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"Consider a simple telephone network consisting of two end offices

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November 14th, 2012 06:23
in Data Communication and Computer Networks by shekhar_hin (Asbury University (KY), Modern literature)

"Consider a simple telephone network consisting of two end offices and one intermediate switch with a 1Mhz full duplex trunk between each end office and the intermediate switch. Assume a 4-Khz channel for each voice call. The average telephone is used to make four calls per 8-hour workday, with a mean call duration of six minutes. Ten percent of the calls are long distance. What is the maximum number of telephones an end office can support?"

Hello to everybody, please provide the solution.

6 Answers
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December 28th, 2012 11:55
princesspeach (Tufts University (MA), General medicine)
"Each telephone makes 0.5 calls/hour at 6 minutes each. Thus a telephone occupies a circuit for 3 minutes per hour. Twenty telephones can share a circuit (although this 100% utilization implies long queuing delays). Since 10% of the calls are long distance, it takes 200 telephones to occupy a long distance (4 kHz) channel full time. The interoffice trunk has 10^6/(4 × 10^3) = 250 channels. With 200 telephones per channel, an end office can support 200 × 250 = 50,000 telephones. Source: http://in.docsity.com/en-docs/Cellular_Systems__Packet_Switching_Networks-Wireless_Networking__LAN_and_Computer_Networks-Quiz_Solution_"

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January 28th, 2013 06:23
dharanidhar (B R Ambedkar National Institute of Technology, Programming)
There must be some formula from the class you took to get this question...I don't know it, but I'd guess that assume 6khz bandwidth for each active phone line, each phone used 24 minutes a day. Use the 6khz to find number of channels per line available, and 24 minutes use per 8 hours (480 minutes) gives 20 time the number of phones (1Mhz divided by 6Khz). Of course, there is some random factor, how many phones are actually in use.

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January 28th, 2013 14:42
dhimant (Allahabad University, Electrical Engineering)
Yes, in order to form an trunk, the link has to be PTP(point-to-point), from one L2 interface, ex. NIC, to one and one only L2 interface, not L1 or hub. Point-to-Point links also specify full-duplex, which simply means the two ends are able to transmit and receive at the same time. An L2 interface is present on PC's, swithches, routers, etc.. Therefore, when connecting an switch to an router for router-on-a-stick, you're connecting their L2 interfaces, which must be both PTP, and therefore, full-duplex as well. You can also form trunks from switches to PC's/servers with extra configuration required on the PC/server.

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January 29th, 2013 07:56
ashis (Agra University, English literature)
A duplex communication system is a point-to-point system composed of two connected parties or devices that can communicate with one another in both directions. An example of a duplex device is a telephone. The people at both ends of a telephone call can speak at the same time, the earphone can reproduce the speech of the other person as the microphone transmits the speech of the local person, because there is a two-way communication channel between them.

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January 30th, 2013 14:09
sangem (Ambedkar University, Delhi, Mechanical Engineering)
A half-duplex (HDX) system provides communication in both directions, but only one direction at a time (not simultaneously). Typically, once a party begins receiving a signal, it must wait for the transmitter to stop transmitting, before replying (antennas are of trans-receiver type in these devices, so as to transmit and receive the signal as well).

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January 31th, 2013 07:03
sankar (Aligarh Muslim University, Mechanics)
A good analogy for a half-duplex system would be a one-lane road with traffic controllers at each end. Traffic can flow in both directions, but only one direction at a time, regulated by the traffic controllers.

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