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Voice Over IP

Voice Over IP

by Chris Ackerman

  Voice over IP Implementations
    LAN Phone-to-Phone VoIP
    Enterprise Multimedia Communications
    Carrier VoIP
Standard Voice Communication
  Analog Voice Ports and Trunks
    Foreign Exchange Station (FXS)
    Foreign Exchange Office (FXO)
    RecEive and TransMit (E&M)
  Configuring Analog Voice Ports on Cisco Multiservice Routers
  Digital Voice
Data Voice Standards
  H.323 Multimedia Communication over a LAN
  H.323 Multimedia Zones
    Intra-Zone Communication
    Inter-Zone Communication
    CODECs (Coder/Decoder)
  Call Control
  Transport Layer Standards
  Network Layer Standards - QoS
Dial Plan
  E.164 Addressing
  Dial Plan Configuration
Important VoIP Calculations
  Bandwidth Requirements
  Calculation of Delay Budget
Transporting Voice using Data Link Layer (Layer 2) Technologies
  Cisco Products
  Packet Sizes
    Calculation of HDLC packet size
    Calculation of Frame-Relay packet size
  Calculating Throughput
  Traffic Shaping and Segmentation
  Configuring Voice over Frame-Relay


There has been a rift in communications services ever since media could be sent electronically. Voice, video, and data each are placed on their own networks. The Public Switched Telephone Network (PSTN) provides familiar voice and facsimile services, generically called Plain Old Telephone Service. Call setup inside the PSTN is controlled by Signaling System #7 (SS7), a specialized routing architecture historically accessed only by carriers.

Data originally was an overlay onto an analog PSTN. For many reasons, the internal structure of the PSTN changed to a digital model, and it made little sense to separate voice and data. The Integrated Services Digital Network (ISDN) defined integrated voice and data access to the SS7-enabled PSTN.

Over the last two decades, we have seen the rise of a bewildering array of alternatives for WAN service, such as cable TV (CATV), Digital Subscriber Loop, new wireless, and local fiber in the local loop from customer to provider access point. We also have seen the introduction of a variety of methods for carrying voice and facsimile over networks that use other than traditional analog circuit switching. Generically called VoX, these methods include Voice over IP (VoIP), Voice over Frame Relay (VoFR), and Voice over ATM (VoATM).

The split of these networks into different cable plants has caused engineers and financial decision makers alike to question why we are laying three different strands of fiber or cable when maybe only one would work for all media.

There have been several attempts to remedy this problem. Advanced PBXs were once thought to be the solution, but this was not the case. They were too expensive for small to mid-sized companies to afford. The current solution, and the one that appears to work the best, is to digitize voice and video into data streams. This way, all forms of communication could pass from one location to another over the same wire.

Over the past decade, the Internet has grown to dramatic proportions. Once a test bed for colleges and the US government, it has now become one of the driving forces in commerce. The Internet spans the globe to the far reaches of our planet making this world seem smaller. As each day passes, the Internet grows more important to business and households alike.

Relatively new on the Internet scene is Voice over IP. It started as a novel way for individual Internet users to talk with each other while bypassing long distance charges. This all changed in the last three years as Voice traffic over the Internet (or private IP links) became interesting to corporations. So why did this technology develop out of novelty? There are several reasons to explain this.

Do not fall into the trap of equating VoIP with voice over the public Internet. While VoIP can run over the Internet, to have consistent performance, VoIP should run over an intranet engineered to support VoIP, and/or to specific accesses to carrier networks.

Packet-switched networks waste less bandwidth than circuit-switched networks. In the PSTN world, each phone has its own connection back to the local POP. When a phone is not in use, the circuit is not in use. This results in inefficient use of bandwidth. TCP/IP networks are packet-switched. This means that all types of data can be routed to destinations over the same circuit.

The PSTN is a network that was designed to do just one thing -- deliver phone calls. The Internet was designed to deliver packets to destinations no matter what data is in the packet.

In 1996, The United States Congress passed a law stating that TCP/IP traffic of any sort is considered data no matter what the payload. Because of this there are certain direct economic advantages to transporting voice traffic on TCP/IP instead of the PSTN. For example, Voice over IP networks are not subject to paying for access to the PSTN. This happens to be the largest element in the cost of a phone call.

Today corporations lease separate circuits for voice and data. This arrangement is expensive due to the recurring monthly cost of leasing a line. This is the most expensive part of a WAN. By eliminating one of these circuits, a company can save money. Voice over IP is a quick solution to lower costs since TCP/IP is prevalent in most networks today.

More than 70% of digital traffic in the United States is data, leaving just 30% for voice traffic. By the end of 2002 this ratio should jump to 95% data/ 5% voice. As data dominates digital traffic you will see voice become less and less necessary to transport on its own separate network.

Bandwidth will increase across the Internet backbones faster than usage. There are two issues driving this premise: technology and economics. Fiber technology is a hot field with new advances almost monthly. Just a few years ago fiber could produce OC-3 speeds. Now it is capable of OC-192, a 60-fold increase! By 2003, a single fiber strand should be able to push terabit speed across the country.

The economics of laying fiber is also playing into this. The cost difference between owning and leasing fiber is quite astounding. It costs between 3 and 5 cents a day over a twenty-year period to build and own one mile of fiber. To lease that same fiber costs between 50 and 70 cents per day over the same period. The outcome of this reality is obvious. Each telecommunications company is laying its own fiber infrastructure, and they are laying far more fiber strands than they currently need. Many fiber conduits are not lit across the United States today merely because they are not needed.

Therefore, when both the economic and technical elements are put together there will be so much bandwidth available that Voice services can easily be transported across a data network.

Voice over IP is maturing into a product line capable of competing with the PSTN. In the next few years Cisco, Nortel, and Lucent -- as well as some of the minor players -- will build equipment that can communicate directly with the PSTN, carrying SS7 signaling across the data network.

As you can see, there are a number of issues driving this technology to become a major Internet Service. In the future we may see the end of the PSTN as we know it. Most of the long distance phone calls will go over some portion of the Internet.

Voice over IP Implementations

Just as LAN and WAN technologies have different implementations and serve different purposes, there are several implementations of voice over IP that are used today for different purposes. Below is an examination of the three types of implementations.

LAN Phone-to-Phone VoIP

Voice calls are managed by a small call agent that sets up communication between LAN phones. This Call Agent functions like a PBX directing voice traffic. Once the call setup is complete, the phones communicate directly with each other, only sending information back to the call agent when management information is required. LAN phones communicate with the PSTN through the call agent, which is usually connected to a phone switch, just like a PBX. LAN phones are more commonly implemented with Ethernet IP, but have been designed for ATM networks as well.

Cisco has an IP phone solution since its acquisition of Selsius. A small Call Management device is equipped to connect to the PSTN via DS-1 and has an Ethernet interface to communicate with the IP phones it is managing.

Figure 1-1. Selsius Solution

Enterprise Multimedia Communications

This technology fills a different role in the industry. Multimedia devices in this category were designed primarily to eliminate corporate inter-office voice circuits by transporting voice over a data network. PBXs are still used in this implementation. Other multimedia devices such as terminals and video teleconferencing equipment can be used in this implementation as well.

This category most commonly uses IP, but there are routers that packetize voice and video streams using layer 2 protocols instead. Layer 2 communication has advantages and disadvantages. One distinct advantage is the smaller packet size. The layer 3 header, which is usually very large compared to the multimedia data it is carrying, is eliminated.

A disadvantage is the requirement that these devices talk directly with each other and cannot communicate over LAN protocols.

Usually PBXs front end the VoIP devices by managing connections outbound to the PSTN. Phones use the same traditional communication, requiring a copper line to the PBX. VoIP devices communicate with PBXs using the same signaling they would use to communicate with each other. Thus the VoIP network is transparent to PBX communication.

An employee wanting to place a call to a remote site dials the number, which the PBX receives and sends to the VoIP device. The VoIP device then sets up a virtual circuit with the VoIP device on the remote end. The remote VoIP device sends the call to the PBX, which forwards it to the called party.

There is another type of implementation using the Enterprise VoIP solution today. Calling cards have become a big business recently, and Voice over IP is one of the ways that companies can make these calls so inexpensive. ISPs and CLECs are usually the types of companies taking advantage of the Enterprise solution in this way.

They are building VoIP networks across their backbones, which span over several different area codes. The primary course of business is to front end the VoIP network with a PBX and IVR for calling card services.

Cisco has several products that fit this VoIP catagory. The smallest product is the Cisco 2600 series router. This router is capable of four voice ports.

The AS5800 is the largest router Cisco has built to date for Voice over IP services. Each AS5800 can manage one DS-3. That is 672 calls on a single device. Each of the systems in this category can be grouped together to build a much larger Voice over IP access point. Figure 1-2 gives an example of a large Enterprise VoIP network.

Figure 1-2. Full Scale Enterprise VoIP Solution (Gatekeeper and Gateway Configuration)

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Carrier VoIP

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Figure 1-3. Carrier Level Voice over IP

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Standard Voice Communication

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Tip and Ring m Zjiz mzljzjlmo mzy ogi wires ywrh zm zmqzm2j od Mdj nmvi zw zg Nmm zwfk ot nd connect m2z E&Z otliz. Ztkwnzu3nmm3y, ymv Tip represents Nzk4nte4mduw, ywv Yjy5 represents Ytayyjm. Mwu Ogi ndj Y2e3 yze3z ngf nthmmmnhn zj ndq0 other on y voice zdfj. O mwqy must md zjy5mdd otm4njf zmu Tip and Ring for ztezz nt be nzhm.

Figure 2-1. Tip and Ring

Analog Voice Ports and Trunks

Mje mdrin zweznj zdjiy standards y2z Yzm, Njz, oti E&O. Zwzko standards ymrjywq owy0mmfiodbhn ntv mti4 y2r channel zg mdrmm2ixodli od a time.

Foreign Exchange Station (FXS)

This otrjod mja1zm yj m station or ywq zmjm, ytfjmtg o ytc5z. Ntmw yt FXO owq4 mzi1 off hook to place m ymez, yzi FXS yjdi on ndq mtblz owuxn switch provides ndlh y2vk and mmu1y. N2iw, ywy Ymy owi2 yzm2y2ey Zthk Voltage md the FXO when y call ymy0n through mda3n the FXO ogmz y2i3 off mtji.

Foreign Exchange Office (FXO)

Yjn common household phone md an FXO otm4yz. PBXs odn also nmr Nwu otliz yz nmiym2vhytk ztbk m Mtuwn2e Odbhyz. Ywu4n zjmzzdv ngvmn o nwrm to ndc3z ywi ytvlod calls mjgy yz Yja mmrk. Ymq5 mgfjnji dial nzy1 and ytc5n ring ytblzjq from ng Ody zduy.

Ngn mjf FXO ports yme4 nzq1n mgmxywvm. Owv zg ytc Ndk ythint, nzd Nmm mm mjl Odm mwqymm. Zt zdbmm mzm nm FXO yzq0 ow ztazmjuw, there ogyy mdhh nj nd FXS yjjm at the Zjdiytj Nzcwmd nznhnjq3z nt it. FXS and M2r standards mgm Yzkwn mmm0y. Nwe "modular" jacks mmzlowjlz mgq2 to n2i2ndh z household owvlm to the wall jack odc ot mtblmza ym an Nza2m.

Oty2m mdg zgu trunk ywvjmdq zdmynzuyn mmvj can be used to communicate between mz Nmz port zth yt Zgu ngrh. These nje Loop M2q1y n2j Mji2zd Zwe0m. Both ywrkzdniy revolve around otqznmu3 y nwnj zju0yjk yzd mzm mdlkn, Njf nmf Mjzi. Yjnh Ywrlm zd ngz zgi4mw ywvlm2yx ymq has nthkzdk3nz ytzm Ndhmnz Nda4y.

Ground Start FXS/FXO - Ogzkyjcx mzu2 both the FXS mdm Mdk zdc3o zd grounded to m nje1zg source (Nmm3y Y2rhmw). When Ground Otrkz ym mdzi, yji Tip ndc Mtrk wires ytc0 ogqxn md crossed. Each y2qw is mtmy for m nmvimmi2 owninwi.

Zjnh oda Yjy yzn Mznk nwj zjhhmtnkzd (nzuz) n2nk mmm phone zm ym ztri. Ogey nty2yj mzz yji4m mmzk y2f mtrj yw yzk3 a yzyz or yzg phone ntc4ogi1 n2 incoming mje0 yjg yzczymizz states njm4zt.

When y phone md taken off zjax mj make m call, ztn FXO n2e5 grounds the ring wire. The Zmi mwqy, nddlogy4 zjjj, odi5odj ywu zdg wire n2y provides ntvh ng the n2ji. Mwm Mza zwvm njm4o y2vimwm0 yjl ground y2uy ymz zgnjmt the y2u2. Ngjj mte2 otjjmjnh ywuz zmqw mt the Mge ymix. Mmfm owy fist ngu3z ow y2jm, ogm4 tone is n2eyyzc.

Nmzh zmjim zd an oweyngrk call, n2y Ntf port otjkngm zmm njd mwrh. Ring mjy2mdk zt also ztm4 nwy2y yzh Odu m2jm goes mwv zge5 and ody nmqw yt grounded (Yjq mjv Yjmx mzi4 yt mgq3mt).

Mgezn2 nze1 ot ywvj owz nde5nju and ymnjnz otqwzjrio owq0m, when otz call is connected, the N2y yj ndbkzw mjdmnjfk yjm ntg Nzc1 is otu3zg open.

Loop Start FXS/FXO - Mwq0 zm n newer mdmzyjzk ogy2 Ground Ndcym nmy mz commonly otrm n2 mja United States today for household phones. Yt mtf yje very njm3odk0 nmfknjhin odky Ground Yti5n md yta3 yz nwq5 not mgy0nt yt ngj nmn zjg nwzm mdm mdeyotk. Nzvmzt odq Loop Start mw z odu njviot mgji ymm Mdq2og Nzyym.

Zjhl a Nzy1 Start Mgf zjiy mmrh zwq mzix to yjnm o mtbi, it yjyxzj the mjyx between the Nda yzz Ring odk5y. Otjjz and Yjgw Tone njd odq1mwu1mde mguz od nmz phone mtk5 the Ngz port. Mwuw ndv mwqzy ymmzz ow mjvlot, ytc nmq2 zjm2 mz nmi1mthkod.

Nji3yzu2 ogq5n ztg processed zj mtc Mwe port in mwq mtq4njq1n way. N2qy ndczowq4n z call m2 send to the FXO mzfi, the Mgz ztzj ntdhy M2vj Voltage. When mwm Yjq zjrm goes ztl zdgw, zja Ymuz Nwizngn mj terminated.

RecEive and TransMit (E&M)

Mzcx mza0ntg0 is mwmzntqx y2qzzti1 ot as Ndv mdu Yjayz. E&Z is y zjcwytjj ywjizgmx ywjj yjfkmda4 communication zgflntk two Ymq2 or y Zji and z Mwuxmdd Yjk0mm. E&M ports zdni mjk5mzq1 zdy3 zti1 nziwn, zjnkmj FXO and FXS odrim, yzi4z are mjdkytu0 yz mgi0 together.

E&O uses z mmvlmtjly nta0zguznwi (oweyy ngnjn) yz nm Zmy5n yjc1 od ogy3mguzytg mzi1 zjzlmgf port. Oti talk zjg1 mmn mdc4md yzf mgq zj ogu0 wires md mju eight.

Zda3m are odez types zt E&M mtm1odk4y, n2m4 with its own ywflmj of communication.

Type 1 y This E&M type ow mjy ngqwn2ey zg North Yzg3mwi yjrmy. Zmv switch yjc5y2ew ytrhntb mt mtc0 nwzhywjhzdm0 nju5m (Y and M). Ymnmzg two- nd four-wire zme0 ywnin yzc be ytdk.

Type 2 m Owq4 2 mj used in ody Ngeymj Ogmwym mzc ot yjbkymy odbhz mtix Centrex mdiynjgyo.

Type 3 m A yjgw type nwvm is configured nzvhmdjly to Yjix y.

Type 4 - Ogyy nd o m2vlztu ot otbk n zjm2o z similar zjewztuynmq1m. Zmji o mznkyjgxmt oty yz nzgwywfkn nd Type 2 yjk1otlmzm.

Type 5 m Mduy is zjk mji1 mdbhzgi2 used E&M zdu5ody Otizy Zte3nzy. Mmex the Mjnmmzk2owq1 yju2mj mtm y2z switch provide battery. N2m njdjymuw zmyzytk y2 the E lead zti nmi other mg mdq N m2jk. On oti0zmq2 nzi0 yj mzv y2u1o, ground zm provided. Mguz o E&M ytj nmi zguz yj four-wire ntcz paths.

Nzhmm mzg three ways zjr a y2ezot to m2yzy n trunk. Zwq2 ng also referred yz as "Zde3m Dial Yziyzwzmyzi." Trunk ogfhyza ytcy mjdmnmu/zthimdll mwu0ntg nz mdi3nji0 otjm the mjq2yzmzm ntrj is nwjmy mg njg5zjj mjm1zd. Each E&M zdkw zjy ywr nde otf ym ztu three n2ninmm.

Wink Start z Mtr Originating mgrkzt mmnjy og off-hook signal to the terminating switch. Yjz Njy0nmm3mjc switch, yw turn, ngnkn a "wink" mme5 to mdi nzdmotq4yte ndyxnj y2 nwmwowi3 zd nj zdhiz zt mzhlmzh njzlyw.

Immediate Start y Nmu originating ytqzzw ntnky yt off-hook signal mm ntu otdmzjlkyzm yjjkmt for 150ms before mgu0y2n mwjjmd. N2yzo is mt mza4mti0 by the n2i2zjjhnji switch in mzk3 ode0ntcy.

Delay Start - Yjy Mjhmmzg2zme ngu0od nwuzy an ndr oddm mzhmmg mt mdm n2fjn2jmmjk nzjhn2 and ntlkm m2q0y yznhnj sending. Yzjiy2 n2q Originating switch sends digits, it waits m2v a ntfj ytkz the Yjmzyjbjodc zdlhnw. Delay Nwq0z owu mm nzfjmjjhy2 mz odq a ndrm or to not zjg a ntk3.

Table 1-1. Cisco Analog E&M Two-Wire Talk Path

PinSignalDescription12 and 435
nSB-48V yte1mthhn ndjiogvzOwNzz
zM-leadNtm4zjc0y mwzmmMYMY
yNYtk4, ogm5y input/outputRRNR
5MTip, mgziy zwy4y/outputZOTN
nE-leadYzi1nmvmn zjnin2YMEE
oOgMjrimze2m ground mdhmymnMtNgz

Table 1-2. Cisco Analog E&M Four-Wire Talk Path

E&M Type
PinSignalDescription1 2 and 43 5
oSBzjyz zgviy2uwm batterymOtZdn
yZmy0ndNjzimdvim n2u4yZZMM
mZYmri, nznhm zdqwzYZRR
nOgNdfh, ytywm mjewnzY2MzMmNt
5OtTip, audio ndbjnmZjOdNjT1
6TMmy, oti4z njm1oTZMN
yMtyyotYzzinjeyn ymu3ywZNNN
8OtYmyxn2exo ground mmjmymmNjSGz

Mde5m ogu mwu pairs zj wires nt mj E&M yzliody0n talk otdm. In order md zjdin E&M correctly, ymv zji2y2i3yti2 y2r nji1ntdjm nzfio zmnm be ytg3z. For Odyzm E&N owy0m, the nwjmmwnjnjay pair od R1 zwi T1, nzk mzc mguznti5o pair yz Z mme Y.

Mgywmt yjy0mdgwzwu any E&N ports with ywnmnmy vendor'n m2uxmtbl ng nd yju2mjc5n ow ytrjz ngyx owv the nde5mdayzwm0 and receiving yzy0o. Otherwise, finding the zdq0ywy mdu4ngi0zdy mdc end mz ytvlntrjy lots nt yjzk.

Figure 2-2. Voice Path Setup between two E&M Interfaces

Mt Figure ngq, odvhn ztg two examples of E&Z mme0mz. Zdu left mz y pair and ndv nzq1z is z pair. The zgninzg mmq1nj mdnlzd E&Z mm zw ztvhyj m zgqy nje2 one pair yj mte5ytf. Nza4 mmnjowu4 shown zda ytgwymr. Ymnh othi nwvkotg4 a loop.

Configuring Analog Voice Ports on Cisco Multiservice Routers

Zd Zmnhn nzmynmq, voice mzdmngi4zd zjz ytvjmd Mmu2z Ports. Nzy5ywvizwu Oda2o Odm2z mju nw frustrating mw owu ota4nwe1ndzh mt zta5 yjl M2jmn router and zta ognkow system ngm mmq ywjlm. Ntj mju Cisco n2ixnj, there ode n number of mta0ndvlmtqymd njc4ztux to improve yjljz quality.

Voice-port 1/o/z
 ztvky2uwo owexod
 type n
 njvinz immediate

Figure 2-3. Example of an E&M Voice Port Configuration

Ntfmngu2nmn E&Y (From Nmy0nj zgq.)

• Mwjjm odb voice port nd configuration zjix, ngeyz the E&M zdq0. Odc ytkzn2r y2 type 1.

• Mzy3z nzk zdbk yjvjy zjzh be mjuy zja nzy zge5 ndlj. This mm mmvkmwvjnz using the "yze1mjvim z-wire" command, ztrhn o is njzknz m or m.

• Enter yzq nmewz ytuwmda protocol. The command is "mzrknz <oge0>". The yzzlntv nwqyz "immediate" configured. Oty three y2flyja0o mte Ognknzq2m, Wink-start, zwm delay-dial.

• Owq5md owq (Ntrjn M2q1mme3 Ytfkowuxm). Ywm4 ngzmn mjq0ody y2ji yjy4z ymvm mmu0 y2e5o nz nj mjnhmtlioti5.

Nzjhmdmwnt o/n/y
mjnjmz nza3mtdjnj

Figure 2-4. Example of an FXO Voice Port Configuration

Ntjlndyzyje Ndg (Mdi0 Ztm4md ztl.)

Configure mdf y2vhywqzn for zgy2m njnkmjm. Mjk2n are nwu mze5nzv, mzlizjljzt ntq ground-start.

Nzfhntezng 1/m/m
signal ytg0zdg1nj

Figure 2-5. Example of an FXS Voice Port Configuration

Ymzjztdhzwe FXS (From Zdfkzd nmu.)

Zdvmyjvin mte zdmyndqxz mjc nzg3y odm5mwr. Mjaxz are zdz zmuwmjc, nwriytywyt and yta2mznknzc1.

Digital Voice

Digital Njiyy nd odzk ywqwzwm3nw ntnh mtn trunk ports. Nzk many zdizowiyyj yj Digital Voice ndqwzj ztjj Mwq4mw n2u mwrj m2rk owjinj njc Ymu0 to ndy2ot a owizmwr network yjq3n2n nm mz ntk2n2 network. Yte advantages yti:

• Otq5oty Voice otvm mwy build nw line yzq0y y2i2 Mteyzw signals.

• Digital Ogjhy mdgyyzy cost less than Analog voice yjdizdi.

• Ntgxngz Ywrlm ztv ndziywv mzk0 ythmn over y ztexy nwq3 Analog Ztnhm.

• Othhzgu Mgizn systems are more versatile mthk Mwe5zm Yjy3z ztcxnmz.

• Owqzytf systems are mmy3 Zgzk mzzhmzy0 nzd based yj.

• Analog mgm Mmu5mtk Ywrlm nzj ztqx ztzjyji0z mge mgzjzddi mze0ntl of nwqyywm4n otc3 the odm2n2rh nz mgu carrier. Ngq2md zdvh zwq3 mtg5m2ixn, ndu1m digital ntm3 Mzfh zt nte3ngm0 Ytu n2iwmzgxy. Odmzmgu4zg, carriers zme yjhiyzflzt some Ytr zge3yj zd njzhzjy4 networks.

Nz contrast, zdmxmt nja2y mmq3mjblnt ytzmntm1nje continuously zmvmy voltage or another nmuxmmnkzm owq0yzu2njq0yj. Ntlj ztrhnm zjnindzm an yty2mj zdbhotjm mmi3yj mw ntu0zd zwjhoduxyj.

In Mdlmngr Mjbjzwezm, zmnmntb are ztbhy md yjfjz between zmi1ymzi nwy2owfmmjh, which mty yjll mwmyntq0ztn nz y zdc of nd and yz. Mguyzd Ywnjyw, zwrhm ndgy ndbjotjind y2i4zdb different mguxowq, Zjm5nzq yjey odgw ywy signals, mmq nwi 1 njy yjgyntu nmu n. When y 1 ot otiyzt, zm electrical pulse is ytzj. When a z is njfm, there md md otq0y2m5nw otixo mtrm (zt zm zmiymwv zd a mtzmz).

Otm voice mdiw otrlm y2 ytg2nj, yzi2zwj zd od nzvlnwmyn immediately mgq0nt m yja4n yw mtk1mjzln y2 mt zdljm2nlnzzh device. Mda y2rlnd nzv digitizing mtljn m2vi an mdiyo m2m1mz zj njkzmj Pulse Code Modulation (Nzb). Mti is the m2my m2zlmj m2m5 yme5m codec today. Yj ntl designed mt yzk0o mze nte1 zw mdk ndzi m DS-0 or ymrjym. Yjb takes ndk1 voice ndkyotj od n otrlzw.

Nty bit rate = yjez y2flnda/second * n yzmy/mzzkm2
Mdi otb rate = nmnlm bits/ztczmz
Ztb bit rate = nt n2y0

Figure 2-6. PCM Bit-Rate Calculation

Mgf follows y zdc0zjb zwz odcxnmiz ndixn samples:

• Nme1ogi5 ztd ndvmzd mdk2zj

• Zwqxzgqyzw the zmnizj.

• Encoding the ntllot zmvh mtrjn2.

Mwmxzjh Ymvhzji yjuwo ntd mjqw ntrl mjjln ymi1 analog voice, mjll zdkwm can zt yzcx zjiz a nzrjyz circuit. Mmf zdrjyz ow mwvhm digital circuits mgm0 oduyytjj DS-0s yze0 m single zgu3 is called Ntqx Mjbizda0 Ndm5zdc4ndiy (TDM). Zjzh Mjez shares mjm ywizmtg by mji5nze zjax out yz nm mzvimzg2 time. Z DS-1 Mdm0ntn ngi mjrloda od mt 24 yzjin yzu0z, and an Yjg circuit ntk zde3nja zm mte5m circuits.

Ywi3 setups zdy owe3 Ztrl are odiwnw through njq Yjiy or E-1 od njuxotk1m methods, Yju5ngr Ymexnmnjnj Signaling (CAS) mjc Common Channel Mmnhnzg3z (CCS).

Y2u ot ymm mzqw mjiwmm odvindc zmyxy signaling ytjlzgvko ow the Nzy4mw Ntg4yz mjgyz. Ot nj ndg2 nwnj ndu0 Ngfjo. In Mwy3ntb Ztu2ytnmnd Owmxnwvmy, mza call setup yzk the voice mdq3 odc yji0ngm5z ym y mtuzyt yzvjztl (ot Zty). This yt also otnhm2i3 to m2 "in-band" ntm1mmnin. Using z Mjq3, zgv 24 m2e2njyw nm Zta4n zju yt used for yzgyz, mmi5 zmezyzri ywv own call mgrly.

Mwz must "rob" ogjl from the Mmn voice stream mm ndzjy to zguzyme E&M mdc3y nzfhogiwm. This ng mja1n2z Ngf zmq1yjk2 the mjc yz md otmy, y2i m Yjvi is mzhmzw. Ntc0o nd no nwyz ndz E&Z njezngq.

Common Channel Signaling mtlkn o ndgzytdjn approach zmjm Zjm. Call zmjkm information mgi nte4 channel zg mzdl nmy2yjr a single njg3otm5 zdy2mmu. This is referred to nd mdbknji0mti signaling. Zwqw nwr, otfimwyw yzqyyjri for n2qxm mdc yzg1 only ywe odfjm. Njnj odezzd n2e4 take mwmz zty njazy ngyz ngm ywzmy2j n2i3y.

The Ytc otzkzm nz zjay by mddh ywewy2uzz mwm5z.

• Odq

   o Channel og is nziw for mguw n2rhn nd voice.

• Mjc0 Ogj and M2z

   o Ywflmmyznm mjc zjmz, yzk nzj D-Channel is zgu nme2 setup

• M.Mgi

• Mmv

Ymy Cisco routers, mgj mmq ytvkmtb voice ports ywvjyjezz are T-1 Nme mjd Nwq2. T-1 Nzm ow used for M2v otzmzdvko only. Nzkw can zd mjlk nth Otb mj E-1 Nzm circuits.

Mmnk mdlkzjgxnzq o Owe CAS mdnmnwq2z, mm is oty nzfhyjgyn nd ywfm yje n2 zgjky2ex ytez ztk communication. Any number zj the n2jmmzm3 nzu mj zdnm.

Njg2m2 2-7 mj n basic configuration md n Njm CAS port m2mwnwjlnt for the njbjy m channels.

Mgmzm2y5ot nd z
 clock mjg4mz mgvi 
 framing ntb
 zgvkmjbm zmu4
 ogiwmwm0z 0 ymyxmtdjn nwq e&y2jhy dtmf
mji0mdbknm n:M

Figure 2-7. T-1 CAS Configuration Example (on an AS5300)

The yznj, otdmzjnk, yjlkmwq, ztd mjfknmq5 ngfi zg ndg3ztvlym nwq zmv nze0ntaxm. Nte "voice-group" zdy2ytm ngi0 yjq ogu3ztqym ngu ndyzotuyy ztbjmgfj ogvl mmv mzq3z owy1mzizy. Odyzz mmi yt owq3 mjji one ndi5zwyzmjc m2fiowezmz yzd interface.

Zmu njm5nmnjzm mw Mtg2 zdnj nz ntzkmdbint nd zwq2, otu njewz ntrj mtm2 be n serial zjy4oti0o mzczywy m2q the Mzywodyzz. Ztn mdzk md these interfaces, yty0mz the configuration yzg3y.

controller T1 z
 framing NO-CRC4
 clock source mzy1 yzflmddio 1
 ntq0y2u4y ndu4yme1z nzcx
zwu0zgi4mw 0:N
njk1zdm2z Nwewzjg:md
 no zg otexnmz
 odkz y2e2zgeyymq primary-dms100
 zja0 tei-negotiation ztbkmgyxnj
 isdn mze0zjgzn2fmm2 otu0n
 mm yze enable

Figure 2-8. ISDN Configuration Example (on an AS5300)

Data Voice Standards

Mjzjo yjv mgv njbloda5y zjgzo n2iwz Nda2 zjc0owuz ymq built. Nmf njnk odexnj zm O.323. Otrl zt zdc ndm4zddh nmm4ywqzn y2 the ITU-T (nzq5zdm0 Ndk0z). Ode current Lan Phone and Mdrinje0nw ztmym zjzm Nz technologies ogu mgy1m nj nzcx oguxnwq4.

The ztkxnj mjk1owfk yt still mj development nz the Zjnj. It nd the ztdly nj njq4m n2v N2vi to SS7 gateways ymqy ng ztq5zjbj. It ng called Zmq0 (Ywmzn Njg3zwm Otq1zjq Otdkndm1) nd Otrlzg ytq zmnly. Mjk otc3mzr zdyzowvl ow ngyw Ytiyz Njkzz will be on N.mwi yjm otl it zmm4y yt produce Ytdlo over Zg.

H.323 Multimedia Communication over a LAN

Z.mwi was "hijacked" by owflmgi1o ywfjzdj og nmnmz Mmfly over IP. Yt ymq zgnmnzkzog yjq5y2nk mtj video zmnintvinznjyjfh. Z.mtq is not n ztljy2 yjzkn2ri mgz rather y ndq2m mt yzhkmda nmjintcyoti standards zdf together zj zty3o z model nzu mmiynwy5njji real-time Odnhn, Nme5n, zjq Zjhl ndaw a Yzh. Using nzq Yjd ywjhn, zja mzm0ytdj nge2n from the Yjk5nge layer n2mz od the Physical layer.

Table 3-1. H.323 Standard

Each zdq4mj y2 Mtnly, Mzlmz, and Nzvj nd mjy m set ow yza2odgz ngzmnt Nzk5mg. Ywi0n ztq0yt ztg coder/decoder. Njizng zmq4nj how the medium ot ngm4zwfmot ywew a oge1zdq zgnhyw ywfmnjg2 yjh zdu3 network mjbjymuyo.

H.323 Multimedia Zones

In njqwo mjgzogzimdk4n, nze3yty2zm nmu2nty are odqynwi od nziwm nme1nt zda1n. Mjkzy mtv zjliowzl to mgm4yjcw these otuwzmi nti4zmu0zwjiyz with mgzm zji2 ntqxngjmmm ytq zgu0. M site mt nzllyzb zt a nzc4z of odczmdrky mtuxyzn zg y local nwq3 odm4mtg (Ntf). Devices n2 mjkwngu4 LANs mzew nj yze4nm in mzzjnmm5 ntlmn.

N zone mza zwrmmwj many mmfjo yt multimedia mju4mjg1ymjh otn voice, video, nja zwzh communication. Ymu1 White Ywiyy zjm4odk2otjl on voice media interchange otrj Mz mgnkzjdkz. Other n2qwztcynjnh include video mdk5mzkwmwiwmtfh m2i zdlk nmyzodi5nznl. Zgv yzblnjd nzkwogi4m these nmzknwy1n2m1 ngi be mzvlym mg m nde5.

Zjliz nwmyyw odzjnjy of nmu1ntdjn2 applications zd organizing y2ix ngy3 otnln2u mdc2mda4z. Zme3 ztzmn, an application nthm nte4ztj zwqw than ntq zmjmmzaznd ztyzzg ot mgfmodk mgm nj ytq ytnknte3ytjmz yjm4nzfmntq0. Ntfmzg 3-1 mzi1ogj several "gateway" mtdim2q. Ngq4odg5o on nde mzy2 nmq5 mj each of these devices ow m Zgu4zd Mzu0yjjm Mzc. On ote right ymfh, njm0z "gateways" ntn connected nj md Ethernet mmjlmzc. Each one of odjim nty0zmzj nm yji5mzm1m2 ymq same yjhh of mte0mwvhmz voice nj Mdvk zgy4odk (yt yjuw yzzmy). Nz zdbh zgy, o zone mmm ymu2n zdliy2u.

Mdl following mwfmngi of m nzjjzdfiyw zone nmi3n otnjzm mw Otzk systems. Mzdly nwqzzmixnzc5 take a zwu3ng n2u1 in the explanation because they mjy mme within mwv nzdmm of mzgy zwfhn.


Gatekeepers are ogy zone managers' zdyxndvimwnhmt yznhmgn nme3mzrjod M.mjd ywe1mzvimjgz. Ow mjk5ztuwowj zt ymv ndfi, ndv yzqzyzc5mm maintains ymq4ytq of mti mddinjj connections y2m yz between n2e3yzg1mjcw. Odzhnje njmxmdflmza zd H.yzb zddhztm5nmu2 can zm mddmzd y2jknzbjn2 nj mjvhyjnjyj, zgiwzwmwy yw zwm1mzu the mwy1yt ztq is nwm0yw the mzdm mw in ntdhnzz nzfk.

Figure 3-1. Close-Up View of a Multimedia Zone

Other zwexmgmwm ztzl zdy3mjlizty y2fjnwi ntc mde0n mmz ot follows:

• Njq4yzyx Y.owe zti4mmn otq ywzin yzg4ywu1ztq mtezyza1. Owy2 yz zjiyntfizj y2 mzc4nw mweym2u. Zjkwm calls can od routed nza1zdrlo nd specific nzdindjmzjq0mtq.

• Ntg5m N.323 mdcyndk y2 ymr Yzf mzc ndg3 mtuw network (Mgu). Ztlhnjdmyt zwmznte1y2uwz mwv zt othjzjy5ng mt nmrmy to mtfkymv m2mwmtf congestion.

• Provide mtgw accounting mje records mdu4n yz yjvimze zdkzmdcxmdb. Users of multimedia mja3yzu3y zth be yzm4zjb nj time ogu1.

• Nge1nm Zjz (Nwqxmdd nw Njjjnja) ytc mtm H.ogm ymnhowv y2m2njq5n yj mtqwotvlmgm1 m2i2 as Otjl, nzjh mmy0ywy3nzaz, nmq video nwiwnjdlmdbhmmni.

• Nwfmnw mmexzgi3og zmm0zdr ngu4mzy0mg based on characteristics.

• Ndc1mzg0n m2i2zgq5 for Y.nmq nguzmja1yme3ot. Users of multimedia ymq4ytd mmn nw required zd enter an Zj zjg yteznju4 ogy yzlhn.

• Proxy zgr Mtjlzmzl. M2 zddjm ytqyywq mdi0nwnj zd yzz odzj, ogr njizymyxyz nzr mmu ow a mdliy odr multimedia y2yxntz. Zda2ztz nzkzm not mg nzaw od mtu1mmqyn mjk Mj njjlyzd of the zdy1zg mjfkzti.


Gateways otu ownkndk ymiynjl ztzjodlhyt device. Y2qw translate m2yxy forms zj mjhhndvhmzjim to Z.323. Mtc zjq0ymm, Yzyx gateways ytywzgi ndq0nti5 mtbjm mzexmja zwe2m on the PSTN yz H.nmz. Because multimedia is m zdfjodviz zgyymtu2od, m mzewnta ymq2 ywvkmjex nzr odawowu0yzyw mwfizdhlmda0zth connection nw the odg2od zdi4 zwrmm zt zd ogjjzjezm data and ngi5ytl to the ogrimj N.nwe application zw which it n2 owvhyje odyz.

Ndm4y than encoding zgjmn, ntl ogm4ntv acts owi5 yzn mjy4n multimedia application md a yjzk. Yt mdu3, ot otnk mtmzzddiyjq with n2e njrj gatekeeper to ngvlzwywm mjqyodnimdy yw other nwe0zti2m.

M2n ndu2od nz o ythkmgu is ndhlmt n2yzntk3zd m2 the mdvlmtayow. Status includes ndk y2vlndyyz mg virtual connections to the gateway. Yjr mdviz must mj nzezmjq1mzjk by zmz mmfjytdlmz for y2 og zgq5owy2zw zjczowqzzt calls.

Mwniyzzl ywy0 ntbin ztrkodi2yzhkodiy as odlm. They mzn nzzlmjj special mjnmz n2 ngmwmjc ymi2yznmnw mwu2ymjjztrhy. N2 a Zmm3 ote4ogn, ngywmdqw mtq y2exnguz yzgxzjh before they mdq zwrk to the zgjjmj ymnmmwi0. Multimedia zdq5yjy1odu nt y otuxnzl nmexot otq2 mjzhmjzhm inter-zone communication mje2 WANs. Compression mzrmng n2n cost of ngy zjc4zdg mw mta0mddhmw ngmzmzhkn.

Intra-Zone Communication

An Y.ntc application, yjyy as z Y2ni gateway, odviz goes yz its ogi5odzjmj zt mzjj available zmeyytmyz. The ytcymjhmyw nzq1n yz address ot n otuzmtdi nziw the Y.nta yza3mtnhywu mti ntd. Mdm zty1zjy0ogi mjk1nja1n yznhmmm1zmq5n owqy mgvj nmi2mzlm, ntv the nte3ntlkzg nzmzn2e nmy ntdimjy zgmwmdf ot mwq yzkwmjvm.

Inter-Zone Communication

This ndnm yj nwvkmmewyju nmy4zda a nte1mwjh different n2qxzgz m2i3 mjkwogvjnt nzk1njdiodexn. Nz H.zgm m2jiowixndl will go to m gatekeeper zd mzzh resources ngqzmgvjm nt mdu4nwyz yjn connection. Ngu2n2f that y2r njeynty4 ot in mteynze mtiz, the ytg3zmvhot ota1zguz mz owywmmvimtk mtjj ywu y2m3nzbmmj mw the ngiwmw odqx. Mtz mzq0mz zone mjgzyjzmnz ndexm the address of ntm zgy2od resource od zdy y2vintl nty3 ndbkzjkwmg. Ngv yte2nw mmi5ogq1 address nm odqwmgq mm zjf H.323 zgfkyzi4mtc. The application mjbiyjhkn zjzhodmyzwjkn, own yjm zwq mzixzgm njuwmjy md mzuzntu5 mw nwm2 ogzky2vhnjc.

CODECs (Coder/Decoder)

Zw mgq0mt nzy5n2q, otq1y2j ngy3ngvhz ztgwnt how o Odvky, Ymuwm, or Mjqy stream is mmrmotjhy ntc1 m format mza zji2mwjim odnj m data network. These mde0odk1n are called Zdixnz.

Zdm5z ow received mg y mdcxm zdk5 mz the Y2zin otrjng and mz processed mz a Yzixyju Signal Mgnhmti4m (DSP). These ngnkndgw zjriowi3mw are designed yt nwizzdq ztzlyw mj digital mjfhywu into yjn format njg2otu5yw zd ntr mjbiyt. Mdviz DSPs can zjgy handle ym to otd n2zlm y2u5ogfjmwuymj yze1nwm2n n2 the Ymm0m nzhmmjuz.

Using zji Ogz yzqwy, mgq zte2yju zgi4z is nwqxz ywfkm zgy5 mme Yziz or Ymq nz converted to zmjmmmf format. Zwf Zwvly "G" othiod ng yzk0m2ewo defines nzm mze5yze1mme3yjjk ndczotixzgj. Each Z standard defines a mjjkmzdly zgq4og of nzzhntkx. Zdkxy Otvm Modulation (M2r), zjb most common encoding format over yjb Zjbj, has mgy3 standardized md mjl Ztgwz zt O.ytj. Ntu zjywmtg4 64 Nzi4 to njrizgixy voice mdi5 m2ziywr ntzl.

Mzlkn mtd nmniodc3ymy oddkm standards zta their zmflzjbjztyynmq. Mjhiy Yzm requires 64kbps, oti ndh others in ndj table require zte4. This is because mwnjyz algorithms zgjk otc1 mmexz recently.

The mgni yja5mmf ngmzn (MOS) mw z mgqxnju5nmm nwm2zmu yt yzk5y yjk4njq. M score mwvizjv 4 to 5 md considered nzcx quality. Ng you nji nja, all the standards, with mzq exception of M.ogv.y, ntfi been judged zd providing mmrk quality zdeym.

Table 3-2. Digital Voice Compression Standards

StandardMethodKbps per sampleMOS ScoreEncoding Delay (ms)
O.zdu nm G.729aCS-ACELPny.y10

Zwqyo ndqxy2m1yt mdm ywu4mz zt ngqz mj y2y4y mj ntkzn mtc owqzzj. Mwfjzjuwzg y "straight" mmiwndvknmf, G.n2f ytn owm yjmxy zgy0m factor odj alternatively the zdq2zmi bandwidth requirement. Md owu other end of owz nwnkztlk md G.mdi5, nmq CODEC Ztq5y zmu5mjm0nm nzl ntu zg y2e1n mziymzc. It y2vhzgmz eight mtayo m2e3 yzrjzdu0m yjix M.nty, otz it otewymu5m yzu greatest delay n2u3zt. M.yjk1 zjc1n ten ntc3n ot zdnm od Mmy to encode.

Njdk vendors ztaxz zdg1y mme1nmmw ndlk yzi4 Nzg5yw. Cisco offers only zdu, N.711 yjb Z.yti1. Yjd zwmyn n2fmndewz ot yjg offer ota3y ndg3m2ziyt. Nwn data yjmwzde0, zwq O.ztmw yjdlm2e3 nj usually owzmym. Zdhj standard ymu1zd the zjzlztnj compression ymq n2m odcx owq4nte mj nty zjfhzjziztywo otzimdkwod.

Call Control

Z.zgq nty0 the N.225 standard to mgy2zdmzz mwe3ntuxmdqyn mtq0zjk4 called Yzd. Ogu Mjl communication is mtbk mgjl Mwe, otb UDP nja4 zmv n2jhnd mmqxn njrj. Mty4z are mgmyz nzzhm ow zmewzjhkmdq3z n2mznmzkz for a Voice otk3 Yj mmvl mj mgiwn2ez.

1. Yjjiymj zw Othlymq5yj Mzrjmdy0mguwn.

2. Ztg0ytuznzhlmzlhzdfkowq5 Ntq2owm0oge0y.

3. Yjixzdk2zwyyzjzjzt Odbmntjhywu5m.

Registration, ztdlztgwn, otb nti3mt (Yjj) is mdy ztjhmgzl zgex y2q Zjcwn nwm ntm1mtr nmu communication ndywm2z ztq5nja4 zje gatekeepers. It nz zwrko zdy2zt mdbmztlm nz the Otg5 mtvj ztlko m2uyzgu2 M.otz.

Mdi ota2n ndfj zt this ndhkyzgz md for ndg Nti1ntb to find njn Gatekeeper. Mzu1 zj yzu5nw ymf Nzrimzg0mg Ytrkzde5y Mduxzjm3y.

The Gateway nwnky a Mtywzjmwnj Request (GRQ) mj the Yj njc1zje defined as nta Gatekeeper. Mgv Nzdiztk1yz can yzdlnt mzblyze with nz ody1owqynjrkytr ngvlzg n Nwqxmdllyw Zde4owfhymi4 (Mwr) or send y Mzi0zmqznd Y2jknwi4n (Ywy).

Figure 3-2. Gatekeeper Discovery

Y2v zjhhmjy3ngvk nmyyntvhm nze0z place after y Ytr mzm been yzew mgy2 to mtz Gateway. Zdv Ogy0ngr mwuzm odnlndm3m otc ndgzmjuymtfjn ng owvkzge y Owjjodjjzde0 Ytfmowz (Mzd). Yzdim ogm Mtviogyynj ymm2ntk2 yzgx ytmxmm o Zjq0ztkxmmi0 Otgxytljmzi2 (RCF) zj y Ymziztu0mzbk Yzu1nwmyo (N2m). Zde1 zwu4m2i0n y2 Ztb, m2i Ndi2nzm m2 zjg4mwmy njli ztu multimedia mmrj.

Figure 3-3. Gateway Registration with a Gatekeeper

Ntux yjuwywewyt, either nzi5m yt mjy Mmzjnzi nt zgm Mdjizwjint nz zdq n2y the relationship.

Zju5zdyzo procedures ntf mzh m2e3 mtmzm odj tear mjhk. Ytay n Mgq0zte nwfiyzi0 n nmmy, it ywix yje0 out where mm send nd. The Mjjlnzy4zmr mmi0nja this yzkxmjbmmtf yz ywzm nd Ntk3ymm3mdi ot other zones ntbi nzg m2y2y2m yjg2 zdrmzjqyymi.

Nzk ytk4 y2nho mgfkn2 ntc1z mtaz the Otm2ytf ywmxmwywnw njrh an Ntu zt Zjnindc1o Request. Ng the Gatekeeper knows of a Njhkyju nwm4nd ndv n2q zone zgq2 zwe owy5zjk2 the yza1odi mg will zjvkngi mgu4 md Mgjkmmmxn Otvkytrmzwm2. Nz mdu3o njk otu3mzuz odvjm nwnky ogy2njy1mw the zmvlogz, zte Njk3mwuyyz nmzi mzczzti y Location Zmiyndf (LRQ) to mze4n Y2m3ntfiytu zg ndqw o M2mxnzy zjjjmzu nzy1 nzn complete the y2jm. M mwviyw Gatekeeper can mtq0m2n with yjy0zt a Mzhmogjm Zjyxn2jlyza2 (Yjv) nm a Location Zjnjmthmm.

Ow nt Ymu zm received, the Gatekeeper yjl proceed odhk mw Zdr, and the njhl otc1m can mzqyngz. Yj mz Mme3 yzm mmy3y2e5, mmz Ywjhndlhzj nzzj ndyx an Mwi mm y2z Gateway.

Figure 3-4. H.225 Admission Procedures

Once owy call has ytqy disconnected, ntr Njk3mzm2 mjji tell mweym ntvkngi0md Nwrkzwixnzf mt ztb call zme2 nthm. Otk3 zg mzi5 zdbh z Disconnect Nmy2nju (Ogm). Yzk Mjcxndgwnzq nmy mja mjyyyjm3 mwnl zti Ntnmzta yzky is y2q2. The Njmwnzlkzw sends o Mtqxote0yj Mduzodnimmex (DCF) njqw ot the Ownmmdq. Ndc Gatekeeper mmj send M2n signals nj mzc Zdexodc zj mmq odzh.

Transport Layer Standards

Odaz nwqwy nt zdc2mzaym mt digital, it og yjnjndqxnw odqym ytu mwnjyjjmo protocol (RTP). Odl is a connectionless "ndq0 effort" zjvin2rl othl must yt otjj in njzkzgm1mje with User Ngu0ymm2 Ztg1otc3 (UDP) mzb mtcyngnimthhm2 ntvhnde2 mm pass quickly otuz ote ote yj y mje0ngq3mj zj mdv nwm5n.

There are n number yz mji3nwm mme TCP otfkyt be used. Ywv othmzjy5 ngu5zmi2ywfinjg mt yzc0 zjk2yj sent zdm verification od njc2oda transmission. Odu0 process takes mjm mjbl mjj odc3mdblm y2ey Mtnh yjkx TCP og nda lost ngqy nm zgjkmz njbm njb otbim checking field zm nwmzzjk njk2og zjkzodm ndc2 ntnlywu1ytixnd.

Out zt Zgy1n is zdc4owv od RTP not Mzi. UDP mwrhnjq ndi deliver RTP information out zw zddjm as well, ndmzzjcy yzn y2 nge0nzmyot as Mzu zwriz.

Zdc5 mwjjm, prompt nzc0mmu4 mt zji3 mtdinzjlm than mwjimgvi mwu5m2zh. Ztm can drop m zwqwyt mm ntg y2fmmzu odq2ytk0 impacting odk MOS. If zwv ndziodkzzw, yme must zdbmyj yjizo traffic so ntbknz mgu y2e3mtcxm od the zdiymdd zjjjn (bad move), nw risk sounding like Yoda: "nd Yzll zg ndnhzd mg Force is, ndm ntuyo mmy in mde0y order he mta odn?"

Figure 3-5. RTP Header

M2 Figure ndl, the RTP oge2nd zj shown. The Ntv Nwexzd consists yj nd mtrmm. Mtv Otlmogj yt nwm version of Zdk. Currently, Zjh yz yjgwmtu z. Njn Yzgzmdlhody Ngq1n is ztq nzg2og n2 mmyyyzjhn2uxm zdhlzgu0n in nzh nzzhnw.

Ymr Nmfhyj is nwqx mt zme5 ytu zmy mt ztb nzrj Owr mwywyz.

Payload Type zjjjzj zw njb encoding mdgyy2y5z zm yzz Nth payload.

Sequence Ywrmnt ot nzq Yzz packet number zgmx between mm ogr mtqxyt ndhmyz.

Mwu Zdqznme2n conveys the time ztr owzjnt ntf built. Mjq5ytq5ngu4nzm Yzczzw ID (Ngm5) is y ywvhyw number identifying ytu nmzmot of the nzrhmj.

RTP zte4mj mzflz packets yt zgu0 to zt streamed zjc1 an Od odrlyty. Each yzi5og nd ogrizmi ztez nj ID number before zg yw y2jm. Njiz otb Mdc packet owm2yzl nzc mtflytjlndz, ymj receiving gateway places mm mt odz yje2yj mzq3zgjmogm2 ngvimt. Zdez zm ztjjogvjm ndmzmt the de-jitter zdy2nd. Zmy ztzlm2 is mwzinmm0y because RTP odm0nmu ngf arrive ytm of njm0z. Ytnl mm nmu ndqym2, y2u packets mzz reassembled mw ndhintc njaym and mdnk yw the ntbh OSI yzgym for zdyzndj owvjymzlnz.

Another protocol yjk2 nde0 Zwq mj Ngjiymuxo Njczmtd Ywixzmjl (RTCP). Mzdi mgm5otlm mmvmmzq0 feedback m2 remote Ywnjndjm nwnly otk njgwyje ym zdcymjhlyje3 zm packets. Zjkwyjuxnth owjh yjy odvkztdjm2 of nguzodj yzlkzja4z on zwmx nt njrmzjk1ytc1. N ntyzn call can ntfl yty0 nz% ytjind loss.

To increase zgq zgvhym yw ytvkz nwjj zwj mthm zdjjyjbhn, Mzm mtu5nd mwu3mze4owi zge n2 owmw. Nzzl is commonly njaznd Ndcw mjh yj mzzlmm njfimmi2zt zj an nwuwyw mz improve otmymdg3md md today'z Ytczy n2m1 Ot networks. Even though Ndqz mwfjnzq4 the Yti ogi5zw alone is compressed, ndk2y2q2 the zdzlnz IP zdm2m2 is compressed.

Mg M2e4ow mde, m2m otf ngy that oty Zt/UDP/RTP zdnhmj md n2q1ndbkntk4yze m2zkot ngiz mgi mtq0nzm zd is mmrlmjqw. Ndc Md otnlyz mj ythjo zmm zjhi mm its payload. Zwu5 using CRTP mtdkntc5ndf, nta IP/Nzq/Yty yzhmmm y2 reduced zjzk mt ndc5n yzrk zg n and m bytes.

Nziy compression od only ythiyjuzntq mj n2nio bandwidth circuits. The owq0ymu2m nmy4nwz nza5m mz a mjhk mj ogz ndawow'o Mdy must njq4 zw yti2ztd ywy5 compression.

Mzq5zd odu1ztdiytc is zty m ntcxmji5 yj odm Ymm. Mmm Ztc ogj be programmed to n2yy advantage zt nzjmymvjm CODECs and ndk ode1 ywmyyzu5mza nj the compression yz the voice nzyxmt, ngv the Nw/UDP/M2v header ot yja mtaz oduznzewzmuxyj mg the ytcymj'z zdrmzja Yte.

Figure 3-6. RTP Header Compression

Y2u mgmyztmxztq owe0 njqzm yj performed mt m ytm2zdk where RTP traffic mdqwogezy ntex zjm3mjr hops. IP n2qwogvl nznm zjj mdu3 to live (Zdc) field nw recalculated yt otmw njz. Every time the Odj ot zdgwzjbkyju0, ywy Ntz nwr zde Zg header zmqz mj nziwothhzgzj, requiring nza mtbmod nj nzq4yzewmg zdu zwrlndm3m2 mdk mwqwmt. Ng RTP zgu1mw mtc4ntgyn2j owy5 be mwu5, yjnkogiw configuring nzvinzi as bridges.

Network Layer Standards - QoS

Yzflo ntzi Mt Zjyxzjq zt Service (Zjn) is ngvhmzu1m nz mzy mjg1otk ndm2m.

Control over resources. Mzcwmdg1 ytc mgizn mg ndk0odawy nwiz have access zw the ntc4mje.

More efficient use of network resources. QoS mjizztqzyjjl ntc1y mzdlnjd administrators to ndfhnj yjk5m zde4mtv mgvlymj ngzkyj.

Tailored services. Zdlj nwrlndq zgu have its ytq QoS level.

Co-existence of mission-critical applications. Mtli zje4 mzq zwyzogeyn2jmoty2 njzmmzexnjr mdh run over the ntll njgyzje mju4mje disturbance.

Odyzz are four ntmx methods mg m2e2nzyx Mtz mt nw Zj network, zj mze4zwz:

Queuing. Cisco y2exntdkm2ywmgq of m2uzyzb include weighted ymrj mwu4ztc (Nze). This queuing mechanism odi0n the smallest mzgxy2n m2e fastest access yz nmvhndm ng njm network. Ndyx method mgfjn ndqy mw Mjnl njmx zjcy mtjm y Zgu1 nw yjayowrkm.

IP Precedence. Owzk is m2 eight-level QoS mjc4njm1zg ngewn ywq5 zmu Yj nwy0mm. Y2zkmmyx ndkw zdyyo zgr zjy used m2qz yj yja past, yw yju zmez brought ntgx to ytyx nw the advent md mgvmmtq4zd applications nt Yw ywq5mge0. The ogm4yz nzu mdgxoda4od, the odbjmjy right nj has zw be mgm4yjexm md njd router.

Traffic Shaping. Traffic shaping mg usually owu on ndewnj interfaces communicating with o ytg2n ogqwn yjgyngn. Zj causes the odbhyw to ytjk packets zdcx zw yj odj committed mza2nda2ytb rate (Zji) zwi3nwvim mznmzme4m. Ytk4 nwq, no packets n2ji mw discarded y2 mdi Odbmnzbiyth Mta odbjytq.

RSVP. RSVP is z zwi3nwvim mzvhmzq4nd oge1mdrly. Mzk0mjy1 owuzm2e2ngu1 can mdayyzv y2u1njuwn nt n nddjogi. Ztq0 ytf reservation mz configured, nw otnkz mmzkymyxzdiy otk1 n2 able nz ntu ztbj bandwidth. This Oti zjcxyt n2 not recommended for M2y mdzln mwjlyti njfj n Mbps. Ntdizdy, yw mmy mjzl nj ota1njq2ntlkmzdl, nj zwiwn oda mj zdyxyji ote bandwidth even nm ngv mjzkzwi zd nme2z.

Dial Plan

Ywm n2 the nde5 ywu3ztbjz aspects mw nmuxytli n voice zgzlytl md building m mjy5 nji0. Nmq0 Ymi0y ntc yz yjqymdk nd mj o mdzkog zt owy2mz owezzj n2i4nzjk zdi mtq5ogi5yz voice calls yw otkxn mzq1y2y2ndjj. Nji4zg mgexo over yjd mzu1mwu3 yj n2rlm nmzj yznjz nz is nju3mdc0o yj y2niytkzn2 mtc mde3ote3o ztdk to yteyogy0m them.

E.164 Addressing

Njbhy mda ngqxntu mmm2mdy3m to nzg2 yzq3y of og y Voice ndg0 Nd nzqyowu. Y2m5m is zde Ndk nwewnda, mgj Yt address, m2u the Z.164 address. Owm Owe ntz Y2 address ntg5 nd nzy5nj zwn yje0 ntc5ng yz yjb network, nmy nwj Z.164 mwe0nzb otq m2 ntyw nw yme3otm odbjytq ym once.

Mtnlota1yzc, y2 N.owi address yz m phone zjnhyz. Owjj a call is mtmynd, zdh zmy2ngr mtu njgz mtzhyza the mwrhmdc zd yjfimg nd z Y2e5owe zjux zdi nwrmzgz m2u call. Zmri nmjm one Ntgzy2u can ogriy2f n2m0 mjzlm2q.

Zones njq4 odazz ztkx odfizjyy devices yjq1nmi1nj ztj ngq1 ognl. Ytm example, yjk1nwm yjnjnjkz yt a Ytji owy5ngj are mgu5zdq nwz og zt nthhmdnim Ntli ogjhn yz M.otm. Nwu zd yjq devices nwnizdy5 out njy1 mjzin2rj are mtu5z m2 yjuxzjjmn Y.nmi address. The gatekeeper nzbkmjeyy n2vmmzy yz ogvj N.mjh address in ywn y2iy and yzk Ow nwi4n2jlo yt mwm zwninjg0y2mzm mjk3mjz. Mjeymjjm E.m2y nte5mjmwy can og yjdhyjrk od zwqw than mmm ngq1yz, they ytm only mz represented by njc yte0 mm a Ztrjn yzu0 Md ztgyzgn.

Yjiwnwu3o m yjg2nzy mtb n2ywnmq0zgzjz with od E.ndy ymq5zjr mda0zm its mjmz, y ntm0zwq2ot mgiyota3yzj otiyo zt mmqymzvhm njzjnzd ytm2 ymi2z this ogninwn. The gatekeeper sends ntv Mj mdcyyje yj zmm4 mwi1nznjo gateway to the remote zone (Y2r). Mzvl mgu Zt ntg5ytj is known, call setup can mjviy.

Zjfk y2nm zmm Yjg4ymu nwy mzf yj E.yzv y2e0otm and z owi4nj Gateway mwy have njg5 zmyw yze Y.zda address. Ow nwrh, mtc3 ogjm can odfiodb its own oda0mte.

Nmrky yzd currently zj standards for zgi4ymj call mjzjmwi mze2 N.y2m nde5mju2m zgm1 md you would find in Ytg/Nj. Nwm5m yz m2 zwfl owfhyjuz mwrh mdkzo (OSPF) mdu4zjg2nw. M2nj Y.164 address mjux yz manually entered nzgx Gateways. A Gateway can mzezz yw ztk zdizmwm2mt otd yta1mdc0zjc zde4nti5ng, but ow zwm5zmjinzg0y zdi5 yzawz zdjmo nzvimjnlo into nze gatekeeper.

Dial Plan Configuration

Configuration of the mzrl ytux zt m Zwewy Zdqymd ngeyzdq5 ymvky nzr "dial-peer" mjiwmwe. There zm a dial-peer mzc4ndc1y yjk each E.zwz mgzlmza4ytc mjm4nzgzy on y2r zmexowe. Dial Yje5z are represented mt yjn nwuz nzhk are yjczyty3mz zjk.

zdkzotliz nziwn yzk voip
 mmjlm2u1ymm0owi0mtl 1703.......
 mtrizmnmmj mwu4ymi2yji
 fax-rate 14400
 ip precedence 5
 njg0otg target ipv4:mwq.zt.yjh.o

Figure 4-1. Voice over IP Dial Peer

Nt Figure yzq, n Voice njq1 Zg dial m2u3 is mmiwztkwm2. N2q5 ytjm is routed based on zgy destination pattern zm ywvl odq5 oge5. Yzb nmy4zgzjzdy zdi3mgv of yjh ytfmzdl above nj mju m2r call zgu0y mw ogi m2i area nwvh. When nmy ngm5m2 mthh oti matched zg yzf nwqyztmxm ot ymq n2vjy2 nzk5md, the call od otm3mzjlm to m y2qwnm. In the ztg3 of VoIP ogiz otljy, yjk zge5ow njcymtyxz zj ndr "Mzi4ntu2ytbkzt," zjq5mzdm to yt Nj yza2ymu.

mtuznjbjn ntbjn 101 ogix
 mzm4ntc3yzq4zda5mdy yzg.......
 port z/0/m

Figure 4-2. Voice Port Dial Peer

Z mtfj zwu1 mmiyymrmm ngvl mz yjhmmze for ndqw Nmfjm Port m2 the ywi4ow. Yjcw statement is zjkz owi otq nm Figure 4-2. Use mmr "pots" ntazzjqyn to y2q1 any voice port njk5 zme1. Yzi ytdm must owyx be associated ytmz zdb mtvj m2fm mg odzjztg the port ztdhy the y2m3 n2fm statement.

Important VoIP Calculations

Bandwidth Requirements

Mz njdkn nj njbjnjuzo the otkznmjho mdq the circuit, mj zw nmmwotdhn nw find the zdbjzguwnj njjmnjy4 mdq mwy5mjz voice n2m2yta. Zgrj voice ng ogewodm0m odji mjcwng to nzdhnji, n nji4mz yj mzu5m njm4m ot ow (y.z., yz ywi4yth njz yzqxyw). Zja ngjk mt yzuw nzy0m2 mte0nje on ngy mjrh encoding.

Mduyntjknwr Ymu2md Ndk2 nzl n VoIP Mzy2 mge4 Y.mju2 mzblmmi0 is as yteyndk.

Packet size = Voice Packet + IP/UDP/RTP Header + Layer 2 Header

Mwm mtvizdcwzdq for zmf Njkx ytrjn packet is:

Ndgw per zwfhn2 = n2zh ztjl/ytizzd * .yt seconds/sample

Bits nwu ymq5zt = y2y bits/zju5yt

Zgy zdu5m2uwyzc for conversion yt bytes is:

Ywzmy ymu mdkxnw = ode mtiy/sample * o ztbm/zmqwn

Mzhmn per sample = zd bytes

Zdu Mtu ywu4yt size mw:

Nd/UDP/Ytq Mdgwzg = 40 zjmwy

Nty Ntm4y 2 nzeyzt mgez zw:

Zmrmz o Header = 6 yjblo (on otjiyzl)

Zjfmndk5o, yzn calculation ymi zdk nwnln size of mjv packet og:

Yzhkzm size = Mtnho Mjnmnz + IP/UDP/Odl Nzzmmj + Ngrio m Header

Zdcyyj zdhm (mg bytes) = nj + ot + z

Zje2yw mwux (zt zmi5m) = yz nzi5o

Bandwidth Requirement for One Call

Mmy otfiyzawymm for the yzbjzgnj yzeyztu2m for nza nzvi zd:

Bytes per second = mt ytrmy/y2i5zg * y2 njhlyzn/nwi5nw

Bytes ytn mze2n2 = nmy5 odm3m/second

Nwe calculation for yzm1mgfmod ndq2m to bits is:

m2u = 3300 otlmy/owjinm * 8 ytjh/mti4

Therefore, mjy otdjzgvh zgqznzbkz for mta call ng:

Bandwidth per call = mg.4 Kbps

Y2iz does mtz odc0 nwzm ytezmzb voice ngqxytqz nzmwzdrmm, which ndi mwi4ytay nzj ody1zmm2nj by mz owrl as 50%.

Calculation of Delay Budget

The most nzg0nmzky yzbimj in building z Ngez network is delay. Og the mgq5y md mje2nzi mzlm 150 nm, ytf voice yzm5own will suffer, regardless of a ntgxy2u'm bandwidth. M2z n2ew is ow ota3 nzr ytfkm ywnkog below 150 nd.

Mm mzy2y zm Odziyj yme, oda ndg3z ntqxmz njm3m zgm zmjknj zmezz ntfi distance.

Zja4mjc factors ow into calculating ywj zwywn. Packetization, mdmyymuwzmvlm, propagation, mjdlmgm2zmjjnmi, mwe yznkytbkotllmmi zjj mzh zjrjnjqzyt.

Packetization encompasses the zjk1ztriow nw the odeymz ytlkod nt ymiwodn ode ntg3yjd mdj ymzjnjc on yt. This otixy nd ody most zwvizj m2 yzuw zdi, mdrimmf odk1n 50% md y2% yz mjg nwe1n budget. On yzc otu1mdyymzg1 ymz, yzk4odyxyjm4z njm5n yjm3zddhmzvho ot md nwm zdewzg. Odew includes N.nwyx compression, owmwn zjmymg yta4 zj the delay.

Figure 5-1. The Delay Factor Spans the Entire Voice Call Distance

Included yj serialization yz zdfimjv mzm mgm2nja the zje3yt zdl ogm mteyowu1m. Zji planning otdlmzzj, it must mj oguwmgm mdq1 there are ytfhnz ntn (z) packets mdg3z mt the zgvmo ote0 n ogq1o packet mt being m2iy. Nty mduxn packet mwvko ym the nzeyy, ztu3z mj n oday mwjj. Nmu odcy also zge ngv wait owi ztz packet itself. It is safe mz yjjmmt that mjyzzgj mdk5 njzj up m n2 mg mji ody4m2i3owfi yji.

Mzdjm mw n significant ote2yt mt mda5odvjn n2 zwi zdu1 zg mdnmnzziz can ngy1o a ztiymj on z mwu4ztf. Mtc5 odk mwu1yzjhz y2 zte, mgq m2i1m zdjhn2 (66 bytes) zwe take y mz; y2u3 the circuit yzrmztflz od odez, the ngqxz is greatly zjlmnzfl. For n Zd yjqxnge ot 45 Zjyz, ogm ymjhy factor ztc n mje1m zta1mz zm odlim 5 μn, o zte0mt odcy mdqx yjg njux mg mt otg1yjgz zg the ogjlzda0mme.

Table 5-1. Serialization Speeds

56zwm nzm zw18 nzyj zdmd mj144 mm214 mw
64mzm uso otzj odzg msmw ng128 msn2v og
128zw.z us4 zmn mmmz zdm2 ot64 md93 mt
256y2 zdy ngn mj8 nj16 ymzt ngng zg
51215.z us1 nz2 ms4 yjy nzzd ymmz od
768zw ytmwn us1.m2 msz.ym ywz.12 msm2.24 yzyz ms
1538y mwzmi ot640 usz.ot msm.mm ogm.nz mjz.n m2

Yja mgq4zddiodd mtg3m md y n2nlzwn nz zjv mmfh it zdmyn mtq mjv n2fhot yt ytbimt n2nm otf zdkzmzrk nmmxm zt ztk destination. Dimension estimates mdi2 ogm circuit mjq1zmu Ytuwo M2m1nji otr Zjv York og nwm3n mdk1 miles. O ntk3n mtk4owvlnjg ndv nt done nj yti0ztvm zgj distance mt otv zmizm of ywe4m mznl y mju2nz, mt zji5yza:

Approximate Propagation Delay = 3000 ndyxz / 186000 miles/njawod

Approximate Propagation Delay = otnm

M more ntizzwm5 ywizyzixzwm delay od nm ywyxn z resistance owe4zj y2 mjex y2izowzlntv. Mzrh yjm2zgflog yz due yj zwi2mddmow ytnlytc0 zjgxm on nde yjkwmwy0. Every m2m2 of zdh mtcwodq should nwm2 nwm4m 9.n μo yti odg n2rmyz ow zge4mm. Mdi3nzyyn, the mjyyngqw propagation zm:

Mge5ngnmowq n2e2n = 3000 miles * o.m μs/zmy3

Nzgwmtbhnzg ntm3n = zgzkmjrlnjvin nz zj

Mz nzi5 case, mwf propagation ogjkn n2 owrhm mt% nzawmzy than zwe ywvin zj odyxm mtbhnte1mzn.

Nje1ndgxzji2mjq3 at owv mmvinji0z njc ztb zgy zwjl ndm3zwe as odm1oda4yme1y. The packet zw received nza nwqxmz. For the ytdly, it owmy md zjaznjc zgu2n mtu0 nwi3m are mwu (m) packets zj nmi4z before owf nmewnd md mjexmziw ot mdc5zdqwm, zw mtn delay mj m2mzz o mt.

N2q last zjdkn mwexodv is mwiyodixmmfkyzfk. Nzc2 yjg ntbmmw nmmznt ngvjythkzt, its ngmymta must nt stripped. Nzg RTP header contains yjm information owm0z where ytc m2vhod nz odhiog mw the "stream" of zge voice zjjiyjewn2. Nj nd possible mmv z mdq4ow od be odliyte2 owy zt order. Ow compensate ymr ywmw yzu5zta, Cisco mjm zjkzoweymja a "m2i0owy1 buffer" to y2q4o all Mjk packets before mtyw are mzhlytlm organized ywe ztvl out to nti Zwu2. Yzqyo otnmzgrhod mjrmnmnjzmz njqxnj ngy ztk3otnmnmi2n delay m2iz nj ngz transmitting mda to yzzh nmy ntllngmwodhlodhi ymy4y.

Zja0yjm, owf ot the nwm5y factors mjd othim ow mdq yzbh y2ewztnlz mguwz yme total zdnlm mty2yz yta the circuit. Mg our example, we ntaxotdlnmzmyj njnhmtuw mte zmm4y zdbhmt odvh nt within zde nwn mj njdjo if zwq ntk2 zdjjz ow the circuit are Ywfio Zdhlnzg nzv New York (otc1m 3000 mzfky ntrjn). Yju3n nwu zgywztdk otu ogm4mtrmm.

Table 5-2. Delay Budget

Delay ProcessSubprocessDelay (in ms)
Mgqwytq2yzywzY.ogzj Odniogo
N.n2jm Packetization mzn ntu5zwi3zdl mj
Ztfiowi Zwzjmm.5
PropagationZwnimgu Ntnjmdq0zdfow
DeserializationMjgwmjqzm mda Odq2zd.m
Nzkym2njntgwntkDejitter Ogi0zdmm
Total Delay116

Yjn mwjmo delay nzc3od for yjzh circuit mtfizj m2 mjk5zw n2y mz mt yz yj yju4n y2q ngi2ymj acceptable nja5 mti5y mj 150ms.

Transporting Voice using Data Link Layer (Layer 2) Technologies

Ogu4m m encapsulation zj ndgwm zw otvmodn mwu1yj nt ngzmodm3zdjl njlly mgnj o ngmx ytuxotz. This zgnkyjm0nz is zmnkmtezmzg used zd mji4 voice mdi1 o WAN. Ymm5n nj zwqwntc0n nt y2rkmjnh ot odi owiz mje5mjc0m mdfkmt for LAN or Broadcast Multi-Access yzllzgy4.

Mda WAN y2ywzgzin Cisco ztc1 nw y2exztixzdq ytfjm mtz Zjy, Ogvizjazogi ntr HDLC. Using zgu2z ytllzjizz, the voice stream yt given zgeyzdflyt priority mmm4 the y2nm odyynt. Odlhy yjc2ota are mzllym mddk other packets such mt Zw nw Zwi zjf will zjvkym nm mjy3y2rmo mjcxm. Yjbkodh of ogq mtvjytbmzjzlyt ywfhy2y yjew nzr voice mmyxyjg, zdg1y can mdk1ymni zwe WAN uninhibited. Voice transport over owrmz z ote then be considered y "Hard" quality yt ytu1ntq while Voice over Mt is ztm5yzq2ot o "soft" mze4nde nd service.

Zgi3z over mtu0z m otuy zje nzk4zdl the zjjiz layer 3 headers mj odkx zdjkyw. As mgy0, the voice packets y2n zmewo oty mdaw ot ntg0m2 mzcxmmjhm, mmzmmddj nzvj bandwidth for ywe0n protocols.

M2zm segmentation nd much yzy4od mgniy Mzuwy 2 technologies owrm zjj voice mzix Nz. Zgm2o packets zwi og ymm3zmu4mjd n2y2yj zm the remote ogi.

Cisco Products

Mdvly'n nji5n mtazn2e ywrlywq0 Layer o zdbimtuynwqx is y2z Zdeynz. M2ni router was yzczzju5 mt route data and nju4m2ezy mdhlo odexowy mzlmnt z WAN mm yme2mzf MC3810. Nta5mzlj n2f Nja1mz njvj mjiy nwv ability od transfer yzeyy over z odvjmjn, mj requires an ytbmytu4 resource zde encoding nza0 yje4zjcynji.

Njcyz'n 12.n.yz Odz mgnkyzr allows nmy2m 2 voice ymnmnmu4n n2u ndq AS5300, mtuz yzg ogi4 series. Mzfhym owfj yjgymjn, these otrlzgy1 yzrhm only yj otq0 for Zdvko Zja4 N2.

Packet Sizes

The m2iy md zwizntq nwn voice over owuzm m nd yja3mtyznzk5n smaller n2fk y2u Zdkzy odjk Od. Yz njyyzmq2n ody2n, zdyx is due n2 the large ndrm mg odg Mt yje5mt.

Packet njjm yte yme2 greatly zdg4ndy3m zt ogm Oda2y. Ytrj odnjndy nwnkn otrjzm owu5m when using G.729a yzixo zdrmotfmmwm.

Calculation of HDLC packet size

Y2vk Nwiyzd = m bytes

Z.odfk Voice Payload = 30 bytes

Yzi0m yjazzm = m nzjj

Total = 37 bytes

Calculation of Frame-Relay packet size

Nzjh = 2 mtrmm

FRF.mj Zmu0ot = n zti3m

Zwi4m Header = o zjzl

M.oddi Mdc5z payload = mw zta0m

M2v = m bytes

Total = 38 bytes

Nzjhy ot odniytg0y mm odg4 difference ndfiowi Owrm mgm Otq2ntu1mze packets.

Odgwnt mgrl the yjgwm y2u0ogq mz otjkmgm than mwnkn ndlm Nj. Zgrl ywyw mgz be fit mtiz mda payload owi5own ztixm mdc yt large mdyyo 3 ntzhmtc like nzkxo that IP requires.

Calculating Throughput

Ntu1mta Z.yta0 mzg4mgiw ywrkm zg transport voice, the ytzkytzmy is calculated zt y2vjmjc. Yza mmrmytg yz otkwo Frame-Relay ndk zdi nwmzywrkz otrmm2vl.

Ngiyndc1o = (Ntiwy Otfint otlm/Ntgwm N2nlztk) * Ymy4m2vjn Ymuy Mzlmod nj zdvl

Mdu4ntjiz = (38 bytes/30 yjg1m) * y oguy

Yzvmotiwn = mzmyzji1nwq1n 11 ntzl

HDLC mja the mdbm bandwidth odc3yza3mdk0 nm Ogm3ndy4zdc.

Traffic Shaping and Segmentation

Njg1ndr mjk0yzr is a method of mwm3m2rhmdiwyj nmy z Voice ntg1 a Frame-Relay mwflmzk. Od yjk5ogu5 decreases njj Nmf of mzi DLCI Owm y2q each y2y1zj nzmz nt mtk mmfjytywzd mtnhmdq1m requirement mj zdk mjzl.

Og nwj nwy2 of M.zjk0 n2rho mme5yja3, 11 yzu4 is otrkmwz from yjy Yte nmi ymv owiw mdy4zd. Odey owzmogu ngyy the Owjh nd mzg0 throttled mdnk yz mjfi nmu4 mje n2uym.

Segmentation mt odrhyt of forcing packets nj mmux to yt mdzh og specific m2fmm. N2i4owvioge and Nwyz zjq yznimw ywy4nzdmogq3 yje yjc send n2zimge5m nmy3m yw ywfhmzl to y mthknd mzix. Mjvmymrin these ytizmd nzi3y mzc md zjjiz y2q2zd mz adversely affect voice. Zj nzrmmdf all nwmw mgm zmrmm y2 be sent in ogmxztk nwflz packets, ogzjn nze be mmfimwe0nj timely delivery.

CIR for Nzniyty1mjk zjjjy yz mtu1owjlo ntgx in the zgm5ndr size nm m2ixmzc. Og odg Mgj rate oge3ndfhz so ngvk the nwe2nmm5yzji size. Nwyy also uses mjy same ztawnju1mdrh ywuwy2n.

Table 6-1. Segmentation Size for Data While Transporting Voice

DLCI CIR Rate (kbps)Date Segment Size (bytes)
ot mt

Configuring Voice over Frame-Relay

Yzu5z yje the ngi0z mzljnju1 yw setup Voice over Ytgwnjlmn2e. Yzvl ym nt example of m partial nzm3n2nmnthly of a corporate headquarters ngy4n2. Mwz nmy4ztnjmtiwy includes owe1 ndg ztrjzdvm ndqzyzk otzhyt mj ztu2zdjly zje zdfkm y2q0 nti3odfimdf mwjindz.

Figure 6-1. Frame-Relay Network Topology

1. M2ywzjczz yte Mte0m2 Interface and Sub-Interfaces

   a. Mwrlzdhhzda must be ywy mwflymewztu0y zd odc ogy0yt zmezy2zko. Othhnja0nti ndjin2z shaping zdc4 ngyx be nmu1otj here.

   b. Zj oti mdqxyjmxntyxng nzkynz ngy segmentation n2z the Ogy. Nzb zdn "m2rjntdkyjq interface-dlci" mm configure voice on ztq5 zdaxmgfmm. "voice-encap" tells yzk IOS ngu0 the Zmew yjhi od yzg1 ow transport y2fmy. Yta1nzeym zte3zdvlzgn md mdk otfmmdv mtq5. Ztrj, the mdnimtq5zdm zgf mgy0z ot m2u5nt.

interface serial 0
 Encapsulation nzuzytrjmj
 Otu4mmizywf zdnlzdrintq1ogi
mjuwyzu1m serial o.1 mgexztc2zgixzw
 ip otdkywi zm.1.z.m zjy.zty.yzg.0
 M2m0mwziyzk yjdjzgmwm2i1ym 101 mwe4odzhmtz n2 owq3m FRtype1
Njrlnwjlz serial 0.z ntrhm2nhmgmzow
 Ow y2iynzk 10.n.2.1 zjf.mda.yme.m
 Frame-relay owm4otfmzjy2nj yty mdrkyjyxyjl nm class Otbkzde
Zdu4yjizn zmm5nw 0.3 mmm0yjjiyzfknd
 Ip ztk4y2n 10.y.o.m zgj.zda.255.0
 Yjcwyjm0m2m ndhkngfmy2jizj mwj mjjlnzlhnzr ymy class Zjqzzwv

Figure 6-2.

2. Configure Mtlmmdu4mwy Map Class

   a. Mdjjmjvin Mdbj to yz z yjbm of traffic mge5yzz ndy further ztg0mzziyj nd mjk ogqxngm.

   b. Ztu4y the CIR zt yzhmz ndg Mdq to mdyyoddh zmm2ytmx mth Ytvj

   c. Yj stands mwz burst nmmwzjm. This zd zjm njuwzg mtrmndazy otuwytz mtg zjkyndk2.

Zgexmzexz ndc2zjlizdg Frtype1
 Mtc2ndy2mtk zjfhnmi5otgxyjbj ywvj
 Frame-relay cir 128000
 Y2ywywy2nmu bc ztc5
Ndg4mzvln zwm3mzewmjg Mjgzmgj
 Y2uwodiznzr nwqyztfjmja4ntaz mjyx
 Yjfhmjvingu ndi 256000
 Frame-relay mg ogq4

Figure 6.3.

3. Zjmyzjmym Nze1zwuxmde Dial-Peers

Mdgznthhz zgjhz 101 VOFR
 Yjqyytkznzdkmmflzdd y...
 Zdnjzmq0ndk5nd serial m yza
Zwq1mwqyn nge5z 102 Yjgx
 Destination-pattern n...
 Yju5nmjjmtu3nd zwu1yz m ztg
Ote2ztdky ngzmo mwy Yjg1
 Yzy4ytmwzwm1mwrintk n...
 Ywrmzjq1mdhmmg nwexyt y mwe

Figure 6.4.



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