slow broadband with wic1-adsl card

Unanswered Question
Mar 6th, 2009

cisco 2651XM router with wic1-adsl card

IOS: c2600-ipbase-mz.123-11.T.bin (12Mb)

broadband = bog standard 8Mb adsl on BT line

I've discovered to my dismay my cisco router only gives me half the

broadband speed of a cheap plastic router (Billion 5200G). If I connect

my PC straight to a Billion 5200G adsl router I am getting about

3800kbps download at, and a file download from came down at about 450Kb/sec.

However if I swap the Billion for my cisco router I only get about

2500kbps at and the same file from MS downloads at approx

290KKB/sec. This is quite a difference and I never expected cisco gear

to give such poor performance - unless I'm doing something wrong that


In testing the cisco I used two different IOS's - a minimal IOS (above)

and a larger IOS with a bare bones running-config (below), no firewalls

or anything and still the speed was slow. Next thing I did was change

the adsl card (I've got two cards) but that made no difference.

Another thing I tried was I took the adsl card out of the cisco router

and configured a route through it out into the Billion router, so

effectively the internet traffic was still going through the cisco

router and the speed was back up to 3800kbps again, which would indicate

the problem is with the WIC1-adsl card. So either these cards aren't

much cop or I haven't configured it correctly.

I duplicated the above test on a second 2651XM router I have and I got

the same results.

Attached is a copy of my running config and a bit extra. If anyone can spot frailties in my config that would affect bradband speed I'd be grateful for any advice.

I have this problem too.
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Giuseppe Larosa Fri, 03/06/2009 - 09:06


use sh dsl int atm0 to check possible link problems on the ADSL line.

the rate is adaptive and the two parts on the line negotiate a speed.

Each receiver has its own sensitivity and so results can be different.

It can be also a question of greater affinity with the modem in the CO. (ATU-C)

Your config looks like correct

To be noted newer IOS can contain a newer version of the WIC firmware so I would try with a newer version rather then one with more features

Hope to help


tonyspcrepairs Fri, 03/06/2009 - 09:44

ok thanks for that advice. I did sh dsl int atm0/0 and I've attached the results. I couldn't see anything amiss but then I'm not experienced. Could you please take a look at showdsl.txt and tell me if you see anything wrong?

I will also try and get a latest IOS.

Giuseppe Larosa Fri, 03/06/2009 - 14:25

Hello Tony,

the show tells the following:

ADSL type: DSL Mode: ITU G.992.1 (G.DMT) Annex A

Noise Margin: 9.5 dB DS = downstream from CO to your router.

Speed (kbps): 4256 DS interleaved

448 upstream interleaved

As you can see the speed in DS is 4256 kbps but the noise margin that tells the ratio between signal power and noise power is 9.5 dB.

It cannot run faster without having many errors: the target of rate negotiation is to find the max speed with an acceptable noise margin.

The negotiated speed can also vary over time depending on the noise conditions.

The two modems periodically perform training again (negotiate again)

The main parameter here is attenuation caused by the distance from the CO.

It would be interesting to gather similar information from the other device when connected to the line to compare.

However, the WIC should be working.

To be noted that if the target of noise margin would be lower an higher speed could be negotiated but with higher bit error rate probability.

Hope to help


Sam Smiley Fri, 03/13/2009 - 11:56

Hi Tony,

I'm not sure if this is true with the base IOS image, I know it is true with the advance & enterprise IOS.

Issue a show controller atm0/0 look for the following in the first 2 screens:

SCC Clockrates:

SCC0 = 7000000 (ATM0/0)

SCC1 = 0

SCC2 = 0

SCC3 = 1000000 (ATM0/0)

By default the SCC0 will show 2600000, you should be able to change this from interface configuration on the atm0/0.

Issue the following on atm0/0:

clock rate aal5 7000000

This will reset the atm interface, once done your speeds should be what they are supposed to be.



tonyspcrepairs Fri, 03/13/2009 - 13:57

sam thanks for your response. I did the changes you mentioned. I don't see any immediate improvement in my broadband speed but that might be because I have to wait for BT wholesale to pick up the changes, I don't know. I appreciate the advice and if my broadband speed improves over the next fews days I'll let you know.

btw I am currently using IOS: c2600-adventerprisek9-mz.124-15.T8.bin

Sam Smiley Mon, 03/16/2009 - 13:13

Hi Tony,

Another thing you may try is setting the MTU on the ATM interfaces. I'll post the relevent DSL info here from one of my XM devices running 12.4.



tonyspcrepairs Mon, 03/16/2009 - 13:41

sam thanks for your futher help. I've implemented the dsl commands you gave into my running config. I was told by my ISP it can take a few days for BT wholesale to do a routine check on the line, so I'm going to let the router run this week (with your amendments in) and see if the speed comes up. Thanks, Tony

tonyspcrepairs Thu, 03/19/2009 - 16:47

sam after doing your dsl.txt amendments and giving it a few days I see my broadband speed has improved. For a few days I was getting about 2500kb/sec. Yesterday it went up to 3800. I did a bit more study and changed the MTU to 1458 and now I'm getting 4300kb/sec and file downloads are peaking at 550kb/sec which is the best I've had for a long time.

Sam Smiley Mon, 03/30/2009 - 18:47

Hey Tony,

I'm glad to hear that it worked out. I know I was pulling my hair out on the first one of these I did with an IOS above advanceip. There are a couple of settings that you can play with in the config to tune it.




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