In this blog, we will investigate redirected dialed number identification service (RDNIS) to aid our understanding of the requirement when forwarding calls from a branch site location to a centralized voicemail solution when the WAN link is down.
Let’s take a look at an RDNIS example… We will discuss the calling (ANI) and called (DNIS) party information transmitted for a call forwarded to voicemail.
When extension 11001 calls extension 11002, the calling party (11001) phone will display the information of the called party (11002) phone. The called party (11002) phone will display the calling party (11001) information in addition to the display name of the phone. When a call forwarding event forwards the call to a voicemail hunt pilot at extension 11900, the calling and called party information changes.
The call to the voicemail pilot point includes calling (11002) and called (11900) party information. Notice that the call forwarding results in the change of the calling party information even though the RTP media stream will be connected from the source IP address of extension 11001 and the destination IP address of the voicemail server. To ensure the voicemail server plays the proper greeting and saves the voicemail for the appropriate user (subscriber in Unity), the original calling and original called party information must be transmitted in addition to the calling and called party.
The original calling party is 11001 and the original called party is 11002. The Unity voicemail server will direct the call to extension 11002 even though the called party presented to the Unity server is 11900.
Skinny Client Control Protocol (SCCP) passes original calling and original called party information between all devices. ISDN circuits pass RDNIS information, but most analog PSTN connections do not support RDNIS. RDNIS support over analog gateways requires the vm-integration configuration given in the last blog.
In the next blog, we will continue discussing SRST options. I have included all of the call forwarding options here for your reference.
Call Forward All [CFA]
Call Forward No Answer [CFNA]
Call Forward Busy [CFB]
Call Forward No Coverage [CFNC]
Call Forward Unregistered [CFUR]
Call Forward on CTI Failure
Call Forward No Bandwidth [CFNB]
Dennis Hartmann, CCIE No. 15651, is a consultant with www.highpoint.com and author of Implementing Cisco Unified Communications Manager, Part 1. Dennis is also a lead instructor at Global Knowledge. Dennis has various certifications, including the Cisco CCVP, CCSI, CCNP, CCIP, and the Microsoft MCSE. Dennis has various specializations including unified communications, data center, routing & switching, service provider (MPLS and optical). Dennis has worked for various Fortune 500 companies, including AT&T, Sprint, Merrill Lynch, KPMG, and Cabletron Systems. He lives with his wife and children in Hopewell Junction, New York.
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