Cisco DSL Mode Tweaks

1. dsl operating-mode auto

To configure the (DSL) operating mode, use the :

Interface Atm0
dsl operating-mode itu-dmt

dsl operating-mode {adsl2 [annex a | annex m] | adsl2+ [annex a | annex m] |
ansi-dmt | auto | itu-dmt}

The router continues switching between modes, in sequence, until the router reaches the state
showtime (which signifies that the connection attempt was successful) and connects using one of the modes.

This switching process is designed specifically for expediting DSL performance.

2. dsl sync mode

To set a preference for Digital Subscriber Line (DSL) synchronization mode, use the :

interface atm0
dsl sync mode itu-dmt

3. dsl sync interval

To set the interval of time between ANSI synchronization and ITU synchronization, use the: interface atm0
dsl sync interval secondsBy default, the DSL synchronization interval is 2 seconds.

Number of seconds between ITU and ANSI synchronization.
This number must be within the range from 2 to 360 seconds.

4. dsl lom

(lom = Loss Of Margin)

 dsl lom number  (1-250)

Enables LoM monitoring and checks for the specified number of consecutive LoM messages.
When message count exceeds configured size it will cause the router  adsl line to resync with the dslam.

5. dsl noise-margin

Amount by which a signal exceeds the minimum amount for proper operation. If dsl noise margin
reaches this peak it will cause the adsl line to resync.

interface atm0
dsl noise-margin -3

6dB or below is bad and will experience no sync or intermittent sync problems
7dB-10dB is fair but does not leave much room for variances in conditions
11dB-20dB is good with no sync problems
20dB-28dB is excellent
29dB or above is outstanding

6. dsl max-tone-bits

Sets the maximum bits per tone limit.
Integer ranges from 2 dB to 14 dB with a granularity of 1 dB.

interface atm0
dsl max-tone-bits 10

7. dsl power-cutback

maximum noise margin that can occur on a digital subscriber line (DSL) before a power cutback happens.
default value of 31
Maximum noise margin in decibels. Range is 1 to 30.

interface atm0
dsl power-cutback 1

8. dsl bitswap both

is for G.DMT – it’s good for the connection in terms of stability. Should be left on, and if I’m not
mistaken I think it’s for adapting to changes on a line (swapping bit allocations).

Bitswapping: adapts to errors on the line:

As line conditions change, bit swapping allows the modem to swap bits around different channels,
without retraining, as each channel becomes more or less capable. If bit swapping is disabled then this
does not happen and the modem needs to retrain in order to adapt to changing line conditions.

Complete Configuration :

Eg :
interface atm0
dsl operating-mode itu-dmt
dsl sync mode itu-dmt
dsl sync interval 30
dsl lom 200
dsl noise-margin -3
dsl max-tone-bits 10
dsl power-cutback 1
dsl bitswap both

On routers that don’t have the below firmware:

Init FW:         init_AMR-4.0.015.bin
Operation FW:    AMR-4.0.015.bin
FW Source:       external
FW Version:      4.0.15

Issue the command :
service internal

A Tip

Remember previously how you had to issue the command “service internal” to configure noise margin
settings…well that is no longer the case with this new firmware! Now it is by default in the atm0 interface
mode, and theres a few other settings you can adjust as well..

cisco877(config-if)#dsl ?
bitswap              Bitswap Feature
enable-training-log  enable the fw training log for Showtime and failure  cases
gain-setting         ADSL programmable gain setting
lom                          Loss Of Margin watch counter for line retrain
max-tone-bits      set maximum bits per tone limit
noise-margin       set noise margin offset
operating-mode   auto or specific ADSL mode
power-cutback     Noise Threshold for Power CutBack
sync                        ADSL sync preferences

Cisco FTP Download of DSL Firmware: adsl_alc_firmware.4-10-9.bin