statically assigned in the device's configuration, or dynamically obtained from a local DHCP server.
The SP
n
services (for
n
= 1, 2, 3, and 4) each use a different local contact port for sending and
receiving SIP messages (defaults are 5060, 5061, 5062, and 5063).
Note that dynamic address binding through periodic registration is not strictly necessary if the local IP
address of the device does not change; the device's contact address can be statically configured on
the Registration Server.
SIP Outbound Proxy Server
An outbound proxy server can be configured on the device such that all outbound requests are sent
via the outbound proxy server instead of directly to the SIP Proxy Server or Registration Server.
If the outbound proxy server is listening at a non-standard port, the correct port value must
be specified in the OutboundProxyPort parameter. The OutboundProxy can use a different
transport protocol from the ProxyServer. The transport protocol to use to communicate
with the OutboundProxy can be set in the OutboundProxyTransport parameters. If
OutboundProxyTransport is TCP or TLS, your device initiates a TCP or TLS connection only with
the OutboundProxy. All subsequent messages exchanged between your device and the servers
MUST use the same connection. If for any reason the connection is closed, your device attempts to
re-establish the connection with the OutboundProxy following an exponential back-off retry pattern.
Even though your device only exchanges messages directly with the OutboundProxy, the
ProxyServer, ProxyServerPort, and ProxyServerTransport parameters are still very
much relevant and important. The reason is that the SIP requests sent by your phone to
the server are formed based on these values, not based on the OutboundProxy value. The
OutboundProxy value should never appear in the SIP requests generated by your device, unless
the OutboundProxy parameter has the same value as ProxyServer.
Some server implementations include the outbound proxy server in a Record-Route header such
that your device shouldn’t respect the locally configured OutboundProxy value after the initial
INVITE is sent for a new call. This behavior can be achieved by enabling the ITSP
Profile X
- SIP
::X_BypassOutboundProxyInCall option. However, this option has no effect when the
OutboundProxyTransport is TCP or TLS, as your device always uses the same connection to
send messages to the server.
DNS Lookup of SIP Servers
When sending out SIP requests to the server, the device looks up the IP address of the server using
standard DNS query if the server is specified as a domain name instead of an IP address.
If an Outbound Proxy Server is configured, it is used instead of the SIP Proxy Server or SIP
Registration Server. The resolution of the server domain name into IP address is performed in the
following manner:
● Try looking up the name as DNS A Record. If not found,
● Try looking up the name as DNS SRV Record. If not found,
● Try looking up the name as DNS SRV Record with “_sip._udp.“ prepended to the host name. If
not found, fail the request.
If the result from the DNS query is an SRV record, the server port is taken from that record also. The
server port value configured on the device is ignored. Otherwise, the server port is taken from the
configured value or uses port 5060 if none is specified.
SIP Outbound Proxy Server
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