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period to be used for the session.
Session timers
minimum
expiration period
This is the minimum session timer expiration period that FLX will
accept when negotiating the expiration period with the remote
phone. It is measured in seconds; the default is 90.
Require reliable
SIP provisional
response
Select this option to implement reliable SIP provisional responses.
By default the setting is unchecked. SIP is a request-response type
of protocol with two types of responses: provisional and final. Final
responses are sent reliably, using an ACK to ensure receipt.
Provisional responses by default are not sent reliably and do not
require an ACK; however, in some cases, such as for PSTN
interoperability support, reliability of provisional types of responses
is needed. Choose this option to add the PRACK (provisional ACK)
message support for reliability.
Enable SIP
traversal behind
symmetric NAT
This option may be used when the phone is behind a symmetric
NAT (Network Address Translation). When enabled, FLX will keep
track of the public IP address from the response of the REGISTER
request. If it detects that the address has changed, it will unregister
the current Contact, update the Contact with the transport address
obtained from the Via header, and register a new Contact to the SIP
registrar. This option will also update the public name of the UDP
transport if STUN is configured.
Suppress SIP
event
subscription
when transferring
calls
When transferring a SIP call, the SIP REFER process automatically
establishes a temporary event subscription to notify the party
initiating the transfer about the receiver’s status in handling the
REFER. In some cases these event subscriptions and notifications
are not needed, such as when forking is not used. Enable this option
to suppress the automatic event subscriptions when transferring
calls. The option is disabled by default.
Allow strict
routing
By default, proxies specified on the SIP Registration page will be
configured as loose-routing proxies. The loose-routing designation
(“;lr”) will be automatically appended to each proxy address when
the proxy is added to the SIP Route header. Older proxies may be
strict-routing (see IETF RFC 2543), not supporting loose routing
(see IETF RFC 3261). Enable this option if you are using strict-
routing proxies. If this option is enabled and you are specifying one
or more loose-routing proxies in the SIP Registration page’s
Outbound Proxy field, then you must manually add the “;lr” suffix to
each loose-routing proxy address. For example, “10.134.123.101;lr”.
Minimize SIP
message size
The SIP protocol specifies that header field names can be in the full
name form or in the abbreviated form. Abbreviated form is useful
when messages might be too large to be carried on the available
transport, for example when exceeding UDP’s Maximum
Transmission Unit (MTU). Enable this option to encode SIP headers
in their short forms to reduce size. By default, the option is not
enabled and SIP headers in outgoing messages will be encoded in
their full names. (See SIP protocol standard, IETF RFC 3261.)