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Jabber iphone no audio issues while on VPN


Hi Team,

Could you please provide some help on this.

We have Jabber iphone users from a region facing no audio issues when connected via VPN. This happens only when they dial to external numbers. Internal network calls works fine.

The traces and jabber problem reports shows that, for the failed calls, the remote end device is using an unusual RTP ports. Remote end device  ( where it leaves our company network ) in these calls are a voice gateway as these are external calls. We see remote end is using 9014, 9656 ports instead of standard RTP/UDP ports 16384-32767. CDR shows the same info as well.

TAC analysed this and advised to get the remote end allocate a proper RTP port to resolve the issue.

The question I have is which device (call manger, GW or is it VPN server ) determine the RTP port to use when the RTP session is about to be established.  

We have ISR4451-X/K9 GW and CUCM 9 running.


Thanks and appreciate your time.


Accepted Solutions


Checking this after many years and leaving update if someone get stuck on the same issue. We fixed the issue by below command added in gateway.


Under Voice service voip add "Rtp-port range 16384 32766"


View solution in original post


Vivek Batra


When you say failed call, do you mean call doesn't get matured or there is no audio?

For external calls, which voice gateway you're using? Is it Cisco gateway?

Technically there should not be any issue in using any port for RTP say 9014/9656 as long as there is firewall in between restring those ports. 

Two end points involved in a call select their RTP ports independently. In your case, those end points are Jabber and Voice Gateway. From Jabber perspective, CUCM decides the port and configure under 'SIP Profile'. From gateway perspective, gateway will decide the RTP port on which it will be listening for RTP packets. VPN server will never decides the RTP ports to be used during a call.

IMO you probably need to check where exactly RTP stream being stucked while going over the network.


Thanks a lot for having a look Vivek,


These call do mature but there is no audio. Its a Cisco voice gateway (ISR4451-X/K9).

As you correctly mentioned the source (iphone) is taking correct ports per our configuration in call manger. But the remote end (voice gateway ) is offering incorrect port. The firewall team doesn't have clue about this whether these ports are blocked. If we block these ports how the call setup will proceed. won't it fail. please advice. 

Is there a way we can force the GW to offer correct ports for RTP and RTCP streams.  


Really appreciate your time.

If we block these ports how the call setup will proceed. won't it fail. please advice. 

I was suggesting to check if those ports are blocked in firewall, open those ports for RTP packets to pass through.

Is there a way we can force the GW to offer correct ports for RTP and RTCP streams.  

I tried to search on that part but couldn't found any command/documentation which allows to change the RTP port range in gateway.