Specifications

3-8
Cisco Cable Modem Termination System Feature Guide
0L-1467-02
Chapter 3 Spectrum Management for the Cisco Cable Modem Termination System
Feature Overview
See Table 3-2 on page 3-8 for a summary of the Guided and Scheduled spectrum management features
and the Cisco IOS release in which it was introduced and subsequently supported.
Traffic Shaping
Traffic shaping basically uses queues to limit data surges that can congest a network. The data is buffered
and then sent into the network in regulated amounts to ensure that the traffic fits within the expected
traffic envelope for the particular connection.
Traffic shaping reduces the chance that information must be retransmitted to hosts on the cable plant.
When cable modems (CMs) have rate limits established, the CMTS typically drops data packets to
enforce the rate limit. Dropping packets from the requesting CM causes the host sending the information
to retransmit its information, which wastes bandwidth on the network. If both hosts sending and
requesting information are on the cable plant, the upstream bandwidth is wasted as well.
Traffic shaping allows the CMTS to perform upstream and downstream rate limiting on the DOCSIS
upstream and downstream channels. Rate limiting is supported in DOCSIS-1.0-99. Rate limiting
restricts the data rate to and from a CM; the MAC scheduler supports traffic-shaping capabilities for
downstream and upstream traffic. Rate limiting ensures that no single CM consumes all of the channel
bandwidth and allows a CMTS administrator to configure different maximum data rates for different
subscribers. Subscribers requiring higher peak rates and willing to pay for higher rates can be configured
with higher peak rate limits in their CM DOCSIS configuration file over regular subscribers, who pay
less and get lower rate limits.
Table 3-2 Summary of Guided and Scheduled Spectrum Management Features by Release
Feature Cisco IOS Release Supported
Traffic Shaping, page 3-8
Upstream Traffic Shaping, page 3-9
Downstream Traffic Shaping, page 3-10
11.3(6)NA, 11.3(9)NA and later releases
11.3(6)NA, 12.0(5)T1, 12.1(2)EC1, and later
releases
Guided Frequency Hopping, page 3-11
1
1. Cisco IOS Release 12.0(5)T1 also provided initial CISCO-CABLE-SPECTRUM MIB with flap-list support.
12.0(5)T1 and later releases for
Cisco uBR-MC1xC cable interface line cards
12.1(4)EC, 12.1(6), 12.1(6)T, 12.0(13)SC, and
later releases for Cisco uBR-MC16E cable
interface line cards
Time-Scheduled Frequency Hopping, page 3-12 12.0(5)T1 and later releases for
Cisco uBR-MC1xC cable interface line cards
12.1(4)EC, 12.1(6), 12.1(6)T, 12.0(13)SC, and
later releases for Cisco uBR-MC16E cable
interface line cards
Dynamic Upstream Modulation (SNR-based),
page 3-12
12.1(3a)EC1 and later releases for
Cisco uBR-MC1xC and Cisco uBR-MC28Ccable
interface line cards
12.1(4)EC, 12.1(6), 12.1(6)T, 12.0(13)SC, and
later releases for Cisco uBR-MC16E cable
interface line cards
Input Power Levels, page 3-13 12.0(6)SC, 12.1(1), 12.1(1)T, 12.1(2)EC1, and
later releases