VoIP—Voice over Internet Protocol

EE290F Spring 2004Xiaoxue Zhao

Content

PSTN-Public Switch Telephone Network Packet-Switched Network Comparison between PSTN and IP Netw

ork VoIP Standards VoIP Services QoS—Quality of Service

PSTN—Components Access Lines (Local Loops)

Connects customer premises to the local voice switch

SwitchesConnect access line to each other

TrunksConnects 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

Trunk Network

COSwitch

COSwitch

PBX

SignalingNetwork

Voice Channel Multiplexing

Residentialcustomers

Businesscustomers

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

Packet—Unit of data containing the network address information

Network Layers “Best effort”

Application

Presentation

Session

Transport

Network

Data Link

Physical

ApplicationServices

Transport (TCP)

IP

NetworkAccess

Virtual Circuits

Virtual Circuit DataDesign 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, most other WANs

Internet Protocol (IP), 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 SolutionsPacketizing 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/GatekeeperControl (GLP, MGCP)

Reliable/UnreliableTransport 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 ArchitectureH.323 for IP Telephony

H.323 Architecture

H.323 terminal

H.323 multipoint control unit (MCU)

H.323 gatekeeper

H.323gateway

H.323terminal

H.323terminal

PSTN

V.70terminal

H.324terminal

Speechterminal

N-ISDN B-ISDNQoSLAN

H.322terminal

Speechterminal

H.320terminal

H.321terminal

LAN

H.323 for IP Telephony

Video Audio Control Data

H.261H.263

(video coding)

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

H.225

Terminal to gatekeepersignaling

H.225

Callsignaling

H.245 T.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)

SIP

Proposed by Internet Engineering Task Force (IETF)

Application layer control protocolBorrow 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: Sky

pe, MSN

Address Info

Internet

Address Info

Call setup andCall data

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

Internet

Gateway

SIP phone

Analogue phone

SIP Server

Signaling and Call setup

Signaling and Call setupCall data

PSTN call PSTN signaling

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 providernetwork

ATA

ATA

SIP Server for both users

Signaling and call setup

Signaling and call setup

Call data

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

EthernetLAN

Gatekeeper

PSTNGateway

IP Router

WAN or Internet

PSTN

ConverterGateway

PC based virtual phone

Analogue phone

Ethernetphone

Carrier Internal Use

Softswitch instead of circuit switch, including H.323 gatekeeper or SIP server

Most based on H.323

Mostly in international calls

CarrierNetwork

H.323Gateway

H.323Gateway

Carrier SoftSwitch

Analogue phone

Analogue phone

Call data

Signaling and set up

Signaling and set up

QoS—Quality of Service

Bandwidth Delay Jitter (Delay Variation) Information Loss Reliability Security

QoS Parameters

References

IP Telephony Walter J. Goralski and Matthew C. Kolon McGraw-Hill

Final Report for the European Commission—IP Voice and Associated Convergent Services