Yealink SIP-T4X Administration Manual page 415

Administrator's Guide for SIP-T4X IP Phones
The following SIP request headers are supported:
Method
Accept
Alert-Info
Allow
Allow-Events
Authorization
Call-ID
Call-Info
Contact
Content-Length
Content-Type
CSeq
Diversion
Event
Expires
From
Max-Forwards
Min-SE
P-Asserted-Identity
P-Preferred-Identity
Proxy-Authenticate
Proxy-Authorization
RAck
Record-Route
Refer-To
Referred-By
Remote-Party-ID
Replaces
400
Supported
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Notes