How Cisco Converged Broadband Routers And Cable Modems Work - Cisco cBR Series Configuration Manual

Cisco Network Registrar for the Cisco CMTS Routers
MAC address of the cable modem in the customer account database. Because a field technician must go to a
subscriber's site to replace a cable modem, you can easily track modem information.
Manually registering and tracking information about a cable subscriber's PC is more difficult. A subscriber
might purchase a new PC or exchange the network interface card (NIC) without notifying you of the change.
Automatic provisioning with CNR reduces the amount of customer service involvement needed to track
customer equipment. To use the provisioning model described in this document, you must still track serial
numbers and MAC addresses for cable modems, but you do not need to track information about the PC or
NIC cards installed at a subscriber site.
The remainder of this document describes how to configure CNR to support this model. The following sections
describe the equipment and servers required for the cable headend, provide an overview of the interaction
between DOCSIS-compatible cable modems and the Cisco universal broadband routers, and provide a guide
on how to configure CNR to support this provisioning model.
How Cisco Converged Broadband Routers and Cable Modems
Work
Cisco converged broadband routers and cable modems are based on the Data Over Cable Service Interface
Specification (DOCSIS) standards. These standards were created by a consortium of cable service providers
called Multimedia Cable Network Systems, Ltd. (MCNS) to that cable headend and cable modem equipment
produced by different vendors will interoperate. The key DOCSIS standards provide the basis for a cable
modem to communicate with any headend equipment and headend equipment to communicate with any cable
modem.
Cable modems are assigned to operate on specific cable channels so activity can be balanced across several
channels. Each Cisco cBR-8 router installed at the headend serves a specific channel. Part of network planning
is to decide which channel each cable modem can use.
A cable modem cannot connect to the network until the following events occur:
• The cable modem initializes and ranges through available frequencies until it finds the first frequency
• The cable modem goes through the DHCP server process and receives a configuration file from the
• One of the parameters in the configuration file tells the cable modem which channel it can use.
• If the assigned channel is not available on the Cisco cBR-8 router to which the cable modem is currently
• During this second DHCP process, the modem will be connected to the correct CMTS. This time, the
that it can use to communicate to the headend. The cable modem might be another vendor's
DOCSIS-compatible device and the headend might have a Cisco cBR-8 router installed. At this point
on the initial connection, the cable modem cannot determine if it is communicating on the correct channel.
server.
connected, it resets itself and comes up on the assigned channel.
configuration file will be loaded. For a DOCSIS-compatible cable modem to access the network, it might
go through the DHCP server two times on two different networks; therefore, one-lease-per-client IP
addressing is critical.
Cisco cBR Series Converged Broadband Routers Application—Voice and Video Configuration Guide

How Cisco Converged Broadband Routers and Cable Modems Work

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