Cisco Systems UBR900

Configuration Options

Configuring the Cisco uBR900 Series Cable Access Routers 19

The following sections describe the initial power-on and provisioning sequences in more detail, as

well as the requirements that must be met by both the cable access router and the CMTS before

provisioning can be successful.

When connected and first powered on, the Cisco uBR900 series cable access router performs the

following boot procedures:

•Boots the Read Only Memory (ROM) from the ROMMON partition of its flash memory.

•Performs a self-test, initializes processor hardware, and boots the main operating system

software—the Cisco IOS release image stored in NVRAM.

Next, the Cisco uBR900 series performs a series of DOCSIS-mandated procedures for automatic

installation and configuration. These procedures are summarized in Table3 and in Figure 5.

Table3 Cable Access Router Initialization Sequences and Events

Sequence Event Description

1Scan for a downstream channel and

establish synchronization with the

CMTS.

The Cisco uBR900 series acquires a downstream channel by

matching the clock sync signal that is regularly sent out by the

CMTS on the downstream channel. The cable access router

saves the last operational frequency in non-volatile memory

and tries to reacquire the saved downstream channel the next

time a request is made.

Note An ideal downstream signal is one that synchronizes

QAM symbol timing, FEC framing, MPEG packetization, and

recognizes downstream sync MAC layer messages.

2Obtain upsteam channel parameters. The cable access router waits for an upstream channel

descriptor (UCD) message from the CMTS and configures

itself for the upstream frequence specified in that message.

3Start ranging for power adjustments. The cable access router waits for the next upstream bandwidth

allocation map message (MAP) from the CMTS to find the

next shared request timeslot. The router then sends a ranging

request message on the next available shared request timeslot,

communicating its UID (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 cable access 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.

Note At this point, the cable access router has established

connectivity with the CMTS but is not yet online. The next

steps allocate “permanent” upstream and downstream

frequencies, as well as the configuration required for IP

network connectivity.