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New Member

Connect delay on PSTN to VoIP Calls

I have three remote sites using the 3600 series router with the HDV / MFT module which provides the site with ISDN PRI connectivity to the PSTN. Each of these sites experience a 4-7 second delay after answering an inbound call from the PSTN before audio is heard. This results in my users having to repeat their greeting and confusion for the calling party.

Anyone else experienced this?


Re: Connect delay on PSTN to VoIP Calls

Often times complex troubleshooting issues are best addressed in an interactive trouble-shooting session with one of our trained technical assistance engineers. While other forum users may be able to help, it’s often difficult to do so for this type of issue.

To utilize the resources at our Technical Assistance Center, please visit and to open a case with one of our TAC engineers, visit

If anyone else in the forum has some advice, please reply to this thread.

Thank you for posting.

New Member

Re: Connect delay on PSTN to VoIP Calls

New Member

Re: Connect delay on PSTN to VoIP Calls

Hi Justin,

I just have look on your answer to the problem of delay to establish a voice connection between IPPhones and PSTN/ISDN.

Like I have the exact same problem, but with a C3640 running 12.2(2)XB (for SRS) and using BRI interface to Telco, I'm going to try upgrade to 12.2(5).

I already knew the famous command 'voice rtp send-recv' but it does not change anything in this case.

However, even if I succeed to solve the problem with the 12.2(5), do you know which IOS version newer than this last could also run SRST ?

Today I only saw SRST was running on 12.2 XB or XT as specific ED. But I did not see yet an LD running it.

Thanks to answer me if you know this easily.