User guide

4-31
Configuration Guide for Cisco DSLAMs with NI-2
OL-2074-03
Chapter 4 Configuring Digital Subscriber Lines
Setting DSL Profile Parameters
CAP Interfaces
Table 4-5 shows the amount of delay (in milliseconds) that results from various combinations of baud
rate, constellation, and cap interleaving-delay settings (short or long) on a 4-port flexi card configured
for CAP. Interleaving delay is applied only in the downstream direction. Interleaving is not used on
upstream traffic.
You can choose the interleaving-delay option none only when 136 k downstream baud rate is enabled.
If you configure the interleaving-delay as none but the line card trains at a downstream bit rate that uses
a baud rate that is other than 136 k, the actual interleaving-delay value is short.
The following table shows the relationship between the interleaving-delay value chosen and the state of
the Reed-Solomon error correction function.
Note If you set interleaving delay to none, the subscriber line might provide service at a higher bit rate than
the one configured. This can happen because setting interleaving delay to none turns off Reed-Solomon
error correction, and turning off error correction reduces the overhead on the line, leaving more
bandwidth available to the subscriber.
Table 4-5 Downstream Interleaving Delay
Constellation
Short or Long
Delay 136 Kbaud 340 Kbaud 680 Kbaud 952 Kbaud
8 short 4.4 ms 4.4 ms – –
long 49 ms 49 ms – –
16 short 3.0 ms 3.0 ms 3.0 ms 2.7 ms
long 31 ms 31 ms 16 ms 11 ms
32 short 2.3 ms 2.3 ms – –
long 24 ms 24 ms – –
64 short 1.9 ms 1.9 ms 1.8 ms 1.7 ms
long 19 ms 19 ms 9.6 ms 6.8 ms
128 short 1.6 ms 1.6 ms – –
long 16 ms 16 ms – –
256 short 1.4 ms 1.4 ms 1.4 ms 1.2 ms
long 14 ms 14 ms 6.8 ms 5.0 ms
256 uncorrected short 1.3 ms 1.3 ms 1.2 ms 1.0 ms
long 12 ms 12 ms 6.0 ms 4.3 ms
Interleave Value Reed-Solomon Relationship
Short RS error correction on
Long RS error correction on
None RS error correction off