One way audio on incoming calls. The caller cannot hear us


i have an open ticket with Flowroute.
not being able to hear the person who answers the phone is precisely the problem. the office resorts on calling back the caller based on the caller id.
i really appreciate your help


@JimS rather than being led around the garden path so to speak by providers, ask one of the users here to assist you directly as paid support. not me, because I am not in your country and will not have insight into your countries tech specifics … thats where Larry @lpneblett and the others here will be able to assist.


Hi was this not an outbound call you dialed xxxxxx94900@
the invite is sent From: 718xxx7284@ to xxxxx94900@ that is your UCM was this not an outbound call
my questions are based on the last call with call-id == 1163ad73-f670-42f3-8531-32aa5dea796c

Also your Network explanation seems like you have double Nat

|Bridged modem|=====> (public IP) Port 1 uplink Adtran
Port 2 ===> what is the Ip here <======= (GW) port 2 Server DHCP to PCs

Port 3====> what is the IP here <======= (GW) Router to phones

You have 2 routers the Adtran and another for the voice network the uplink for the voice router is port 2 of the Adtran what is its IP… You have possible double NAT

                              You have double nat here if you have 2 routers


Hi Telecomsolutions
Not sure about the call you are referring to. What I uploaded was an incoming call but is possible that someone was calling out at the same time without my knowledge.

About the double NAT. The Adtran has three ports. One WAN connected to the modem add two LANs, one connected to the network switches (server and PCs) and one connected to the VoIP POE switches (UCM and phones). There is no second router.

Thanks for trying to help.


Hey Jim,

Are the UCM RTP settings to udp 10,000 to 11,000 ??? or are they UDP 10,000 to 20,000 ?

UDP 5060 is setting up the signalling which isnt a problem, the issue is the RTP stream that isnt negotiated correctly. When you call out, the UCM negotiates the RTP correctly, but incoming seems to have an overide to use different ports somewhere causing the failure.

RTP rewrites on the router?



Hi Kev,

I started with UDP 10,000-20,000, tested 10,000 to 11,000 down to 10,000 to 10,250 all changes on both the UCM and the router.

I see nothing on the router that could be rewriting RTPs.


After several hours checking through the Router and setup - it appears that the NetVanta has and is the culprit causing many different issues.

Jim and I were able to get it working on a few occassions but shall have to see if the calls are bothway audio when the office is online during business hours.


I want to thank lpneblett (who is in the middle of a storm in Texas) and scottsip for the many hours wrestling with Netvanta trying to help me. Their assessment is right on the money about the router, as confirmed by Netvanta tech support this morning.

First the tech support rep was surprised that VoIP works at all with the current settings. Then I was told that in order for it to work, I would have to purchase an “SBC license” from them (something that is not mentioned in their documentation), install it and then go through a myriad steps to make it work with the PBX and the SIP provider (Flowroute). Needless to say, I have a new router coming in and I am switching tomorrow, something I was not looking forward to.

I will report how that goes.


well it will be a big day today for Jim and the office he works in as the new router went in today and hopefully rectifies the issues unless the IT guy doesnt program the needed qos / prioritisations etc…


I get to do that chore


well done to you both for assisting in what seems like with have been a never ending blame game. Very impressed with effort from forum members.


Thrilled to say that after the installation of the new router, the network and phone systems are up and running the way they are supposed to.
Thank you all for for your help, this forum is awesome.
But I want to especially thank scottsip and lpneblett for spending many hours drilling down to my system, trying to find the problem. If it wasn’t for them, I would still be in the abyss.
Like I said, this forum is awesome.