Specifications

Release Notes for Cisco uBR924 Cable Access Router for Cisco IOS Release 12.1(5)T

OL-0385-04 Rev. B0 (2/2001)

New and Changed Information

DOCSIS 1.0+ Extensions

In addition to the other quality-of-service (QoS) features, DOCSIS 1.1 supports a number of features

that are required for the delivery of high-quality voice traffic. To use these features before the DOCSIS

1.1 specification is finalized, Cisco has created the DOCSIS 1.0+ extensions that contain the most

important of these features:

• Concatenation—DOCSIS concatenation combines multiple upstream packets into one packet to

reduce packet overhead and overall latency, and to increase transmission efficiency. Using

concatenation, a DOCSIS cable modem makes only one bandwidth request for multiple packets, as

opposed to making a different bandwidth request for each individual packet; this technique is

especially effective for bursty real-time traffic, such as voice calls.

• Dynamic Multi-SID Assignment—To give priority to voice traffic, the Cisco uBR924 router

assigns a different SID to each voice port. Without the DOCSIS 1.0+ extensions, the router creates

these SIDs during the provisioning process, and the SIDs remain in effect until the router is

rebooted with a different configuration. As part of this process, a minimum guaranteed bandwidth

is permanently allocated to the voice ports; this bandwidth is reserved to the voice ports even if no

calls are being made.

To avoid potentially wasting bandwidth in this manner, the DOCSIS 1.0+ extensions support the

dynamic creation of multiple SIDs. New MAC messages dynamically add, delete, and modify SIDs

when needed. When a phone connected to the router is taken off-hook, the Cisco uBR924 router

creates a SID that has the QoS parameters needed for that particular voice call. When the call

terminates, the router deletes the SID, releasing its bandwidth for use elsewhere.

The DOCSIS 1.0+ features are introduced in Cisco IOS Software Release 12.0(7)XR and 12.1(1)T.

Note Both the Cisco uBR924 Cable Access Router and the CMTS must support the dynamic

multi-SID and concatenation features for them to be used on the cable network. If you are

using the Cisco uBR7200 series universal broadband router as the CMTS, Cisco IOS

Release 12.0(7)XR or 12.1(1)T (or later) is required on both the Cisco uBR924 and

Cisco uBR7200 series routers to use these features.

Dynamic Host Configuration Protocol Proxy Support

The Dynamic Host Configuration Protocol (DHCP) Proxy Support feature helps to automate the

configuration of the Cisco uBR924 Cable Access Router in two situations:

• When the Cisco uBR924 Cable Access Router is configured for routing mode, an IP address must

be assigned to its Ethernet interface. The DHCP Proxy Support feature allows an external DHCP

server to assign an IP address to the Ethernet interface, as opposed to having to assign it manually

with the appropriate CLI commands.

• When network address translation (NAT) is used, an inside global address pool must be created on

the Ethernet interface. The DHCP Proxy Support feature allows a DHCP server to assign an IP

address that automatically creates the NAT address pool, as opposed to manually specifying a static

IP address with the appropriate CLI commands.

When configured for DHCP Proxy Support, during startup the Cisco uBR924 Cable Access Router

sends a proxy DHCP request to the DHCP server using the Ethernet interface’s MAC address. The

DHCP server replies with a second IP address that the router assigns to either the Ethernet interface or

to the NAT pool, depending on which option was specified.