User guide

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Configuration Guide for Cisco DSLAMs with NI-2
OL-2074-03
Chapter 4 Configuring Digital Subscriber Lines
Setting DSL Profile Parameters
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
Minimum Bitrates:
Interleave Path: downstream: 0 kb/s, upstream: 0 kb/s
Fast Path: downstream: 0 kb/s, upstream: 0 kb/s
Margin: downstream: 6 dB, upstream: 6 dB
Interleaving Delay: downstream: 16000 usecs, upstream: 16000 usecs
Check Bytes (FEC):
Interleave Path: downstream: 4, upstream: 6
Fast Path: downstream: 0, upstream: 0
RS Codeword Size: downstream: 16, upstream: 8
Trellis Coding: Disabled
Overhead Framing: Mode 3
Operating Mode: Automatic
Training Mode: Quick
Minrate blocking: Disabled
SNR Monitoring: Disabled
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Setting FEC Check (Redundancy) Bytes
This section describes how to set upstream and downstream interleaved FEC check (redundancy) bytes
per Reed-Solomon (RS) codeword for a specific profile for DMT interfaces. The higher the check byte
setting, the better the error correction, but the check bytes subtract from user bytes.
The configured number of FEC check bytes must be an even number in the range 0 to 16. The default
(the value assigned when a DSL profile is created) is 16 check bytes for both the upstream and
downstream directions.
If possible, the DSLAM sets the actual number of FEC check bytes to match the value configured in the
profile. However, depending upon the bit rate to which the port finally trains, some settings of FEC
check bytes may not be achievable. In this case, the DSLAM chooses an actual number of FEC check
bytes that is closest (numerically) to the configured number of FEC check bytes. Table 4-7 lists the
values of FEC check bytes that are achievable for all bit rates.
Table 4-7 Achievable Combinations of FEC Check Bytes and Symbols per Reed-Solomon Codeword
for Different Bit Rate Ranges
Bit Rate Range (kbps)
Symbols per RS
Codeword Allowed FEC Check Bytes Allowed
8032 to 3616 1 0, 2, 4, 6, 8, 10, 12, 14, 16
3584 to 3168 1 or 2 0, 2, 4, 6, 8, 10, 12, 14, 16
3136 to 1760 2 0, 2, 4, 6, 8, 10, 12, 14, 16
1728 to 1568 2 or 4 0, 2, 4, 6, 8, 10, 12, 14, 16
Note A value of 2, 6, 10, or 14 is allowed only
when symbols per RS codeword = 2.
1536 to 832 4 0, 4, 8, 12, 16