Initial Power-On Sequence - Cisco uBR924 Installation Manual

Chapter 1 Product Overview

Initial Power-On Sequence

When connected and first powered on, the Cisco uBR924 cable access router performs the following
DOCSIS-mandated procedure for automatic installation and configuration:
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The router boots the Read Only Memory (ROM) from the ROMMON partition of its Flash memory.
The router performs a self-test, initializes processor hardware, and boots the main operating system
software—the Cisco IOS release image stored in Flash memory.
The router acquires a temporary downstream channel by matching the clock sync signal that is
regularly sent out by the CMTS in the downstream frequency range.
The router then waits for an Upstream Channel Descriptor (UCD) message from the CMTS and
configures itself for the upstream frequency specified in that message.
The router waits for the next upstream bandwidth allocation map message (MAP). These messages
are regularly sent from the CMTS to find the next available shared request timeslot. The router then
uses this timeslot to send a ranging request message to the CMTS, communicating the router's user
ID (UID, which includes its unique MAC address), using a temporary service identifier (SID) of 0
(zero) to indicate it has not yet been allocated an upstream channel.
In reply to the router's ranging request, the CMTS sends a ranging response containing a temporary
SID to be used for the initial router configuration and bandwidth allocation. As needed, the router
adjusts its transmit power levels using the power increment value given by the CMTS in its ranging
response message.
At this point, the router has established connectivity with the CMTS but is not yet
online. The next steps allocate permanent upstream and downstream frequencies,
as well the configuration required for IP network connectivity.
After the next MAP message broadcast, the router uses a shared request timeslot to invoke the
Dynamic Host Configuration Protocol (DHCP) to establish IP connectivity with the TCP/IP
network at the headend.
The DHCP server—typically a dedicated server at the headend, but it could also be a CMTS such
as a Cisco uBR7200 series universal broadband router—sends a response containing the router's IP
address, as well as the IP addresses for the default gateway and time of day (ToD) server. It also
sends the IP address for the authorized Trivial File Transfer Protocol (TFTP) server from which the
router should download its DOCSIS configuration file. Depending on the particular network
configuration, other information could be provided, such as the IP addresses for a syslog server or
security server.
The router configures itself for the specified IP address and gets the current date and time from the
specified ToD server.
Using the TFTP protocol, the router downloads the specified DOCSIS configuration file and
configures itself for the appropriate parameters. The DOCSIS configuration file defines the router's
operating mode such as the provisioned downstream and upstream service assignments, assigned
frequencies, data rates, modulation schemes, Class of Service (CoS), type of services to support,
and other parameters. Cisco provides tools to help automate the creation of configuration files.
Cisco uBR924 Cable Access Router Description
Cisco uBR924 Router Hardware Installation Guide
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