What are two reasons for using layered protocols?1. To reduce design complexity.
2. Hide implementation, providing services thought interface.
What is the principal difference between connectionless communication and connection-oriented communication?Connection-oriented communication - order of delivery guaranteed, connectionless - messages routed independently, order of delivery not guaranteed.
List two ways in which the OSI reference model and the TCP/IP reference model are the same. Now list two ways in which they differ.1. The TCP/IP doesn't have application and presentation layers
2. The IP layer of TCP/IP is same functionality as network layer of OSI, the layers below IP protocol is a great void, meaning every network implements it's own physical and data link layers as they want.
Compare the delay in sending an x-bit message over a k-hop path in a circuit-switched network and in a (lightly loaded) packet-switched network. The circuit set up time is s sec, the propagation delay is d sec per hop, the packet size is p bits, and the data rate is b bps. Under what conditions does the packet network have a lower delay?1. With circuit switching: t = s + x/b + kd. Where s circuit set up time, x/b time taken to send out the message, kd is delay of switching k hops each taking time of d.
2. With packet switching: t = x/b + (k - 1)p/b + kd. Where (k - 1)p/b is time taken by the last packet to reach its destination, because it will be retransmitted k - 1 times by intermediate routers.
3. So, under condition that s > (k – 1) p/b, the packet network have a low delay.
