AudioCodes Mediant 500 E-SBC, User Manual

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User's Manual 460 Document #: LTRT-10437
Mediant 500 E-SBC
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Forwarding early media after REFER while attempting to avoid transcoding (by
sending session update)
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Interoperate with environments were different SIP UAs lack basic SIP functionality
such as re-INVITE, UPDATE, PRACK, Delayed Offer, re-INVITE without SDP
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Session updates after connect to avoid transcoding
The handling of REFER can be configured for all calls, using the global parameter
SBCReferBehavior. For configuring different REFER handling options for different UAs
(i.e., IP Groups), use the IP Profile table parameter, 'SBC Remote Refer Behavior'.

Local handling of REFER: This option is used for UAs that do not support REFER.
Upon receipt of a REFER request, instead of forwarding it to the IP Group, the device
handles it locally. It generates a new INVITE to the alternative destination according to
the rules in the IP-to-IP Routing table (where the 'Call Trigger' field is set to
REFER ). It
is also possible to specify the IP Group that sent the REFER request, as matching
criteria for the re-routing rule in this table ('ReRoute IP Group ID' field).
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Transparent handling: The device forwards the REFER with the Refer-To header
unchanged.
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Re-routing through SBC: The device changes the Refer-To header so that the re-
routed INVITE is sent through the SBC application.

IP Group Name: The device sets the host part in the REFER message to the name
configured for the IP Group in the IP Group table.
27.7.4 Interworking SIP PRACK Messages
The device supports interworking of SIP Provisional Response ACKnowledgement
(PRACK) messages (18x). While some UAs may not support PRACK (RFC 3262) others
may require it. The device can be configured to resolve this interoperable issue and enable
sessions between such endpoints. SIP PRACK handling is configured using the IP Profile
parameter, 'SBC Prack Mode':

Optional: PRACK is optional for these UAs. If required, the device performs the
PRACK process on behalf of the destination UA.

Mandatory: PRACK is required for these UAs. Calls from UAs that do not support
PRACK are rejected. Calls destined to these UAs are also required to support
PRACK.

Transparent (default): The device does not intervene with the PRACK process and
forwards the request as is.
27.7.5 Interworking SIP Session Timer
The device supports interworking of the SIP signaling keep-alive mechanism. The SIP
standard provides a signaling keep-alive mechanism using re-INVITE and UPDATE
messages. In certain setups, keep-alive may be required by some SIP UAs while for others
it may not be supported. The device can resolve this mismatch by performing the keep-
alive process on behalf of SIP UAs that do not support it.
For configuring the handling of session expires, use the IP Profile parameter, 'SBC Session
Expires Mode'.