08级网络试卷

计算机网络08级试题

NOTE: This is a CLOSED BOOK, 120-minute exam. No textbooks, notes or dictionaries are allowed. It consists of four sections with a total of 100 marks. You are encouraged to WRITE YOUR ANSWERS IN ENGLISH. If you do, you will get 1-5 marks additionally. Thank you, and Good luck! Section One: Multiple Choice (10 Marks):

Please choose the best answer for each of the following ten questions. C1. The sliding window protocol is used at the

(A) physical layer and data link layer

(B) data link layer and network layer

(C) data link layer and transport layer

(D) transport layer and application layer

D2. The Transmission Control Protocol (TCP) is

(A) a connectionless network layer protocol

(B) a connection-oriented network layer protocol

(C) a connectionless transport layer protocol

(D) a connection-oriented(面向连接的) transport layer protocol

B3. Packet-switched networks move data in separate, small blocks, i.e. packets, (A) based on the destination MAC address in each frame.

(B) based on the destination IP address in each packet.

(C) based on the packet size.

(D) along a dedicated point-to-point connections set up during the call. D4. Which one of following networking devices has two or more different IP addresses with different net-id?

(A) Repeater (B) Hub

(C) Bridge (D) Router

A5.”00:e0:f9:23:a8:20” is

(A) a MAC address (B) an IP address

(C) a Port number (D) none of above

D6. Which layer provides communication between two processes running on two different hosts.

(A) Physical layer (B) Data link layer

(C) Network layer (D) Transport layer

C7. The Ethernet standard defines a minimum frames size as 64 bytes because

(A) users never send small data files.

(B)Ethernet can not define a small sending window.

(C) the CSMA/CD is characterized by “non-deterministic when sending”.

(D) none of the above.

B8. On an Ethernet, a host always listens to the channel while it is transmitting data. As soon as detecting a collision, it aborts transmission, waits for a while, and then retransmit the same frame. The amount of

waiting time is

(A) a constant. i.e. one second.

(B) determined by the binary exponential back-off algorithm.

(C) determined by the receiving host.

(D) determined by the network administrator.

A9.Which kind of delay in a packet-switched network depends on congestion level of router?

(A) Queuing delay（排队时延）

(B) Transmission delay（发送时延）

(C) Propagation delay（传播时延）

(D) Nodal processing delay（节点处理时延）

C10. According to the OSI model, the Network Layer decides

(A) how to transmit bits to the channel.

(B) how to transmit frames to adjacent node (neighbour), over a single link.

(C) how to route packets to a host on the other side, across networks.

(D) how to send data segments to a process running on another host, across networks

Section Two: Blank Filing (20 Marks)

Please fill blanks in the following sentences/descriptions.

11. TCP provides a connection-oriented, reliable, byte stream service. The term connection-oriented means the two applications using TCP

must establish _connection_______ before they can exchange data. TCP includes _flow control_________mechanism for each of these byte streams that allows the receiver to limit how much data the

sender.

12. Using "Stop and Wait" protocol, if the ___timer_______goes off before the acknowledgement comes in, the sender will retransmit the

frame. However, frame retransmissions may introduce duplicate frames received by receiver. One solution is to ___sequence numbers ______for every frame, so that the receiver can distinguish between new frames and old copies.

13. In terminology "100BaseT", "100" stands for__data rate______ , ”Base” stands for_baseband_ ___, ”T” stands for___twisted pair star network_____.

14. If nodes are connected using an Ethernet hub and twisted pair, the

physical topology of the network is ___star_____, however, the logical topology is ____bus line___.

5. From the In ternet’s point of view, two or more LANS, which are

connected by Repeaters at the ____physical____ Layer or Bridges at the ___data link_____ Layer, have the same net-id. i.e. It is considered as a single network.

16. In the Internet, routers running at the ___network____ Layer connect two or more networks, with different net-id.

17. In IEEE 802.11 WLAN, a sender is allowed to "reserve" channel rather than random access of data frames, in order to avoid collisions of long data frames. In this mechanism, the sender first transmits

___RTS____ to receiver using ________ media access protocol. The receiver, after having got it, broadcasts __CTS______ inn response to it.

18. In CSMA/CD Ethernet, when a station has data to send, it first listens to the channel. Only when it detects that __channel is idle_______, it begins to transmit frame, meanwhile listens to the channel in all time. It aborts transmission as soon as it detects a collision__________ rather than finish transmit ting it’s frames. 19. In an IEEE802.11 WLAN with Infrastructure mode, an __Access Point(接入点)____ provides access to wired network. Via this device, mobile stations in the WLAN can communicate with stations on wired network.

20. In the Internet, ___ARP________ protocol is used to map IP addresses onto MAC addresses. However, ____Name Server______ is used to translate host names to IP Addresses. Section Three: Networking Terminology (40 Marks)

21. Please describe "Carr ier Sense Multiple Access (CSMA)” (10 Marks)

22. (10 Marks) Four LANs (LAN1, LAN2, LAN3, and LAN4) are interconnected by router R13, R24 and R34.

(1)Please configure default gateway for Host H11 and H22 respectively.

(2)Please configure the following routing tables manually for router R24 and R34 respectively.

Router R24

Router R34

23. (10 Marks) Please explain the TCP Transmission Policy in the following figure. (P583)

24. (10 Marks) The following figure illustrates the basic operation of a TCP control mechanism which is widely used in the Internet. What is this mechanism used for? What are two phases that the mechanism includes? (Note: A detailed description is not necessary. However, you need to

indicate the phases on the figure.) (P596)

Section Four: Problems and Solutions (30 Marks)

25. (16 Marks) A large number of consecutive IP address are available starting at 192.168.0.0. Suppose that four organizations, A, B, C, and D, request 1000, 4000, 2000, and 8000 addresses, respectively, and in that order. For each of these, give the first IP address assigned, the last IP address assigned, and the mask in the w.x.y.z/s notation (Note: all the

requests are rounded up to a power of two).(课后习题5.27)

26. (14 Marks) An Ethernet consists of 5 segments connected by 4 repeaters.

Each segment is 500 meter long.

The signal propagation speed is 2x108 m/sec.

The delay caused by each repeater is 2.5 μsec.

The Transmission rate (bandwidth) is 10 Mbps.

Now we have two hosts, say A and B, which are located at far ends of the LAN.

(1) (7 Marks) Please calculate the signal propagation delay from Host A to B.

(2) (7 Marks) When hosts compete the shared the channel using CSMA/CD, please calculate the minimum frame size (in bit) for any sending host to detect the collision.