Polycom SIP 3.0.2 Administrator's Manual page 231

Header
Diversion
Error-Info
Event
Expires
From
In-Reply-To
Max-Forwards
Min-Expires
Min-SE
MIME-Version
Organization
P-Asserted-Identity
P-Preferred-Identity
Priority
Proxy-Authenticate
Proxy-Authorization
Proxy-Require
RAck
Record-Route
Refer-To
Referred-By
Remote-Party-ID
Replaces
Reply-To
Require
Retry-After
Route
RSeq
Server
Session-Expires
Supported Notes
Yes
No
Yes
Yes
Yes
No
Yes
No
Yes
No
No
Yes
Yes
No
Yes
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes
No
Yes
No
Yes
Yes
No
Yes
Session Initiation Protocol (SIP)
B - 5