Polycom 3725-76302-001LI manual Apply the Resolve to external SIP peer action, there is

DMA Operations Guide External SIP Peer

Table 5-14Add External SIP Peer dialog box

Field	Description
Destination network	Host name, FQDN, or network domain label of the SIP
	peer, with or without port and URL parameters.
	If specified, this value by default replaces the non-user
	portion of a URL (after the @ symbol) of the To header
	and Request-URI for forwarded messages, and just the
	Request-URI for REGISTER messages.
	If Type is set to Microsoft, this field is required, is used
	for the peer’s domain, and is implicitly added to the
	Domain List (if not already there).
Port	The SIP signaling port number. Defaults to the standard
	UDP/TCP port, 5060. If the peer server is using a
	different port number, specify it.
	If left blank, the system uses the full RFC 3263
	procedure to determine the port via DNS.
Use route header	Add a Route header with the peer’s Next hop address
	value to the message. Applies to both forwarded
	messages and external REGISTER messages.
	If not selected, the only valid Request-URI
	configurations are those that use the peer's Next hop
	address value for the URI host.
Prefix range	The dial string prefix(es) assigned to this SIP peer.
	Enter a single prefix (44), a range of prefixes (44-47), or
	multiple prefixes separated by commas (44,46)
	If your dial plan uses the Dial services by prefix dial rule
	(in the default dial plan) to route calls to services, all dial
	strings beginning with an assigned prefix are forwarded
	to this SIP peer for resolution.
	Note: For a SIP peer, the dial string must either include
	the protocol or consist of only the prefix and user name
	(no @domain). For instance, if the SIP peer’s prefix is
	123, the dial string for a call to alice@polycom.com
	must be one of the following:
	sip:123alice@polycom.com
	sips:123alice@polycom.com
	123alice
	If your dial plan instead uses a rule that you create to
	apply the Resolve to external SIP peer action, there is
	no need to specify a prefix.
Strip prefix	If selected, the system strips the prefix when a call that
	includes a prefix is routed to this peer.

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