Cisco uBR10-SRP-OC12SML Specifications download pdf (Page 41)

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Cisco uBR10012 Universal Broadband Router Software Configuration Guide

OL-1520-08

Chapter1 Overview of CiscouBR10012 Universal Broadband Router Software

Supported Software Features for the CiscouBR10012 Router

In DOCSIS 1.0, the CM explicitly requests upstream bandwidth—either in contention or piggyback to

grant minislots—for every single packet it wants to send upstream. This limits the maximum upstream

data throughput that a CM can receive due to the inherent “request to grant” round-trip latency each

packet incurs on the cable system. To support this per-cable-modem upstream throughput increase, the

CiscouBR10012router software is enhanced. The CMTS can now receive a concatenated burst of

multiple MAC frames from the same CM.

Note Both the CMTS and CM must support this capability.

DOCSIS 1.0 Downstream Rate Shaping with Type of Service (ToS)

This feature supports buffering downstream grants to rate-exceeding cable interfaces, without incurring

TCP-related timeouts and retransmits. This feature uses the three precedence bits in the ToS field in the

IP header to specify class of service assignment for each packet.

Those packets with the IP precedence bit set in the IP packet are given higher priority. This allows the

CMTS administrator to calculate the data rate for a given flow, in addition to the data rate configured on

a per CM basis.

IP Precedence-Based Downstream Rate Limits

DOCSIS 1.0 provides QoS, based on the SID. Each QoS profile carries a parameter maximum

downstream rate, which is used to provide peak rate limiting and traffic shaping on the downstream.

When higher-priority and traffic data are combined for a particular CM, rate-exceeded data packets

might shut down or delay higher-priority packets, thereby degrading quality. IP precedence bits can be

used as a basic differentiator to provide independent rate limits for different traffic streams.

DOCSIS 1.0 Downstream Signal Test Commands

The cable downstream if-output command provides several test capabilities and is enhanced with the

following options to generate test signals on the downstream interface.

• cable downstream if-output prbs—Shuts down the downstream interface and outputs a

Pseudo-Random Bit Stream (PRBS) test signal.

• cable downstream if-output continuous wave—Shuts down the downstream interface and outputs

an unmodulated carrier signal.

Note The previous cable downstream if-output command has not changed and continues to output a

standard modulated signal. The no cable downstream if-output command has not changed and stops

all signal output and shuts down the interface.

For additional command information, refer to the CiscoBroadband Cable Command Reference Guide.

DOCSIS 1.0 Modem Power Enhancement Adjustments for Low SNR Failures

This feature allows CiscouBR10012router to adjust better when a CM seems to bounce—the CM

requires frequent power adjustments in opposite directions. When this occurs, instead of making large

power adjustments for each correction, the administrator can configure the CiscouBR10012router to

calculate the average value of the power corrections before making power adjustments:

• cable upstream power-adjust threshold—This command now accepts a range of 0to10dB (the

previous range was 0to2dB).

• cable upstream power-adjust noise % of power adjustment—This command sets the threshold

value (in percent) for a particular upstream, switching between regular power adjustments and the

noise power-adjustment method.

The noise power-adjustment method uses an averaging algorithm before sending any correction. For

additional command information, refer to the CiscoBroadband Cable Command Reference Guide.

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