IBC Television Distribution Technology 99 1 CABLE MODEMS AND THE RETURN CHANNEL PATH FOR INTERACTIVE SERVICES: DOCSIS VS. DVB- A PERFORMANCE EVALUATION

The development of a standard for interactive multimedia services over Community Antenna Television (CATV) networks is drawing interest from the data communications, telecommunications, broadcasting and the entertainment industries. Until recently, the solutions available for data transfer over Hybrid Fibre Coax (HFC) CATV networks were based on proprietary random access protocols and consequently they cannot be used in an open system and are limited when delivering digital audio and video streams. A unified standard is required, that will allow the development of interoperable hardware and drive down the cost of implementation. In Europe the Digital Video broadcasting (DVB) Cable Modem specification may be adopted. The simulated performance characteristics of this system show that bursty traffic can only be sustained by the Ôreserved access modeÕ and constant bit rate/real-time variable bit rate services by the Ôfixed-rate access modeÕ. In contrast the Data Over Cable Service Interface Specifications (DOCSIS), adopted in North America, uses a prioritised service mechanism which is well suited to supporting bursty traffic but which relies upon proprietary implementations of the DOCSIS features to provide constant bit rate services using a Committed Information Rate approach