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New Member

IPT, Half Duplex and slight echo


Has anyone run into intrasite echo problems using the gigastack GBIC's on the 3500 switches? I know if you use both ports on the gigastack the connection becomes half duplex. When I call an IP Phone from an IP phone on the same network I get a very slight echo, kind of a hollow sound. From reading the documentation on echo I understand that this is impossible. I'm thinking the root problem is that the customer has 3548 switches cascaded using gigastack GBICs. No two phones are on the same switch. I plan on putting 2 phones on the same switch to prove my theory, just wanted to see if anyone else has run into this issue?


New Member

Re: IPT, Half Duplex and slight echo

I don't think the problem is the half-duplex limitation when you use the giga-stacks as much as it is the concern that QoS doesn't work in this configuration. It is not a recommended configuration in telephony backbones; however, I have seen this type of connection in use with no problems.

I also believe that if you use a seperate GBIC for each uplink rather than splitting two ways off of one GBIC, the QoS issue goes away. Can anyone else out there verify this one way or another? If that is not the case, I would use SX GBICs to uplink at least the switches that have phones connected.

As far as echo goes, if you have gone through all the CCO recommended steps and you don't see something on this forum, I would open a TAC case. There are lots of firmware loads for the phones and IOS images for your switches; they should be able to point you toward a fix.

If you can, post your results of the phone move - it will be interesting to see what happens.

New Member

Re: IPT, Half Duplex and slight echo


We currently have four switches in a gigastack configuration. The switches are 3524s with inline power for phones. We use 7960 phones. We have the switches cascaded one to another so two of them have both ports on the GBIC connected. We have phones located on all four switches. One thing I remember we did when we had problems with the initial deployment was to remove the redundant path between the switches. The IOS version we have can support it (12.0 5 WC3b) but we felt it was causing some problems with our STP convergence. It may be that the redundant path causes the hollow sound (slight echo) that you hear. You may want to try that also and see how it works.

Also make sure that your IOS version can support the gigastack topology that you have.



New Member

Re: IPT, Half Duplex and slight echo

Thanks for the update. We moved the phones to the first switch in the cahin which has a direct connection to the 6509. Still an echo/hollow sound. Also the phones are getting a slight buzzing sound. My only guess on that is the fact that they use power cubes. I'll let you know how it turns out.

New Member

Re: IPT, Half Duplex and slight echo


Yes we have exactly the same problem with a number of different switch configurations. Common to all phones are the following:

- No power cubes (all use inline power)

- IPT switches are 3524-PWR

- Stacked via gigastack GBICs to either 3548XL, 3524XL or 3550

- Call Manager 3.1 installed

- IP phones are either 7960 or 7910

The echo is not always present, only sometimes!

I would be interested in the definitive cause of the problem (and a solution if one exists!).


New Member

Re: IPT, Half Duplex and slight echo

You need to do a latency test across the network. Latency can casue echo to be preceptible.

Also, the handset volume can also contribute to echo. As folks crank it up, you may experience echo. Try turning down the volume and see if it goes away.

Headsets often casue echo problems. Try lowering the volume there too. Another test is to mute the headset and see if it goes away.

New Member

Re: IPT, Half Duplex and slight echo

Thanks for all of the responses. Here is an update. I took the gigastacks out of the picture and put the phones on the same switch. Still had the problem. We did notice that if we turned the volume down to about 3/4 the echo was almost unnoticable (good suggestion). At this point we are thinking it may be a power problem. The phones use the power cubes. Power cubes do not ship with power cords. So we are sing spare cords from old PCs. We noticed that the echo/buzz varied in severity depending on what outlet we plugged it into. Pluging into a UPS provided substantial improvment. I am wondering if the power cords Cisco ships for the power cubes are shielded or something. I have TAC on it. More later.

New Member

Re: IPT, Half Duplex and slight echo

We found there is a known bug for echo on handsets with volume over 75%. CSCdv05279. It should have been fixed with load P00303020205. I am at P00303020211 and still get the echo (reverb). It seems the power cables that ship with the power cubes are standard cords. At this point we are living with the issue, thinking it is the power source.

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