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Configuring Spectrum Management on an Upstream Cable Interface

Cisco uBR7200 Series MC16S Cable Modem Card Spectrum Management 17

cable modulation-proﬁle

Deﬁne the elements that are used in a cable modulation proﬁle. You can have up to 8

cable modulation proﬁles. Proﬁle 1 is the default.

Caution If you change a modulation proﬁle, you also make changes to the physical layer.

Changing physical layer characteristics affects router performance and function; therefore, this task

should only be used by an expert user.

cable modulation-proﬁle proﬁle number parameter value

no cable modulation-proﬁle

Syntax Description

proﬁle number Speciﬁes the modulation proﬁle for which you are specifying a parameter value or speciﬁes the

number of the modulation proﬁle you wish to remove from your router conﬁguration. Valid

range is from 1 to 8.

parameter • The modulation proﬁle values that can be changed are:

• Interval usage code (iuc)—Valid values are initial, long, reqdata, request, short, station.

To use the cable modulation-proﬁle command correctly, enter a line with all parameters for

each upstream burst type. An incomplete burst proﬁle causes unreliable operation, or loss of

modem connectivity.

Errors or incompatible conﬁgurations in the burst proﬁle(s) cause modems to either drop

connectivity, drop short or long data packets, or fail to connect to the network. It is possible to

build a burst proﬁle set for which no implementation of a DOCSIS receiver is capable of

receiving the modem’s transmission.

• Fec-tbytes—The number of bytes that can be corrected per FEC codeword. Valid range is

0 to 10 bytes, where 0 means no FEC.

The data rates 160 Ksymbol/sec and 2560 Ksymbol/sec are highly sensitive to unique word

length, preamble length, and FEC sizing. Incorrect choices for these values can cause poor or

no connectivity at these symbol rates.

• Fec-len—FEC codeword length. Valid range is 8 to 254 bits.

• Burst-len—Maximum burst length in bytes. 0 means no limit on burst length.

• Guard-t—Guard time in symbols. The time between successive bursts.

• Mod—Modulation. Valid values are 16qam and qpsk.

• Scrambler—Enable or disable scrambler. Valid values are scrambler and no-scrambler.

Turning the scrambler off can cause packet loss, and is only used in lab testing environments.

• Seed—Scrambler seed in hexadecimal format. Valid range is 0x0000 to 0x7FFF.

• Diff—Enable or disable differential encoding. Valid values are diff and no-diff.

• Pre-len—Preamble length in bits. Valid range is 2 to 128 bits.

• Last-cw—Handling of FEC for last codeword. Valid values are ﬁxed for ﬁxed codeword

length and shortened for shortened last code word.

• Uw-len—Upstream unique word length. Enter uw8 for 8-bit unique words or uw16 for 16-bit

unique code words.

value The value for the parameter you are assigning to a given modulation proﬁle.

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Cisco MC16S Bedienungsanleitung Seite 17