1. What are two reasons for using layered protocols? What is one possible disadv
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Question
1. What are two reasons for using layered protocols? What is one possible disadvantage of using layered protocols?
2. An image is 1600 × 1200 pixels with 3 bytes/pixel. Assume the image is uncompressed. How long does it take to transmit it over a 56-kbps modem channel? Over a 1-Mbps cable modem?
3. Calculate the end-to-end transit time for a packet for both GEO (altitude: 35,800 km), MEO (altitude: 18,000 km) and LEO (altitude: 750 km) satellites.
4. Three packet-switching networks each contain n nodes. The first network has a star topology with a central switch, the second is a (bidirectional) ring, and the third is fully interconnected, with a wire from every node to every other node. What are the best-, average-, and worst-case transmission paths in hops?
Explanation / Answer
1. The two reasons for using layered protocols are:
a. It breaks up the design problem into smaller and more manageable pieces.
b. Protocols can be changed easily without affecting higher or lower layers.
One possible disadvantage of using layered protocols is redundancy and overall lower performance.
2. The image is 1024*768*3 bytes or 2,359,296 bytes. This is 18,874,368 bits.
At 56,000 bits/sec, it takes about 337.042 sec to transmit it over a 56 kbps modem channel.
At 1,000,000 bits/sec, it takes about 18.874 sec to transmit it over a 1 Mbps cable modem.
3. The end to end transit time for a packet for both GEO, MEO and LEO satellites are:
a. Transit time by GEO=(35800*2)/300000=0.24sec
b. Transit time by MEO=(18000*2)/300000=0.12sec
c. Transit time by LEO=(750*2)/300000=0.005sec
4. Three networks each contain ‘n’ nodes.
a. The first is star topology with a central router because in a start topology, transmission path from one node to other node will be ‘2’ in all cases (through central router).
The best, average and worst case transmission paths in hops in star network is (2,2,2).
b. The second is a bidirectional ring because in bidirectional ring topology, transmission path from one node to other node is ‘1’ if nodes are adjacent and ‘n/2’ if nodes are far away.
The best, average and worst case transmission paths in hops in bidirectional ring network is (1,n/2,n/2).
c. The third is fully interconnected (every node is connected to every other) because in a fully connected topology, the transmission path from one node to other is ‘1’ because all nodes are connected to all other nodes.
The best, average and worst case transmission paths in hops in fully connected network is (1,1,1).
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