Home » Cisco » 400-051 » How many bearer channels are available to carry voice traffic?
Refer to the exhibit.
From this NFAS-enabled T1 PRI configuration on a Cisco IOS router, how many bearer channels are available to carry voice traffic?
A. 91
B. 92
C. 93
D. 94
E. 95
Correct Answer: E
Explanation/Reference:
Explanation:
A T1 circuit typically carries 24 individual timeslots. Each timeslot in turn carries a single telephone call. When a T1 circuit is used to carry Primary Rate
ISDN one of the timeslots is used to carry the D channel. A single Primary Rate ISDN circuit is thus sometimes described as 23B + D. There are 23 bearer channels carrying voice or data, and one D channel carrying the Common Channel Signaling. In this case, there are 96 total channels in the group, but only 1 will be needed for use as the D channel, leaving 95 available for bearer channels.
Correct answer is D.
The primary and backup T1s only support 23 channels.
The primary and backup T1s reserve 1 channel.
This is not the correct answer. The correct answer is D (94). If you configure a backup D channel, only 23 B channels can be used on the backup T1 controller because the D channel on the backup is unavailable.
http://www.cisco.com/c/en/us/support/docs/dial-access/integrated-services-digital-networks-isdn-channel-associated-signaling-cas/9584-quadt1-nfas.html