Mid%20Term%20Exam%202007%20Solutions

# Mid%20Term%20Exam%202007%20Solutions - Engineering Science...

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Engineering Science 427 - - 1 - - Simon Fraser University School of Engineering Science Engineering Science 427 Mid-Term Examination Date: March 8 2007 Time: 1 hour and 50 minutes All Questions Equal Marks Question 1: (see Section 5.7 of your text LGW) The average buffer occupancy of a statistical multiplexer (data concentrator) is to be calculated. In this device, the input packets from terminals connected to it are merged in order of arrival in a buffer and are then read out first come – first served over an outgoing transmission link. An M/M/1/ model is to be used to represent the concentrator. Ten terminals are connected to the statistical multiplexer. Each terminal generates, on average, a packet every 5 seconds. The packet lengths are exponentially distributed, with a mean of 960 bits. A 2400 bit/second outgoing link is used. Calculate the average buffer occupancy, under these conditions. Solution: The arrival rate of packets to the buffer is: 1 10 2 5 λ = ×= packets/second The mean service time is: 1 960 0.4 2400 μ == seconds The traffic intensity is then: 0.8 ρ The average buffer occupancy under these conditions is then: () 2 0.64 3.2 11 0 . 8 Eq = −− packets

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Engineering Science 427 - - 2 - - Question 2: (see Section 7.3.1 of your text LGW) A 64-kilobyte message (64 × 1024 bytes) is to be transmitted over two hops in a network. The network limits packets to a maximum size of 2 kilobytes (2 × 1024 bytes), and each packet has a 32-byte header. The transmission lines in the network are error free and have a capacity of 50 Mbps (50 × 10 6 bps). Each hop is 1000 km long.
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## This note was uploaded on 10/09/2009 for the course ENSC 1156 taught by Professor Rhardy during the Spring '07 term at Simon Fraser.

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Mid%20Term%20Exam%202007%20Solutions - Engineering Science...

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