H.323 Protocol Suite Guoyou He Helsinki University of Technology ghe@cc.hut.fi

1. H.323 Protocol Suite Guoyou He Helsinki University of Technology ghe@cc.hut.fi

2. 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

3. 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.

4. 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.

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

6. 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

7. 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 inmany 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.

8. H.323 Architecture

9. H.323 Architecture (cont.) H.323 protocol stack

10. 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

11. 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

12. 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

13. H.323 Architecture (cont.) • Multipoint Control Unit (MCU) • Responsible for managing multipoint conferencingbetween 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

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

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

16. 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

17. 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

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

19. 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

20. 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

21. Registration, Admission, and Status (RAS) (cont.) Gatekeeper discovery

22. Registration, Admission, and Status (RAS) (cont.) Endpoint registration

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

24. 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

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

26. Direct Call Signaling • During the admission confirmation, Gatekeeper indicates that the endpoints can exchange call-signaling messages directly

27. 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

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

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

30. 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

31. 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

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

33. 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

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

35. 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.

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

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

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

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

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

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

42. Gateway Decomposition with H.248 • Decomposition gateway

43. Alternate Gatekeepers

44. Endpoint Capacity Reporting

45. Services • HTTP-based Service Control • Stimulus-based Control • Call completion

46. 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

47. Further Features are under developing on H.323 • Generic Extensibility Framework • Inter-working or integrating with other protocols • Mobility • Robustness

48. Mobility

49. 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

50. 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