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High Availability SIP-Based Call Flow

Note: It is highly recommended that you use UDP instead of TCP for SIP signaling. TCP stack
timeout delays can cause significant delays to the caller during failures.

This section describes the relationship among Unified CVP solution components from the
perspective of a SIP-based call flow. We begin with a hypothetical comprehensive model
incoming call, and trace its effect on each component with a particular view toward how that
component finds the next component downstream. In the process, we will be describing the
system’s high availability architecture.

Please refer to the following diagram.

Figure 7: SIP-Based High Availability Component Layout

Although not shown in the diagram, a Media Server can be connected to the VXML Gateway.
Contact Server Switches (CSSs) can be placed between the VXML Gateway and the VoiceXML
Server, between the VXML Gateway and the ASR/TTS Server, between the VXML Gateway
and the Media Server.

PSTN should be
contracted to fail over to

Multiple Ingress
Gateways can be

New call from PSTN to Ingress Gateway

other TDM connections

deployed, each with its

when the selected
connection is down.

own array of TDM
connections.

If the selected SIP Proxy
Server either does not

Up to two SIP Proxy
Servers are supported.

New Call from Ingress Gateway to SIP Proxy Server

respond within a time-out

Either an Ingress dial peer

period, or responds with

can reference DNS (which

a 500-level message to

can return either SIP

Planning Guide for Cisco Unified Customer Voice Portal 4.0(1)