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computer networking

Questions and Answers of Computer Networking

Both HTTP and FTP can retrieve a file from a server. Which protocol should we use to download a file?
In Chapter 1, we mentioned that the TCP/IP suite, unlike the OSI model, has no presentation layer. But an application-layer protocol can include some of the features defined in this layer if needed.
Are the HELO and MAIL FROM commands both necessary in SMTP? Why or why not?
In Chapter 1, we mentioned that the TCP/IP suite, unlike the OSI model, has no session layer. But an application-layer protocol can include some of the features defined in this layer if needed. Does
In Figure 26.13 in the text, what is the difference between the MAIL FROM in the envelope and the FROM in the header?Figure 26.13 Figure 26.13 Format of an e-mail Behrouz Forouzan 20122 Olive Street
In FTP, assume a client with user name John needs to store a video clip called video2 on the directory /top/videos/general on the server. Show the commands and responses exchanged between the client
Alice has been on a long trip without checking her e-mail. She then finds out that she has lost some e-mails or attachments her friends claim they have sent to her. What can be the problem?
In FTP, a user (Jane) wants to retrieve an EBCDIC file named huge from /usr/users/report directory using the ephemeral port 61017. The file is so large that the user wants to compress it before it is
Assume a TELNET client uses ASCII to represent characters, but the TELNET server uses EBCDIC to represent characters. How can the client log into the server when character representations are
In FTP, a user (Jan) wants to make a new directory called Jan under the directory/usr/usrs/letters. Show all of the commands and responses.
The TELNET application has no commands such as those found in FTP or HTTP to allow the user to do something such as transfer a file or access a web page. In what way can this application be useful?
In FTP, a user (Maria) wants to move a file named file1 from /usr/users/report directory to the directory /usr/top/letters. Note that this is a case of renaming a file. We first need to give the name
Can a host use a TELNET client to get services provided by other clientserver applications such as FTP or HTTP?
In DNS, which of the following are FQDNs and which are PQDNs?a. xxxb. xxx.yyy.netc. zzz.yyy.xxx.edu.
Assume we design a new client-server application program that requires persistent connection. Can we use UDP as the underlying transport-layer protocol for this new application?
Write a method in Java to change an unsigned 32-bit integer representing a mask to an integer representing a prefix (/n).
Explain how a client process finds the IP address and the port number to be inserted in a remote socket address.
Write a method in Java to change an integer representing a prefix to an unsigned 32-bit integer representing the numeric mask.
A source socket address is a combination of an IP address and a port number. Explain what each section identifies.
Write a method in Java to add a given prefix (as an integer) at the end of an IP address to create a string representing the CIDR notation (“x.y.z.t/n”).
Which of the following can be a source of data?a. A keyboardb. A monitorc. A socket
Modify, compile, and test the client program in Table 25.17 and the server program in Table 25.16 to simulate a local DNS client and server. The server has a short table made of two columns, domain
Write a method in Java to extract the IP address (without the prefix) as a string in dotted-decimal notation from a string representing the CIDR notation (“x.y.z.t/n”).
A new application is to be designed using the client-server paradigm. If only small messages need to be exchanged between the client and the server without concern for message loss or corruption,
Modify, compile, and test the client program in Table 25.17 and the server program in Table 25.16 to allow the client to provide the pathname of a short file stored on the server host. The server
Write a method in Java to extract the prefix of an address (as an integer) given a string representing a CIDR notation in the form “x.y.z.t/n”.
Most of the operating systems installed on personal computers come with several client processes, but normally no server processes. Explain the reason.
Modify, compile, and test the client program in Table 25.13 and the server program in Table 25.12 to do the following: The client program needs to read the request string from a file and store the
Write a method in Java to convert a 32-bit integer to a string representing an IP address in the form “x.y.z.t”.
Can a program written to use the services of UDP be run on a computer that has installed TCP as the only transport-layer protocol? Explain.
Write a program to make the TCP client program in Table 25.4 more generic to be able to send any request created by the program. Table 25.4 Echo client program using TCP 1 / TCP echo client program 2
Write a method in Java to accept a string representing an IP address in the form “x.y.z.t” and change it to an unsigned integer.
In the client-server paradigm, explain why a server should be run all the time, but a client can be run when it is needed.
Write a program to make the TCP server program in Table 25.3 more generic: to receive a request, to process the request, and to send back the response. Table 25.3 Echo server program using the
Assume we want to make the TCP client program in Table 25.2 more generic to be able to send a string and to handle the response received from the server. Show how this can be done. Table 25.2 Echo
Explain which entity provides service and which one receives service in the client-server paradigm.
Write a program to make the UDP client program in Table 25.2 more generic to be able to send any request created by the client program. Table 25.2 Echo client program using UDP I/ UDP echo client
In Figure 25.12 in the text, how is the socket created for data transfer at the server site?Figure 25.12 Figure 25.12 Socket data structure Length Family Port number IP address Family Type Protocol
If the client in the previous exercise sends 7600 data chunks and the server sends 570 data chunks, show the contents of the three packets exchanged during association termination.Previous ExerciseAn
Assume a TCP client is expecting to receive byte 3001. It receives a segment with the sequence number 3001 that carries 400 bytes. If the client has no data to be sent at this moment and has
How is an IP address represented in Java?
Write a method in Java to find the last address in the block when one of the addresses in the block is given as a string representing a CIDR notation.
How does Java distinguish between IPv4 and IPv6 addresses?
Write a method in Java to find the size of a block when one address in the block (in CIDR notation) is given.
A port number in the TCP/IP protocol suite is an unsigned 16-bit integer. How can we represent a port number in Java using a 32-bit integer?
Write a method in Java to find the range of addresses when the beginning and the ending addresses are given.
Why do you think that Java uses an instance of a class instead of just an integer to represent an IP address?
You know that the IP address of a computer is “23.14.76.44”. Write a statement in Java to create an InetAddress object associated with this address.
Repeat Example 25.4 using the service of TCP.
Why do you think that Java provides no constructors for the InetAddress class?
You know that the domain name of a computer is “aBusiness.com”. Write a statement in Java to create an InetAddress object associated with that computer.
Assume we add a new protocol to the application layer. What changes do we need to make to other layers?
Write a program to make the UDP server program in Table 25.1 more generic: to receive a request, to process the request, and to send back the response.Table 25.1 Table 25.1 Echo server program using
In Figure 25.10 in the text, how does the server know that a client has requested a service? Figure 25.10 Sockets used in TCP communication Server O Connection establishment Client 1 Data transfer
In SCTP, the value of the cumulative TSN in a SACK is 23. The value of the previous cumulative TSN in the SACK was 29. What is the problem?
An SCTP client opens an association using an initial tag of 806, an initial TSN of 14534, and a window size of 20,000. The server responds with an initial tag of 2000, an initial TSN of 670, and a
In SCTP, a packet is carrying two DATA chunks, each containing 22 bytes of user data. What is the size of each DATA chunk? What is the total size of the packet?
The following is a dump of an SCTP general header in hexadecimal format.04320017 00000001 00000000a. What is the source port number?b. What is the destination port number?c. What is the value of the
Which of the six rules we described for ACK generation can be applied to the case where a client or a server receives a FIN segment from the other end?
In SCTP, the following is a dump of a DATA chunk in hexadecimal format.00000015 00000005 0003000A 00000000 48656C6C 6F000000a. Is this an ordered or unordered chunk?b. Is this the first, the last,
Which of the six rules we described for ACK generation in TCP can be applied to the case where a client receives a SYN + ACK segment from a server?
An SCTP association is in the COOKIE-WAIT state. It receives an INIT chunk; what does it need to do?
Which of the six rules we described for ACK generation in TCP can be applied to the case where a server receives a SYN segment from a client?
An SCTP association is in the ESTABLISHED state. It receives a SHUTDOWN chunk. If the host does not have any outstanding or pending data, what does it need to do?
If originally RTTS = 14 ms and α is set to 0.2, calculate the new RTTS after the following events (times are relative to event 1):Event 1: 00 ms Segment 1 was sent.Event 2: 06 ms Segment 2 was
Assume a TCP server is expecting to receive byte 6001. It receives a segment with the sequence number 6001 that carries 2000 bytes. If the server has bytes 4001 to 5000 to send, what should the
In a TCP connection, the window size fluctuates between 60,000 bytes and 30,000 bytes. If the average RTT is 30 ms, what is the throughput of the connection?
The ssthresh value for a Reno TCP station is set to 8 MSS. The station is now in the slow-start state with cwnd = 5 MSS and ssthresh = 8 MSS. Show the values of cwnd, ssthresh, and the current and
Assume a TCP server is expecting to receive byte 2401. It receives a segment with the sequence number 2401 that carries 500 bytes. If the server has no data to send at this moment and has not
The ssthresh value for a Taho TCP station is set to 6 MSS. The station now is in the slow-start state with cwnd = 4 MSS. Show the values of cwnd, sstresh, and the state of the station before and
Assume a TCP server is missing bytes 2001 to 3000. The server receives a segment with sequence number 2001 that carries 400 bytes. What is the reaction of the TCP server to this event? Can you
In a TCP connection, assume that maximum segment size (MSS) is 1000 bytes. The client process has 5400 bytes to send to the server process, which has no bytes to respond (unidirectional
Assume a TCP client expects to receive byte 2001, but it receives a segment with sequence number 1201. What is the reaction of the TCP client to this event? Can you justify the reaction?
We discuss the new option of SACKs for TCP on the book website, but for the moment assume that we add an 8-byte NAK option to the end of the TCP segment, which can hold two 32-bit sequence numbers.
Assume a TCP server expects to receive byte 2001, but it receives a segment with sequence number 2200. What is the reaction of the TCP server to this event? Can you justify the reaction?
Although new TCP implementations use the SACK option to report the out of order and duplicate range of bytes, explain how old implementations can indicate that the bytes in a received segment are out
Is the use of checksum for error control optional or mandatory ina. UDP?b. TCP?
As we have explained in the text, the TCP sliding window, when used without new SACK options, is a combination of the Go-Back-N and the Selective- Repeat protocols. Explain which aspects of the TCP
In a TCP segment, what does an acknowledgment number identify?
For a clearer view of Nagle’s algorithm, let us repeat the previous problem, but let the server transport layer acknowledge a segment when there is a previous segment that has not been acknowledged
In TCP, assume a client has 100 bytes to send. The client creates 10 bytes at a time in each 10 ms and delivers them to the transport layer. The server acknowledges each segment immediately or if a
In a TCP segment, what does a sequence number identify?
Can you mention some tasks that can be done by one or a combination of TCP segments?
Using Figure 24.19, explain how flow control can be achieved at the receiver site in TCP (from the receiving TCP to the receiving application).
In TCP, can the sender window be smaller, larger, or the same size as the receiver window?
Using Figure 24.19, explain how flow control can be achieved at the sender site in TCP (from the sending TCP to the sending application). Draw a representation.
We used the terms passive open and active open in discussing a connectionoriented communication using TCP. Assume there is a telephone conversation between Alice and Bob. Since a telephone
UDP is a message-oriented protocol. TCP is a byte-oriented protocol. If an application needs to protect the boundaries of its message, which protocol should be used, UDP or TCP?
Assume Alice, the client, creates a TCP connection with Bob, the server. They exchange data and close the connection. Now Alice starts a new connection with Bob by sending a new SYN segment. The
Assume Alice uses her browser to open two connections to the HTTP server running on Bob’s server. How can these two connections be distinguished by the TCP?
Assume Alice, the client, creates a connection with Bob, the server. They exchange data and close the connection. Now Alice starts a new connection with Bob by sending a new SYN segment. Before Bob
We said that TCP provides a connection-oriented service between the two application programs. A connection in this case needs a connection identifier that distinguishes one connection from another.
Eve, the intruder, sends a user datagram to Bob, the server, using Alice’s IP address. Can Eve, pretending to be Alice, receive a response from Bob?
Can you explain how TCP, which uses the services provided by the unreliable IP, can provide reliable communication?
Eve, the intruder, sends a SYN segment to Bob, the server, using Alice’s IP address. Can Eve create a TCP connection with Bob by pretending that she is Alice? Assume that Bob uses a different ISN
Assume a client sends a SYN segment to a server. When the server checks the well-known port number, it finds that no process defined by the port number is running. What is the server supposed to do
Figure 24.15 shows the client and server in the transition diagram for the common scenario using a four-handshake closing. Change the diagram to show the three-handshake closing.
Most of the flags can be used together in a segment. Give an example of two flags that cannot be used simultaneously because they are ambiguous.
Distinguish between a time-out event and the threeduplicate-ACKs event. Which one is a stronger sign of congestion in the network? Why?
In TCP, what type of flag can totally close the communication in both directions?

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