Information Technology Reference
In-Depth Information
is dialed over the LEC PSTN link, as long as a channel is available. This call costs more
than using the IXC circuit, but it works—the call does not fail, and business continuity is
maintained.
In this example, cost is the design driver: The IXC is less expensive than the LEC circuit,
so the IXC is the desired target for all long-distance calls. However, if the IXC is busy (or
has failed), it is acceptable that long-distance calls be placed out the LEC circuit so that
service is not interrupted.
Route Group
A Route Group is a list of devices (gateways or trunks) that are configured to support cir-
cuits to the PSTN or to remote CUCM clusters in distributed designs. Route Groups are
commonly configured to contain devices with common signaling characteristics (for ex-
ample, a set of PSTN PRI gateways in one group and a set of WAN IP trunks to a remote
cluster in another).
The distribution algorithm of a Route Group is configurable; selecting Top-Down causes
the devices in the group to be used in top-down order for each new call, while selecting
Circular uses the devices in round-robin order. The specific context and requirements of
the system determines which algorithm is appropriate.
Note:
The Local Route Group feature allows the administrator to define a Route Group
in the Device Pool, and reference that local Route Group in the Route List. Doing so effec-
tively decouples the location of a PSTN gateway from the Route Patterns that target the
gateway. This feature greatly reduces the complexity of dial-plan design in systems with
many locations.
Gateways and Trunks
Gateways and trunks are the devices that physically terminate and support circuits to the
PSTN, to digital or analog PBXs, and to IP WAN circuits to remote clusters or IP-TSP cir-
cuits to service providers.
CUCM supports various gateway devices and interfaces, controlling them with either
peer-to-peer gateway protocols (H.323 and SIP) or gateway control protocols (MGCP
and SCCP).
Figure 10-8 shows the call-routing elements previously described.
Gateway
Route Pattern
9.1 [2-9]XX[2-9]XXXXXX
Route Group
IXC_RG
IXC
Gateway
Route List
LD_PSTN_RL
Route Group
1st
2nd
LEG_RG
LEC
Key
To p i c
Figure 10-8
Call-Routing Elements
