Scalable voip mobility intedration and deployment- P4: The term voice mobility can mean a number of different things to different people. Two words that can be quite trendy by themselves, but stuck together as if forgotten at a bus station long past the last ride of the night, the phrase rings a number of different, and at times discordant, bells. | 28 Chapter 2 Table SIP BYE from Caller to Proxy BYE sip 7020@ SIP Via SIP UDP 5060 branch z9hG4bK1818649196 From 7010 sip 7010@ tag 1687298419 To sip 7020@ tag as500634a6 Call-ID 2114455679@ CSeq 21 BYE Max-Forwards 70 Content-Length 0 In-Progress Codes 100 Trying sent by any endpoint when it needs to inform the requester that it is handling the request but might not return quickly enough to prevent the sender from thinking the message was lost. 180 Ringing sent by the called party while it is ringing the phone. 181 Call is Being Forwarded might be sent by a proxy to the caller when the call is being forwarded to another destination such as a second handset or voicemail. You may never see this one. 182 Queued sent by a server running a phone bank informing the caller that the call is on hold to be answered. It can also be sent at a chokepoint when lines are busy but one of the proxies does not want to give up on establishing the call just yet. Success Code 200 OK the request succeeded. If the request was an INVITE the message has the session description for the audio channel. Redirection Codes 301 Moved Permanently sent by a proxy or possibly an endpoint when a user has permanently changed his or her phone number to something else. The Contact header should have the forwarding address. 302 Moved Temporarily sent when the call is being forwarded. The Contact header will have where the call needs to be forwarded to and the caller must start a new call to that forwarding address. Request Failure Codes 400 Bad Request sent when the SIP message is not formatted properly. This is a good sign of interoperability issues between advanced features of different products. Voice Mobility Technologies 29 401 Unauthorized sent by a device when it requires SIP authorization. 403 Forbidden sent for a number of reasons. Usually this happens when a caller is not allowed to use a certain feature perhaps
