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New Member

Low Voice Quality on LAN

i have a CCM 3.2.2 in a LAN switched network ( cisco and HP switch ) with 60 ipphone.

More 7910 ipphone telephones have insufficient quality, and many times the calls are dropped.

The codec on LAN is the G711 and the voice-gateway is a Cisco3640 with BRI voice-card.

how can i resolve the problem?



Re: Low Voice Quality on LAN

How many nodes do you have on network? Around 60? Regardless, you shouldn't have LAN issues, but you never know. First, which calls are dropped? Calls out the gateway or IP Phone to IP Phone calls? Obviously, check the stats on the switches and see if there are any errors anywhere, if so, clear the counters and see if you can make a correlation next time there is bad quality. Typically, if there is a traffic problem, you will see bad quality, but the call won't drop (at least not at first).

If it is the calls out the gateway that are giving you issues, let us know and we can start troubleshooting that. Keep us informed.


New Member

Re: Low Voice Quality on LAN

I don't have collision or network problem in a Cisco3640gateway, MCS and 79XX phone, but the network problem are on 7910: collision and deferred.

7910 support only 10mbit halfduplex!

however, the problem are only on the external call, via voice-gateway.

i think that i have a jitter-delay problem.....

the cisco 3940 run the 12.2(8)T5 IOS.


New Member

Re: Low Voice Quality on LAN

First, upgrade the 3640 to 12.2(11)T1.

Second, make sure the switches are set to autodetect speed and duplex. Don't force them.

Third, make sure the switches are capable of layer 2 QoS and are supporting it.

Fourth, make sure the phones are getting (or configured for) the correct VLAN, and the switch ports are trunking the VLANs correctly. The voice should be on a seperate VLAN from the data.

This should get you a start...

New Member

Re: Low Voice Quality on LAN

You mention that the 7910 is running at half-duplex. We use the 7910s with a 10/100 port and they all run at full duplex. I assume you are using the single port version, even so I would expect this to be a full duplex port. I can't see anything on CCO to state otherwise. This may well be your problem because voice does not run well across half-duplex.

New Member

Re: Low Voice Quality on LAN

The most 7910s are with 1 port, and they work at 10mbit half duplex.

many cisco IPphones are plugged on cisco switch.

I'm upgrading the c3640 IOS, until the 12.2(12a).


New Member

Re: Low Voice Quality on LAN

Let me get this straight you are using an ISDN BRI 2B and 1D channel and you are using G711 CODEC with 60 phones. With overhead on the packets is that not 80k per conversation going across 128k circuit. So after the first call it will hog the BW. Also is it off net calls that suck or both on and off net calls.

Re: Low Voice Quality on LAN


That's not quite correct. The guy is using a BRI -Voice card, therefore the gateway is a normal voice gateway with only 2 circuits. the 3640 does the normal IP-Circuit switched conversion as with any other gateway.

However I agree there isn't enough info on what the problem really is. When does the problem occur, are the phones using the internal switch and if so are they plugged into the HP switch.

Come on people give us something to work with here!!!!!!!