Installation guide

3-42
Cisco uBR7100 Series Universal Broadband Router Software Configuration Guide
OL-2238-03
Chapter 3 Configuring the Cisco Cable Interface
Configuring Cable Modulation Profiles
• Scrambler—Enable or disable scrambler. Valid values are scrambler and no-scrambler. Scrambler is
used to create an almost random sequence of transmission symbols, which ensures an even spectral
distribution of energy transmitted within the channel. The scrambler seed is an initial value that is
used to start the pseudo-randomizer to scramble the bits. Because both the transmitter and receiver
know the seed value, the scrambling can be reversed at the receiver, leaving only the original data.
• 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. Differential
encoding is a technique wherein the information is transmitted by the phase change between two
modulation symbols instead of by the absolute phase of a symbol. This technique makes the absolute
phase of the received signal insignificant and has the effect of doubling the BER for the same C/N.
• Pre-len—Preamble length in bits. Valid range is 2 to 128 bits. Preamble length (and Preamble offset)
are used to define a synchronizing string of modulation symbols used to let the receiver find the
phase and timing of the transmitted burst.
• 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.
To create or change a cable modulation profile, use the following command in global configuration
mode.
In the following example, the request burst for cable modulation profile 2 is defined to have 0 fec-tbytes,
16 kbytes fec-len, a burst-len of 1, a guard time of 8, a mod value of qpsk, scrambler enabled with a seed
value of 152, differential encoding disabled, a preamble length of 64 bits, a fixed code word length, and
8-bit unique words for upstream unique word length.
CMTS01(config)# cable modulation-profile 2 request 0 16 1 8 qpsk scrambler 152 no-diff 64
fixed uw8
To remove a cable modulation profile, use the no cable modulation-profile profile command in global
configuration mode. You can use this command to remove all modulation profiles except for modulation
profile 1.
Tip Entering no cable modulation-profile 1 sets all parameters in profile 1 to the default values.
Verifying Cable Modulation Profiles
To determine if a cable modulation profile is created, enter the show cable modulation-profile
command.
A sample output is shown in the following example:
CMTS01# show cable modulation-profile
Mo IUC Type Preamb Diff FEC err FEC Scrambl Max Guard Last Scrambl Preamb
length enco correct T seed B time CW offset
bytes size size short
Command Purpose
CMTS01(config)# cable modulation-profile profile iuc
fec-tbytes fec-len burst-len guard-t mod scrambler seed
diff pre-len last-cw uw-len
Create a new cable modulation profile
with a profile number or modify an
existing profile.