cans: an h.323 signalling service rhodes university broadband 2 computer science department

CANS: An H.323 Signalling Service

Rhodes University

Broadband 2

Computer Science Department

Rhodes University/Computer Science

03/09/2002

Today’s Presentation

• Overview

• H.323 Services– Non-Signalling and Signalling

• Example (AlarmClock Service)

• Summary


03/09/2002

Overview

• H.323 is an IP communications signalling protocol

• Without services it is simply an ‘ancient telephone’ sitting on an advanced underlying network - waste

• Services include but not limited to conventional telephone services (CT)

• IP communications protocol must define mechanisms to create new services


03/09/2002

Signalling vs. Non-signalling Services

• Non-signalling service is simply an H.323 compliant terminal with embedded “intelligence”– E.g. EmailReader, MarkReader

• Signalling service requires information that the protocol itself needs to handle or pass consistently– E.g. Call Transfer SS(H.450.2)


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Non-signalling service Creation

• Requires limited knowledge of H.323 protocol

• Can wrap a number of conventional applications within H.323 compliant terminal

• Can develop powerful applications quickly

• Very easy to deploy – no additional signalling info


03/09/2002

Signalling Service Creation

• Requires extensive knowledge of H.323 protocol– Includes knowledge of ASN.1 structures

– Extended to other description languages (ABNF)

– Release documents to standardise new services

– Interoperability Bake-offs for product testing

• More restrictive as a result of maintaining interoperability – trade-off

• Interoperability not guaranteed but recovery is


03/09/2002

H.323: Std Signalling Service Mechanisms

• As of H.323 version 4, there are 3 ways of extending the H.323 protocol messages (H.225) – H.450 - Supplementary Services (SS

Framework)– H.460 - Generic Extensibility Framework

(GEF)– Non-Standard Parameters (Property of

underlying message description – ASN.1)


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Other Std Service Creation Features

• Annexes to Recommendation H.323

• Example = Annex K – HTTP-Based Control of H.323 Services

• Allows service providers to provide users with a flexible way of controlling the services they use (using HTTP)

• AlarmClock service uses Annex K


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Example Service

• Implemented a service to demonstrate the use of the H.323 service extension mechanisms

• Made use of both H.450 (SS) and H.460 (GEF)

• Finally, demonstrate the use of Annex K

• What does the service do?


03/09/2002

AlarmClock Service

• A service that enables H.323 users (SoftPhone or Telephone) to request a service (reminder) call at a specified time on a specified device

• The service (CallBack) call can be made to both SoftPhones & Telephones (extended to include SMS messages using an MGCP SMS Gateway)


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Example Scenario (Setup)

PictureTel

H.323 AlarmClock

Server

H.323 SoftPhone

Invoke

ReturnError

OpenURL(Register.html)


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Example Scenario (CallBack)

H.323 AlarmClock

Server

Initiate H.323 Call via gateway

PSTN Telephone

user


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ASN.1 Structure (Callback details)


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ACSGW

PictureTel


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GW

ACS

ILLEGAL !!!!!


03/09/2002

GW ACS

GW ACS

PictureTel


03/09/2002

Summary

• H.323 is flexible

• Still maintains a high std of interoperability

• A wealth of really exciting services can be developed using H.323

• H.323 is moving forward every day (lots of industry support)


03/09/2002

We also acknowledge the bursary support of the National Research Foundation and

Microsoft.

This work was undertaken in the

Distributed Multimedia Centre of Excellence at Rhodes University

with financial support from

Telkom, Comparex Africa, Letlapa Mobile Solutions and THRIP.

cans: an h.323 signalling service rhodes university broadband 2 computer science department

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