Is BYE hop by hop? or end to end?

Question

I am currently learning Session Initiation protocol. In that, started learning basic call flow of session Initiation Protocol. While studying that, in one source there mentioned that BYE request method is hop by hop,but in another source there mentioned that BYE request method is end to end. So now I am bit confused with that, Whether BYE request method is hop by hop or end to end??? Anybody help me out this. Also refer a good source for sip protocol.

Answer 1

Since a SIP BYE can only be a mid-dialog request (neither SIP UA pertaining to the dialog is allowed to send a BYE before the INVITE transaction completes or if the final answer is non 2xx), it logically follows that it can only be routed using the dialog's routing set -- according to RFC 3261, this mechanism is dubbed "loose routing". Now, since "loose routing" logically conflicts with "hop-by-hop routing", it follows that BYEs can only be "end-to-end" requests.