User guide

4-35
Configuration Guide for Cisco DSLAMs with NI-2
OL-2074-03
Chapter 4 Configuring Digital Subscriber Lines
Setting DSL Profile Parameters
To set upstream and downstream FEC check (redundancy) bytes for a specific profile, follow these steps:
This command retrains the port if you change the parameter value. Setting a parameter to its previous
value does not cause a retrain. If a port is training when you change this parameter, the port untrains and
retrains to the new parameter value.
It is normally desirable to keep the ratio of check bytes to user bytes roughly constant regardless of the
bit rate. This requires you to change both the check bytes and the codeword size parameters.
When the training mode is set to quick, the DSLAM automatically chooses the check bytes value.
However, if check bytes is set to zero and the training mode is quick, the system always uses a check
bytes value of 0.
Example
This example sets the FEC check bytes for the default profile to 6 upstream and 4 downstream and
displays the results:
DSLAM# configure terminal
DSLAM(config)# dsl-profile default
DSLAM(cfg-dsl-profile)# dmt check-bytes interleaved downstream 4 upstream 6
DSLAM(cfg-dsl-profile)# end
DSLAM# show dsl profile default
dsl profile default:
Link Traps Enabled: NO
Alarms Enabled: NO
ATM Payload Scrambling: Enabled
DMT profile parameters
Maximum Bitrates:
Interleave Path: downstream: 640 kb/s, upstream: 128 kb/s
Fast Path: downstream: 0 kb/s, upstream: 0 kb/s
800 to 768 4 or 8 0, 4, 8, 12, 16
Note A value of 4 or 12 is allowed only when
symbols per RS codeword = 4.
736 to 384 8 0, 8, 16
352 to 0 16 0, 16
Table 4-7 Achievable Combinations of FEC Check Bytes and Symbols per Reed-Solomon Codeword
for Different Bit Rate Ranges (continued)
Bit Rate Range (kbps)
Symbols per RS
Codeword Allowed FEC Check Bytes Allowed
Command Task
Step 1
DSLAM# configure terminal
Go to global configuration mode.
Step 2
DSLAM(config)# dsl-profile profile-name
Go to profile configuration mode and specify the
profile-name for which you want to set FEC
check bytes.
Step 3
DSLAM(cfg-dsl-profile)# dmt check-bytes {fast |
interleaved} downstream bytes upstream bytes
Set the check bytes on the specified latency path to the
specified number of bytes downstream and
bytes upstream.