MP-1xx SIP
MP-1xx SIP User’s Manual 154 Document #: LTRT-65404
8.4.1.2 Receiving Hold / Retrieve
• When an active call receives REINVITE message with either the IP address 0.0.0.0 or the
“inactive” string in SDP, the gateway stops sending RTP and plays a local Held Tone.
• When an active call receives REINVITE message with “sendonly” string in SDP, the gateway
stops sending RTP and listens to the remote party. In this mode, it is expected that on-hold
music (or any other hold tone) is to be played (over IP) by the remote party.
8.4.2 Consultation / Alternate
• The consolation feature is relevant only for the holding party (applicable only to the MP-
1xx/FXS gateway).
• After holding a call (by pressing hook-flash), the holding party hears dial tone and can now
initiate a new call that is called a consultation call.
• While hearing dial tone, or when dialing to the new destination (before dialing is complete)
the user can retrieve the held call by pressing hook-flash.
• The held call can’t be retrieved while Ringback tone is heard.
• After the consultation call is connected, the user can switch between the held and active call
by pressing hook-flash.
8.4.3 Call Transfer
There are two types of call transfers:
• Consultation Transfer (Refer + Replaces)
• Blind Transfer (Refer)
The common way to perform a consultation transfer is as follows:
In the transfer scenario there are three parties:
Party A = transferring, Party B = transferred, Party C = transferred to.
• A Calls B.
• B answers.
• A presses the hook-flash and puts B on-hold (party B hears a hold tone)
• A dials C.
• After A completed dialing C, he can perform the transfer by onhook the A phone.
• After the transfer is completed B and C parties are engaged in a call.
The transfer can be initiated at any of the following stages of the call between A to C:
a. Just after completing dialing C phone number - Transfer from setup.
b. While hearing Ringback – Transfer from alert.
c. While speaking to C – Transfer from active.
Blind transfer is performed after we have a call between A and B, and party A decides to transfer
the call to C immediately without speaking with C.
The result of the transfer is a call between B and C (just like consultation transfer only skipping
the consultation stage).
Note the following SIP issues:
• Transfer is initiated by sending Refer with Replaces.
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