Initiating Sip Call Forking; Configuring Sip Forking Initiated By Sip Proxy - AudioCodes Mediant 4000 SBC User Manual

CHAPTER 28 Advanced SBC Features

Initiating SIP Call Forking

The SBC device supports call forking of an incoming call to multiple SBC users (destinations). Call
forking is supported by the device's capability of registering multiple SIP client user phone contacts
(mobile and fixed-line extensions) under the same Address of Record (AOR) in its registration
database. This feature can be implemented in the following example scenarios:
■ An enterprise Help Desk, where incoming customer calls are simultaneously sent to multiple
customer service agent extensions.
■ An employee's phone devices, where the incoming call is simultaneously sent to multiple
devices (e.g., to the employee's office phone and mobile SIP phone).
■ An enterprise reception desk, where an incoming call is simultaneously sent to multiple
receptionists.
The device supports various modes of call forking. For example, in Parallel call forking mode, the
device sends the INVITE message simultaneously to all the users registered under the same AOR,
resulting in the ringing of all extensions; the first extension to pick up the call receives the call, and
all other extensions stop ringing. The Call Forking feature is configured by creating a User-type IP
Group and configuring the IP Groups table's parameter, 'SBC Client Forking Mode' (see
Configuring IP
The device can also fork INVITE messages received for a Request-URI of a specific contact
(user), belonging to the destination IP Group User-type, registered in the database to all other users
located under the same AOR as the specific contact. This is configured by the
[SBCSendInviteToAllContacts] parameter.

Configuring SIP Forking Initiated by SIP Proxy

The device can handle the receipt of multiple SIP 18x responses as a result of SIP forking initiated
by a proxy server. This occurs when the device forwards an INVITE, received from a user agent
(UA), to a proxy server and the proxy server then forks the INVITE request to multiple UAs. Several
UAs may answer and the device may therefore, receive several replies (responses) for the single
INVITE request. Each response has a different 'tag' value in the SIP To header.
During call setup, forked SIP responses may result in a single SDP offer with two or more SDP
answers. The device "hides" all the forked responses from the INVITE-initiating UA, except the
first received response ("active" UA) and it forwards only subsequent requests and responses from
this active UA to the INVITE-initiating UA. All requests/responses from the other UAs are handled
by the device; SDP offers from these UAs are answered with an "inactive" media.
The device supports two forking modes:
■ Latch On First: The device forwards only the first received 18x response to the INVITE-
initiating UA and disregards subsequently received 18x forking responses (with or without
SDP).
■ Sequential: The device forwards all 18x responses to the INVITE-initiating UA, sequentially
(one after another). If 18x arrives with an offer only, only the first offer is forwarded to the
INVITE-initiating UA.
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To configure the call forking mode:
1. Open the SBC General Settings page (Setup menu > Signaling & Media tab > SBC folder >
SBC General Settings).
2. From the 'Forking Handling Mode' drop-down list (SBCForkingHandlingMode), select the
required mode:
3. Click Apply.
Groups).
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Mediant 4000 SBC | User's Manual