Voip-voice Over Internet Protocol

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 CO Switch

CO Switch

Trunk Trunk Network Network

PBX Residential customers

Signalin Signalin gg Network Network

Business customers

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  Packet—Unit of data

containing the network address information  Network Layers  “Best effort”

Application Presentation

Application Services

Session Transport Network Data Link Physical

Transport (TCP) IP Network Access

Virtual Circuits Virtual Circuit

Data

Design philosophy

Connection-oriented

Connectionless

Addressing entity

Circuit identifiers

Node and network addresses

Unit of information

Packet, frame, cell

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, Internet Protocol (IP), most other WANs Ethernet, most other LANs

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)

Application Layer

Gateway/Gatekeeper Control (GLP, MGCP)

Reliable/Unreliable Transport services (TCP/UDP)

Transport Layer

Internet Protocol (IP)

Network Layer

Packet Network Infrastructure

Network interface Layer

H.323  Packet-Based Multimedia

Communications Systems  H.323 Architecture  H.323 for IP Telephony

H.323 Architecture H.323 multipoint control unit (MCU)

H.323 terminal

LAN H.323 gatekeeper

QoS LAN

PSTN

V.70 terminal

H.324 terminal

H.323 gateway

Speech terminal

H.322 terminal

H.323 terminal

H.323 terminal

N-ISDN

Speech terminal

B-ISDN

H.320 terminal

H.321 terminal

H.323 for IP Telephony Video

Audio

H.261 H.263 (video coding)

G.711 G.722 G.723 G.728 G.729

RTP

RTCP

RTP

Control H.225

H.225

Terminal to gatekeeper signaling

Call signaling

Data H.245

T.120 (Multipoint data transfer)

RTCP

(Real-time (Real-time (Real-time (Real-time Protocol) Control Protocol) Control Protocol) 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  IP connection  Voice-enabled

device  Examples: Skype, MSN

Call setup and Call data

Address Info

Internet Internet

Address Info

Independent of Internet Access PSTN PSTN  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

Analogue phone PSTN signaling

PSTN call

Gateway Signaling and Call setup

Call data

SIP Server Interne Interne tt

SIP phone

Signaling and Call setup

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)

Call data

ATA

ATA

Access Access provide provide rr networ networ kk

Signaling and call setup

Signaling and call setup

SIP Server for both users

Corporate Internal Use on Business LAN / WAN Ethernet phone

PSTN Gateway

PST PST NN

 No service

provider  In-house telephony on LAN or WAN  Services are those of a fullfeatured PBX

Converter Gateway

Ethernet Ethernet LAN LAN

Analogue phone

IP Router

Gatekeeper PC based virtual phone

WAN WANor or Internet Internet

Carrier Internal Use  Softswitch

instead of circuit switch, including H.323 gatekeeper or SIP server  Most based on H.323  Mostly in international calls

H.323 Gateway

Analogue phone

Call data

Carrier Carrier Network Network H.323 Gateway Signaling and set up

Analogue phone

Signaling and set up

Carrier SoftSwitch

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