1. VoIP—Voice over Internet Protocol EE290F Spring 2004 Xiaoxue Zhao

2. Content  PSTN-Public Switch Telephone Network  Packet-Switched Network  Comparison between PSTN and IP Network  VoIP Standards  VoIP Services  QoS—Quality of Service

3. PSTN—Components  Access Lines (Local Loops) Connects customer premises to the local voice switch  Switches Connect access line to each other  Trunks Connects voice switches to each other  PBX—Private Branch Exchange  Signaling—Connectionless PSTN Used for basic call set up, management, tear down and enhanced call features etc.

4. PSTN—Structure Trunk Network CO Switch CO Switch PBX Signalin g Network Signalin g Network Voice Channel Multiplexing Residential customers Business customers Access lines

5. PSTN—Features  Connection-Oriented, Circuit-Switched  Guaranteed Bandwidth “All the bandwidth all the time.”  Stable Delays Connection Establishment Information Transfer Connection Release Connection-OrientedConnectionless

6. Packet-Switched Network  Packet—Unit of data containing the network address information  Network Layers  “Best effort” Application Presentation Session Transport Network Data Link Physical Application Services Transport (TCP) IP Network Access

7. Virtual Circuits Virtual CircuitData Design philosophyConnection-orientedConnectionless Addressing entityCircuit identifiersNode and network addresses Unit of informationPacket, frame, cell Network entitiesSwitchesRouters Bandwidth useAll allowed by networkDepends on number and size of frames ExamplesFrame relay, X.25, ATM, most other WANs Internet Protocol (IP), Ethernet, most other LANs

8. Comparison Network FeaturesPSTN (Voice)Internet (Data) SwitchCircuit SwitchedPacket Switched ConnectionConnection OrientedConnectionless Bit RateFixed and low <=64kb/sWide variation to Gb/s BurstsNonexistentHigh (100/1000:1) Error toleranceUser error controlError free Info resendingCan not (real time)Can be done very fast DelayMust be low and stableCan be high and vary

9. Packetizing Voice VoIP IssuesSolutions Packetizing delaySmall packets for VoIP Serial delayPriorities and jitter buffers “High” bit-rate voice (64kb/s)Voice compression Constant-bit-rate voice (PMC)Silence suppression and comfort noise Resend due to errorsReal-time Transport Protocol (RTP)

10. Why VoIP?  Cost Reduction  Simplicity  Advanced Applications Web-enabled call centers Collaborative white boarding Remote telecommuting

11. VoIP Standards  H.323—ITU-T  Session Initialization Protocol (SIP)—IETF Voice Coding Methods (ITU-T G series, etc.) Call Control/Session Initialization (H.225, H.245, SIP) Timing (RTP) Gateway/Gatekeeper Control (GLP, MGCP) Reliable/Unreliable Transport services (TCP/UDP) Internet Protocol (IP) Packet Network Infrastructure Application Layer Transport Layer Network interface Layer Network Layer

12. H.323  Packet-Based Multimedia Communications Systems  H.323 Architecture  H.323 for IP Telephony

13. H.323 Architecture H.323 terminal H.323 multipoint control unit (MCU) H.323 gatekeeper H.323 gateway H.323 terminal H.323 terminal PSTN V.70 terminal H.324 terminal Speech terminal N-ISDNB-ISDN QoS LAN H.322 terminal Speech terminal H.320 terminal H.321 terminal LAN

14. H.323 for IP Telephony VideoAudioControlData H.261 H.263 (video coding) G.711 G.722 G.723 G.728 G.729 H.225 Terminal to gatekeeper signaling H.225 Call signaling H.245T.120 (Multipoint data transfer) RTP (Real- time Protocol) RTCP (Real- time Control Protocol) RTP (Real- time Protocol) RTCP (Real- time Control Protocol) Unreliable transport (UDP)Reliable transport (TCP)

15. SIP  Proposed by Internet Engineering Task Force (IETF)  Application layer control protocol  Borrow design and architecture from the Hypertext Transfer Protocol (HTTP)

16. VoIP Services  Self-provided Customer  Independent of Internet access  Provided by broadband access service provider  Corporate Internal Use on Business LAN / WAN  Carrier Internal Use

17. Self-Provided Customer  IP connection  Voice-enabled device  Examples: Skype, MSN Address Info Internet Address Info Call setup and Call data

18. Independent of Internet Access  Customer in agreement with IP telephony company, independent of ISP  Uses gateway to connect to PSTN  Calls can be made to either VoIP users or PSTN users  IP connection and Voice-enabled device  Examples: Vonage, Packet8, Net2Phone PSTN Interne t Gateway SIP phone Analogue phone SIP Server Signaling and Call setup Signaling and Call setup Call data PSTN call PSTN signaling

19. Provided by Broadband Access Service Provider  Customer in agreement with IP telephony company with is also ISP  Uses gateway to connect to PSTN  Provider is in control of the network so offer quality guarantees  Analogue terminal adapters are provided  Example: Yahoo!BB (Japan) Access provide r networ k Access provide r networ k ATA SIP Server for both users Signaling and call setup Signaling and call setup Call data

20. Corporate Internal Use on Business LAN / WAN  No service provider  In-house telephony on LAN or WAN  Services are those of a full- featured PBX Ethernet LAN Ethernet LAN Gatekeeper PSTN Gateway IP Router WAN or Internet PST N Converter Gateway PC based virtual phone Analogue phone Ethernet phone

21. Carrier Internal Use  Softswitch instead of circuit switch, including H.323 gatekeeper or SIP server  Most based on H.323  Mostly in international calls Carrier Network Carrier Network H.323 Gateway H.323 Gateway Carrier SoftSwitch Analogue phone Call data Signaling and set up

22. QoS—Quality of Service  Bandwidth  Delay  Jitter (Delay Variation)  Information Loss  Reliability  Security QoS Parameters

23. References  IP Telephony Walter J. Goralski and Matthew C. Kolon McGraw-Hill  Final Report for the European Commission—IP Voice and Associated Convergent Services