Call Forking; Initiating Sip Call Forking; Sip Forking Initiated By Sip Proxy Server - AudioCodes Mediant 800B User Manual

User's Manual
35.4

Call Forking

This section describes various Call Forking features supported by the device.

35.4.1 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 Group table's
parameter, 'SBC Client Forking Mode' (see ''Configuring IP Groups'' on page 349).
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
using the SBCSendInviteToAllContacts parameter.

35.4.2 SIP Forking Initiated by SIP Proxy Server

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 sends 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, configured by the SBCForkingHandlingMode
parameter:

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.
Version 7.0 691 Mediant 800B Gateway and E- SBC
35. Advanced SBC Features