Download - Protocols Suite
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)