Provisioning the Cable Modem
Cable modems communicate with their CMTS across whatever physical
networks connect them. The service provider must have the necessary auxiliary
services, such as DHCP, TFTP, and Time of Day (TOD), available at its headend.
When a cable modem boots, it registers with the CMTS and acquires its
configuration using the following steps:
Step 1. The cable modem scans for a downstream channel to use for
communication with the CMTS. Once it finds a channel, the CM
locks it in.
Step 2. CMTS tells the CM the parameters to use for upstream messages.
Step 3. Communication is established at Layers 1 and 2 (physical and
data link layers).
Step 4. The cable modem broadcasts for a DHCP server. It obtains an IP
address, the address of the TFTP and TOD servers, and the name
of the TFTP file to download.
Step 5. The cable modem downloads the DOCSIS configuration file from
the TFTP server.
Step 6. The cable modem forwards the configuration file to the CMTS
and attempts to register with it. If the configuration is valid, the
modem is registered. The two devices negotiate QoS and security
settings.
Step 7. The user device—either a PC or a router—requests an IP address,
DNS server, and default gateway information from the cable provider.