ter two or three bursts the voice processing system answers the call and thus stops the ringing current from the tele- Sometimes referred to as DC5 or DC10 signalling systems the Ear phone exchange by looping the circuit. The caller is also then and Mouth telephone interfaces are used by VPSs when connecting connected through to the voice service. Since there is no pre-selec- to ACDs or PABXs. tion of the service (cf. DDI), the caller may have to interact with the There are many types of E&M interfaces, depending on region voice processing system to then select the service required. Caller and PABX. E&M can be configured to support both incoming charging commences as soon as the voice processing system and/or outgoing calls. The E&M interface is designed to avoid answers the call. incoming and outgoing call collisions by operating a simple signall- The call may be terminated by the exchange temporarily remov- ing protocol. These interfaces are falling out of use in voice process- ing the battery from the circuit, or in some exchanges by the voice ing applications. This is because in many applications it is desirable processing system un-looping the line. This type of connection can to be able to connect the caller to a live operator. To do this using support both incoming and outgoing calls. E&M interfaces would require the voice processing system to route There is a problem for this kind of connection associated with the caller out on another circuit back to the PABX (so-called detecting the release of the call by the calling party. There may be tromboning). The voice processing systems call handling capacity no firm indication to the equipment that the caller has released from is reduced because it is associated with the call for its complete the telephone network. For example, some PABX systems may give duration. Also, twice the numbers of ports are required both on the dial tone when the caller releases, some may give silence. PABX and the voice processing system compared with using nor- Anatomy of a voice pr