Which two analog telephony signaling methods are most vulnerable to glare conditions? (Choose two.)
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A. B. C. D. E. F.AE.
The loop start signaling method is more common and is typically used by residential phone lines.
When a voice port is configured with loop start signaling, the device (telephone) closes the circuit loop that signals the CO voice port to provide dial tone; an incoming call is signaled on the CO by supplying a predefined voltage on the line.
The loop start signaling method has one main disadvantage in that it has no method of preventing both sides of the connection from attempting to seize the line at the same time; this condition is referred to as glare.
Because of this, loop start signaling is typically not used on high demand circuits.
With immediate-start, the calling side of the connection seizes the line by going off hook on the E-lead and address information is sent using dual-tone multifrequency (DTMF) digits.
Immediate start signaling is vulnerable to glare just like loop-start signaling.
Analog telephony signaling methods are used to transmit voice signals over traditional telephone networks. They are vulnerable to various types of interference, including glare conditions, which occur when a signal from one telephone line interferes with another.
Two analog telephony signaling methods that are particularly vulnerable to glare conditions are:
FXS Loop-start: This signaling method is used to connect analog telephones and fax machines to a telephone network. In a loop-start signaling configuration, the telephone line is closed when the phone is on-hook (i.e., not in use). When the user goes off-hook (i.e., picks up the receiver), the phone creates a short circuit that signals the network to send a dial tone. This signaling method is vulnerable to glare conditions because if two phones on different lines go off-hook at the same time, the network may not be able to distinguish between them and may not send a dial tone to either phone.
FXO Ground-start: This signaling method is used to connect telephone equipment, such as PBXs (private branch exchanges), to a telephone network. In a ground-start signaling configuration, the PBX sends a ground signal to the network to request a dial tone. This signaling method is vulnerable to glare conditions because if two PBXs on different lines request a dial tone at the same time, the network may not be able to distinguish between them and may not send a dial tone to either PBX.
The other signaling methods listed in the question (E&M Wink-start, E&M Delay-dial, E&M Immediate-start, and E&M Feature Group D) are also vulnerable to glare conditions to some extent, but they are not as susceptible as FXS Loop-start and FXO Ground-start. E&M signaling methods use a combination of electrical pulses and ground signals to transmit voice and signaling information between devices. The exact signaling method used depends on the specific E&M protocol being used, and each protocol has its own strengths and weaknesses when it comes to glare conditions.