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Webcast-Catalyst9k
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ADSL2+ speeds dropping by half

Hi, I have Cisco 877s all over Australia connected to ADSL2+. All are running IOS version c870-advipservicesk9-mz.124-4.T7 and firmware version 3.010. The issue is that they will be running at around 22mb/1mb for a few weeks then for some reason they will drop to 10mb/1mb. The drop sometimes occurs after a router has lost sync with the DSLAM and it also tends to happen after a power outages, however, sometimes it just happens for no reason.

Before the drop in speed the router reports the DSL mode as:

DSL Mode: ITU G.992.5 (ADSL2+) Annex A

however after the drop it reports it as:

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

To resolve the issue I either have to reboot the device or shut down the ATM interface and bring it up a couple of seconds later. Both of these methods instantly resolve the issue and the router then regains the lost 10mb.

Does anyone know what could be causing this issue? Could it be some sort of mechanisim built into IOS? Or maybe it has something to do with CRC errors? I have tried two different IOSs and two different firmware versions neither of which have fixed the issue.

1 REPLY
Hall of Fame Super Gold

Re: ADSL2+ speeds dropping by half

Hi,

the issue is almost certainly a defect in firmware that syncs at the wrong speed, since you are running latest firmware I suggest to contact the TAC for this one, they may be aware of the problem and cisco plans to fix it.

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