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CANS: An H.323 Signalling Service

Rhodes University. Computer Science Department. CANS: An H.323 Signalling Service. Broadband 2. Today’s Presentation. Overview H.323 Services Non-Signalling and Signalling Example (AlarmClock Service) Summary. Overview. H.323 is an IP communications signalling protocol

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CANS: An H.323 Signalling Service

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  1. Rhodes University Computer Science Department CANS: An H.323 Signalling Service Broadband 2

  2. Today’s Presentation • Overview • H.323 Services • Non-Signalling and Signalling • Example (AlarmClock Service) • Summary

  3. 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

  4. 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)

  5. 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

  6. 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

  7. 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)

  8. 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

  9. 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?

  10. 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)

  11. H.323 AlarmClock Server Example Scenario (Setup) Invoke ReturnError OpenURL(Register.html) H.323 SoftPhone

  12. Example Scenario (CallBack) Initiate H.323 Call via gateway PSTN Telephone user H.323 AlarmClock Server

  13. ASN.1 Structure (Callback details)

  14. ACS GW

  15. GW ACS ILLEGAL !!!!!

  16. GW ACS GW ACS

  17. 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)

  18. 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. We also acknowledge the bursary support of the National Research Foundation and Microsoft.

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