Protocols SuiteBy: Aleksandr Gidenko

What is H.323? H.323 is a multimedia conferencing protocol for

voice, video and data over IP-based networks that

do not provide a guaranteed Quality of Service

(QoS).

It was designed to operate over complex networks,

such as the Internet.

H.323 was first approved in February 1996 and

was published by the ITU in November 1996.

VoIP Usage

“By mid-2007, there were 11.8 million consumer VoIP subscribers in the U.S. (more than 10 percent of U.S.

households), according to a recent report from TeleGeography. By the end of 2007, this number is

projected to reach 15.2 million subscribers and to 23.3 million by the end of 2011.”

H.323 Usage

- Public Switched Telephone Network

H.323 Protocol Stack

TCP/IP

OSI

H.323 Protocol Stack (cont.)

H.225.0

Registration, Admission and Status (RAS)

Used in gatekeeper discovery and endpoint

registration.

RAS is unreliable. H.255 recommends time-outs

and retry counts for some messages.

H.225.0 (Q.931)

Call Setup and Termination

Used to setup connections between endpoints.

Creates a reliable control channel using TCP on

port 1720.

H.245 Control Signaling

Handles transmission capabilities and mode preferences.

Used to exchange end-to-end messages between

endpoints.

Resolves call media and established media flow.

RTP

Real-time Transport Protocol (RTP) is used to

transport real-time media such as audio and video

over IP networks.

Provides timing information and transport-level

sequencing.

Uses application-level framing and integrated layer

processing.

RTCP

The RTP control protocol (RTCP) handles the transmission of

control packets to all participants in the session.

RTCP Functions: (Outlined in RFC 1889)

1.Quality of Service (QoS) and congestion control

2.Identification

3.Session size estimation and scaling

4.Session control

RTCP Packet Types:

1.Sender Report (SR)

2.Receiver Report (RR)

3.Source Description (SDES)

4.Goodbye (BYE)

5.Application Specific

H.323 Communication

H.323 Call

...

If time permits...

Lets get technical

Headers

RTP Header

RTCP Header

V = Version

P = Padding

X = Extension

M = Marker

CSRC = Contributing Source

SSRC = Synchronization Source

Headers (cont.)

H.225.0 HeaderH.225.0

Information Elements

“The structure of H.225 follows

the Q.931 standard”

MessagesH.225.0 - RAS

RRQ – Registration Request

RCF – Registration Confirmation

RRJ – Registration Rejection

ARQ – Admission Request

ACF – Admission Confirmation

ARJ – Admission Rejection

BRQ – Bandwidth Request

BCF – Bandwidth Confirmation

BRJ – Bandwidth Rejection

DRQ – Disengage Request

DCF – Disengage Confirmation

DRJ – Disengage Rejection

IRQ – Info Request

IRR – Info Request Response

RIP – Request in Progress (RAS timers)

LRQ – Location Request

H.225.0 - Q.931

000 xxxxx Call establishment messages:

00001 ALERTING

00010 CALL PROCEEDING

00111 CONNECT

01111 CONNECT KNOWLEDGE

00011 PROGRESS

00101 SETUP

01101 SETUP ACKNOWLEDGE

001 xxxxx Call information phase messages:

00110 RESUME

01110 RESUME ACKNOWLEDGE

00010 RESUME REJECT

00101 SUSPEND

01101 SUSPEND ACKNOWLEDGE

00001 SUSPEND REJECT

00000 USER INFORMATION

010 xxxxx Call clearing messages:

00101 DISCONNECT

01101 RELEASE

11010 RELEASE COMPLETE

00110 RESTART

01110 RESTART ACKNOWLEDGE

011 xxxxx Miscellaneous messages:

00000 SEGMENT

11001 CONGESTION CONTROL

11011 INFORMATION

01110 NOTIFY

11101 STATUS

10101 STATUS ENQUIRY

Messages (cont.)H.245

Message Function

Master-Slave Determination Determines which terminal is the master and which is the slave. Possible

replies: Acknowledge, Reject, Release (in case of a time out).

Terminal Capability Set Contains information about a terminal's capability to transmit and receive

multimedia streams. Possible replies: Acknowledge, Reject, Release.

Open Logical Channel Opens a logical channel for transport of audiovisual and data information.

Possible replies: Acknowledge, Reject, Confirm.

Close Logical Channel Closes a logical channel between two endpoints. Possible replies:

Acknowledge

Request Mode Used by a receive terminal to request particular modes of transmission

from a transmit terminal. General mode types include

VideoMode, AudioMode, DataMode and

Encryption Mode. Possible replies:

Acknowledge, Reject, Release.

Send Terminal Capability Set Commands the far-end terminal to indicate its transmit and receive

capabilities by sending one or more Terminal Capability Sets.

End Session Command Indicates the end of the H.245 session. After transmission, the terminal

will not send any more H.245 messages.

Terms

ITU - International Telecommunications Union

MCU – Multipoint Control Unit

MC – Multipoint Controller

MP – Multipoint Processor

MGC – Media Gateway Controller

MG – Media Gateway

RTP/RTCP – Real-time Transport Protocol / Real-time Transport Control Protocol

SIP – Session Initiation Protocol (Competitor Protocol for VoIP)

IETF - Internet Engineering Task Force)

References

Information Site: http://www.packetizer.com/ipmc/h323/

Protocol Overview: http://www.en.voipforo.com/H323/H323_objetives.php

Primer: http://www.packetizer.com/ipmc/h323/papers/primer/

H.323 VS SIP: http://www.tspt.net.et/documentation/VOIP/H_323versusSIP.htm

Open Source Project: http://www.h323plus.org/

Open Source Project: http://www.openh323.org/

Javvin: http://www.javvin.com/

VoIP Usage: http://techuntangled.com/us-voip-market-skyrockets-as-cable-companies-lead-the-way

Online

Book

Stallings, William. Data and Computer Communications

Images

http://www.provu.co.uk/ipvideo_wvp2100.html

http://www.packetizer.com/ipmc/h323/images/h323_logo.gif

http://www.networkdictionary.com/howto/VOIPUsingH323ProtocolWork.php

http://www.h323forum.org/

http://www.protocols.com/pbook/h323.htm

http://www.ncih.net/h323/h323link.html

http://www.networkdictionary.com/howto/VOIPUsingH323ProtocolWork.php

http://techuntangled.com/us-voip-market-skyrockets-as-cable-companies-lead-the-way

http://www.humanproductivitylab.com/archive_blogs/2006/10/22/cisco_joins_videoconference_fo_1.php

Side Notes

RTP - RFC 1889 RTCP - RFC 1889

“It is a part of the ITU-T H.32x series of protocols, which also address multimedia

communications over Integrated Services Digital Network (ISDN), Public Switched

Telephone Network (PSTN) or Signaling System 7 (SS7), and 3G mobile networks.”

(http://en.wikipedia.org/wiki/H.323)

“H.323 is an ITU VOIP protocol. It was created at about the same time as SIP, but was

more widely adopted and deployed earlier. Today, most of the world's VoIP traffic is carried

over H.323 networks, with billions of minutes of traffic being carried every month.”

(http://www.voip-info.org/wiki/view/H.323)

SIP is an application-level control protocol.

Video codecs: H.261, H.263, H.264 Audio codecs: G.711, G.729, G.729a, G.723.1, G.726 Text codecs: T.140 (from Wikipedia)