Baseband and passband transport systems for interactive video services

摘要

As essentially none of the existing telecommunication networks are capable of providing interactive video services (IVS), network providers have begun to consider the network architecture that is best to deploy. Two approaches have received most of the consideration. Because of the embedded base of broadcast, coax-based cable TV networks and because of the unconfirmed demand for IVS, much attention has been paid to upgrading these networks to provide IVS transport even though extensive modification would be required. These networks are referred to as passband networks because of the use of modulated subcarriers as the signal transport mechanism. The alternative approach under consideration is the use of fiber-to-the-curb transport systems. Because such networks transport IVS directly as baseband signals without subcarrier modulation, they are known as baseband networks. The paper compares the baseband and passband approaches in several areas including: compatibility with the optical transmission medium; compatibility with IVS source/sink equipment; compatibility with the emerging telecommunications interoffice and feeder networks; and the cost of deployment. The recent history in which passband and baseband approaches competed to become the preferred transport mechanism in LAN applications is reviewed. The fact that in that case baseband emerged as the preferred approach has important implications for the selection of the preferred approach in today's IVS applications. The constituent elements and transport requirements of the end-to-end network for delivering IVS are reviewed.