H.323 Overview

Demystifying Multimedia Conferencing Over the Internet

Using the H.323 Set of Standards

Numbers to know:

• H.225 - call setup, establishment, tear-down

• H.245 - media capability negotiation

• H.261 & H.263 - video codecs

• G.7xx - audio codecs

H.323 Architecture

Audio and Video codecs

H.225 Layer

H.245 Q.931 RASAudio and Video I/O

How does all this work?

( the signaling example )

How does all this work?

Calling party opens H.323 client

How does all this work?

Q.931 Setup

Setup

How does all this work?

Q.931 Alerting (ringing)

Alerting

How does all this work?

Q.931 Connect

Connect

How does all this work?

H.245 terminal capabilities

termCapSet

How does all this work?

H.245 terminal capabilities

termCapAck

How does all this work?

H.245 determine Master/Slave

mSDet

How does all this work?

H.245 determine Master/Slave

mSDetAck

How does all this work?

H.245 determine Master/Slave

mSDetConfirm

How does all this work?

H.245 open channel (RTP)

openReq

How does all this work?

H.245 open channel (RTP)

openAck

How does all this work?

RTP connection

connected

How does all this work?

H.245 End Session

endSession

How does all this work?

Q.931 Release Complete

ReleaseComplete

Gatekeeper

• Purpose is to manage resources in a zone

• Uses RAS signaling

• Provides address resolution

• Alias Address Modification

• Approves calls based on bandwidth

• Dialed Digit Translation (PSTN)

• Directory Services

Advanced Features

• Interoperability with PSTN

• Centralized, decentralized, and hybrid multicast conferences through MCU

• Datastream and multicast encryption (H.235)

• Cascading MC’s for large conferences

• FastStart connection (similar to SIP)

H.323 Issues

• Interoperability issues between clients

• Massive, monolithic, closed specification

• Not designed to be readily extensible

• Competition from simpler, open, IETF standards (SIP, SDP, RTP)

Why is this important?

• Stress test of real latency sensitive data

• H.323 central to QoS issues

• Authentication carried out through CiNIC?