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Yet another one-way audio issue

Hi guys,


A strange one, as it seems. Setup:


ISDN - 2911 - CUCM - IP Phone


Calls go through ISDN via 2911 to the IP phone, got silence from ISDN to IP phone. It does work well the other way, I can hear voice coming from IP Phone to ISDN.


The strange part here is the fact, that some of rtp packets go from the gateway to IP phone, but only a few and the gateway seems to stop sending them almost immediately (tx values do not change during the period of the call and for some reason there are both rtp and rtcp counters >0, even though there is no rtcp configured):


cnhngz01er01#sh voip rtp connections detail

VoIP RTP Port Usage Information:

Max Ports Available: 8091, Ports Reserved: 101, Ports in Use: 1

Port range not configured

                                        Min   Max   Ports     Ports     Ports 

Media-Address Range                     Port  Port  Available Reserved  In-use


Global Media Pool                       16384 32766 8091      101       1     


VoIP RTP active connections :

No. CallId     dstCallId  LocalRTP RmtRTP   LocalIP                                     RemoteIP                                  MPSS  VRF

1     1208       1207       16464    24594                                                 NO    NA                 

 callId 1208 (dir=2): called=4949 calling=0286161872700 redirect= loopback=NO confID=-1 mode=3 rtp(tx:124/rx:34228) rtcp(tx:136/rx:0) MPSS NO VRF NA                   peer callId 1207: called=26899249 calling=02161872700 redirect= , confID:0

 , vrf = NA                     1 context 0x2323C7F8 xmitFunc 0x35E87950

Found 1 active RTP connections


 From the ip phone side I see the same amount of both received and transmitted packets.


I have tried (just in case) configure both sip and h323 between 2911 and CUCM - with the same result. The only difference I have noticed is that in case of SIP the amount of packets sent from the gateway to the ip phone is a bit lower, than in case of h323 (~17 vs ~130).


Sh run, sh inv and some debugs are enclosed.


I would appreciate any help on this.

Kind regards, Andrew C.
3 Replies 3

Georgios Fotiadis
Rising star
Rising star

Is there a firewall (or ACL) between the 2911 and the IP phones (or CUCM) subnet? Note that the 2911 uses its loopback address for H.323 communication. Also, make sure that you do not have any routing issue.

Have you verified through the IP phone's GUI that they are sending/receiving packets?

Please rate if you find this helpful.

It has been resolved after replacing the router with the brand-new ISR 4k. 


As for your answer - I have covered all of that in the initial post, actually.

Kind regards, Andrew C.


Can you enable ip routing command on the global level of the router and check if one audio still exist?.


If still after applying the command and still issue presist, can you run these debugs on the gateway?.


1.    debug ccsip messages

2.    debug isdn q931







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