Talk:E and M signaling

Comments
Anyone have comments? Its kinda late for me to be thinkin' clearly tonights. I'll check this tommorow. --Othtim Hi Im working on a NOKIA 4 wire E&M card it is different in how it uses the M end the M end on a Nokia card requires an earth (the nokia card actually has a negitive battery behind its sensor ) when it sees the earth is triggers the earth at the remote end in the normal manner. this is called (by Nokia ) "non-inverted e&m signalling" it might be worth adding somthing to this effect it would have saved me a bit of confusion cos I was trying to inject a -48v just like I always did

good luck Derek

There are variants of E & M, at least 5 types. These make use of various versions of signal state for the E & M lines.

Depending on which side of the communication link you are on (Side A & Side B) the signal is referenced to GND & -48VDC

More info is available from manufacturers documentation (eg Harris who make Mux/Demux units with E & M interfaces) including pictures etc.

From the CISCO site that discusses E&M the best: E&M Type I—This is the most common interface in North America.

Type I uses two leads for supervisor signaling: E, and M.

During inactivity, the E-lead is open and the M-lead is connected to the ground.

The PBX (that acts as trunk circuit side) connects the M-lead to the battery in order to indicate the off-hook condition.

The Cisco router/gateway (signaling unit) connects the E-lead to the ground in order to indicate the off-hook condition.

E&M Type II—Two signaling nodes can be connected back-to-back.

Type II uses four leads for supervision signaling: E, M, SB, and SG.

During inactivity both the E-lead and M-lead are open.

The PBX (that acts as trunk circuit side) connects the M-lead to the signal battery (SB) lead connected to the battery of the signaling side in order to indicate the off-hook condition.

The Cisco router / gateway (signaling unit) connects the E-lead to the signal ground (SG) lead connected to the ground of the trunk circuit side in order to indicate the off-hook condition.

E&M Type III—This is not commonly used in modern systems.

Type III uses four leads for supervision signaling: E, M, SB, and SG.

During inactivity, the E-lead is open and the M-lead is set to the ground connected to the SG lead of the signaling side.

The PBX (that acts as trunk circuit side) disconnects the M-lead from the SG lead and connects it to the SB lead of the signaling side in order to indicate the off-hook condition.

The Cisco router / gateway (signaling unit) connects the E-lead to the ground in order to indicate the off-hook condition.

E&M Type IV—This is not supported by Cisco routers / gateways.

E&M Type V—Type V is symmetrical and allows two signaling nodes to be connected back-to-back. This is the most common interface type used outside of North America.

Type V uses two leads for supervisor signaling: E, and M.

During inactivity the E-lead and M-lead are open.

The PBX ( that acts as trunk circuit side) connects the M-lead to the ground in order to indicate the off-hook condition.

The Cisco router / gateway (signaling unit) connects the E-lead to the ground in order to indicate off-hook condition.

Audio Implementation (two-wire / four-wire) There are two distinct types of audio interface (two-wire or four-wire). These implementations describe the number of wires used in order to transmit audio signals.

With the two-wire implementation, full-duplex audio signals are transmitted over a single pair which consists of tip (T) and ring (R) leads.

The four-wire implementation provides separate paths to receive and send audio signals which consists of T, R and T1, R1 leads.

Note: Even though an E&M circuit can be called a four-wire E&M circuit, it is likely to have six to eight physical wires, based on the signaling type and audio implementation used.

This is a good discussion of the various types of E&M signalling. It should replace most of the E&M information in the article.

Ron 03:59, 15 December 2006 (UTC)

Engineering and Maintenance
I had always understood that “E&M” stood for ‘Engineering and Maintenance’; not ‘ear and mouth’. When a link was being set up the main bandwidth was used for the subscriber’s circuits, but a bit of capacity was taken off the top or bottom for the technicians to use when setting up or maintaining the link. Perhaps it’s a British v. American difference?? Percy Cameron (talk) 04:08, 23 September 2008 (UTC)

You have explained inband supervision but that's quite a different thing from an order wire, so no, I see no reason to regard this derivation as any less a telephonic folk story than the ear and mouth version. Far as I see, no authoritative documentation or evidence has shown up for any theory of origin; all are mere speculation. And the Brits, far as I know, didn't use this terminology at all until they learned it from the Yanks in the 1960s when its existence was well documented in design diagrams but its origin had already been lost. Jim.henderson (talk) 07:19, 28 September 2008 (UTC)