Polycom SIP 2.2.0 사용자 설명서

 Session Initiation Protocol (SIP)

B - 9

The phone supports both currently accepted means of signaling hold. 
The first method, no longer recommended due in part to the RTCP problems 

associated with it, is to set the “c” destination addresses for the media streams 

in the SDP to zero, for example, c=0.0.0.0.
The second, and preferred, method is to signal the media directions with the 

“a” SDP media attributes sendonly, recvonly, inactive, or sendrecv. The hold 

signaling method used by the phone is configurable (refer to 

on 

), but both methods are supported when signaled by the remote end 

point.

The phone fully supports RFC 3262 - Reliability of Provisional Responses.

The phone supports transfer using the REFER method specified in 

draft-ietf-sip-cc-transfer-05 and RFC 3515.

The phone supports the delayed media negotiations (INVITE without SDP) 

associated with third party call control applications.

The phone is compatible with the Presence and Instant Messaging features of 

Microsoft Windows

 

Messenger 5.1. In a future release, support for the 

Presence and Instant Message recommendations in the SIP Instant Messaging 

and Presence Leveraging Extensions (SIMPLE) proposals will be provided by 

the following Internet drafts or their successors:

• draft-ietf-simple-cpim-mapping-01

• draft-ietf-simple-presence-07

• draft-ietf-simple-presencelist-package-00

• draft-ietf-simple-winfo-format-02

• draft-ietf-simple-winfo-package-02

Even if the phone is set to use c=0.0.0.0, it will not do so if it gets any sendrecv, 
sendonly, or inactive from the server. These flags will cause it to revert to the other 
hold method.