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Voice over IP

Voice over IP

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Voice over IP

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  1. Voice over IP

  2. Agenda • Advantages of packet switching for voice communications • VoIP applications • VoIP technology overview • VoIP standards • Quality-of-Service in VoIP networks • Addressability in VoIP networks • VoIP regulatory considerations

  3. What is VoIP? • Technical answer: “the ability to make phone calls over IP-based data network” • Commercial answer: ”the Multi-Billion Revenue Opportunity for the 21st Century” • VoIP > IP Telephony • typically “IP Telephony” indicates using IP terminals • most VoIP is between normal telephones • VoIP < “Voice over Packet” • includes Voice over Frame Relay, ATM, xDSL, Ethernet, WiFi

  4. Circuit switching served voice wellfor 100 years! Signal Transfer Point • Transmission circuits and switch path assigned during call setup for the duration of the call • Call blocks if not enough network resources available • Essentially one class of service: 3.5 kHz, 64 kb/s • Poorly matched for bursty data transmission Signal System 7 Data link Trunk Group Loop User - A User - B Central Office - A Transit Office Central Office - B Class 5 Switching System Connection ThroughSwitching Fabric Class 4 Switching System

  5. Packet Payload Input Buffer Routing Fabric Header Output Buffer Hdr. Trans Hdr. Trans Packet SwitchingWell-matched for data transmission • Great fit for bursty data transmission! • Packets sent at full rate of transmission facility • Supports variable information transfer rates • Resources not consumed when nothing to send • Potential to eliminate call setup phase • But … • Transmission capacity used for header • Buffering introduces varying delays, like speaking to man on moon

  6. IP network PSTN network VoIP Network Architecture • Media gateways provide voice packetization • Gatekeepers provides call control logic and permissions • Gateway provides interworking with ISDN, SS7 and signaling of PSTN (POTS) Gateway Gatekeeper Media Gateway Media Gateway

  7. Advantages of VoIP • Lack of access charges, flat rate or volume based IP • Cheap setup costs competition with POTS • Cheaper switching systems • Per Gb/s, IP routers cheaper than TDM Class 5 switching systems • Ability to operate one network for voice and data • Cost savings through use oflow-bit-rate voice • Ability to offer more complex services • E.g., Multimedia, conferencing calls • Intelligent terminals (e.g., PC) • Better (graphical) user interface • Clean slate design: • Separation of feature intelligencefrom switching fabric supplier • Self-provisioning networks

  8. PSTN Vs VoIP Network Costs • Network costs (transmission and switching costs) contribute only 10-15 % of overall cost of a voice call terminated by an ILEC or a PTT, and 20-30% of overall costs for calls not terminated by a ILEC or a PTT • Of the network costs, switching costs range between 50 % of network costs for domestic calls to 15 % of network costs for international calls, transmission costs contributing the rest • Negligible savings in transmission costs through the use of VoIP: lower bandwidth for VoIP offset by need for over-provisioning bandwidth to ensure quality • TDM Switch costs in traditional PSTN replaced by cost of Router plus cost of Gateway and new billing systems No network cost savings, and very likely a cost penalty, in the initial years, in going from PSTN voice to VoIP for public networks

  9. PSTN versus VoIP

  10. VoIP versus Voice-over-the-Internet • Voice-over-the-Internet • No bandwidth guarantees • No prioritization of traffic within network • All traffic receives “best effort” service • Each Internet user is at the mercy of all other users • Voice quality ranges from acceptable to atrocious However • Internet technology continues to evolve (e.g., IPv6) • Development of Next Generation Internet

  11. What does “Carrier Grade” really mean? • “Five 9’s” reliability (down time of 5 minutes a year) • Full redundancy of electronics, power supplies, fans, etc. • No down time for upgrades or maintenance • Accounting and billing capabilities • Interoperability with legacy telecommunications equipment • Feature parity with equipment it replaces • Service quality measurements • Support for CALEA, unbundling, and other governmental mandates • NEBS compliance for operation in central offices • Both safety and performance requirements • Scalability to millions of subscribers • Integration into the myriad of Operations Support Systems

  12. VoIP market Voice over Internet Protocol (VoIP) gateway sales will increase 280 percent during the next five years, reaching $3.8 billion in 2003, according to research by Cahners In-Stat Group. IP TELEPHONY OVER LAN MARKET FORECASTED TO GROW 138% AVERAGE ANNUALLY OVER NEXT 5 YEARSSeptember 22, 1999 - IP Telephony [IP PABXes], according to a study from The Phillips Group-InfoTech, will spawn a $1.9 billion industry by the year 2004 with an average annual industry growth of 138 percent over the next 5 years. IDC Forecasts IP Telephony Market Will Soar to 2.7 Billion Minutes of Use and $480 Million in Revenues by Year end 1999 Business Use Will Accelerate in 2001 September 1, 1999 - The worldwide Internet protocol (IP) telephony will explode from 310 million minutes of use in 1998 to 2.7 billion by year end 1999. By 2004, IP telephony minutes will reach 135 billion. Revenues for this service will skyrocket from $480 million in 1999 to $19 billion by 2004. IP Telephony Services: Market Review and Forecast, 1998-2004.

  13. Growth in VoIP • Early growth from expense savings • Later growth from revenue generation from new services • Early deployment by enterprises and CLECs • Later deployment by incumbent carriers (source: Frost & Sullivan)

  14. VoIP Applications • Some trends can be discerned: • First wave: Bypassing the PSTN • Second wave: Replacing the PSTN • Third wave: Value-added services PSTN DLC Class 5 Class 5 DLC

  15. PSTN bypass – IP Telephony (PC to PC) • Microsoft NetMeeting or similar • through dial-up/adsl/cable connection to ISP • All VoIP processing in the PC • no special infrastructure required • Issues: • software compatibility • QoS / latency over public Internet • Strange dialing RADIUS server RADIUS server Internet modem modem RAS RAS DLC Class 5 Class 5 DLC

  16. PSTN bypass – IP Telephony (PC to PHONE) • From Multimedia PC to any PHONE • First applications 1993 • Required: • VoIP gateway on the phone side • gateway manager • billing system (unless free) • Issues: • software compatibility • QoS / latency over public Internet RADIUS server Gate Keeper Internet modem RAS VoIP Gateway DLC Class 5 Class 5 DLC

  17. PSTN bypass – IP Telephony (phone to phone) • From any PHONE to any PHONE • First VoIP application – 1995 • Caused by high international tariffs • Required: • VoIP gateway on both sides • gateway manager • billing system (unless free) • Issues: • QoS / latency over public Internet • sometimes it takes 24 digits to reach a subscriber… Gate Keeper IP network VoIP Gateway VoIP Gateway DLC Class 5 Class 5 DLC

  18. PSTN bypass – IP Telephony (phone to pc) • From any PHONE to any PC • First VoIP application – 2004 • Try to replace PSTN • Required: • VoIP gateway on PSTN side • MSN numbers • gateway manager • billing system (unless free) • Issues: • QoS / latency over public Internet Gate Keeper RADIUS server IP network modem VoIP Gateway RAS DLC Class 5 Class 5 DLC

  19. PSTN replacement – Softswitch • Replace complete Class 4 / Class 5 switch • very ambitious undertaking! • different introduction strategies • Required • Softswitch - contains Call Control & Mgmt software • Trunking Gateway – interfaces to “legacy” PSTN • Access Gateway – interfaces to DLCs • Issues: • immaturity of standards (MGCP vs Megaco debate) Soft switch IP network Trunking Gateway Access Gateway DLC Class 5 DLC

  20. PSTN replacement – Integrated access network • Integrating Access Gateway into DLC • Required: • “Next Gen” DLC, with integrated IP gateway • Issues: • immaturity of standards Soft switch IP network NexGen DLC NexGen DLC

  21. PSTN bypass – IP PABX • Two steps: • A. PABX with integrated IP gateway • B. Fully integrated enterprise LAN • Required: • IP PABX • IP phones (step 2) • Issues: • dial plan configuration not easy! • how to quarantee QoS on LAN? (step 2) A B IP network IP-phone IP-PABX IP-PABX PSTN

  22. Soft switch Integrated Access Device IP network PSTN replacement – Integrated Access Devices • Target: single voice/data access network • for example wireless access network • Home networks • companies • Required: • Integrated Access Device (IAD) • gateway to PSTN somewhere • Issues: • immaturity of standards Gate Keeper Integrated Access Device PSTN VoIP Gateway Class 5

  23. Value Added Services • Converged services • Internet Call Waiting • Click to Call • Unified messaging • … • Video telephony (3rd time right?)

  24. Standards for VoIP

  25. The H.323 Protocol Stack Data applications System control user interface Mic Camera H.225 RAS channel Q.931 call setup H.245 control Audio And Video Control RTCP Audio codec G.711 G.723 G.729 Video Codec H.261 H.263 T.120 RTP Transport Layer (TCP or UTP) IP

  26. H.225 RAS Control • Gatekeeper • Optional network entity • Offers bandwidth control services • Offers address translation to enable use of aliases • H.225 • Operates between a Gatekeeper and the endpoints it controls • Provides functions of discovery, registration, admission, bandwidth change, disengage Gatekeeper Endpoint H.225 Multiport Control Unit Gateway

  27. Call Signaling in H.232 • Q.931 • Establishes and tears down calls between endpoints • (Q.931 is the signaling protocol for the ISDN user-network interface) • H.245 • Negotiates and establishes media streams between call participants • Takes care of multiplexing multiple media streams for functions such as lip synchronization between audio and video Q.931 H.245

  28. Session Initiation Protocol (SIP) • User to user protocol • Developed by IETF (RFC 2543) • Establishes and maintains session level information • Creating and tearing down of sessions, session parameters, and media type • Supports personal mobility • Heavily influenced by http protocol • A light weight protocol compared to H.323 • Fewer messages required on a typical call • Allows for faster call setup • Flexible in enabling other information to be included messages • Allows user devices to exchange specialized information to enable new services • E.g., indicate when a busy terminal will become free • Example SIP addressing; sip:9729965000@gateway

  29. Internet call processing • Decentralized (independent, self-reliant, user to user): • ITU H.323 • IETF Session Initiation Protocol (SIP) • Centralized (intelligence in Softswitch): • IETF MEGACO • ITU H.248

  30. To other Softswitches SIP-T MGCP Or Megaco Softswitch IP Network PSTN Network Trunk Gateway Access Gateway Softswitch Architecture • Softswitch separates function of Gateway from the media gateway

  31. ATM QoS Parameters • Peak-to-peak cell delay variation • Maximum cell transfer delay • Cell loss ratio • Cell error ratio • Severely errored cell block ratio • Cell misinsertion rate Negotiated at start of call Controlled via Network design

  32. Real-Time Multimedia over ATM (RMOA) • Developed by ATM Forum • More efficient and scalable than H.323 VoIP over ATM • New type of gateway: the H.323 to H.323 gateway • Placed at the edges of an ATM network • Intercepts H.323 signaling messages to set up virtual circuits in the ATM network • Efficient: IP and UDP headers not carried on the ATM network • Takes advantage of QoS capabilities of the ATM network PSTN Switch H.323 Gateway H.323 Gateway PSTN Switch IP Network ATM network VoIP Gateway VoIP Gateway

  33. Application RSVP Process RSVP Process Routing Process Policy Control Policy Control Control Control Admission Control Admission Control Packet Classifier Packet Scheduler Packet Classifier Packet Scheduler Resource Reservation Protocol (RSVP) Host Router • Specified in RFC 2215 • Reserves resources along path from received back to sender • Implements various services • Guaranteed service – no packet loss and minimal delay • Controlled load service – service like a lightly loaded network • Number of parameters associated with each service • Comprehensive, close to circuit emulation, but at significant cost

  34. Meter Classifier Marker Shaper / Dropper Adding QoS to IP Networks: Diffserv • Relatively simple means for prioritization traffic (RFC 2475) • Makes use of the IPv4 Type of Service (TOS) field • Defines two types of packet forwarding: • Expedited Forwarding – assigns a minimum departure rates greater than the per-agreed maximum arrival rate • Assured Forwarding – packets are forwarded with high probability if arrive no faster that per-agreed maximum • Keeps core relatively simple • Pushes processing to the edge

  35. VoIP access via DSL and Cable Modems

  36. InternetService PSTN Cable Telephony • Where to put the RJ-11 telephone jack? • On cable modem • On set-top box • On separate telephony modem • On interface on side of house • Local powering or network powering options Video Content Head end Fiber Node Gateway

  37. What is DOCSIS?(Data Over Cable System Interface Specifications) • Started 12/95 by MCNS consortium (Multimedia Cable Network System) • Goal: Interoperable cable modems and Cable Modem Termination Systems (CMTS) • Steamed rolled slower (ATM-based) IEEE 802.14 standardization process • Gaining momentum in Europe as EuroDOCSIS (8 MHz channelization) • Testing and certification by Cable Labs

  38. Who are the DOCSIS Cable Modem Suppliers? • 3Com • Ambit • Arris Interactive • Askey Computer Corp. • Best Data • Castlenet • Cisco Systems • Com21 • Dassault • DeltaKable • DX Antenna • ELSA • E-Tech • Future Networks • GadLine • Toshiba • Turbocom • General Instrument • GVC • Joohong • Motorola • Net N Sys • Nortel • Philips • Powercom • Samsung • Sohoware • Sony • Tarayon • Thomson • Zoom • ZyXel

  39. North America Cable TelephonyMarket Size • Cable projected to capture 15 % telephony market share by 2005 • Shift from proprietary TDM solutions towards VoIP DOCSIS • Residential VoIP happening first in the Cable Access Market

  40. Voice over DSL • Integrated Access Device (IAD) provides LAN interface and provides multiple telephone interfaces • IAD could be integrated into NID at side of the home • Voice Gateway provides same switch interface as though lines were concentrated on a Digital Loop Carrier system • GR303 allows for number portability, billing and additional voice features CO CO / CEV PSTN GR303 Voice Gate Way HOME/BUSINESS ADSL DS3 / OC-3 Class 5 Switch Data Network 4-16 1 VC for Voice ATM Switch DSLAM LAN 1 VC for Data Integrated Access Device

  41. IP ATM DMT Analog Spectrum Voice over ADSL Alternatives • Voice over IP Layer 3 • Choice of Voice over ATM in initial implementations • AAL-2 • Low-delay, clear 64 kb/s PCM and 32 kb/s ADPCM • QoS support within ATM • Full PSTN quality • V.90 modem support • Support for Voice over IP gaining momentum • Maturing of QoS capabilities • Potential of IAD becoming a SIP terminal Layer 2 • Voice over ATM Alternatives for VoDSL • Voice over TDM Layer 1 • Voice in separate spectrum(e.g., ADSL over DAML)

  42. Quality issues for the transport of voice over packet-based networks

  43. The three essential stages of packet-based voice transport one-way Mouth-to-Ear (M2E) delay overall distortion (codec & packet loss) (Concatenation of) Packet-based Network(s) Encoding and packetization stage Dejittering and decoding stage Packet transport stage Echo controlperformed close to destination

  44. Components of the M2E delay • Packetization delay is chosen by the source terminal or ingress GW • Minimal delay and queuing delay depend on QoS provided by traversed network(s) • Each network component has its specific contribution • Dejittering delay is chosen by the destination terminal or egress GW Total minimal delay Total queuing delay Packetization delay Dejittering delay M2E delay

  45. Pdf(delay) Dejitteringdelay Packet loss Minimal delay Delay of first packet M2Edelay Trade-off M2E delay vs. packet loss in destination or egress GW • Static dejittering mechanism = delay first packet over dejittering delay and then read dejittering buffer periodically • Choose dejittering delay on save side: for the case when first packet is the fastest possible • Adaptive dejittering

  46. Contributions to distortion • Voice compression • encoding/decoding • voice activity detection • transcoding • Packet loss • in network • in dejittering buffer • Remarks • packet loss concealment techniques • trade-off packet loss vs. delay when choosing the dejittering delay

  47. Trade-offs • Network (transport) parameters • minimal delay • delay jitter • packet loss Echo control Dejittering delay Packet size Header compression Codec Efficiency of transport Voice quality

  48. Speech Coding Techniques • Waveform coding – Tries to preserve the time-domain picture of the signal • Sampling – 2 X highest frequency preserved • Quantizing – the accuracy of each sample • Linear – simple digital / analog conversion • Logarithmic – more accuracy for weak signals • Adaptive – match measurement to size of signal • Sounds great at high bit rates but degrades quickly at lower bit rates • Vocoding – Tries to represent the characteristics of the human voice • Prametric Vocoders • Dozen coefficients to define vocal tract • Indication of voiced or unvoiced • Excitation energy • Pitch • Synthetic sounding at all bit rates but works OK at low bit rates • Vector Quanitization – Matches information signal with entries in a code book. • Uses lots of processing power but provides the best quality at lower bit rates

  49. Major Parameters of Standard Codecs

  50. Influence of packet loss on distortion