Homework 3 assignment for ECE374 Posted: 03/15/13 Due: 03/29/13

Transcription

1 ECE74: Homework 1 Homework assignment for ECE74 Posted: 0/1/1 Due: 0/9/1 Note: In all written assignments, please show as much of our work as ou can. Even if ou get a wrong answer, ou can get partial credit if ou show our work. If ou make a mistake, it will also help the grader show ou where ou made a mistake. Problem 1 (10 Points): Suppose datagrams are limited to 1,00 btes (including header) between source Host A and destination Host B. Assuming a 0- bte IP header, how man datagrams would be required to send and MP consisting of million btes? Eplain how ou computed our answer! MP file size = million btes. Assume the data is carried in TCP segments, with each TCP segment also having 0 btes of header. Then each datagram can carr =140 btes of the MP file 10 Number of datagrams required = = 4. All but the last datagram will be 1, btes; the last datagram will be = 1000 btes. Note that here there is no fragmentation the source host does not create datagrams larger than 100 btes, and these datagrams are smaller than the MTUs of the links. Problem (0 Points): Consider the network setup shown in Figure 1. Suppose that the ISP instead assigns the router the address and that the network address of the home network is /4. a. Assign addresses to all interfaces in the home network. b. Suppose each host has two ongoing TCP connections, all to port 80 at host Provide the si corresponding entries in the NAT translation table.

2 ECE74: Homework 1 Figure 1 a) Home addresses: , , with the router interface being b) NAT Translation Table WAN Side LAN Side , , , , , , , , , , , , 4 Problem (0 Points): Consider the following network. With the indicated link costs, use Djikstra s shortest- path algorithm to compute the shortest path from to all network nodes. Show how the algorithm works b computing a table below.

3 ECE74: Homework z 8 7 v 4 t w 4 u Step N D(t),p(t) D(u),p(u) D(v),p(v) D(w),p(w) D(),p() D(z),p(z) 0,,, 8, 1 4 Step N D(t),p(t) D(u),p(u) D(v),p(v) D(w),p(w) D(),p() D(z),p(z) 0,,, 8, 1 v 7,v 8,v -,, 8, vw 7,v 8,v - -, 8, vw 7,v 8,v , 4 vwz 7,v 8,v vwzt - 8,v vwztu Problem 4 (0 Points): Consider the network shown below, and assume that each node initiall knows the cost to each of its neighbors. Consider the distance- vector algorithm and show the distance table entries at node z.

4 ECE74: Homework 1 4 u 1 v z v From z 0 v From z 0 v 0 From z

5 ECE74: Homework v 0 From z Problem (1 Points): In Figure, consider the path information that reaches stub networks W, X, and Y. Based on the information available at W and X, what are their respective views of the network topolog? Justif our answer. The topolog view at Y is shown in Figure. Figure Figure

6 ECE74: Homework 1 w A B w A B C C X s view of the topolog W s view of the topolog In the above solution, X does not know about the AC link since X does not receive an advertised route to w or to that contain the AC link (i.e., X receives no advertisement containing both AS A and AS C on the path to a destination. Problem (1 Points): Consider the two basic approaches identified for achieving broadcast, unicast emulation and network- laer (i.e., router- assisted) broadcast, and suppose spanning- tree broadcast is used to achieve network- laer broadcast. Consider a single sender and receivers. Suppose the sender is connected to the receivers b a binar tree of routers. What is the cost of sending a broadcast packet, in the case of unicast- emulation and network- laer broadcast, for this topolog? Here, each time a packet (or a cop of a packet) is sent over a single link, it incurs a unit of cost. What topolog for interconnecting the sender, receivers, and routers will bring the cost of the unicast emulation and true network- laer broadcast as far apart as possible? You can chose as man routers as ou d like. The receives are shown connected to the sender in the binar tree configuration shown above. With network-laer broadcast, a cop of the message is forwarded over each link eactl once. There are thus link crossings ( ). With unicast emulation,

7 ECE74: Homework 7 the sender unicasts a cop to each receiver over a path with hops. There are thus 10 link crossings (*).