Polycom SOUNDPOINT SIP 3.1 - Manual (Page 287)

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