Call Forward - AudioCodes Mediant 3000 User Manual

The Explicit Call Transfer (ECT, according to ETS-300-367, 368, 369) supplementary
service is supported for PRI trunks. This service provides the served user who has two
calls to ask the network to connect these two calls together and release its connection to
both parties. The two calls can be incoming or outgoing calls. This service is similar to NI2
Two B-Channel Transfer (TBCT) Supplementary Service. The main difference is that in
ECT one of the calls must be in HELD state.
18.5.2.2.2 Consultation Transfer for QSIG Path Replacement
The device can interwork consultation call transfer requests for ISDN QSIG-to-IP calls.
When the device receives a request for a consultation call transfer from the PBX, the
device sends a SIP REFER message with a Replaces header to the SIP UA to transfer it to
another SIP UA. Once the two SIP UA parties are successfully connected, the device
requests the PBX to disconnect the ISDN call, thereby freeing resources on the PBX.
For example, assume legacy PBX user "A" has two established calls connected through
the device – one with remote SIP UA "B" and the other with SIP UA "C". In this scenario,
user "A" initiates a consultation call transfer to connect "B" with "C". The device receives
the consultation call transfer request from the PBX and then connects "B" with "C", by
sending "B" a REFER message with a Replaces header (i.e., replace caller "A" with "C").
Upon receipt of a SIP NOTIFY 200 message in response to the REFER, the device sends
a Q.931 DISCONNECT messages to the PBX, notifying the PBX that it can disconnect the
ISDN calls (of user "A").
This feature is enabled by the QSIGPathReplacementMode parameter.
18.5.2.2.3 Blind Call Transfer
Blind call transfer is done after a call is established between call parties A and B, and party
A decides to immediately transfer the call to C without speaking to C. The result of the
transfer is a call between B and C (similar to consultation transfer, but skipping the
consultation stage).

18.5.2.3 Call Forward

The device supports Call Deflection (ETS-300-207-1) for Euro ISDN and QSIG (ETSI TS
102 393) for Network and User sides, which provides IP-ISDN interworking of call
forwarding (call diversion) when the device receives a SIP 302 response.
Call forward performed by the SIP side: Upon receipt of a Facility message with Call
Rerouting IE from the PSTN, the device initiates a SIP transfer process by sending a SIP
302 (including the Call Rerouting destination number) to the IP in response to the remote
SIP entity's INVITE message. The device then responds with a Disconnect message to the
PSTN side.
Call forward performed by the PSTN side: When the device sends the INVITE message to
the remote SIP entity and receives a SIP 302 response, the device sends a Facility
message with the same IE mentioned above to the PSTN, and waits for the PSTN side to
disconnect the call. This is configured using the CallReroutingMode.
Notes:
SIP User's Manual
•
When call forward is initiated, the device sends a SIP 302 response with
a contact that contains the phone number from the forward table and its
corresponding IP address from the routing table (or when a proxy is
used, the proxy's IP address).
•
For receiving call forward, the device handles SIP 3xx responses for
redirecting calls with a new contact.
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Mediant 3000
Document #: LTRT-89712