Cisco SPA504G Hardphone conifg with BCM 7.5.0

Question

Hi all,
I am having some issue configuring a Cisco SPA504G Hardphone with SAP BCM. Network connectivity seems to be fine from tests done with wireshark however the buttons on the phone remain Orange and it says it cannot be registered with the SIP proxy. Not Registered(No Response) is the error on the phone.
Can you suggest what might be causing the problem and how to resolve it?
Many thanks,
Gordon.

Answer 1

Hi Gordon,
It looks to me that the 200 OK responses are retried in intervalls of 0,5, 1, 2, 4, 8 seconds (which is how retries should go) which could indicate a network or NAT problem. 200 OKs to INVITEs are acknowledged and it is maybe such 200 OKs that we see (but there are no ACKs). 200 OKs to REGISTER requests are not acknowledged and thus, the 200 OKs would not be resent (but there would be new registration attemps). There is also a "481 Transaction / Dialog does not exist" response to some request (REGISTER?).
Clearly the request related to the 200 OK response arrived at the server because the server replies with 200 OK. If the 200 OK don't find its way back to the phone, then the phone wouldn't send any ACK either which would cause the server to resend the 200 OK. Possible causes could be, for example, incomplete routes or NAT problems.
There are some factors affecting the response address that SIP Bridge uses, such as transport protocol (TCP/TLS - attempt existing connection), Via header info, presence of rport parameter and so on. SIP also specifies that in-dialog requests (e.g. BYE) shall be sent to the address specified in the Contact header.
I have found out in NAT tests with a rather old Cisco 2811 router that when UDP is used then also all headers in SIP messages are translated (SIP aware NAT) and desk phones work fine.
When TCP is used, then only some of the headers are translated and some additional things are needed before desk phones work properly. These additional things can be, for example, usage of STUN/TURN or maybe in some cases DNS resolution resulting in inside addresses on the inside and outside addresses on the outside.
Anyway, I think that your problem lies with the NAT traversal, route configurations and/or Firewall access-lists rather than the phone model not being among those tested.This can be verified by testing the phone in a network that is not behind NAT, preferably the server network. I also suggest that you try using UDP unless it is restricted on a Firewall. SIP Bridge accepts all incoming transport protocols.
Kind Regards,
Mikael