Chapter 4. Single-Site Off-Net Calling
This chapter reviews the configuration PSTN gateways and dial plans for the support of off-net calling.
Gateway Overview
A gateway is a device that can translates between different signaling and media, which is often divided into two types:
• Analog: Connects an analog device or line to a CUCM environment
• Digital: Connects a digital trunk, such as a T1, to a CUCM environment
Gateways must provide the following:
• DTMF relay
• Supplementary services
• CM redundancy
• Call survivability
Following are four protocols that gateways use to communicate with CUCM.
• H.323: Peer-to-peer protocol; requires its own dial plan
• MGCP: Client/server protocol; relies on CUCM for dial plan; supports PRI Backhaul
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