Firmware 4.1.1.01-sp.bin breaks SIP calls on Cisco SMB RV082 V3

I am using Cisco SMB RV082 V3 router on my home PC for a long time now and this is the first time I am noticing something like this has ever happened. I have recently upgraded the firmware of this router to version 4.1.1.01-sp.bin. After I updated the firmware, I started getting inconsistency in the SIP calls. They will break in between or fluctuate. Also the router has started rejecting the sip messages. Can someone tell me why this is happening?

From what you are trying to tell in your question, I can say that when you are receiving or making an SIP call, the Cisco SMB RV082 V3 router is checking for the Ethernet trace. So every time you make a call this tracing leads to setup of different port of different IP address. This happens because the NAT call sets up a new NAT registry in the router leading to this problem. The SIP calls are set to have a short registration times. Due to this, the call has to keep changing the port during each session. I think that this process is not being completed properly leading to the inconsistency that you are noticing.

The SIP and NAT are responsible for working of the router, but due to the new firmware upgrade they do not work properly with each other in most of the cases, one of them is the SIP calls. But according to me, if the port forwarding method is used in this system, I think we can fix this problem easily. By port forwarding method, I mean to use the static IPs in the router for receiving and making the SIP calls. I think the best method to perform this task is by providing the external ports for the public IPs and let the private IPs be stored in the DHCP pool. You can try this out to see if it works properly or not. I am not sure, but if this method works, then the problem of improper SIP calls in Cisco SMB RV082 V3 router might be solved.

I think that the firmware that you have installed has reduced the time of the registration period for the UDP NAT sessions. I think this is why the SIP based messages are being rejected by the Cisco SMB RV082 V3 router. I mean these SIP messages are used to check if the NAT connection is alive or not. If the SIP messages stop it means that the NAT connection has broken and so is the chance of the connection being connection being broken more. The problem that has occurred in the working of Cisco SMB RV082 V3 is causing the PBX to block the replies to the port 5060, which is responsible for dealing with the public IPs. Also the firmware 4.1.1.01-sp.bin that you have mentioned has increased the registering time for PBX from 30 seconds to 300 seconds.

The actual reason of this problem with the SIP calls in Cisco SMB RV082 V3 router is that firmware 4.1.1.01-sp.bin disconnects the SIP connection and maps a new NAT network for every call that is registered. Also the port that the NAT network opens and uses does not get re-used in the same session. So if by mistake the NAT mapping comes on the used port, it takes time to establish the broken connections. Also the time till which the registration has been increased in Cisco SMB RV082 V3 router by the firmware 4.1.1.01-sp.bin. Thus you see the inconsistency in the SIP calls.

I think that transferring the SIP calls to the public IP using the port 5080 may be logical, but if thought practically then it might create problems for SIP ALG in the router. If you can trace the calls in the router using Asterix based PBX, then you will notice that PBX will not be transferring any of the RTP of the SIP call unless you SIP endpoints start reacting to it and then send replies back to it. The main problem that is happening in Cisco SMB RV082 V3 router is that PBX is not able to generate signals properly leading to this problem.