What do the response codes mean in SIP messages as displayed in packet capture?
In the packet capture the response codes are found under the displayed Packet Info column. The utility used for this info is WireShark. The superimposed "Follow UDP Stream" is obtained by right clicking one of the packets in the conversation and select "Follow UDP Stream
SIP/2.0 allows six values for the first digit:
1xx: Provisional — request received, continuing to process the request;
Provisional responses, also known as informational responses, indicate that the server contacted is performing some further action and does not yet have a definitive response. A server sends a 1xx response if it expects to take more than 200 ms to obtain a final response. Note that 1xx responses are not transmitted reliably. They never cause the client to send an ACK. Provisional (1xx) responses MAY contain message bodies, including session descriptions.
2xx: Success — the action was successfully received, understood, and accepted;
3xx: Redirection — further action needs to be taken in order to complete the request;
4xx: Client Error — the request contains bad syntax or cannot be fulfilled at this server;
5xx: Server Error — the server failed to fulfill an apparently valid request;
6xx: Global Failure — the request cannot be fulfilled at any server.
In a successful registration there are mandatory request and response that will be seen in the capture
SIP IP Phone
SIP Proxy Server
The SIP IP phone supports initial INVITEs as well as mid-call INVITEs, which are used for call hold and call transfer.
The gateway supports mid-call INVITEs with the same call ID but different SDP session parameters (to change the transport address).
The SIP proxy server proxies SIP INVITE requests.
The SIP proxy server proxies the SIP ACK method.1
The gateway does not generate OPTIONS. However, it will respond to OPTIONS requests.
The SIP proxy server proxies OPTIONS.
The SIP proxy server proxies the SIP CANCEL method.2
The SIP IP phone supports both user and device registration.
The SIP proxy server supports both user and device registration.