DOCSIS Cable Modem Provisioning

The cable modem provisioning  process includes the following steps:

• Scanning, Downstream & Upstream Synchronization, Ranging

A cable modem starts scanning for downstream channels. From the discovered downstream frequency the cable modem can get DOCSIS control messages from CMTS. In the next step cable modem needs to find the DOCSIS upstream channel as well.  The CMTS sends Upstream Channel Descriptor (UCD) messages every two seconds. Once an upstream channel is selected, the cable modem begins the ranging process.

• Obtaining IP Address and other configurations

 Cable modem sends a broadcast DHCP request via the CMTS to the DHCP Server. DHCP Server provides IP Address, network configuration, configuration file, addresses of TFTP server and ToD server.

• Time-of-Day Synchronization

The cable modem obtains the current time and date information using the Time protocol. The time server then returns the current time and date in the ToD response. The cable modem sets its clocks to GMT +/- offset.

•  Getting the Configuration file

After DHCP operation, the cable modem initiates a TFTP request to download the configuration file from the TFTP Server. The IP address of the TFTP server and the name of the configuration file are specified in the previously received DHCP messages.

Registration

The cable modem checks the file's validity after receiving its configuration file. The configuration file contains MIC(message integrity check), it is used to examine the configuration file's contents, so that it wasn’t  corrupted or changed before they get to the cable modem. The CMTS does a message integrity check. The CMTS calculates the value using a shared secret or password. The provisioning system uses this password or shared secret for MIC calculation, but the cable modem is unaware of it. As a result, the CMTS can tell whether the cable modem tried to change their configuration. The CMTS MIC is calculated by the provisioning system and is included in the configuration file that the modem passes transparently to the CMTS.

To be continued ...