AudioCodes Mediant 500 MSBR, User Manual

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Version 7.2 635 Mediant 500 MSBR
User's Manual 32. SBC Overview
Note: If the Request-URI contains the "tel:" URI or "user=phone" parameter, the
device searches only for the user part.
32.4.3 General Registration Request Processing
The device's general handling of registration requests (REGISTER messages) for
unregistered users is as follows:

The device routes REGISTER requests according to the IP-to-IP Routing table. If the
destination is a User-type IP Group, the device does not forward the registration;
instead, it accepts (replies with a SIP 200 OK response) or rejects (replies with a SIP
4xx) the request according to the user's IP Group configuration.

Alternative routing can be configured for REGISTER requests, in the IP-to-IP Routing
table.

By default, the Expires header has the same value in incoming and outgoing
REGISTER messages. However, you can modify the Expires value using the following
parameters: SBCUserRegistrationTime, SBCProxyRegistrationTime,
SBCRandomizeExpires, and SBCSurvivabilityRegistrationTime. You can also modify
the Expires value of REGISTER requests received from users located behind NAT,
using the IP Profile parameters IpProfile_SBCUserBehindUdpNATRegistrationTime
and IpProfile_SBCUserBehindTcpNATRegistrationTime.

By default, the Contact header in outgoing REGISTER message is different than the
Contact header in the incoming REGISTER. The user part of the Contact is populated
with a unique contact generated by the device and associated with the specific
registration. The IP address in the host part is changed to the address of the device.
Alternatively, the original user can be retained in the Contact header and used in the
outgoing REGISTER request (using the SBCKeepContactUserinRegister parameter).
32.4.4 Registration Refreshes
Registration refreshes are incoming REGISTER requests from users that are registered in
the device's registration database. The device sends these refreshes to the serving proxy
only if the serving proxy's Expires time is about to expire; otherwise, the device responds
with a 200 OK to the user without routing the REGISTER. Each such refresh also refreshes
the internal timer set on the device for this specific registration.
The device automatically notifies SIP proxy / registrar servers of users that are registered
in its registration database and whose registration timeout has expired. When a user's
registration timer expires, the device removes the user's record from the database and
sends an un-register notification (REGISTER message with the Expires header set to 0) to
the proxy/registrar. This occurs only if a REGISTER message is sent to an IP Group
destination type (in the IP-to-IP Routing table).
You can also apply a graceful period to unregistered requests, using the 'User Registration
Grace Time' parameter (SBCUserRegistrationGraceTime):

You can configure the device to add extra time (grace period) to the expiration timer of
registered users in the database. If you configure this grace period, the device keeps
the user in the database (and does not send an un-register to the registrar server),
allowing the user to send a "late" re-registration to the device. The device removes the
user from the database only when this additional time expires.

The graceful period is also used before removing a user from the registration
database when the device receives a successful unregister response (200 OK) from