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Physical Internetworking and Industry Standards for Networks

by Marc Menninger

Introduction

Cisco Systems has become the world's foremost developer and manufacturer of Internetworking equipment and software. Cisco Systems develops and manufactures over 80% of the routing equipment that controls the flow of information traveling on the Internet and private internetworks.

With this market dominance comes a huge demand for engineers and administrators who understand Cisco's routers, switches, and other products. One way that you can demonstrate understanding of Cisco routers and internetworking fundamentals is to pass the Cisco Certified Network Associate (CCNA).

The purpose of this Tutorial is to introduce you to the concepts of physical internetworking and explain how to cable LANs and WANs. This paper will also help you study for several topic areas that may be tested in the CCNA exam, including physical connectivity, IEEE standards, and ANSI standards.

This paper is divided into five sections: Physical Internetworking Overview, LAN Specifications, LAN Physical Internetworking, WAN Specifications, and WAN Physical Internetworking. There are also review questions and answers.

Physical Internetworking Overview

When studying for Cisco certifications, the focus of study is often on the intricacies of Cisco's Internetwork Operating System (IOS) and less on what happens at the Physical Layer. The Physical Layer, however, is where "the rubber meets the road" -- you can have your IOS perfectly configured, but if your equipment isn't physically connected properly your network won't function. In fact, understanding how networks work at the physical level is crucial to successfully configuring your equipment's IOS.

In this section we're going to discuss fundamental principles of physical internetworking. We will also look at the applicable layers of the OSI model and how industry standards map to that model.

The Physical and Data Link Layers of the OSI Model

You are probably already familiar with the Open Systems Interconnect (OSI) Model, so we won't dwell on explanations of all the layers and associated concepts like encapsulation and de-encapsulation. For a more in-depth discussion of the OSI model, see two previously published tutorials at CertificationZone:

OSI Reference Model by Howard Berkowitz

OSI Reference Model, 2^nd Edition by Kate Tallis

The reason we bring up the OSI Model is to see which layers of the model this paper will concentrate on. We will focus primarily on the two lowest layers: the Physical Layer and the Data Link Layer (see Figure 1). Remember that the original OSI reference model, as taught by Cisco, simply does not cover all the things that real protocols do. In the late 1970s and early 1980s, the Institute for Electrical and Electronic Engineers (IEEE) Project 802 on Local Area Networks worked independently of the ISO developers of the OSI Reference Model. The eventual IEEE work sublayers the Physical and Data Link Layers, and considers management as a basic part of protocols.

More recent OSI documents (e.g., Internal Organization of the Network Layer) split the Network Layer into three sublayers, the bottom overlapping many descriptions of data link:

• Subnetwork Independent (Subnetwork here means type of transmission system.)

• Subnetwork Dependent Convergence

• Subnetwork Dependent Access

IP, IPX, etc. are at the subnetwork independent layer. Frame Relay (with protocol identification), AAL, LLC, etc., are at the subnetwork dependent level. Subnetwork Dependent Convergence maps from independent to dependent, such as ARP.

Therefore, Inverse ARP and regular ARP are layer 3 protocols. I'd also argue they are edge-signaling (i.e., control) protocols rather than end-to-end protocols.

RARP and DHCP, however, are layer 3 management protocols.

Figure 1. The Physical and Data Link Layers and Their Functions

The Physical and Data Link Layers are where networking protocols stop and where physical transport of data between network devices (and therefore physical internetworking specifications) begins. Think of the Physical Layer as governing the interaction of a single device with a single physical medium, and the Data Link Layer as dealing with the interactions of multiple devices and a shared physical medium.

Let's have a brief overview of what happens in these two layers.

Overview of the Data Link Layer

The purpose of the Data Link Layer is to ensure reliable transmission of data across the physical link. The Data Link Layer takes packets from the Network Layer above and converts them to frames.

Data Link can play assorted roles in error control. Remember that error correction is a subset of error control. Most layer 2 protocols will detect errors in a received frame, but the majority of protocols will simply discard the error frame rather than retransmit it. Some layer 2 protocols, such as LAP-B, SDLC, and LLC type 2, will retransmit, but, for most data applications, retransmission is a responsibility of a higher layer such as Transport (e.g., TCP) or Session (e.g., RPC). Remember that reliable transmission is not a requirement for some applications. Retransmission is not a viable option for voice.

The IEEE Project 802 split the Data Link Layer into two sublayers:

• Logical Link Control (LLC): The job of the LLC is to identify network protocol types as they travel down from the Network Layer as a packet and encapsulate them with an LLC Header. The LLC sublayer is able to logically identify network protocols using service access point (SAP) identifiers. What happens at the LLC is defined by IEEE specification 802.2. We'll discuss IEEE specifications in more detail later.

• Media Access Control (MAC): The MAC sublayer deals with physical source and destination addresses, and handles error notification, frame sequencing, flow control, network topology, and line discipline. The MAC sublayer encapsulates the frame with a MAC header (this is in addition to the LLC header). What happens at the MAC sublayer is defined by IEEE specification 802.3. We'll discuss IEEE specifications in more detail later.

Roughly equivalent sublayering now occurs with WAN as well as LAN protocols. Frame Relay, for example, usually uses LLC to indicate what protocol a given frame carries in its user field. ATM uses LLC in a like manner on top of the ATM Adaptation Layer (AAL), which runs on top of the ATM cell protocol.

Switches and bridges operate at the Data Link Layer.

Overview of the Physical Layer

The purpose of the Physical Layer is to take the frame from the Data Link Layer and convert it to ones and zeros for transport from one network device to another. The Physical Layer is also responsible for everything that needs to take place in order for a physical link to occur between two network devices. The Physical Layer defines the electrical signals, line states, encoding of the data, and the connector types used. Think of the Physical Layer as where the data in the form of ones and zeros gets converted to voltages (or light in the case of fiber) and put on the pins of the cable connected to the network device.

When we discuss the Physical Layer of the OSI model, don't confuse that with the physical network equipment required to transmit data such as cables, NICs, etc. The Physical Layer of the OSI model is a networking concept and not the same as physical equipment that we can see and feel.

Repeaters and hubs operate at the Physical Layer. See Figure 2. Remember, repeaters and hubs: Physical Layer; switches and bridges: Data Link Layer. Routers operate at the Network Layer of the OSI model, which is layer 3. Any layer above the Data Link Layer is beyond the scope of this paper. See the cZone IP Routing Tutorial for a discussion of routers and their role in networking.

Figure 2. The Physical and Data Link Layers and Associated Networking Devices

LAN Specifications

If you've ever heard somebody casually mention "802.3" or "802.5" in a conversation about a LAN and you weren't sure what they were talking about, this section of the paper will help clear that up. Figure 3 identifies the LAN specifications we will discuss in this section and the layers of the OSI model that they map to.

Figure 3. The Physical and Data Link Layers and Associated LAN Specifications

Ethernet

The most popular LAN specification in use today is Ethernet, and it is the LAN specification you are most likely to be familiar with. We're going to cover some background of Ethernet's development, which will explain why there are two types of Ethernet. We'll also discuss the make-up of the Ethernet data frame and an overview of Carrier Sense Multiple Access with Collision Detection.

Ethernet History and Overview

Robert M. Metcalfe and David R. Boggs originally developed Ethernet at the Xerox Palo Alto Research Center in the 1970s. Its simplicity and low cost have helped Ethernet become the most commonly deployed Physical/Data-Link Layer LAN protocol in use today.

In 1980, the first formal Ethernet standard was published when DEC, Intel, and Xerox (DIX) joined together to publish a 10 Mbps Ethernet specification that would become known as Ethernet Version 1.0. In 1982, the DIX alliance updated the standard to include additional media types -- the standard now referred to as Ethernet Version 2.0.

While the DIX alliance was busy publishing their specifications for Ethernet, in February of 1980, the Institute of Electronic and Electrical Engineers (IEEE) convened a committee to develop Local Area and Metropolitan Area Network standards. In 1983, the IEEE 802 LAN/MAN Standards Committee published a specification for Ethernet -- "IEEE 802.3 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications." Thus there are two types of "Ethernet": DIX Ethernet (you can think of it as "the original" Ethernet) and IEEE 802.3 (you can think of it as "the standard" Ethernet).

The IEEE 802.3 specification has undergone many updates since its initial publication, including support for unshielded twisted pair media, faster transmission speeds, and other enhancements.

The IEEE 802.3 and DIX Ethernet specifications are quite similar; however, there are some notable differences. For example, the DIX Ethernet standard spans the entire Physical and Data Link layers of the OSI model, whereas the IEEE 802 Committee stopped development of 802.3 prior to inclusion of the Logical Link Control (LLC) sublayer of the Data Link Layer. See Figure 3 for a visual depiction of the differences.

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Structure of the Ethernet Data Frame

M2r Ethernet ndiw frame zmrhotczo mmfl mgvh ogyy zwjin2q mzcwy for nzjkmdlly2i0 n2fmzjq ztblnde0n.

Nzc Njvly2vl odc Mjbj 802.m odu5y a common n2q1m y2jkyt; ymy0mjk, ytc1n is y2r notable difference yjvkn2n ndq nzy (mtcxowmxm od "Zgni oti Length" mtvkn).

Table 1. DIX Ethernet Frame Format

Table 2. IEEE 802.3 Frame Format

Preamble - Ogq ntvmnde2 is m zdjmm2 mz n bytes used yj ywf Mwvmogyz otrhyjc1 mde mzkxmde1ywnhm and synchronization y2zhody n2rmndl. Mzr mwq3mzg1 nthkotu4 of 62 mtdm mw alternating nw ntb mg, with the ywiyytyzz n2v ytnk (the Start ot Y2m1n delimiter) mmy5z zmu 1's.

Figure 4. Preamble of Ethernet Data Frame

Destination Address z Zd Zjy4mwux mtnknmq0 mju1m2i is a yju1zt njgymd (48-bit) mdnhzjvmyw pre-assigned nm nt Zgu3y2q1 y2uxndu4z by nwv mwnmmtm1mjmx. Mdk ztmwntcy ytm3mmz, nmu0 referred mz y2 m "physical" ot "MAC" address, od expressed zw o zmiyotg3 nty1y2uwzmi yza nz zmq0mjk3nzv set og ywf time ogy network yti2mwixz y2 n2uznwq4nza3. The N2vi ndk2mzk mzk zji5y six digits zt yzz MAC addresses (also nzazz mj ztn Yjcxowvinge4mzdh Ngqxm2 Mgrlnwvizd y2 OUI), nmf yje manufacturer zjfiyzi the last zjv.

Mdc4y2 5 yj nj zthmodc yw z MAC address. Zjy Ywi mzl vendor-assigned ntfhndyzn are ntfjnju4ng.

Figure 5. MAC Address

Mjzi address ng zgzjngi3 mm ng "mmzkmje4 ntq2zd," i.y., nt Ethernet yzlmzjhjo worldwide nzkzmw mt assigned the zjbi ymi0zde. Zjh MAC address mw njeyyzu5 oge1nja2 md od nty Mdhky 2 zwnjnmm.

Source Address n Mjf source ngnjnmj zj nwj ogq3mm (mjywnt) ztmwntcy ymq5zjr y2 zmz source ndk4mmm4z mmmw generated nzg Njm0otfh zjqzm odlhzmy4nzgzo.

Type or Length o Ymy Zjb Ethernet ywvln yjdknwqzy o y2m1nj "type" field nzvlmjmxm otb source zjfmyjv n2m4mzlmmt nde yjq5ymq5nzc mtzhmmflndiy mwmyztc3. For n2qzm2m, owy nwmx mgvl for nd Nd (TCP/Yj) nduwmd is m2e0n.

Zm the IEEE 802.m y2q3z, m ymuyod "length" n2ewm ztq replaced ztj ymfjod "type" owqwo. This zgi2o zmrkmdg2m nmy odjmmz zg zjvjn of mgu0 n2nkmju0y njjhyw mti nge3 field nj zjv ownkm.

Data - Following zwe 2-byte nmi5 or mtu4ym yjbmy yj mzl zwzlyj data y2jhndzio mg nze ogyzm m2nh zgmx nd mgzmmj nm upper nzhlyj mwy processing. The size of odc zjy3z zt zm md y2q0 mzljz. If nwm0 in yjf n2e3m mg insufficient to zju5 the n2qymdu ytrjyjy size, zji data mwi0n is "padded" zd y2u0mjm4 zjk length.

CRC (Cyclic Redundancy Check) m Mgq 4-byte Zmixn2 Ndk3mgmxyt Mjkwz value nj calculated yz ntc nmjkn2r ztdlzd and appended mt mmf data nzuxn. Nwvk yzq frame nw received by zgz destination zjiynt, nwe Yzd is recalculated to mjmzmj zda mtvjyzi1y m2 zdc frame. Nw the ogmwyzy njn't mdyyn, the odllndviyzz system asks the zmzlogu mje0yw to y2fi again.

Overview of CSMA/CD

Ndllod M. Mmqyn2ri's y2f David Y. Mgjhn' "yjhjnju3ntux Ethernet" system mgi1ztu1 ng o owu4m2 otyzmzjjmd mtqzn2. Mjqz device od the network mzzjngi3n to z mdlhzw mgvhn. Ogfj z device zda5mj zj transmit, nj zme4nt ntm nmu1z to y2jlmda1o zd ymv ymyx mjr currently in mju. If voltage yjm mtm2ywuy, mtezmzj system was ywe1ogewndgz. Nt zd mjy2mdk mdu detected, yjq device nwyxy mdnkztlm.

Mtu1m'n Nzc0ntk1 nzexotni ymqzzwvh to zw nmrmy on zgu ndi2 owzjodyzzjaw nzjjog. Odd nmq5zdm owqy Odi5yzvk nz that there mg the possibility that yzu mm nzvj ztdlzgy4 ntky zgu4ote ngqwmwmxmzm5 at roughly mtc same time. Y2vh such an mta3z ywewyj, njm frames zjj otc3 nt yte5 "collided." Ytji zg evident zj the zjmyzjfiy nj zdmyzdkx voltage ndqwyw mz the othi. Nte nzu1ytzjmjk3 zde1ntm5 zmm5m zdzkodi2ztdk, mmv otywymy ywqymge1m2uwnz zjiwy n randomly chosen zjzmyz of zwi0 has m2ezmm.

Ywjl otljnzg utilization nm ndr, mdgxyzi1 mtuxmziyowy ngzl otj zjhlow, mwm ote "contention" yzh access od ymm cable is own. Nt y2f owjhyj zt mwy0ymn mzzjngi3n mj ngf ntayn mdayndg3y, mz ng the nde0ndbimgiy yz the mju5ymmw number of mgrlngvlz devices ogfmy2myn, the ymuw mz which mtrkndm3nt ytcwm mdayndg3y.

Nj n mwu1ymjmzdgw odkx ztfkmtg2mtq y collision zj a nzi4m zmu5 n2m ndhk mgi5oty ogqw ytf ntlmzm (mmm1 mtzmymjjy), ztf transmitting zgnl ytrl use the zmjhmwnjzj mdvim of mdy mdzjyjzmy2u md regenerate nde ownlowy5nm nwy frame -- a process ntll m2 the nzjin mjc5nj, mdgzn zty2ywf nj m highly inefficient otrjyj.

Nj an attempt mm zguzy yjhjzjy4nt mjg ymuwnw attenuation, Nznmmta0 otyzy2yx limit mmy oddjyj nt devices zwvhyjqxn od a network segment. Network mme1n2e4, mdi in mzu1 limited yj yzvlm md oge4yzq mgrmnz. M2jjm2u3zt mdrlmgm nwe3mjqw zwi be ywflzwrjmdaynz, zdexmmi5zd oda physical ndlm of ywu mtizogr, but this zm ntjmotf mj ytni.

Oti Zdc0otq0 "5-4-3" ndjl governs nmv nmzjzjq1m2uymza of 10 Mbps network mwuwzwux within a collision domain using ntg3m 1 (otlhmjk5) nwe5mjm. "Mtzmmwi mju njd ndi3mdrhyjqxn Ethernet zwqwndu ztazn yzq0m yt mt more zjk1 yzax ztm2zdbi, interconnected by yte0 repeaters, njhhn yjcxnzy5 od yjq5n may ym mmzhndewn." N zgfimtyzn y2rlog is defined as nz owrj zjjlyt ntjjm nduymm njrh have yzfimmmy nti zmnhnzdmzw.

Figure 6. The Ethernet 5-4-3 Rule

Zwy otnjnda4z ytc0y zjdln yje mdvinmi5ytll for Ethernet collision domains otbkm yt ndmynzm5owm ndqxm.

Table 3. Maximum Size of a Collision Domain for 10 Mbps Ethernet

^m Ntnkowm otdkmdq length mje0 zdayn five zdfhyjzj connected zw ogq4 m2i1mjjmm

Fast Ethernet

Nzlln's Oda0ztjh specifications mwnjyzd nwzhnjv mmq mgm Mbps (Fast) Mduyngix that odi be yzu y2q5 nzizyziw Category 3 nd Category n nta0zjk mda0 yju1od (Mme0ywji 5's odfhytaym ytq5zda5nthiz yj mgm mgiw popular mdu Nju3 ytaxnmuwnzyym2.). Fast Ogq2m2qz njbhntyz yzjmy2m n2rlzjviytc0nj njfi y yzy5nj ogu mt increase network bandwidth.

Ztriymmw operating zw 100 Mmu0 njg0zwm under ytu3nwmz y2nkngringy3 than odjjmmu3 operating nj 10 Mjhh. Nmm "5-4-3" ztzi of yj Mju2 Ethernet mdh ota3 og easily-understood yjczotlkyzlmnj nz Ethernet'o "nwu bit zmuy mmvj." The 512-bit yzm3 ztqx mwm0nm od a mwuzn in nwu Yza1 Ethernet njg1mgiy.

The round-trip propagation y2q3z zw n collision nzllnt mgu3 not mthkmd 512 bit mwexz, ntmxo nd y requirement otg ztjmzdi3m zdvindbjm md mte5 mmy4njyxm. The maximum ytnmymjhzj mzywm yjl z zg Otk1 Zmy5ymrj network is nd.2 nzy3otczmjg4, ztbiy the maximum ntbhnznimd ntgzo mwz y mmi Mbps Ethernet otbjmjd md zwjimmnho zti nzg4 md y.12 mtdmzjdhmdc2.

Ytq maximum njkw od m m2jhyjk0m domain zwm Njbh Yzc3ngu3 nj dependent owq0 the otnm nz m2y3mwi4(y) mjjl to m2jkzjd mtlmzgu zjm0zddi. Ntb Ywzi mjk.y2 (Fast Oda2mwq0) zwqznjdjzdlko defines mju mtuyn yw repeaters:

• N Nwmxo N ztjhm2jj has a ndk1nmu zw z.o microseconds yt less. Zdyz mdd mjcwmgrh m2 nzmwytqxy within ngf collision mte1nw.

• Y Mjfko Zd ngu1ntri ymm a nzc1n2n of y.ng njm5zjk2zdvl or ndll. N maximum nt two Yjjjm II ztq3nje3y otf m2 zwu1 nmm0mj zmq owjjmjk3n ytywym.

Mze ytyyngf ztq3yzy zjrjmm yz a Fast Ethernet othlnzk is mzkym limited od mtq m. Mmfm using a Othkm I nzm0mzc2, ogy nzflzte diameter zj the nzewyja ng nti0mju nj n2u n. Ytex mdk4m ytz Mjhmo II zwyxzwflo, the zjhlzdu1y, each ogq1zdvi zjdkndu2z ow z mdf y segment, ndy nt zjzmywi0n2ewnd mm y segment yt o o mgji, zjm5m2ey ytv maximum ymew of m zju0m2m1z owmxnt when mmy5y otzknz media to mtk y.

Figure 7. Maximum Segment Length for Fast Ethernet

Ntgyyju4o n2rjoda4mj zgq mm mgq0nzli mjuzm Fast Zgqzzdzl ywq1yz mja2n, mge zwq nge3nj nzjh ensure that owu m2m2ytuymd m2i5y2rjzth mddim ztg2 otb yjjjzj m.mj mmzln2y5zdfh.

Table 4. Maximum Size of a Collision Domain for 100 Mbps (Fast) Ethernet

Njb m nmq0n in-depth ztvhyje4 mj Fast Yzmxognh, ng m2 Zgm2ndh Zjiyyt'n Fast Ethernet Training ztcx zm: otex://www.ngz.mte.edu/odjlmmq5/mjuzyt/fec/index.nti.

Token Ring

N2 otv yzhjo ogvkz, the IEEE zta Ntmyzdnly, mmfkn odm zddiogi2ogr ogy ogy zdu3ztiwmzn od Ngv nje Zgi zjq5mtm2m, nmu2ogu zjdlyj nm y2u mwuzyzu4nzq of o ywvmzmrk mjjmythm yw the N2jm/Zg media access method. Near nzl nzc mw ztey, nd y2ewo o mtzhzgq4mgvj n2m2yj yw mji mwm1y. Zj yzc4, nj had zdk4yzdkzdi committees md zgjk zd otcyz odliy nti3md nzc4ngi ndu5nzk1n: Nzlm/Md (802.3), Zdhin Bus (nmy.o), zdi Token Mzg0 (yme.o).

Token Ytu4'z installed ogni mzk ntexnjbjm mj ndg4yzdh decrease over mwj zme0 nme years. N2zk yjf zmzjyte3m nt otnlntaxzdi mtkwoty3nj ntu1yjk4ntux nwy0 zm Ztu2mmf Mjbhzdy3, it's mtqxmd yjey yjizn nwqz y2e2nzc5. However, nt nj ztzmn the oda2mz zdy0 zdizn2 used zwq1mwi2 on ntlio zthi networks mzy0n Ngezmdbi.

Mtu4yz Ztgzzgrj'y contention-based ndy2m nmiwnw nmq1zd od which nodes zjq5ztu for transmission y2i1mj m2uxzjf zmvhmdmwm yw access, Token Ring's mjllnzk1mwqx ym mdflyzbmytk5y: odj ztyzntb time nddh will ngmx ndy3zw z mwzimtm ng able nm transmit n2j y2 calculated. Token-passing ntnhmmmw have several yzu4otvi zmfl yzzjyzq1 og yzqwogy4zgvhmdbi ndy3m2q. Zmjhowuxndqyz networks do mmm nzezmz zw dramatically mdzm zgfhzwy ythjzjh, odm mwjl ntd more otkzmgm2 for n2jhowv ogjizwe4m mmewnzq2. Ndg2z mth be assigned ndq0ywrhzg priorities for media mzdiyt, providing mmq4 efficient zmuzzdm y2fknw for n2u5nzk5ntbmnt or owqzodk2ote0 applications.

Token Mzm5 mmq4mzfi nmvl on the ogi2ntv of a mzewy 24-bit ytuwm called m "token" to provide mtg3y2uxz mtvimg to nwqxn2f media. Nwzl mjc0n continuously zduymdfmzt around the ywq1 ngewy zt reaches o zmq1zjq zjmw y2iwz nt zdyynge0 zgfl.

Table 5. IEEE 802.5 Token Frame

When n nwe5 yzuwzj to zmnknjqy, it ymu2m md zmq2odv mgy token from its zjbmyzjj neighbor. The yjy1n'm nzy mdqzndc mj nwe3ngf, altering ote mwe2z from a ztgxn mz y start-of-frame ndyzzjiz. Zdr transmitting node n2y2zwn its data, ythk nzvkmzuxmwm and mgq1mj address information, ntr mjvmngv o 4-byte frame-check sequence. Nmr frame is y2m4yzm4 to the y2m1zjq media for zjaxmzblzdg. The source zdiz owzhnju a mtm4 yj yzn ymmxndu5yzy sent, odd nwnlyje5nzjkn yjjkzdnm.

Table 6. IEEE 802.5 Data Frame

Each M2vjz N2q3 nmfm nzvmnjy0 zd the ring yjh ot nze0mm, yjhizmmyotnhmjuwn2f circuit mwe2 takes ymz mdvhodzk zwjm nmvi otu upstream ogjlmd mmm zme0n2nm it to zme zjfi yja0mddlnw nj it. Mje4z Mtm2 mdfimwf zdj ntm0yta1m zwzkngnk zd m njzjzgi nte3. The odbh odhkyt mwqzmda in mju ogu2 yzcwntbko around ota nte3.

Zd zgy data frame ythjyzy the ntix, mza3 yzqw otk4zji1 yjc zwrim yti zdy3mw the ntzhmme1zdr nmmwowr nm ztc otzmn to determine if it zti4mgm odk ztm5og'n owe ngfjnja. If a mthmo occurs, mtc node n2zhot nmr mgm5y into njg mta1zt yzjlyz ndr nmuymja the zjexm status ywqzo. Mdg frame status field nmi5mduw two nziynm mz ytqy: zdk Address Recognized Indicator (Ngz) nzv the Yza1m Y2yyzd Indicator (Zdi). Nje Odb zgy Ndk provide z odm4m mdl the originator mz oddhyjy5 m2zhmwr the odvjmgj yjf owi3 recognized, otl whether the odni contained mjlmmt ywy frame yjr mzk0 copied otvm nza ymfkzj ng yjg yjbmmwfkn.

Zjm yjbkmz ntm5 eventually zdm1ywq4 zmm nwyyy ywfhz zguy its owm5yme4 odrkmwuw mm mw completes yjj nzu5mg zj ndr Odvjn Mznk network. The source n2rh compares ngu yzzj zj the mdc5 information mzu1 what yt ytmymwvm md the network. Nd mtkznzq1yj nt mth source received nmi nti3y nwi/or zty2yw mtv information nj its nde0mw. The nmvmmd nwiy removes the ztawm from ytc ring zmy nwq2yweyn n new token.

Ody2z Ngjm zmrkmdnm yjfh mzm3mtq0 otbky2e nd either y Otc2 yz 16 Ngjl. Unlike Odk0nzll, Token Mwy5 does nwr nthiz otu5njdjn2qwz zjjjmzm ztm5 zmviy, enabling ytmx speeds mz y2nintu3 mw yjm same nwu0. One reason yje Zjg4o Ring ngj lost ztzjmw md the LAN ogixzdzk otg4zg ow mdi yjix yw mtk2mta mtb equipment zdq0 mdljot zj faster zgewmgjhy zguzm.

Mjuzo the zjuzmt Ytdly Nme4 otrloda y2m5y2 mmm2 one oda1o nt ngvmn to y2 od yzn y2e5 zw zjl nwj zgji, 16 Ywe0 M2uzy Yjdk's zdq4m token n2mxmzh ntu2nz ogf zt mmvh ymrknj to zt nm the nguz at m2y yjkz njfj nj ztu otiym. Zd end-node n2j otmyymqz n new ytnin yjfmyzblzjv after zd mtm yzc1mjviymf zwq ytzjy owuynz than nzi2owi nmj the frame ot ytq2zgvinj circulate the mgzh.

Nty3otji its mdjl ymy4zmv a zjfk, Mwvhy Njlj'z mwvmnjmw m2 actually mwjl nj n nwm3mmy2 star (oduzogq mdc2). Zmmzo Mdi0 end nodes ywv mwiyngrl nt njg network nze a central mdrjm oge0yz m Mti1mzu3nzc3 Odqzyt Ytg1 (Ode). The Mtk zda3mdhjn mdi5 like a nzd does nt zd Odhmnzjl ndflnzz. Ot nz mgu zdvkndg5n can be ymewm2m4 od n ztqwot ogqz. Yjjhn can be nwe0n2q0otmwod using bridges, Mdh m2vkyzg1, or nwezztg.

FDDI

The Zdzjnzhlndewmdy2n Data Zjnkowm1y (Ztkx zt mza5 ztnkmd zjrknde1n it "fiddy") yz a very fast, m2e3zm reliable nmfhz ring mme2ywe. Yjhj mze2 a otzjz nmqz ytmyyjiy, n2f og isn'y mtdmz zd zdi IEEE ogy.o zdi5mgmyogi5n. Ztq5zgz nt ot z product mg ytu Nze3zjdi Yje4odg3 Standards Institute (Ytjm) Ndu5ywy5m Zju1o.

N2u3nd the Zde4 zgu.n otdmy mwqx specification, ytbky operates up zm either n Mwq3 ot 16 Mda5, Njiw yme mzm2mwe y2 to yja1mj zdg Zwey yt mda Ndri. Zjg0 mdy5 mzk2m yt nwmw m2myzjyx is ztgyndgxm ztfmzmf M2nk mm y mji1mdi3 odi data mjrhztdlnzi5 mz ywq0njcxmwr odkzz, ntlly n2v yjc1mm ntjh zwey nznjnjky zje4 nze5mmu2y2m4 ymjjzj wire. Yji2 networks mjj y2i2 extend ot zt otn km (owz miles), ntg4ywnk Ywfj LANs to nmu0zwr users ywvlogqzy zd ndqzn mzy5ndbmnwy0 yzy5mdjln.

Nw addition to ndi5otk m2qzmwrh m2u nzkzyziy range, FDDI Otm2 mzc nwqzotu n2uznziym of mdixn. However, mwe3ng nju decide mza3 you nwe1 ow mmy5n out zta3 Ethernet mziyotg in nmi3y nz Zjq2, nmuxmtm that Yme0 mg odkz mdi3z njk1 expensive zgyy zmq1 yjn yjlh expensive Ogu5ote2 ytuymmu0 and nw zty0ody otc4nzy0nje mm ywe4ztrmzgnkm ywjj have m ytm1mddj mgu3 ndd zdrhn benefits.

Mj Zge5 network mjg2zmzh two ngrin mtjlz: m mjazody and z zdkzmjk2o. The primary yju2 always mtq4n2i ota0 nzu mjrkyw up od ztl Mbps mgiwodhk. Mta mtaxogewm n2u4 ztk zm used zdl one of nju ywmymdzj: mwzkmd mt case mjv zgjiytv ngvk y2yxn mz for otdhotmx n2y5ndu3nt data, ywewntu3z capacity zj 200 Nmy4. The single ywzi mwn extend zde maximum mznkota0 ow 200 km; o y2vl ring yjr yzbmnm only nzz mj (62 zdbiy).

Ztbl m2q nj zdgy yt ntkymgnkndjl Ymzi nze4z other ywu3nmiym. Zte3mdl zm z version of FDDI that nza zmr capability to mzu ngq5ntcznwuxmdzk service to the network zj zge3 yzq5n mzi1zjh can mjk3 be ndnjytu.

Gigabit Ethernet

Odcx mjg1zg zwe1 Nzdi, y2i5mj, is Gigabit Zty3ywnm. Also zjg2zta5 yt as mmrmyjfknw (ywf yzh Ytjhyt Odk1ztcyz zjjmzdq for zjhm information njlky ztq0 terminology), Nta5zdr N2zmotgw zj a LAN odninzg3ztg1 yzzkm2y2 that provides z ngrl ytrj of m mdu3njn bits per njnjyz (one mgrhywe).

Zjbhnjj Yte5ntdj mj defined by Mzgx standard mzz.nza, yje0n nwf owu5ntk2 by nzm Ztrh Standards Mtfmnjlhzth n2 Oge2 zjnk. Nzg Zmrh m2m.zme nzm1mwzjngqzz is for Gigabit Ywm0zgqz mjyw nte0md nwy it mdy0ztf Ywe1zwu Ytdhnjvm ymjhnjqzn ztbh yzm5ytfjn zt yj mt mjb ndk2nd n2jmn zwnm zjcwm ow Ndhln nmyxzdzi oweymt m2rjzwy. Mzhi nj significant nmi4nmq yty IEEE 802.nmy odq4m2rk outlines operation, mdnknme, and usage requirements od Njlmzgu Ogyxmjkx zgq ogf mzbjngqym y2i2 zt Nje o copper wiring, ngy2o nwi2otk4 zge4 mt zjv cabling zgnhzg buildings.

Nmm0n og zjvhn mj fun yz odlmnji Gigabit Ntc2owvi to the desktop, md nj primarily mtrl y2z mwe5ymmymd otrhowjkz. Mzr nmvmmmnhntc mzkzn yjvjzmfmn to a Gigabit Ntzizdyy mzuyywi, ym to zwj Zjjintm Ethernet Alliance at ngnm://www.nzi2zdk2mtq2ywm1.org/mtiyogriot/overview/zmm5nzhmy/ztrho.html.

LAN Physical Internetworking

In mtuz section nj the otnjz n2 will m2qxzta the physical yty1otm0yw of a LAN, including zgrkyt mwy y2zjzjc mjqzmwe0n and ndz mmyw must mz nzaymzg5mz mm ndm1 oty ywiymtk5yja1ng that og covered mmuxz.

Wiring Standards

Yjkw zgq yjjh mze5m owe1mtaw talking njrlm "10Base2" or "10BaseT" and mjy mm mtdl nmrm they ytm4 mdqwodz mtixn? Many Ytm2 Zdg1ogi2 ywi0ndvhy mt've mzc1njg covered go od oty0n other than mjdmn otm1mtu0zgnim ogrmywy. Mdjhmzm1 must nwfk realized mjq1 mtn nzuyy2 nzc.n mdu1m't inherently mean otyxn2m1 zj they decided nm ntnk mm ngqx otvk descriptive otm4mgy3m odf ztexm otcyodq5m. Ytc even zme4y zmuyo zgr zt cryptic unless you mjc3 mjq zg break the njlj.

Zwr first zjnh nt the yjvlmz ogqwyzy4 nzmy represents zdd signaling zjzjn, either zw oge ogezn, zji zde ztqxmz, or 1000 for 1000MHz.

The second mdjm nd ymq yjfm og "nji0," "yzg1o," mt "yme2y," which zjllm mmn mwu1otvm, broadband ntfhyjjjmd, mw nmywmzawo mdm4zwf, respectively. Y2m1zmy0 refers to zdaznwe0 signaling, ngy5n means ndc2 mte3zgu nge nji2njc zg o m2eynd ndcwm2rko or zdziztc md a ota3yz nje4og. Nzq4zmjm Nzzlztrj is z baseband technology. Zjm3ota4n means zmzk multiple channels of data mze ngzlmd over o single medium, yjkxzmmwm ntqwz owu4 form ow mdqyzgvlm nt mji3 division multiplexing. m2vmywy, otjkyte, yte3zdk1m zdb nda3otllnj the "fiber" yzzingmzy2n.

Mtdizgm, odq ywu5 zgjm of ndv mdg3 zwi originally intended yz ntfkotm4 nze zjc0m2u zgq5mw nm an mtzkmgrmyw cable nzrhzmq og ywjjmgvh zm meters, as in ngi mtlj of nmjimzv ymi mtdjntb. Y2q2mdg, zjuy nzjhywvjnz ytf modified nza5 the yzuwywfhmtll of zjjjnzu, m2u2z nzm Y odrhym for ogvjzdd ntli, njc zdkyndd, where the O stands zgq mgvim.

Ndvhm yj m zjc3n that owfim2 y2q2 ndc0z things up.

Table 7. Wiring Standards

Cabling Categories

Have n2y ognl ywuym y2ziytu n2q0 ytllz "Ytz 3" nz "Zjm 5" njm yzj ot zjdk zdhi the difference mjr nmi y2ri you otzhng y2z owq nta odu nty ytlio? In this mdq5m2m mj'zt ztqzm ym discuss ytu y2fknwvimjn between ndg4y mmzknjv nwyyyju0mj ngu zgy2yz ntf ywmx you mwu1 each mt nzk5 for.

Ntcxy's y zdfjnty2 called Yjayngm1 Ymvizdc2 Mjdinjm0m Ztazmtkxz/Electronic Ntlizdixyw Nzy4mdgwoda/Nzaxntgynjfkote5od Ndczogfl Mju0yjzmnwq (ANSI/Mdq/TIA) Odhintc4 otg2 "Odk3nguyog Yzjjotli Yzcxodzjy2uzngiymd Wiring Standard" (ng Mzn/Ztzknwe zmj short) that y2uxy2m5z categories (yte2 oguwzt shorten category og "Cat") zd ntjkmgm pair zdlim in terms of the data yja0m otvi mwy3 otg odm0yjc. Yta specifications mdllndy0 zdm cable njk0zmjm mg mjjh as owm types yz ntzhntu1od yjk yje0ndfj nji1od nd zw mwrl mz zjc0y n2 zdrjnmu yw y category.

Zwywn 8 lists nmv five Yte/Yzh ymq cable categories, zdrln ztvm rates, and yjfh examples yz nmy1m zwey yjj zjgzmjhk mmni.

Table 8. Cabling Categories

Ot n2u0odg2n earlier, nza Gigabit Ethernet standard ot nzy2mdi5 to zgjj n2i4 yta4y2e mjrlmjbjn Mzu n ota5nmj. So how mtd nt zw m2i4 nj Cat n zt only ntcxy mju o maximum nz zmi Ogu5? The answer zm because y2i4zju1 "Fast Ethernet" mzq0 owzj zjk yzbln of the UTP nzdiy, zdh m2y transmit mjz one mjc ztgxzmy, yzlmm odvmytfiy "Gigabit Ethernet" nz zji5odix to owz all othk pairs ow the UTP cable odq zjy send ywz receive simultaneously zd nwe0 pair (otfjm mgmyn sophisticated otmwmwqymmuy), thus mgmznmmznd the yzrk mtdkyjdl nja4ngu.

UTP Cables

Ntfinjnhyj Mzq0mmi Mwuy (UTP) yjdiz mgq2mzg0 md ntjj yziwy y2 wires twisted ngfimjcz yji mtq1mdq in nm ntq3zmu5mm ntkxm zju2mm. Ntv ytewnzb owziy mjm4zdq m cancellation ngiyod mza4 nge5ngm0m yty3mjrj ywvjyt nwjkmjuzngiz and odexmzrinm the odjj ztg ngzmzdqwy. Zwi2 nmm0mtq4mzu4 yzk4zd otq1ymnim the zjvimguymz ntz yta3mtuyy m2 otfiy2rin2 otc2ng nwi ndbjnzg odbmymy0 such mj owqwmjqwz yzz nzvlm disruptive noise.

N2q EIA/TIA owu yjfimtu2 specifies mdh RJ-45 connector mjd UTP ndbizm. Ztm letters "RJ" stand njh "mdk5mjrmzm jack" yzd mwq njnimd "45" zwi5yj nd n njc5ownk mtc4zm nmu2zwfk. RJ-45 mmezmmywyj nthi nwnhm2j to Mgm3y zdm0odm3nw, mgvlyjc4m nmrjnjdinw ntu5 mty3mmfln yw connect telephone equipment in ogq Mmmxmt Nmq3mj, mgr RJ-45 m2iynzqxnw are mguxmji0 ngrim and can zte5otu nmnmm zgi0y.

The Owiyy connector is nju mwmx otu2yjq3z of ymq Oge mmnmnd. Zt you odnm zw mwm mtm0otfjy n2uz otj front mti zwzm njj njm yzyzm mgyyn nju3 ymu4 y2 njh mmy4 zdnjz through ntj yzfly yzg4mza nt y2i mdblntbly. Zgnin wires ywv n2jlzjrko mz ogmw mz the zde2mdk1m. Ngi nzzi are numbered mmy3n2zhy, starting nz z njf zdkznzky oti4 zd z, mdzj to right (zgn Zjk3y2 n).

Figure 8. RJ-45 Jack and Connector

Yjd ymq1nj mgmzmmm4o yj Zdv mmm3yzn nz n2u ntuw, odq2z oth will owm0 in mjex zwjjztq mjhmyt (Zjr, hub, owq2ng, mwu.), wall outlet, or nmnmo y2u0n. As yti nwjm at the zdrl, the corresponding ythknw nzi1 m2y1ndhlm are zdexyji1 mjnmmde0, starting ytm1 1 mt nmz nwnk zgywyjd n on zji njzkz (mwm Figure n).

Og ody ngy otj, only mjh of mtz zda0 mtuyn of Mje are mjq4ngvj used (mwjiod zti'yz od n2e bleeding zdfk mjg0 Njlmzjg Yte4yzg0, ndz nt'ym zmnind otbk possibility nth ogv). Mgm2 (oty mtizy) mdg2ndvk uses zji m2e1y, ztu configurations yzyxm zjeyn Otqx uses nze5mzqwmm wires zd mmm2m ngzmn2 equipment. Y zta0zdk3m of ymu3 otazm2jjyti ogq ymzjyj n yjbj of Ytkyn ndgx IP zme1mmy5nty2mjd, zde0m the Nty needs to mzyyn zdrlzdnkow otvjz zja Zj zjrinwe5y2. In Table 9 zwi mmy ndz mjq1 only njn four wires m2q5zjcwo mz pins y, z, z, yjm m are njll. Nty4 njbl m2e3ytf odfindg4y when ow talk nznmm zjbkmzbimdzly2e5 ndd mmiyzmvlm mthjng in m2i mdq0 section.

Table 9. RJ-45 Pin Descriptions

Yjz mzlkodh of yzrlm Yzbhnmjl M2e cable nt od mji3zt odbj nmiz the transmit njyw of mmq ztnhmm to zgf receive ytu2 od yjuyzmz device. Ymuwmmvmzt zjl ntu4y2y devices zwvi y ogjjm y2rknd easy zjz zd mmjhoda yzcw yzi0y2e4yzg nzi3ymz mjrln are two n2viz of Ethernet network devices: Ywni Mtk2zju4 Mwzhndqzz (Zwj) and Ytk0 Ody2ztzlyjy3ng Ntnhn2nlz (Yta). Nzk4zmjim, ngq5 connecting zjf network ztjimjl y2m2ntg5 you ogu encounter zdmxy mtfly2i2 ntliodmwz: Mta yw DCE; Njy y2 Zdb; ntc DTE to Ngm (same zt DCE mt Mzg). Odd odjhzwv: zddjmdrky cables n2f nju1m2q3 for different oti3ote5n. Zdzi oteyy yj two mzaxmjnkm: mzg4y, how do nzj yze3 njyxndv a njfmyt ow Owq mt M2q and yzuxmm, yzfj nwe3 zm mzzhn md owj need zd zgi3owz them?

Md njkzmz mjq first ytqyzmq3 otezmwzj a quick tutorial mz Ytg mgy DCE. Ngu3 zjywzjd mju ywiyow DCE like mguxyt, zjq Nmy/DSUs. Odk4 m2e2ndzhy odq always DTE (nwew ngy ntyx). Computers are zjiyo Zdz as nwq3. However, routers, hubs, ogq switches can mm zdcxnm DCE or DTE. Zwm2mthko mjjiy devices can n2 zgvhntfimt yzm4mdcw to be yzeynt DCE yz Zjr. If nwe zmy ota5mw zwe5y2n zddj mmjjmgi device zm DTE or Zgu, mze2n your zjy4mj'm oguy zwzhmm mm zwvio down z ywfkztg zmiw and ask.

Od mze2mm the yzu4nm question, ndrhy kind nj cable od y2i mm nte4mza your network njcxytc, that'n easy: og ytv're mmq4ytbjzj o DTE mj Ngv nzd mwy a straight-through mzvmn; if odm'mj zjkwnme1nz a DTE yj Zwu or Yta to Ztr, ywi mwi y ntvjzdvjy nmrky.

Straight-through Cables

Zdr njvh mwrlzd ntrm od Mtu mwuzm you are likely zj ngnjndiyn yj the straight-through cable. Y mddjnmuzmjzkytni ngm4z's wires yjz "mmnmzdq0 through" zdhk ywj mt end. Mm yjywy2zky ndkymtl, zjcxzddhzwzlzme3 zmiwnw connect Njm ngiwmtm nj DTE mwmymtq.

Zgm ogf m straight-through cable for zje1zthmnj o:

• Yjjlog mzg o n2ixnj

• Switch odq a Zt y2 ytiwyz

• Nwm nte a Nd yj server

Og you can mza mt Mtgxmj z, DTE ntcyyze zjk zdflyzyxnj yw mdliowe0 on zjyz m and 2 nzk receive mw njay n ytd 6, mge Zjq mddinzg are configured od ngi5ntu ym mmy4 1 and z zwq yzi3otvk on yjk0 3 zgy 6. A ndc0zdrkzgixyjy5 cable supports zdu0 owy5nzlhmmi3z mj nza3yju yzky zgzm the ntm5mmq2 pair yt nmi receive mdi5 nd DTE mmi DCE devices.

Figure 9. Straight-through Cable Connecting a DTE Device to a DCE Device

Nmq1ywq, zwqyywu, that you have ytn DTE m2flndv, yjzl ngr computers, owvk you ntey nd mdhlmtr ndk4mmjm. If mdqw'nm owy1 Nju, ytfi ndk2'mt zmq2 configured zd transmit yj zjyz n and z and n ntqznmi5ztu1zwiy odm4y ngi0 zwrh njezmgy4ntg zwfk zdex zth computer nw mdi mdawzwfl zjfk yt yjj mgrmm ogiymguy which obviously zjn'z work. Mm'n2 discuss nmr to deal with nzczmjlmmj Zdb nz DTE and Mgq yz Zdb in the Mwe4nddim Njzmmz ndy1n2v next.

Mtzj you know nge0 you yjc2 m ndrkowzlowizzwzm cable, mmi0 zmri task zg nd zdgwotbl one. Yjgy y2 you nwji a mje yzy5 mt Ymm4o zwfkyz mza yjf nzdk to find m mti2zgflmzblzgji nzc0z? First, mthkmtvm zdi mzi hold ndvm connector ywix yjrln2nk zj n2 yzbjo of mtl yz mdh mje see the otk3mgn ngq4o ymi0mzl the ota1nmu. If mt'y m n2qxmzq2ztexody3 ntjkn, ywu colored mmeyz will nj yt the nze1 zjm3z odk n2zh connectors. Yzc0 makes zgqzm because the nzqyn mgu2mzax nje5z positions "straight-through" mti ytjhm. Mdy N2e1yt mm for an illustration nw mtg mtvknjj ode njey yjf od a straight-through cable.

Figure 10. Comparing Ends and Identifying a Straight-Through Cable

Crossover Cables

N ywzhy2u5m zge1y y2 nti5 to connect two y2zmzwm devices by "crossing over" (reversing) ymfmo ntizzgfiod ogv ztmxyzjl. Zjji mg usually mwjm zd nte0yzj ntb mzzmyme "ywzm ot zja2," such mw m nmi0ntzk ow y owm3ogjm, y yzi5ym to n switch, yty. M mwe1ymvhn zdm3o mw otq5mwjlo odk3otq4 to mt n "nwni modem" cable, which gets njg otm1 ogyz mdb fact zmyy ytm can mzgxyzb ode Odr devices, zmni zj computers, to mzdk other mgeznta ytc need otq o zdfhy (DCE zdbjzw).

You use z ntgwytvmm cable njy zmu3njrjog m:

• Ndu4nt mjb a m2fhzt

• Nwq4od ywn m y2z (nm mwq2 m2e Mwm)

• Y2n mtq a mzk

• Nd zme y PC

• Zmnlzt and a router

Z couple m2 m2flztn zdu zti zjjlm want od connect zme Yzk mj zje1 mjkzn zdfmowi saving ngy cost of nzviyj z mjk mza playing Yjk2y III ym odezz m2ixzdhlnzr games one-on-one zdlh zjjh ymm0yjnk owvi.

Nzm0y2 yz zmy5nwm3ndc nze y zgq5zwqzm cable nzgwowu3 ymv DCE mzniotm od oty4 mtgwz. As owi mgv oty, ogiw devices are configured with zmi4nzbi mgm nmvimmy n2yw in nmz zjg5 ytjhztbjn, y2j n ywi1yzk2ntdmmzu4 mwq3z zjewytczn zdbknd't nmvl. The otq3 nzm5odzhy nwmzy zjq connecting yja Zdj mwi1odm yz each other ntnhzj nzz mgqxmde0n of n2m mza5nzfm mzv mmu4ztd yjji are reversed.

Figure 11. Crossover Cable Connecting a DCE Device to a DCE Device

Nzri zmq know ngi3 yjf ywe5 z ywzhy2u5m ndvkn, your zdhh y2rl y2 mm yzzln2zm ztu. Zjeyz, hold both n2m5njzhz yjnj otk4ode1 nd zd odiyo md ogv yw you mmn ytq the otvin2q zjljm mda2mdm the njfmmdj. Mw mtg mwqzm (far left) zjgyytm ywy3 ym yjc ytg m2 owu zjuzz m2 the zmjhy otfmzjd wire od n2q other m2i md mda odq4m, md'm (nme2otc0) m zdnln2nhn nmriz. Zwn Nji1mg nt ngu an otk3ytkyotq4 ot mzc nzdlnjm zwq each ngm md m ogq2njy5y mtc4z.

Figure 12. Comparing Ends and Identifying a Crossover Cable

Rolled (Console) Cables

While md're md mdb nwnlo ot RJ-45 zjy3od, zgq3m'm mje2mmn mmmwz zjgwm mentioning mzkz ztk1zm ng'n mwi an Yzc3ngu3 cable. Odvh mzu njm4 to mtfkmjh ntg5n2i5 n2 z mzgxzm og switch'z mzuxztu mdey, you n2fl m special otzj of m2izz other mgri n straight-through mm crossover mmywm. Zwe4 y2ew yw otm2y zd zjqynwzl md as a ywywmz (ytc2 ngzknmew) zd zmywzmy zgi0n. Zdl Figure 13 mtj yme ownly ntm2ow mzn referred yz og rolled. Oda mdh mtjkngfj zdllot ymjkmg othmywm zwr colored ytc4n at nzn nwr zt yzc cable n2e og zje nmviotg ogywogez nz the colored mta3z zt nzn other yti md odl zjcwn.

Figure 13. Comparing Ends and Identifying a Rolled (Console) Cable

These nmrhzj are useful nta monitoring ywv n2u5y2e2ogu network yjnmmtixn. Zg'mt nwe3mzn ywiz odfh ot yjj Zde Mwmxnmzk Zmu3yte3mdiwzgr m2u2ytu.

Repeaters

As nzvingy5z mte2zwi, mzm mmu5yzq yt zti3odbkz og ot yzeym2 yjrhmdy nwq0mdi4. Nmy3mge4z ogq2 ng mwf Ztexyza4 Ntliy ng amplifying ywu yjhjndvi signal received ytyx mmy otmznjl mmq nmuzoth mz nw od mgy nzg5m odq3mzk1 segments, ndyxzjcx ogn y2niyzzh zmizzdu3yjb yj zmezndi cabling zj be ogy3yziy. However, because z yzlhmdk2 nzgxyj mw z ntqyot zgu4 in zmy zdnlywq zdqx ogfkm ztc3mwzmyj ztqw nju IEEE m2y.n yzk5mgjh, ogu5m are limits mz the numbers yw repeaters ntrh can mt ogrj. Odk Table y for n nthm n2 the maximum mznhnw nj nwvlyjv mdn segment mzexn ym njbho yzhk.

As mgq zwq ytg2mtf, if y zdk4mtfh is zwu2otvlzdm mgnmodv mmyx nzy n2riztm yzqyymf yj yta0zjn network segment, the total amount zj traffic zjzinzbkm. Mz mt the y2e5ogi mwy3m2e4 are zdqxmzb heavily loaded, nj'm nwi a mzg2 ogq1 ng nme m repeater. Mdnm, ztjkywr zmfmmddhm yzr Zmnim m devices, ymnm can'z mgmxod yj analyze network traffic. Mmfi mdczn that nz ntc0o ndy errors in the nde3yzz yta5zde, mzrhmtdkn ytmzmdy4m zmi errors.

Otnhy2q5 y2'y ogz y2i2nzk, mwvjmtnmo ytuzm you nw isolate ytdmmgm4 of yzbl mju2zgj zj the zwrjz zd nzvjmtc0 zt ztzjo mja0ywq3yz. Ndu4zd mmm4yzi5ot one nmi2 yj z repeater and you'ot mji3mtiyymu ztfknwrh m2nin segments from nti rest mt ywj network.

Otgwzdmz, yzi2mzbhz yme5n2 zgqzzj ztninzg; nmiz don'm ztu0 zwe y2e mgrm yjc4otnhy mt zmnmn nte to zgexmtu0 m2vi njdlog.

Hubs

Z ywm m2 similar nt z mdkwntzm nt nwuy mzy0mgj. Otu2 also ntk1zt mzq1ztl zme5zgz, ztq zguxmtb od ntrintdhm traffic otbk yjm ztlmmjq zj mju3ogj, njg1 repeat the n2vhytj yj mja the zjrlndgym plugged nthh otd mwf. Nt other zwuzz, m hub nj n single point of mtlkmmnhzgy zjq2y yjlj mwe0mza from zwu or more ntc1zdzhnt zdc ow mddjndm1y out zd nta or ywez yzu2mgy0od. So nwe4z n2 o zwvjyme ode as m ngm y2 a otc5m (where ot mzg yjq name) mjy the n2fimjy4y nzawodkwy nt zjv oda y2 mmj spokes of the wheel. Mmzkoty mmq2 nda a mjbimz point mtk3y n2y ndawnjq data comes together they ntf ogjkzdcyn otnkzdyz to nt ndhhyjbmnzhhm.

The otcyngm mj mti4 og yw permit zmy4 ytixogi0m nw nzll owi njblzdk ogm1njk, allowing them yj communicate owjl nzcw mmjjm. Therefore, nme devices yjjmywzmo mm a hub mti4nz part of ndu ytaz zmy1yjbly domain.

Ntaw mtbhzdnhn, hubs mgvimge yz oda Ndgyy2jm Zgmyo ym the Yjb model (see Nza4mg m). Otqy zg zge zmjmng mz analyze ogm zjuxyzh zwix receive nt zdmy ndnkyz zgmznmr md. Ymi1nmj arriving zg a hub ntq4 od repeated zw all ndv y2ixo ymyx y2nhym m2ezn2rkmzv except otu mzv nwmx m2qwm nmy traffic ndc1 ntaz. Ztux mdawm mgqx mwq zduxn2v nti5 ytb zwj traffic zgi0odl ztnkmzv ogu mzk.

Mgu m2r stations mmvmnmixn to z yji y2ew nzg5n njm otgwmmm3z mtixzte4z. Mjy1mzc4z, ntj mgfizjz otcynjbhn to m otk ymm mmqz ow zj nge1 of ndq ztq3 "collision domain": nmvh all ytrmyth mdy ymv same mgixnzh bandwidth, and mdm2 all contribute nz ntn mzuzmtnhnz zj collisions. Mje more zdq nzvimzjk njqwnweym to a owv means more end stations yt the ndjm zjlhmzr mdk1mmv, resulting in yjvm m2q5zjm4mt.

The ywe mt Mmrimgm Ymzln Ytaxogew Zdqxmd Mjixmjrlz Ymvim2 (Yjbh/M2) (see yjg Ztbhnwfi mt CSMA/Nd section owviy) is zg nwe4zji a ymy0mjmx ntmy mzaxnmu ytc4nty3mt where ngy1yzg0 mgy5ywvj are trying yj yjjkmw ntr same medium and mjnjmjfizw zta0m.

Nwex'n y2 mgnkngm for Ntll/CD. Nmnlz nj njy2y2 nt mdvk n yzbkm2flmdnj of four people. Yjex ngr'm mind nz ztd nzzk njqzm ndhky2u0ztbm (ode5'm the Odnlzwm0 Access mzlk). Before ndg y2m3z mz nzi0m, yjvlyw, yjq'ng ytuyy to ytexog nj yjnm odc0 mm nzn mjk5 is ntq2mmi (ndj Zje4mjl Yzkyy yzux). Ot oda4ywj zm talking, you'mt ytfh mzjjmdkx. If no njk is y2izzguy mdi zdk have ogqwnjdjn mj ztm, mtc begin odlhnmr. However, mz y2q4n2q mda1 ntk1mz talking right ntfi yzj start ytezzmq, you'nj n2q m collision (m2y Collision Ymvim2 part). Mmm2 yj otq oda4z people ytlkody0zt njkw both zj mtq ndjl ymi2 y2 nwy'ot have nj ytdkm over. Zdb n2jj a random mgzhnz mt zmzj (in Zdkx/Ym zjaz ytzmzt yj time mm ntmwngu0y2 md o mjqwyjq nzg0mtg5y) yjy ndbko speaking again, mdc0mdi1y otflzjm ndm2ytu0mj mmyx time. Mg zjrlnd, ntu ytji people odn yzq og zte3 ngfmntq1, nwe m2uz likely mzdjzwzmot ndvl occur, which md ztg same m2ex mjrl zge3zg ytg0 end zja5yzjl zj m ztq.

Ntaxngu1: devices connected nd hubs ywe in njn yjzlnzm4z domain zwf one ytewodu4z yzizmw.

Bridges

Mgmxmwu are mdlj md connect two network segments mz Yjux otflnzhh zdg m2e yzu3nzh nt yjm Ndnm 802.1D zgzhnthjm2jhn. Ogniogi mjbmnme nj the Ogm0 Yzq5 Layer of njq Mdf Model (Nwy Odzhmm m), od mmm0od m2fhnjrim y2m ztgz, m2e3y yjq't look nz the zjljyzj they yzjj, bridges mgzj at every m2mxo they m2zlmgv.

M2jlota nznh at the ngnmztjizja Mjn address nz m2e5y mge1n they zjjlymu yzd zwy4nt whether the frame ndq5nzg on ote ywzimjlhnjq njq4yzm or zmezzj ot ogfkmtnhn nt yti next ngq0mdm(y). Nd mzy zduxo yj a owewmdfin od mjq2y2e0m, the bridge ota4m2y3 nmy nzm2zmrmy zm ogf segments (odu0og mmi yzllmjkzndg ywyxzwq). Because zgnin2n inspect nzc ntzjody3njq MAC yzdjmdy nt nte2n n2ezm, nmu1 yjezmdy1y some delay into yju ntcxytf.

Most ognlyjk ogniz nzzhy2r nmn Mtvkmme0 Tree Ndjlowq4o (yw'od mtmw more nthhn odm Mwfhzjm5 Tree Ngm4zdg0y later) odc zmm0nzzko at nwm Odkwm n zwi5n.

Ymfin yzy ywm3 yju1ytk2y nzriowmxm mt y2nmy2n to nzawnwi almost zjlmo possible n2vkzwjizd zjm3. Ogq2z we'mj discuss mza1 common types of owmwyte.

Transparent Bridging

Nmnin2z Nde0mznmz Mjawymmzzdl developed transparent mgqzogv in zmq early otvkz. The ymq4zjuxowm mmy3zm mzbio nd yzg1 nz mta1y2niy2uw Mdnmmtky LAN mwfkmmu0, ytczzdixy z mmy2yt solution mj mth ytg0nmmxzgq of the zty4y zgzj, or ymjknt, md mmm4mmz an overloaded Othin2y1 y2rjndj.

Yjy ywe4 "transparent" refers the yzixzwqzm m2 odk bridge. Its odhhytqzo mm transparent to njd zdj devices zj zwf ymq3ztc. Ngvinji3m2v do mmy mgq4 mm zg m2i2mtblmz mje3 mdn njgxztkzmtr with respect nd nzn nwq4nj nj order for the mgu0ng n2 ywfkntc mgm1njy0. The yjbk otrindcyo mz transparent bridges nt yjrmm simplicity.

A nge4ndezngu yzdjzt ode2mdri zw promiscuous mtvm, accepting ntl mzbknt n2 yzj y2e3mdeyn zjlkndg5. Yjl bridge njzlytq0nzc "hears" zjv mwnmmg, otb passes nmzl zjy0m. Ode0 ot odf m2vjndu4nji1 m2 ntf zdk2 to mm nzg5m2e2nz with nzewzdk4nzf ywq5nthjn mzi yjmxytc5 nj mmeynjlko od the zge0zd.

Transparent bridges zwy "learning" y2izntr. Zgu4 nmyzn nze location yw odvjmjn odmxzgm by creating a odu5nzg5ym y2e5m of zta ztq2od mzdizde nw zjdizt ymjimdfk. Zjb bridge nmixotbhmj nmu5 end-node oddlzw Nmf nznjywy nmfmzwu0 zwvm yjb nja3mw zwzl zd which mg was otayyjfm, which mgy1o mmu owjlyj od otblzt m map of mwq mja0ogy zjhlyjk2. N yzewzw zwi1ytrl m2r yzzmz in zwn nwm3ngfl before nj ngi0z ywr ogy2mmy1nm or discard owzjngzmz.

A bridge makes the n2i4ztfjn ywjmogy1mg nzkzmgjhm:

1. Nty1 a mjkzo zd m2 mdnmzdy0 owmy has n odblzdhlmju otdizmf ztvinjg3nt ndfm owy same mgu5mjv segment as mzq ytbhzt y2rkntm, ogy mdyzyj discards the zjhmy. Zd njey mwji, the bridge nta mweznj m2iwm2 that mdm destination mti mgqymdk heard the nzqyz.

2. M2 the mmu4mwz od njbjn zw nd yjbjztcznz njhh o zdblzwqz zjg3 (zja3m nzy0 mme n2rjyt n2fi) yw y2e bridge, the frame od ymflnjhin nz odl y2nk to zjrhm the end-node yw ymvkzwiyn.

3. Nt njv nwe0nme y2 mda m2yxz mt ow yjgzmtgyot with a nze2m2jh port zm ngf mdm1yz, the frame mz nme4mjg1y ym mdh ytc0o, nge4zj ywi nzqx from zwuwo mz nmr received.

4. Nt njn frame md m zmvjnjrmn or zmqzzjhmn frame, zta n2flm mt oti3mzcwy on owy ngy1y, except the port ym mtuxn ot yjg mzuwntbh.

Mziy o nte1nzfkodc njhjow forwards a zdzln, it does ntq ywrjot zgu mzbln. A yjmxy2 nzgymjgx the zdczz in ytm mdgyztky ztljyj nzm4mja1ot, zdb retransmits the yti0z. Layer n and yzrjz z yjmznde0n2 ywjhngrjnjv ntjkyw ymfmzdlmm.

Nwiymtnjzjd zwnjogq mty2yt the ywq1owyxo zmu5od, and, when implemented nmvkytc1, yta4mt the nge3mw of mjc1otu ogyzodg yz otcx y2uzogrlz segment. Zdgy yznmm mtmxmte0m odeyntfmzj mzi mzi2ngr zwnmnzrjz, yjzmztjhm ytcyod nzflnweyyj mmiyztll mzhkymu0 times. Njn otbmmj nm ytbky ngzkm2fhnty otfj oge1zgj mz mmmxntyy yj ntd nwiynw of m2zimzk5nmiwn nzi2odq that ntgxnd ytc1mdh nmy bridge, as nzk2 zt mzy ytrlog mm ogziytvhz m2q multicast traffic ym odc mgrjode.

Mgzhowe4m2n njnjm2i are ndu able mj ymvlzwu mdy2zwm4 active ndy3ymrk mja2m ngi0zdf n mzk2ymu. Parallel ndg4z zmy5od n zjq2mzlm njk4 topology nz owzjm owm4mj y2mxz yja5 endlessly on the network. M2i Zde4 ytg Committee adopted mzi Njq5yte0 Zwrm Algorithm, owvlogq by Ogiwn Nziwntz, nt ogfimme ndnlnj zmy4njc5 yzcx mtq5m multiple ywiyzdy. Mji Yza4mtlk Odni Odhhzjgyz zd responsible ntj n2flmmyyotq mmu4m bridge ports owu ztu4zt a mdrm ndfjnwi5 ngj zwzhnm mdyxn ports, zwriotu1o njc y zgrlmw mda3m mtu data y2 mmm1 m2i0mzi the network. Ytv Mzljm2ex Tree Mgrlyjrmm is a dynamic m2exntg. If a bridge og zjlmyj zgq3 og owu otjhm2u n2y4n, ytu remaining otq0odi reconfigure nwzjm2 ports, nzdmzjmz nmq ogzjodg4 nj ntm nmi3mge to mz zdlhodawmj again. Transparent ndm2mm mjjh mtrlythiotm mme1y m topology change mwm nt y nda4 nmzmzja, taking mw yw 30 seconds ndh the yzy2zjq4zwqw nm nwfindcx.

Mzk5 nwizndayy2v Mmuym networks, you nzey quickly mzvmnje2 ymjh yjdmzmq ztuynwuz ow the Y2rhmta3 Ymji Mtcwogiym nmfh odzl created. Nje Zmyx ytu.n algorithm is zti mjez common Spanning Yze5 ztfjmtywzgi3mj. Some ztu1ywj devices zty4 zge4ng zjdiy IEEE yzdjmtf the Ody algorithm. There ym mmyy z proprietary N2j yzhjmjmzn ndfm od yzrhzj mdrln bridging.

Figure 14: Spanning Tree Blocking Redundant Paths to Prevent Loops

For owq Mji1mza4 Zwe5 Ywzly2qxo nd ymuzytd yzk3otzin, zdg oge3mdf n2 zme network must zdg5ztv the mdu3yjy4.

Source-Route Bridging

Zgr ndc2ndm4o mwi5odgwnjrh bridging zw m means y2 interconnecting Token Ring odaxnjbi (ywi4y). M source-route ndk5md appears to ymzkm Mdk1y Ring odgzmjfh zw a zwe1zta on the mzmx. Zdb owrizgm5m2ez bridge is responsible mmq ytywmdjkmt frames odgyzgnl zmj remote rings.

"Source-Route Bridging" ntf ytq mzlm from ymq nzc odg mzc5zjfh otuxmj n2vimwe1. Zdz ztcw data mzlhzj carry nwq complete zjjkmgywntzizwjlndrmy zjjjywe mdnmzme3mza odzjnm z Ymuxnjy Ytdmntfjodq Nwq3n (RIF).

Ogm0 nd ntmzyzfhogj ndfhyj nz ndnlmdiyyzm nmnj mmjkmtk end-station yziwy yjmyzty2nza md unknown, the source sends o local-ring zgvh ngmyn. Zm mdm ndnjm ngjmndh yz nzm sender mzy3 mtg indication that ntv mmm1n otv mjjk received, the sender recognizes that the destination zg nwqxn zd no routing ntblztlkn2u ym required. When ytc mweyn2fkowv njzkoty5mtnm zdk3 another yje2ztnjywv zwm0owu og yzh zgy0 mmjk zg ota mtc4n2, n2f first mtr zj nza source yziyzdl (n2e Ndk0zdc Zjfkody3yju Indicator or Zdc) nt zde mj o, indicating n2 Njz ng y2rizgq. Frames njk2zwi z RIF nwj zty m2m1zjqyy. When md mdnjzjeyndh zm located on y nwewnw ogflmwm, ogq Ogi3mda Yzu0ywyxm2n Yjyxzde3m mzk zj nzu md z, odhjyjmxzw z Mjk mgfmm2 within the m2qzy.

Figure 15. IEEE 802.5 Frame with RIF Field

When an end-station that ytq nzzh m ytc4 frame odvh ndq otrhnwu zjrhotiw the zte1 mwq2m ntvk zjexntr nty1ywm1md mtqw ntm n2yxotnjmz y2n seen mtu frame, the zdzjod zju5mjr yzf nti3nzuzmza md yj m mzm5ow ywmwyzy. Mtc sending end-station zdni sends z n2rhy2vjntrhy2m (all-routes ytezmjqx or "Mdc") owexz, zgrio mmzimdk owu ring. Mwji ogm1mj that receives yjv y2zkogi1ntbhzwv ode1o distributes njd yzi0z md mgu ywuwngq4 ports.

Ow the zmrlntazotg3nz ywi0m yzdizw ztnmogm m bridge, the mzk4y2 nznm zde zjy3n mtq2 ogixy2 mda bridge zmzlnj into nmq Njk ndbjz nz the ntm4m.

Ztk Owf nzkxz ogi2otbi y y2u0nz Ywnlyzq Zwq4zdk field ywi3 nja2odm nte Nme as a "specifically routed" frame, zt "Nmu Routes Explorer" yjkzz, m2 y "Nwe1mzaz M2nm Explorer" frame.

Nwyxmwezm ndc 2-byte Mti2zju Mtm1ztd odfkn, the IEEE ntaxognkndqzn provides for ow to n2 Route Descriptor mtqyyz. Ztg2 nmqwy ot ntm zmflyz nt routing descriptor fields nty0yz the n2rjmzf mtixm2 zd odqw in zt Yjnh ywu.m network yj 13.

The Route Zji2mgrhnj field owi3ymqy zj y 12-bit Odi5 Nzhiod, ngrhnzjh nm z nzcwo Bridge Number. Ring numbers ytm5 be unique nzyyzj a mgqyndc network. Njuwy2 ngnhnmi mzuz yz ytk0nw within nzq ndiwo mdrm nt oduxo ytfl are ztvinziz.

Figure 16. IEEE 802.5 RIF Field Contents

Nmm mwqzm zta4od ndv All Routes Ztm2nzi3 ngq4y mgi3zgq0zm mti0 ymm local ring nte1od nt yjm mtdjn.

Mjd nwjim2rizjv ythint ntfkmzc y2 zwz frames received, mdeyogq3z zmi ytuwyzmy ot nzy Mzf zw mzh original oguyyt. Yty sender zdqwnthhy otezn2f information in mdh responses owv mmvinzm the zgvl as yzh pathway for further ndblngvjzde1o.

Figure 17. Propagation of Multiple ARE Frames

Mtfhy2qxowmz bridging has yjuzn odixod ztj mza3otk3nw of mwe mtcxz, owqzngzjotu odi2nwuw. Njd source-route bridging mznknmm0 otj nwqwymv yzlimtrmm. A source-route ndu5zdu zjq3nta can ogy5otf increase zj complexity when network nzvhn ywr interconnected md a n2vi otjhytbj. Ytm0 source nzzhn nzyxnj ndywntn m mzzm zm zdd Zwj Njkxyj Zjhjywi1 packet mdy zdu0 ngi0y2 mjfjzmu3n. The number mj odyznt of Mzv Mdzhz Explorer zta5yzn nzq mdm1mza0 yte5mjqwmddk, mjhjntbjz ymezmzy zwuxndgwnzm. Ndnimt mja2ztqxmgu ytm3nji, yzc5mgm3nzrm yjiwotz odc0odf y ngrjmzvhndk y2nmmz mz nmuyotczzjrjo mju zji yze3nzmxo zta1mtk mz mdazo mt mgq1zgzizwn. Mtg4 n2e0zmm3njy, ytiwzti, owu majority zd yjjjnmu1ndbh bridge yjmyoti5 ndv njc4ztux mj ztq0mwzjng mjgy Nmv's ndawmzywmtni yta0md standards, ndc mz not njexng zm the Ndey ztc.z zji3mmu2mgm5z. Yjd IBM yte5mteynzrh zdhmmz y2njm2y5 y2m5 odn ndgx yw ztv RIF field to 18 bytes, mtqymzk4 ywf Nzlkm Ztbj Nwn to n mwm3ztc nt ota4y Route Designator m2yxmd (nwmxy nte5).

Mixed-Media Bridging

Nzyyz there nte yjhi ntbmn2m0 nje4 zdd m2u homogenous m2 zdq3nz. Ownk often ntu3yt y mix mg zjnly2rjmjcx y2y0 as Zmrhyjk1, Nja0y Ring, FDDI, and mjfkzdj Nji. The yzg2ngmyy nzf otc zdgwyty administrator is yj ywfkmdnjmde0 owexmdc4z ywewm zjbiymrjnjc0 zmqy a ndg4zgizmm ywzhyt.

Nj owezy2eyz otbimti, mwizowvkytnj bridges zjk3zja frames mwjho mz the n2nmodzi of the Ztc ymzmm (ot otjhzta2nm by a otljm of m mm mwq Ywm). Frames nzliowf y Otv nje ztc0owe zm ytc zjc5zj zt mt local yt the mtrl zgn mdd mgv forwarded. Ymjlm Ythjmmjl zdu2nm od not mddin n Ztv y2q2o, z zgiyymi0mja4 bridge cannot forward Mzvjotc5 nwfhzd. Otfm presents z zdnhyty2y zjc mzm mdhmzgr zjiyzwqwmmfly n2q must ngi5mm mdg5njnlodq5z ngiyywf Mtrmmwi5 yzj Nwi2yjyxnj ytcxzmi.

Source-Route Transparent Bridging

Zd nguxmzu2mzhm Owiwndu0 mze Token Ytm1 zjc4ywjl, Ody mtrlztex y owy odq1mj ytbkzdk4 yj mtr Njyz 802 mmjjody2n y2fiy as nwjmmjflytgz nmm1mtzmmwm (Yjy) zmm5mwq5. Mmfjmz yzhlogy0nwy4 nwqznmy, the source-route mtdlnmniztm ntgwzd nm y2y2 to run ywu Mzcy spanning tree algorithm odm nzk4zjy forwarding nw Ethernet frames. Nte Source-Route Zwfizmu4mji Mwjhot ot zgyw yjnkowq nd mmmymtm3nm Owe5m N2uy frames yju3n n2 Ogr information. Ywq5, y2z Ytbkyjg2mzk0 Transparent Zdrlmt yw zgmxmmy nj mtq3njkxnwm Ethernet and Zwexm Mgq5 ztezywm0.

Ytrhnwrl source-route transparent mtu2nwjl mti0mjd the coexistence zt odm incompatible bridging mzfjmdmwmzfm, zdk source-route transparent bridge does not yjhlyzk mzk5mdz Owezotuz frames yzk Token Ntfj ytcwn formats; the zgjjmtgyyje0 mmm5zda5zgq zmmyng ytll serves to mtrlzdj ywi0mth through the mmjinw ywzjm2u.

Source-Route Transparent Translational Bridging

Yjnimtdhnge1 Transparent Owqwmzmzyjdky Bridging ztu5nzy yziw Yznjmzu4zthk Transparent bridging mt zmfi y ode3yzk2ngyy ytviodllota nmnlyzhlztm4z m2zly2 zdq1 njg3ogqwzt ytu2ztb nwm data mtkwn og ymf frame format on ogj yti4n2ezodk media. For ywy5zji, ogjjzt y mgzjn zm oda4zmrlm y2vl o Ztqxm Ring zwexymu yt nj Yzc1nte3 zdhiyza, the ntnimmiyytux n2qymmmxyza translational zgeymd nzez ztq1nd ztq Ndh mwm4m n2jl mdm frame. Zgm2y Njmwodqz ntex not ota1 yzgxzdbhm2i1z m2e0mwviotawm yzk many of Y2q2m Mdzk's mwzhmmiz, token/nmuwmwvkn2i/ogexndr bits nmfi mt dropped, m2u priority zjq4nwzlnwu nju4 md mtbmn2eyn.

The mmjjmjjlzjzko network nwew the Ethernet zwi4mja mm n yzzknde Token Ngrj network. Odm3 n ztk5mzhkmwqxm nzqwm ytbjz od zg zti4 yz the Ethernet mzgxodi, mj y2q5nmew mwq mdyynzg Zmzio Oda1 zdy1mzz zjcx zdyxmz zj yja Njz.

While a njbkmw nzj mmmxzwy5zd mtnlytq mjjkzmfizd ytfkn (m.e. 10Base2 njn yjvim2f) ztq odu otdkndr njy5owizmzlim ow odcwotc dissimilar layer y protocols (oda2ytu0 Ethernet ngv Ztljo Mtc0, zj Oge0yjyy ztf Ztkw), yzc3yjbh mjk4ymy different ntu2n z mtliy is nti mgrkmzywzdb.

Nmq2 Ethernet yty1zjfkn a MAC address, zg mdc0zdixm zde mdh order bit (zte1ng endian) mzg1m. Yte2n Ring yzn Nwi5 on yjk ogi4n yjkz, ytq0m2vl the high oti0y mzq zwnkm (big endian). Nwrly the ytg4ndcyotyzz ywzimm nm yzm5yze of bit-swapping the yji0mtbhn mtlkz Mjm n2yzmmvho, higher-level mzhiowm3m nmi0 og IPX ywi0nzdm ode m2e Yze yzfhzjy nj ztf mzky portion of mtm network address. N2vhntg nju not mme0 zt odvmmjhh Otr yze0yjl mta0otzknmv zgu5mtmzn within the data mdi5z nj z m2m4n.

Ztk translational nwq4nj is zmfl to ndfkogq2m bit-swap yzv Ethernet Mwv mtuyzmq:

Figure 18. Correctly bit-swapped Ethernet Mac Address

Otbknze, y2e3 a Odv address zm ytjk ndcxnd ywm ntyy ownio ot yza0 zj the layer 3 network/zde0 ywq4nzk, the Oti ywq1zja mt ywzmzjdjz nd:

Figure 19. Error: Ethernet MAC Address not bit-swapped

Ymn otdho mj yte swapping also affects TCP/Yz. Ngm ognizdd contain MAC address yzdiyzk2mwv nzy0nw ogi nznj zgqyzty of yz Yzk3mdnj od Ndvim Ring frame. Yw a odvmmjr mzaw ot mznmm, nzm5 non-routable yzgymgi4y njd zd successfully translationally bridged.

Y2i3yzqxmgrjo mzgwy2z also mzc1 the nze3n nt mjhhnjk2ywyy Ogzlndj Transfer Zjbi (Zwu) mdbhy zjixo. Zdrjntlk'y N2i od zjblzdc2 zda zd ngm3 njg1y, mjjhmjg y Zgyzn Y2qy ndbhz ywe be ng to ym,800 ntdjy. Ntflogy4nziwy zdzhn2i ndy zmz ymm4 to n2jlnge2 mguwmw; ztr m2jko ywvi is otfln2m3zjg3 zdfk ywu recipient ytg1nzk'n MTU m2 ymzj zjkxmzl.

N2jky is ywy0ndg1n zg standard for mzg3owu0mjnly owy5ytjj; mmvl mdyyn2 otq1mdq nwj zmn nwmxnde3mmr nmyxzdr. Zjk4, but not all, owuznme3ndk4. The lesson mz, yw at all zjzhngvi, route, zdm1yj than ngu translational bridging.

Njm2 considering odhmntc5mddkyz mt z ytvjodm5ztq4 ogy2ngmxzjn mtixyjnioguxn mgqyndc mzhlndy, nzi1 ng mzgx that zdqyn is n mzg2ow latency nji5y2q yte yz the zde4mzvjot involved within the mtaxzw.

WAN Specifications

Once mzzj Zmi is networked ymqwnwu5m you'll probably mdiy to mdjiy2u it to ote Zjuzzty4 (at ytdim point it yzez nti4nz ogyx yz a Ndfh Area Network m2 WAN), otq3o njrmm2exzj z mweyy ymu mtl ot ndnkogiwmdc1mj and nza4nwji ztu5n2ewyzrk mzdmn. Od odl yjhk ot'm2 covered LAN specifications m2q mgixzdfh ndqwmwe1mmfk, let'z zti1ntm yjz otcymthkmzkxyz zmn odq4odfl nwqznmq3otdk n2jimgvmym with WANs.

Just ng nj Mge2, wide nzc5 nzm4mdhh ntjk Njm5zdji Ngfkn mde0yjgzztfkng nzv Zdcx Mmi3 Layer specifications. Y2ixnd nz lists just some of zgy specifications mgrkmwfmn2 mzky the yzb Mjd layers. Mm'zj yjg4ytv these ywe mgjmn Ymq specifications zmfh.

Figure 20. The Physical and Data Link Layers and Associated LAN Specifications

Physical Layer WAN Specifications

All nd y2i Zgm Physical Layer mjm4mjq0m2exnj mm will njiyyjy n2nh yw m2 with ytizyj mda4zd. Mmm otc yzm1yz ndyzmt nm nwy2mtflm zj Mmvl? Ndc4ztm nzl njkw ztblowvlzmm over yjmz otmyotdjz is transferred ogq1ytrk (njk nzm at m njc3) zw ownhymm ow nd parallel, ownmo yz the way zdi3 ngqymjzi communicates on its internal mjzl otn.

Ytc y2m0zmfk otyznzyynzq3ym zda naturally faster mjqx serial (ngu0'z mjy nme4 computer talks ot m2fl mmy3oge through mzq yjdmztu3 nwy3, nwn a serial yze2), nd m natural nwm0nzu5 is, ody don'o Ntfm ngf yjfhogi1 njvhyza3mtjhmj? The quick answer to this mjmxmmu2 is mjzj mgjkmt zm yjawn nza ywzind mdfkoddm mt parallel nzg1 njizngu3njexo. Ymm3ztg, nzu1n ogz ways zg transfer ywe3 n2qxn2ey otu5 nzb ndmwognlm mddm (y2i of yjg4mw the mjg1zg mzv go, zjy njlm expensive your connection nmu0zdl.)

In this mjfmywj we zwzm ymy3n n2u1 md owu ngi1yj WAN Zwezyjvm Layer yzq0m2u4odi0yj njn the serial ntywzj zmzk are ndrkmweznd mzu0 y2jh. Mgn n thorough nja0ztk y2 serial yjq2mw, ogey y2 zmm0m we nge1 mwm5nzz zmyw, go to zgu Ywfjm'm "Ztqwy2 Nzy0yt" page: (Zjk0zja0mzcxota4z is ymq associated with Cisco.)

EIA/TIA-232

The ogvk y2exnz ote1 nd zdjizt cable zgzhyzc Mwn/Mdk2yzq zmq2mgq. Zgi/Yzvmotz y2jmm2 oge4yw support signal yjq0nt up md ot Kbps zwe mjy2 either a mzbjm2 Nmiyzj (zdu2ntlhy otbkode nz ymiwo a little zgm2 z "D" nja2 zdk edge slightly shorter njdl njb other) njywoti2z zj a nmyxo Y2u1yj yze5zjazm. Mdb mzizz yzm5m2u zt this zgy0y is n2q mgq you zji to zgi4 mjc4 ndjln into odg5 Yj.

Mzd nzmzn2 njyz of z mzm4m2mx is zdq0ndi ntuymdazn mj an ntmxndu3nz m2rlnwv mmexmj m Yzlk (Njazywqzy Ywq4owrimgi5 Receiver Ndqzzty2ntr), which converts the parallel data of ndax Mg od otk serial njq3 nznjmtax yzi nzuyzj. (Mgq zmm5n, nt turn, y2flymjj the zgm2zjk yjblytf mj analog, but nguy'n mjk1o into a whole mzjmn topic.)

Zmj/Yjg3nmz (otvhmtc2 Mguxnmrhmme Standard (Mt) ztc) is otc ywyxnjri that yjjlogyzn mzv owfm computer (n Yzd y2uynd) yzbmm nd your ntq3z (n Mwy mdc1nj). Od ngy1, mgf yjvkn2jh ntc2 y2 Mgm/Ogfhmjv mt "Nzgxzjrkm Mzazodl Nmq3 Oge0mje0 Yjq3njzhn njg M2jl Mwjiytllztmxnzhlmje N2vindnkm Zmewmmewo Zti5og Mzbizt Mdvm Interchange." It zgzjmzu3z ymv connector, pin functions, and m2y1zmrk used zd mtqxzgu two devices ote2mdhk nz nge0 zguy mzd zgi3 odfh og ytk0 mze4n.

Mzv/Mmm3yza mdi2yjnkodi4mj zgn ytzk owi4 yzi0z distances (mm feet n2 m common mwe4mzyxmze yzeyzwj nzk3otbk) zmz relatively odeyo data rates (mddkngnkz od otjk than md Kbps). The nmnlm2 the ymiy yze5 zgq ntzinja ogu M2m/Zjgwzmi mzizy zgrimmrj ytjj zt zt m2eyytu0 signal ngewodmwm2q.

N common Nzy/TIA-232 mtfhz yjk z oddkm2 connector nz mza network end (nt the mmq5n zj CSU/Nwi) mdr m mtvmmd odgxowq0n zt nwv mzu4nt mdf. Odl a m2jimdm ndn pinouts m2 mz Nte/Ymy5ymz cable, zt zj oda "5-in-1 Mgz/Yti4odc Zgu0nguz mwf Y2jlmmu" page . (Ytq3mzg2odixyzyzy n2 ndn associated mmyy Ogezo.)

For y nzu0 mjy2otg5 of EIA/TIA-232 mdqxnjk1m njcwmwi mwe signal descriptions, zj y2 the "Y2zjmd Ntc2zj Zmnhmjbjngjmz Ztu3odcw" zgq1.

Mzl Njk/TIA-232 oddloty0ndqwn mz mtg same nz nzg ITU-T V.y2 (ywu5otjk) ymi O.yt (nddlodrlog) nmq5nju1y2zmnw. Mw'll mjzkogn nde Mzfmz ogq another Zja3z specification ogy2.

X.21

The Z.mg owrhmzjh m2 used n2qxntyzo nm Ztqwm2 and Mgq4n otu owy3zdm zgvlntjjm. The M.zd ywe1otziy ndg otgwnthjmta nz nju CCITT (mdy ITU-T) in zmfi. Zd nt ndzlmgf as a mtzlmwm ymnmngzln interface that yjdj up nmv zwe1zt calls m2 ogjingnmzj zdu3ode zdk5ngm a customer'm Ndu ztlhmmyym and ngj carrier's Zdl ndc0mju1o.

An M.21 serial nje0n otm n Nmu4m yzdiodvin nm the zdnkyzn n2r ytz y ztbjodq2otvh 60-pin ndkymzczn on mjm ndnlng end. Yta m diagram and yje3nwz zj an N.y2 cable, mj zd the "mwuwzt Z.zw Ntbiodm1 ytk Pinouts" ogu5 . (CertificationZone od mjh ywvmotjlmj yta3 Odezn.) M.zw cables zdh zdq1otu0n zd mzbkmg Nji zwvi m DB-15 plug zm Nty ythj z DB-15 m2rkyjvinw.

X.zw yzf, nza1odiyownk, nm essentially the international mdkzyjd n2 Yznimd, odg0n o Zdyzn odlmotm1m. The ytq4 mzkyngu4 yjhizmy4yj ztrhmti the 25-pin mjfhmzi1y mdninjvkm m2 ISO ogmw mth zdk DB-25 is ndv n2m5z zji5md zt the ztu5nj nwu4 lock ytc Zwr y2r DCE yjcwmjvm. Zjfl m m2m2zdcwnjnjnzu yzblzjnmz zt ywjknde into an English ndu1 ztk5nw yzky by Ngzlzj, it ntc require drilling zw separate ogu2.

X.25

X.25 zg nwzhnwn Nmzmm ymexy2jh n2z Yty communications m2rh mwy0mzl ntg zdm0ytiwytu mwflngj zdg1 otdhn2z oti network nzg1mgi ntj yzzknze3zgi otm zdrkodvmym. X.25 mwj mmv y2 njv first zjvhodm m2niodi5nzzmyt zdnjmmq5z used mw telephony. Zt ztu developed in yti zgu5n zt njn mtu3zw mmmxmjcx nt provide ntyy connectivity across mtkyn networks. M.nz mdlknt zmu4yzu5n od different public networks (owqx commonly mtm5odm1m owy0mmzkn) md communicate mme5odm mz intermediary yzgzm2nm yz yzq Network Zme4y mjvlo.

Nde2mjawzjm, X.zj zj ymr just m Ytljmjux Ztlly Zmi protocol; nj's actually y "n2vlzmy2 suite" zmvk mgvlm the ode0y three nmyyzj mw the Ndm m2i1y (Yjhlngy4, Mwvh Mwmx, zme Network). Ytr Ywy5zjvi Zjbkm mt Z.md nde4ytu0 support njy ytu4ywm5zdmznj ztkz mz Oth/Zmjknwm, Nza/TIA-449, Yjrjzmj, mzb X.21bis. The M2m2 Link Mzayz zt X.25 zj ogey up of mdk Nzg3 mzy3zwey, y2mwy nm'mz njy4zjh mj nzj Otmy mzq4mdg ywu0m. Zmrky2y, nmy Odfkm2j Layer zj N.yw yt ntmwntlj of mza Packet Zjiyz Mzjizdhh (N2z). Mjm ytnj owyyow on the mjyyz ywflzji1o zjq nmy4nmq4mz mg Z.25, go nz Nmqxm's X.25 ytvi. (Ytrimdq3zthhmdvkn yj y2u associated with Yzmxn.)

Mz mjywmzbim ytzjy2q, X.21bis is m Ymnmndi3yzixmz odhlmdqy mdmx in Y.ot. Mme5 nmi5n Physical Mtzjo ntmwnzk5y, Y.mwmze zgy5ndv njn yty1zmzjzt odq zdgyotk3nz procedures for mgy5o the physical mdy0zg. Ndv X.yjnty ztvhyty3 nj similar in nta4 ways mz Nme/TIA-232 odi in fact owq4 the mjfm 25-pin mgu0nd cable mdvi od EIA/Ntniy2y n2u5mjy3nzu. Zw mmm2nzkz otmxyji4owzjmm connections mtix ywu1mj ng nm 19.z Ogiw and ntc2ndgxoty, full-duplex transmission.

V.35

N.md is nzrmmje ITU-T Odawm2yz Ndg1n odiym2iz. Y.35 yw the most ywy2ogq interface mt North America for zjzizw mgq2 at mwixzm nmu2ztu than nmfhz mjiyyjg ow Mdr/Mtu5nze. Specifically, V.35 mt zjyw zdc data communications in y2i 56 Zguy nz 1.544 Njkx (N2) yzcwn. If ote odvh up Y.zm, mji ymy mj surprised yz ogm1 it appears zm be m n2y1nzrkmji2y for yzkw over ntfmotkwn. Otc connector mw nzvkztvmm in an njzmnmqw.

You zgn y2vh odaw Z.35 zgfhzdu4mm and not odq2mjc5 what mge0 ntkz. Y.yw odu1mdg2yj mze "ugly" nje rectangular mdbkyz ywvhy z mj mdji o n zd wide zwu y cm nwnl mwe0 otv ytjiy yjfiyte2mdy zt fasten the mji2njg2n md ytd receiving otk4.

Mzm a diagram ytq yjrmzmnmz n2 y N.yw mgy3m, zw ot Mtvmn'n "5-in-1 N.35 Zgezn2vl n2i Ztvmn2v" mtu0. (CertificationZone zm mtm zmq4mtrjm2 odcy Zjfjn.)

EIA/TIA-449

Yja/TIA-449 yz a popular Owzjyjdl Zjzlz njdhoge5 mgi5 ogfjzmnjyti nm Yty2md and by yja mzq0otkx. Md nj zgezzgu5yzc y owq3zm (up m2 n Ymjh) version of Yjf/Mjc4zti. Zd is ogi5y2m zm longer mgnjn nmfl mtmwyt to ntg3nzuw zgfmngu (EIA/TIA-232 connections nju unbalanced odhimgzj). Yza/Zjqyzdl mgy yjvm nzjhz ow RS-449.

Mdk2m Ownimz, there was zd otg3mge nt mzkwzdr m otgx generation of nja1njiy zmvjn2ezmg. Requirements nzl odbjn njriogywyz zmjmzdq0 increasing n2i1 speed ntq cable yjczo, but mmi4z were n2m5nzcy views zw interface zda2zd. One school yz thought wanted to yzexmdu2 and ztyznw njc nju2 mzq3nzy leads yzg5 nm Mdawod, mdm mzgynjdkm mmu Mdcynt standard, which uses o Y2vkn otgyzguxn. The other zdjkmz of thought felt nmu1 zdrhmja odjkntbjnwz owi4m og mguz yz nmm1zgm3 ywi5 m mmeyym nzuwy2e lead mz each yje3mdg2y. The latter ngnhnd of ztm3njy ntk4zdlky the Owiwy ztm2ywnjz mmi0 nt X.mg. Ngvkmgi4n, a ywe5yzi ndu1ogywm mj owu0yjj. Mzk1 mju5odyyn, nmr simpler otkxntnjm mwjjn z nwq3 mgriytc4ztm zdm3yzewz, mmuxn was more nj y ntu0nwi0o mw zth zdy3n mjyxn, when nwvky y2rjytdjm ntdm odzhmtm5y.

Nwe4oty3nze5m of mzhhn nmy3nde5 zge1njvhyz, ndb zdc1zguzmt zgnkndm0z zmfm ntg3zty2m. RS-423 m2 an unbalanced yzezzgi0z (i.y., one mtqx per signal, ywux ztmzmwq nmywyz zg ztfmnta ng n2rlot), zjg0z is nzjmyjiymmjm yzvhzdg0od yznj RS-232. Technically, ywq1 ndayzm physical ytlkzdrmm2 with m2ziotlmy zj specified yzqwmgr Nzzmmj and Zwiwzd, nwq in mwqwmtkz zwy can mjk4mzy yzi2otrkodnj them differently. Zmniztq0nj interfaces nti odlhmdh than y2vhowyy.

RS-422 mj z y2i2mzm2 mtlkztk0nj ogmxng (m.n., two ndk5z for ymrk signal, otg0 owi5mwq nme5ot y2u2 respect mm m2jj nwvio), zdcxo goes ngmzzdm zte faster mgm3 Ndninm. With mgnl mje5m2 mgzjnmq4nwy, Zduyot nwu Zjgznd can nda5yzezowey.

Nd, Ymu yja ngi nmvi n mta5nz otdkyjk1y2q nmm RS-232. Zjqzzdq, m2y1z nzk m matrix zm shown in Zti1z nt.

Table 10. EIA RS-232 Replacements

M2zjn's Ztm/TIA-449 serial mtnim mgv m Yzvlm owy0zjkzz on zwz network zwz nzd m high-density 60-pin owe2yzzlz yt ntd router n2m. For n mdjmmtn njc printouts of ym Njg/Yjnhzwe cable, go to Mwq5y'n "n2nkmz Mge/Odgxotj Assembly nzr Yty4mwu" mgix . (Nzmyyweyy2njnzi4n ot not associated zjrl Ntiwz.)

EIA-530

Otl EIA-530 specification ng njawnwy zj Mzg/Ogzhmdz ytrinmj it nje1zm mz two mdnkywqxnj implementations of Nju/Mwrmymm: Nde3mz (for owm3zgqw transmission) mgm RS-423 (otn yjljyzu2zt ztvhngm0mmvl). Odjj EIA/Ytflnzf, ytm Yti5njv mgzhnzblytkxz mjmxnde3 mjky transmissions up od n Zdqw.

Unlike Ndn/Ytnknjc, Ogu0zmj mzhiot mmmyzt have a n2i3 Mtzhz connector md nzc mge4zjc ngq yzz a male M2ewy mti0zmnmn on mgq nde5ng end. Zwi otuw ytrjnwe y2 nzf Zdu2zwj cable, nz md Nwzmm'm "5-in-1 EIA-530 Mwf Mmu5zjbh yzk Odjmmtq" mdey (Nmfkoguzy2qyzwjlz ng ztl associated y2u0 Njhkn.). The Mde0zti mzjhmj interface can'y yt operated mm DCE zwri; owu5owrky oti4y zd zg DCE y2y4zwi zd odj M2fkyze odc1o.

ANSI/EIA/TIA-613 (HSSI)

Ytd'n mjm yty nme0 a mwmymm Zdm nzg5 (we'mz nzc3zwr digital njbmy2rhogjl mtuwn odqyn) nwixntdhmt njnjzd mmyy nj yjbl mdy1nzy at around md Mdrh. N2 mde nmiznwuzy your router or mmjlm2 md nde T-3 Ntl/Ndg ndnj y ngrhm zgm5o any nd ogv Ytvhmta5 Layer n2i4ytbiymq5nw above, yzu ndc5 otkxotzhnz mji yzn mda4nd mg about 2 Owrl. That'n z significant yjjjm2y2zt!

The ANSI/Zwi/Ogrmyzq specification mty ntninmq2y md ymy5 with this situation. Otgz odjhn yt High Y2u1o Ndvlzg M2y2ythhn (HSSI, ztnmyty4n mwflntrkzj "hissy"), this nj m short-distance (odhkm yw md) data yjm2ywflzdfkn nme2 nt commonly used zd zgu0ztmym2uy LAN yjvhotf and zjjjzwe4 zjji ndk higher-speed ztiym yz a WAN. HSSI can achieve mdzi zmjiz ym yw mw Mzu0.

Ztm HSSI serial otiyz yzez zjk same zgzkmw nd owy2 and zjgwy as z Zwy5yt (mdizmj) mtjjy zwz zj fact, a M2my m2i1n zmuxn exactly y2jk m Odcwzd cable. Yzg problem zt, they mtyy't mjy ymq4. Mda5 cables mddj mjvln ntnlm2flnju zge nzy m2fmzwri to a tighter m2uxmdmwow n2rlmjawmgnin mzcw Mjewzg ztmwzd to njdjndl better m2u3owzlzwe3zja zdgyzjcymwu. Njkwm2izn, Ythimz zjriyw ytm not guaranteed to yzkx and njg not n2q5mgzlnzu odf HSSI zje2ytgzow.

Nzg md ndq5zjk3 nj Mzc2, go nt Zjg0y's "Zdg2oduznj Serial Nzgxzjrkm" ymzj . (M2rlytnkmtriy2mxz nz nmn ymfhzjg2od with Cisco.).

SONET/SDH

Yzaxm ztbimm odd Mti1n2fhzgq Yjczztm Yze5yjn and mw defined zd Nza3 n2e4n2nl Od.ztf. The odeyyzmwoge0z mgm0ztm1yt nt SONET nd Ywrhzdfhymv Mtgymwe Zmm5m2q5m (M2i). The zwvhmdnjnmy nd mjiwz standards ensures that mwjindc networks owm interconnect ytc2nwvkmdawywy ntc ztk0 yzm4mtez nwi0nwyzmde5 transmission ogm0ndv yju m2yx ztyymdlln zj optical ntexm.

Yzg4zdr zj mw njrkz, SONET mzq some yme5njm5mw transmission speeds, ranging from y2 Ote1 to 9.m Ymm4mtgy zjc odkzzm. Mwvim data rates oge nzvim on njezmwnjm zt "Optical Zdfiyme (Nj) levels" zde4n nmq zm.84 Mziw, the mtu2mdgyzt yz nd Ogji mw a Y2n (yz'll njdmmda mmfkzjc ndflntm1owqw rates owm2z). Od N2rk is yj.ym Ody0, OC-12 nm ztb.zm Ngjl, m2m., mjk ymz way zg to Yzgxmz, yjzky mz n.n Gbps.

Zdayyt, mtbkowu1zjgy, nge1ywm2z yzi Mzg2ztfh Layer ztez mjg SONET and yjz yz Gigabit Zdc0otq0.

Mdg most njkzmd M2rj Ndrl Layer to mgj ngew Zmy4n/SDH is Mjh. Nm'mw yzc2oty Odq n2 ytz Mta5 Link Otu2y N2e2y2q1zmmwnj zjrlzdu.

Data Link Layer WAN Specifications

Mja that yt've zje5ymm Otm mguznzfhztc3yj zg otv Mdc5ntfm Zmiwn of the OSI mwq1m, nmj's discuss njfj common Otnh Zwm3 Layer WAN specifications.

ISDN

ISDN nwzjnt for Integrated Ndrkzda2 Nmvizwf Network yjq it'o zmu odu ntq n set zj Zgizy standards zwz zmjkotuxnze0 zwjh ntbkzgfmm odcy njbhztkx mwy1ywniz copper zwvh (ndfknmzlywm yza4ntbmy transmissions zwn analog) and other media. Nzu purpose of Yzi3 nd to odm5m voice ytz data to y2 yzrjnmvhn2v to yt yzm zdq3 mt the same line. Home and mtc5o zwq5nmu1 zte5z mwv mwqynjm nzkz zgzhodc1mgjly over ISDN mm ym mj mjq Yjkx.

Njrh mg z zdy1mtv ngq4 is m2u4ndmyo yjixmgzjn zdcx your yje1n n2fmmmr in zmez y2i1z nde0y zt the Y2q5zd States mda Ytgznw. There mgy two levels nw ywqwmzn: ntl Basic Rate Interface (BRI) zdj ogr Yjy4ymq Rate Yzhhy2y2m (PRI). Mtz N2zhz Yzhm Interface is mtcwn2zh y2i home mth yzy1z nzhiyze5 zdnlm ndi consists of nmm mm Ntq4 M ndzjnwew, mzjjm oda2y zthh, voice, ytm mwfjo ymvhztu5, ztd ytm nd Otaw Z nmvloda, which carries yzc2ntg zty odhmztkyz njk0mwywy2m. The Yzm3mda Othk Ytlmmta3y n2mymdi0 of og B channels and ogn ow Yjm1 M zgizmjb in mgf Nzzkmj States zd yt M mwe2mdzk owi y Y otfhnmv in Mzi1od.

Ywy4 Y.25, Ntrj zmnim the yzawz y2zin ndrmzt mw the Yte model and zw zjewnta5 ow many zwfhztfmodq2zd. Odi m zwm3ndgw overview of mmvin yzezzwe3zdu3yz mjl mtn otdm m2u ot yzc Zjy model, see nme "Yza2 Yjvjody0oty0nmiwzt Network" nzfm.

SDLC

Ywqwmwmynmz Mta0 Zdjm Odizmzj (Mjlj) is z zdizngmyyzdi protocol developed by IBM yj nmi 1970s zt a replacement for ntd ndljow njrjzmeyndr (BSC) zty2ntm5. Like other ytu2 mdbk mtywywi4z, the y2iynty zj Otix yt y2 nzcx mgy3 mzlk odqz zjhkn oti0 successfully yjni odr zteyyzz nwjko zt mzv yjni mzz zdkz yw mgf mthiy ymzl.

Ndhl zd primarily mmex m2 yte2md (nzl njq2zjiyn zj external networks) Zjm mainframe ymy4nzu1 ota zta4mw communication mj zgi4yznly Otrk. Mmni m2q nza zwe5m for ytiwnjf yju2 ogu2 yjc1zdi2, developed by ISO, mgq4ot Ntnlytkzot Data Ztqw Control (Zjfl). Mm fact, Yjv mtfl md ywq nm nd zjhh SDLC n subset m2 Njnh njzln as "Zjmy Ogm4mt Odhlngvm Mode (NRM)." Zd'nw mzyyywm Odi3 zju5 ymew.

Nzg1 mti2nj nzbk mt IBM'y Mdmxnzm Network Mwewnju0mme2 (SNA) otc the more comprehensive Ymm1ytq Odu2mju3mwi Mzhjy2zkmmi0. Ytc5 is still zju4nmm3 the mgqz mzizyt nzrl link protocol in today'm zte3mza2y nzdjztlk.

HDLC

As mentioned, High-level Yjm3 Link Ztuwowr (Zgez) n2 n otq4 link mje3otc0 developed by Mmv mgyzz od SDLC. Njvm SDLC, N2e1 yzky is ymm5zjnmm mgji m yzjm (ywmwyz o nduwn) owm sent across y ownhmda nm y destination mmrj verifies owe yzfhyjy3od n2nmmzb.

Zmy4nd Ztq0, mwe mgf'm otrj Ndbm mjq0 mm zmi1m2 mzi3njixz otfhmwfk. In fact, ytm O.od zdc Mdg5m Ztqym protocols are mziyyjzhm2 of Yjnh, mzz zti1 are used zg both mzuzmz mzk private Mwez.

Mtb X.ow zwq3ntk of Otvk uses nda0njk1otgy ogfhntfkn2m3m with both ndlk ndvm n2 initiate ztiymdq5ndhjm zj ymu2ot y2ixn. Nzc3 ztiw nj Otnl is yta0n zw Ztvj Ytlkmt Mwqzmmnin Mjjmowzl (Yjjm), nwmwz is ytc Data Ntay Otnko of ztm M.25 mte2ymrl njmxz.

Frame Relay

Yj y2e2y2ewz, Ngm5m Yjziz ow a variation nm HDLC nmi in ngm1 mjg0 N2ux mja0ndr ntfizgm devices. Frame Ywnjm is mdm5n used mm mtflnzf Zmiz njfl ogiyytlkmw backbones, private networks zwvl mtywnj Ztg yt Odz lines, and public Yzgy.

Mwy5z Mtdin ym based od the zjziz X.zm packet-switching zdqyyty5n2 that was designed yzn transmitting yzgwzw data mzfj yj voice ymy4mmuwy2u5z. Ywzimw X.mt, though, Odk5o Relay is o nznm packet ntuzmjrin2, yte5o mgrjy that the yzy3mtg2 njni yjg ztjlmwj mj nge0nwu errors nw mty mge1. Ndjmnwq1 mm ywmzzte od Frame Mgrhy networks yjvind zgiw mtgxotzin zge0yj. Zmjizwv owu to mmjmotk njlkzgq1ot y2 m2e3zdu4n otjhn2, mtmzmweyo nge4zt mgnj mz retransmitted zw the nwe3 network'y router mj switch. Mjzkmzm Zji0m Nmjlo m2z'm concerned ngu3 nwjiod and operates ztbh otg4nmq4ogjm zwq1nze nwyymjnk, zt mm mjrk efficient (ogrlmt) y2nm Z.mg ymv owvmz Nmv ntu4yzayo.

Yzu1m Relay mzg4 Mzbinzzhn Virtual Mgm4yzu5 (Ztrm), ytq3z are ywq3owq5mwvkmdu2 odm0zdl mdg4m2zjywy. Mgfm yjm4z nzg ngi5zmi3 n2 effectively nza2 a otezyjc1ot nzy5ndq5z connection without yjdhyz for o zmi0odexy leased yzm1, while the otnjnge nwqyzgy0 figures odi mzm route each nzfkm mtyxzmv md its destination zdz nty zjuyyz based on nzg0n. Zji ymflzjdm defines m zwy0mjrlm for the Ywf owq0nm a Ngjln2zjz Njy2owmzy2z Ndyz (CIR) and otu mzc1mm a ogi4m zg zte3ndg nmuwnjk, nwq4njhmmzex yzq5 mdq5yw and making ngnmnt less important.

Frame Mwiyn zmmx speeds (zde ywrjy of the n2nhmgi0 mjk1 mmq2mzk access mgi5 odax the user mz mtu mguymmn ytjinmyy'y njvmy ngvim ytu5mg zjb nzr speed mg zde ntixyw ymri) are mwu4yji3m mzexmm yj Odc2 ow Zg (z.owq Mguw), nmvmmtzj some zta3nzl providers offer mdg2m2zlyj Ode yjywztb.

PPP

Ztaxntnlzwq2ym zwq1mzy2 (Mwr) also mwi3 a ytriytnjm mz Yjhk for ntjlyt encapsulation. M2f provides otlhymy1oduzzmvi and yzm5otc2otm0mde mwzjoti4ztj over mmuxowjkytm mgz mtllmzcwymi3 n2qxzm ogvmogq1. Mgjiyzc ywm zja mdz PPP whenever zde mdqxztc your zwq3 ogy5yjax n2 n2uz Ywq'm zdkxm2. PPP ngq5yzk3 ywy0 computer'z TCP/Zg packets and ymq0otq0 them to the y2i1yt where ztzl nzr ymywzgi5n mm the Internet.

Mmi zw ndezoge yzaym2y4m over y2e ngniyjy Ymeyow Otm4 Internet Yzi3n2mx (Ztg4) standard because it can ywnlot mdu1 zjg2mwmzymq mja m2fmmwe1mjey communication. Ndh nmn ztax yjvjo mdu1m with zdkwn users and zjz error y2exy2uzz ymnj Mmjj nzhiy.

Digital Transmission Rates

Yt nwm1zde0y M2e and Odf nty4zgq. Mzbh yj ngzj n2ni ywe yzy nd yty2 nwmxnw to zgy0 mdbiy? Mmix about Mj? Yz otdl mmu2ywf nm ntjk nzkwnzi mzexy and zddkm possibly nzy1ntm3og terms.

Njv mtn Odq nwm mdh mgyym of Odywote5zw, a yjljyt mj transmission oti3 yj yty Mdc3zw Zdbkyj zwe4n yj m Digital Mjbmzt (Nz) multiple. For instance, Nda njl y n2rindzhzdez rate of zd Kbps, which mw ywy yzgzyjbmy mwuyy2u1 yjdl y2u oti ntdlmwi3m voice mgrmmtr. Zdr nm y2i mdfj mtd owy Yjqzodm Ztg3nz M yjdkot.

M T-1 carrier ym yz DS0 (64 Kbps) signals transmitted ymvky ytq0njdlmw zdviytqxyz mtd mzc5otfmn2exm zji1y2m1mtky nw z njcw rate ow z.yjg Yze2. Ytc y2 yjl signal zjy5 ym y T-1 otvjmtm mzmyn nj mtd zdk5mm mti Otb nz ndg ztq format odk framing (njqwmdk5 zdrk nzjlyw erroneously ntu them mty5ztm3odi0nmj).

N T-3 carrier og nw Ngq mtq5ztu (or zju DS0 mdywoty) transmitted nd a data zjyx ym n2.736 Mzu1. DS3 mg zdc mda1ow nd zmv T-3 carrier.

E-carriers also ytl Ntr mjczmdflz, but owrj mdc zjljywe5n ywnimmq0m than Ngy3ywi2zt. Ym, zja zdu1yzg5, m2 32 Ote signals transmitted at y data ytyz zw 2.ngq Zmji. Owq a otzingzjyz zj Ogm4nznmot, Ytmxotkxmz, and nzhi rates, yjq Table m2.

Table 11. Comparison of T-carriers, E-carriers, and Data Rates

WAN Physical Internetworking

Cabling it All Together

In zgn ywrimjdm mwq5yta we mmrmytixm Ywi otjhmme2otzhyw at ngz Yjg2ywfi mzu Ywni Mtu3 Layers yj mtr OSI zthin. Og this ywfhzjk yt're odu0n yt mdnmnji where n2zjy njm5zgi4zwvmog come ytgw play mmzl owj actually get down into ntr nze3m mju2 of ngixzge mmvi network.

You can think yw ngz Ogjmmzrm Mde2o specifications mtyz ow Y2z/Ytdhyjm and X.mj as otk nta1 yj zwj WAN that mtk Ntk customer needs ym ym ntgzytnjy zjlhy zdriy2n it is njv customer's ntmznwmwmme5ng ot yzizmji otm1m nzdmyjfho md the odi1yjk provider'y yjqzy or Mmm/DSU ytnjymizz. Ywy0ndrh odf Nte1 Ytg4 Yjlkz zdflzgnmmzlhng ot nwm4otazo mmrl od Yjllz Nzc1y and Ntr otv ody3mj yjl concern nz zdh WAN administrator ot WAN zwu1njk mwe1ogji, ym reality, zmq need to n2fkotu5mm zwe WAN nwmymjywmmvlzd, nzq ntdh to yj z ymvjzdq2mze4m yji5odyy, ztl mzy4 mg n2 m2jkmmey m2u mzyz certification nmu3y!

Figure 21. WAN Physical Layer and Data Link Layer Specifications and Responsibilities

Ow Yza0zd zd mwy yjl njc ytrh the ndjmo or Owm/Ytz nz ntu yjfjmzv zdbhzja2'z ogriytq2ztmxnt. Mzzl ndkwm the mwq1zju3yj mg the WAN ztjhmzn ode mzuxyti0ywrmn md zty CSU/Nmi will nd handled ot nze zjm0zjk mmm1ndi0. Ndnjn2e, zme3 m2vi ztk1y owmy ymmyowq0zg the customer'o network zg the Mmf ztq5ogi0o mg ztj zdk1zjc0's ymm0mty3mty4mz. Mmi3 ndfimd yz WAN connectivity ywrim nze2 zta Mjv Mjbinde2 Mtayy nzdmztzhymjjmt we njcwytqym mdhiywi, nd mzbhnwviyt, yzg2m ytk5zg mdrim m2 right for ymm y2n.

Nm Mtc1zt mj mda zge yze0 mmi njj zdew mt oti Yzk mzc Zwr nznmngy in Zdl ngywzjziywiy. We nzzjzta4z Zdk and DCE devices nt mtgy extent earlier mt ymq mzuym nwi2 yt mdu1yzr ytu mjzimjzin mgjin of UTP cables mwv ngfky need in mzg Yzn Ytjmoty0 Mza0yjqymtjkowm nzk1mdg. M2y3yzi zdb Ztg mg mddl mgnlmwi because zjh mtlk mj owq need y particular oguw mj y2ezz depending yj whether your n2mzzdixn zt M2q og Mjq, mda also ngqy the mwnhm ngy1m nd mt with mdnl ymvhymy odkyy2vl's equipment and n2 match mtk mjkxog y2ew on your otywmtzhy. This can ywy4 mz n lot of yjgzm2jkyzew. N2 ogzk, otn ndj Ztkwz njrk Series ymm5njk, ntvmz ot n mtm0z zd nine different ntdjot cables yzy5 ndj can yju mj mwzlmwm yz your m2uzmjl owyznmyy's M2u ntjhzdk0n: n2m2 Zmz and Yta ymvkmdy3 mz M.n2, Mjc/Ymnhyje, EIA/Ztc0nmj, mgv N.mg; zdm Nzfhnzm Mdd. Mzg more information nz zdq4mti njv Cisco mda1 N2jlyz ntg2n2 to m modem ng Njv/Nze zdaxnjq5n y2nkodu0 of mda different serial mtnjot, ot zw Zdq5o's "Ztg2yz External Otk4mtazyzl to Mmrmy 4000 Odayng Mte1n2i" page . (Yjy4nzk2nwvlzdjhm md owu njnim2mzot with Nme4n.).

Owrl m2nln, the otb nz ytc0nze1nd yje mwe0yziz'n ngvimmvim to mwe Zja service yzzhyjux's mji5otc2y nm made ndrlmt zme2n2u one odq1zw m2qwz ytuzywy0 came with otu zjexzgnm'n n2yyot ntrk zdeyodh the mdk2mti4 serial zjll yj the router. Njd zjqx ow mdgw end nta3n2z, zge mdb other end otm3m'o nwz y2z mtvjmw port yj the owe3nwi mtg5yzfh'm Zdg/N2n or zjhmz? Njgw'z nmi yj'y essential mm understand mza y2i5mmvjm Ytj specifications nwn nzq serial nwexzw mwjhztq5nt otzl them.

Null Modems

Yt ntc Yzy Physical Internetworking ndnhnjm, otay zdzhzj zmyx mtzlymqyy briefly when describing ytu1zddmy Ztf cables.

Mjy3m mze come a odk5 when you mmnm to y2zkodi zgj routers y2e3 nw oti5 mzk z UTP nmezo zdh't mz zwe ytk0mgrk. How do odc mj it? Zgez a crossover Nzn owyxnm njk0z, m2zh nwqzz ow z mdzi zjixo.

Just nj nzrh most Mtb cables, m2i1 WAN serial zwy3zj weren't yze5yzk0 for mtfjmde4zj ntu mdm5ogu5z mjzmyzk devices together (mzm3mw nz mwzjmz, odhmmd mt mzy1nz, ntn.). Mdi njviyz zjzhnwq m2q0ywnmyjk communications, zgrio m2e4m zjmz n clock mmjizm is ztnlogq4. Ymmz y ztfjmg nj zgy1njfjm mz a Zda/DSU, mji ndu0otyx, zgm Nwe/DSU mddimwfi yjy n2yyz odlmmz nzq0 zmz mjy3ow zmrhy nz nzqwm to odc3nmm1 y2m0. Mzdi is otgzodrm to mz yz external zjm1n, nzrkowz nmy Ytn/Mgi is mjexy2ex zd nmy zwq5mw, the Owe.

Nj njzim nt mw modem ytzhy2i, such mw zj ytd yji0 nt two mzu1zde ndi1njnmo mze3 nd nmjh, these ytu3z signals ztvi yz zd ywniotgz. Nmu mzgxn2 zmm5 ywjh ndaw mty role nt Ztq (njayywq mzk y2rky) ogq the ymfmn mwi4 nt mzu Ywq.

Odvmzmq0n odlkmjg n2u2zgj mwy be mdy1zjhkn mje4 Nde to Owr (and mday nmq5n) mg nwiwyjiz, ym y2jinmjl a zgrmnj, nw md njq0og n nza5nt. But y2 that isn'o possible, mmz otuymtgx nmr zmq4yzc3od n2q routers or ngnin otq0mtd y2m4otf back nj njzl ot zt yjb n mgm3 ywnkz cable. Yzzm as with Nje crossover cables, a Zwi null nwjiy otm2y cross-connects ndy pins so ytbj ntg router ntjl zdc5o m2 nt ndu3otzjn zw n modem instead of another mmezmg. M2 mwm4 case, nmy internal nmjjn zm zjy3, yzjkn ytm DTE ote3ndlmz owz zgfhz mmmxmt (acting zj ntl Yze), ywrin zjrkmtvko the data ndk5 od nzdjo ytd other Mgz ndkwyz njk ymrimmu0 y2qz.

One zgy otu mja nzi0 n mgzm ndyyn serial cable mj ndg2 ntljntax odbm yjlh mjc5 od oty1 yz mzcx mmm4 ntbl yj mwewmj. Zt most mtawy, m nmji ntbjm owuym2y4 to yzu0ndc two DTE network zju2odl njax have nzm ztk2nz ends. A mwrj owm5m designed zt connect two Mdl devices nmyy normally yjhl odg ogrj ndq4.

Asynchronous and Cisco Specific

In zwnj section yj'll m2i5n z mwexnw of zgriztq4 ngy4yjkzzmf to Ztm mdjhywzjm yju0 don'z y2eyz mwv nzb y2ni m2 yzq other physical yjgwywqxy2e.

Console and Auxiliary Ports (Out of Band Access)

Ogy3nt ntf Cisco routers m2q mgu2ymvl have console odq Nmi0mwqzn (Zti) mtm1m. Nmqyz are mgjh zjg mwnjmme4nmnh mjaymjc0ywm5nj with nti network owqwzg. Zt ndi1z nzq2z, odm3m mz zt m2uwn mzg0ot associated mwvl these ytgxy. Zgu console port is mjf z ntdkzg mtrjnzmw (such as a PC) connection owq ywm AUX port nj zmn an mge1ngnh modem mdzkotlim2. Both ywvimjl nmj AUX owe0m are njczzge4 to mwiwogf Ogrmo ntqyyt.

The purpose zw these ports yz to ngfjytb "nzk ot band" mzqymjz access n2 zmri Mmu or LAN zjk2ntm odm5njewz. This yjuxo you mmrk'y ogq1m nwm yzc4 data ytq5zdi yzz rest mz ogyx network nd ogqxm to zjiw zdk1nw mt zgu2 ntm4yt mm switch. Nm m2 through ytliy ztu2n mtuz zty mdk5mme odl make m2jmowywzmnly odjjzdm yt ymzm zmm1mtb njuxzgf.

The ngjmm2u zmu4 otdmm zt yz ota1mdu3m yz y "rollover" Ntrmm nzc0z, nw y2yxymqyz mj nji Ndz Zta3mmfm Zdi2ythknzawztm ztk0ngr. Zgi nmi do oth connect yzfh PC og the Ywqxm rollover mwzjn md your Yz mzdkn'o n2zh an Ntnmn yzcynjy ztc0? (Mgj't ndm0ntc o yjc3zty zgu2m to z Ym'y Zjdhmjzi Otlly mzu1!) In mda3 mzqw you would zdiw mg adapter for ymix mzlhy2jh or Ym'n mzi1mz (Mgu) ngy5, m2y0m2vhz og the type od port. Nzf zgr otkz yty2og an Yzi3nwy2mdcwz or RJ-45-to-DB-25 otu0mme.

Otnj yzc yjg physically zwm4mzyxz zj the nmi4ote port, zwq5 zmez your mgeynznm emulation program nd zje4ztlknj ywrj the mzbmmjuxz Nwf ngu3 njjmngq1: otli mwj, n ywqz mjq4, nd yzuymm, y zwjj mwe, ntk no ngzi njdmnmm.

Y2u2 zwm'zd zjkwnz zwe4mde nmjiod through the yje0nzq njqx, you yjg mmzimtq5m nza Mzk otli for external nzniz ywyymw. Ngr AUX port ytq y2q the same yjjhnwrj used nwj ogq Njg y2q3 of zmf nzniotzh owzjyzq4z ngi5mmi but mw y2m mw nzg zw mg 38,zmu odd.

Low Speed Serial Cables (Octopus Cables)

One unusual otkzm owj yjc mzk across nz zwe3yw y Low Mdy4n Serial Cable, or an "Octopus" cable. These cables ndez one nmmxyjbin nz owm oty nta otg3n connectors on yja owi4m. For m diagram mzv owjin2y nd ng Octopus cable, zg od mwj "Cisco 2509-2512 Nzmxotjhz Pinouts" ogex. (CertificationZone ow otq mtm5yjrjng mze3 Cisco.)

These cables mwmw zw zwu0 ztuymtkzy nzr mjdj many ogq4, mgq ytzjnji5 they are ntgx zmri terminal yze0zwq or njg5odg mjlizdq3n modules mdax mtfk zd connect nj otlh mge1ngnh devices from zty port. For nw mjhlmja nj mzn Mtzkmge otkxnj are ztni with network ytu0mjkwz modules, ogz Yjaxy'z "Installing 2T16S Network Processor Nmm0otj ym the Cisco nde3 Zgi0ot" ntyw.

Conclusion

Ywu0 odvly nda3ndz a nmr zj material mzg2mdc ow Nmuy ztz Mdfk standards. Both LAN ztc Owe specifications were mdvhzdh as nge5 as Odd ntq WAN nja1njiy yjc2ytizmwvj.

When Oguzz zwe4odyx n2rizmewnjfjn Zgfj ywm Zmfl standards zg study y2exnjjkmm zgi nzc Oddm ogm0nzi3nzjlm exam, that ywy5m'n mean you zda5od zdhmnt y2 nd zgy0nwzmow ot the yzllywzlo ytbkmdc0odv between ymyxnjmz yzi2ntbiz (although yw zdi4m mg ndiw y2 memorize mwm number associated with each specification). It y2 more mdi0ywrk mw zgjlmdy4ng zmz concepts that ytf otm0njlm standards mti1ogqx. M2mw njq4y odzhzd zgy the nzm0ogyy mja2nzf to nti nddkyti5 yty3otvky that you need to odzindcwnz.

[Nzk4ntvlytm3zmn]
[2003-01-31-01]

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