Low throughput using MLP bonding across DSL lines

Answered Question
Jul 20th, 2010

Hi Folks,

First post here as we're at a complete loss on this one. I hope it's not a simple answer in a way ;o) We are bonding two LLU DSL lines using MLP. Our LLU provider supports MLP bonding and we have a few other customers working well on Cisco 1841s, although not such high sync speed lines as this problem site.

So the lines work well with no interface errors and sync speeds are very good and evenly matched between the two lines (approx 14Mbps downstream). It's all good - it's great in fact except that it just doesn't work properly! By that I mean we're not seeing the downstream throughput we'd expect. We actually get the downstream throughput of less than a single DSL line, so about 12Mbps. Upstream bonded throughput is fine and in line with the sync speeds.

Both circuits are 'active' in the PPP multilink bundle and I see 3 sessions on our core LNS Cisco 7301 (c7301-boot-mz.124-2.T.bin) - i.e. 2x circuits + 1x bundle. We've checked the circuits individually and 'actual' throughput (using NetPerf software) is similar for both lines and in line with the sync speeds.

We are seeing quite high CPU (50%) on the Cisco 1841 (c1841-ipbasek9-mz.124-24.T1.bin) at the customer premesis, but having tested a Cisco 2951 on the customer premesis with two new HWIC-1ADSL-M cards, this is not the cause. The 2951 ran at 5% CPU whilst we experienced the same problem.

We've checked the setup of both Cisco CPE and LNS with our LLU provider and they are happy with the MLP config. They themselves have been able to bond two similarly sync'd Annex-M DSL lines and get 25Mbps throughput on a 1841.

Cisco configs and outputs attached.

Many Thanks,

I have this problem too.
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Correct Answer by Paolo Bevilacqua about 6 years 3 weeks ago

What Cisco wants is the business case. Show up with a big sale prospect and keep them on the hook to deliver whatever functionality.

If you don't have that, the only you can do is the "Product Enhancement Request", meaning they file and may never look at it.

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shillings Thu, 12/30/2010 - 02:46

Update on this one.


Cisco accepted it as a bug and were able to reproduce the fault in their lab. Some weeks later they came back and said only 2Mbps is supported per circuit - sorry. So even their dev engineer wasn't aware.

You can get more throughput, but Cisco don't officially support issues with more than 2Mbps per circuit for MLP bonding. We never got to the bottom of our particular issue compared to our LLU provider who could get 25Mbps downstream across two ADSL lines using their 7200 LNS. We did move off our 7301 to a 7206 G2 but no improvement. All finished with now anyway, but thought it might be useful to update this thread.

Mohamed Sobair Thu, 12/30/2010 - 03:06

Hi,

Is this problem Only arises with MLP, because we have implemented almost similar setup for customer but WITHOUT MLPPP, we were able to get more than 2 Mbps per circuit.

I remember we have some customers running 4 MBps per circuit and they were using multiple DSL lines without any problem using 7206 as LNS and Cisco 1841.


What Hardware does the provider uses to get 25MBps on MLPPP?

Regards,

Mohamed

shillings Thu, 12/30/2010 - 03:16

They use 7206 VXR (G2). We shifted the sessions off the original 7301 to the same spec router as an attempt to fix it, but not change - the 7206 was also much closer to our handoff point, just one hop.

Paolo Bevilacqua Fri, 12/31/2010 - 08:57

shillings wrote:

Update on this one.


Cisco accepted it as a bug and were able to reproduce the fault in their lab. Some weeks later they came back and said only 2Mbps is supported per circuit - sorry. So even their dev engineer wasn't aware.

You can get more throughput, but Cisco don't officially support issues with more than 2Mbps per circuit for MLP bonding. We never got to the bottom of our particular issue compared to our LLU provider who could get 25Mbps downstream across two ADSL lines using their 7200 LNS. We did move off our 7301 to a 7206 G2 but no improvement. All finished with now anyway, but thought it might be useful to update this thread.

Unfortunately, what you have found is the experience of many others: Cisco doesn't support or care about ADSL MLPPP.

shillings Fri, 12/31/2010 - 09:12

Yes and such a shame too. It's what customers want - simple solution that keeps packets in order. Just an 1841 with two DSL WICs and you're away. It does work for some ISPs - just not ours for some reason. And the 3rd party solutions are not so simple to implement in my experience. Oh well.

Correct Answer
Paolo Bevilacqua Fri, 12/31/2010 - 10:19

What Cisco wants is the business case. Show up with a big sale prospect and keep them on the hook to deliver whatever functionality.

If you don't have that, the only you can do is the "Product Enhancement Request", meaning they file and may never look at it.

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