Cisco MC16S Instrukcja Użytkownika Pobierz pdf (Strona 23)

Configuring Spectrum Management on an Upstream Cable Interface

Cisco uBR7200 Series MC16S Cable Modem Card Spectrum Management 23

cable upstream channel-width

Enter the channel width in hertz (Hz). Valid values are 200000 Hz (160 kilosymbols per second

[ksps]), 400000 Hz (320 ksps), 800000 Hz (640 ksps), 1600000 Hz (1280 ksps), and 3200000 Hz

(2560 ksps). The default is 1600000 Hz.

The MC16S cable modem card features advanced spectrum management capability that allows you

to scan the upstream spectrum for clean channel widths of varying size. By entering an optional

second channel width value in the appropriate command line, you can instruct the MC16S to

hierarchically search for clean upstream channels of 3.2 MHz, 1.6 MHz, 800 kHz, 400 kHz, and

200 kHz width. The spectrum management card on the MC16S will scan the upstream spectrum for

clean (usable) channels of the greatest speciﬁed width. If no acceptable channels of the speciﬁed

width can be found, the spectrum management card automatically begins to scan the upstream

spectrum for the next largest available channel width. For example, if the spectrum management card

is unable to ﬁnd a usable 1.6 MHz upstream channel, it will automatically begin searching for usable

800 kHz channels. To ensure that only one speciﬁed upstream channel width is ever used in a given

upstream segment leading to an MC16S, simply enter the same channel width twice in the

appropriate command line.

Note If you change the channel width, the symbol rate changes accordingly

(channel width = 1.25 * symbol rate). Higher symbol rates are more susceptible to RF noise and

interference. If you use a symbol rate or modulation format beyond the capabilities of your HFC

network, you might experience packet loss or loss of cable modem connectivity.

Note For QAM-16 channel widths of 400 kHz (320 ksps) or greater, Cisco recommends that you

use 16-QAM modulation only for long and short data and that you use QPSK for request, initial, and

station communication. For QAM-16 channel widths of 200 kHz (160 ksps), all communication

must be able to use 16-QAM. That is, 160 ksps with 16-QAM requires an exceptional signal-to-noise

ratio (SNR) in your upstream channel(s). When you use QAM-16 for request, initial, and station

maintenance messages with channel widths greater than 400 kHz, the QAM-16 preamble and

message data takes longer to transmit than the QPSK format. To change the modulation values, see

the “cable upstream hopping blind” section on page 26.

To specify an upstream channel width, use the cable upstream channel-width interface

conﬁguration command. Use the no form of this command to set the channel width to 1600000 for

a port number.

cable upstream portnum channel-width width1 width2

no cable upstream portnum channel-width

Syntax Description

portnum Speciﬁes the port number.

width1 Speciﬁes upstream channel width in hertz (Hz). Valid values are

200000 (160000 symbols/sec), 400000 (320000 symbols/sec),

800000 (640000 symbols/sec), 1600000 (1280000 symbols/sec),

and 3200000 (2560000 symbols/sec).

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