H.323 Protocol Suite Guoyou He Helsinki University of Technology [email protected]

H.323 Protocol SuiteGuoyou He

Helsinki University of Technology

[email protected]

H.323 Protocol Suite Introduction What is H.323 Protocol H.323 Version History H.323 Architecture Call Signaling Call Connection Procedures New Features of H.323 Version 4 Comments on H.323 Conclusions

Introduction

Numerous multimedia applications and services are available .

New technology and applications are constantly evolving (e.g. multimedia computer, compression technique, multimedia networks, and transport mechnanisms etc.).

Standards and technology for multimedia communications are evolving at at a prodigious pace.

Many standards have been specified to provide interoperability for equipment from multiple vendors. H.323 is one of them.

What is H.323 suite H.323 is a standard specified for Packet-based

Multimedia Communications Systems by ITU-T. H.323 defines systems and functions for audiovisual

services over packet switched networks which may not provide a guaranteed Quality of Service.

H.323 suite is an ´Umbrella´ standard, references to other standards and ITU recommendations.

Interoperability with other multimedia networks is the primary goal for developing H.323.

Version 1 was approved in June, 1996.

What is H.323 Suite (cont.)H.323 Standards

Network Non-guaranteed Bandwidth packet-switched networks (e.g. IP)

Video H.261, H.263

Audio G.711, G.722, G.728, G.723, G.729

Call signaling and media packetisation

H.225

Call Control H.245

Multipoint H.323

Data T.120

H.323 Version Suites Version 1 – June, 1996

Named “Visual telephone systems and equipment for local area networks which provide a non-guaranteed quality of service”

Multimedia conferencing on a LAN Defined network elements and overall call comdel

Version 2 – January, 1998 Name changed to “Packet-based multimedia communications

systems” More efficient procedures for two-party call setup, e.g. fast call Brought in H.235 Security (Authentication of participant, Integrity of

data, Encryption, and digital signature) Supplementary Services (H.450), Integration of data conferencing

with T.120 Support media over ATM

H.323 Version Suites (cont.) Version 3 – September, 1999

Geared for better PSTN integration and scability (alternate resources, multiplexing signaling channels)

Expanded supplementary services (H.450)

Version 4 – November, 2000 Introduced a lot of new enhancements in many important areas,

including reliability, scalability, and flexibility. New features help facilitate more scalable Gateway and MCU Added more new services New features for usage information reporting, better bandwidth

management, etc.

H.323 Architecture

H.323 Architecture (cont.)

H.323 protocol stack

L_1 Varies

L_2 Varies

IP

UDP UDP or TCP

RTP/RTCP

Audio Codec G.711 G.722 G.723 G.728 G.729

Video Codec

H.261 H.263

Data

Interface

T.120

System Control

CALL RAS H.245 Control Control Control H.225 H.225

System Control User Interface

Data App.

Video I/O

Audio I/O

H.323 Architecture (cont.) H.323 standards specifies the elements, protocols,

and procedures providing multimedia communication over packet-based networks. The four main enlements are: Terminals Gateways Multipoint Control Unit (MCU) GateKeeper

H.323 Architecture (cont.) Terminals

Including Video I/O equipment, Audio I/O equipment, User Data Applications, PC, and System Control User Interface etc.

Used for real-time bidirectional multimedia communications Compatible with the terminals on the inter-working networks Client Endpoing on the network Must support audio

G.711 (64 Kb/s) is mandatory G.722 (48, 56, and 64 kbps channels), G.723 (5.3 and 6.3 kbps channels), G.728 (16

kbps channel), and G.729 (8 kbps channel) are specified low bit rate voice Video, data support optional

H.261 mandatory if video is supported H.245, H.225 required for control functions Real-time Transport Protocol (RTP) used for media packet

H.323 Architecture (cont.) Gateways

Supports interoperability with other terminal types Provides translation functions between H.323 and circuit-switched

networks Translating protocols for call setup and release Converting media format between different networks Gateways are optional in H.323 networks

H.323 Architecture (cont.) Multipoint Control Unit (MCU)

Responsible for managing multipoint conferencing between three or more H.323 terminals.

Two functional parts Multipoint controller (MC) – mandatory

Supports the negotiation of capabilities with all terminals control the resources in the multicast operation Conference control -> What media streams go where May also located in terminal, gateway, or gatekeeper

Multipoint processor (MP) – optional Is the central processor of some or all the voice, video, and data streams for

a multipoint conference Mixes, switches, and processes media streams

H.323 Architecture (cont.) MCU (Centralized/Decentralized multipoint conference)

H.323 Architecture (cont.) MCU (Hybrid multipoint conference)

H.323 Architecture (cont.) Gatekeeper (Required functions)

Admission control for the network Bandwidth control and management Address resolution

978-555-4567 204.124.46.19) E.164 Number Network address

Communicates using the RAS protocol Manages all terminals, gateways, MCUs in an H.323

zone Optional element in H.323 network, but Must be

consulted if present

H.323 Architecture (cont.) Gatekeeper (Optional functions)

Call control signaling- May process messages or pass them on

Call management-May be based on address translation function

- Call screening

- Call forwarding/redirection

- Call routing Time of day Network congestion Least cost

Call Signaling Addresses Registration, Admission, and Status (RAS) H.225 Call Signaling and H.245 Control

Signaling

Addresses Each entity has at least one network address

- To uniquely identifies the H.323 entity on the network. Some entities may share a network address

- e.g. a terminal and a co-located MC For each network address, each H.323 entity may have

several Transport layer Service Access Point (TSAP) identifiers- These TSAP identifiers allow multiplexing of several channels

sharing the same network address An endpoint may also have one or more alias addresses.

- May represent the endpoint - May represent the conferences that the endpoint is hosting

Registration, Admission, and Status (RAS) Used between H.323 endpoints and gatekeepers

Gatekeeper discovery- determine which Gatekeeper to register with

Static (well-known Gatekeepr) Dynamic (multicast)

Endpoint registration- join a zone, and informs the Gatekeeper of its transport address and alias address- done in the configuration process- occurs before any calls and may occur periodically

Endpoint location- transport address is determined

Admission control- restrict the entry of an endpoint into a zone

Bandwidth change- modify the call bandwidth during a call

Disengagement control- disassociate an endpoint from a gatekeeper and it zone

Registration, Admission, and Status (RAS) (cont.)

Gatekeeper discovery

Endpoint Gatekeeper

GRQ

GCF/GRJ

Registration, Admission, and Status (RAS) (cont.)

Endpoint registration

Endpoint Gatekeeper

RCF/RRJ

Endpoint initiated Unregister Request

Gatekeeper initiated Unregister Request

RRQ

URQ

UCF/URJ

URQ

UCF

H.225 Call signaling and H.245 Control signaling H.225 Call signaling H.245 Control signaling

H.225 Call Signaling Setup connections between H.323

endpoints Over which real-time data is transported Is reliable channel used to carry H.225 call

control messages Two kind of call signaling method

Gatekeeper-routed Call Signaling Direct Call Signaling

Gatekeeper-routed Call Signaling Admission messages are on RAS channels Call-signaling messages are on the call-signaling channel

T1521280-96

1 2 3 4 5 6 78

Endpoint 1 Endpoint 2

Gatekeeper cloud

RAS Channel Messages

Call Signalling Channel Messages

1 ARQ2 ACF/ARJ3 Setup4 Setup5 ARQ6 ACF/ARJ7 Connect8 Connect

Direct Call Signaling During the admission confirmation, Gatekeeper indicates that the endpoints can

exchange call-signaling messages directly

T1521290-96

1 2 4 5

6

3


Gatekeeper cloud



1 ARQ2 ACF/ARJ3 Setup4 ARQ5 ACF/ARJ6 Connect

H.245 Control Signaling When Gatekeeper routed call signaling is

used H.245 control channel is established directly

between the endpoints H.245 control channel is routed between the

endpoints through the Gatekeeper When Direct endpoint call signaling is used

H.245 control channel can only be connected directly between the endpoints

H.245 Control Signaling (cont.) H.245 control channel is established directly between the endpoints

T1521300-96

1 2 3 4 5 6 78

9



H.245 Control Channel Messages

1 ARQ2 ACF/ARJ3 Setup4 Setup5 ARQ6 ACF/ARJ7 Connect8 Connect9 H.245 Channel


Gatekeeper cloud

H.245 Control Signaling H.245 control channel is routed between the endpoints through the Gatekeeper

T1521310-96

1 2 3 4 5 6 78 9 10

1 ARQ2 ACF/ARJ3 Setup4 Setup5 ARQ6 ACF/ARJ7 Connect8 Connect9 H.245 Channel10 H.245 Channel



H.245 Control Channel Messages


Gatekeeper cloud

Call Connection Procedures Step A: Call setup Step B: Initial communication and

capability exchange Step C: Establishment of audiovisual

communication Step D: Call services Step E: Call termination

Step A: Call setup Different call setup cases

all combinations of Direct Routed Call signaling (DRC)/Gatekeeper Routed Call signaling (GRC) with same or different Gatekeepers;

Fast connect procedures; Call forwarding using facility (restarts the

procedure); setting up conferences

Step A: Call setup (cont.) Both endpoints registered to the same Gatekeeper, direct call signaling

T1527160-97


ARQ (1)

ACF/ARJ (2)

Setup (3)

Call proceeding (4)

Gatekeeper 1

Alerting (7)

Connect (8)

ARQ (5)

ACF/ARJ (6)

RAS Messages

Call Signalling Messages

Step B: Initial communication and capability exchange Capability exchange

Endpoints establish the H.245 control channel after call setup message from step A

H.245 procedures are used over the H.245 control channel - for the capability exchange

- to open the media channels

Master/Slave determination To resolve conflicts between two endpoints which both:

- can be the MC for a conference

- are attempting to open a bidirectional channel

H.245 tunneling

Step B: Initial communication and capability exchange H.245 Control signaling flow, control channel is established directly between the endpoints

OpenLogicalChannel(13)

OpenLogicalChannelAck(16)

OpenLogicalChannelAck(14)

TerminalCapabilitySetAck(12)

TerminalCapabilitySet(11)

TerminalCapabilitySetAck(10)

Endpoint 1 Gatekeeper Endpoint 2

TerminalCapabilitySet(9)


H.245 Message

Step C: Establishment of audiovisual communication The audio and video streams

transmitted in the logical channels setup in H.245, transported over dynamic Transport layer Service

Access Point (TSAP) Identifiers using an unreliable protocol.

Data communications transmitted in the logical channels setup in H.245, transported using a reliable protocol.

Step C: Establishment of audiovisual communication (cont.) Media stream and media control flow

RTCP Messages(20)

RTCP Messages(19)

RTP Media Stream(18)


RTP Media Stream(17)

RTP media stream and RTCP Messages

Step D: Call services Bandwidth change Status Conference expansion Multicast cascading H.450 Supplementary services

Step D: Call services Bandwidth change may requested by both Gatekeeper or endpoints during a conference

BRQ(25)


CloseLogicalChannel(23)


BRQ(21)

OpenLogicalChAck(27)

BCF/BRJ(22)

BCF/BRJ(26)

RAS messages H.245 messages

Step E: Call termination Any endpoint can request terminate a call All logical channels are closed Terminating a conference is done by MC

DRQ(31)

Release Complete (30)

End Sesion Command(29)


End Session Command(28)

RAS Message

DRQ(32)

DCF(33) DCF(34)

H.225 Signaling Messages

H.245 Message

New Feature of H.323 Version 4 Scalability, Reliability, and Flexibility Services “Must Have” Features Further Features are under developing

on H.323

Scalability, Reliability, and Flexibility Gateway Decomposition with H.248 Alternate Gatekeepers Endpoint Capacity Reporting

Gateway Decomposition with H.248 Decomposition gateway

Alternate Gatekeepers

Endpoint Capacity Reporting

Services HTTP-based Service Control Stimulus-based Control Call completion

Must Have” Features Usage Information Reporting Tones and Announcements Alias Mapping Better Bandwidth Management (multicast) Fax Enhancements Tunneling other protocols H.323 specific URL Call Credit-related capabilities Multiplexing audio and video

Further Features are under developing on H.323 Generic Extensibility Framework Inter-working or integrating with other

protocols Mobility Robustness

Mobility

Comments on H.323 H.323 is a very complex system with all of kinds of features for

multimedia communications H.323 allows the use of multiple codecs H.323 is scalable H.323 is a proven technology used in large networks. It has excellent

integration with PSTN. Multimedia conferencing shows the real potential for H.323 used in

multimedia communication Many equipment manufacturers, software vendors, and service

providers have built products and services supporting H.323. It greatly supports the success of H.323.

Under the challenge of new technologies

Conclusions H.323 is organized around four major facilities: (a) terminals, (b)

Gateways, (c) Gatekeeper, and (d) MCUs A principal technology for the transmission of real-time audio, video,

and data communication over packet-based networks Multipoint and point-to-point sessions. A rich and complex specification Scalable, reliable, flexible system, Supplementary services, and new features are powerful Faces great compression from some newly developed protocols Reducing the complexity of H.323, and simplifying its usage are

essential

H.323 Protocol Suite Guoyou He Helsinki University of Technology [email protected]

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