Protocols Suite
By: 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
OSI
TCP/IP
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)
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 Header
“The structure of H.225 follows
the Q.931 standard”
H.225.0
Information Elements
Messages
H.225.0 - RAS
RRQ
RCF
RRJ
ARQ
ACF
ARJ
BRQ
BCF
BRJ
DRQ
DCF
DRJ
IRQ
IRR
RIP
– Registration Request
– Registration Confirmation
– Registration Rejection
– Admission Request
– Admission Confirmation
– Admission Rejection
– Bandwidth Request
– Bandwidth Confirmation
– Bandwidth Rejection
– Disengage Request
– Disengage Confirmation
– Disengage Rejection
– Info Request
– Info Request Response
– Request in Progress (RAS timers)
LRQ – Location Request
000
00001
00010
00111
01111
00011
00101
01101
001
00110
01110
00010
00101
01101
00001
00000
010
00101
01101
11010
00110
01110
011
00000
11001
11011
01110
11101
xxxxx
xxxxx
xxxxx
xxxxx
H.225.0 - Q.931
Call establishment messages:
ALERTING
CALL PROCEEDING
CONNECT
CONNECT KNOWLEDGE
PROGRESS
SETUP
SETUP ACKNOWLEDGE
Call information phase messages:
RESUME
RESUME ACKNOWLEDGE
RESUME REJECT
SUSPEND
SUSPEND ACKNOWLEDGE
SUSPEND REJECT
USER INFORMATION
Call clearing messages:
DISCONNECT
RELEASE
RELEASE COMPLETE
RESTART
RESTART ACKNOWLEDGE
Miscellaneous messages:
SEGMENT
CONGESTION CONTROL
INFORMATION
NOTIFY
STATUS
Messages (cont.)
H.245
Message
Master-Slave Determination
Function
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
End Session Command
Commands the far-end terminal to indicate its transmit and receive
capabilities by sending one or more Terminal Capability Sets.
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
Online
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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-w
Book
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Stallings, William. Data and Computer Communications
Images
http://www.h323forum.org/
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.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
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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