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External SIP Peer
On the External SIP Peers page, you can add or remove SIP servers or devices from the list of SIP peers
to which the system can route calls and from which it may receive calls.
This is a supercluster-wide configuration. But note that a Polycom RealPresence DMA system supercluster
can provide proxy service for any or all domains in the enterprise, allowing the SIP function to be distributed,
but managed centrally. This may reduce the need for external SIP peer servers (other than SIP session
border controllers, or SBCs).
Multiple External SIP Peers
The RealPresence DMA system can use multiple SIP peers to resolve dial strings. If a SIP peer experiences
an outage, it is marked as unresponsive, and the RealPresence DMA system stops using it until it becomes
responsive again. If you add multiple SIP peers to the system, you can configure how the system selects
which SIP peer to use to resolve dial strings using a dial rule with the Resolve to external SIP peer action.
When you configure a dial rule that uses the Resolve to external SIP peer action, you can choose which
of two selection policies (All in parallel (forking) or Weighted round-robin) the system uses to resolve
dial strings to SIP peers. If you select All in parallel (forking), the system tries all SIP peers simultaneously.
If you select Weighted round-robin, you can assign each SIP peer a weight, with a higher weight giving a
SIP peer higher priority, and the system tries each SIP peer sequentially according to the SIP peer’s
assigned weight. You can change the weight for each SIP peer using the dialog’s Edit weight button.
Unresponsive SIP peers are considered only when there are no responsive peers that can complete the call.
See Dial Rules for more information.
The following table describes the fields in the list of SIP peers on the External SIP Peers page.
Note: SBC configuration
SIP SBCs to be reached by prefix-based dialing (rule 4 of the default dial plan; see The Default Dial
Plan and Suggestions for Modifications) are added to the External SIP Peers page.
SBCs to be reached by a dial rule using the Resolve to external address or Resolve to IP address
action (rules 5 and 6, respectively, of the default dial plan) are configured on a per-site basis (see Edit
Site Dialog).
For most configurations, SBCs should be configured on a per-site basis, so that calls to endpoints
outside the enterprise network are routed to the SBC for the originating site.
Note: SIP peer availability and third-party network equipment
The RealPresence DMA system periodically uses SIP OPTIONS messages to verify connectivity with
SIP peers. If a SIP peer fails to respond or responds with a specified set of status codes, the system
removes that SIP peer from service. In some situations, a third-party device can respond on behalf of
the SIP peer. If the RealPresence DMA system receives any other status code when the queried SIP
peer is experiencing an outage, that SIP peer could incorrectly be marked as healthy.
Because of this, it is possible for a SIP peer’s service status to enter a “flapping” state. In this
scenario, the RealPresence DMA system attempts to use the incorrectly marked SIP peer, but when
the SIP peer fails to respond, the RealPresence DMA system removes the SIP peer from service.
However, the RealPresence DMA system receives a non-specified status code response for the next
availability query, so puts the SIP peer back in service.