channel Therefore a field in the router table contains the index of the used radio channel i e a pointer to an entry in the channel table Figure 15 illustrates the relation between the router table and the channel table It also shows how a mobile station can listen to different channels page 30 SNMP Application for the MINT Router RouterTable Channel Table a MSI a Channel Table BSI me OCHI ue MS3 me CH2 ue BS2 4 Figure 15 A simple example for entries to Router and Channel Tables The Bas
40. ength according to the power control algorithm Then it SETs at A the column Designated Signal Strength in the rtTable entry describing B to the computed value rtEntry 6 rtRss OBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS optional DESCRIPTION The Received Signal Strength in dBm of the last received frame rtEntry 7 rtErss OBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS optional DESCRIPTION The Average Received Signal Strength in dBm over the last n frames where the n is a constant chosen by the implementor rtEntry 8 rtVrss OBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS optional page 48 SNMP Application for the MINT Router DESCRIPTION The Variance of the Received Signal Strength dBm 2 over the last n frames The n is a constant of the implementation rtEntry 9 rtBerOBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS optional DESCRIPTION Measurement of the Bit Error Rate BER for the communication with the described router The BER is actually a real value between 0 and 1 To use an INTEGER syntax for it the value of mhBer is mhBer BER 1000 rtEntry 10 rtFerOBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS optional DESCRIPTION Measurement of the Frame Error Rate FER for a communication with the described router The FER is actually a real value between 0 and 1 To use an INTEGER syntax
41. f about 20 ms we get aware that the execution of the power control loop in realtime is particularly critical The goal is to execute the power control loop roughly 100 times per second So far this performance was not achieved The CMU software develop ment package contains a set of sample manager programs for generating Get or Set Request PDUs They use a synchronous request scheme i e the manager remains blocked on a given request until either a response is received or the request times out Figure 16 shows that this is not a suitable method for the power control The time span between the release of a request and the reception of a response must not me wasted with waiting because there may be several other BS MS relationships which need power control as well Therefore an asynchronous scheme had to be developed In the current applica tion the Get Request PDUs for the RSS are generated periodically by internal interrupts The Set Request PDUs for the DSS are generated at the reception of the Get Response PDU for the RSS In the synchronous request scheme it is trivial to associate a response PDU with its context as there is always just one outstanding request In an asynchronous scheme an incoming response PDU has first of all to page 32 SNMP Application for the MINT Router be associated to its request BS MS MINT Cell Manager MINT Get Request RSS Get Response RSS Compute DSS Set Request DSS Set Request RSS
42. f the high polling frequency A management program which uses an asynchronous querying mechanism was developed The goal 100 iterations of the power control loop per second could not be met yet The long response time of the system is due to the fact that the manager and the agent operate at the application level of the protocol stack and this implies long end to end latencies Shorter response times can still be achieved by a streamlining of the code Not much effort has been put in this yet In the wireless system messages to and from the mobile MINTs will be sent over a radio link at a rate page 36 SNMP Application for the MINT Router of 1 Mbit s compared to the 10 Mbit s of an Ethernet It is not yet certain to what extent this will worsten the end to end latency of the SNMP messages for the mobile MINTs Other mobile communi cation systems use dedicated beaconing channels for this kind of signalling information The designers of the MINT hardware consider that in the future the router can be extended by another radio interface In that case one radio interface could be dedicated to beaconing page 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 SNMP Application for the MINT Router Bibliography Marshall T Rose The Simple Book an introduction to Internet management Prentice Hall 2nd edition 1991 Uyless Black Network Management Standards The OSI SNMP and
43. face specific MIB module at The address translation group consists of a Table which allows for mapping of Network addresses IP addr to Physical addresses e g Ethernet addr This group is being obsoleted The ipNetToMediaTable of the ip group will take over its role ip The internet protocol group contains information about the IP machine As the MINT will run the Mobile IP it will be necessary to develop a similar mobilelp group tcp This group contains objects describing the state of the connection oriented transport layer protocol tcp udp This group contains objects describing the state of the connectionless trans port layer protocol udp The MINT MIB The standard MIB II defines object groups for managing protocols and physical interfaces In wired systems the physical caracteristics of incoming packets are independant of the sender and its dis tance The electrical characteristics are given by the station which forwards the packet on the last hop It is therefore sufficient to measure the caracteristics of the physical interface which receives them If we consider the interface to a radio device we notice that for the different radio links the incoming signals may have different caracteristics They are given by the distance of the sender which might change slowly in time and by the characteristics of the radio channel which can change fast This shows that in our case it is not sufficient to control only
44. ference was made between System Management and Network Management System Management is the task of exploiting a computer in the best possible way watching hardware devices page 15 SNMP Application for the MINT Router scheduling program executions etc In the beginning computers existed in a small number were bulky expensive and barely interconnected In this situation there was no need for integrated manage ment i e management systems which allow for controlling products of different vendors from one management platform Each system had its own management facilities When systems got more and more interconnected managing the interconnection framework became an issue In this context the managed systems are routing and switching equipment with all their hardware devices and the software running on them This task is referred to as Network Management The next trend was towards distrib uted computer networks where the processing power was spread out over the network workstations PCs Data also started to be stored in a distributed manner still being available from any point in the network Therefore the degree of interconnection increased again The difference between System Management and Network Management now became fuzzy since managing one could not be done without managing the other With this evolution integrated NM became definitely desirable They were needed to control the resources of data networks detecting and repairing fa
45. ferent channels does not have to be done as fast as the adaption of the trans mitting power of a station In the context of the NM task for the Walkstation II project it is suitable to classify the desired response times into three groups Without insisting too much on this terminology we can call them medium term minutes hours short term seconds very short term lt seconds We will see in section 3 4 that response times which are significantly below 1 second i e 1 10 ms are very difficult to handle by a NM process running at the application layer page 12 SNMP Application for the MINT Router Spatial dimension Search for CDMA key System manag a station allocation Cell manag Updating ot routing tabl Handover execution Power control Station manag minutes Time dimension lt seconds seconds Figure 6 An example for the two dimensional representation of the NM functions In the spatial dimension we distinguish between the management of single stations the management of cells and the management of the system as a whole The desired response time for the functions can roughly be classified in three terms It is obvious that we find a concentration of functions around the diagonal of this diagram The management of the system does not have the same realtime requirements as the station management page 13 SNMP Application for the MINT Router 3 Network Management
46. for it the value of mhFer is mhFer FER 1000 rtEntry 11 rtRecTstampOBJECT TYPE SYNTAX TimeStamp ACCESS read only STATUS optional DESCRIPTION The time stamp of the last frame received from the designated MINT Router rtEntry 12 rtSentTstampOBJECT TYPE SYNTAX TimeStamp ACCESS read only STATUS optional DESCRIPTION The time stamp of the last frame sent to the designated MINT Router rtEntry 13 The ch channel subgroup defines data which are specific to a channel ch OBJECT IDENTIFIER mint 2 chTable OBJECT TYPE SYNTAX SEQUENCE OF ChEntry ACCESS not accessible STATUS optional DESCRIPTION There is one row entry for each channel on which the MINT router is transmitting and or page 49 SNMP Application for the MINT Router receiving The chTable contains complementary information to the one in the rtTable which is common to the subset of the Mobile Hosts and Base Stations accessing the same channel Therefore each row of the rtTable has an entry which refers to a row entry in the chTable ch 1 chEntry OBJECT TYPE SYNTAX ChEntry ACCESS not accessible STATUS optional DESCRIPTION The fields of a row element are described below INDEX chId chTable 1 ChEntry SEQUENCE chId Channel Index INTEGER chRowStatus Row Status RowSatus chSpreadCode Spreading Code BIT STRING chEErss Average of rtErss INTE
47. gly the number of supported ASN 1 types and adding some ASN 1 macros to define objects textual conventions which is similar to ASN 1 subtyping etc The resulting text file containing a MIB turns out to be barely readable The tree structure in which the objects are located is hidden because the object identifiers are usually defined by a relative path starting at the object s parent and this is most often not enough to recognize the larger context A browser which is able to parse the SMI ASN 1 text file display graphically the MIB tree and provide a Graphi cal User Interface is desirable Although this seems to be a problem that every MIB designer encoun ters it was previously solved only by commercial software providers A search in the corresponding mailing list samp psi com and newsgroup comp protocols snmp confirmed that there were no Public Domain MIB browsers On the other hand having installed the CMU package which is able to some extent to parse a MIB and to store it into C structures I didn t have to start from scratch programming a browser When I had combined the slightly modified CMU code with my own program I created a Graphical User Interface using the Shell Script language Tcl Tk The resulting tool is able to read a MIB file and to display it in the form of a tree The user can specify the depth and the width of the tree and click with the mouse into the node which should be the top node of the drawn tree When clicking with an
48. h a party has about its correspondents As we have seen above this database specifies for each party its transport authentication and privacy attributes It contains entries for parties which execute locally i e at the same location as the owner of the page 22 SNMP Application for the MINT Router database as well as entries for remote parties e The the MIB view database defines a subset of objects in a MIB using a rather sophisticated mech anism e The context of an SNMP party refers either to a MIB view or to a Proxy relationship see above Only the MIB views are explained hereafter The reader is invited to refer to 1 for more detail about the Proxy relationship e The access privileges database creates a relation between the parties and the contexts Each entry to this database states for a party to which context it has access and which message types it is allowed to use e g party_n has access to context_m with get get next and set commands One party can have access to several contexts Context mib 2 1 MIB view say se say ia se 3 a SEN Na e e eee Figure 12 The roles of the databases which contain the security data The MIB View database defines object groups in a MIB to which the same access rules apply The Context database refers to MIB view or a Proxy relationship not shown in the figure The Party database specifies the Agent
49. hen they wait after the channel is free while listening a random time before they start transmitting With this method it is less likely that several stations which have data to send access the channel at the same time as soon as the last user has released it Of course this is paid with a reduced efficiency of the channel 2 3 The Radio Transceiver At the Electronic Systems Design laboratory of KTH Daniel Kerek and his team are developing the radio part for the Walkstation II project Their approach is based on a spread spectrum radio transceiver which operates at a frequency of 2 GHz One or more virtual channels are assigned to a cell i e inside one cell then all the stations use the same spreading code We recall from section 2 2 that the scheme by which a channel is shared between the users is called CSMA CA In the Walkstation I project CDMA was rather chosen than FDMA or TDMA for the simplicity of its implementation The usage of FDMA would have required a more complex analog part of the radio transceiver TDMA is not suitable because of its synchronization problems between the traffic of different cells Measure ments with channels at this frequency range in a closed room with persons moving around showed typical coherence times of the channel of 20 ms This will be important in our considerations concern ing power control of the radio transmitter The spreading codes are 13 bits long i e 13 chips per bit 2 4 The Mobile IP pr
50. ilures etc Of course Integrated Management was a hard job without standard management interfaces as the nodes in a net work came from different vendors A management application had to be able to connect to all kind of page 16 SNMP Application for the MINT Router interfaces and handle data structures for all the managed entities Figure 9 a To avoid this kind of Management System Managed System 1 Managed System 3 Managed System 2 Heterogeneous internet Figure 9 a Sch 1 3 System specific NM schemes Management System Standard scheme Managed System 1 Managed System 3 Figure 9 b Managed System 2 Heterogeneous internet Figure 9 Network Management Systems are faced with networks which interconnect systems of many different vendors In the past an NM system had to support all the management schemes specific to the different kind of equipment a This made the development of NM applications very complex and inflexible Today there are different standards of NM protocols The task of supporting the standard management interfaces for the devices with their specific features is shifted towards the manufacturers who know their products best To the NM Applications the vendor specific characteristics become transparent problems the NM standard protocols were created They brought abstraction of many sy
51. in the MIB with a corresponding statement in the file page 44 SNMP Application for the MINT Router mib txt which is part of the CMU package The difference is usually apparent and the problem can easily be fixed without changing the functional content of the MIB e It would be nice to have an additional command which could be invoked for instance by a double click on the object which displays the DESCRIPTION clause of the object The C structure tree in the file parse h provides a field description Unfortunately it is not assigned correctly in the function read_mib inthe file parse c e Even though a widget is correctly destroyed by destroying its parent there seems to be a problem with the creation an destruction of a huge number of widgets After some extensive walks the browser might crash and the X Window manager complains about exceeding some constant The browser must be started again and everything is fine This problem is probably due to a bug in the Tk library This bug should usually not affect other X windows However it happened once that an emacs window was killed The case could not be reproduced but in order to avoid trouble the user should make sure that the current work of other applications is saved before running the browser In the CMU MIB buffer each parent node contains a pointer to a chained list of its children Unfortu nately this list starts with the last parsed child and ends with the first parsed child
52. le Host MH registers with a Foreign Agent FA which assigns it a temporary IP Address The Home Agent HA which keeps track of the MH s position has knowledge about this Address and encapsulates and forwards the arriving packets to it The FA decapsulates and delivers the original P Packets to the MH 2 5 The Management Task Within the context which was decribed in the preceeding sections of this Chapter it is now possible to state the requirements which the Network Management task is supposed to fulfill Managing a commu nication system includes among other things controlling hardware interfaces and protocols Fortunately when developing a NM application one does not have to start from scratch with the implementation of the protocol As we will see in the introducton to the Simple Network Management Protocol SNMP section 3 2 all SNMP applications have many things in common The implementation of some of these standard functionalities is available in software development packages The requirements which are specific to the Walkstation II project must still be analyzed and met It is possible to look at the required functionalities in two dimensions a space dimension and a time dimension This rather rough view of things is refined in section 3 3 Space dimension If we look at the planned system in space we establish that it is cellular Let us consider the cell as the medium level in the space dimension Each cell has its own Base Statio
53. ll as to connect to several types of wireless net works The standard configuration of the MINT has two sets of communication interfaces One of them is dedicated to the connection with the Mobile Host MH if the MINT is part of a Mobile Station It is used to connect to the wired subnetwork if the MINT is part of a Base Station The other set is in both cases the interface to the wireless communication device The MINT will have an infrared transceiver which can work at very high bitrates up to 10 Mbits s but is rather limited in coverage area and a spread spectrum radio transceiver which is described later in this report For the rest of this report we will only consider the latter device As stated in section 2 1 the Media Access MAC layer protocol for the radio channel works much like a Carrier Sense Multiple Access system with Collision Avoid ance CSMA CA i e some what differently that the control of an Ethernet which uses Carrier Sense Multiple Access system with Collision Detection CSMA CD It is not possible for a Radio Trans page 8 SNMP Application for the MINT Router ceiver to check whether collisions occur while it is sending though because it recieves its own signal which is much stronger than any other To resolve this problem Tomoki Oshawa from the TS Lab has developed a system with Collision Avoidance CSMA CA In his approach all the stations which have information to send wait for the channel to be available t
54. mergency management etc As many processes in industrial contexts it has also the capability of extending the set of managed devices at runtime e g a router which was down is brought up and sends a start up trap It might also change the schemes of management sessions e g change to data encryption mode The Agent Process The agent process is usually simpler to program than the management process It is normally a dae mon i e an invisible server which runs as a background job Similarly to the Management Process at start up time it reads the MIB and Party configuration files to know which variables it is supposed to handle which manager is allowed to send Requests and to which it must send traps It then waits for incoming requests and local events which ask for a reaction Since an Agent does usually not run on a dedicated machine its code should be as small as possible and require little processing time The implementations There are several software development packages which implement the SNMP standard They consist of libraries written in the C programming language Different modules are usually merged to one big C code library The modules implement thematic blocks of functionalities E g one module contains a MIB compiler which generates C data structures from object definitions in SMI ASN1 Another one handles the transport layer services Using these libraries allows the programmer of a new application to focus on the applic
55. mory of the managed entity As there is no uniform way to handle object instances the task of a database language starts where the one of the MIB stops Consider for instance the standard data base problem of consistency when data of Table A depends on some data of Table B The SNMP Agent has a priori no means to check how a con ceptual variable relates to another Therefore there is a set of simple rules that MIB designers apply which do not necessarily correspond to the principles of data base languages e g 13 Too much information creates as much a problem as not enough information Begin slowly and try to specify only the key objects to be managed Objects must have demonstrated current use and should not define as placeholders for future implementation The security schemes and the Parties 1 states that an SNMPv2 party or simply a party is an execution environment residing in an agent or management application The notion of party was added to the SNMP framework by version 2 Par ties are used in the context of security in order to identify the different actors and their rights in a NM system With other words an entity which is involved in a management system Agent or Manager is known to the others by a correspond entry in their party data base Such an entry has associated with it three sets of attributes the transport attributes the authentication attributes and the privacy attributes The transport attributes
56. n BS which routes the packets to and from the fixed network It also has its own virtual channel s and a set of Mobile Stations MS inside its area The requirements for NM at the cell level are The control of the channel This is done by watching the number of users accessing it the total power in the channel the average values of the Bit Error Rate BER and the Frame Error Rate FER Keeping track of the MSs which can be reached in the cell On a lower layer in space we find the various Stations MSs and BSs inside a cell which definitely page 11 SNMP Application for the MINT Router need some individual management The requirements to NM at the Station level are Watching the received signal strength when a Station communicates with a correspondent Control the transmitting power of a station Watching over the BER and the FER Checking the state of other channels from the point of view of the station in regard to a possible handover The system which we consider as the highest level in space consists of several cells The requirements for NM at the system level are Assigning different CDMA codes to the virtual channels Watching the traffic distribution over the cells Time dimension If we look at the NM system in time we can state that not all the NM functions need to be invoked with the same frequency and with the same realtime requirements For instance the assignment of the spreading codes to the dif
57. n but passive i e no power control is needed Eventually it can be active e The spreading code which is used on the link This information can be used to identify the channel The field Designated Signal Strength DSS is written by the agent and read by the driver At each device driver the device driver and the agent exchange their tables This scheme of information exchange is not operational yet 3 3 4 The Manager The cell manager is basically one process which controls variables on the BS and MS MINTs For instance the creation of a Get Request PDU in order to retrieve the value of the average Frame Error Rate in a channel does not need any particular explanations A rather complex part of the management is the power control of the Mobile MINT Since the radio device driver is not yet ready the current application does not deal with real measurements Its purpose is to study the mechanisms of synchro nous and asynchronous requests and to make performance measurements The fact that the cell man agement process is executed on a workstation rather than on the BS MINT subsection 3 3 1 implies that during each iteration of the power control loop two Request PDUs must be sent to MINTs The manager first has to retrieve the Received Signal Strength RSS from the Base Station Then it sends a Set PDU concerning the Designated Signal Strength to the Mobile MINT Figure 16 If we take into account the expected coherence time of the channel o
58. nal DESCRIPTION This Table contains measurements statistics and designated values for the communication with all the other MINT Routers whithin reach Each router is represented by a row in the table fee fone dy rtEntry OBJECT TYPE SYNTAX RtEntry ACCESS not accessible STATUS optional DESCRIPTION The fields of a row in the rtTable are described below INDEX rtIndex rtTable 1 page 46 SNMP Application for the MINT Router RtEntry SEQUENCE rtIndex row number INTEGER rtRowStatus Row Status RowSatus rtLocLinkAddress Local MAC address PhysAddress rtRemLinkAddress Remote MAC address PhysAddress rtChannelId channel table index INTEGER rtDss Designated Signal Strength DSS INTEGER rtRss Received Signal Strength RSS INTEGER rtErss Average RSS INTEGER rtVrss Variance of the RSS INTEGER rtBer Bit Error Rate INTEGER rtFer Frame Error Rate INTEGER rtRecTstamp Last Received Time Stamp TimeStamp rtSentTstamp Last Sent time Stamp TimeStamp rtIndex OBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS optional DESCRIPTION This index is used as the row number in the mhTable it is not yet clear to me if we can address the row entries rather by the Ethernet Address of the MINT In that case we could drop this column rtEntry 1 rtRowStatus OBJECT TYPE SYNTAX RowStatus MAX ACCESS read create STATUS optional DESCRIPTION The s
59. object A path leading to an object in a MIB is specified by an object identifier In other words an object identifier is a registration point in the MIB tree Such a registration point may simply be a placeholder for a subtree or it may define a syntax i e a type of a managed object The SNMP terminology page 21 SNMP Application for the MINT Router makes an important difference between objects and variables A variable consists of an object identity and an associated instance Therefore simple variables are found at the leafes of the tree The defini tion of tabular objects is somewhat more complex 1 13 Variables are the operands in SNMP oper ations A MIB contains the object definitions of an SNMP application It does not contain the actual values of the variables and thus it lacks the facilities of a common database system Unfortunately the SMI is also far from being a data base language Conceptual variables and conceptual rows of a table are fre quent terms in the SNMP literature They simply mean that if an object is defined in a MIB as accessi ble e g read write the Agent is supposed to handle its instance i e to execute GET and SET operations on its value The management process has no knowledge about where and how the value of a variable is physically stored It can be read from resp written to a device driver every time a GET resp SET command is received or it can simply reside in the me
60. other mouse button the whole path in the tree which leads to the object is displayed The user should at least read the paragraph Bugs and proposed improvements before running the code This software tool still needs a lot of improvements It should be considered as an example of a MIB browser rather than as a commercial product The users are invited to send comments to the e mail address oelhafen it kth se The author disclaims all warranties page 39 SNMP Application for the MINT Router page 40 SNMP Application for the MINT Router mib 2 OBJECT IDENTIFIER mgmt interfaces OBJECT IDENTIFIER mib 2 2 ifNumber OBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS mandatory DESCRIPTION The number of network interfaces interfaces 1 ifTable OBJECT TYPE SYNTAX SEQUENCE OF IfEntry ACCESS not accessible STATUS mandatory DESCRIPTION A list of interface entries interfaces 2 mib 2 1 Soe Py se a Cres se ry se system 1 interfaces 2 ifEntry OBJECT TYPE SYNTAX IfEntry ACCESS not accessible STATUS mandatory DESCRIPTION An interface INDEX ifIndex n ifTable 1 TfEntry SEQUENCE ifIndex INTEGER ifDescr DisplayString ifType INTEGER Figure la ifIndex OBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS mandatory DESCRIPTION A unique value for each interface ifEntry 1 br wish ifDescr
61. otocol The Network Integration of a Mobile Host MH 10 11 13 is a problem that can be treated sepa rately from the issues of wireless communication E g if the MH moves around inside its home sub network which might have several cells the solution to message routing turns out to be trivial because the Gateway which connects the subnetwork to the Internet will have to route the packets in the same way as for any fixed host Problems arise when the MH moves to another subnetwork Because IP makes an implicit assumption that the host s attachment point remains fixed currently defined routing protocols select a path to a host based on the network number contained in the host s IP address Figure 4 shows a scenario where the MH tries to communicate from a foreign LAN with a host of its home LAN page 9 SNMP Application for the MINT Router Foreign LAN Request i Res Figure 4 In this scenario a Mobile Host MH is attached to a foreign LAN and tries to contact a server on his home LAN The request will reach the server as the IP Address of the corresponding packet allows for finding the fixed host in the Internet On the other hand the response message will never reach its destination since the IP addressing scheme associates the MH s IP Address with a location which is on its home LAN The Gateway G of the home LAN has no means to know where the MH is and consequently discards the packet
62. r Professor Gerald Maguire He answered many questions in the context of my work with an impressive competence Furhtermore he helped me to acquire a method of independant work Yuri Ismailov s excellent experience in software development was of much benefit for me during my work I thank him for the time he took to advise me and for the many interesting discussions I had with him Parag Pruthi gave me some valuable ideas for the outline of this report I also owe him much gratitude for his constructive corrections of parts of the report Many thanks to Frank Reichert for the documentation he gave me and for allowing me to include some of his figures into the current report I would like to express my deep gratitude to the computer system administrators Jim Svensson and Fredrik Ljungberg who answered my many questions and helped me to find solutions to problems con cerning software development and the installation of software packages on the local computer systems Thanks to all the members of the Teleinformatics Department who have welcomed me into their labo ratories Many thanks for the friendly human atmosphere they created for my working environment page 3 SNMP Application for the MINT Router 1 Introduction Mobile Communication is an area which has been growing steadily over the last few years While Mobile Telephony has already reached a high level of penetration and has been realized in large inter national systems Mobile Da
63. r the X Window System Tk extends the core Tcl facilities with additional commands for building user interfaces Like Tcl Tk is implemented as a library of C procedures so it too can be used in many different applications Individual applications can also extend the base Tk features with new user interface widgets and geometry managers written in C In Tcl and in Tk new commands can be defined in a C library or in a shell script file The former has the advantage of faster execution but it is relatively hard to debug because for every modification in the C code the whole program must be recompiled The latter is easier to debug as the script files are interpreted and can be run interactively step by step Therefore when programming Tcl Tk applications a trade off must be made between programming user commands in C or in the script language Installation of the MIB browser software The software was developed on a UNIX machine running SUN OS 4 1 3 As it does not contain any specific system calls it should be compatible with most UNIX systems It was tested under both the X Window System and Openwindows According to the Tcl Tk specifications it should also run under Motif However this remains still to be tried It is necessary that the Tcl Tk module already be installed on the system The only configuration needed is in the Makefile Look for the line TCLBASE afs it kth se src packages tcl and replace afs it kth se src packages tcl
64. recall that in SNMP the notion variable stands for a pair formed of an object together with its instance A MIB only defines objects which are handled by an agent but it does not say how exactly the values are accessed This section describes how the CMU code must be extended to support a simple integer typed variable Goal We want to support simple i e non tabular instances of two objects The actual value will reside as a C variable in memory A manager process will be allowed to apply get and set commands to it The variable are defined as follows in the MIB this is a complete MIB module which can be compiled MINT MIB DEFINITIONS BEGIN enterprises OBJECT IDENTIFIER iso org 3 dod 6 internet 1 private 4 1 KTH OBJECT IDENTIFIER enterprises 933 myFirst OBJECT IDENTIFIER KTH 1 myFirstInt OBJECT TYPE SYNTAX INTEGER ACCESS read write STATUS optional DESCRIPTION The first integer variable for testing myFirst 1 myFirstString OBJECT TYPE SYNTAX DisplayString ACCESS read write STATUS optional DESCRIPTION The first string variable for testing myFirst 2 END Add in file cmu snmp2 agent snmp_vars c the definition of a new subtree of variables in our case it consists of an integer valued and a string valued leaf object these are the values of the magic number define MYFIRSTINT 0 define MYFIRSTSTRING 1 struct variable is defined in snmp_vars h struct
65. rnet Engineering Task Force IETF in RFCs Figure 10 shows an extract of the standard MIB Its existence is not only essential for developing Network Management NM applications it also helps interoperability of NM products released by different suppliers There is a clear need for defining objects which describe the specific properties of the managed network entities for instance the configuration parameters of the new radio device for the MINT Router This leads to enterprise specific MIBs which are integrated into the MIB tree under a branch called enterprises MIB developers have to acquire a subtree number under the enterprise branch from the Internet Assigned Number Authority IANA The assignments are made via E Mail For instance the number we got for our enterprise specific MIB is 933 and the actual structure of the subtree under this branch is then left to us mib 2 1 Wai system 1 ifTable 2 ifEntry 1 NG san ss an x Figure 11 The organization of objects in an SNMP MIB resembles to the structure of subdirectories in a Filesystem Only leaf objects can represent variables Non leaf objects are just used to represent subtrees of the MIB The figure shows parts of a subtree extracted from the standard mib 2 Each branch has a textual name label and an index subidentifier Labels and subidentifiers can both be used to form an Object Identifier i e the specification of the whole path leading to an
66. rs Although a MINT router shall basically have the same capabilities for executing programs as any UNIX machine running the cell level manager on the Base Station MINT might cause too much processing load and prevent the MINT from accomplishing its actual task the routing of IP packets to and from the fixed network Therefore the cell level manager executes at a workstation of the fixed network This solution also has the important advantage that an even more powerful computer can be used This might be necessary when the number of mobile MINTs per cell increases Furthermore the symmetric relationship between BS MINTs and mobile MINTs allow for using the same type of Agent s process for both entities This simplifies also the design of the Management Information Base Besides the mentioned advantages the decision of taking away the cell manager from the BS has the drawback of creating more management traffic because all the information about the BS must be retrieved by means of SNMP requests SNMP is the common network management protocol of the TCP IP suite There are various impe lementations of SNMP freely available in the form of software development packages Besides the implementation of the protocol machine they usually contain C libraries with important blocks of code for Agents and Manageers Unfortunately most of the SNMP implementations are not documented at all and their code is barely commented The package released by the Carnegie
67. s and Managers which are known to the owner of the database The Access database creates a relation between the parties and their context specifying the priorities The Management Process We saw that SNMP uses the connectionless transport layer protocol UDP and that UDP does neither end to end error control nor retransmission if a message got corrupted This might seem risky for an application which is supposed to keep a network running If error detection and retransmission is not done at the transport layer this does not mean that it is not done at all It is simply left to higher layers SNMP may still handle sessions how the OSI model suggests to do in protocol layer 6 This can imply page 23 SNMP Application for the MINT Router that a message is retransmitted as long as no correct answer is received Appendix B gives an insight into how session are handled in the CMU development package The first thing a Manager does at start up is read the MIB and the Party configuration files It knows now the Agents which it has to communicate with Depending on the implementation it opens sessions with the agents Each session might follow different schemes One might need Authentication without Encryption another might need both and a third one none of them The Manager is now ready to start its work sending out Request messages and accepting Reply messages It is basically a control process with all the problems from realtime requirements to e
68. specify the parties network address and portnumber as well as the used trans port protocol usually UDP The authentication attributes specify basically the used authentication scheme and the secret codes There are currently only two authentication schemes in the proposed standards noAuth no authentication and the v2mdS5AuthProtocol which is based on the MD5 Mes sage Digest Algorithm RFC 1321 Eventually the privacy attributes specifies the data encryption scheme There are also two possibilities for encryption the noPriv protocol no privacy and the desPrivProtocol which is based on the Data Encryption Standard DES US Federal Information Processing Standards Publications 46 1 and 81 Let us look at this security scheme from a practical point of view The current NM application for the Walkstation II project makes use of the trivial scheme for authentication and encryption i e noAuth and noPriv This still does not mean that an Agent accepts all sort of requests wherever they come from concerning any variable Before an Agent becomes operational it must be configured carefully i e it must be told exactly which party has access to which variables with which priority In order to create this relation between objects and parties SNMPv2 needs four different data bases One for pari ties one for MIB views one for contexts and one for access privileges Let us look at each in turn e The party database contains the information whic
69. stem specific details about managed devices and allowed designers of NM applications to focus on their actual task of managing subsystems Figure 9b page 17 SNMP Application for the MINT Router Some common Network Management Protocols Some of the NM frameworks which are widely used 2 are CMIP CMOL and SNMP The Common Management Information Protocol CMIP is part of the OSI protocol suite The Common Manage ment information protocol Over logical Link control CMOL is the IEEE approach to the management of LANs Its name is confusing since some of the IEEE LANs may not use CMIP The Simple Network Management Protocol SNMP is used in the Internet together with the TCP IP protocol suite As the NM Application for the Walkstation II project is based on SNMP section 3 2 is dedicated to explain the SNMP framework in more detail These three frameworks follow the same general principle which is mainly based on three elements Figure 10 the Management Process or Manager the Agent or Agent Process and the Management Information Base MIB The Management Process executes at the Management Station MS It sends Management Station Managed devices Managed station Figure 10 The three basic elements of a Network Management system The Agent is the process executing at the managed entity It has direct access to the managed objects The Management Process or Manager runs at the Management Station It asks the
70. t a suitable method for the power control The time span between the release of a request and the reception of a response must not me wasted with waiting because there may be several other BS MS relationships which need power control as well Therefore an asynchronous scheme had to be developed In the current application the Get Request PDUs for the RSS are generated periodically by internal interrupts The Set Request PDUs for the DSS are generated at the reception of the Get Response PDU for the RSS In synchronous request scheme it is trivial to associate a response PDU with its context as there is always just one outstanding request In an asynchronous scheme an incom ing response PDU must be associated to its request The C library of the CMU package still provides some facilities for sessions with asynchronous requests They can be combined to obtain powerful instruments for handling asynchronous requests Session handling A relationship between the management process and the agent must be setup by initializing an SNMP session use the function snmp_open At this moment it is possible to specify a function referred to as callback which must be invoked when a PDU is received for that particular session The callback function must be able to handle the incoming PDU For instance at the reception of a Get RSS Response PDU from the BS MINT the corresoponding callback function sends a Set PDU Request to the mobile MINT Waiting for events
71. ta Networks are just developing As computers become smaller less expensive and more powerful the user s demand for mobility increases People will no longer be will ing to use their computers only from a fixed location s Standards for Digital Mobile Telephony already exist in Europe GSM DECT in the United States e g Qualcomm System and in Japan e g PHP However Mobile Data Communication will bring additional requirements to these systems In order to allow hosts to migrate without losing the benefit of their full processing power the bandwidth of today s communication systems must be increased Furthermore the network should be strongly interconnected with the existing fixed computer net works Unfortunately many of those have properties which inhibit mobility They were developed at a time when the assumption was that all the hosts are fixed New frameworks of mobile computers will have to cope with these properties These are just some of the many problems which must be resolved to create this new generation of wireless systems Besides supporting host migration they will allow for data services which combine voice and video Multimedia the remote access to a data base via a wire less link applications using Data Multicast etc Management is without any doubt a crucially important component of such a mobile communication system Network Management is a broad field An operator of a communication system may want to moni
72. tatus of a conceptual row in the Router Table rtEntry 2 rtLocLinkAddress OBJECT TYPE SYNTAX PhysAddress ACCESS read only STATUS optional DESCRIPTION Ethernet Address of the local LAN interface As a MINT Router especially a BS MINT can have several radio LAN interfaces with we need to specify over which interface a destination MINT can be reached rtEntry 3 page 47 SNMP Application for the MINT Router rtRemLinkAddress OBJECT TYPE SYNTAX PhysAddress ACCESS read only STATUS optional DESCRIPTION Ethernet Address of the interface in the remote MINT Router rtEntry 4 rtChannelId OBJECT TYPE SYNTAX INTEGER ACCESS read only STATUS optional DESCRIPTION This is a reference to the row entry with the same ID in the chTable where the spreading code and other features of the corresponding channel are stored rtEntry 5 rtDss OBJECT TYPE SYNTAX INTEGER ACCESS read write STATUS optional DESCRIPTION The Designated Signal Strength dBm represents the power with which the owner of this information must transmit when communicating with the Router described in this row So the management process controls the Signal strength for the transmission from A for instance a MH associated Router to B for instance a BS associated Router as follows It GETs from B the column Received Signal Strength in the rtTable entry describing A It computes the desired signal str
73. that OSI managers believe in connection oriented transport services in order to make sure that the sent messages always reach their destination Internet mangers do not arguing that emergency management in a congested network is more likely to succeed with connectionless transport services Retransmissions are therefore handled manually i e by the Application Layer Interconnection of NM subsystems using different protocols standards Since CMIP and SNMP are both established in interconnected data networks we find the problem of managing hybrid networks Figure 9 again on a higher level 3 An NM system is potentially in charge of managing parts of two networks which use different NM protocol standards For this reason there are CMIP programs running on the top of the TCP IP protocol suite and SNMP programs running on the top of the OSI protocol stack They are referred to as CMIP for the Internet a successor of CMOT and SNMP over OST 3 2 An Introduction to the Simple Network Management Protocol SNMP The History In 1988 the first SNMP specifications were finished At that time there were very few network man agement applications or protocols available Much of the networking infrastructure gateways and servers was built on UNIX platforms That was a good starting point for free and commercial SNMP UNIX products These products took over in Internet management and soon met the customer s most pressing needs Like
74. tor the system s behaviour under any conditions He may want to detect faults and taking meas ures in order to isolate and repair them These are just a few examples of NM functions To provide them an NM application needs to control all kind of objects in a communication network Examples of such objects are hardware components or subsystems of network devices programs and their interac tion with the environment whole clusters of machines forming subnetworks etc The support for Mobility can make the management task particularly complex The existence of radio links brings up a new set of specific variables which must be controlled Furthermore mobility implies that the system must in some way keep track on its users in order to provide services for them wherever they are The purpose of the Walkstation II project 8 is to create a testbed for a wireless Local Area Network LAN with access to the Internet Figure 1 To the user the system should be transparent i e he or she should be able to work on a mobile computer exactly in the same way as on any other host in the Internet The network services should be available in a continuous and seamless fashion even if the user changes location during a session page 4 SNMP Application for the MINT Router a basestation GHz RADIO Infrared INTER i ae NET Figure 1 The system will give mobile users access to a Local Area Network LAN which is connected via a Gatewa
75. truct variable vp IN pointer to variable entry that points here register oid name IN OUT input name requested output name found register int length IN OUT length of input and output oid s int exact IN TRUE if an exact match was requested int var_len OUT length of variable or 0 if function returned int write method OUT pointer to function to set variable otherwise 0 inspire yourself on the examples in the file snmp vars c for this part switch vp gt magic case MYFIRSTINT return u_char amp myInt case MYFIRSTSTRING var_len strlen myString write_ method writeMyFirst return u_char myString Note the assignment write_ method writeMyFirst This is also a pointer to function Not all conceptual variables need a write function For some variables it might be possible to do a set by writing to the address pointed at by the return value of the generic function A write_method is needed for example if the value of the variable is set by a device driver call The write_method can include any action The Agent can now answer request PDUs from the manager Make sure before running it that the man ager party is allowed to access the variable This is done by a suitable configuration of the Agent in the page 53 SNMP Application for the MINT Router files view conf context conf party conf and acl conf which are in the directory cmu snmp
76. ust be installed for using ISODE SNMPv2 is actually the ISODE ISO Development Environment package The advantage of this package is that there is literature about this particular implementation Unfortu nately it caused a lot of trouble during runtime so that it had to be considered unsuitable for the Walk station II Management Especially if one takes into account that the application must be compiled and debugged in a crossdevelopment environment the libraries should be programmed in a readable relia page 24 SNMP Application for the MINT Router ble and extendable way rather than be very complete and highly sophisticated The SNMPv2 package by the CMU matched better this required profile Table 1 summarizes the features of these three soft ware packages In its last column comments stands for the comments included in the library source code Table 1 Comparison between SNMP development packages Name Supplier SNMP Package Installation Documents versions size Sommen Development Kit 1 1 3M feasible poor ISODE SNMPv2 difficult good CMU SNMP easy satisfactory There are two more public domain implementations of SNMP which are widely used and accepted by the Internet community Tricklet is a product of the Delft University of Technology Netherlands It uses part of the ISODE SNMPv 2 package for the MIB compilation The most recent implementation of SNMP was released in late 1993 by the Twente University of
77. v2 The principle Figure 10 which shows the framework of many NM protocols is valid for SNMP too As mentioned above SNMP also uses an object oriented approach to handle the management information The Man agement Information Base MIB defines the syntax of the objects as well as their organisation The MIB does not contain the definition of the methods which apply to the managed objects This is partly implied by the SNMP specification which defines a standard set of operations Get This operation is used to obtain a value of an identified object Set This operation is used to set a value on an object Getnext This operation is used to obtain the value of the object following the specified one Getbulk This operation is used to obtain the values of a whole block of values following the specified object Inform Message exchange between managers Trap A message which is initiated by the Agent The set of SNMP Protocol Data Unit PDU types is basically given by this set of operations Most of them need a Request PDU and Response PDU This set of operations looks quite limited for a frame work which claims to be object oriented In fact more specific operations can be realised in the imple mentation of the Agent E g an agent could support a variable called bootFlag Each time a Set PDU with the value 1 is received the Agent could reboot the machine and send a Trap PDU when it is back up SNMP provides a means for managing
78. variable myFirst_variables MYFIRSTINT INTEGER RWRITE var_myFirst 1 1 MYFIRSTSTRING STRING RWRITE var_myFirst 1 2 i var_myFirst is a pointer to a function which is able to access the actual values of the conceptual var iables It is a generic function for all the variables which are grouped under the same subtree The magic number MYFIRSTINT and MYFIRSTSTRING is an integer which will be passed as a parame ter to the function var_myFirst It will allow the function to decide which variable of the subtree should be grabbed page 52 SNMP Application for the MINT Router Now add your new variable subtree in the list list of all the subtrees of conceptual variables still in snmp_vars c define KTH 1 3 6 1 4 1 933 That s the OId of the KTH enterprise MIB remember struct subtree subtrees KTH 1 8 struct variable myFirst_ variables sizeof myFirst variables sizeof myFirst variables sizeof myFirst_ variables MIB 1 7 struct variable system_variables sizeof system variables sizeof system_ variables sizeof system variables The type struct subtree was defined in the same file snmp_vars c above All what remains to do now is the implementation of the generic function var_myFirst In our case for Get requests it will return a pointer to the corresponding variables var_myFirst vp name length exact var_len write method register s
79. x Unfortunately due to lack of time this part of the work could not be achieved With the new version of the MACH kernel for the MINT which will be able to run a UNIX emulator the crossdevelopment environment remains still in use page 31 SNMP Application for the MINT Router The MINT MIB support For the time until the device driver is available the MIB variables are all contained in a structure which is a straightforward translation of the ASN 1 SMI definition into C types In the final implementation of the agent there will be no uniform manner of accessing the radio specific parameters of a MINT router Some variables reside in memory e g the BER and FER measured for a given radio link Another set of variables is directly obtained from the radio device driver The radio device driver and the agent process will both have a table with entries for all the radio links to the other MINTs The driver fills in its table with measurements corresponding to the incoming packets Each entry contains fields for e The identification of the remote MINT MAC and IP adresses e The Received Signal Strength RSS of the last received packet e The average Signal Strength since the last call to the device driver e A number indicating the state of the link It allows the agent to see if there has been any activity on the link since the driver was polled last The link can be new if the corresponding MINT was received for the first time It can be know
80. y G to the Internet As a mobile host is typically a portable computer the mobility support functions will be distributed onto the Base Station and an entity which will be associated with the mobile station The organisations who cooperate with the Royal Institute of Technology KTH in this project are Elle mtel Ericsson Radio Systems Hewlett Packard NUTEK and Telia Research At KTH there are three groups involved The Radio Systems RS Lab is in charge of developing a strategy for the allocation of the needed radio resources The Electronics System Design Lab has developed a new Radio Trans ceiver which satisfies the special requirements of the planned wireless LAN The Telecommunication Systems Lab has the task of defining protocols for use with personal computing and communication systems writing the necessary software and assembling the different elements of the planned network This report is organized as follows Chapter 2 is a short description of these elements and of the Walk station II Project as a whole It also states the general requirements for Network Management which exist in this context Chapter 3 focuses on the Network Management issues It introduces the commu nication protocol which we have used and the general design of the management application It also shows how the concepts of the architecture are realized with the selected tools The reader who is inter ested in technical details is refered to the Appendix page

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