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Voice over Wireless - the first syllable is swallowed

Frederik Schon
Level 1
Level 1


i have a problem with voice over wireless in a big campus network. When a user makes a call from one 7925 phone to another sometimes the first three words (Hello here is Mr. X) are not transceived to the other site. It seems that the rtp stream is not fully ready. After one second everything works fine. Does anybody have similar problems?


2x WISM2 with

500x 3500 Series Access Point (500)

800x 7925 IP Phones

Kind Regards

11 Replies 11

It's a big VoWLAN deployment & hope you followed the Cisco recommened VoWLAN guidelines for such deployment given below.



If someone initiate a call from wired VoIP phone to 7925, do you experience the same (ie wireless phone user cannot hear first few words )

Provide us "show wlan " output to get an idea about settings you have configured on this voice WLAN.





is there somebody with same problems? We have 2 customers with the same problems. Both using 5508 Controller.


best regards

Are they using identical code version ? what are the similarities between those two customer setup ?

I would say this behavior is a bug if they specific to a particular code. Here is a similar issue with respect to FlexConnect local switching




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Cisco Employee
Cisco Employee

Should expect up to 1000 ms delay to setup the call.
With the 792x release, this area has been enhanced, so if you haven't done so yet, try firmware.

Sent from Cisco Technical Support iPhone App


we tested with the new phone software version ( But the problems are not solved. We tested also with a different Data rate set (6 mandatory, 12 and 24 supported). But nothing is different.

I noticed now, that Admission Control for Voice is deactivated. Could this generate those problems? Very interesting is, that this problem occur when you are next to the access point. And it is only from one wifi phone to another!

Has anybody similar problems with the controller Version

Kind regards

Cisco Employee
Cisco Employee

Will still be about 500 ms or so to setup the call, especially 792x to 792x.
But no issues with the rest of the call.

Also suggest to migrate to

Sent from Cisco Technical Support iPhone App

Yes thats right, no issues with the rest of the call.

Im also thinking about it to migrate to Because on other sites everything works fine with this version.

I asked cisco tac of known bugs in But they said to me thats nothing known connected to those problems...

Your QoS is set to Platinum and Platinum QoS is configured for 802.1p?

802.1p Tag for Platinum set to 6?

Noticed that after upgrading from to the 802.1p Tag has been changed to 5.

For version 7.4 and 7.5, which version is more stable? because somebody told me  that version 7.4 seems to have a lot of bug ago, it is right?

Hi Bacike,

I would stick with (7.4 MR1) or if you need latest 7.4.111.x (7.4MR2 pre-release). Previous version of 7.4.x had multiple bugs. Now almost 1 year since 7.4  code released & even cisco recommend to go for 7.4.MR1 if you are in that train. Here is 7.4MR1 release notes

7.5. code is there for less than 6 months & no MR (maintenance release) available.  Here is Release notes.

Any software code you will have bugs, so you have to read release notes of each & decide which one to go. Unless new feature required only available in 7.5 I would suggest to go with



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