WP10: Interworking Specifications

or << Bridging TESUS 1 Narrowband and Broadband Networks >>.

Step 2 of TESUS 1 Project includes interworking specifications between narrowband and broadband networks. Such capabilities will be mandatory for TESUS 2, which will run simultaneously on Narrowband equipments to be installed during step 1 of TESUS 1 and the experimental ATM platform to be installed during step 2 of TESUS 1.

Diagram 8: NB - BB Bridge

Bridging the two worlds is not trivial as it implicitely comprises that optimal performances will be maintained in both subnetworks. Interworking is too often understood as basic interconnection where the more powerful system backs off in a lower quality common mode, matching the lower performances of the other system. This can obviously not be tolerated for the TESUS project as it goes right against the purpose of the intended experimentation. Indeed, it must be kept in mind that narrowband usem will always exist, even in the final stages of the system deployment. It would then be nonsense to limit the overall quality of service whenever a narrowband participant joins a collaborative session.

The previous considerations imply that the bridge device will do more than minimal system matching. It will rather comprise functions like true transcoding, service adaptation and filtering, smart signalling translation, etc.

Broadband video will use high-quality (and hence high-bitrate between 4 and 15 Mbps) video-coding standards (eventually MPEG 2) while narrowband video will most probably remain limited to 384 kbps H.261 standard. True bidirectional transcoding is thus required. Broadband audio will probably use Hi-Fi coding schemes (like MPEG audio or straight CD format) while narrowband audio will continue to use telephony standards like G.711 or G.722. Here again, true bidirectional transcoding funtionalities are required.

What is called 'System Layer', which carries control information like synchronization, requires particular attention. Broadband protocol stack includes 'ATM Adaptation Layer' and 'Service Specific Convergence Functions' which has to be matched with H.221 and H.320 standards for narrowband videotelephony, and conversely.

Furthermore, signalling between the two subnetworks has to be translated to permit interoperability. Eventually, data links have to be established in a transparent way to allow complete collaborative working. An important aspect of the design of the bridge device will be its dimensioning. The experience gained through the 2 phases of the project will definitely be necessary to come up with reliable statistics of, for instance, the number of simultaneous collaborative sessions, the number of participants in each session, etc.

Deliverable 10 is the conclusion of this WP as well as the final report of TESUS 1.

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Universitätsrechenzentrum Basel / Dieter Glatz