Solutions for Home work2

5)A factor in the delay of a store-and-forward packet-switching system is how long it takes to store 
and forward a packet through a switch. If switching time is 10microseconds, is this likely to be a major
factor in the response of a client-server system where the client is in New York and the server is in California? 
Assume the propagation speed in copper and fiber to be 2/3 the speed of light in vacuum.

Solution:
No. The speed of propagation is 200,000 km/sec or 200 meters/microsec. In 10 microsec the signal travels 2km. 
Thus, each switch adds a equivalent of 2kms of extra cable. If the client and server are seperated by 5000 km, 
traversing even 50 switches adds only 100km to the total path, which is only 2%. Thus, switching delay is not a 
major factor under these circumstances.

6) A client-server system uses a satellite network, with the satellite at a height of 40,000 km. What is the 
best-case delay in response to a request?

Solution:
The request has to go up and come down, and the response has to go up and come down. The total path length 
traversed is thus 160,000 km. The speed of light in air and vacuum is 300,000 km/sec, so the propagation delay alone is 
160,000/300,000 sec or about 533 msec.