Revolabs FLX2 VoIP Advanced - Manual (Page 64)

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Session timers
expiration period The expiration period is the interval at which the phone will
consider the SIP session timed out if it does not receive a refresh
message from the remote phone. It is measured in seconds; the
default is 1800. At call negotiation, the nodes will negotiate the
expiration 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