Domain 1 - Describe Cisco VoIP Implementations

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2 Maual ONT (642-8) Domai 1 - Describe Cisco VoIP Implemetatios Advatages of VoIP Over Traditioal Switches Voice over IP etworks have may advatages over traditioal circuit switched voice etworks. These advatages iclude improved badwidth utilizatio, cosolidated etwork expeses, ad uified messagig itegratio. Traditioal circuit switched etworks utilize a complete 64-kpbs chael; withi T carrier etworks this is called a DS0. Withi a T-1 there are 24 DS0 chaels equalig Mbps. Packet based voice like VoIP allows more efficiet use of this space through compressio. This compressio allows a umber of chaels of voice to be trasported over a sigle DS0. The highest level of compressio that is curretly used is 8:1; meaig a sigle DS0 ca trasport 8 chaels of voice. Up util the creatio of VoIP, voice ad data etworks were separate. VoIP eables these two etworks to be cosolidated ito oe. Cost is the obvious advatage of havig a cosolidated etwork. Havig to desig ad maitai two separate etworks is cost prohibitive whe it ca be doe with oly oe. VoIP eables uified messagig itegratio. A phoe ca become ot oly a way to talk to someoe but also the ability to itegrate with video service, database services ad several other techologies which eable easier commuicatios throughout a compay. VoIP Compoets Like ormal telephoy systems, VoIP has a umber of compoets which are used to commuicate i various ways. These compoets iclude phoes, gateways, gatekeepers, call agets, Multipoit Cotrol Uits (MCU), Digital Sigal Processors (DSP) ad various applicatio ad database servers. Phoes Gateways Gatekeepers Call Agets Multipoit Cotrol Uits (MCU) Just like ormal telephoy systems, phoes are used to commuicate via voice. However, with VoIP ad Video over IP these phoes are exteded to ot oly provide audio commuicatio but also provide video commuicatios. A gateway is a device which is used to commuicate betwee two differet types of etwork. I VoIP applicatios, this ca be used for multiple thigs icludig coectig aalog phoe systems to VoIP systems or coectig from a PBX ito a VoIP etwork. i.e. Usig a stadard phoe over IP (Voage). Gatekeepers are used for two purposes, to perform some call routig ad call lookups (IP to Phoe Number), ad to perform Call Admissio Cotrol (CAC). Call Agets are used whe a cetral cotrol model is used; this essetially meas that call admiistratio is doe via a cetral locatio. This icludes call routig, traslatios, call setup ad teardow amog other thigs. MCU s are used i coferece commuicatios, specifically the MCU is used to combie multiple streams of traffic ad joi them together seamlessly. Table cotiued o ext page LearSmart Cloud Classroom: Video Traiig s Mauals

3 Maual ONT (642-8) Digital Sigal Processors (DSP) Applicatio ad Database Servers Withi VoIP, The DSP is used heavily. The DSP s i a VoIP etwork are used to covert aalog sigals to digital sigals ad compress them. Several differet servers ca be used i a VoIP implemetatio; this icludes applicatio servers for Call loggig ad cofiguratio maagemet amog others. Database servers ca also be itegrated with VoIP, this eables XML- based iformatio to be available at the phoe level. Aalog & Digital Iterfaces I order to commuicate with ay etwork, iterfaces must be used. Withi a VoIP etwork there are two differet groups of iterfaces; aalog ad digital. Aalog Iterfaces Iside voice etworks there are three differet types of aalog iterfaces; Foreig Exchage Office (FXO), Foreig Exchage Statio (FXS) ad Earth ad Mageto (E&M). FXO ad FXS iterfaces are used with oe aother, the FXO iterface is coected to the telephoy switch ad the FXS iterface coected to the telephoe equipmet (phoe). Whe a call comes i, the FXO iterface is alerted via rig voltage from the switch the the FXO iterface tries to trasport the sigal to the FXS. The FXS is resposible for receivig the sigal from the FXO ad providig battery, dial toe ad other sigalig to the telephoe equipmet. The E&M iterfaces are typically used to coect Private Brach Exchages (PBX) which exists iside offices. The PBX is essetially a small telephoy switch that allows differet features to be used iside a office eviromet; these types of features iclude extesios, forwardig, ad coferecig amog others. There are five differet types of E&M iterface; types I through V (1 through 5). The details of each iterface are beyod the scope of this maual but types I ad V are the most commo; Type I is typical i North America ad Type V is typical outside North America. Digital Iterface Withi VoIP there are a couple of differet digital iterfaces; Basic Rate Iterface (BRI), T1 ad E1 beig the mai oes. A BRI is used for small office coectivity ad provides two chaels of voice (64 kbps each), which are called B-Chaels ad a idepedet sigalig chael (16-kbps), kow as the D-Chael. T1 sigalig ofte gets cofused because there are two differet ways to sigal with a T1 iterface. The two differet ways are Chael-Associated Sigalig (CAS) ad Commo Chael Sigalig (CCS). CAS utilizes what is called robbed-bit sigalig, this is because T1 s are divided ito frames which fit ito either a Superframe (SF 12 Frames) or a Exteded Superframe (ESF 24 Frames). Each frame icludes 24 timeslots which are used for the 24 T1 chaels ad each frame icludes 8 bits of each chael plus a framig bit. I CAS sigalig the 6 th ad 12 th chaels have their low order bit robbed for use i sigalig. CCS sigals a completely differet way, it utilizes oe full 64-kbps chael for sigalig ad leaves the other 23 chaels for traffic; this cofiguratio is typically called a Primary Rate Iterface (PRI). Havig defied this, BRI is cosidered a CCS iterface utilizig oe full 16-kbps sigalig chael. E1 s all operate the same i a CCS cofiguratio (sometimes they ca be icorrectly called CAS). A E1 iterface icludes a total of 32 chaels, with 30 beig used for traffic. E1 s are split similar to T1 s except their framig is a little differet. E1 s are split ito multiframes which iclude 16 cotiguous frames ad each frame icludes 8-bits of each chael. The 1 st ad 17 th chaels are used for frame sychroizatio ad sigalig, accordigly. There are o framig bits withi a E1 like T1 s have. LearSmart Cloud Classroom: Video Traiig s Mauals

4 Maual ONT (642-8) Traffic Packetizatio I order for a aalog voice sigal to be trasmitted across a digital etwork, it must first be digitized. This is doe through a process kow as packetizatio. Packetizatio has four differet phases; samplig, quatizatio, ecodig ad compressio. As show i the followig figure, packetizatio takes a aalog waveform ad coverts it ito a stream of digital 1 s ad 0 s. 1 secod Figure 1 - Packetizatio Samplig The first step i digitizig a sigal is to tur the aalog wave ito somethig that ca be digitized. This is doe through samplig which is also called Pulse Amplitude Modulatio (PAM); samplig takes slices of the aalog wave at cosistet itervals. Withi samplig, the Nyquist theorem is followed. This theorem states that i order to adequately digitally represet a aalog sigal, the aalog sigal must be sampled at a rate of twice the highest aalog frequecy. Withi voice etworks the frequecy rages from 300 to 3400 Hz is trasmitted, because of simplicity it was decided to sample from 0 to 4000 Hz over digital lies. Whe followig the Nyquist theorem, this meas that this sigal must be sampled at 8000 Hz which traslates to 8000 samples per secod. I order to demostrate this process the followig figures have bee created. Istead of showig 8000 Hz samplig the followig examples show 40 Hz samplig, to keep it simple. First a aalog sigal must be separated ito pieces, because 40 Hz samplig is beig show, this aalog sigal is split ito 40 differet pieces (samples). LearSmart Cloud Classroom: Video Traiig s Mauals

5 Maual ONT (642-8) secod Figure 2 - Separatig the Aalog Sigal From these, pieces or samples are take which best represet the aalog sigal; this is show i the followig figure: secod Figure 3 - Creatig Samples From this figure it is see that the digital samples represet a sigal similar to the aalog sigal beig coverted. Obviously, the more samples that are take the more like the origial aalog sigal the digital represetatio will be. LearSmart Cloud Classroom: Video Traiig s Mauals

6 Maual ONT (642-8) Quatizatio What this stage of processig does is it calculates a mathematical value for each sample take, this is also called compadig. The rage of umbers that ca be assiged is from -127 to +127, as see from the followig figure each sample is give a umber secod Figure 4 - Quatizatio There are two mai algorithms which are used to calculate these umbers, µ-law ad a-law. µ-law (mulaw) is the formal stadard i North America ad i Japa; a-law is what is used i the rest of the iteratioal commuity. It is also stadard i µ-law coutries to covert to a-law i order to commuicate with a-law coutries. LearSmart Cloud Classroom: Video Traiig s Mauals