/mcpIntroduction This document describes an explanation of Cisco IOS® and Cisco IOS XE Call Routing. Prerequisites Requirements While there are no formal prerequisites needed to read this document, it is written with the expectation that the reader already has some knowledge of underlying voice signaling protocols that are used to establish and connect phone calls. These protocols are referenced many times throughout. Signaling Protocols: Session Initiation Protocol (SIP), H323 (h225 / h245), Media Gateway Control Protocol (MGCP), Skinny Client Control Protocol (SCCP), ISDN Q931, E1 R2. Media Protocols: Real Time Protocol (RTP), voice codecs, video codecs. Analog Technologies: Ear and Mouth (E&M), Foreign Exchange Subscriber (FXS) and Foreign Exchange Office (FXO). Components Used The information in this document is based on these software and hardware versions: Cisco IOS and Cisco IOS XE Gateways • 2800 / 3800 / 2900 / 3900 / 4300 / 4400 / CSR1000v / CAT8000v / ASR100X / C8200 / C8300 / ISR1100 • The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command. Background Information This document addresses the mechanisms behind inbound and outbound dial-peer matching with Plain Old Telephone Service (POTS) and Voice over IP (VoIP) Network call legs. In addition to dial-peer information, this document covers important topics that pertain to call routing. These include digit manipulation, a quick overview of Session Initiation Protocol (SIP) message manipulation, a few methods for restricting calling capabilities, a quick media and signaling binding overview, and lastly a bit of troubleshooting. This document utilizes configuration examples as well as debug and show command outputs as reference points. The many features in this document are clearly marked with the version the feature was introduced to both Cisco IOS and Cisco IOS XE. This information can also be referenced quickly in the Command and Feature Roadmap section. If there is a very notable defect, it is linked within the text so that readers are aware. Common Definitions