fxs port and one way voice communications

Unanswered Question
Jun 4th, 2007


I have an interesting issues I have been working on for the last day or so and have been unable to find a solution.

The hardware Cisco 1760-v with the pmdm-256-4 module, 1 x 7940 and 1 x 7905 phones with sccp images and vic2-2fxs module. The two issue I having are

no dial tone on the fxs ports, and can not dial a valid ext into the analog phone. When dialing the FXS ext from a ip phone, the analog phone rings, you have

two way voice from the analog phone to the ip phone but the IP phone/router dose not seem to be send voice back to the analog ext.

Can anyone please point out why these issues are happening?

The IOS I'm using is IOS (tm) C1700 Software (C1700-IPVOICE-M), Version 12.3(22), RELEASE SOFTWARE (fc2)

the config looks like this

interface FastEthernet0/0

ip address

speed auto


ip default-gateway

ip classless

ip route

no ip http server



voice-port 2/0

cptone AU


voice-port 2/1

cptone AU




dial-peer voice 801 pots

destination-pattern 0419705725

port 2/0

forward-digits all


dial-peer voice 100 pots

destination-pattern 199

port 2/0


dial-peer voice 101 pots

destination-pattern 200

port 2/1




max-ephones 15

max-dn 50

ip source-address port 2000

transfer-system full-consult



ephone-dn 11

number 201 no-reg both



ephone 1

mac-address 0012.0101.067F

type 7940

button 1:11



I have this problem too.
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adrianeurell Wed, 06/06/2007 - 02:57

I have been looking this issue and suspect the DSP may be a little faulty or a codec issue? - need some advice on how to debug it correctly.

I can dial from any phone to another phone on the router and they ring, if I call from an analog phone to a voip phone

they can hear the voice from the analog phone but no return voice back to the analog phone.

If I call the other analog phone to analog phone it rings but no voice in either direction.

If I call voip to voip all is working well.

Has anyone come across this issue before? I know out of ideas and could use some help



dgahm Wed, 06/06/2007 - 10:57


Can you post the result of a show voice dsp command?


adrianeurell Wed, 06/06/2007 - 16:19

Router#sh voice dsp



==== === == ======== ======= ===== ======= === == ========= == ===== ============

C549 000 00 g711ulaw 9.2.2 Idle Idle 0 0 2/0 NA 0 501/376

C549 000 01 g711ulaw 9.2.2 Idle Idle 0 0 2/1 NA 0 3200/3006

Active Voice Call details

Current total analog signalling channels: 2

Current max allowed digital timeslot for voice: 0

Current active transcoding sessions: 0

Current free transcoding sessions: 0

Current active conferencing sessions: 0

Current free conferencing sessions: 0

Current number of DSP group: 1

Group 0:

Current allocated analog signalling channels: 2

Current free analog signalling channels: 0

Current allocated digital signalling channels: 0

Current free digital signalling channels: 0

Port(s) served: 2/0 2/1

Current Available MIPS: 100

SPMM DSPRM State Image D-sig D-sig A-sig A-sig Mips Voice/Xcode

Dsp Dsp allocate free allocate free Free Chan

0/0 0 UP FIXHC 0 0 2 0 100 0

edsp 001 01 g711ulaw 0.1 IDLE 50/0/11.1

edsp 002 02 g729r8 p 0.1 IDLE 50/0/11.2

edsp 003 01 g711ulaw 0.1 IDLE 50/0/12.1

edsp 004 02 g729r8 p 0.1 IDLE 50/0/12.2

Paolo Bevilacqua Thu, 06/07/2007 - 04:13

This is very strange.

Which firmware do you have on the phones ? Can you try upgrading, eg the 7940 to 7.2(4) ?

adrianeurell Sun, 06/10/2007 - 15:43

Yes - I know it is a strange one - The phones are running 7.2(4.0). I trying to get another DSP and try it out if it is the issue. A friend has loaned me a 1760 and and the fault seems to follow the DSP. I have been unable to find a way to prove there is a fault with the DSP.

Paolo Bevilacqua Sun, 06/10/2007 - 16:05

Ok, while you are on a call, press question mark key on the phone, twice quickly. This will bring up RTP statistics. Check the packet counters.

Perhaps this will not reveal much, just that the phone's RTP streams are OK.

But in first place, the fact you have no dialtone on FXS, seems to indicate either a faulty VIC, or faulty DSP. Why don't you try reseating both of them in a different slot.

adrianeurell Sun, 06/10/2007 - 18:26

The stats on the 7940 phone look fine, there is data moving and the codec are g711u. I have tried slots 0,1,2 on both 1760 routers so I'm thinking it is not the router, this issue presents it's self on both vic2-2fxs and vic2-2fxo and I know in the case of the fxs card it was pulled from a working test lab. I trying to get a pvdm in the next couple of days so I will see how it perform and if it fixes my problem, unless there are any other ideas?

adrianeurell Wed, 06/20/2007 - 01:58

Well, I have installed another DSP into the router and it has fixed the issues.


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