Implementing PSTN Backup for On-Net Intersite Calls cisco ccsp training center in delhi gurgaon

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Figure 4-8 shows a multisite deployment with two sites. Each site has its own CUCM
cluster. Intersite calls use the intercluster trunk (ICT) or a SIP trunk over the IP WAN to the
other cluster. The route patterns with the site codes point to route lists, which point to route
groups that have the ICT as the first option and the PSTN gateway as the second option. If
the IP WAN link fails for any reason, because both sites have access to the PSTN, the PSTN
is used as a backup for intersite calls. Note that proper digit manipulation must take place
if the calls are routed through the PSTN.
Figure 4-8 Implementing PSTN Backup for On-Net Intersite Calls
Main Site Remote Site
1001-1099 1001-1099
Digit-Manipulation Requirements for PSTN Backup of
On-Net Intersite Calls
PSTN backup for on-net calls can be easily provided by route lists and route groups giving
priority to the intercluster trunk over the PSTN gateway, as shown in Figure 4-9.
When using a PSTN backup for on-net calls, you must address internal versus external
dialing. Although on-net calls usually use site codes and directory numbers, calls that are
sent through the PSTN have to use E.164 numbers. Digit-manipulation requirements vary,
depending on the path that is taken for the call:
• Digit-manipulation requirements when using the ICT, which is the first choice in the
route list and route group:
—At the calling site: The access and site code are removed from DNIS.
—At the receiving site: The access and site code are added to the ANI.
(This can also be done on the calling site.)
Chapter 4: Implementing a Dial Plan for Multisite Deployments
Figure 4-9 Digit-Manipulation Requirements for PSTN Backup of On-Net Intersite Calls
• Digit-manipulation requirements when using the PSTN (secondary choice in the route
list and route group)
—At the calling site: The internal DNIS comprising an access code, site
code, and directory number is transformed into the PSTN number of
the called phone. The ANI is transformed into the PSTN number of the
calling phone.
NOTE If DID is not supported, the site's PSTN number is used in DNIS and ANI
instead of the IP Phone's PSTN number.
mplementing Tail-End Hop-Off
—At the receiving site: The PSTN ANI is recognized as a PSTN number of
an on-net connected site and is transformed into the internal number: access
and site code, followed by the directory number of the calling phone (if
DID is used at the calling site) or of the attendant of the calling site (if DID
is not used at the calling site). The DNIS is transformed into an internal
directory number and is routed to the IP Phone (if DID is used at the
receiving site) or to an attendant (if DID is not used at the receiving site).