NBX V3000 Flashing Red Lights - What does this mean

We have an older 3Com NBX V3000 Analog phone system and today, we've been having some issues where the user inside the office can hear the caller just fine, but the caller outside the office is unable to hear due to static and/or choppiness.  I noticed that the 3Com V3000 had a flashing red line next to the Ethernet port (see picture)Picture of NBX V3000 with red ethernet lights.

Any help would be appreciated.  If it helps, we have some old 30 networking switches that need to be replaced as well.
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The online manual states: ...
 Red Alarm — Indicates one of these conditions:
■ Loss of Signal (LOS)
■ Loss of Framing (LOF) also known as Out of Frame (OOF)

-- So check cabling.
sscalAuthor Commented:
Thanks.  We swapped out a couple of network switches this morning, but that didn't improve anything.  I'll swap out the cable this evening or tomorrow morning when no one is in the office.
Well, since you did swap out the network switches, then check configuration on them.  It could be things like VLAN settings, firewall, QoS.   If switches are still onsite and downtime window is sufficient you can try plugging them back in and just see if problem goes away with same cables.   That will tell you it is switch configuration vs cabling.

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sscalAuthor Commented:
I'm not a networking or a telephony guy.  What should I be looking for in the configuration?  Is it possible the Ethernet card on the NBX V3000 is failing?
sscalAuthor Commented:
We had an outside vendor come by and they confirmed it was a cabling issue, as you had suggestion.

Sorry fro the delay in closing this.
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