Cisco CME PSTN Connectivity Options

This chapter covers the following topics:

• Cisco CallManager Express (CME) analog and digital Public Switched Telephone Network (PSTN) interface hardware, configuration, and features
• PSTN call switching and routing options
• Digit manipulation tools to translate phone numbers
• PSTN trunk failover options

In previous chapters, you learned about the Cisco IP Communications (IPC) Express platforms and architecture, Cisco IOS voice infrastructure software features, and configuring call routing features between endpoints such as IP phones and Public Switched Telephone Network (PSTN) interfaces.

This chapter focuses on the hardware options, configurations, and detailed features that Cisco IPC Express offers for connecting your business to the PSTN. This PSTN connectivity is not particular to Cisco IPC Express but is part of the generic voice-enabled feature set of the Cisco router platforms.

Router PSTN connectivity is generically referred to as voice gateway functionality, offering a gateway for voice over IP (VoIP) calls to, and from, traditional analog or digital PSTN or private branch exchange (PBX) calls. You can use a router voice gateway to connect to PSTN central office (CO) switches, private branch exchanges (PBXs), Key Systems, time-division multiplexing (TDM)-based interactive voice response (IVR) systems, traditional TDM-based voice mail systems, and any other legacy (non-IP) voice processing or telephone equipment.

This chapter explores several aspects of Cisco CME connectivity to the PSTN, including the following:

• Standards-based telephony signaling systems and protocols supported by Cisco IOS, which, in turn, determine what traditional TDM or analog systems you can connect to and what features you get when using this type of connection
• A brief overview of the Cisco voice gateway hardware choices and the voice port densities and features they provide
• Sample Cisco IOS configurations for different types of PSTN connections
• Network design and call switching considerations for connecting to the PSTN from your IP network

Traditional telephony terminology is used throughout this chapter. It has a more precise meaning here than in other chapters, because the topic of discussion is connecting a traditional telephony system, the PSTN. If you are unfamiliar with the telephony meanings of terms such as trunks, lines, caller ID, direct inward dial (DID), and dialed number information service (DNIS), refer to the glossary to review these terms.