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Cisco uBR10012 Universal Broadband Router Software Configuration Guide
OL-1520-05
AppendixA DOCSIS and CMTS Architectural Overview
DOCSIS Specification Summary
Overview of DOCSIS NTSC Cable Plants
DOCSIS-compliant cableplants that support North American channel plans use ITU J.83 AnnexB RF.
Figure0-1 illustrates a DOCSIS two-way architecture.
Figure0-1 DOCSIS Two-Way Architecture
Larger cable companies typically have high-speed fiber backbones that carry Internet data, voice, and
video between the following cable company facilities:
•Regional processing centers
•Headends
•Hubs
The fiber backbone can be made up of OC-3 (155 Mbps) to OC-48 (2488 Mbps) SONET or ATM rings.
The backbone network can connect to other networks, including the Public Switched Telephone
Network (PSTN), to other cable system backbones, or to public Internet interconnect points that multiple
ISPs use.
The CMTS MAC domain typically includes one or more downstream paths and one or more upstream
paths. Depending on the CMTS configuration, the CMTS MAC domain can be defined to have its
downstreams on one cable interface line card with its upstreams on another card, or one or more CMTS
MAC domains per cable interface line card.
Cisco provides high-speed routers to route interactive traffic between the backbone and Ethernet in the
headend internal network. Signaling protocols maintain the network intelligence needed to route traffic
optimally, automatically building and maintaining routing tables to direct traffic and signal failures for
rerouting in the network.