1 Type of Question

Task-oriented Question that should result in a number of Recommendations.

2 Motivations

Rapid development of IP technologies enables cable television networks to be a versatile infrastructure for various multimedia services. Based on Recommendation J.112, "Transmission Systems for Interactive Cable Television Services", Voice over IP/Video over IP services over IP-based cable television networks are expected to be available to the market soon. New Recommendations for these applications are strongly required to meet the demand of new services in a timely manner.

IP-based cable television networks at a very high level have to connect with three networks: HFC access network, IP network and PSTN. In consideration of Voice over IP/Video over IP applications in IP-based cable television networks, functional components noted below in clause 3 should be studied in relationship with the three networks. System Architecture should describe the specifications of the functional components and define the interfaces between these networks and IP-based cable television networks.

Voice over IP application requires strict latency and packet-loss control in IP-based cable television networks to compete with the same services over PSTN. Video over IP application needs more bandwidth than voice applications. It is not necessary to develop new codecs for the applications, however it is required to specify which codecs should be mandatory to guarantee the basic voice/

video services over IP-based cable television networks. The new Recommendations shall describe the mandatory and optional requirements for audio and video codecs in the Voice over IP/Video over IP applications in accordance with the classified QoS level.

In the application of Voice over IP/Video over IP, signalling interfaces are important issues for session control for signalling, and for transcoding of media streams between IP-based cable television networks and PSTN. For this purpose some gateway functions, one for signalling and one for media, will be required between the two networks. Signalling interfaces on media gateway and signalling gateway should be studied for the connection between IP-based cable television networks and PSTN. The media gateway should provide actual bearer circuit interfaces and transcode the media stream, while the signalling gateway should exchange the signalling information between the two networks. The Recommendation should also include protocol descriptions on call signalling for the three networks: IP-based network, PSTN and IP Network.

There should be an adapter between the telephone and IP-based cable television network. An adapter device, that should have a conversion function between voice/video signals and IP packets, signalling functions, and a function of cable modem. Like ordinary telephone numbers associated with each telephone, an IP address should be assigned to the adapter to identify source and destination address. An adapter device that contains a subscriber-side interface to the telephone and a network-side signalling interface to call control elements in the network should be studied for the applications. The adapter shall provide codecs and all signalling and encapsulation functions required for media transport and call signalling. MAC addresses and IP addresses shall be assigned to the adapter. The Recommendation for the adapter device that contains such functions should be specified to support Voice over IP/Video over IP applications over IP-based cable television networks.

Classified operation services under defined QoS should be available in IP-based cable television networks. However QoS requirements and definitions still remain unspecified. The transmission of streaming packets such as voice or video signals require very stringent specifications for real-time operation. QoS requirements and classified QoS definitions should be studied and specified for Voice over IP/Video over IP applications. In most cases packet loss and latency in the packet streams are strictly related to the level of QoS. A feedback control method of minimizing packet loss and latency from the receiver device should be studied based on the analysis of received IP packets.

3 Questions

3.1 System architecture for Voice over IP/Video over IP applications in IP-based cable television networks

- What type of call signalling protocol should be used for these applications?

- What class of Quality of Service (QoS) should be used for these applications?

- What media stream transport and encoding methods should be included in the new Recommendation?

- What device provisioning method should be appropriate for these applications?

- What type of event messaging should be required for these applications?

- What class of security and privacy should be required for these applications?

3.2 Audio and video codecs for Voice over IP/Video over IP applications in IP-based cable television networks

- What type of audio and video codecs should be specified for these applications?

- What parameters should be specified for latency and packet-loss control?

- What class of QoS should be applied to these applications in relationship with each codec parameter?

3.3 Signalling interfaces used in IP-based cable television networks, PSTN and IP networks for Voice over IP/Video over IP applications

- What PSTN gateway signalling protocols should be specified?

- What media gateway functions should be specified for the applications?

- What protocols should be specified for Internet signalling?

3.4 Adapters for Voice over IP/Video over IP applications in IP-based cable television networks

- What type of codecs should be provided in the adapter to guarantee QoS level?

- What signalling protocol should be used?

- What audio indicators should be provided in the adapter to phones, such as dial tone, ring-back tone, call waiting tone, etc.?

- How many and what type of analogue interfaces (plugs) should be provided in the adapter?

- What event should be messaged to IP-based network?

- What provisioning method should be applied to the adapter?

- How many IP addresses and MAC addresses are required?

3.5 QoS requirements and definitions for Voice over IP/Video over IP applications

- What requirements and classifications should be studied for QoS?

- What method of controlling QoS should be specified for these applications?

- What method of minimizing packet loss and latency should be specified in new Recommendations?

4 Expected results and anticipated target dates

A new set of Recommendations is expected in the first half of year 2001.

5 Relationships

a) Recommendations: J.112, H.323, H.245, H.225, G.711, G.728, G.729/A

b) Relevant Standardization bodies: IETF

NOTE - In performing the above studies, effort should be made to adopt network independent solutions and special solutions for cable networks should be avoided where possible. Close collaboration will therefore be required with study groups working on architecture and IP networking studies (specifically Study Groups 11, 13 and 16).