Cvoice question 4

In North America, which E&M signaling type is used most often for geographically separated equipment?

A. Type I
B. Type II
C. Type III
D. Type IV
E. Type V

Answer: B

Explanation

This information is quoted from
http://www.cisco.com/en/US/tech/tk1077/technologies_tech_note09186a0080093f60.shtml

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.
Although above information specifies E&M Type 1 is the most commonly used interface in North America but this type generates significant delay in the signaling operation when transmitting between geographically separated equipment and affects voice signal quality (because of significant inductance and capacitance of the long wires) so Type 2 is often used instead.