Installation guide

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Cisco uBR7100 Series Universal Broadband Router Software Configuration Guide
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Chapter 3 Configuring the Cisco Cable Interface
Configuring Cable Modulation Profiles
1 request qpsk 64 no 0x0 0x10 0x152 1 8 no yes 56
1 initial qpsk 128 no 0x5 0x22 0x152 0 48 no yes 0
1 station qpsk 128 no 0x5 0x22 0x152 0 48 no yes 0
1 short qpsk 72 no 0x5 0x4B 0x152 0 8 no yes 48
Note If you have CBR scheduling parameters and IP precedence rate limits defined in the QoS profile, the
command output reveals this. Refer to the “Monitoring and Maintaining QoS for Higher Priority Traffic”
section on page 3-47. The show cable modulation-profile and show interface cable commands are
enhanced to reflect the state of the new MAC scheduler for the specified upstream port.
Tip If you are having difficulty with verification, ensure that the system is in global configuration mode, and
that you typed the correct modulation profile number and elements when you entered the command.
The preamble offset is calculated from the modulation profile entries. The preamble offset is the distance
the CMTS looks into the preamble to determine where the preamble starts. The CMTS does not need to
look at the entire preamble in all instances. A shorter preamble has less overhead and time associated
with that type of burst request. In general, you should use an offset of “0” for initial/station maintenance
because you need to separate these packets as distinctly as possible.
The offset for QPSK is shorter because of the way DOCSIS specifies the preamble. For QPSK, it only
takes a preamble length of 256 bits to separate frames, whereas with QAM-16, the date rate is much
higher. Utilization of a larger preamble is necessary.
Configuring QoS Profiles
The Cisco uBR7100 series CMTS supports multiple QoS profiles. QoS profile 1 is used during
cable interface registration and QoS profile 2 is the default QoS profile. Both of these profiles are
preconfigured and cannot be removed. However, you can modify these profiles and create additional Q0S
profiles for various traffic flows.
To create or change a QoS profile, use the first command below, plus as many of the additional
commands as are necessary to make the changes you require. All of the QoS profile commands are global
configuration commands.
Command Purpose
CMTS01(config)# cable qos-profile
groupnum
Create a new QoS profile with a profile number of
groupnum
, or modify an existing profile.
CMTS01(config)# cable qos-profile
groupnum ip-precedence bits
Set the bits in the Type of Service (ToS) byte that
enable you to configure individual data rate limits on
a per-modem basis. Valid values are from 0 to 7.
CMTS01(config)# cable qos-profile
groupnum guaranteed-upstream rate
Set the guaranteed minimum upstream rate in kbps.
Valid values are from 0 to 100000 kbps. Default = 0
(no reserved rate).
CMTS01(config)# cable qos-profile
groupnum max-burst size
Set the maximum upstream transmit burst size in
minislots that the cable modem can send for any
single transmit burst. Valid values are from 0 to 255
minislots. Default = 0 (no limit).