HP 180 Degree Turn User's Manual
Contents
1. What About Gigabit Hubs A Would limit network diameter to 20 25 meters Gigabit Ethernet Solutions Frame Bursting Carrier Extension No GE Hubs available on the market today gt forget it No CSMAICD defined for 10GE C Herbert Haas 2005 03 11 Remember Hubs simulate a half duplex coaxial cable inside hence limiting the total network diameter For Gigabit Ethernet this limitation would be about 25 meters which is rather impracticable for professional usage Although some countermeasures had been specified in the standard such as frame bursting and carrier extension no vendor developed an GE hub as for today Thus Forget GE Hubs The 10 GE specification does neither consider copper connections nor hubs 10 GE can only run over fiber At this point please remember the initial idea in the mid 1970s Bus CSMA CD short distances no network nodes Today Structured cabling point to point or star never CSMA CD WAN capabilities sophisticated switching devices in between MAC Control Frames A Additional functionality easily integrated Currently only Pause Frame supported lt Always 64 bytes 2 44 4 MAC ctrl opcode MAC ctrl parameters MAC ctrl opcode Defines function of control frame MAC ctrl parameters control parameter data always filled up to 44 bytes C Herbert Haas 2005 03 11 Different data rates between switch2. The Ethernet Evolution The 180 Degree Turn C Herbert Haas 2005 03 11 Use common sense in routing cable Avoid wrapping coax around sources of strong electric or magnetic fields Do not wrap the cable around flourescent light ballasts or cyclotrons for example Ethernet Headstart Product Information and Installation Guide Bell Technologies pg 11 History Initial Idea A Shared media CSMA CD as access algorithm COAX Cables Half duplex communication Low latency No networking nodes except repeaters One collision domain and also one broadcast domain 10 Mbit s shared by 5 hosts gt 2 Mbit s each C Herbert Haas 2005 03 11 The initial idea of Ethernet was completely different than what is used today under the term Ethernet The original new concept of Ethernet was the use of a shared media and an Aloha based access algorithm called Carrier Sense Multiple Access with Collision Detection CSMA CD Coaxial cables were used as shared medium allowing a simple coupling of station to bus like topology Coax cables were used in baseband mode thus allowing only unicast transmissions Therefore CSMA CD was used to let Ethernet operate under the events of frequent collisions Another important point No intermediate network devices should be used in order to keep latency as small as possible Soon
3. Link Aggregation Control Protocol LACP AY 1 Gbit s or even 10 Gbit s long reach connection C Herbert Haas 2005 03 11 Today Gigabit and even 10 Gigabit Ethernet is available Only twisted pair and more and more fiber cables are used between switches allowing full duplex collision free connections Since collisions cannot occur anymore there is no need for a collision window anymore From this it follows that there is virtually no distance limit between each two Ethernet devices Recent experiments demonstrated the interconnection of two Ethernet Switches over a span of more than 100 km Thus Ethernet became a WAN technology Today many carriers use Ethernet instead of ATM SONET SDH or other rather expensive technologies GE and 10GE is relatively cheap and much simpler to deploy Furthermore it easily integrates into existing low rate Ethernet environments allowing a homogeneous interconnection between multiple Ethernet LAN sites Basically the deployment is plug and play If the link speed is still too slow so called Etherchannels can be configured between each two switches by combining several ports to one logical connection Note that it is not possible to deploy parallel connections between two switches without an Etherchannel configuration because the Spanning Tree Protocol STP would cut off all redundant links Depending on the vendor up to eight ports can be combined to constitute one Etherchannel
4. repeaters were invented to be the only exception for a while An Ethernet segment is a coax cable probably extended by repeaters The segment constitutes one collision domain only one station may send at the same time and one broadcast domain any station receives the current frame sent Therefore the total bandwidth is shared by the number of devices attached to the segment For example 10 devices attached means that each device can send 1 Mbit s of data on average Ethernet technologies at that time 1975 80s 10Base2 and 10Base5 History Multiport Repeaters A Demand for structured cabling voice grade twisted pair 10BaseT Cat3 Cat4 Multiport repeater Hub created Still one collision domain CSMA CD in a box C Herbert Haas 2005 03 11 Later Ethernet devices supporting structured cabling were created in order to reuse the voice grade twisted pair cables already installed in buildings 10BaseT had been specified to support Cat3 cables voice grade or better for example Cat4 and today Cat5 Cat6 and Cat7 Hub devices were necessary to interconnect several stations These hub devices were basically multi port repeaters simulating the half duplex coax cable which is known as CSMA CD in a box Logically nothing has changed we have still one single collision and broadcast domain Note that the Ethernet topol
5. Sas i L O C Herbert Haas 2005 03 11 6 Several vendors built advanced bridges which are partly or fully implemented in hardware The introduced latency could be dramatically lowered and furthermore other features were introduced for example full duplex communication on twisted pair cables different frame rates on different ports special forwarding techniques e g cut through or fragment free Content Addressable Memory CAM tables and much more Of course marketing rules demand for another designation for this machine the switch was born Suddenly a collision free plug and play Ethernet was available Simply use twisted pair cabling only and enable autonegotiation to automatically determine the line speed on each port of course manual configurations would also do This way switched Ethernet become very scalable Furthermore Virtual LANs VLANs were invented to split the LAN into several broadcast domains VLANs improve security utilization and allows for logical borders between workgroups No collisions gt no distance limitations Gigabit Ethernet becomes WAN technology Over 100 km link span already Combine several links to Etherchannels Acts as single link from the spanning tree view Cisco Port Aggregation Protocol PAgP IEEE 802 1ad
6. The IEEE 802 3u defines the widely used Fast Ethernet variants most importantly those utilizing the 100BaseX signaling scheme The 100BaseX signaling consists of several details but basically it utilizes 4B5B block coding over only two pairs of regular Cat 5 twisted pair cables or two strand 50 125 or 62 5 125 um multimode fiber optic cables 100Base4T signaling has been specified to support 100 Mbit s over Cat3 cables This mode allows half duplex operation only and uses a 8B6T code over 4 pairs of wires one pair for collision detection three pairs for data transmission One unidirectional pair is used for sending only and two bi directional pairs for both sending and receiving The 100VG AnyLAN technology had been created by HP and AT amp T in 1992 to support deterministic medium access for realtime applications This technology was standardized by the IEEE 802 12 working group The access method is called demand priority 100VG AnyLAN supports voice grade cables VG but requires special hub hardware The 802 12 working group is no longer active 12 4B 5B Coding A 16 code groups 4x25 Mbit s PCS 32 code 4B 5B Encoder Decoder groups 125 MBaud te C Herbert Haas 2005 03 11 The diagram above shows the basic principle of the 4B5B block coding principle which is used by 802 3u and also by FDDI The basic idea is to transform any arbitrary 4 bit word into a relatively balanced 5
7. ace design is very complicated and therefore relatively expensive Using Cat 6 or Cat 7 cables allow 500 Mbaud x 2 pairs that is 2 pairs are designated for TX and the other 2 pairs are used for RX This dramatically reduces the price but requires better cables which are not really expensive but slightly thicker Legacy cable ducts might be too small in diameter 18 Several Physical Media Supported A Logical Link Control LLC Data Link Layer PHY 1 10 Mbit s 10 Mbit s 100 Mbit s 1000 Mbit s AUI Attachment Unit Interface PLS Physical Layer Signaling MDI Medium Dependent Interface PCS Physical Coding Sublayer MII Media Independent Interface GMIl Gigabit Media Independent Interface PMA Physical Medium Attachment MAU Medium Attachment Unit PMD Physical Medium Dependent C Herbert Haas 2005 03 11 The diagram above shows various physical media designs supported by the official GE standard Each modern GE card could theoretically support the old 10 Mbit s standard as well However many vendors create GE NICs that only support GE or GE and FE who would connect a precious GE interface with another interface which is 100 times slower 19 10 Gigabit Ethernet IEEE 802 3ae A Only optical support 850nm MM 1310nm 1550 nm SM only No copper PHY anymore Different implementations at the moment standardization not finished 8B 10B IBM SONET SDH support XAUI Zowie
8. bit word This is done by a fast table lookup Balancing the code has many advantages better bandwidth utilization better laser efficiency constant temperature better bit synchronization PLL etc Note that the signaling overhead is 5 4 12 5 13 Gigabit Ethernet C Herbert Haas 2005 03 11 Gigabit Ethernet has been defined in March 1996 by the working group IEEE 802 3z The GMII represents a abstract interface between the common Ethernet layer 2 and different signaling layers below Two important signaling techniques had been defines The standard 802 3z defines 1000Base X signaling which uses 8B10B block coding and the 802 3ab standard uses 1000Base T signaling The latter is only used over twisted pair cables UTP Cat 5 or better while 1000BaseX is only used over fiber with one exception the twinax cable 1000BaseCX which is basically a shielded twisted pair cable BTW The X stands for block coding 14 GE Signaling A IEEE 802 3 IEEE 802 3z ANSI X3T11 Ethernet Gigabit Ethernet Fibre Channel 802 2 LLC IEEE 802 2 LLC CSMA CD pee CSMA CD or full ET ETA MAC Reconciliation Reconciliation Sublayer C Herbert Haas 2005 03 11 Gigabit Ethernet layers have been defined by adaptation of the LLC and MAC layers of classical Ethernet and the physical layers of the ANSI Fiber Channel technology A so called reconciliation layer is used in between for seamless interopera
9. each other including different data rates 10 100 1000 Mbit s half or full duplex operation MAC control frames capabilities etc Original Ethernet utilized so called Normal Link Pulses NLPs to verify layer 2 connectivity NLPs are single pulses which must be received periodically between regular frames If NLPs are received the green LED on the NIC is turned on Newer Ethernet cards realize auto negotiation by sending a sequence of NLPs which is called a Fast Link Pulse FLP sequence Fast Link Pulses A Modern Ethernet NICs send bursts of Fast Link Pulses FLP consisting of 17 33 NLPs for Autonegotiation signalling Each representing a 16 bit word GE sends several pages C Herbert Haas 2005 03 11 A series of FLPs constitute an autonegotiation frame The whole frame consists of 33 timeslots where each odd numbered timeslot consists of a real NLP and each even timeslot is either a NLP or empty representing 1 or 0 Thus each FLP sequence consists of a 16 bit word Note that GE Ethernet sends several such pages 100 Mbit Ethernet Overview IEEE 802 3u IEEE 802 12 Signaling Schemes Demand Priority 100BaseT4 100BaseFX 100BaseTX half duplex HP and AT amp T invention for real time 400BaseT applications C Herbert Haas 2005 03 11 The diagram above gives an overview of 100 Mbit s Ethernet technologies which are differentiated into IEEE 802 3u and IEEE 802 12 standards
10. es and different performance levels often lead to congestion conditions full buffers and frame drops Traditional Ethernet flow control was only supported on half duplex links by enforcing collisions to occur and hereby triggering the truncated exponential backoff algorithm Just let a collision occur and the aggressive sender will be silent for a while A much finer method is to send some dummy frames just before the backoff timer allows sending This way the other station never comes to send again Both methods are considered as ugly and only work on half duplex lines Therefore the MAC Control frames were specified allowing for active flow control Now the receiver sends this special frame notifying the sender to be silent for N slot times The MAC Control frame originates in a new Ethernet layer the MAC Control Layer and will support also other functionalities but currently only the Pause frame has been specified Auto Negotiation A Enables each two Ethernet devices to exchange information about their capabilities Signal rate CSMA CD half or full duplex Using Link Integrity Test Pulse Sequence Normal Link Pulse NLP technique is used in 10BaseT to check the link state green LED 10 Mbit s LAN devices send every 16 8 ms a 100ns lasting NLP no signal on the wire means disconnected C Herbert Haas 2005 03 11 Several Ethernet operating modes had been defined which are incompatible to
11. instead of GMIl C Herbert Haas 2005 03 11 10 GE only supports optical links Note that GE is actually a synchronous protocol There is no statistical multiplexing done at the physical layer anymore because optical switching at that bit rate only allows synchronous transmissions The GMII has been replaced or enhanced by the so called XAUI known as Zowie Note At the time of writing this module the 10 GE standard was not fully finished Though some vendors already offer 10 GE interface cards for their switches These interfaces are very expensive but the investment ensures backward compatibility to lower Ethernet rates and at the same time provides a very high speed WAN interface An alternative technology would be OC192 which requires a very expensive and complex SONET SDH environment 20 GE and 10GE use synchronous physical sublayer Recommendation Don t use GE over copper wires Radiation EMI Grounding problems High BER Thick cable bundles especially Cat 7 C Herbert Haas 2005 03 11 Both GE and 10GE are synchronous physical technologies on fiber It not recommended to use GE over copper wires anymore although 802 3ab would specify it This is because the whole electrical hardware cables and connectors are re used from older Ethernet technologies and have not been designed to support such high frequencies For example the RJ45 connector is not HF proof Furthermore shielded t
12. ogy became star shaped History Bridges Store and forwarding according destination MAC address Separated collision domains Improved network performance Still one broadcast domain domains in this example Three collision C Herbert Haas 2005 03 11 Bridges were invented for performance reasons It seemed to be impractical that each additional station reduces the average per station bandwidth by 1 n On the other hand the benefit of sharing a medium for communication should be still maintained which was expressed by Metcalfe s law Bridges are store and forwarding devices introducing significant delay that can filter traffic based on the destination MAC addresses to avoid unnecessary flooding of frames to certain segments Thus bridges segment the LAN into several collision domains Broadcasts are still forwarded to allow layer 3 connectivity ARP etc so the bridged network is still a single broadcast domain History Switches A Switch Multiport Bridges with HW acceleration Full duplex gt Collision free Ethernet gt No CSMA CD necessary anymore Different data rates at the same time supported Autonegotiation VLAN splits LAN into several broadcast domains Collision free plug amp play scalable Ethernet 1000 Mbit s 100 Mbit s OT JT 7I S464
13. smissions using 850 nm and 1300 nm respectively The long wave can be used with both single mode SMF and multimode fibers MMF Only SMF can be used for WAN transmissions because of the much lower dispersion effects Note that there are several other implementations offered by different vendors such as using very long wavelengths at 1550 nm together with DWDM configurations The twinax cable is basically a shielded twisted pair cable 17 1000BaseT A Defined by 802 3ab task force UTP Uses all 4 line pairs simultaneously for duplex transmission echo cancellation 5 level PAM coding 4 levels encode 2 bits extra level used for Forward Error Correction FEC Signal rate 4 x 125 Mbaud 4 x 250Mbit s data rate Cat 5 links max 100 m all 4pairs cable must conform to the requirements of ANSI TIA EIA 568 A Only 1 CSMA CD repeater allowed in a collision domain C Herbert Haas 2005 03 11 It is very difficult to transmit Gigabit speeds over unshielded twisted pair cables Only a mix of multiple transmission techniques ensure that this high data rate can be transmitted over a UTP Cat5 cable For example all 4 pairs are used together for both directions Echo cancellation ensures that the sending signal does not confuse the received signal 5 level PAM is used for encoding instead of 8B10B because of its much lower symbol rate Now we have only 125 Mbaud x 4 instead of 1250 Mbaud The interf
14. tion The physical layer of the Fiber Channel technology uses 8B10B block coding 15 GE 8B 10B Coding Only used by 1000BaseX 256 code groups 8 x 125 Mbit s PCS 8B 10B Encoder Decoder 1024 code groups 125 million code groups per second 1250 Mbaud C Herbert Haas 2005 03 11 8B10B block coding is very similar to 4B5B block coding but allows fully balanced 10 bit codewords Actually there are not enough balanced 10 bit codewords available Note that there are 256 8 bit codewords which need to be mapped on 1024 10 bit codewords But instead of using a fully balanced 10 bit codeword for each 8 bit codeword some 8 bit codewords are represented by two 10 bit codewords which are sent in an alternating manner That is both associated 10 bit words are bit complementary Again the signaling overhead is 12 5 that is 1250 Mbaud is necessary to transmit a bit stream of 1000 Mbit s 16 1000BaseX Two different wavelengths supported Full duplex only 1000Base SX short wave 850 nm MMF 1000Base LX long wave 1300 nm MMF or SMF 1000Base CxX Twinax Cable high quality 150 Ohm balanced shielded copper cable About 25 m distance limit DB 9 or the newer HSSDC connector C Herbert Haas 2005 03 11 Gigabit Ethernet can be transmitted over various types of fiber Currently at least two types are specified short and long wave tran
15. wisted pair cables require a very good grounding seldom found in reality The Bit Error Rate BER is typically so high that the effective data rate is much lower than GE for example 30 only 21 Summary vv Ethernet evolved in the opposite direction Collision free WAN qualified Switched Several coding styles gt Complex PHY architecture Plug amp play through autonegotiation Much simpler than ATM but no BISDN solution might change aas 2005 03 11 22 Why tends high speed Ethernet to synchronous PHY Can attach a 100 Mbit s port toa 1000 Mbit s port via fiber What is the idea of Etherchannels Maximum bit rate difference to multiple parallel links C Herbert Haas 2005 03 11 23 Q1 On fiber its difficult to deal with asynchronous transmission photons cannot be buffered easily store and forward problems Q2 No autonegotiation on fiber does not care for data rates Q3 normal parallel links would be disabled by STP Etherchannel supports up to 8 links C Herbert Haas 2005 03 11 24
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