CPE 448 Exam #2 (50 pts) April Name Class: 448

Transcription

1 Name Class: 448 1) (5 pts) Draw the three way handshake used to establish a TCP connection. Show all SYN and ACK packets. Also show all sequence and acknowledgement numbers associated with the SYN and ACK packets. 2)(4 pts) The original algorithm for computing a timeout value for a TCP connection is being used with the parameter If the current estimated RTT is 100 milliseconds and the sample RTT for the most recent transmission is 75 milliseconds. a) What is the new estimated RTT? b) What is the timeout time used for this new estimated RTT? Page 1 of 8

2 3) (8 pts) A router is managing three flows using fair queuing. The router can transmit one packet every 1 unit of wall clock time. A queue is considered active if it has 1 or more packets present and/or a packet is being transmitted from that queue. Start the wall clock time at 1 and the fair queue clock (denoted by Ai) starts at 1.0 at that time. For each packet shown provide the wall clock time when the packet is transmitted. The packets arrive at the router at the wall time specified and packet designations are shown in parentheses next to the times of arrival. All packets are the same size and transmission time ties are resolved in the order A, B, C. Flow A: 1, 3 (packets numbered as A1, A3) Flow B: 1, 2 (packets numbered as B1, B2) Flow C: 2, 3 (packets numbered as C2, C3) Fill in the chart below for your answer. Ai is to be updated for all active wall clock times. Queues Sending Queue wall clock Ai Arrivals Fi Sent Flow A Flow B Flow C Packet Fi Order Page 2 of 8

3 4) (5 pts) Consider the following network where R1, R2 and R3 are service providers with customers A, B, C and D. C A R1 R3 R2 B D The following CIDR addresses(shown as hex numbers) have been given to the providers and their customers Address Name A1.A1.0.0/16 A2.A2.0.0/16 A3.A3.0.0/16 A3.A3.A0.0/20 A3.A3.B0.0/20 A1.A1.C0.0/20 A2.A2.D0.0/20 Fill in the routing table below for R1, R2 and R3 so that a packet that arrives at any router is most efficiently (fewest number of hops) sent towards its destination R1 R2 R3 A B C D Provider R1 Provider R2 Provider R3 Address Next Hop Address Next Hop Address Next Hop Page 3 of 8

4 5) (6 pts) Answer the following short answer questions. (1 point each) a) What does it mean when a network provides Best Effort Service/Delivery b) Assuming there are no reserved network/broadcast addresses, give the number of possible host addresses for each of the network classes listed below: Class A Networks: Class B Networks: Class C Networks: c) In IP version 6, how many bits make up the IP source or IP destination address? d) For the Distance Vector Routing Protocol, what information does a node exchange and which nodes receive this information? e) For the Link State Routing Protocol, what information does a node exchange and which nodes receive this information? f) For the Distance Vector and Link State routing protocols, what is the starting assumption used by both? Page 4 of 8

5 6) (4 pts) A router has the following (CIDR) entries in its routing table Address/mask Next Hop /22 Router /22 Router /23 Interface /23 Interface 1 Default Router 3 What is the next hop that the router selects when it receives IP packets with the addresses shown below. Show all of your work or explain how you determined the next hop. a) a) Next Hop b) b) Next Hop c) c) Next Hop d) d) Next Hop Page 5 of 8

6 7) (6 pts) You are designing a reliable byte stream protocol (not TCP) to operate over a 1x10 9 bps network and it is using a sliding window for flow control. The maximum segment lifetime for the network is 90 seconds. The time for keeping the transmission pipe full is taken to be the RTT of the network which is 50ms. a) What is the minimum number of bits necessary for the Advertised Window field of your protocol header? Round up to the next integer value (i.e. if you calculate bits necessary, then you will give your minimum number of bits necessary as 21) b) What is the minimum number of bits necessary for the Sequence Number field of your protocol header? Round up to the next integer value (i.e. if you calculate bits necessary, then you will give your minimum number of bits necessary as 21) c) Using your answer from part b, how long will it take for the sequence numbers to actually wrap around? Page 6 of 8

7 8) (6 pts) Fragmentation. Consider a packet that is transmitted from host A to host B in the following hypothetical network. The maximum transmission unit (MTU) size in bytes is shown on each link. The header length for a packet sent on any link is 40 bytes. The MTU value includes this header value (i.e. if the MTU is 600 Bytes, then 40 Bytes are header information and 560 Bytes are data) A R1 R2 B a) Host A is transmitting data packets with a size of 700 data Bytes. For a single 700 Byte data packet transmitted from A to B, determine for each link the number of packets that are sent and the amount of data each packet holds. b) Before transmitting any information, Host A performs MTU discovery for the network. The result of the MTU discovery is the smallest MTU of 200 Bytes (which consists of 160 Bytes of data and a 40 byte header). How many packets does Host A now use to transmit 700 Bytes of data? For each of the packets transmitted, provide the number of bytes of data contained in the packet. Page 7 of 8

8 9) (6 pts) Perform the link state routing algorithm on this page. Link State: The Link State Routing Algorithm (Dijkstra s or forward search algorithm) is to be performed for node B. The link state packets sent by the nodes in the network are shown below. When finished, provide the routing table for node B. Link state packets are in the form of (destination, cost, next hop) Node A Node B Node C Node D Node E Node F D,3,D C,10,C B,10,B A,3,A A,1,A A,2,A E,1,E D,2,D D,4,D B,2,B C,3,C B,8,B F,2,F F,8,F E,3,E C,4,C Confirmed Tentative (B, 0, -) Node B Routing Table Destination Cost NextHop A C D E F Page 8 of 8