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DMA Operations Guide Dial Rules
230 Polycom, Inc.
• In some circumstances (depending on the dial plan and the network
topology and configuration), dial rules using the Resolve to external
address action (like Rule 5 of the default dial plan) or the Resolve to IP
address action (like Rule 6) can enable dialing loops to develop, especially
if servers reference each other either directly or via DNS.
Common ways to avoid dialing loops include:
— Use domain restrictions to ensure that the DMA system and its peers
are each responsible for specific domains (see “Add External SIP Peer
Dialog Box” on page 97 and “Domains” on page 224).
— Use a preliminary script like the sample script “SUBSTITUTE
DOMAIN (SIP)” (see “Sample Preliminary and Postliminary Scripts”
on page 236) to change the domain of a SIP URI dial string to
something that won’t create a dialing loop.
— Use a postliminary script to similarly change the domain before
sending to a peer.
— Use configuration options on the peers to prevent loops.
• If your enterprise includes another gatekeeper and you want to route calls
to that gatekeeper without a prefix, add a dial rule using the Resolve to
external gatekeeper action.
• If your enterprise includes a SIP peer proxy server and you want to route
calls to that peer server without a prefix, add a dial rule using the Resolve
to external SIP peer action.
If you have multiple SIP peers, a call matching the rule is routed to the first
one to answer. You may want to specify the domain(s) for which each is
responsible (see “Add External SIP Peer Dialog Box” on page 97).
When routing to a peer proxy, the Polycom DMA system gives up its
ability to route the call to other locations if the peer rejects the call.
Consequently, a dial rule using the Resolve to external SIP peer action
should generally be the last rule in the dial plan.