Service Providers
Polycom, Inc.
34
●
SPn Service
::AuthUsername
=
Not Blank
where
X
= A or B,
n
= 1, 2, 3, or 4. Otherwise, the service is considered disabled.
SIP Registration
Devices can be set to periodically register with a SIP Proxy Server or SIP Registration Server. SIP Proxy
Server and SIP Registration Server can be different, although they are usually the same in practice. SIP
Proxy Server is a required parameter that must be configured on the device. The Registration Server is
optional and assumed to be the same as the SIP Proxy Server if it is not configured on the device.
The main purpose of registration is to create and maintain a dynamic binding of the SIP account to the
device’s local contact address. The service provider can also rely on this periodic message to infer if the
device is online and functional. Each device takes only one local IP address that is either 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).
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 since
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 should not 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
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.
