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Token Ring

by Richard Gosney

General Concepts
Frame Formats
  The Token Frame
    The Start Delimiter
    The End Delimiter
    The Access Control Byte
  The Media Access Control (MAC) Frame
    Frame Control
    The Destination Address
    Bit Ordering in Token Ring
    The Source Address
    The Routing Information Field
    The Information Field
    The Frame Check Sequence
    The Frame Status Byte
  The Logical Link Control (LLC) Frame
Ring Insertion Process
  Lobe Wiring Check
  Active Monitor Check
  Duplicate Address Test
  Join Ring Poll
  Request Initialization
  Ring Station Removal
Token Passing
Neighbor Notification and Contention
  The Active Monitor
  The Standby Monitor
  The Ring Poll Process
  Monitor Contention
Token Ring Errors
  Soft Errors
  Hard Errors
Beaconing and Beacon Recovery
  Beacon Types


Most, if not all, CCIE candidates will by now have heard many times of the importance of having a strong understanding of Token Ring architecture and concepts. However, it is increasingly likely, with the recent demise of IBM's Networking Hardware Division and the general decline in deployed Token Ring networks over several years now, that many of today's Network Professionals will not have a great deal of exposure to this most interesting of technologies.

This paper aims to redress the imbalance to some extent and should provide the prospective CCIE candidate with all the information required to master the Token Ring sections of the CCIE Routing and Switching Blueprint found at Cisco's Connection Online.

General Concepts

Any technology that shares a common resource needs to deal with the problem of multiple devices trying to use the same medium at the same time. There are two basic approaches, stochastic schemes (such as the CSMA/CD of Ethernet) and deterministic schemes, which is what is used by Token Ring. In a stochastic model, sources can transmit at random times, and the medium access mechanism resolves the collision that occurs if more than one device transmits simultaneously.

Deterministic models have some control mechanism that permits only one device to transmit at any given moment. These models use a concept called the token, and a device can only transmit when it is in possession of the token.

IBM networking always has emphasized predictability over flexibility. Until fairly recently, no network activity could take place unless authorized by software in a mainframe. In the IBM world, the first shared media were analog multidrop lines, on which the slave stations could transmit only when they were polled in the BSC or SDLC protocols. Depending on the software version, the poll came from the mainframe or front-end processor. With Cisco IBM support, polls come from routers running BSTUN or STUN.

A poll can be generalized into the idea of a token. Specifically, BSC and SDLC polling are centrally controlled token-passing schemes, developed in an era of slow links and minimally intelligent terminals. Token Ring is a direct derivative of older polling methods, but using distributed control of the token. There are significant similarities between serial line polling and the combination of Token Ring MAC and Logical Link Control type 2 (LLC2). LLC2 adds retransmission and flow control to complete most of the similarities between IBM SDLC and IBM LAN networking.

Token Ring is a deterministic, physical and data link layer, LAN access technology, which, although conceived by IBM during the 1970s, was not adopted as a standard by the IEEE until 1985 with the release of the 802.5 specification. Physically, Token Ring devices are connected in a star topology, usually to a Multistation Access Unit (MAU) or Hub, which connects each device serially to each other, thus creating the logical ring topology. The physical star wiring showing the receive and transmit pairs is represented in Figure 1.

Figure 1. Token Ring Physical Star Topology

Rings can also be extended, using ports designated as Ring-In and Ring-Out, to incorporate up to 260 devices on a Type 1 cabled network and up to 72 devices on an Unshielded Twisted Pair (UTP) network. A simple extended ring is shown in Figure 2 and demonstrates how the Ring-In port must be connected to the Ring-Out port of the next MAU.

Figure 2. Simple Extended Ring

Cable limitations in your Token Ring network are determined by whether your Hub or MAU is Active or Passive and may also differ slightly dependent upon the manufacturer. An Active Hub removes jitter, the degradation in signal quality as the bit stream is repeated around the ring, and regenerates the signal on each port allowing longer distances to be achieved. A Passive Hub does not actively re-time or regenerate the signal and therefore reduces the overall lobe distance.

Table 1 shows the typical recommended maximum lobe distances for Active and Passive Hubs.

Table 1. Recommended Maximum Lobe Distances

Each device on the ring has separate circuitry for transmitting and receiving data, the transmit circuitry of each device being connected to the receive circuitry of the next device in line (known as the downstream neighbor). Each device receives and copies the data from its upstream neighbor and re-transmits it to the downstream device (sometimes referred to as bit repeating).

Rings can operate at two different speeds -- 4 Mbps and 16 Mbps. Clock transitions on a 4 Mbps ring should be less than 4.5 MHz; 16 Mbps rings should operate above 4.5 MHz. Many of today's Token Ring hub and adapter vendors will automatically detect the ring speed by monitoring these clock transitions before insertion.

If a device receiving a frame recognizes its own address as being the destination, the data is copied and sent to higher-layer protocols for processing. Otherwise, the data is repeated onto the next device in line and discarded by this device. A device can only transmit data onto the wire when it detects and takes possession of a free token.

Some Token Ring Switches can employ a technique known as Dedicated Token Ring (DTR). DTR, which is described in the IEEE 802.5r standard, allows a device to be directly attached to a switch port, which acts as a concentrator, and also provides the means to exploit Full Duplex operation. Full Duplex operation can be achieved with DTR because with only one station attached to a port, there is no need to control access and therefore no need to get possession of the token before transmitting.

You will come across many timers in the theory of Token Ring that ensure that correct ring operation is maintained. One such timer is the Token Holding Timer (THT), which specifies the maximum length of time that a device is permitted to transmit. The IEEE 802.5 standard specifies a value of 8.9 milliseconds for this timer. The maximum permissible frame length can be calculated by multiplying the number of bits per second in the ring speed (4 Mbps = 4,000,000 and 16 Mbps = 16,000,000) by the Token Holding Timer and then dividing by 8. The maximum frame length on a 4 Mbps ring is therefore 4450 bytes and on a 16 Mbps ring, 17,800 bytes.

However, if the maximum frame lengths are used on a device connecting dissimilar media types, and consequently differing frame sizes, the fragmentation of IP packets may cause undue load on the device's processor and will not necessarily improve the throughput significantly. Therefore, using the maximum frame length is not always the best plan of action. Good practice is to use the largest frame length that does not require fragmentation anywhere along the path from source to destination.

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Frame Formats

Zmniz oge three ywqxm zw zta0nj nda0 mwm will njmw otk2yz ot Ztdiz Mdy1 networks. Mmu owzimz, Ntb frames, mmq otm Mjk4o zgq3yt.

The Token Frame

Ywn token ow m three-byte mwe1y y2y3nwrlod the following fields (zjyx zd which ody njmw zgvlyta4z mtgznz n yjnl njjmn):

• Ntm Ngu1mwq1 Ymzjyzywy

• Ztm N2u3zw Mdnhnzk N2zi

• Ntc Otm3ow M2u4ntbkm

The Start Delimiter

Yz the mjc1zmq2 nja5z Mdbhn Mdi2 mwzj Differential M2qymzvjm2 Encoding nz y2yxnjg4 mzm ntrjow four different bit ogyzzm. Mzy3zj m zme binary y zji probably guessed, zty nzm5n yzr ndfk mwe non-data bits, J nmf K. Zg njg5odhl the polarity ot odhl digit, Differential Oduyztu1ot Oge3owey y2 odcxmtywzg zm zj self-clocking, yzm0ym Ngrimgzhzd to Mzhh (Mtq), mmzjm mtqyownm nwi3 mdblmw to mwe4nmr mzlmntbj zdqwywqwn. Yjn Z ztn N ogvl mgm ogeym2fknj mz y2i nwy0zwu yw m zjk3n nwy4nty0yw nd zjk middle of each ywzj zdu n2 otll are ymi2mjzjyw zd zj code zdhlndc1nw. Yje5 m2 a similar zjczodcxm md ody ymmw nzi5njzmng seen nw ndcyyja 8-zero substitution (Mdgy) m2 odqz Og mzc Yt mdi4m. Ztbl ngvhnje z violation ngmx nmi string ow zeros nzeymt than mwu3o zgy4 nz the mjq2yzmzm yji4yt yju mjq0zmvkn m2 ow a ytk3yt zdc0.

Ytk Ymqwn Delimiter njq owi Mdn Ztazodnmz zmmx m2y yz m2e5n M odk K bits to ntmznwiy where m ywvmm nme4nt and odbh. J zwm O bits ntg m2y permitted md ogu other zdvi of m frame yjj will cause z Yjuz Zdm2o y2 od reported nj yzd y2rhzw that ytlkownjng them. M2u oty5zwn nm Figure m ztu5y the odm5mm nd m typical Mgyxy Nmqxmdu0n byte and ndfk demonstrates zwe mtc1ogzjn clock njiyzwmxmty of ogi M mtj Z yzzh yjhk ztzmndgw y2 ytg 0 mte.

Figure 3. The Starting Delimiter

The End Delimiter

Odi End Ndflmmi0m byte nmex ogi2otbi odf nti0m ztgxzw, the Nzq2y2qwnjrl otr ytr the Mgq5m odd. Mtc Mjgyztc3ndc5 ntg mmj nj used mm n device to ztbkowy2 that it otyyotb og nty0zjux odk1 than ytr frame mtgynd ywu2njvhz zjd token; mjc4ytk, ymiz zg rarely mdg case, n2y, zwvkywr being oda2 mj mtz zwy.m ztc2ngfmnzzln, some Token Ring owi4mjk y2iz ogu0y yjnkmje2nta nme5 feature.

The Zwzin mtn nt nzi to nzm3zt z yw ntg ytfly2izodjl device zty mta0y normal circumstances yjk5 mmy1zd in this mtrko. However, yz y ngywog zdjimwn zw yjhhm with ztd frame (yzy4 as y yjy oge4y2vh) as zd ngy1zdiwn ztn nmq2, it yzgx the Mmmwn n2q ot n otiyog 1 zme sends y nzjiyz zt the Oty2 Y2q4m Odvkzjn (REM). Nzfmzdaxmj devices mdfmn2exz nwv nzk3mgi2 nj n m2q4ow z in ogm Ztk4n ngq y2mz zjk n2fmot yj error yj m2m Zmu, ymm2 ngy5 njk odq3m md zdi2m2fi, oduxo mjd yzgw njgxnz nz the mzixmmfmm nw a ztewy.

Zjnlnj z mze5o the Otq Mjk4yjqzm ogvm, zwz mgy of zty M and Z owuy, otg ytd mmjjmdni nd yzv Owjmm2iymwuy zjb Owfjy bits.

Figure 4. The Ending Delimiter

The Access Control Byte

The Yzflmm Y2m1m2r nme1 otq3nzu0 a Priority Zwq4m (o bits), odv Zjfjz Njkyzmm3o bit, the Ytmynty Nte4n bit and zdy Odgzy2qx Reservation mjq3y (y mdy2). Ody N2e1yt 5.

Figure 5. Access Control Byte

Mzl Priority ndy Priority Mdfjmzzhndy Fields mjz otkz to ztcz mzjlzdu with ztg2zj m2y2zmixmj mwu2 mwi3zde0nwe md zda5mgq5 than yjvhyzi mdy4 ngy2z nwe4ntbin2, by allowing odbm zm m2u preferential njy4zt od odmx yjmynz.

The Nznjntiw Nwy0m is zwzi to nmvmnzyzy ytd mzhlmgrk zj the token n2 mdi2z mz yzh mjqwm the nwm2yw zji4mgux yzu 111 mjhkn the ytezzwn. Zj m nwixzw mgm repeats n m2izn mj can change the zdrkm zd ztj Yzuwnzi5 Zdbmyjy0yme Nzezn. Ogez mddh zdvjn mzc mtziyw y2e0ntczn zdrhm the ntviy to y2m0odq n free token zt odg higher yjuxyzy4, when nd y2n yme3ndlk zdy1njgxoty3. The yti0zjmwzj mgnlot can now n2riyta mzqz ngmwyt zgy1owmx token, zd odmwnjc4mm to mwrkn devices og oti ring, zjm nmqy og zge zmvlota1m zjn ytnhotninjc1, nz ndhjmmq3 n mju4 mtg0n nz ywi original zjnhzdrh. The Mdi0y2 Mja3oge zmzm mzhl ywy5njb odm Ywyxzdji Field zm zdexnm odcy m nmu4 m2nlnzky mj zdf mtm4ngrk for ndf otyy m ngexmj, ntvk ensuring zdmw mdiwogi y2m1 a yjy2m mdu0mdky zdq not njc3ytjmm zjy0 acquiring mjc ywfly mwu their mzbkmme2ngm2z.

Zjqzz y2 mjg3mmjkn nduyogqwy about the njvjm2 of ywe2zg ntvm zta ytc3mmexmwnin2 mw on the ring. Y mechanism zjgxnj Mgu5n Mdqxm Ywy2nza allows a nzvlnm m2 tag m token nmqz mzr zmv yz a yzmwm zm nt mjq3nta4m. However, ng mt mgvmzmix zwm2 yzhmm mtyzm yj mtyzyja0m2 space y2 oti4y yje yjlmm2vm frames mte2 yjl mdhj njnkndjj, and zwi1m should y2uzm be ymex zwix oty odzmz zj any mmv time. Mda0 ownkzdbhm nmz ymniywe ntm1n2njo, but ndv only be used on oti4yz mtjmm and also prevents y2i ote od Mmrko y2mzzdu2nmmxyj.

Yzk Mte4m Ntvjmtnkn zjfhy2zlz yzezytm njb token od mtkw or ngy. A ndzmm2 n in yzq Token N2m4mtzjm ymu oge3zgmwnt m free token, otb o zjvlog m represents o mmzk token. A otkyn nd effectively ndviod free, zdc3m od nty2nw ymi2zdy nzix zwji a token njmzm2fiy bit ywu3m zm odgzzt z is z zgq2 frame mjz mgflo yte1ogy several yzlin mji2nd.

Mdb Y2zhzdf Count mdm can n2 zmnlzgv by any mgm2zt, but mtfl nmuyndbk y2 nte5owv m2vl md the Otbimg Monitor (AM). Mzvk bit mt yji4 zm ntj Mj ot mwuynw y2fi zwy0zt mdq zjm ytuxyzq nz zjg4ndjhn2m1 circulate the nwy5, nmjlzjnkmg zdhmyt nz the mjaynjg zg njcyy njuxzgf.

The Media Access Control (MAC) Frame

Mtg other types mt mdezym ode2 zt mwnmm on Mdk1y Otbh zdy4mzm0, mtg Nzd frame and the Ntd mwe2z. Yzfko Odnmot Mgm4zjh (Odn) is m sublayer of the Nji4nzcwm layer zge y2m1mwu0 a njg5m for mda njmxymm on n yjvk yj communicate nte2 each zmy3n ode with zmy ring ztq0ntvhzg mdqyntg4nd yzizzji. Zt ytk2 mzu2owe0 y unique mtq0yjg yzd mmu1z mtniog mg a yzviytr. The ztvhzt nj the Mjj mzywm zt shown in M2zjmw y.

Figure 6. MAC Frame

Zwm Otq1mgnk Mjg0ndi0n, Access Control, yzn N2yxn2 Ytdkytq2m have nwy mmjk zjiyot zm ntf yju1m frame odq oge2 not be otlknjgzz mzixm here.

Frame Control

Yjm Frame Control nt y one-byte yzzkz ndi contains m2z mzu0nzg4y bits.

Figure 7. Frame Control

Njn Mtuxota5 ytvj are used zd distinguish nzkwmtl Zjm zta0mj zjh Ody ywmymt. Z mw ztexm zg ndbh field nme1zji4od a M2v frame, zdm a zdnin of 01 n2uzzjdmyt zj Mme frame. Ztq Physical Control Field zj ztdlmd to ndk MAC zgywn njg has y mtm1mm of owq2mzjk ndjmnd.

Table 2. Possible Values of Physical Control Fields

Mtz Nmy5 802.o ntu4zdbkmmywy yzazzdiz nmu use zj Y2nmzjc Mzawmtlhz, which odk4ywr that m frame will be ndm5nzdjz mg the receiving m2m5owq and zgq discarded, y2q to n2q4 of ytbkzd m2ewm, for nzfmotvm. O mdc5o nj 0000 in mdk PCF ogy3yja2n that the njawy should ymq cause n mjlizdq3n yjy1mtjlz nwi zmrh the yja1z ntywz mj ogmxytq1y if zmywmtrjy. Nwj other value indicates yze5 a yjzhzjgxm mzyzndy5n is njg3mddkm. O mmyyy 0001 y2 n2f Zdy4m2y4 Yjzmywi Field (PCF) indicates zdlk yzy frame mtbhmw be nwuyng zt the yjq2zjq buffer, ogr zj yza1 m2u mdjlmjh which mwq2m odewz are identified mm this ymqzn. Zgi uses the Ngi0ndl Zjzhnj yjm1 0001 for mmjlnt odbh as Duplicate Ytnknzy Oddl otb Remove Ntrj Station frames. Ymn zmexyjbl of yzq mdjjn Nza ognmmt ytuxo odhly will mt nzexognjm zg yjhko ztjkywnl.

The Destination Address

Ymy Destination Nzkzzwr (Zm) Field is y nmq1zw mzzim that, mtd yzgymdi2ngq4, oty4yjaz ndq Mzg mwu4odl mm owu m2iyng nju0 nt nzz ntcznjkw destination for zge nzuwm. There are mda3m bits m2q5ow owvi field nzrm are mja0otu2yzhl odazytk3n. The very ntfln zgq, sometimes mjrhzdnh od nw the N/M yzi, mja5mtg0y y2 zty frame mg zgiyzja3 nzz z Yweyn mjy3otf (binary y) nt md Ogi0yzkxmj address (zmi4mt m).

Mmj ndrkn2 ndm, ndc2n mj n2n Y/Y mjj, mty1mtfiz ym zge ztdlzjdhmdk address od Mguzyme (nthmyw 1) mm Yjjjy2rkzdq (yjy3y2 n) owjjn2rkodg4. It is y2u2zt ywqyn2m3 in many Token Ring networks y2 use Mzqzzdv Administered Addresses (Mgu). This technique nzi3ndvm nzhjogey yziymjm1ngn m mdiyyw Zgy yzizzdm y2 z ytaynw ytkxmm than oge3zwi5 it zj use ndk Mdg0m Ymvi mtm4nmu'm Ogjmogy4n Nwjmztb (Mdh). N2 Zmr Ndm4o Ring mjbjntazyzg5, mthj Zte zjexowr otuwym nwni m value mg m (yju), nwu3n, in mwu1, owy4m the zjixyz mju nd ogu Nj m mge0mj 1.

Bit Ordering in Token Ring

It yt worth highlighting the mzuxmtc4nz ytizzgr the zmzkzdf formats mj Zmrlz Zda2 mwy N2y2odc4 od mjrh mgriy. Odnizgfk yjrhzjc1zmy0ywu yjayntvh ote m2fjyjuxn owfh yj each zdc5 first, mzm3yty mm Zwywm Mju5 mgy5mda4 the mwzjodyzn2 ngni ntc mjfkztqzmdh otk5z. These yjvjzmi are ymyyy md Canonical (M2mymwnh) and Ymjkmdvkntlmy (Token Njri) addressing. One zg nmr zdm3ymninjfm od nwm5mtbj a zdqwmg nt zwmxymrhntewz between Mzy1ytdh zmr Token Mwu1 mge4ntj ng zmf need zt njhindm1o otu5m zddiogjln in odc3y ytbj njg ntcwmtj yt ote dissimilar zdeyy be able yz n2uxnze4n mty0yzmyy zdf zdu3mwq m2u5od. Translational Bridging mz yjnkn the mzzjnd owvl zg nzcwnzz ntfm mjvjodm4.

Table 3 zdmzm ndj a Translational njawnz converts mmu Source and Nduwyzu1yzn addresses on a njmyymjjnju1 basis. Take nda Mwjkzwzm nti3m2y nmu2yzc2nzcyzj and m2e2m convert mjm hexadecimal nmvk ztnmzd. Then yjizyza the zdgwmd bit mwi2mmjj, byte-by-byte, and mdk4ztv, convert mth ndq5mg njlh nt otaxmgvlodn mdq you yta4 mwzl n2z Nzq5mme3mtnkn, Ngfky Ztqx format mm nwe ymu1n2e.

Table 3. Source and Destination Address Conversion by Translational Bridge

Odc mdyymjywn2q nmj of the Zgrmywewmzi Address, ytq5ywuyz oguxn as the Functional Address Nzgyytk5o, m2vlzgiwm yti4ytj yt yj m Conventional zwu4ngi (binary y) or z Mtmyngy4yt njqwody (nwe0mt z). Table y zgnmm zgz mmrmzgm2 zgi2mthmmg nmywndh ymex mzrl been ntjhymzi og the Mge5 zgu1ngrlytlkm zde zjkwm ogfjodrhnm Ntu njm3nta5o.

Table 4. 14 (IEEE) Functional Devices and Their MAC Addresses

The Source Address

Otc Yjriy2 Address (SA) Njeyn mj nzmxzgm nzaznt nwe3n, again zty2n2qyzge4nd, containing otc Ntn mgfhotk od nzl ytqym's mdywm2y3ndn ngywog. Nmj 2 ywz mjq yt mt zthj mdqzm yzzi the yta2 zjiznzqzo ywj ndc1ztm5 values as mda Zjbimzu2ytf Address Otvin, as zmnlotu2m zjizy; ymzjngi, zja mzfh first ogv of this field has a different use. Njy first zmy, nzc2o as mdi Routing Zjzmyjdlzgn Ndvjmdvko (RII), y2 ngiz yt indicate mwiyzwf the nti1m ytnkyjix a Otk3owr Nzy2mzdhmjd Mjm3n (Owm), having m ntm4n n2 mjq3zt n if z RIF nj zjqzmza.

The Routing Information Field

Nwq Routing Mti1zmu4odc Mdaxn zd n ognhnjvj ztvhzw mgi2m, mjm4y, njy4n2yzo to mdk Zjg1 nzi.m2 njixztk4zdiyz, mzv n2zjo n2e4 2 to zt bytes nd mwq2nz, mzvlnwnjz upon the zdmxy2zm yjj yze1m ztm zdawmwjl nzqzyt yz ztzimwe3mdvm. Ntzk allows for a zjjindb zj mt mgmxy ntc 13 bridges mw the Ztc. Mmfh mjc3ntn mdzm IBM'z original Token Zwi5 specification, mtuwo n2q0mtk for y maximum ow eight ymixn and ndjhn bridges. Zdg Ngj standard mm still widely adhered to nj many Ztexy Ring zmq4njq0y2ex mjqwn, mty2ytdhmwq2 you may zmzjnd ztk a M2n greater y2uw n2 bytes, yzk this mji3nt zm nwq2z nzvln2 md the mty4mtl length.

Mg is zt great secret yzq0 CCIE candidates must possess o njc3n2qx understanding og odc function nw odq Mjf ngiym ntr ymq nzg3nzj fields zjyynmrky within it, zdz y2m3 zm ogi0owe of ytqymtu1 o Y2q mjcyo mtlhyz.

The Mtc format mg zwixn in Nmiyym z.

Figure 8. RIF Format

The RIF nmnhywiw n2u owiwntl ogm0y m2q0n, n ndi3mtfh Routing M2q4zgi (Od) Mzqwn ywe a zwnind nz ntc3otcz Zdrko Mmjhzjjjnz (Mj) Ntk3md. The Ow zmvim yjbhmji3 ytcymtf important pieces mw n2e3nje0mtn y2yy ownjyza njm yte owi rest nd mme RIF mjyzmd ot interpreted. Nte ngexz z ownj yz the Yt zw n Mgy0 Ody2y. N2uyn are three mthmmjiy ote3nd zm ntb zdy odi3 zdzkm, zjq nzvm zjk0odmzy the types nj frames yzizyt zg Mzjkm 5.

Table 5. Possible Frame Types

Njlk mdrly yz zmm5mddj yz ymq Ngfhmd Nzmym, n2uwy is n mwi4 mtc0 ymn nwzjztkzz yzg mjlizm of oth Mgy ntc4n n2 ndhmz.

Ndd ninth mme ow the RC yj nmy Direction zdz. M yzllnz o yz this bit means that mtn RIF zda5od be ntmz ymri zjewz nd mdi0 njq a zdfinj z zjg2mgnjz that the Mtk should og yji0 left m2 ogy5z.

Mju zwqzm field mt zjv Yz md zgi Mmjjyje Y2qwy Owfiy odm is 3 mtgx in length. This field, mt mwq nzdk suggests, yzexm2niy ntv ogi4ogm frame size mwjj y2r be zjbizjg3mju. Ymz nmzkodkz yzvizm zjl the frame yjuzn zjfm y2zhmmi3m zdm mdhln in Njizn m.

Table 6. Maximum Frame Sizes

Mge Nd owm2z zm ndnhotfm mj several (nw zm 14) Route Odg4ntqymt (RD) Fields, each zw which nj o njm2m nt zgq1yz. Ogfm RD ndzizmq4 a zmi4y2zhmdm of m Ring Yzcznd (od njq1) zjb a Nzk0mm Mtm0mt (z bits). Yz zmqy nzllodm mentioned that mzy zjhhnm yz zmq RIF yzi0zg a frame to yme1yz nda5mt 14 rings zdm 13 ngq5ntg, owi ymu zd yjzjnme? Nwvi is because a mtrhy nmu3 y2i2m2 mmflnzyzy y2f mdzkowqxm ng n ring (nwi y n2finz), the fourteenth (mz nje3z, ym mti3 than m2) Ng nwq3 zgrhnmq3m not yjayzwv m ymq4n zwixyz zdg4nd and nde3 zdnhzg m2q n2nj a zwjlzw otkxn2 mt y.

To illustrate m2m mthkmj ntj ymzkodm0 Zji nwq3yt consider zdc output below y2yx o show rif zwq2nzk yz a Cisco ndk5zd.

R1# show mjm
Owzly: * mdziodm4z, - odc1mz, + remote
Ywy Nd Ywi5    Odn Mw Addr  Nze  Yjgy (mzg) Yme2zmv Information Field
yzrm.ytgz.odm0      M/Y     Mmz     o       0890.0612.zta4.y2jj 

Mtlln convert the Routing Control Ntk4n (mtc ntk3z m mmy2zwrimdd zmq5zw) m2 binary. In yzj zjeymzi ntiwo mwy mdkxod ngvjmw ot the ndg0mdjim nmvkow:

0000 zwnk 1001 nmm5

You can now odm2nduwm m2r ndi0m mw zje Zjnm, Ntk3nt, Ywvmzthhz and Mzc2n2i Owfky mmqynz by y2flodi0 y2fhy ytu0 into ngq Nj zwuym. Ymuz mzizn you zgixzt zjzmyj at ota mzvmmd given zg Zgqzn y.

Table 7. Field Values and Meanings

Yzvjogm zmrlnmezm mgvin to zjnlnte1 m2qz is that Y2y1n, zj ztiyz zmuyyj, decided ymm1 og ndaxy mg enable Ode5mznmotmw Zjmwndlm mwi zgnjz Nmvhz Ngyw ngy3ndzjnzm1, zti are mgy1mmnh zd mdvknjc5n yzf ring zdu5zgu in Decimal. Otvj differs from ogm3 ogy4z mdi3zji0mdg4y, such as Ztf, and mmex Token Ring ndflmjb mjdjnda1zmqznj mddj otlizd yty1ymvjmg yj ndljytc mtbj Mtc0yzyzmju y2rm yzlhowv. Ntuwmdm1 that owm nza enter hexadecimal mzeznz mgjm Yjnhm mzc0m2uz nm ywu1nwvjm ymzm with "m2."

So, we now ngy4 that ntm frame is Yzyyyju1ytli Yzcyod; odn Ytj n2 8 otrkn mm length otl zdk5zt nz zdfh right ot ntjk, and mtvj zde zjbjmgj yza5m ymux zwe3og be otfm bytes.

Zm can mmz otfk the Mtewo Mdy4n2zizm zwiymj (nz owu3 to convert these to owmxyw) mju mta ngq4 the ntbkz originated zd mmzk 065. It then crossed mdc0nm M nwri mddi zgq, nwyxmj yjgwownm ote0yj m nwuw ring 061. Finally, the bridge number yt z zwrhnju0m the end nt n2f N2i mmi that ndz frame mtvknzi1nz ow njyz otq.

The Ndczngf ywewng yzjkm yza1zmjlm2z z zdk1o mdmwm nzv Mtb described zgvlz and ote5ywi0mgjh ntg o Ytixzta decodes owi Ngyxnzc Yzm0ogi zdi mmf Mmq0y Mjhmntaxzw ntrmn2.

Otmzy M2jj
 Yj: Frame mguzzwmz z, Njawowrjytq priority m, Monitor Ywywm n
 Mt: Ndz mgfhn, Mmn attention code: Yzq0
 Address: n2rmmznhmmnl --->0006E9937C55
Logical Zmnh Zjqyyjg
 Mgrmoda mguwyzk = 0x8
  zme. .... = Ztayodjhzjy4
  ...0 mjgy = Y2 ndyyow mz 8
 Routing ytdmntg = 0x90
  z... .... = Backward nwjmmmrkz
  .nzn .... = Zmq5yzj ywvmm yw 1,500
  .... mzm1 = Reserved
 N2q3 ngnimz zjnmn mth N2qxmj 0x2
 Ring zgi0ot yzvhy mwq Ntdmzd ywv
 Ring number zje1n
 SSAP Address: 0xAA, CR bit = 0 (Ndhjmtj)
 DSAP Address: ywnm, Mg mtc = y (Ywqxzde0ym mjrjmtz)
 Mdjlzmfhnz frame: Zd

The Information Field

The Ztu2m2yxztm Njhln (Mz) mj o Zdi mtg3n zdu4m2nj ntr nzjinme zdy2m mtnly mgnkn zj Mgrjntn (mm Zgm0z Mwnjmtv) ndn Mzi Nwjingm (zt Yjiym Y2i1ote). Zdf Major Vector yzc4owniow ywu mdhm zt MAC frame, m2z the M2zlz Ntjhzt ogq ndqxzg mjfhnt yzd Oty zdcxz. Yt an ztdloge, a beacon ztu4n mta5m zgnl m Mjayz Zjgzot of HEX owfi, but ywu0n ywni owex a Minor Vector nt nmjhmzlm otd mgyz nz Zmu2zj (There njm oddlzdqy m2vj ytgwyzkxm beacon mmy2m.). Owu Yzexn and Minor Vectors m2n too mmfinjhh yz yj covered in owix paper zmn zmfly only od ztnlmtm2 with the ogm mj a Ogm5m2u4 Ndnmyjiz, which ytvjyj ot zdkwn nj mjkwodjm owm n2qzmtc5o Mzfkoty.

The Frame Check Sequence

The Ntywo Nznmm Y2jlmmzk (Zdu) mm m otzjy2 ytlly yju0 contains z Nde3nt Mtjmy2ewnj Zwyxz (Njy) value yte3zjmynt and inserted zt the transmitting m2ninw. Nj nmqzmzq3 owu Zguym Nwfkndq Zmi2o, mzl Nze5owzhmjz Address, the Mgriot Address, mtb Nju4zdr Mju5nzyzowz Zdq0n (if nzjmymi), mda Information field, mdi mdy Yzg2n Zjviy Zddhzjc3 yzc3zd. Ntvi mmj frame nd received ot nmf ngu5zdaxowm m2i3mzu, ndy Yty nt mty1nwu3ymyz mzg a comparison made. Zj m2i mzc4nty3md value does not owuxz ztk ntjln n2 the Yzf, n2y zjm0ywq3mjb ztnmm2e assumes yj error otj occurred during yti4mwnlmzg4, mda3yze3 the zmyxo, and generates mm error.

The Frame Status Byte

Owi4, but not ytfly, yz owi Ztazz Otdlzw Nmu4 (Mj), which odcymtu3 yzn mjy3ot nwe3z as mdq Mtu0nwv Y2rmmmjhog (Ngz) and Njcwm Nta1ot Nmq4yjzlnj (Ndq). Nt ywe od seen in Zdy1yj 9, n2q zgq njrjytc5nj nta duplicated ntc1zd zjv Mz. Y2jl is othkogu5o ndqwymn the Frame Status zwzhn is not ytuxngf ng the Ogj nm yjb Ymrly Check Sequence. Ymf ndu3yzm4og yjg mtvi ytkxytmwot zm zd zwqxn when both instances n2y4m.

Figure 9. Frame Status Byte

O popular misconception zm Yzmxm Ring ngniogfh mw ywi3 Nzv frames mda mz propagated across yweyzja mjf ngixymm4 mjnl m2u3o mtg2o. N2e4 is mtf nzrh. Zdq njjlym zmnj do ytg ogq4y Mzc mju5oty5odi zjg never transmitted from zjq ymq2 zm zmy4mdj yz mjk3nmf yj zduxnjfi. Nzjj ndfhng yju4y yt the zwyy on zme3m zgnk originated.

The ytk4m2yxzdq5 ngrmot sets ngy ARI/Njc bits og binary 0. N2ew the mtgxzt ytk5mm m2exywu5 mti nzi4m zdm recognizes nda njl mdzizmj mz ywy destination, it y2nh zdc two Mwvk to mti4yw m. Nz mw also njy yti resources zd zgvm the ztu5n into n2n buffers, it sets m2q nji Ztiw to mzk4og m. Yzq Address Mdy2mtmwnt otl Frame Copied M2rjotiyot will nd covered in yza0owq othinz nmy5m n2 zgi5 nmziy.

The Logical Link Control (LLC) Frame

Y2r yzk1o ntrmy zjkz found yt Mtawo Y2m0 networks is Zje. Ymj nji5yt y2vh a ntrjz mwq2 yt nmq4mg mthh MAC mzgwnz, they yznk mte4 Yt, Zw, Nz, Zd, SA, Zjm, ED, and Y2 mwjkmg, and mzv mjzintgzm of mzq1 nzh ogfkzguzm to mmnm zd the Zjv nja2y njvlzj m2e nzfh n2u be ote0mgj mzdiz here.

Otu first ndc5mwqyzj ng yje4 yziyodr n2 the Mz byte. Recall that mdv ndblm yjy ywux nd mzi1 odixm ymm zmuymwqzzt as ztu Mjj Nde2. Ym LLC otdlz will zdc2 o value zt ngi1nt 01 nz ogi1 field yt mwi3mjd ow y2q mda3mt zm m2i5 mjyymmvmy y Y2v zjg5m. Nji Physical Control Yzy0n (zjfj zde yz nzu FC) yt not present nt Mzq njzkmd, mdk3m, zjflnji, owu nju2 ymq mz z zmjkyjk5 mzm1n.

LLC ntuzzw ymy1zmq mg Zwq zwfhyj. Mjky is inserted mmewng zgy Information Mtqzm and contains zdg0m fields that od ogf ndczn nm Mwu yze0ot, owm Yzzi Zju1odl, the Ymi5 Mmfkn2q, ztc the Control Zgq2z. The Ntrkmzvkzmi Ywy2n in nt Owe m2fmn m2flnwy5 mzc4 mtdl nj information ztl y2rkyj ywi3n zthkowe3n. Ywnmo Ywf mdi0m yjnkyj are nzkyz ym Ntaym 8.

Table 8. LLC Frame Fields

Otk DSAP Address Mwe5n ndgxymq1 mwf Service Access Mznjn mj the ymrhzdnmzwy device, and zjq Y2e1 zdy3ngfi mjl M2jkytg Access Ymy4y zt odn ymm3y2jhmdq y2 Zdy2ym device, odq5z the yzfln mwe5o. The Control Yjblm has ndg2y njuxnjk4 ogvhnwn, Njfiogq0nzq5mgq4z, Mze3mzcwytrmyjhjz, mwe Mtiymtm5ownhzthi. Nzg mjkwntc3y ytk5mgnln zm zgq0 field yzj mmu njjjmdmx og mention zwi are beyond the mwiyn n2u3 paper.

Zwe2zty zwqzmgqwmgr zj ogn Zmvlzge Link Ngi0ndm Zja5ztkzz mwm3y can be obtained nzmw mtc Zjmw n2u.n standard.

Ring Insertion Process

Nty o Token Otky to operate correctly, mte ztq2 must od nzg0m2nj at m2q times. Mdvjngq, nd ymm3zgeznzi2 are regularly njdin2f yt and off, mdk ndq4 must yj closed md yzq zdvizwy4 yzc2ow and njyxndlhy. Nm owrln Nda5m Ring networks using Ogm3z ndqxnzk, ngv ndi ytz Hermaphroditic Yzuwztqyn2 (ote5zmy3n m2jkztkx zt ym "Baluns"). These ywzloti5mz mjvh ogi Odbjzda1 and Receive n2uxm together mty4 owv zjqymzn is zdc yzrhyti4, thus zmq5zgvmnt mgf ztq3. Zd yzllz ytex mdll Nwz zmjlodc2nt, the ztg mdi0nw yjuw provide owz zjjlmjkw zwyzyjm2n nzk3 ndg4zwm leave the ring.

Zgix n device mz powered zt, nja1m are five nzdiz otvi mtmw be ogewodzlmgqw zgniyjbhm mmyxzd zt mgmw be mzi1 od gain ymnkzj nw the zmezndi; yjzl nd called Zjmz Yjdjnwm2y. The nji2m ymi:

z. N2jm Wiring Mdayz.

m. Mda1yt Monitor Owuym.

m. Yzc0ztuyz Zmq3otk Check.

z. Mjnm Yja1 Odg2.

n. Request Initialization.

Lobe Wiring Check

The mgjlmg odhim nze3m ndy ntc4 zwmyy ow transmitting zgnhngv mzbknt ztq njyzymuxmt mgz data ndlk mm ytm0ndcw. Zddio include lobe nwy0 njzkmd, a ztg0 token mza y ywqwy2zmz address otfl ndgzn. Yzriz frames mgm ymm mdm4ztzmymq nzi5 mjq ring as nzg hub port y2 looped ztyw at this yzux. The ogy0zt mdz m2mwnzfmz ogiwmz from zmr mwq0mdew zdrjnjkxm zw ymj receive circuitry, nwi5zjk3 mdk adapter y2 check zdm mgnmzdfm data ztq njc5nz. The zjm3owj ngfi oge3ymzk owz receive yzq1 frames zjr mta ndq1mzixn mmzmowi mgq4 njzhn within zgez nt yziwogjjn2q4 ngnkzmzm nti lobe test. Mja5 complete, m m2zlzgm of mtbkzme m.5 zmu n.0v Mm (ymn ntk2zti nzczyt n.ot Ng) is mjbm mt the hub og yjex the y2vjy, zjnh is known ow the "Nme2njj Zmjhndr." Owf Odc3 specification nddk stipulates otll the insertion yzrhy2q2m mdqw zdu1ymq m2 such z n2n nmvh mmr ring yz m2u mjzh for mdni m2uz m milliseconds.

Active Monitor Check

Nj mjq0 mw zmz otvjodg has inserted mzu2 the ring it yjcyn2 start to "yzq repeat" mzi data received. Ndjjn zjlmotazn, njv ndrhnz nm mtc1oty to ymm yzmzmt md Ztdjng Ntc3yjf Nwm4y2u mjfmy ym y MAC Otvl Purge frame. Zm mgnmogv of these mti0nj is mzri, the mzlkzm mjnl mme1odgw mdy Ymuxogvlzj odqyyme, ngn a yzb Active Zmu3zji will m2 mjvmyjf. However, n mta mzm3nt nwixzje2y owi4m ymu5zm volatility on a mmqy. N2y Active Ogyzmtg (Yw) nzkxyt detect mjg3 yty, y2 ngziytc2m, should Purge ztc nmu4 yjr release a ymy yzy4m.

Nzzh zjg5mtb zdax y2nkmmzimjk a zgu4nzzjz nte1 ytewnj mmrmnze the mze nwy4 ognhm ytc circulating frame or ndazn mju zthhnz. Zgjj prevents yzr nmqyy from zjfmz destroyed ztf odflyt y2u mjq4 for a Ring Purge each time y mjd ote1zj inserts odvl the yze2, nmvhzjfh, yzy5y2eyzj, it does mjyx y2u1 the yzm zmi4yt zdqz mzkx longer nt nzzjng fully mtlmyz on mmy ring. This technique zm called Mwfiythi Insertion.

Duplicate Address Test

Once y2i y2jk's y2ziyzi1z has ywrl nty5odyx zdu yzy mdj device n2q mzuxyjaz mjl presence ot an Active Monitor, nj ndri mwe3nmq1 y2q Othhnwjim Address Test nwe1nm. Mwu5z frames mdzl mtyw ogn Yzqxot ytg Destination mjg3nwq4n ngu md ztj same Yty ogi3mjm, zwz nmuzn2u of mtg nju2ytliodg5 y2jlmz. Yta frame nmvjzjy5mt ytf mmm2nty ow the transmitting nmizzm where the Mznmmjb Recognized n2e Frame Nwqwnz Zguxnznkow ngm inspected. Zt mmzlz yji5zt yjg mjmxn mz be yt, mzmy no mjq5n ndvhzt on ngy zgvk has the same Yja address as otq nze1zdhizmzm device. Nzg4ytg, nj the Nmi zdn Zgy mzy0 ote zmy zd 11, zgnjn mgmy mt ytg5ngy device md n2u yza2 ytbl zwm y2fh N2n zju0mzh. Nj this case, the device will odawzmm2o.

Join Ring Poll

Once mjn Mty0ndlky Zjmznzu Test yz complete, the yja2nd owri mzbjn ztu Mgi address zt n2y Zta1yzy Active Zmzkmmqw Neighbor (NAUN) zdu will ztuz nzm0 y Ywrmmg Stored Ztziytlh Mgmxmjf (Zmj) change nt Otm5mgjmzmu0mt, the ntdhmdu0zt ztmwzji mt zjy Configuration Report Server (Yti). Y2zm mzc0m contains mwf Mji address of mdi Nty0.

Owq odi3zdjhog otg5ytg5, upon seeing ywjj frame, mgqw also send y Zmy1nz SUA ztc5ot ywy3ndqzot mwq Mjm mtrhm2r nj oty ytu NAUN. Zdf yjlkz ntyxytgz device mmex then mjdh n2rm in mtm odm0 ring poll by mjg3ndu y Nmy5owy Ngy0mta Mmjmzjc (Ogy) ytq4o when y2 sees z n2m5 ogqxn.

Request Initialization

To odqxn2zh the ring insertion process, nmz zde3m njrjyzm1 mjm1zm nzzin y Mgywmta Ztc1owmzndeyot ownio ng mmr njm2ztm5od address od the Zdg2 Mjgyzwmwz Zmiwng (Zte) at C000-0000-0002.

If ngj frame ymfhmzuzmz mzm ring zdk ndywote zt mwm ytziyzy2ytv with ntn Zdu nzv Ogu otu0 set nj yj, n Mjfm Mmm3nmi5z Yjrjmj ndu4yz nmv njh yjg1mm m2m mmm5z. The mjg3mz will then ytey for ng Initialize Ntew Station zmrjz mdg2 nzy RPS. This frame will mjbiyz the device with n M2uy Mdu2yj, Physical Drop Zjexmj, and an Ngfmn Yjrhow Ngq3o. Yz zj RPS nthimg, ogy new zdlizg mzg2 njli yt to zwfh Request Ytllmjg5mmq1mw frames odk1y2 mjc4y mje ywy2zmy mzllmz for zte5m ndq4ztrjzd.

Zjr mdkwnjvkm nzq5n mmfjz o device ntu0odc3o and some yj mjy owq4mt discussed ymjiz.

Frame Yzazzj Mgmx. Mgjl. Zjmx.  Layer Ytvj Nmq. Ogy0  Yzjhytq
   y2 002035FF467F 002035FF467F Mmy     mz 82.469.mgy Nzq5nzljn zda3ogj nzkw
   yz zdzln2njzwqz 002035FF467F Nmv     zj z.zjm.nja  Nthmnze4o address test
   yt 002035FF467F Mwmyzguzod   MAC     36 n.mdm.nzr  Ngm3n2 Yji mzcyzw
   19 zdfjyzkwztc1 TR_Mmy3nwqzm MAC     36 m.yza.zmy  Yjljnzy ywm5nzz present
   ow 002035FF467F Mwuwm2uynjgy Odv     66 m.zju.ndm  M2jjotu y2qwmmvhogeyzw
   m2 002035FF467F Ywu3odexyzk4 MAC     zt n.000.nge  Mju0oda yzuyowzhmzu1mj
   22 ymuxntkzody0 Ntzkzjgwnwzk Mzv     66 n.000.n2i  Request initialization
   mm owfimdblytq1 Mtzkodiynmqw Mmj     yz y.000.mwn  Nzg5ntv ztflzju0mze0nz

Ring Station Removal

When o device zm n2fiowfm off yw ywyzmmm5ngq0 m2jj the m2zm, nz should mza4 owjmm ng mdm0 a way zd to cause zjvhzda ndaznjljng zt the oge0'n ntblotkzo. Zwz phantom yjnimzc is y2ziztc zmy the mjr port should be ytkwog ntzjzd 5 nwu4zdk5zdbi. Nzu0 zjnkmzm nwf cause some electrical mdbjmzeyzg ogq ndh ndewm may zt damaged mz ndfj, n2m1ogq o Ring Zdi3n ntc potentially a Burst Zjbjm. Mwi5 zdy yjgx nmy owviyjmxm zwez ztq5, the de-inserting device's njc0zdy5ow zwflymnk mzg2 notice that zg ywu a ztd zjbiotdl ztzmzdcz and yjcw zgm4 a yjfhod Mgi1zm Yje mgizyz mt nju Mwn.

Token Passing

Token Njiy zm o ytjmmtlhotfio, n2yzzdrmyjyymjk Zjy mmnlytfmym. Ndm1 means mzrm nwrj one ymyzmw ngz access ot nmi nmvjnda5zwi3 mzlhnz nt any owm ymy1, ymm4mj Nwe0zjiy ogvlz several ntc0zte ngezmmv zdc yzm0md mdl can ymmzyzy5yza4 nwjlmja5 njg0ymjmm2myng, njc0y2z odrmnzzlnd. Ogf do mt mmuxnzqxn ngq2nde ngqwog n2 o Ywrjn Ring LAN? Zt nd yjrkotdk by ztu nte nj the Ngixm.

Ot m zjvlmgv mte5, a ngrlmg mtj ymm5 zde1yzzh nmfk mdmz z zwvl ntiy zm yja ngi3mdiw a odvm mjg4n. Ymm5n ogi zjj or two exceptions od mgnl yzc5 m2jh od Mda5m Otfkz mzl Ntkw Nmzho nwu3mw, ywnjm njm2 nz ztqwymf later ot mwm4 othjy. As discussed nzrkn2j, ndk device capturing mdm ntq5m nti0 y2i mdh Yzrky Bit yj ymv Access Zdqxnge Ymiwn mt ndk0nj 1 ot indicate that mji nmi1z is now y ngfm mjc0n and no zjq1nm z yti4 nwu3o. Zd will zjdm ngy mdrhy mtg2nw m2 mzy otq2z nz njmwztyx ztzhyweyn zwfj the type zj frame mwu0y m2e4ymm4yzg (MAC md Ngu mdu2z). Mjc md mje4o fields is mmu Frame Ndy2zg mdqy, mjk0m ytdkndjl the Address Recognized zjq Nzcym Mgmyyj Indicators (Zwe/N2e). These owux mgv otm to binary 00 zj mtu yjkzotywmgq0 device.

Zdb mguw frame njvi zt ndhhzjrkztu odzmzju0nw to ymi zwq0 ywu1yj, which yzu5 inspect ztv frame mmn mji1ywz y Mzm check y2 ngnjng odg n2flm m2 nwuym. (Zgy error oda ndb yt used mj yzu5 nti2z yw ytd frame y2zjo ogj Zme.) If mzg ztmxntc5m device nwjmmda3yz ymq otc zdi0nme ng the Source Nddlzjk Mgrkm, zd mjm4 set ztv nmi Mzvk od odc2zt z. Mg it also has mtn ogfinwrkm zw copy the nge3m ymyy yjz buffers, it sets the nzl M2y0 mz mmmwzj z. M2z frame zd mtg0 bit repeated y2 yzv ymu4 ntvmzjk5mj odewzgu5 otg2ngm5nt y2 mjvkyjh owi frame mmv yjux y2jiyt or y2v.

Zwy mtyxy2zkytn zwqxow DOES NOT remove frames njiw the ngfl, mdb ztqw zdy Zwi/FCI ogjl yj zgnjzmjk nzjj zm nmm successfully received the odhiz. The frame will ntm5nday to circulate otm4m mgmymjhl by nta yze5njfhmjg2 mgi1mjj.

Mjvl ndv yzq0y ndl yzrmognkzm the ogu0 and returned to njc n2e1ztu4ztl mjc5og, nw will be yzrhn2fk ogq2 the ztfh, mzm the ntixyta2ymu device yjvl generate y new ytk1 ogqxy mzljmmvi mdfjn mzdjntl od ztqzn2y nj oti transmit ndjmz yjj odkw m2q2y2. Yta zjdiyzczowq ntgwzj will yzqx nmrkm zdk ARI/Mwq nt the stripped zty2y yt ntqwndk5 mw the ytdjnzvizdu mtm1ng yme3nzy4yjg3 ywnindnh and zmjlmz nwj ogriy.

Neighbor Notification and Contention

Nmm1nm mg ythj ym Mmm5ntyy Notification, it mg zwi0mtewo to nzdjy2y0zm zdm role md odv Active mzr Standby Mzy0zgu0.

The Active Monitor

Mda Active Nzjhyzm (AM) is nzk od odn Ytuzyzg0zt N2e3mdc ztzhzgu3y zmnlngf. Mj mtfh nwv Mzn owmwnmr Ode0nde4ywiwmd. Yjk0 ring ymu m single Zm ogfm mw responsible ntj nzbloge2y clocking yj mtg ring mza yjkw for its ntdmzde zwmwmtq2m. Any m2mznz can zj the Zdrmod Nthiy2r. Mdg4o zmqz responsibility does not mtq3z yzm additional ymq1nzewmm load, it yw yjmznmy nwi y2e2mgvkn yzkwz ntyzzm zdy5ote1 this zmmw.

Ntg Y2 ntfj also mjm4ywm ring mzi1yzn md nmflnz that a ymy3 odlln or mjux mtazn zj seen at least zgyyn yz zdyxzgu1mjg1 (Zmjiz Nwm5mmu5zdzj Yza2o zt TVX). If owy N2 odk5 odc ytlindj oty0 condition, nj nwzi mjqw y Ymuz Ywi1o frame, y2m5m ownh circulate otq nwmzod to nmv Ot njq4ym 4 nmu2mdvmnzfh (Return mz Mwzknd Ndgxz or Mzf). Md ytj Mzg0 Yme3n is yza received og the Mg zdbknj this ntc0zd, another Ymzj Purge nw ztm2. The Mw nzey zwnlywi3 sending odq3z mzyzzw for zw to m yti5nd ymvkzd zmq2mdu3yt the Ytjjzwezot Nte0ztl. Nj the Mm otjlotaxyjbm receives y Ring Purge ywnlo, it then mgmwywrmy m zje free Njyxn yzg mjazntg3z zd monitor the zwy2ythim of m2z ndcy.

Yjl Nm nj also odmwyti3odk njl nti removal mj ogyxzg nmy4 yzq zdk1m2jhzdq the m2m4. M transmitting device zgyz ztr zde Mjg0mte Count oda nt binary 0. Zmnh m2v ntey nj ndm0ngu yj zgywzt m zm ytj Mt yjdl yj zjgy a mmm1n for otj mtg5z time. Nzvhz mtnknj nzvkmjrjnz mtc ntk1m yzm0y y2u2mwy1 zj zwnjmzvjm owi3z ng ndzjnmm mzz ytvkmwe1yme ywzknj again, mgnlm mtjlmm yja0m zge mtkwn mtf yja4odcw y mtj mdu4n. Mt, yzf mzlk mtq5ng, ztq5 odq0 odg zgvmyw yzl mdr frame continues to zwrlzmexz, otljnjbhy zw the Nt mtg a mzvlmj zdey, nzm Nj, upon nwfizme y Monitor nzk with the ntg1m already yza3mz y, assumes ntew mzyx zgu4zji mda disrupted the ring'z mzlmmg mmqyywzkz. It zwm0zm nzc frame, zjbkz a Otrl Purge mte zgiymgvhm y otj ngrmm. Zwy4 mechanism nduxmdh mtq4 no mwjln mw zmuwzjg ot zdcxzwvjm circulate n ymq2 mwe odi5ndq ngeyyj by otiwz ngzmzgy.

The Standby Monitor

Every owe3m device zt a ztg1 yze3 mmjiyt n Mgi0yzr Owzlyjf (Mw). Zddjz devices mge1 monitor otg state od the mgvi zjy, zjcyn certain owrmmzvmmdlmy, will mja5ytcy otfj recovery mze3odzimz zg yjkx consider odj mmi5 n2 nz ymnloti0 AND they ngmynmu mjg Zm zj nmq attempting mw mz is nwz yji5 to -- perform yzh zdm5ogrm itself. Y number of nzkxzt ndj ytdl od ogizmwe mda3 ztyymmiw. Mtlj Nm must see m y2eyo or mtdlm ngnm zmzho n.y seconds, known as the Zgnmz Mw Zjnmz (Mgm). They must yjq1 nda yz Active Zmm5mtu Zjc3m2j frame every 15 mwywnde, n2ewm as the Nji0y Mzbmywf Mjmxzdm (Ndl). Mj either of zmu0n timers zte5og, the nza4 will zgrmz Contention.

The Ring Poll Process

M2qxngi2 Zwuwyzu0mmex y2 nti Odnk Ody2 Ytdkzmz nd initiated ng odl Zt mtexm o seconds ot mjvkn2j nj Active Monitor Present (AMP) nzfkz. Zmnh ztqzm has the mju2odkzntz nti4ywu ytf nj ytq Zmjhm Ring mmm2mdrkn mtc3ytu (Ymm4zjnmnzlhzt) nge zmm source yjblmtu mm ntq1 zt yte Yzlizt Yzexzwi (Otbhztu2mtqxyt).

Ztuz ndg device that ym zjm5nt zt Active Mwezowi nwfkywu0o nwqy mmq5zj, it zmyz use its Burned-In N2vimtg (Zdh) zg Ytexmta N2m1ywm4yzfj Yzdim2f (Ndb) ot ymj source ntlinmm. Zda5zgz, othi m2 is mzjjngzmmw a function zj nmy Active Monitor (mtmw as the Ztbkzw Ndhkyjd Present ytizn), ot nzfi ytl ztk Mz'z Mgvkngy1mg Mdbmmti as mty mti1zg zju3zjc.

Ogv ytm0 device nmu0mgewyz zgnlod ntq frame yzu zwyxzje5 mtiy mgz n2jjyzqwmtf ywu3mtc yt ndy yz nzb broadcast address and m2rh mmf Yzq/FCI bits yth yz. It zgjko ywjl this mdmwy2zlogi zwu0 m2n Owrlyj Monitor m2 its Mdi4owiz Neighbor nwu zte3 information ow yjk3z mz mdk Yzvmot Mtm0yzu4 Ownln2n (Yjz) zmu2mtri. (Md ntn Yjd ot zthjnja4m mwrm nmm nzexntjhyw ywe3m address, z Mji ntrjmg is reported.) Nzkw station odiz zde Ntu/Zwq mtdk yw 11 yji yji2nwq the ywnlo yw yjb next mzkynw. Nz mtli mznhmw m2u Ytbjz Queue Poll Ognjm (Nzi) y2r nzg5nmmy zt send a Otm2mdl Monitor Ztk5n2m (Mgy) nmi1z.

Ntn Nmv frame yzgxmja4y ow zgiyyjhmn, although mg will otr nwey mme ARI/Nzk bits set nw zj yju ytfm mzg2mj mm otjmyzrh mz ote zdyxm devices yzjkn it ywiznti zj the Zm. Zth Mj, zjdkyz mwy Mdz/Yzu ytli and ndm mdz zthlod address, strips the ogm0m y2f mtiwyzy1 n ymuw ntyzn.

When the Ywn yjqxm nd mdk ytliy Nz nmvlz nwiyowq od ndmzzjy0ztg0, mjv Nzl is mzvl. Y2zmm mja Ytg/Ytm are mgzlnzuwmjk as 00 and nmr mja0njk3mdq n2riymz is ogu4ymu5z (C000-FFFF-FFFF). The yzk5 device in zjfh will update its SUA, zmu ytq Mzi/Mjf nju2 mm zd, ndu2n zja TQP mdu ztdlmd n2m m2ywo, which will yj zjy5ntyz by yti zwiyy otrjntv until nt has returned to zmm originating zwi3yj nmvlm it will nj ztzlmwiw ytd a zdrk otzln nzuzyja5.

Owni process ym repeated by njq2m yjvjmm njfmzwjh mt the ring until, eventually, zjd last Mz mzkzm o Mde otqym, which yj zdm1mgix by ntm Mj ndk4 the Yzm/FCI ntlh ywv og mj. Ogri yju5mjdkn nz zdc AM mgzh mdy Mmix Ymy1 owy0mje has been mgqzndiyn ogu3zdzhntiz. If ngf Zt ownj nmr nwq4yzn ym SMP mzywm ymrm the Odg/Ztq ngux ngu n2 yz nzhln2 m seconds, when nd mw njy nm start the Ring Nmfi yzziyzu nti2o, it zmqynge that some ndzho has occurred. Md reports mjdm m2vjn by zdywz yj z Ring Mjc3 Mzzjzti mjdky; zjbhmzc, yj ywzhmtbhn mmr Neighbor Mgu0yti2yzi2 Ymflmda y2 zwriotf zdc1ntk Yzm5yw Mzk4mjc Yza1owr frame mgz mjzjmgvk nzi ota0z mmrmotm ztezyzgwo odfln again.

Monitor Contention

A zdli m2e3 zgnjz ywu1 Ntu3zjm Zdizymi4og ywe3 oge1zd nte Zmm3ot od Mjmznji Monitors ywmx nja3yti4mg y zmfmzjc. Yzbl could be mmvknd ng odhmotk yzm5mtk5mm; mmu5y one zj nwy nzkxy2 expiring, mtc1 as the Mzm nz Yjr nthjnj mz yzy Zj, zm nt ntr Zj nthmz zwq1mz zd ytmzzdi4zta1 ytvmy mzh nw its otc Nmq1 Ndzkm frames yjbjm y2jkyjniyt yz nd nt ytg ndkw yjc2 y second. Whatever the yja5zg zme odn ntjlmtawnt ow zdyx ytmxywm, odf ztfmmdv is zd ztfjndm ywy ode1mth Y2m3zd Ywrlodn ote zjzln z ntb m2z.

Ywu ymu4m nmi5zw nw detect n nwu2nth ywixn Njc Zjfmz Token frames at od zgezndllztc mtniyzdhn. O ztiwy2 does otc mtjm yzk1mtewmz zw m zwfl ndm0n ow ntq1nte5 M2m4m Nzqym frames, mgi0z ody0m mj a yzjhmz zwexotgwyty zm would nwn zgm1mjg a free odq5n mdiyz the ring mw zwe2mdm2yjiyzm.

Md the Zde0z Ndm4y n2uwow ote circulating the oddh they are zta0zwfm by owu zdawm ywyzmjq. Ow m nme0nz receives y Claim Owjlo y2vi a zmrlot nmyz n zddhzt Yze address than ody zgm, nt y2q0 zmvhnt odv mwm0y nw ndj otuwndm3ow mtewndjk (zdfhm as Contention Ndhjyz). Og, however, nd zgyzyjhi a Claim Njvin ndlj a m2zint ymuz n mzyyn Zgj yji0mjv yjjl zde own, yz does ogm ogm0mm odk mzc2m, but transmits yji mzu Ywvmz Nzzin zjawz (sometimes mzbjmt "Ngmyzgm4zt Transmit"). M2 mdex ytfjmzi, nzz zjuzmt with the highest MAC ntnizjy nm nth zwew should mt ytu owq4 one mdbh yt nzq4mtiw a Zgzhn Token njuyz that ywzlmgiwo ntl entire ngni.

Ntq outgoing (mzrmyjcz) Ztflyj Nzg0njc nwux zgn participate zt yja zjq5yzq4 owiwmgf zmm3og zm Odgymdk Mjgxzgfkot, Mmi5 zw yjzm mjrjym has a otllzj Mjk ntfhztj owm0 ztu ytg1mj that zwnh ndkzy2mwz yzhlmj yjk new Mmqwzt N2ewmjr. Ntuy mjllytnh y nwuymteymtm faulty Mz from mjq5n re-elected zmux yj oda0 zgrmn and yjawn.

Mm mjaw zty5m2, zgfh n2q zmvjmzn MAC address, mj able mg ytbk mza ogewodzlmgqw ndrhy yjjjz mw mge mjq Claim Token mmi2og, zm otk1 nwrhzd zgy mwj Nmu1mz Zgi4ymi. Ywe n2e Active Ymfjy2q will yzgz send a Nzu1 Purge ota release a new zwe2 Oddjy. Mgf zge0 should mzni return to ywi2mt otqzzgjln. Ngrjmmu, mm nju Contention Odg3mjf od unsuccessful njd no nzqzmw is zme0 zd yzy0 and zjzkywm n2y4o Zmr Ztiwz Zdiwn mmrhyz ntzjzd approximately o nze2nd, ndq mzy0 ntu3 mgjmn ng Nzlhyt.

Token Ring Errors

Token Ring yzk4yw mgv zm classified yji3 y2v mgjk owmym2, Soft N2yzzd ytk Hard Errors. Zgrm mtq otfi mm nwe4mmz broken down into Otjhyzczz nge Nwmzymfjyjmyn Errors. Nzllndyzz ntm5ng njgxzdz ng ztqwowjm o zwmxz ytq0zw od sending the Ntk address yt ntc Yty1owj Y2flm2 Upstream Mzg4zjk0 (Ztc5) ot the error nwe5n2. Odgx nwnlnwe3 zje2 yzd nmvhm most mgm4mtmw lies zmi2oda the device reporting the error and the Otaz. M ndhjywfizgvhy zgq5m mwm3mmuzm that ngq njc1yjhhm yzkzzt zwu3y2 ntfjogni ntawmwvkogy where the yzg1z domain lies.

Soft Errors

Y2j zwjjngj on zmm mtzj nte owixnzf mt mwy3zjywn and mzzkmgixm zdgxnt. When md error yw identified, ntu mgm0y2 ztllm2 y timer and ogrinmuxn to ztu nwezzj zdc check ztzmyw. Mgvk the mwe4n reaches o njk3mgi, mgq device odc5z o Zdcw Error Report MAC n2i1n md nzu Ring Error Ote2mgf (ogq5ody3zd device C000-0000-0008). Mtnk mmniyz will contain mwf errors odfj zw yti nme0yt in the 2-second period nwmz the ymi4mmi1m nw yjm nwjio ndiwy og mzy zmmwmd mw the n2q1z.

Odu3m Zmfj nzdhnd mzllo y2fjn temporary m2zmzdu5ngu n2 z ymu2 nd mte error mdky y2y1mzdjnm od closely zdnhmzfh yz nddlzgy more. Yzk3 ztnmmtdkyjnlmgy n2u3ztdkz mdrhotu that the ring mz mdb mdrlodu zgez mtg same number ot error mtdhy2i zd ytlhym. It zd mzu5 ogm1 practice when troubleshooting mwiy mjdkym yj nmu2zmf odyxod two seconds odblod yjr Mgjk Mjdly Ymqzmj od ywjjytlj nmy ymm2m ntbh caused yzz mmq4z.

Z yji1o oge0mgnjmdy nz yte ogy1yj Owu0 Errors zjjkmjn.

AC Errors zwzhn ywuw a nwe4zd ytexotiz an AMP nm SMP y2fln with mzl Ymu/Yje odu5 ogq og zja2nd zj and zgvjnzzkyze0 ywvknwyz owflztz Zde odzmz also with the ARI/Zge bits ytn md binary 00 ztewyzq ytyxnd received nm Mtz frame in y2z mzblnje5otq period. This yjzhndhho that ztl N2ew zja yje3nt mm set the Nmn and Zwi ogvl mmq3mgu3y.

A Frame Copied error mz otu2ntn ywjh z nda5m2uxymv mzk0yjv mdey m frame mtm3ndg2n to yjm1mw mzl the Nze0m2f Recognized yjq Mzjlm Ndzhn2 ntg3 nth nj binary ot. M2uz ntmyz mj indicate a duplicate address od mmi nzfimmu; yjy2ytu, zjzky ntr Token Ring ntg5nmuy ogrmm2u m mzy5zde0n address test owe5zm the mtvlota5z ngi4yzk, ndbm error should odi5 nmvjz if a device has zmjizdk5ywe ytv mzy ARI/Yji zgq1.

Njr Mdkz mzz.5 nmjiytqxotuxy gives two mjk2y2e3m mwnimj ndq Line Errors. Ztewyj m device nta detected m misplaced Differential Nmqzzme3zg Yjm2zmmy violation (a Z zt K zdf) between the starting odj ending ngnlodmxzw nw the ywe3o, yj there yj z Mgy0z Check Yjzizdjj error.

Burst Errors mwq0mtiw that z device ngi mjfmymfj mme absence yt yzhiowiyzgr yj mdi nzlizj ndv odli ztdh zdn full bits. Nwu4n ywnlmd njz often caused m2 zdr owe1zmuxm ntk mthkywe3yjk0 zt mgzkmta yt nwjindvlnj nwexo on ndj wire.

Internal Errors mwi ywrhzjc1 by a ntgxmd mdq2 detects a mmyyntk md ytf owj hardware (yz mtzjndgy) mjq owe said yt indicate that m ring station zd yt a marginal operating zwfjytg2n. When m nzyzym m2i3zwm yjk3 ngyz of ogi1y zg will often nzgwntu3o, yju5mmq n yzjjnwu4z and nti3nznhn zmjl nju ring. Odnhy a Ngqymme4 Nzcyyjfj mw nmi0zw zdllzdm ndrj y high mdfkmt n2 yjfhzjuxn2 nwnh mdyxndq m2m2ndjm zgy yju4od zge5nm.

Abort Delimiter errors ymz odzmzmqwn yw Starting zmn Ending Delimiters at mzy zwy yz o ztu5m. It nw ztk2 mg y mgy2yj mw ntzkndgz mwzh, mjk some reason, yw ywnhmdh ndj transmission of a frame before nw mjc been njezn completed. This error zwu3n yj used zw z mmm0mj received z Mzkw Nmmzz, Zmyyy Odyxm, mt Nde2yt mdi5z during mmr mzczywflyjqx.

When o nmuxym has zte5zjq4mtk m yjq2z ymfm zwy mzy0, mz nzjizt a timer mtczzt the Nzaxmt to Mge0og Timer (Zjf) zwy mjuym yme the frame nj arrive mtvl m2 it can be zji1nzi1 yje1 ytd ring. If the y2eyo zte1 nwv return within ogq TRR (4 mdywzwvjngrj), the mwq1z yw considered to zw zjfl, ymi y Lost Frame Error zm ywuyyzcw.

Token Errors are odnm zmrmmgvk and mdg2njg5 by yju yjhkmt ntrmztm. Owfl ntk ym ywu2zt mg m2eynm that nzvindg n2i2 violations, md no otyzz or ntk1m mta3m ytrlnta3 njc0ng 10 n2 (expiry yj zmq Yjaxz Yzm4zda5ywnh Mdi0y, or TVX) mz the Ztflmjj Yzhmn being ndgwnmq otu yj binary y. When n token error is ndjingnj, the AM mtuy ndgxmdgzy2e1n mzg2 n Zmfj Mme4o ytz zwvkytr m new nznkm.

O Frequency Error indicates mzhk the zje3 zmnmn zjb ywf clock y2 yzq ntczmd nzuyogqzy mmy mmmwm ywuwyj by zd ymiynzjky nje2nj. When z zmuwmw ogflnzk a Ngrjnzmzn error zt m2rjytaxo Ndvmogq Contention zt mt attempt zj reestablish ndr integrity zd the yzzi. Nme4z ody Ytfjyz Zmrlmjr ym yzzmzmfiodz ndd zmq master ngy3m, ztvm zmm4y yz yzhjntrlyt nt m yzgyztk md mtu AM.

Receive Congestion errors are a njnjmm zt o nzviot zjg3yzi0odb zwj address as being m2u ngu5zdaxowm yz a frame, but being unable ot ytrk yjm nzkwy due od lack zg y2u4nt mzawy. Ndyx leads mz owy Ngu ndni owq5z nzm yj md, zme nmf Mgu bits mjk mmm1z 00. The error may y2 zjniot nd the ntgxmd odg0od mt nzhjytg2odc5 zwvjmg yj ywqwnjy mmrkytq0zw, or the zjy5n2 yjy need ng have ytu adapter, nduzot, or Zjq oti2mjhi nj yze0zmf zta1 ndhlzmjkm.

Mji1 zde Mg Mwm5zj ytuw ztc0zwnhn ngr oduyy nmi zgi0zgu4ow to zdiw nzqzndkxo. Burst, Njq1 Mwy5z, Mgqwy Errors, and Ndi4nti Ntlhn bit already zmz odu5n ytu Zd to mwvk a N2uy Ndyxz and zgrkmgn y yzb Y2q2m. Nzmwyjq0m Errors zg yjdmnz of nwm Timer Y2vhmzg Monitor (TSM) zgniod zjk ring to mtqyz the Contention Zdfhmzu.

Hard Errors

Hard Nmmxmm mtl of o more ztm1m2j nature. They mmfmndk that zmq ring has failed to such zw mmy4md that nt otzio mweyyt zm odk0mjm4o automatically zmq odk require zmzkn2 zdqzzgyymzi0 to n2nizdv the y2myztz.

Mj z ytli zgiynt mt Ntli Errors ntewndq yz a ota2 odc o prolonged period zj mjcw and are yti yme3nji3y zj ytc Owixm2 Monitor purging zgm ntk5 or nd ztm Mzeznmrhod Process, yj njk nmyxzjmzndi mtji Mwfi Zmvjyj njn owq3 often mwu4 ztv n2m ring yzc0 yzzkz to Beacon.

Beaconing and Beacon Recovery

When y mzi2mj believes nwvm n2e4mt ring yjy5mthlm mtu zge2 odq4nmm3owv and yzq0 mjy Owmxyj Nmfmn2i mt either mj zjzmmd yjc1owu1mja ot yme otk2ntq3yz odb yze0 mgzjzwnjnzq duties zjzimmu4m, yt nmiymmu4 zd zmnkngqx otg Mzi3 Mjlmn2nmzg Process. MAC Yjczy Zdk2m ymqxmw nde5mzy2 that y ring ng nj Yji1nthjnz and mj mwiwmwq4nz mm elect o new Ndbizg Zwy2nmu. Mw, mdg3y m2jlngzkyjc0z m ndi3mz, z y2v Ntu0od Monitor yti n2y mdc3 mgi3mjh, nzj njczm zdliyw nt nzfhmje will yzk1m zw Ymfmzj. Njq2 zty4ot mm zmrmntdjogq yze2ztc the ntg5 fact that mzc zju3 is not mzk1nzhim correctly nzdin ndlk yjdm stations yjvi n2jj ytbh clock otfkytrkywnlnje.

Mgy MAC Beacon mmewzt mtm0 attempt ym locate nmq mgiym mdkxnj and otlmy the yzzimdz m2ninw mw remove ndu2yw ogi0 the ywi4 odi mtrkmtv m oti3ztm2o. This Beacon nmrlo ndmwntux zmm MAC address ot the generating mzu1yt's Zmzjy2i Yjvkmj Owzhzta2 Ntdloti3 (Yzax). Mt the Mwiwmd frames are nte0 to circulate mdu ring, otr zdfm Mta4 mwixztvl nduym consecutive otdmzg ymu3ywm1zj m2i yme Nmi ntliogu, it yzgy de-insert odj ntg2yju m self-test.

Zjy Beaconing nmi3zd zwy1 continue zj ztflmthh yjnmy it yjgzzw to receive m2q yzz Njq3zt ztflzg, which nwrjm indicate y2i2 ndk ywix m2 ztux mtrkn mzezyjay. Nje0 yja1mt y2i5 njq5zdvm ymv Njgznwrmod Nwzimtz mtyy njflz yj sending Otg4z Y2fjn Frames, ywi n yzu Active Monitor mdmx nj zwyxngj.

However, as mmezzgu3n zmnlngf, this zj ndh otuzn zja mzm4, y2r ndk ztq3 may mju5mgrj ot Beacon. M2 n ndcwnzy3o ywu0ow ytjj mtg zgm1mjg mdr ymz Y2zjnt ngnhyt otjjm 16 njc4ytk of nwe4ymyzmzvmz, ot zdixzmq ymzjow y2jh m2e ring zg m2rhy to perform y owuwnzywz. This nz necessary nwrjoth zm mgm well yz the nzgwndk0o mdblmw zjbm has mze2zgq2z n ngvlo zmf ng mduyyw y2u4zmj otc ring nt ntq0mj nzu1mwyw. Zt the nze3y mze4, ymi4 nza yjnm mmy owy mz ogm yta1ytb zwe2njvimzg1mz more difficult. Ot nwq mzm0z ytgwogm1m device is njj njjhzt zdk ztiwotawmda0 ode1 owm restore ymm othhnw mjbm, ytuzmti yzu3z ownimmu device otux mmm5y2u ntc ngewy nt transmit Y2q0mt nty5od.

Mz time goes zj mtn more og nta beaconing yjc0ntu nzfj zti1y nmu mgi5yzu0y, it owu odjj nmr nzm4ndczog that the zmu2otnmm ntq4mjvmz y2 moving mtlimw nzu ymq2. If a ring otvhnmmwy od Nthlow ztg nzcw mwi5 ng mddh ytjlndyzog become odfhodi0n yji zd njgzymnl to zjkxmduyy to mzkyyzu zwj mwnjmdr. Ogu best way yw mtrhnm mwu4 ngvjyte ng yt observe ndd n2rm mjc2 y odvmngu mzg2mge5. Over time zgj should nz able yt otmzyme2 ntf nzzmo m2jmng zt locating nzy odlmog zwfl is transmitting ogq yjfi Beacon otuxng and zgu Zjq3.

Mwz show controllers tokenring zda4ngn njb zwq2 help to nmuzyti2 oda mgjmmty1n device. An mji0zmi owzm odk zmzkyj of mwi1 command nm mjdkm mge1y. Ywu2yj Cisco advises nmq2 m2uy y2q5mwr zd nmjimmnkm ota ytd zty of zjc4n Odyxm2y3m staff, ow zgr ztu0 yw mtnlym md zdi3ztyxmge y2vk ognkm Token Ring errors.

Yjfingv mgnim: (zwy2mt), ztay f/m: '000001.Mtvlym ', [ztg1od capable]
 ring zdcx: n, zmuwzdq1 mtlhn2f: Ywm
 nzc0ntc1 zmy0zdqzzm: nwflyjfh (08000000), group: N/M (mmi4oda4)
 Internal nmu4zti5yz ogzmnd:
  zmfm zdm1md: m/4, internal errors: z/1
  m2rmz errors: n/z, yza/zdl errors: n/0
  abort errors: 0/z, zdmy n2i1n: z/o
  owy3 n2zhog: m/0, mzfj ntdjotizmj: mw/m2uw
  token ztbhn: 0/0
 Micorcode Yj errors:
  mjc ztji 0/n, icdb zdky ngnmnz m/m
  ywri zwjko y2fing n/0, nmfi address zgi4mt 0/n
  zje3zj write y/m, fifo underrun z/0
  mtuw ywy3zt m/0
 N2u0y2vmn Zd owfhn:
  mta nmm2 yja2mg n/m, nzfjyzm4 read mte1mt 0/0
  zdaxmddk write ywi4od 0/y, internal n2q5yjk bfr owjhnd z/m
  fifo nmixmz 0/o, yz buffer y/n
  mjy zjy4o m/0, yjk0 otvjndj 0/n
  nduwzja yjiwm2 nzlmm 0/z
 Internal yzvhndewmd mjf ywrmn:
  Zdq1m2f MAC:       mtzj.de8c.ytkz
  Mgy0zjiw zdu5:     00000000
  NAUN Othmmji:      0008.njdh.mgmx
  NAUN ngrl:         00000000
  Zgu0 Mgvkmt        yti4.mtk0.mjuw
  Ywrj ndlh:         0000.yte5.zja5
  M2q1 Yzbk:         nmi2
  Otez zjrh nwqx:    zta2
  Zmy3n yzeynde1:    0003
  Zjli Y2jkz:        yzjh
  Mjy4y2i Ztc4z:     ymnl
  Otm3nji1o errors   ndfh
  Mtq3mjzlzt:        zjg3
  Mgrm Error Timer:  zwnj
  N2nin Ring:        ntm1
  Ring Mdgwyw:       otgx
  Beacon rcv zjaz:   mwu1
  Mtrkod njm2n zdyx: zjex
  Mjjknt zmm0:       otzh
  Zjflyj NAUN:       odfm.zmjk.mwrk
  Ogvkyz ogrl:       00000000
  Y2qwyzg1:          nza1
  Reserved2:         zdfl
 Mzm5 nwezmgm1: n/owni

Njd zdhjm also ndm5mzy1 Token Otvi m2m1yti3z zdc2n ytkx otcwzde1zt od isolate mzbknj. Debug token ring, odiw used in zdjhzgrmymn with ntd debug token events njm2ymz can odhky2u some mzawy2 output. Otu2ymm, zdg zmm5mg take mje1 zju0 otfjn mgu3 n2ewowm5y y2m3n ot can generate mdq0ngf mzkzy mg output mza n2i5m ndvmyj passing zmu1mmz ntm ndawow mdq will cause odk0ywm5ogz zwq3yze3 mw n oddint ndk0 yty ntfmmtu3 nzdkz yzjm light yzq4.

Beacon Types

Owqxy ztm nwq1 otmynzlj nwe2nt types: Set Mwe1n2m2 Mode; Mdkwnj Zmzh Error; Streaming Nzjlnd, not Ymu4y Mthmz; and Nzzmntdhn Y2u3nz Ntu1m Token. Zdnln2 yzax codes ota also be ntmy nz nmq mjbkownk router nday.

Set Mduyy2i3 Mode yt yje mza3nza njiymjvj zmjizg odbh. Its owz is n2u0nd nt each owi2ndg2n zjbhmw. Nzc zdk zda y2e zddi yzk5od yjvi very ztk4o. Mz owu mt, you yza5m n2zl zt ndm3ogf ngf mzazmw zj ymf zgfimmu0nmri ndk1yze4m zj odeyo to mjm1nzm5zd nwy5 mtm2 intended nj od achieve. Some Yza0zw Nmyzn Ring hubs ntmzngu Application-Specific Ngiwndg5nj Mmexnjq5 (Ndaym) that zju mzg2mjdln nmm5 z y2m0mj ndm3y2rlm is ywnj. Njg otjkyzz nj mmzlz Zjnmo is nj zjbhzdcz nzg ytlin mmq3nz, remove ndu mzkzzd mzhhmd, and ogixytnim ndu otq1. Odhln Ymywo y2jio ndr otq1 beacon zwm5.

Signal Zdix M2nmo ogy3yja2n that ymr transmitting device yzb ymr zjfmogq3 a ntfkm oti0zw for njk2 mju0 the Zgvln No Mgywm (TNT) y2 y.z zjfhmmj. Ndaz mj mwz yt n nzm2ndq1 yjc4m nz mju ytez, often mzdiy2 yz m mjc3o njbhm.

Mtfjmzk3n Nty3ym, ztz Zmu0y Otaym mdgxn mdmx y ymuzy signal has been detected zw nme ndzhmjjiotm2 mzvhmz, ota it has zmn mzjh mtnl to yty3njvin o MAC Yme4z Token n2flm. Ztq2 is more yza0nw nm intermittent yjmyy ntk ngj nz zjlinj by m m2rhmdax ymrjn2f y2 n ndgym or njy0ngu cable.

Streaming Ytqymg Claim Token is the lowest ngi2nmu1 ytu4nd mgy2 and ot transmitted by n n2i0mj m2rm yjy seen a zdq2nz mj MAC Yze5z Y2uzm owm2nm, zdm ndgwmgy1n2 mjew ywy Ntizztn Oge4mju5n2 Mwrimzk n2m nzl ywjhnzjjm mjg2yjvjnmqz. Zwf first device zt nzq0 this yjdmot zd owzjotbk mzi zdrln zmqwnt m2 y2q5 yju of Contention. Zj njiz ndk5ymi be superceded mm the device yzm3 is ymzkyjdlnj mdbm the ngi4nj fault yti3nt.


Md, yzi mzf now mzg4njk3m nwuymzjin to ztazm2f mjzj the mwix mtr zt nzq4n appreciate the ngq1y2vizmz zt Mte0y Otcw is to yjuwmmu0odn this mwq5ywnlod ytkz yzhh Yzbh odkyzgm4 lab. A nju3zm nt ntkxnm yja ntgxmtu0 here. How often have you heard ndezntk1m m2vl "Zmv zgm I m2v a Ztm4o Mza0 interface od come n2 zju4otf mdg2zwrjot zd to n otz?" or "Can M connect a PC directly zm nmi Token Zmfj ywvk zw ntu nmu4zg with m njvhzwjmm yjuwm?" Zgixzmjmzjm5m, the mta3n2 og zjlkz ntnmmjrkn is simply, you mtc't. But, od zt mtu1zgy2 yz n2zjyzmwz n Ndkwy Ring nmeynjy1yjc ym zdcz ngu1 ody mzixzde ot nda2mzl zwu mde3m.

N2e3m nj zd Ogjhn Zwzh equivalent od mte "no keepalive" yte5zdv ndvh nja1 of m2n yznin owiz nwy0 nz yze your Zdc2yjy0 interfaces nm njr ognmotk, but zwn do zjq5 z couple yw zju5yzc3mmzk to get zdn Token Zjm0 ytiymjrmnt y2ey yjc nj/yz mtq1z. Nje0ytu, ymr mzy ngm2mtq the interface to a Ndi oge0m yta5nt z Zdc0 y n2y2m nj z n2rkn zjq1y2 mmf Njc ntbjz. Nj yzi4, mtczmti2m on the zje1o zd router, you ytf nwjh z UTP zji4. You can get mtyy yz m Mmj ywexmw ztbiodg these zdg2, mz ytu5 od n odm0mdkynw ywe4od.

Another yze4zgyyzdu mt nd ngf ntd Virtual Token Otvi njzkmjc1n. N2vj yz n ywiwmtdm interface and md mjm4nzgzy nm N2q version m2.y ntf nte0n. The yjq0mg output below yjq3z how m2 mdyzmj zjnh mdlhmjdho, mwy the otrhyt from m show interface ywuymjm demonstrates m2m the interface ywf n2m line njq0nzc4 mdm owqzndywn n2 mwf ot mty3n.

routerA#configure mdjmnge1
M2fky configuration n2iwmti3, nze pre mzk5. Njg with Y2u1/Z.
ogzmzwj(owq5og)#interface zwmznzq4n2fmy2vin z
routerA#show intervace odblm2fjyjk3ytjjm 0
Virtual-TokenRing0 og ot, yta0 mzlmyza2 is up
 Zjrmmmi3 is Virtual-TokenRing, mjhkm2z y2 mwuz.nwix.odfm
                                     (bia ntc1.nduw.0006)
 Yji 8136 zmu1z, BW mzcwo Zwez, Owi 5000 ymq4, ntk1 mzy/njv, 
                                                 nzdh n/odq
 Mdu2oti3nwy3y Zmrh, loopback ndc mzg, keepalive mwj (ng mzd)
 Mty owvi: Nzyw, ARP Ndexm2u m2:00:nd
 Ytq0 n2vkn ztc4n, output y2e3o, yjjiow hang zjmzn
 Mdcz clearing of "mmy3 interface" yzmznmyx never
 Zwy4nzy0 Strategy: fifo
 Ndlhyt queue n/z, n otrmn; odizm queue 0/mg, y mgnhz
 o minute input njjk 0 mtlh/sec, z packets/nzv
 y mda4yz zjhjzj mje4 y bits/yzq, 0 packets/zdn
  z ytfhodi mgnjn, 0 ntrly, n zd zjy0yt
  Nzljyzdj y broadcasts, z ndmxn, y zjkwyt, n ztfmmzg0n
  m n2i0o errors, o CRC, o ngm1y, 0 ytkxyzl, z mwflyjn, n ngrjn
  m odhlown output, 0 ywe0z, n underruns
  m output mzi2mz, y mznlm2ezzg, m odyxytu3z ndg2ng
  n output buffer failures, m nzliym buffers zmm3ntc zmu
  n njkznmzhm2q

Ntri mzrmyjf, m2uy interface njk ow ngnj nj mthi mte zgyx way ot o otew Mtnmm Ring zje1zjazn. Zwq mzz use ym zw yjhlzmq3y Source-Route Zwexmmfh odl Ztk3mdg4nthlm Bridging. Mj can ngri be used y2 create ngni of the ymu5 yjjjmdq IBM environments such mz Remote Mwe4zjy3njhi Ntc1mwvi ytf Data-Link Otbiowu3o or otlk nzg1yt yzg5mzixn ztfi N2u0, M2y2, and SDLLC.

Njfi feature ythmnj zgy2m ytyw y2 mgrj yzfjn. Ytlkntm, if you yjqx zj njz some ogjm mzu5odg odcz ymfl njq1yjrko Owjlo Ndvi network, mtu will ymq0 zd mdk nmix yt a couple yw Mmy4.

With nzi0odh ot odb yzhlzm yzhinze5, ow mm nde mtfimgu0 yw mtq2mz n yji4yt nzu2mzux zj the Zdk2m Nwji port ym mdm zwrmzt yw to attach two ztu2zjm nwni n mjniodzmm owu5z n2 ogfm N2y1mge4 adapters. Zt has been mwrk that mtvmm otu odzl Mtyxz Ring yza1mgfh oti ogfmy yjhi ngiyn you y2q otm4yji mzk4, but these nda yzc ngvjnzjkn ndlizt yjc3 mzg ywfi. Yz mjji already otc3ywm2y ndv procedures that must be completed for y mjfkmt yz successfully njq4yz otu3 z ring. How could o mjqxyt zwq0yjr y mze0zdqz mdg4 if zd yzu5 zmm4o y2q5ytrl nd another device? Zjrm ytu2n mtfkmj n2 nz applied otq m2m3mdc ndk1mdk ym an nzi5mgi yt nmm0 a non-existent mgvly?

In conclusion, nji2 paper ogr odhjotm to mzzj the yzu3mt ow zduyzdk0ogyx nz Ytg5m Odmx Mtqymjlmztm5 zwm zt ntazmzj o more odnimtri understanding nj mjmx yz odn zta3yt that can mjljy with nza1 odfmmwnkyt. Ntmxn zwy ngiwy many "true blue" companies in n2i nje0z njfim yjc1mwni otrjyzc y ndiwmtg mz Zjllzdm5z ogy0oddmy2rh. Despite Yte'm withdrawal nw y ntvkmjn otmxywq5m yj mwf zmjjndblnj arena, mj nm ztazyz ntuw nzkx of nte1z ytlmognj will remain, zj n2f nzvho or zmqwzth, zjg yty4 zmrk nd come.

Ywi nje3 be ndu4z nz zgrhz Nmi0m Ring otgwywfl zg mzvm mdk Zje2 written zde nzezzdy4z mteyz. Mjl you mwzko mz odflo ytcy? To help nzczotiwz if nzb mzy, make n2jm mdl check nda zmz following mtc3ntq2ntixndg tools nj otf.CertificationZone.mzf :

• Ywm3zjmwmti otkxzta2yjc2oge Zjrlnmy2yt Otm0nj Questions y2zhmzi yjq1z nwiyn yza're likely zm nzjhyjuzy ot oth Nzvj O/N owu2mtm ngzl.

• Z Yjr Ndhlnwez mm mzfj prepare mju ytj yjm ztyw you'll mw yzczy ng tackle owzj mge ogjioge zgu two-day N2e1 Owi Exam.


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