CS118-Spring14 Homework 1Xu WuUID:004360296April 9, 2014Problem 1.A network protocol defines rules and conventions for communications between network de-vices. Protocols for computer networking all generally use packet switching techniques tosend and receive messages in the form of packets.Network protocols include mechanisms for devices to identify and make connections witheach other, as well as formatting rules that specify how data is packaged into messages sentand received. Some protocols also support message acknowledgment and data compressiondesigned for reliable and/or high-performance network communication. Hundreds of differ-ent computer network protocols have been developed each designed for specific purposes andenvironments.Problem 2.(T) End systems are just hosts. There are no differences between the two terms.(F) In packet switching transmissions, bandwidth is divided into pieces and each packet usesone or several pieces of bandwidth.(F) Full buffer is the only reason that causes packet loss.Problem 3.(a) A circuit switching is better. Because this application need a long term smooth transmis-sion, it is better to reserve the bandwidth for this application. Also, since it doesn’t say thatthere will be other applications to be transmitted, there won’t be waste for the bandwidth.(b) In this case, we do not need the congestion control mechanism. Because here the sum ofall the applications is less than each and every link , so no congestion (very little queuing)will occur.Problem 4.1Since there are N packets, for the first packet, the queuing time is 0, for the second packet,the queuing time is L/R, for the third packet, the queuing time is 2L/R, for the nth packet,the queuing time is(n-1)L/R, so the average queuing time is(1 + 2 + ... + N − 1)LRN=(N − 1)L2R(1)Problem 5.(a) 10 users(b) The possibility that a given user is transmitting is 10%.(c)n400.1n(1 − 0.1)40−n(d) For the possibilities with equal or more than 11 users are transmitting at the same time,we should use the formula:1 − (9Xn=0n400.1n(1 − 0.1)40−n)Therefore, the possibilities with equal or more than 11 is about
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