Voice Over IP

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Voice Over IP

CS158B Project

By

Shing Chau

Jerry Ko

Ying Li

Agenda

Introduction

Economics of VoIP

VoIP and OSI model comparison

H.323 vs. SIP

RSVP & RTP

Demonstration

Introduction

VoIP

Transmission of voice traffic in packets

Internet as the transmission medium

IP rather than by traditional circuit transmission

-

IP originally for data

-

adaptation to voice network protocols (SIP, H.323, RSVP, RTCP, RTP)

Economics of VoIP

Traditional TDM

Dedicated Circuit switched networks

Dedicated voice-only bandwidth

IP

Uses packet switched networks

Many Services, one network (voice, data)

Leverages existing data infrastructure

Flat monthly rate both long distance and local

Various configurations

VoIP and OSI model Comparison

Session Initiation

Three things takes place in a VoIP session:

Signaling

Encoding

Transmission

Two common protocols used:

H.323

International Standard

Session Initiation Protocol (SIP)

H.323

H.323 vs. SIP

Origin

Transport

Emphasis

H.323

ITU

Mostly TCP

Telephony

SIP

IETF

Mostly UDP

Multimedia

RTP (Real-Time Protocol)

How to send voice over RTP?

Application collects the encoded data in chunks

The audio chunk along with the RTP header form the RTP packet

RTP header contains:

Payload type (7 bits)

Sequence number (16 bits)

Timestamp field (32 bits)

Synchronization source identifier field (32 bits)

RSVP

(Resource Reservation Protocol)

Why a guaranteed QoS is needed?

Voice and Video applications traffic can be transmitted continuously

It requires a guaranteed QoS, in terms of minimum available bandwidth or maximum delay, over the entire path of traffic

How to make the resource reservations?

Path messages contain:

Previous hop address

A session identifier

A sender template (the sender

’ s IP address and port number )

A sender T Spec (maximum data rate, maximum delay, etc)

Reservation messages contain:

Reservation Style

Flow Spec

Filter Spec

Summary

Rsession Initiation

SIP (SNMP): simple

H.323 (CMIP): complex

QoS

RSVP

Voice Transmission

RTP

SIP Call Flow

Invite

100 Trying

180 Ringing

200 OK

ACK

RTP

H.323 Call Flow

TCP connection

H.225 Messages (Setup)

H.225 (CallProceeding, Alerting)

H.225 (Connect)

TCP connection

Terminal Capability Set

MasterSlaveDetermination

OpenLogicalChanel

OpenLogicalChanelAck

RTP stream

RTP stream

RTCP stream

Reference

Voice Over IP -

by Uyless Black, a guide to Internet voice communications, covers many protocols

Computer Networking

Networking

-chapter 7 Multimedia

Course offering

-EE284 Convergent Voice and Data Networks,

multimedia in data networks, QoS, Coding,

Signaling, and Inter-working

Thank You!

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