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Model Specific Packet Loss

Hello Everyone,

I have the following situation. I am getting packet loss on extended pings to 7960 and 7940 phones. I am averaging about 85% return even from the switches that the phones are plugged into. This packet loss is in direct correlation to voice quality issues from the same phones. I can take a 7912, put it in place of a 7960 or 40 and the packet loss disappears. Even if I give the phones the same IP addresses. Nothing else changes, not the VLANS, not the configs on the switch, nothing. Does anyone have an idea on what could be causing this? I am running the latest phone loads and have tried downgrading the phone loads with the same results. One last clue. The voice quality issue did not (so I am told) manifest itself until the phones were moved to a new cluster from 3.3 to 4.1. The supporting network infrastructure did not change at all though. Most but not all of the 7960s and 7940s have PCs connected but even the ones that don't still have the same problem. PLease bear in mind the issue goes away as soon as a 7912 is placed, even with a PC connected and NONE of the 7912s network wide seem to have this problem. All the phones were purchased over a long period of time so bad hardware should not be the issue

Any thoughts?

All replies will be rated.

Hall of Fame Super Red

Re: Model Specific Packet Loss

Hi Travis,

Long time... hope things (other than this) are going well for you! Can you please let us know the exact version of CCM and phone firmware you are running. I had a look for bugs that might be related to this, but it would help to narrow this down.

Have you tried putting a sniffer on to see what is happening? (probably)

I did come across one bug that was somewhat ambiguous that was in reference to problems created by the NIC settings on the CCM box being set to auto/auto.


Let us know, and take care!


New Member

Re: Model Specific Packet Loss

I know I had a concern once that the phones were experiencing packet loss, but it was explained to me by TAC that the phones are designed to do that to prevent DOS attacks and the likes.

If you ping it from a workstation not attached to the phone do you still get packet loss. The replies from a switch or router are too fast for the phones, so they will drop some of the pings.

Your post says that the issue goes away with replacing it with a 7912. Does the voice quality issue go away as well, or just the packet loss?

Re: Model Specific Packet Loss

Hello Rob and Matt,

thanks for the replies. Call Manager is 4.1(3)sr3b. It appears if I ping from a workstation not attached to the phone I don't get packet loss on the pings. I understand what you are saying about the switch being too fast but then why do I not get packet loss on pings from the 7912s? So far the voice quality issues go away when a 7912 is placed and come back with a 7960 is placed and I have tried different units to rule out hardware issues. Exact same results all the time.

Any thoughts?

New Member

Re: Model Specific Packet Loss

Hey Travis...

You have me scratching my head on this one. What is the topolgy of this network and have you tried any sniffers? I am curious if you may have something on the network segment that is doing a DOS attack. I have been looking for documentation for differences in the 2 model phones, and I ran across this :

I am grasping at straws on this, so hopefully you will come up with a better idea.

Also, didn't I work with you at Nexus for a little while?

Good luck

Re: Model Specific Packet Loss

Thanks Matt,

to be honest I have consulted at so many places over the years that I really don't remember most of the companies. Drop me a line at with a few more details about the gig. Could be.

Thanks for the help on this one

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