Chapter 7
Reading Organizer
After completion of this chapter, you should be able to:
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Describe the purpose of the transport layer in managing the transportation of data in end-toend communication.
Describe characteristics of the TCP and UDP protocols, including port numbers and their uses.
Explain how TCP session establishment and termination processes facilitate reliable
communication.
Explain how TCP protocol data units are transmitted and acknowledged to guarantee delivery.
Explain the UDP client processes to establish communication with a server.
Determine whether high-reliability TCP transmissions, or non-guaranteed UDP transmissions,
are best suited for common applications.
7.1 Transport Layer Protocols
1. Explain the purpose of the transport layer.
The transport layer is responsible for establishing a temporary communication session between
two applications and delivering data between them.
2. What are the primary responsibilities of transport layer protocols?
a. Tracking the individual communication between applications on the source and destination
hosts
b. Segmenting data for manageability and reassembling segmented data into streams of
application data at the destination
c. Identifying the proper application for each communication stream
3. At the transport layer, each particular set of data flowing between a source application and a
destination application is known as a ___conversation___.
4. TCP/IP provides two transport layer protocols. These are:
a. Transmission Control Protocol (TCP)
b. User Datagram Protocol (UDP),
5. Explain how TCP and UDP differ from each other.
TCP is considered a reliable, full-featured transport layer protocol, which ensures that all of the data
arrives at the destination. In contrast, UDP is a very simple transport layer protocol that does not
provide for any reliability.
6. TCP’s reliability functions provide more robust communication between applications. What are two
possible issues that can be incurred by this reliability?
a. additional overhead
b. possible delays
7. With UDP, there are no ___transport___ layer processes that inform the sender if successful delivery
has occurred.
8. Application developers must choose which transport protocol type is appropriate based on the
requirements of the applications. What are two examples of where a TCP is more appropriate.
a. When segments must arrive in a very specific sequence to be processed successfully.
b. When all data must be fully received before any of it is considered useful.
9. List the applications where UDP is the preferred transfer protocol?
a. streaming audio
b. video
c. Voice over IP (VoIP).
10. Label the following application protocols with its correct transport layer delivery method. Either
TCP, UDP, or Both.
____TCP_____ HTTP
____Both____ DNS
____UDP____ TFTP
____TCP_____ Telnet
____UDP_____ IPTV
____TCP_____ FTP
____UDP_____ DHCP
____UDP_____ SNMP
____UDP_____ VoIP
____TCP_____ SMTP
11. TCP was initially described in RFC 793. In addition to supporting the basic functions of data
segmentation and reassembly, TCP also provides:
a. Connection-oriented conversations by establishing sessions
b. Reliable delivery
c. Ordered data reconstruction
d. Flow control
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12. TCP is a connection-oriented protocol. Explain what a connection-oriented protocol is.
A connection that negotiates and establishes a permanent connection (or session) between
source and destination devices prior to forwarding any traffic.
13. How does TCP ensure that its segments are reassembled into the proper order?
By numbering and sequencing the segments,
14. What is a stateful protocol?
It is a protocol that keeps track of the state of the communication session.
15. What are some examples of applications that use TCP?
a. web browsers
b. email
c. file transfers
16. List the features used to describe UDP.
a. Connectionless
b. Unreliable Delivery
c. No Ordered Data Reconstruction
d. No Flow Control
17. What are the pieces of communication in UDP called?
Datagrams
18. UDP is a stateless protocol. Explain what this means.
Neither the client, nor the server, is obligated to keep track of the state of the communication
19. Why does a client place a destination port number in a segment?
To tell the destination server what service is being requested.
20. What is the purpose of the source port number?
It is randomly generated by the sending device to identify a conversation between two devices.
21. The combination of the source and destination IP addresses and the source and destination port
numbers is known as a socket. What is a socket used for?
To identify the server and service being requested by the client.
22. Label the following port number ranges.
________Well-Known Ports_______ 0 to 1023
________Registered Ports________ 1024 to 49151
___Private and/or Dynamic Ports___ 49152 to 65535
23. What are the well-known port numbers associated with the following protocols?
___21___ FTP
___23___ Telnet
__25____ SMTP
___80___ HTTP
___143__ IMAP
___69___ TFTP
___520__RIP
___53___ DNS
___161__SNMP
24. What DOS command can be used to see which active TCP connections are open and running on a
networked host?
netstat
25. Why is dividing application data into segments necessary?
It ensures that data is transmitted within the limits of the media and that data from different
applications can be multiplexed on to the media.
26. The transport layer divides the data into pieces and adds a header for delivery over the network.
List what information is included with the TCP and UDP headers.
TCP Header –
a. source and destination ports
b. sequence number
c. acknowledgment of received segments
d. flow control
UDP Header –
a. source and destination ports
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27. Label each of the following delivery method characteristics as either TCP or UDP.
___UDP____ Less Overhead
___UDP___ Fast Transmission Requirements
___UDP____ No Acknowledgment of Receipt
___TCP____ Guaranteed Delivery
___TCP____ Ordered Delivery
___UDP____ Connectionless
___TCP____ Sequenced Message Segments
___UDP____ No ordered Delivery
___TCP____ Flow Control
___TCP____ Session Establishment
7.2 TCP and UDP
28. The key distinction between TCP and UDP is reliability. The reliability of TCP communication is
obtained through the use of ___connection-oriented___ sessions.
29. Explain what occurs during a three-way handshake.
a. It establishes that the destination device is present on the network
b. It verifies that the destination device has an active service and is accepting requests on the
destination port number that the initiating client intends to use for the session
c. It informs the destination device that the source client intends to establish a communication
session on that port number
30. Explain the three steps in TCP connection establishment.
a. The initiating client requests a client-to-server communication session with the server.
b. The server acknowledges the client-to-server communication session and requests a serverto-client communication session.
c. The initiating client acknowledges the server-to-client communication session.
31. How can security be added to the data network?
a. Denying the establishment of TCP sessions
b. Only allowing sessions to be established for specific services
c. Only allowing traffic as a part of already established sessions
32. To end each one-way TCP session, a two-way handshake is used which consists of…
a. FIN segment
b. ACK segment
33. Add the correct descriptor to its appropriate place in the graphic.
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34. What information is assigned to each header to ensure that it is reassembled in the correct order?
Sequence numbers
35. What are the sequence (SEQ) number and acknowledgement (ACK) numbers used together for?
To confirm receipt of the bytes of data contained in the transmitted segments.
36. What advantage does selective acknowledgements (SACKs) offer?
It is possible for the destination to acknowledge bytes in discontinuous segments and the host
would only need to retransmit the missing data.
37. Explain the purpose of flow control?
Flow control helps maintain the reliability of TCP transmission by adjusting the rate of data flow
between source and destination for a given session
38. Explain how flow control is accomplished.
By limiting the amount of data segments forwarded at one time and by requiring
acknowledgments of receipt prior to sending more
39. TCP uses ___window sizes___ to attempt to manage the rate of transmission to the maximum flow
that the network and destination device can support, while minimizing loss and retransmissions.
40. Explain how dynamic window sizes work.
When network resources are constrained, TCP can reduce the window size to require that
received segments be acknowledged more frequently. This effectively slows down the rate of
transmission because the source waits for data to be acknowledged more frequently.
41. Application layer protocols that use UDP include:
a. Domain Name System (DNS)
b. Simple Network Management Protocol (SNMP)
c. Dynamic Host Configuration Protocol (DHCP)
d. Routing Information Protocol (RIP)
e. Trivial File Transfer Protocol (TFTP)
f. IP telephony or Voice over IP (VoIP)
g. Online games
42. UDP is said to be transaction-based. What does this mean?
When an application has data to send, it simply sends the data.
43. Which applications use TCP?
A. Hypertext Transfer Protocol (HTTP)
b. File Transfer Protocol (FTP)
c. Simple Mail Transfer Protocol (SMTP)
d. Telnet
44. There are three types of applications that are best suited for UDP. Explain each.
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a. Applications that can tolerate some data loss, but require little or no delay
b. Applications with simple request and reply transactions
c. Unidirectional communications where reliability is not required or can be handled by the
application