HP 180 Degree Turn Product Review
1 2005/03/11 ( C) Herbe rt Haa s The Ethe rnet Ev olution The 180 Degree Turn
2 âUse common s ense in r outing cable. Avoid wrappin g coax around source s of strong electric or m agnetic fields. Do not wrap the cable around flourescent light ballasts or cyclotrons, for exa mple.â E thernet Headst art Product, Information and I nstallat ion Gui de, Bell Technologies, pg. 11
3 3 (C) Herbe rt Haa s 2005/03/11 History : Initi al Idea î Shared media î CSMA /CD as access algorithm î CO A X Ca bles î Half duplex communication î Low latency î No networking nodes (except repeaters) î One collision domain a nd also one broadcast domain 10 M bit/s sha red by 5 hosts î 2 Mbit/s ea ch !!! The ini ti al id ea o f Ether net w as comp let el y diff eren t than wh at i s used t oda y under the term "Et hernet". The ori ginal new conc ept of Ethernet was th e use of a shared m edi a and an Aloh a based ac cess al gorith m, cal led Ca rri er Sense Multiple Access with Collision Detection (CSMA /CD). Coaxial cab les were used as shared medium, allowin g a simple coupli ng of station to bus-like topology. Coax-cables were used i n baseband mode, thus allowing onl y unicast transmissions. Therefore , CSMA/CD was used to let Ethernet oper ate under the events of frequent colli sions. Another important point: No intermediat e network devices should be us ed in order to keep lat enc y as small as possible. Soon repeaters were invent ed to be the only exception for a whil e. An Ethernet segment is a coax cable, probabl y extended b y repeaters. The segment constitutes one collision domain (only o ne station may s end at the sam e time) and on e bro adc ast dom ain (an y st ation r ec eiv es the cu rren t fram e sen t). Therefore, the tot al bandwidt h is shared by the number of devic es attached t o the segment . For exam ple 1 0 devi ces att ached means that each d evi ce can s en d 1 Mbit/s of data on avera ge. Ethernet t echnologies at t hat time (1975-80s): 10 Base2 and 10Base5
4 4 (C) Herbe rt Haa s 2005/03/11 Histor y: Multi port Rep eaters î Demand for st ructu red cab ling (v oice-grade twist ed- pair) î 10BaseT (C at3, Cat 4, ...) î Multipo rt repeater ("Hub ") created î Still one c ollisi on dom ain ("CS M A/CD in a b ox") Later, Eth ern et dev ic es suppo rtin g structu red c abl ing wer e cr eat ed in ord er t o reuse the voice-gr ade twisted-pair c ables alread y installed in buildin gs. 10BaseT had been specifi ed to support Cat3 c ables (voice grade) or bet ter, for exam ple Cat4 (and toda y Cat5, Cat6, and Cat7). Hub devices were necessar y to interconnect seve ral stations. Thes e hub devic es were b asic all y mult i-port repe ater s, sim ulatin g th e half -dupl ex co ax-c abl e, whi ch is known as "CSMA/CD in a box". Logicall y, nothing has changed, we ha ve still one single collision and broadcast domain. Note that the Ethernet topology became star-shaped.
5 5 (C) Herbe rt Haa s 2005/03/11 Histor y: Bridges î Store a nd forw ar ding accor ding des tinati on M AC address î Separa ted c ollisio n domains î Improved netw ork performan ce î Still one broad cast domain Thre e collision domains in this example ! Bridg es were i nvent ed fo r perf orman ce r easo ns. It s eemed t o be i mpra cti cal t hat each additional st ation reduc es the average pe r-station bandwidth b y 1/n. On the other hand the benefit of sharing a medium for communication shou ld be still maint ain ed (whi ch w as ex pressed b y Metc alfe 's law). Bridg es are st ore and fo rwardi ng dev ic es (int roduci ng si gnifi cant del a y) that can filter traffi c based on the destinat ion MAC addresses to avoid unne cessary flooding of frames to c ertain segments. Thus, bridges se gment the LAN into several collis ion domains. Broadcasts are stil l forwarded to allow l ayer 3 connectivit y (ARP etc), so the bridged network is still a single bro adcast domain.
6 6 (C) Herbe rt Haa s 2005/03/11 Histor y: S w itches î Switch = Multiport Br idges with HW acceleration î Full duplex î Collision-free Ethern et î No CSM A /CD necessary any more î Different dat a rates at t he same ti me supported î Autonegot iation î VLAN splits LAN into several br oadcast domains 1 0 Mbit/s 100 Mbit/s 1 00 Mbit/s 1000 Mbit/s Collisio n-free plug & pla y scalabl e Etherne t ! Several vendors built advanced bridges, which are partl y or full y implemented in hardware. The introdu ced latenc y could be dramatic all y lowered and furth ermor e oth er feat ur es were i ntr oduced , for exam ple fu ll dup lex communication on twis ted pair c ables, different fr ame rat es on different ports, special forwarding t echniques (e,g, cut th rough or fragment free), Cont ent Address able M emor y (CAM ) tabl es, and m uch m ore. Of cours e mark eti ng rul es demand for another desi gnation for this machin e: the switch was born. Suddenly, a collision fre e plug and pla y Ethernet was availabl e. Simply use twisted pair cabli ng only and enable autonegotiati on to automati call y determine the line speed on each port (of course manual configurations would also do). This wa y, switched Ethe rne t be come v er y scal able. Furthermore , Virtual LANs (VL ANs) were invented to split the LAN into several broadcast domains. VLANs improve securit y, utilization, and allows for logical borders between workgroups.
7 7 (C) Herbe rt Haa s 2005/03/11 Today î No coll isions î no d istance li mitation s ! î Gigabi t Ethernet beco mes W A N technology ! î Over 10 0 km link s pan alre ady î Combine sev eral links to " Etherchannels " î Acts as si ngle link fr om the span ning-tr ee view ⢠Cisco: Port A ggregation Protocol (PAgP) ⢠IEEE 802.1ad: Link A ggregation Control Protocol (L A CP) 1 Gbit/s or even 10 G bit/s long re ach conne ction !!! Today, Gigabit and even 10 Gigabit Ethe rnet is avail able. Onl y twisted pair and more and mor e fib er cab l es are us ed bet ween swit ches , allowi ng fu ll dup le x collision-free conn ections. Si nce collisions cannot occur an ymore, there is no need for a collision w indow anymore! Fro m this it follows, that there is virtua lly no distance limit between each two Ethernet devices. Recen t ex perim ents d em onstrat ed th e int er connec tio n of two Et hern et Sw itch es over a span of more than 100 km! Thus Ethernet became a WAN t echnology! Today, man y carrie rs use Ethernet inst ead of ATM/SONET/SDH or other rather expensive technolo gies. GE and 10GE is relativel y cheap and much simpl er to deploy. F urthermore it easil y integrates into existing low -rate Ethernet environments, allowin g a homogeneous inte rconnection between mul tiple Ethernet LAN site s. Basically, the deployment is plug and play. If the link speed is still too slow, so-called "Eth erchannels" can be configured between each two switch es by combining several ports to one logical connection. Note that it is not poss ible to deploy parallel connections between two sw itches without an Ether channel configurati on because the Spannin g Tree Protocol (STP) would cut off all redund ant links. Depending on the vendor , up to eight ports can b e combined to constitute one "Ether chan nel".
8 8 (C) Herbe rt Haa s 2005/03/11 What About Giga bit H ubs? î Would limit netw ork diameter to 20- 25 meters (Gigabit Ethernet) î Solu tions î Fram e B ur sti ng î Carri er E xten sio n î No GE-H ubs available on the market today î forget i t! î No C SMA/CD de fined for 10GE (!) Remember: Hubs simulate a half- duplex coaxial cable inside, hence limiting the total network d iameter. For Gigabit Ethernet this limitation would be about 25 meters, which is rathe r impracti cable for professional usa ge. Although some countermeasures had b een specified in th e standard, such as frame burstin g and carrier extension, no v endor developed an GE hub as for toda y . Thus: Forget GE Hubs! The 10 GE specific ation does neither consid er copper connec tions nor hubs. 10 GE can onl y run over fiber. At this point please remember the initial idea in th e mid 1970s: B us, CSMA /CD, short distances, no network nodes. Today: Structured cabling (point-to-poin t or star), never CSMA/CD, W AN capabiliti es, sophisticated swit ching devices in be tween.
9 9 (C) Herbe rt Haa s 2005/03/11 MAC Cont rol Frames î A dditional functiona lity easi ly integrated î Curr en tly o nly Pause-Frame supported preamble FCS MAC-ct rl par amet ers MAC-ctrl op cod e 8808h SA DA 8 bytes 6 6 2 2 44 4 Al w ay s 64 bytes MAC-ctrl op cod e ........... Defines fu nction of control fr ame MAC-ct rl par amet ers .... control param eter data (al way s filled up to 44 by t es) Differ ent da ta rates b etw een sw itch es (and d iffer ent perfo rman ce lev els) often lead to con gestion conditions, full buffers, and fra me drops. Tradition al Ethernet flow control was onl y supported on half-dupl ex links b y e nforcing colli sions to occur and hereb y triggering the truncat ed exponential b ackoff algorithm. J ust let a collision occu r and the aggressive sender will be silent for a while. A much finer method is to send some dummy frames just before the b ackoff timer allows sending . This way the other s tation never comes to send again. Both methods are consid ered as ugly and onl y w ork on half duplex l ines. There fore t he MA C Cont rol fr ames w ere spe cifi ed , allow ing fo r act ive flow control. Now the receiv er sends this special fr ame, notif ying the sender to be silent for N slot times. The MAC Control frame originat es in a new Eth ernet la yerâthe MAC Control Layerâand will support also othe r functionaliti es, but currentl y only the "Pause" frame h as be en sp ecifi ed.
10 10 (C) Herbe rt Haa s 2005/03/11 Auto Ne gotia tion î Enables each t wo Ethernet dev ices to exchange info rmation about the ir capabi lit ies î Signal rate, CSM A /CD, half- or full-duplex î Using L ink -Integ rity-Tes t-Pul se-Seq uence î Normal-Link-P ulse (NLP) technique is used in 10BaseT to chec k the link st ate (gre en LED) î 10 Mbit/s L AN devices send e very 16. 8 ms a 100ns la sting N LP, no sign al on th e wir e means disconne cted Sever al Et hern et ope rati ng mod es had b een defin ed , which are i ncomp ati ble t o each other, in cluding different d ata rat es (10, 100, 1000 Mbit/s), half or full duplex operation, MAC control fr ames capabiliti es, etc. Orig inal Ethernet utiliz ed so-called N ormal Link Pulses (NL Ps) to verify layer 2 connectivit y. NL Ps are single pulses whi ch must be rece ived periodi call y betw een re gula r fram es. If NLPs ar e re ceived , th e gre en LED o n th e NIC i s turned on. Newer Et hern et c ards r ea lize auto n egot iati on b y sendin g a sequ ence o f NL Ps, which i s call ed a Fast Link P ulse (F LP) sequen ce.
11 11 (C) Herbe rt Haa s 2005/03/11 Fast Link Puls es î Modern Ethernet NICs send bursts of Fast-Link-Pulses (FLP) consisting of 17-33 NLPs for Autonegotiation signa lling î Each representing a 16 bit w ord î GE sen ds se ver al "pa ge s" A ser ies of FL Ps constitute an autonegotiation frame. The wh ole frame consists of 33 timeslots, where ea ch odd numbered tim eslot consists of a real N L P and each even tim eslot is eith er a NLP or empt y, representing 1 or 0. Thus, each FLP sequence consists of a 16 bit word. Note th at GE Eth ernet send s sever al such "pa ges".
12 12 (C) Herbe rt Haa s 2005/03/11 100 Mbit Ethernet O verview Fast Eth ernet 100Base 4T Signaling Fast Eth ernet 100BaseX Signaling 100BaseTX 100BaseFX 100BaseT4 (half duplex) 100VG-A nyLA N "100Bas eT" HP and AT&T inventi on for real t ime applicat ions IEEE 80 2.3u Signaling S cheme s IEEE 80 2.12 Demand Prio rity The diagram abov e gives an overview of 100 Mbit /s Ethernet technolo gies, which are different iated into IEEE 802.3u and IEEE 802.12 stand ards. The IEEE 802.3u defines the widely used Fast Ethe rnet variants, m ost importantl y those utilizing the 100BaseX signaling scheme. The 100BaseX signaling consists of several details, but b asicall y it utilizes 4B5B bloc k coding over onl y two pairs of regular Cat 5 twist ed pair cables or two strand 50/ 125 or 62.5/125- Fm multimode fiber-optic cables. 100Base4T signaling has been specif ied to support 100 Mbit/s over Cat 3 cables. This mode allows half du plex operation onl y and uses a 8B6T code over 4 pairs of wires; one pair for coll ision detecti on, three pair s for data transmission. One unidirectional p air is used for sending onl y and two bi-directiona l pairs for both sending and receiving. The 100VG-AnyLAN technology had been cre ated b y HP and AT&T in 1992 to support deterministi c medium a ccess for realtime applications. This te chnology was standardized b y the IEEE 802.12 working group. The ac cess method is called "dem and priorit y ". 100VG-AnyLAN supports voice grade cabl es (VG) but requires special hub h ardware. The 802.12 working group is no longer acti ve.
13 13 (C) Herbe rt Haa s 2005/03/11 4B/5B Codi ng 4B/5B Encoder/Decoder PM A PCS MII 1 0 0 0 0 1 0 1 0 16 code groups 32 code groups 4 x 25 Mbit/s 125 MBaud The diagram abov e shows the basic principle of th e 4B5B block coding principl e, which is used by 802.3u and also b y FDDI. The basic ide a is to transform an y arbitrar y 4 bit word into a (relativ ely) balanc ed 5 bit word. This is done by a fast table lookup. Balancing the code has many adva ntages: better bandwidth utilization, better laser effici ency (constant temp erature), bette r bit-synchroniz ation (PLL), etc. Note that the sig naling overhead is 5/4 î 12.5 %.
14 14 (C) Herbe rt Haa s 2005/03/11 Gigabit Ethe rnet Media A ccess Cont rol (MA C) Gigabit M edia Independe nt Interf ace ( GMII) 1000Bas e-X 8B/10B enco der/dec oder 1000Bas e-T encoder /decoder 1000Bas e-LX LWL Fiber Opt ic 1000Bas e-SX SWL Fiber Opt ic 1000Bas e-CX Shielded Balanced Copper 1000Bas e-T UTP Cat 5e IEEE 80 2.3z phy si cal lay er IEEE 80 2.3ab phy sical lay er Gigabit Ethern et has been defin ed in March 1996 b y the working group IEEE 802.3z. The GMII represents a abstr act interfa ce between the common Eth ernet layer 2 and different sig naling layers below. Two importa nt signaling techniques had been defines: The standard 802.3z defin es 1000Base-X signaling which uses 8B10B block coding and the 802.3 ab standard uses 1000Base-T si gnaling. The latter is onl y used over twisted pair cabl es (UTP Cat 5 or bett er), while 1000BaseX is only used over fiber, with on e exception, the twin ax cabl e (1000BaseCX), which is basicall y a shielded twisted pair c able. BTW: The "X" stands for block codin g.
15 15 (C) Herbe rt Haa s 2005/03/11 GE Signa ling PMA PCS 802.2 LLC 802.3 CSMA /CD 802.3 PHY FC-4 upper lay er mappin g FC-3 comm on servic es FC-2 signalling FC-0 interface and me dia FC-1 enco der/de coder IEEE 80 2.2 LLC CSMA/CD or full dupl ex MAC PMD IEEE 80 2.3 Ethernet ANSI X3 T11 Fibre Chan nel IEEE 80 2.3z Gigabit Ethernet Reconcili ation Su blay er PHY Gigabit Ethern et la yers have been defined by adap tation of the LLC and MAC la yers of cl assi cal Et hern et an d th e ph y sic al l a yers of th e ANSI Fib er Chan nel technolog y. A so- called reconcili ation la yer is used in between for seamles s interoperation. Th e physical la yer of the Fiber Channel t echnolog y use s 8B10B block coding.
16 16 (C) Herbe rt Haa s 2005/03/11 GE 8B/1 0B C oding 8B/10B Encoder/Decoder PM A PCS GMII 256 code groups 1024 code groups 8 x 125 Mbit/s 125 million code groups per second 1250 Mbaud 1 Only used by 1000Bas eX 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 8B10B block coding is ver y similar to 4B5B bloc k coding but allows full y balanced 10-bit codewords. Actuall y, there are not enough bal anced 10-bit codewords availabl e. Note that th ere are 256 8-bit cod ewords which need to be mapped on 1024 10-bit c odewords. But instead of using a full y balanced 10-bit codeword for each 8-bit cod eword, some 8-bit codewords are r epresented b y two 10-bit codewords, which are sent in an alternatin g manner. That is, both associ ated 10 -bit words are bi t-co mpl emen tar y. Again, the signaling ove rhead is 12.5%, that is 1250 M baud is necessary to transmit a bit stream of 1000 Mbit/s.
17 17 (C) Herbe rt Haa s 2005/03/11 1000BaseX î T wo different waveleng ths suppor ted î Full duplex only î 1000Ba se-SX: short w ave, 85 0 nm MMF î 1000Ba se-LX: long wa ve, 1300 nm M M F or SMF î 1000Base-C X: î Twinax C able (hi gh qualit y 150 O hm bal anced shielded copper c able) î About 25 m di stance li mit, DB-9 or th e newer HSSD C connector Gigabi t Et hern et can be t ransmi tt ed over v ariou s types of fi ber. C urrent l y (at least) two t ypes are specified, short and long wave transmissions, using 850 nm and 1300 nm respectivel y. 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 mu ch lower dispersion effects. Note th at th ere are s ever al oth er imp lem ent ations offe red b y differ ent v end ors, such as using very long wavelengths at 1550 nm together with DWDM configurations. The twi nax c abl e is bas ic all y a shield ed tw ist ed pa ir cab le.
18 18 (C) Herbe rt Haa s 2005/03/11 1000BaseT î Defined by 802.3ab t ask force î UTP î Uses all 4 line pair s simulta neousl y for duplex transmission ! (echo cancellation) î 5 level PA M coding ⢠4 levels encod e 2 bits extra level used fo r Forward Error Corre ction ( FEC) î Signal rate: 4 x 125 Mbaud = 4 x 25 0Mbit/s data rate ⢠Cat. 5 links, max 100 m ; all 4pai rs, cable must conform to the requirements of A NSI/TI A / EIA-568- A î Only 1 CSM A/CD repeater allowed in a collision domain It is very difficult to t ransmit Gigabit speeds over unshielded twist ed pair cabl es. Only a mix of multiple transmissio n techniques ensure that this high data rate can be tr ansmit ted o ver a UTP Cat5 cabl e. Fo r ex ampl e all 4 pai rs ar e used to geth er for both directions. E cho cancellation ensures that the sendin g signal does not confuse the receiv ed signal. 5 lev el PAM is used for encoding instead of 8 B10B because of its much low er symbol rate. Now we hav e only 125 Mbaud x 4 instead of 1250 Mbaud. The int erf ace d esi gn is ver y compl ic ated and th eref ore relat ivel y ex pensiv e. Using Cat 6 or Cat 7 cabl es allow 500 Mbaud x 2 pairs, that is 2 pai rs are design ated fo r TX and th e oth er 2 p airs ar e used f or RX. This dram ati cal ly reduc es the p ric e but requi res bet ter cabl es, whi ch ar e not r eal l y expensi ve bu t slightly thicker. Legacy cable ducts might be too small in diameter.
19 19 (C) Herbe rt Haa s 2005/03/11 Several Physical Media S upported Logical Link C ontrol LLC MAC Control (optio nal) Media Access Control M AC PLS AUI P MA (MA U ) MDI Medi um Reconciliation Reconciliation Reconciliation PCS PM A PMD GMII MDI PLS AUI PM A MII MDI PCS PM A PMD MII MDI Medi um Medi um Med ium Data Link La yer PHY 1-10 Mbit/s 10 Mbit/s 100 Mbit/s 1000 Mbit/s AUI Attachment Un it Interface, PL S Physical Layer Signaling, MDI Medium Dependent I nterface PCS Ph ysical Coding Sub layer, MII Media Independent Interface, GMII Gigabit Media Independent Interface, PM A Physic al Medium Attachment, MA U Medium Attachm ent Unit, PMD Phy sic al M edium Dependent The diagram abov e shows various physical media designs supported by the official GE standa rd. Each modern GE c ard could theoreti call y support the old 10 Mbit/s standard as well. However m any vendors create GE N ICs that only support GE or GE and FEâwho would connect a precious GE interfac e with another interf ace, which is 100 ti mes slower?
20 20 (C) Herbe rt Haa s 2005/03/11 10 Gigabit Ethernet / IEEE 802.3ae î Only optical support î 850nm (MM) / 1310nm /1550 n m (SM only ) î No copper P HY anymore ! î Different implementations at the moment â standardizat ion not finished! î 8B/10B (IBM) , SONET/SDH sup port, ⦠î X A U I ("Zo w ie" ) inste ad of GM II 10 GE only supports optical links. Note th at GE is actuall y a synchronous protocol! There is no statistical multiplexing done at the physical layer anymore, because optic al switching at that bit rate onl y allows synchronous transmissions. The GMII has been replac ed (or enhanced) b y the so-called XAUI, known as "Zowie". Note: At the tim e of writing this module, th e 10 GE standard was not full y finished. Though, some vendors alr eady offer 10 GE interfa ce cards for their switches. Thes e int erfac es ar e ver y expen sive bu t th e inv estm ent en sures b ackwa rd compatibility to lower Ethernet rates and at the same tim e provides a very hig h speed WAN interfac e. An alternativ e technology would be OC192, whic h requires a ver y expensive and complex SONET/SDH environment.
21 21 (C) Herbe rt Haa s 2005/03/11 Note î GE and 10GE use synchronous physical sublay er !!! î Recommendation: Don't use GE over copper w ires î Radiation/ EMI î Grounding p r oblems î High BER î Thick cab le bund les (especia lly C at-7) Both GE and 10GE are synchronous ph y sical t echnologies on fib er. It not recommended to use G E over copper wires an ymore although 802.3ab wou ld speci f y it. This is bec ause t he who le el ect ric al har dwar e (cab les an d con ne ctors) are re-used from older Et hernet te chnologies and have not been d esigned to support such high frequenci es. For example the RJ 45 connector is not HF proof. Furthermore, shielded twisted pair cables requi re a ver y good grounding, seldom found in realit y. The Bit Error Rate (BER) i s t ypical l y so high th at th e eff ectiv e d ata r ate i s much l ower than GE, for example 30% onl y.
22 22 (C) Herbe rt Haa s 2005/03/11 Summar y î Ethernet evolv ed in the opposite di rection: î Collision free î W A N qualified î Switched î Seve ral coding sty les î Comp lex PH Y architectu re î Plug & play through autonegot iation î Much si mpler than A TM but no BISDN solution â might change!
23 23 (C) Herbe rt Haa s 2005/03/11 Quizz î Why tends hig h-speed Ethernet to synchronous PHY? î Can I attach a 100 Mbit/s port to a 1000 Mbit/s port vi a fiber? î What is the idea of Etherchannels? (Maximum bit rate, difference to multip le par all el lin ks)
24 24 (C) Herbe rt Haa s 2005/03/11 Hints î Q1: On fiber its difficult to deal w ith asynchronous transmission, phot ons cannot be buffered easily, store and forward problems î Q2: N o, autonegotiation on fiber does not care for data rates î Q3: "normal" parallel links would be disabled by STP, Etherchan nel supports up to 8 links
2 âUse common s ense in r outing cable. Avoid wrappin g coax around source s of strong electric or m agnetic fields. Do not wrap the cable around flourescent light ballasts or cyclotrons, for exa mple.â E thernet Headst art Product, Information and I nstallat ion Gui de, Bell Technologies, pg. 11
3 3 (C) Herbe rt Haa s 2005/03/11 History : Initi al Idea î Shared media î CSMA /CD as access algorithm î CO A X Ca bles î Half duplex communication î Low latency î No networking nodes (except repeaters) î One collision domain a nd also one broadcast domain 10 M bit/s sha red by 5 hosts î 2 Mbit/s ea ch !!! The ini ti al id ea o f Ether net w as comp let el y diff eren t than wh at i s used t oda y under the term "Et hernet". The ori ginal new conc ept of Ethernet was th e use of a shared m edi a and an Aloh a based ac cess al gorith m, cal led Ca rri er Sense Multiple Access with Collision Detection (CSMA /CD). Coaxial cab les were used as shared medium, allowin g a simple coupli ng of station to bus-like topology. Coax-cables were used i n baseband mode, thus allowing onl y unicast transmissions. Therefore , CSMA/CD was used to let Ethernet oper ate under the events of frequent colli sions. Another important point: No intermediat e network devices should be us ed in order to keep lat enc y as small as possible. Soon repeaters were invent ed to be the only exception for a whil e. An Ethernet segment is a coax cable, probabl y extended b y repeaters. The segment constitutes one collision domain (only o ne station may s end at the sam e time) and on e bro adc ast dom ain (an y st ation r ec eiv es the cu rren t fram e sen t). Therefore, the tot al bandwidt h is shared by the number of devic es attached t o the segment . For exam ple 1 0 devi ces att ached means that each d evi ce can s en d 1 Mbit/s of data on avera ge. Ethernet t echnologies at t hat time (1975-80s): 10 Base2 and 10Base5
4 4 (C) Herbe rt Haa s 2005/03/11 Histor y: Multi port Rep eaters î Demand for st ructu red cab ling (v oice-grade twist ed- pair) î 10BaseT (C at3, Cat 4, ...) î Multipo rt repeater ("Hub ") created î Still one c ollisi on dom ain ("CS M A/CD in a b ox") Later, Eth ern et dev ic es suppo rtin g structu red c abl ing wer e cr eat ed in ord er t o reuse the voice-gr ade twisted-pair c ables alread y installed in buildin gs. 10BaseT had been specifi ed to support Cat3 c ables (voice grade) or bet ter, for exam ple Cat4 (and toda y Cat5, Cat6, and Cat7). Hub devices were necessar y to interconnect seve ral stations. Thes e hub devic es were b asic all y mult i-port repe ater s, sim ulatin g th e half -dupl ex co ax-c abl e, whi ch is known as "CSMA/CD in a box". Logicall y, nothing has changed, we ha ve still one single collision and broadcast domain. Note that the Ethernet topology became star-shaped.
5 5 (C) Herbe rt Haa s 2005/03/11 Histor y: Bridges î Store a nd forw ar ding accor ding des tinati on M AC address î Separa ted c ollisio n domains î Improved netw ork performan ce î Still one broad cast domain Thre e collision domains in this example ! Bridg es were i nvent ed fo r perf orman ce r easo ns. It s eemed t o be i mpra cti cal t hat each additional st ation reduc es the average pe r-station bandwidth b y 1/n. On the other hand the benefit of sharing a medium for communication shou ld be still maint ain ed (whi ch w as ex pressed b y Metc alfe 's law). Bridg es are st ore and fo rwardi ng dev ic es (int roduci ng si gnifi cant del a y) that can filter traffi c based on the destinat ion MAC addresses to avoid unne cessary flooding of frames to c ertain segments. Thus, bridges se gment the LAN into several collis ion domains. Broadcasts are stil l forwarded to allow l ayer 3 connectivit y (ARP etc), so the bridged network is still a single bro adcast domain.
6 6 (C) Herbe rt Haa s 2005/03/11 Histor y: S w itches î Switch = Multiport Br idges with HW acceleration î Full duplex î Collision-free Ethern et î No CSM A /CD necessary any more î Different dat a rates at t he same ti me supported î Autonegot iation î VLAN splits LAN into several br oadcast domains 1 0 Mbit/s 100 Mbit/s 1 00 Mbit/s 1000 Mbit/s Collisio n-free plug & pla y scalabl e Etherne t ! Several vendors built advanced bridges, which are partl y or full y implemented in hardware. The introdu ced latenc y could be dramatic all y lowered and furth ermor e oth er feat ur es were i ntr oduced , for exam ple fu ll dup lex communication on twis ted pair c ables, different fr ame rat es on different ports, special forwarding t echniques (e,g, cut th rough or fragment free), Cont ent Address able M emor y (CAM ) tabl es, and m uch m ore. Of cours e mark eti ng rul es demand for another desi gnation for this machin e: the switch was born. Suddenly, a collision fre e plug and pla y Ethernet was availabl e. Simply use twisted pair cabli ng only and enable autonegotiati on to automati call y determine the line speed on each port (of course manual configurations would also do). This wa y, switched Ethe rne t be come v er y scal able. Furthermore , Virtual LANs (VL ANs) were invented to split the LAN into several broadcast domains. VLANs improve securit y, utilization, and allows for logical borders between workgroups.
7 7 (C) Herbe rt Haa s 2005/03/11 Today î No coll isions î no d istance li mitation s ! î Gigabi t Ethernet beco mes W A N technology ! î Over 10 0 km link s pan alre ady î Combine sev eral links to " Etherchannels " î Acts as si ngle link fr om the span ning-tr ee view ⢠Cisco: Port A ggregation Protocol (PAgP) ⢠IEEE 802.1ad: Link A ggregation Control Protocol (L A CP) 1 Gbit/s or even 10 G bit/s long re ach conne ction !!! Today, Gigabit and even 10 Gigabit Ethe rnet is avail able. Onl y twisted pair and more and mor e fib er cab l es are us ed bet ween swit ches , allowi ng fu ll dup le x collision-free conn ections. Si nce collisions cannot occur an ymore, there is no need for a collision w indow anymore! Fro m this it follows, that there is virtua lly no distance limit between each two Ethernet devices. Recen t ex perim ents d em onstrat ed th e int er connec tio n of two Et hern et Sw itch es over a span of more than 100 km! Thus Ethernet became a WAN t echnology! Today, man y carrie rs use Ethernet inst ead of ATM/SONET/SDH or other rather expensive technolo gies. GE and 10GE is relativel y cheap and much simpl er to deploy. F urthermore it easil y integrates into existing low -rate Ethernet environments, allowin g a homogeneous inte rconnection between mul tiple Ethernet LAN site s. Basically, the deployment is plug and play. If the link speed is still too slow, so-called "Eth erchannels" can be configured between each two switch es by combining several ports to one logical connection. Note that it is not poss ible to deploy parallel connections between two sw itches without an Ether channel configurati on because the Spannin g Tree Protocol (STP) would cut off all redund ant links. Depending on the vendor , up to eight ports can b e combined to constitute one "Ether chan nel".
8 8 (C) Herbe rt Haa s 2005/03/11 What About Giga bit H ubs? î Would limit netw ork diameter to 20- 25 meters (Gigabit Ethernet) î Solu tions î Fram e B ur sti ng î Carri er E xten sio n î No GE-H ubs available on the market today î forget i t! î No C SMA/CD de fined for 10GE (!) Remember: Hubs simulate a half- duplex coaxial cable inside, hence limiting the total network d iameter. For Gigabit Ethernet this limitation would be about 25 meters, which is rathe r impracti cable for professional usa ge. Although some countermeasures had b een specified in th e standard, such as frame burstin g and carrier extension, no v endor developed an GE hub as for toda y . Thus: Forget GE Hubs! The 10 GE specific ation does neither consid er copper connec tions nor hubs. 10 GE can onl y run over fiber. At this point please remember the initial idea in th e mid 1970s: B us, CSMA /CD, short distances, no network nodes. Today: Structured cabling (point-to-poin t or star), never CSMA/CD, W AN capabiliti es, sophisticated swit ching devices in be tween.
9 9 (C) Herbe rt Haa s 2005/03/11 MAC Cont rol Frames î A dditional functiona lity easi ly integrated î Curr en tly o nly Pause-Frame supported preamble FCS MAC-ct rl par amet ers MAC-ctrl op cod e 8808h SA DA 8 bytes 6 6 2 2 44 4 Al w ay s 64 bytes MAC-ctrl op cod e ........... Defines fu nction of control fr ame MAC-ct rl par amet ers .... control param eter data (al way s filled up to 44 by t es) Differ ent da ta rates b etw een sw itch es (and d iffer ent perfo rman ce lev els) often lead to con gestion conditions, full buffers, and fra me drops. Tradition al Ethernet flow control was onl y supported on half-dupl ex links b y e nforcing colli sions to occur and hereb y triggering the truncat ed exponential b ackoff algorithm. J ust let a collision occu r and the aggressive sender will be silent for a while. A much finer method is to send some dummy frames just before the b ackoff timer allows sending . This way the other s tation never comes to send again. Both methods are consid ered as ugly and onl y w ork on half duplex l ines. There fore t he MA C Cont rol fr ames w ere spe cifi ed , allow ing fo r act ive flow control. Now the receiv er sends this special fr ame, notif ying the sender to be silent for N slot times. The MAC Control frame originat es in a new Eth ernet la yerâthe MAC Control Layerâand will support also othe r functionaliti es, but currentl y only the "Pause" frame h as be en sp ecifi ed.
10 10 (C) Herbe rt Haa s 2005/03/11 Auto Ne gotia tion î Enables each t wo Ethernet dev ices to exchange info rmation about the ir capabi lit ies î Signal rate, CSM A /CD, half- or full-duplex î Using L ink -Integ rity-Tes t-Pul se-Seq uence î Normal-Link-P ulse (NLP) technique is used in 10BaseT to chec k the link st ate (gre en LED) î 10 Mbit/s L AN devices send e very 16. 8 ms a 100ns la sting N LP, no sign al on th e wir e means disconne cted Sever al Et hern et ope rati ng mod es had b een defin ed , which are i ncomp ati ble t o each other, in cluding different d ata rat es (10, 100, 1000 Mbit/s), half or full duplex operation, MAC control fr ames capabiliti es, etc. Orig inal Ethernet utiliz ed so-called N ormal Link Pulses (NL Ps) to verify layer 2 connectivit y. NL Ps are single pulses whi ch must be rece ived periodi call y betw een re gula r fram es. If NLPs ar e re ceived , th e gre en LED o n th e NIC i s turned on. Newer Et hern et c ards r ea lize auto n egot iati on b y sendin g a sequ ence o f NL Ps, which i s call ed a Fast Link P ulse (F LP) sequen ce.
11 11 (C) Herbe rt Haa s 2005/03/11 Fast Link Puls es î Modern Ethernet NICs send bursts of Fast-Link-Pulses (FLP) consisting of 17-33 NLPs for Autonegotiation signa lling î Each representing a 16 bit w ord î GE sen ds se ver al "pa ge s" A ser ies of FL Ps constitute an autonegotiation frame. The wh ole frame consists of 33 timeslots, where ea ch odd numbered tim eslot consists of a real N L P and each even tim eslot is eith er a NLP or empt y, representing 1 or 0. Thus, each FLP sequence consists of a 16 bit word. Note th at GE Eth ernet send s sever al such "pa ges".
12 12 (C) Herbe rt Haa s 2005/03/11 100 Mbit Ethernet O verview Fast Eth ernet 100Base 4T Signaling Fast Eth ernet 100BaseX Signaling 100BaseTX 100BaseFX 100BaseT4 (half duplex) 100VG-A nyLA N "100Bas eT" HP and AT&T inventi on for real t ime applicat ions IEEE 80 2.3u Signaling S cheme s IEEE 80 2.12 Demand Prio rity The diagram abov e gives an overview of 100 Mbit /s Ethernet technolo gies, which are different iated into IEEE 802.3u and IEEE 802.12 stand ards. The IEEE 802.3u defines the widely used Fast Ethe rnet variants, m ost importantl y those utilizing the 100BaseX signaling scheme. The 100BaseX signaling consists of several details, but b asicall y it utilizes 4B5B bloc k coding over onl y two pairs of regular Cat 5 twist ed pair cables or two strand 50/ 125 or 62.5/125- Fm multimode fiber-optic cables. 100Base4T signaling has been specif ied to support 100 Mbit/s over Cat 3 cables. This mode allows half du plex operation onl y and uses a 8B6T code over 4 pairs of wires; one pair for coll ision detecti on, three pair s for data transmission. One unidirectional p air is used for sending onl y and two bi-directiona l pairs for both sending and receiving. The 100VG-AnyLAN technology had been cre ated b y HP and AT&T in 1992 to support deterministi c medium a ccess for realtime applications. This te chnology was standardized b y the IEEE 802.12 working group. The ac cess method is called "dem and priorit y ". 100VG-AnyLAN supports voice grade cabl es (VG) but requires special hub h ardware. The 802.12 working group is no longer acti ve.
13 13 (C) Herbe rt Haa s 2005/03/11 4B/5B Codi ng 4B/5B Encoder/Decoder PM A PCS MII 1 0 0 0 0 1 0 1 0 16 code groups 32 code groups 4 x 25 Mbit/s 125 MBaud The diagram abov e shows the basic principle of th e 4B5B block coding principl e, which is used by 802.3u and also b y FDDI. The basic ide a is to transform an y arbitrar y 4 bit word into a (relativ ely) balanc ed 5 bit word. This is done by a fast table lookup. Balancing the code has many adva ntages: better bandwidth utilization, better laser effici ency (constant temp erature), bette r bit-synchroniz ation (PLL), etc. Note that the sig naling overhead is 5/4 î 12.5 %.
14 14 (C) Herbe rt Haa s 2005/03/11 Gigabit Ethe rnet Media A ccess Cont rol (MA C) Gigabit M edia Independe nt Interf ace ( GMII) 1000Bas e-X 8B/10B enco der/dec oder 1000Bas e-T encoder /decoder 1000Bas e-LX LWL Fiber Opt ic 1000Bas e-SX SWL Fiber Opt ic 1000Bas e-CX Shielded Balanced Copper 1000Bas e-T UTP Cat 5e IEEE 80 2.3z phy si cal lay er IEEE 80 2.3ab phy sical lay er Gigabit Ethern et has been defin ed in March 1996 b y the working group IEEE 802.3z. The GMII represents a abstr act interfa ce between the common Eth ernet layer 2 and different sig naling layers below. Two importa nt signaling techniques had been defines: The standard 802.3z defin es 1000Base-X signaling which uses 8B10B block coding and the 802.3 ab standard uses 1000Base-T si gnaling. The latter is onl y used over twisted pair cabl es (UTP Cat 5 or bett er), while 1000BaseX is only used over fiber, with on e exception, the twin ax cabl e (1000BaseCX), which is basicall y a shielded twisted pair c able. BTW: The "X" stands for block codin g.
15 15 (C) Herbe rt Haa s 2005/03/11 GE Signa ling PMA PCS 802.2 LLC 802.3 CSMA /CD 802.3 PHY FC-4 upper lay er mappin g FC-3 comm on servic es FC-2 signalling FC-0 interface and me dia FC-1 enco der/de coder IEEE 80 2.2 LLC CSMA/CD or full dupl ex MAC PMD IEEE 80 2.3 Ethernet ANSI X3 T11 Fibre Chan nel IEEE 80 2.3z Gigabit Ethernet Reconcili ation Su blay er PHY Gigabit Ethern et la yers have been defined by adap tation of the LLC and MAC la yers of cl assi cal Et hern et an d th e ph y sic al l a yers of th e ANSI Fib er Chan nel technolog y. A so- called reconcili ation la yer is used in between for seamles s interoperation. Th e physical la yer of the Fiber Channel t echnolog y use s 8B10B block coding.
16 16 (C) Herbe rt Haa s 2005/03/11 GE 8B/1 0B C oding 8B/10B Encoder/Decoder PM A PCS GMII 256 code groups 1024 code groups 8 x 125 Mbit/s 125 million code groups per second 1250 Mbaud 1 Only used by 1000Bas eX 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 8B10B block coding is ver y similar to 4B5B bloc k coding but allows full y balanced 10-bit codewords. Actuall y, there are not enough bal anced 10-bit codewords availabl e. Note that th ere are 256 8-bit cod ewords which need to be mapped on 1024 10-bit c odewords. But instead of using a full y balanced 10-bit codeword for each 8-bit cod eword, some 8-bit codewords are r epresented b y two 10-bit codewords, which are sent in an alternatin g manner. That is, both associ ated 10 -bit words are bi t-co mpl emen tar y. Again, the signaling ove rhead is 12.5%, that is 1250 M baud is necessary to transmit a bit stream of 1000 Mbit/s.
17 17 (C) Herbe rt Haa s 2005/03/11 1000BaseX î T wo different waveleng ths suppor ted î Full duplex only î 1000Ba se-SX: short w ave, 85 0 nm MMF î 1000Ba se-LX: long wa ve, 1300 nm M M F or SMF î 1000Base-C X: î Twinax C able (hi gh qualit y 150 O hm bal anced shielded copper c able) î About 25 m di stance li mit, DB-9 or th e newer HSSD C connector Gigabi t Et hern et can be t ransmi tt ed over v ariou s types of fi ber. C urrent l y (at least) two t ypes are specified, short and long wave transmissions, using 850 nm and 1300 nm respectivel y. 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 mu ch lower dispersion effects. Note th at th ere are s ever al oth er imp lem ent ations offe red b y differ ent v end ors, such as using very long wavelengths at 1550 nm together with DWDM configurations. The twi nax c abl e is bas ic all y a shield ed tw ist ed pa ir cab le.
18 18 (C) Herbe rt Haa s 2005/03/11 1000BaseT î Defined by 802.3ab t ask force î UTP î Uses all 4 line pair s simulta neousl y for duplex transmission ! (echo cancellation) î 5 level PA M coding ⢠4 levels encod e 2 bits extra level used fo r Forward Error Corre ction ( FEC) î Signal rate: 4 x 125 Mbaud = 4 x 25 0Mbit/s data rate ⢠Cat. 5 links, max 100 m ; all 4pai rs, cable must conform to the requirements of A NSI/TI A / EIA-568- A î Only 1 CSM A/CD repeater allowed in a collision domain It is very difficult to t ransmit Gigabit speeds over unshielded twist ed pair cabl es. Only a mix of multiple transmissio n techniques ensure that this high data rate can be tr ansmit ted o ver a UTP Cat5 cabl e. Fo r ex ampl e all 4 pai rs ar e used to geth er for both directions. E cho cancellation ensures that the sendin g signal does not confuse the receiv ed signal. 5 lev el PAM is used for encoding instead of 8 B10B because of its much low er symbol rate. Now we hav e only 125 Mbaud x 4 instead of 1250 Mbaud. The int erf ace d esi gn is ver y compl ic ated and th eref ore relat ivel y ex pensiv e. Using Cat 6 or Cat 7 cabl es allow 500 Mbaud x 2 pairs, that is 2 pai rs are design ated fo r TX and th e oth er 2 p airs ar e used f or RX. This dram ati cal ly reduc es the p ric e but requi res bet ter cabl es, whi ch ar e not r eal l y expensi ve bu t slightly thicker. Legacy cable ducts might be too small in diameter.
19 19 (C) Herbe rt Haa s 2005/03/11 Several Physical Media S upported Logical Link C ontrol LLC MAC Control (optio nal) Media Access Control M AC PLS AUI P MA (MA U ) MDI Medi um Reconciliation Reconciliation Reconciliation PCS PM A PMD GMII MDI PLS AUI PM A MII MDI PCS PM A PMD MII MDI Medi um Medi um Med ium Data Link La yer PHY 1-10 Mbit/s 10 Mbit/s 100 Mbit/s 1000 Mbit/s AUI Attachment Un it Interface, PL S Physical Layer Signaling, MDI Medium Dependent I nterface PCS Ph ysical Coding Sub layer, MII Media Independent Interface, GMII Gigabit Media Independent Interface, PM A Physic al Medium Attachment, MA U Medium Attachm ent Unit, PMD Phy sic al M edium Dependent The diagram abov e shows various physical media designs supported by the official GE standa rd. Each modern GE c ard could theoreti call y support the old 10 Mbit/s standard as well. However m any vendors create GE N ICs that only support GE or GE and FEâwho would connect a precious GE interfac e with another interf ace, which is 100 ti mes slower?
20 20 (C) Herbe rt Haa s 2005/03/11 10 Gigabit Ethernet / IEEE 802.3ae î Only optical support î 850nm (MM) / 1310nm /1550 n m (SM only ) î No copper P HY anymore ! î Different implementations at the moment â standardizat ion not finished! î 8B/10B (IBM) , SONET/SDH sup port, ⦠î X A U I ("Zo w ie" ) inste ad of GM II 10 GE only supports optical links. Note th at GE is actuall y a synchronous protocol! There is no statistical multiplexing done at the physical layer anymore, because optic al switching at that bit rate onl y allows synchronous transmissions. The GMII has been replac ed (or enhanced) b y the so-called XAUI, known as "Zowie". Note: At the tim e of writing this module, th e 10 GE standard was not full y finished. Though, some vendors alr eady offer 10 GE interfa ce cards for their switches. Thes e int erfac es ar e ver y expen sive bu t th e inv estm ent en sures b ackwa rd compatibility to lower Ethernet rates and at the same tim e provides a very hig h speed WAN interfac e. An alternativ e technology would be OC192, whic h requires a ver y expensive and complex SONET/SDH environment.
21 21 (C) Herbe rt Haa s 2005/03/11 Note î GE and 10GE use synchronous physical sublay er !!! î Recommendation: Don't use GE over copper w ires î Radiation/ EMI î Grounding p r oblems î High BER î Thick cab le bund les (especia lly C at-7) Both GE and 10GE are synchronous ph y sical t echnologies on fib er. It not recommended to use G E over copper wires an ymore although 802.3ab wou ld speci f y it. This is bec ause t he who le el ect ric al har dwar e (cab les an d con ne ctors) are re-used from older Et hernet te chnologies and have not been d esigned to support such high frequenci es. For example the RJ 45 connector is not HF proof. Furthermore, shielded twisted pair cables requi re a ver y good grounding, seldom found in realit y. The Bit Error Rate (BER) i s t ypical l y so high th at th e eff ectiv e d ata r ate i s much l ower than GE, for example 30% onl y.
22 22 (C) Herbe rt Haa s 2005/03/11 Summar y î Ethernet evolv ed in the opposite di rection: î Collision free î W A N qualified î Switched î Seve ral coding sty les î Comp lex PH Y architectu re î Plug & play through autonegot iation î Much si mpler than A TM but no BISDN solution â might change!
23 23 (C) Herbe rt Haa s 2005/03/11 Quizz î Why tends hig h-speed Ethernet to synchronous PHY? î Can I attach a 100 Mbit/s port to a 1000 Mbit/s port vi a fiber? î What is the idea of Etherchannels? (Maximum bit rate, difference to multip le par all el lin ks)
24 24 (C) Herbe rt Haa s 2005/03/11 Hints î Q1: On fiber its difficult to deal w ith asynchronous transmission, phot ons cannot be buffered easily, store and forward problems î Q2: N o, autonegotiation on fiber does not care for data rates î Q3: "normal" parallel links would be disabled by STP, Etherchan nel supports up to 8 links