宁波大学.计算机网络A.试卷

名姓 号学 宁波大学 2011 / 2012 学年第 1 学期考试卷（A） 学号：______________姓名：______________

课号：_ 101G09X0X_ 课名： 计算机网络__ (答题卡和每页试卷均请写上姓名学号，答案请填在答题卡上)

I.

Choose the single correct answer from following choose. (1.5*20=30) [Correct checked:1.5; Other wise:0]

1.Which physical media has high-speed operation and low error rate:

8.FTP client browses remote directory by sending commands over:

[] A.Fiber optic cable

[] A.connection-less [] B.Coaxial cable [] B.free connection [] C.Twisted pair [] C.data connection [] D.Radio

[] D.control connection

2.If no free buffers in router, the arriving packets will be:

9.Which can satisfy client request without involving origin server:

[] A.dropped

[] A.Web caches

[] B.queued [] B.Write caches [] C.returned [] C.TCP buffer [] D.marked

[] D.Router buffer

3.Which can provides delay measurement from source to router along end-end Internet path towards 10.UDP socket identified by: destination： [] A.two-tuple (source IP address, source port number)

[] A.Ping [] B.two-tuple (dest IP address, dest port number) [] B.Traceroute [] C.two-tuple (source IP address, dest port number) [] C.Ipconfig [] D.two-tuple (dest IP address, source port number)

[] D.Nslookup

11.In GBN,when receiver receive a out-of-order packet,then discard and re-ACK the packet with: 4.In TCP/IP, which layer can make routing of datagrams from source to destination:

[] A. highest in-order sequence # [] A.Applicaion

[] B. lowest in-order sequence # [] B.Transport [] C. highest in-order port # [] C.Network

[] D. lowest in-order port #

[] D.Data Link

12.In RDT Approachs, which is designed for performance: 5.Web page consists of ( ) which includes several referenced objects：

[] A. checksum [] A.referenced HTML-file [] B. pipeline [] B.host HTML-file [] C. sequence # [] C.path HTML-file [] D. ACK or NAK

[] D.base HTML-file

13.Queued datagram at front of router’s queue prevents others in queue from moving forward is: 6.What is the default persistent model in HTTP/1.1: [] A.Head-of-the-Line (HOL) blocking [] A.Nonpersistent HTTP

[] B.Hops-of-the-Line (HOL) blocking [] B.Persistent without pipelining [] C.Head-of-the-List (HOL) blocking [] C.Persistent with pipelining [] D.Hops-of-the-List (HOL) blocking

[] D.Nonpersistent with pipelining

14.What’s a network ? From IP address perspective they can physically reach each other without 7.Web server maintains no information about past client requests, so HTTP is: intervening router and the device interfaces with: [] A.stateful [] A. same IP address

[] B.stateless [] B. same TCP port #

[] C.satisfied [] C. same network part of IP address [] D.unsatisfied [] D. same host part of IP address

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宁波大学 2011 / 2012 学年第 1 学期考试卷（A） 学号：______________姓名：______________

课号：_ 101G09X0X_ 课名： 计算机网络__ (答题卡和每页试卷均请写上姓名学号，答案请填在答题卡上)

15. Large IP datagram divided (“fragmented”) within network,it will be reassembled:

[] A. only at last router [] B. only at final destination [] C. only at next router

[] D. maybe at next router

16.Which is not a common Intra-AS routing protocols: [] A.RIP: Routing Information Protocol [] B.OSPF: Open Shortest Path First

[] C.IGRP: Interior Gateway Routing Protocol

[] D.ICMP: Interior Control Message Protocol

17.Which is not a MAC Random Access protocol in Ethernet: [] A.SCMA [] B.SCMA/CA [] C.SCMA/CD

[] D.Slotted SCMA

18.In DHCP client-server scenario, which message has DHCP-options field: [] A. host broadcasts “DHCP discover” [] B. DHCP server responds with “DHCP offer” [] C. host requests IP address: “DHCP request”

[] D. DHCP server sends address: “DHCP ack”

19.How to determine MAC address of host B, If knowing host B’s IP address?

[] A.ARP [] B.RARP [] C.RAP

[] D.RIP

20. Which device can break subnet into LAN segments:

[] A.IP mask [] B.NAT [] C.Router [] D.Switch

II.

Choose the multiple correct answer from following choose. (2*10=20) [All correct checked:2; Part correct checked:1; No checked:0; Full checked:0] 1.Which is the part of network structure:

[] A.network edge [] B.network core [] C.network user [] D.access networks

2.How to connect end systems to edge router? [] A.Microsoft access networks [] B.Residential access networks [] C.Institutional access networks

[] D.Mobile access networks

3.What kind of transport service does an application need? [] A.Data loss [] B.Timing [] C.Bandwidth

[] D.Security

4.Electronic Mail three phases of transfer is: [] A.handshaking (greeting) [] B.transfer of messages

[] C.opens the 2nd TCP connection

[] D.close

5.In TCP Connection Management, initialize TCP variables include： [] A.sequence # [] B.buffers

[] C.Sender MTU

[] D.RcvWindow

6.How does sender perceive congestion?

[] A.timeout [] B.3 duplicate ACKs [] C.3 duplicate data

[] D.slow start

7.TCP Congestion Control use three mechanisms:

[] A.additive increase and multiplicative decrease [] B.slow start

[] C.Conservative after timeout events

[] D.additive decrease and multiplicative increase

8.What are the Key Network-Layer Functions:

[] A.forwarding [] B.routing [] C.connection setup [] D.flow control

学号 姓名 第 2 页 共 4 页

宁波大学 2011 / 2012 学年第 1 学期考试卷（A） 学号：______________姓名：______________

课号：_ 101G09X0X_ 课名： 计算机网络__ (答题卡和每页试卷均请写上姓名学号，答案请填在答题卡上)

9.Link Layer Services include: [] A.Reliable delivery between adjacent nodes [] B.Flow Control between adjacent nodes [] C.Connection Manage

[] D.Error Detection and Correction

10.MAC Protocol’s taxonomy, three broad classes is: [] A.Channel Partitioning [] B.Random Access [] C.Taking turns [] D.Advertisement

III. Fill the blank from options. (1.5*16=24)

1).The network protocols define 1 , 2 of message sent and received among network entities, and 3 on message transmission, receipt.

(options: delay / format / policy / order / request / replay / actions taken / price / interface )

2).InTCP Congestion Control, after 3 duplicate ACKs CongWin is cut in ___4___ and window then grows____5____. But after timeout event, CongWin instead set to___6___, window then grows____7____, when it up to a ___8_____ again, then grows linearly.

(options: half / double / 1 MSS / 0 MSS / linearly / exponentially / threshold / top / bottom )

3).Please fill the general format of Http request message:

HTTP request message general format 9.[ ] sp 10.[ ] sp 11.[ ] 12.[ ] Host A ：1025 –> Host D：80 IV.

Question (26)

1.As follow, LAN1 connect to LAN2 via a router:

In session 1, Host A send a HTTP connection to WEB server D，if Host A initial TCP port 1025，Host D use TCP port 80；

In session 2, Host A send a HTTP connection to WEB server B，if Host A initial TCP port 1026，Host B use TCP port 80；

学号 姓名

Fill it: (9) Session Step Host A –> ROUTER ROUTER –> Host D Host A ：1026 Host A –> Host B –> Host B：80 Source MAC Destination MAC Source IP Destination IP Source Port# Destination Port# … … 13.[ ] 16. [ ] : 14.[ ] 15. [ ]

2.Read and answer：(17)

Two of the most important fields in the TCP segment header are the sequence number field and the acknowledgment number field. These fields are a critical part of TCP's reliable data transfer service. But before discussing how these fields are used to provide reliable data transfer, let us first explain what exactly TCP puts in these fields. TCP views data as an unstructured, but ordered, stream of bytes. TCP's use of sequence numbers reflects this view in that sequence numbers are over the stream of transmitted bytes and not over the series of transmitted segments. The sequence

Entity Body

(options: header field name / URL / field value / version / method / Cr Lf/ 200 OK )

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名姓 号学 宁波大学 2011 / 2012 学年第 1 学期考试卷（A） 学号：______________姓名：______________

课号：_ 101G09X0X_ 课名： 计算机网络__ (答题卡和每页试卷均请写上姓名学号，答案请填在答题卡上)

number for a segment is the byte-stream number of the first byte in the segment. to the people programming a TCP implementation. There are basically two choices: Let's look at an example. Suppose that a process in host A wants to send a stream of either (i) the receiver immediately discards out-of-order bytes; or (ii) the receiver data to a process in host B over a TCP connection. The TCP in host A will implicitly keeps the out-of-order bytes and waits for the missing bytes to fill in the gaps. Clearly, number each byte in the data stream. Suppose that the data stream consists of a file the latter choice is more efficient in terms of network bandwidth, whereas the former consisting of 500,000 bytes, that the MSS is 1,000 bytes, and that the first byte of choice significantly simplifies the TCP code. Throughout the remainder of this the data stream is numbered zero. As shown in Figure 3.5-3, TCP constructs 500 introductory discussion of TCP, we focus on the former implementation, that is, we segments out of the data stream. The first segment gets assigned sequence number assume that the TCP receiver discards out-of-order segments.

0, the second segment gets assigned sequence number 1000, the third segment gets In Figure 3.5.3 we assumed that the initial sequence number was zero. In truth, assigned sequence number 2000, and so on.. Each sequence number is inserted in both sides of a TCP connection randomly choose an initial sequence number. This is the sequence number field in the header of the appropriate TCP segment.

done to minimize the possibility a segment that is still present in the network from an earlier, already-terminated connection between two hosts is mistaken for a valid segment in a later connection between these same two hosts (who also happen to be using the same port numbers as the old connection) .

Question 1: Does TCP's use of sequence numbers over the series of transmitted segments? (3) Figure 3.5-3: Dividing file data into TCP segments.

Question 2: What does the sequence number for a segment means? For example. (4)

Now let us consider acknowledgment numbers. These are a little trickier than Question 3: What does the acknowledgment number means, that host A puts in its segment to host B?(3) sequence numbers. Recall that TCP is full duplex, so that host A may be receiving data Question 4: How does TCPs to choose an initial sequence number? (3)

from host B while it sends data to host B (as part of the same TCP connection). Each Question 5: What does a host do when it receives out of order segments in a TCP connection? (4)

of the segments that arrive from host B have a sequence number for the data flowing

from B to A. The acknowledgment number that host A puts in its segment is sequence number of the next byte host A is expecting from host B. It is good to look at a few (所有答案请填在答题卡上，答在试卷上的答案一律无效)

examples to understand what is going on here. Suppose that host A has received all bytes numbered 0 through 535 from B and suppose that it is about to send a segment to host B. In other words, host A is waiting for byte 536 and all the subsequent bytes in host B's data stream. So host A puts 536 in the acknowledgment number field of the segment it sends to B.

As another example, suppose that host A has received one segment from host B containing bytes 0 through 535 and another segment containing bytes 900 through 1,000. For some reason host A has not yet received bytes 536 through 899. In this example, host A is still waiting for byte 536 (and beyond) in order to recreate B's data stream. Thus, A's next segment to B will contain 536 in the acknowledgment number field. Because TCP only acknowledges bytes up to the first missing byte in the stream, TCP is said to provide cumulative acknowledgements.

This last example also brings up an important but subtle issue. Host A received the third segment (bytes 900 through 1,000) before receiving the second segment (bytes 536 through 899). Thus, the third segment arrived out of order. The subtle issue is: What does a host do when it receives out of order segments in a TCP connection? Interestingly, the TCP RFCs do not impose any rules here, and leave the decision up

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