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Polycom, Inc. 121
External H.323 SBC
On the External H.323 SBC page, you can add or remove H.323 SBCs (session border controllers) that the
system can use to reach endpoints outside the enterprise network via prefix-based dialing (Polycom VBP
appliances are supported). In an H.323 environment, H.323 SBCs regulate access across the firewall.
This is a supercluster-wide configuration.
There are three reasons to configure an H.323 SBC on the External H.323 SBC page:
● To create a prefix service that allows dialing through the specific SBC by prefix. An SBC configured
on this page must have a prefix or prefix range assigned to it and can only be reached by dialing its
prefix(es).
● To define a postliminary script to be applied when dialing through the specific SBC.
● For bandwidth management.
The Polycom RealPresence DMA system is capable of performing call admission control (CAC) while
processing an LRQ from a neighbor gatekeeper. This allows the system to reject the call for resource
or policy reasons early in the setup process (in response to the LRQ), rather than waiting until later
in the call setup.
In order to perform early CAC, the Polycom RealPresence DMA system must know the caller’s media
address, which isn’t provided in the LRQ and is unknowable for an ordinary gatekeeper. If the
gatekeeper is also an SBC, however, it proxies the media. The Polycom RealPresence DMA system
can assume that its media address is the same as its signaling address, and proceed with early CAC.
The Polycom RealPresence DMA system performs early CAC only in response to LRQs received
from SBCs configured on the External H.323 SBC page.
The following table describes the fields in the list.
Note: SBC configuration
Only H.323 SBCs are added to the External H.323 SBC page. SIP SBCs are configured as SIP peers
(see External SIP Peer) and/or on a per-site basis (see Edit Site Dialog).
H.323 SBCs that are added to the External H.323 SBC page are reached by prefix-based dialing
(rule 4 of the default dial plan; see The Default Dial Plan and Suggestions for Modifications).
SBCs to be reached by a dial rule using the Resolve to IP address action (rule 6 of the default dial
plan) are configured on a per-site basis (see Edit Site Dialog).
In general, H.323 SBCs should be configured on a per-site basis, so that calls to endpoints outside the
enterprise network are routed to the SBC assigned to the originating site.
Column Description
Name The name of the SBC.
Description Brief description of the SBC.
Address Host name or IP address of the SBC.
Prefix Range The dial string prefix(es) assigned to this SBC.
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 SBC for resolution.
Enabled Indicates whether the system is using the SBC.