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E&M

There are 5 types E&M. When we talking about E&M 2/4 signaling wire, is that only for the analog trunk E&M or also refer to T1 CAS E&M? If it's also for T1 CAS, how can I know use 2 wire or 4 wire in South America?

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Re: E&M

E&M interface is mainly used for analog trunking. E&M interfaces normally will have the option of two or four wire operation. Rather than referring to the total number of physical connections on the port, two or four wire operation relates to the how audio is passed between the devices. Two wire operation means the transmitting and receiving audio signals are passed through a single pair of wires (one pair equals two wires). Four wire operation separates the direction of the signal and uses one pair for transmitting and another pair for receiving audio. The document http://www.cisco.com/en/US/products/hw/gatecont/ps2250/products_tech_note09186a008009452e.shtml explains about the E&M interface type and the wiring arrangements.

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