[Asterisk-Users] Cisco 7940/7960 ethernet ports

[Mike Ciholas]

On Mon, 8 Sep 2003, Travis Johnson wrote:

> We are having a problem with Cisco 7940 and 7960 phones when
> the PC is plugged into the 2nd ethernet port on the phone. It
> will drop the PC's connection for about 30 seconds, then bring
> the connection back up for about 30 seconds. It does this
> continually regardless of how the port is configured on the
> phone.
> 
> Has anyone else seen this problem/issue?

I've not seen this or used Cisco phones (yet), but I have 
witnessed a similar issue and it appears to be related to link 
negotiation of the ethernet switch to the PC.

Try this (just as a test): use a long ethernet cable between the
phone and the PC, say 50-100ft.

If that "fixes" it, then the ethernet signal is "too strong".  
Sometimes, using really short cables and due to manufacturing
tolerances, the signal can be too strong and the link will fail.  
This is a complex thing having to do with equalization, eye
patterns, and possible high frequency noise on the wire. How long
it takes to "fail" a link varies, but 30 seconds may be the time
needed for the error threshold to be reached.  The long cable
filters the signal somewhat and lowers the amplitude.

Another test: use a different NIC in the PC (as different as you 
can).

Another test: force PC to be 10 Mbs link.

Another test: look at PC NIC statistics and see if you are 
receiving bad frames (CRC, format error, etc).

Ultimately, you may find that certain NICs with certain phones 
just do this and you have to find another brand/model NIC to make 
this happy.

Disclaimer: everything in the email could be wrong.

-- 
Mike Ciholas                            (812) 476-2721 voice
CIHOLAS Enterprises                     (812) 476-2881 fax
2626 Kotter Ave, Unit D                 mikec at ciholas.com
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