575 LRE and data transfer problems

Unanswered Question
May 31st, 2007

575 LRE and data transfer problems


I have a connection from my provider using the Cisco 575 LRE, configured for 10 Mbit/s. I don't know the make and model of the switch but I assume it is likely a Cisco device also.

I'm experiencing problems with the LRE connection whenever big files are being transfered simultaneously in both down- and upstream directions to/from a PC. The data transfer may slow down to a stall and all WAN connectivity may become momentarily blocked. Transfer speeds and reliability always seem good as long as big files don't get transferred in both directions at the same time.

What could cause this problem? My service provider says that they see no problems in their end and they are unable to help me. I don't know how extensively they have looked into any possibility of problems though.

I've tried different 100Mbit network cards, replacing ethernet and phone cabling and changing duplex settings and MTU, but nothing has completely solved the problem so far. Forcing network cards to full-duplex does prevent the worst slowdown and hanging described above, but limits upload speed to around half of the maximum available.

Not sure if this is meaningful here, but my service provider claims they have the switch my CPE is connected to configured for full-duplex, but when I have a PC network card set to autonegotiation, it will always result in a 100baseTX half-duplex link with the 575 - this is the case where I get maximum speed in either one direction but also the mentioned problems with bi-directional transfer.

I don't know what more I can do to the PCs here to solve this problem and I don't have access to configuring the CPE device, because I don't own the switch it is connected to. I can only think of trying to ask my ISP to read this thread if someone has a possible solution that requires actions on their behalf.

Any help would be much appreciated.

I have this problem too.
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Paolo Bevilacqua Fri, 06/01/2007 - 16:40


Stalls and performances drops in large files transfer are invariably due to packet loss somewhere in the path.

Unfortunately there isn't much that you can do with full cooperation from the ISP.

The first test would to try file transfers with an host that is located very close to the circuit access end, or at least within the ISP infrastructure.

scottmac Sat, 06/02/2007 - 05:03

The problem, as you describe it, is most likely cabling ...it could be the cable between your PC(s) and the 575 (most likely), or between the 575 and the switch.

What you are seeing are the effects of crosstalk (signal from one pair interfereing with the other pair), that's why you see it in full-duplex mode and not (so much) in half-duplex (with half-duplex, only one side talks at a time).

The only part you would be likely be able to change would be the connections on your side of the 575 ... so, try another cable; preferably a store-bought cable and in good shape (twisted, crushed, kinked, stretched, and poorly constructed cables are a Very Bad Thing).

LRE was designed to handle voice-grade cabling, but if you're at near the extreme length, you may see some degradation.

Good Luck


jhs140779 Sun, 06/03/2007 - 22:45

Well I described somewhat the opposite actually. In more detail:

Half-duplex and download only: Max. speed.

Half-duplex and upload only: Max. speed.

Half-duplex and transfer in both directions: Both transfers will stall often and all other connectivity will also be blacked out for short amounts of time.

Full-duplex and download only: Max. speed.

Full-duplex and upload only: Less than half of max. speed and will fluctuate somewhat.

Full-duplex and transfer in both directions: Download near max. speed. Upload speed reduced to around 2-5%.

But the duplex is only set for my network card as the 575 LRE can only be configured from the switch. So I don't know if a duplex mismatch is playing some part here.


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