Hybrid Fiber/Coax in the Public Telecomunications Infrastructure
IEEE Communications Magazine, April 1995
Hybrid fiber/coax to the home will integrate existing cable systems in phases,
driven by entertainment and advertisement. Network management, end user
hardware costs, and protocol/modulation standards will present highly visible
short-term problems but the long-term impact will be enormous.
- Today: add channels by adding amps. Noise and amplifier limits cause
performance problems above 450MHz (=60 NTSC channels).
- HFC (laser modulated with analog RF signal) can reduce serving area
of a single coax bus to 100 homes (from 10-20K now), with 750MHz down and
5-30MHz up from each residence.
- Challenge: spectrum management, esp. for limited return path, and
integration of multiple physical networks. Configuration, performance, fault
tolerance, security, accounting.
- Phase 1 integration: driven by operational economies (consolidation),
better advertising revenue due to targeting smaller segments, pay per view
(near VOD). Goal: Star topology with fiber near top (like optical
ring). Assumes that SONET, ATM, MPEG-2 will be interoperable; still
- Phase 2: dedicated bandwidth for VOD (big fraction), online services,
telephone via cable. In practice, a variety of modulation schemes and protocols
will probably have been developed to fit each app. Trivium: due to
high S/N ratio, high quality coax can support 64 QAM and has a Shannon capacity
of 233 Mbit/s!
- Optical transition node (OTN; optical to RF conversion) can manage
"dedicated" parts of spectrum, do highly targeted ad insertion,
interface to rest of network bidirectionally (SONET).
- Phase 3: more BW allocated to digital services; allows more flexible
BW management too.
Claim that powering the user's box from the cable connector will be a challenge
as the end user hardware becomes more sophisticated. Why can't users just
plug into wall outlets?
Back to index