VoIP—Voice over Internet Protocol EE290F Spring 2004 Xiaoxue Zhao

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

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.

PSTN—Structure Voice Channel Multiplexing Access lines Trunk Network CO Switch PBX Signaling Network Voice Channel Multiplexing Residential customers Business Access lines

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

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

Virtual Circuits Virtual Circuit Data Design philosophy Connection-oriented Connectionless Addressing entity Circuit identifiers Node and network addresses Unit of information Packet, frame, cell Network entities Switches Routers Bandwidth use All allowed by network Depends on number and size of frames Examples Frame relay, X.25, ATM, most other WANs Internet Protocol (IP), Ethernet, most other LANs

Fixed and low <=64kb/s Comparison Network Features PSTN (Voice) Internet (Data) Switch Circuit Switched Packet Switched Connection Connection Oriented Connectionless Bit Rate Fixed and low <=64kb/s Wide variation to Gb/s Bursts Nonexistent High (100/1000:1) Error tolerance User error control Error free Info resending Can not (real time) Can be done very fast Delay Must be low and stable Can be high and vary

Packetizing Voice VoIP Issues Solutions Packetizing delay Small packets for VoIP Serial delay Priorities and jitter buffers “High” bit-rate voice (64kb/s) Voice compression Constant-bit-rate voice (PMC) Silence suppression and comfort noise Resend due to errors Real-time Transport Protocol (RTP)

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

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

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

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

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

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

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

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

Independent of Internet Access PSTN Internet Gateway SIP phone Analogue phone SIP Server Signaling and Call setup Signaling and Call setup Call data PSTN call PSTN signaling 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

Provided by Broadband Access Service Provider network ATA SIP Server for both users Signaling and call setup Signaling and call setup Call data 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)

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

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

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

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