[SIPForum-discussion] SIP "From" header field question

[mtsai at sunrisetelecom.com]

Hi,
 
RFC3261 says the "From" header field can be the format of "sip:user at hostname", where hostname can be a domain name or an IP address:
 
1. Should it be the IP address of the local UA, or the registrar, or the outbound proxy? Is there any specification describing this? RFC3261does not seem to clarify this.
2. Is there any difference for the "From" among different SIP messages(INVITE, REGISTER, and others)?
 
Thanks in advance!
 
 
Matt