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VoIP System with Gateways

dieter-tucker
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VoIP System with Gateways

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  1. ECEN5553 Telecom SystemsWeek #9[19a] "IT Helps Passengers, Crew Navigate…"[19b] "Open source IP PBX saves serious cash…"[19c] "SIP Trunking: The Savings Are There…"[20] "All-Optical Networking- Evolution, Benefits…"Exam #2 31 October – Local No later than 7 November – Remote DLTerm Paper 7 November – Local 14 November – Remote DL

  2. VoIP System with Gateways 2 Voice Switch/ Gateways 1 B Voice Switch/ Gateways 3 4 Routers A MPLS could nail down paths. DiffServ could give voice priority.

  3. Network Used for Numerical Results to follow... OC-3 Access 2 Voice Switch/ Gateways 1 Routers B Voice Switch/ Gateways 3 4 OC-12 VoIP Backbone A G.729 Coders. MPLS could nail down paths. 20 msec end-to-end propagation delay

  4. 150 msec End-to-End Delay1 Frame per packet Voice Coding Delay (.015)+ Packet Assembly Delay (1*.010) + End-to-End Propagation Delay (.020)+ Service Times + worst case Queuing Delays at the voice source and all intermediate packet switches + Receiver De-Jitter Buffer Delay+ Voice Decoding Delay (.010) = 55 msec 95 msec to spend - trunks can be heavily loaded But most bits moved are overhead (47 out of 57B).

  5. Gateway A to Gateway B Path Packet M Time Packet 1 Packet 4M M Packets Packet 4M Worst Case Delivery Packet M Packet 1 IAT Packet 1 Packet 1 Packet 1 Our Packet Distance GA R4 R3 R2 GB OC-3 OC-12 OC-12 OC-3

  6. 150 msec End-to-End Delay5 Frames per packet Voice Coding Delay (.015)+ Packet Assembly Delay (5*.010) + End-to-End Propagation Delay (.020)+ Service Times + worst case Queuing Delays at the voice source and all intermediate packet switches + Receiver De-Jitter Buffer Delay+ Voice Decoding Delay (.010) = 95 msec 55 msec to spend Optimal for this example.

  7. 150 msec End-to-End Delay10 Frames per packet Voice Coding Delay (.015)+ Packet Assembly Delay (10*.010) + End-to-End Propagation Delay (.020)+ Service Times + worst case Queuing Delays at the voice source and all intermediate packet switches + Receiver De-Jitter Buffer Delay+ Voice Decoding Delay (.010) = 145 msec 5 msec to spend - Trunks can't carry much traffic But traffic carried is 2/3 voice (100 out of 147B).

  8. Ten Voice Frames per Packet Trunk Capacity limits (622.08 Mbps trunk) 594.4 Mbps * 100 msec/IAT = 59.44 Mb/IAT Packet Size = 47B + 100B = 1,176 bits (59.44 Mb/IAT) / (1,176 bits/packet) = 50,544 packets can be moved every 100 msec End-to-End Delivery Delay Time to inject on 622.08 Mbps line = 1,176 / 594.4 Mbps = 1.978 micro sec Time to inject on 155.52 Mbps line = 1,176 / 148.6 Mbps = 7.914 micro sec 5 msec > (M +1)7.914 micro + 2*1.978 micro M < 630 calls Can support 4*M = 2,520 OC-12 calls

  9. 150 msec End-to-End Delay11 Frames per packet Voice Coding Delay (.015)+ Packet Assembly Delay (11*.010) + End-to-End Propagation Delay (.020)+ Service Times + worst case Queuing Delays at the voice source and all intermediate packet switches + Receiver De-Jitter Buffer Delay+ Voice Decoding Delay (.010) White Items = 155 msec 0 msec to spend Impossible to meet delivery specification.

  10. Voice Calls Possible Over an OC-12 Trunk(G.729 Fixed Rate Coder) fixed 40000 100 msec 150 msec 30000 Trunk Voice calls supportable 20000 POTS can support 8,192 calls on an OC-12 10000 0 1 2 3 4 5 6 7 8 9 10 11 Number of Frames per Packet

  11. G.729 Variable Rate Coderwith Silence Suppression On a typical interactive conversation…A Specific Voice is Active 40% of timeCoder generates 8 Kbps Voice is Quiet 60% of timeTransmit 0 Kbps Average of 3.2 Kbps generated per simplex call

  12. Full Mesh CO CO CO CO N(N-1)/2 Links 4*3/2 = 6 Links for this example.

  13. Hierarchical CO CO TO CO CO One connection per Central Office.

  14. CO Connectivity CO TO CO TO CO CO Hierarchical Direct Connect 2nd Parallel Hierarchical Minimum of two diverse routes out of Central Office.

  15. POTS Connectivity Small Cities have a COBig Cities have CO’s Hierarchical system, add High Usage Direct Lines between CO’s Tandem (Trunk-to-Trunk) Switches Minimum of two physically separate routes out of all switches desired Best compromise of cost & reliability

  16. POTS Items in a typical wired phone:microphone & speakerhybriddialing circuitry (DTMF)on/off hook switchring circuitry Items in a typical CO:crosspoint switchhybridsA/D & D/A convertersecho cancelersTDM or VoIP

  17. Home Phone Speaker Ring Circuitry On Hook Hybrid Off Hook Dialing Circuitry Wall Socket Microphone 4 Wire 2 Wire

  18. Home Phone Speaker Inbound Audio Ring Circuitry On Hook Hybrid Off Hook Dialing Circuitry Wall Socket Microphone 4 Wire 2 Wire

  19. Home Phone Speaker Sidetone Ring Circuitry On Hook Outbound Audio Hybrid Off Hook Dialing Circuitry Wall Socket Microphone 4 Wire 2 Wire

  20. One Wire To get audio out of speaker, need a closed path to get a voltage drop across the speaker inputs Need two 'wires' to get a voltage drop across a speaker one wire can be an actual wire second 'wire' can be the earth Very Susceptible to static Speaker Microphone Earth Ground

  21. Two Wires Speaker Microphone • Resistant to static • Susceptible to EM interference over long distances • Twisting the wires slashes interferenceUsed widely after 1891 • This configuration provides one-way commo • Need another mic, speaker, & 2 more wires

  22. Two Wires Hybrids allow Telco Two Wire lines to carry both outbound and inbound traffic short distances (local loop) Two wire local loops, instead of 4 wire saves $$ on cable plant Speaker Hybrid Hybrid

  23. Four Wires Easier to amplify traffic moving one direction Telco Four Wire lines 2, one-way, 2 wire connections Long distance Microphone Speaker Amp Amp Speaker Microphone

  24. Dual Tone Multifrequency

  25. POTS Connectivity (1920) Copper Local Loop Copper Local Loop Copper Long Haul CO CO Phone Phone 4 Wire 2 Wire 2 Wire 4 Wire 4 Wire Analog

  26. POTS Connectivity (1970) Copper Local Loop Copper Local Loop Copper Long Haul CO CO Phone Phone 4 Wire 2 Wire 2 Wire 4 Wire 4 Wire Digital TDM 64 Kbps Analog Analog

  27. POTS Connectivity (1990) Copper Local Loop Copper Local Loop Fiber Optic Trunk CO CO Phone Phone 4 Wire 2 Wire ‘4 Wire’ 2 Wire 4 Wire Digital TDM 64 Kbps Analog Analog

  28. Simplified Central Office Switch Space Switch TDM deMux D/A Local Loops Echo Canceler Hybrid TDM Mux + A/D 2 Wire T1 Line 4 Wire Analog Digital

  29. Simplified CO-to-CO connectivity Space Switch TDM deMux D/A Local Loops Echo Canceler Hybrid TDM Mux + A/D Space Switch TDM deMux D/A Local Loops Echo Canceler Hybrid TDM Mux + A/D

  30. The Legacy Phone System... Parts are 4 wire (headset and long haul) 4 wire = two unidirectional simplex signals simplex signals make amplification a lot easier Parts are 2 wire (local loop) 2 wire = one bi-directional full duplex signal Turn-of-the-century decision to save $$$ and go 2 wire on local loops Parts are analog (phone & local loop) About 70-80% of U.S. Local Loops are copper all-the-way Parts are digital (long haul, most CO switches, some local loops) About 20-30% of U.S. Local Loops use Digital Loop Carriers

  31. The Legacy Phone System... 4 Wire to 2 Wire Conversion at Central Office Hybrids can cause some problems Singing (Cure: Attenuation) Echoes (Cure: Echo Canceler) Analog to Digital Conversion points also cause some problems CO Switch filters on analog voice lines, necessary to limit noise and interference on voice circuits, limit dial-up modem data speeds to about 33 Kbps Trend is to an all-digital system U.S. long haul POTS voice circuits use digital Time Division Multiplexing or VOIP

  32. TDM One 8 bit time slot provided for each phone call every 1/8000th second. frequency 1 24 bits in 1/8000 second (192 Kbps) 2 3 time 1 etc.

  33. Integrated Services Digital Network Copper Local Loop Copper Local Loop Fiber Optic Trunk CO CO Phone Phone 4 Wire 2 Wire ‘4 Wire’ 2 Wire 4 Wire Digital TDM 64 Kbps

  34. PC Modems & POTS Band Pass Filter suppresses energy outside voice bandwidth (about 3,500 Hz) A/D Converter Twisted Pair Cable Band Pass Filter ≈ 3.5 KHz Sampler Fs = 8 KHz Code 8 bits/sample Quantize 256 levels 64 Kbps

  35. PC Dial-Up Modems & POTS PC Bit Stream has a significant amount of energy outside 3.5 KHz filter BW. Modems squash the energy into the pass band of the filter (at a much reduced bit rate). A/D Converter Twisted Pair Cable PC Band Pass Filter ≈ 3.5 KHz) Sampler Fs = 8 KHz Code 8 bits/sample Quantize 256 levels 64 Kbps

  36. PSTN Digital Hierarchy • Now obsolete except for some T1 & T3on Local Loops

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