Unified CVP can use different types of gateways depending on the deployment model. This section discusses each type of voice gateway and their effects in a distributed deployment.
Ingress or Egress Voice Gateway at the Branch
In this deployment model, Ingress Voice Gateways located at a branch office are typically used to provide callers with access using local phone numbers instead of using centralized or non-geographic numbers. This capability is important in international deployments spanning multiple countries. Egress Gateways are located at branches either for localized PSTN breakout or for integration of decentralized TDM platforms into the Unified CVP switching solution. All other Unified CVP components are centrally located, and WAN links provide data connectivity from each branch location to the central data center.
Ingress or VoiceXML Gateway at the Branch
Consider other voice services that run at the branch that can affect Ingress or VoiceXML Gateways. For example, the branch is a remote Cisco Unified Communications Manager (Unified CM) site supporting both ACD (Agent Desktop provides call control capabilities ready/not ready, wrap up.) agent and non-agent phones. In this model, the PSTN gateway is used for ingress of Unified CVP calls as well as Ingress and Egress of normal user calls. In circumstances when the VoiceXML and Voice Gateway functions reside at the same branch location but on separate devices, special attention has to be given to the dial plan to ensure that the VRU leg is sent to the local VoiceXML resource. This is because the Unified CVP Call Server settransferlabel label applies only to coresident VoiceXML and Voice Gateway configurations.
When the Ingress Voice Gateway and the VoiceXML Gateway at a branch do not reside on the same Gateway, there are two ways to ensure that the calls are handled within the branch and not sent through the WAN to a different VoiceXML Gateway:
Configure Unified ICM with multiple customers, one Unified ICM configuration.
The Unified ICM configuration differentiates between calls based on the Dialed Number. The Dialed Number is associated with a customer representing the branch site. When a NetworkVRU is needed, the NetworkVRU associated with the customer in Unified ICM is selected and the caller is sent to that NetworkVRU. This method allows you to have multiple NetworkVRUs, each with a unique label. The disadvantage of this method is that each NetworkVRU requires its own VRU scripts in Unified ICM.
Configure Unified CVP using the SigDigits feature.
The SigDigits feature allows you to use the dial plan on the SIP Proxy to route calls to the correct site. When the call arrives at an Ingress Voice Gateway, the gateway prepends digits before sending the call to Unified CVP. Those prepended digits are unique to that site for a dial plan.
When the call arrives at Unified CVP, Unified CVP strips the prepended digits and stores them in memory, resulting in the original DID on which the call arrived. Unified CVP then notifies Unified ICM of the call arrival using the original DID and matches a Dialed Number in Unified ICM.
When Unified ICM returns a label to Unified CVP to transfer the call to a VoiceXML gateway for IVR treatment or to transfer the call to an agent phone, Unified CVP prepends the digits that it stored in memory before initiating the transfer. The dial plan in the SIP Proxy must be configured with the prepended digits to ensure that the calls with a certain prepended digit string are sent to specific VoiceXML Gateways or Egress Gateways.
When the VoiceXML Gateway receives the call, the CVP bootstrap service is configured to strip the digits again, so that when the IVR leg of the call is set up, the original DN is used on the incoming VoiceXML request.
The digits can be prepended to translation route DNs, and that the egress or receiving component (such as Unified CM) may need to strip digits to see the original DN.
The term SigDigits is used to describe this feature because the command in Unified CVP to turn on the feature and specify how many significant digits should be stripped is called Prepend Digits for SIP in the operations console.
This method is preferred because it involves the least amount of Unified ICM configuration overhead: a single NetworkVRU and single set of VRU scripts and Unified ICM routing scripts. This allows all of the Unified CVP Servers and VoiceXML Gateways to function as a single network-wide virtual IVR from the perspective of Unified ICM.
The SigDigits feature can also be used to solve multicluster call admission control problems. (See Call Admission Control Considerations, for more information.)
Colocated VXML Servers and VoiceXML Gateways
Either all gateways and servers are centralized or each site has its own set of colocated Unified CVP VXML Servers and VoiceXML Gateways.
Colocation has the following advantages:
A WAN outage does not impact self-service applications.
No WAN bandwidth is required for VoiceXML.
Colocation has the following disadvantages:
Extra Unified CVP VXML Servers are required when using replicated branch offices.
Additional overhead is required when deploying applications to multiple Unified CVP VXML Servers.
Gateways at Branch with Centralized VXML Server
Advantages of centralized VoiceXML:
Administration and reporting are centralized.
Unified CVP VXML Server capacity can be shared among branch offices.
Disadvantages of centralized VoiceXML:
Branch survivability is limited.
WAN bandwidth must be sized for additional VoiceXML over HTTP traffic.