Explanation
Dial-peers are the configuration objects that define the dial plan on a Cisco Voice Gateway/CUBE. Dial-peers are used to match the incoming and outgoing calls based on the destination patterns, and to apply the dial-peer attributes, such as codec, digit manipulation, voice-class, and call routing. Dial-peers can be of different types, such as POTS (Plain Old Telephone Service), VoIP (Voice over IP), or VXML (Voice XML). ATR, voice-class, and Voip voice are not the objects that define the dial plan, but they are some of the attributes that can be applied to the dial-peers.
References: Configuring Voice Gateways, Dial Plan, Configuring a Dial Plan