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Rhodes University/Computer Science
03/09/2002
Today’s Presentation
• Overview
• H.323 Services– Non-Signalling and Signalling
• Example (AlarmClock Service)
• Summary
Rhodes University/Computer Science
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
Rhodes University/Computer Science
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)
Rhodes University/Computer Science
03/09/2002
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
Rhodes University/Computer Science
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
Rhodes University/Computer Science
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)
Rhodes University/Computer Science
03/09/2002
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
Rhodes University/Computer Science
03/09/2002
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?
Rhodes University/Computer Science
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)
Rhodes University/Computer Science
03/09/2002
Example Scenario (Setup)
PictureTel
H.323 AlarmClock
Server
H.323 SoftPhone
Invoke
ReturnError
OpenURL(Register.html)
Rhodes University/Computer Science
03/09/2002
Example Scenario (CallBack)
H.323 AlarmClock
Server
Initiate H.323 Call via gateway
PSTN Telephone
user
Rhodes University/Computer Science
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)
Rhodes University/Computer Science
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.