Key Terms 469
protocol stack A set of related communications protocols that operate together and,
as a group, address communication at some or all of the seven layers of the OSI refer-
ence model. Not every protocol stack covers each layer of the model, and often a single
protocol in the stack addresses a number of layers at once. TCP/IP is a typical protocol
stack.
routed protocol Any network protocol that provides enough information in its net-
work layer address to allow a packet to be forwarded from one host to another host
based on the addressing scheme.
router A network-layer device that uses one or more metrics to determine the optimal
path along which network traffic should be forwarded. Routers forward packets from
one network to another based on network-layer information contained in routing
updates. Occasionally called a gateway (although this definition of gateway is becoming
increasingly outdated).
Routing Information Protocol (RIP) An IGP supplied with UNIX BSD systems. The
most common IGP in the Internet. RIP uses hop count as a routing metric.
routing metric A method by which a routing algorithm determines that one route is
better than another. This information is stored in routing tables and is sent in routing
updates. Metrics include bandwidth, communication cost, delay, hop count, load,
MTU, path cost, and reliability. Sometimes simply called a metric.
routing protocol A protocol that accomplishes routing through the implementation of
a specific routing algorithm. Examples of routing protocols are IGRP, OSPF, and RIP.
routing table A table stored in a router or some other internetworking device that
keeps track of routes to particular network destinations and, in some cases, metrics
associated with those routes.
subnet address A portion of an IP address that is specified as the subnetwork by the
subnet mask.
subnet mask A 32-bit address mask used in IP to indicate the bits of an IP address
that are used for the subnet address. Sometimes simply called a mask.
subnetwork 1. In IP networks, a network sharing a particular subnet address. Sub-
networks are networks arbitrarily segmented by a network administrator to provide

a multilevel, hierarchical routing structure while shielding the subnetwork from the
addressing complexity of attached networks. Sometimes called a subnet. 2. In OSI net-
works, a collection of ESs and ISs under the control of a single administrative domain
and using a single network access protocol.
1102.book Page 469 Tuesday, May 20, 2003 2:53 PM
470 Chapter 8: Routing Fundamentals and Subnets
Check Your Understanding
Complete all the review questions to test your understanding of the topics and con-
cepts in this chapter. Answers are listed in Appendix C, “Check Your Understanding
Answer Key.”
1. How many bits are in an IP address?
A. 16
B. 32
C. 64
D. None of the above
2. What is the maximum value of each octet in an IP address?
A. 28
B. 255
C. 256
D. None of the above
3. The network number plays what part in an IP address?
A. It specifies the network to which the host belongs.
B. It specifies the identity of the computer on the network.
C. It specifies which node on the subnetwork is being addressed.
D. It specifies which networks the device can communicate with.
4. The host number plays what part in an IP address?
A. It designates the identity of the computer on the network.
B. It designates which node on the subnetwork is being addressed.
C. It designates the network to which the host belongs.
D. It designates which hosts the device can communicate with.

5. What is the decimal equivalent of the binary number 101101?
A. 32
B. 35
C. 45
D. 44
1102.book Page 470 Tuesday, May 20, 2003 2:53 PM
Check Your Understanding 471
6. Convert the decimal number 192.5.34.11 to its binary form.
A. 11000000.00000101.00100010.00001011
B. 11000101.01010111.00011000.10111000
C. 01001011.10010011.00111001.00110111
D. 11000000.00001010.01000010.00001011
7. Convert the binary IP address 11000000.00000101.00100010.00001011 to its
decimal form.
A. 190.4.34.11
B. 192.4.34.10
C. 192.4.32.11
D. None of the above
8. What portion of the Class B address 154.19.2.7 is the network address?
A. 154
B. 154.19
C. 154.19.2
D. 154.19.2.7
9. What portion of the IP address 129.219.51.18 represents the network?
A. 129.219
B. 129
C. 14.1
D. 1
10. Which of the following addresses is an example of a broadcast address on the
network 123.10.0.0 with a subnet mask of 255.255.0.0?

A. 123.255.255.255
B. 123.10.255.255
C. 123.13.0.0
D. 123.1.1.1
1102.book Page 471 Tuesday, May 20, 2003 2:53 PM
472 Chapter 8: Routing Fundamentals and Subnets
11. How many host addresses can be used in a Class C network?
A. 253
B. 254
C. 255
D. 256
12. How many subnets can a Class B network have?
A. 16
B. 256
C. 128
D. None of the above
13. What is the minimum number of bits that can be borrowed to form a subnet?
A. 1
B. 2
C. 4
D. None of the above
14. What is the primary reason for using subnets?
A. To reduce the size of the collision domain
B. To increase the number of host addresses
C. To reduce the size of the broadcast domain
D. None of the above
15. How many bits are in a subnet mask?
A. 16
B. 32
C. 64

D. None of the above
16. Performing the Boolean function as a router would on the IP addresses 131.8.2.5
and 255.0.0.0, what is the network/subnetwork address?
A. 131.8.1.0
B. 131.8.0.0
C. 131.8.2.0
D. None of the above
1102.book Page 472 Tuesday, May 20, 2003 2:53 PM
Check Your Understanding 473
17. How many bits can be borrowed to create a subnet for a Class C network?
A. 2
B. 4
C. 6
D. None of the above
18. With a Class C address of 197.15.22.31 and a subnet mask of 255.255.255.224,
how many bits have been borrowed to create a subnet?
A. 1
B. 2
C. 3
D. None of the above
19. Performing the Boolean function as a router would on the IP addresses
172.16.2.120 and 255.255.255.0, what is the subnet address?
A. 172.0.0.0
B. 172.16.0.0
C. 172.16.2.0
D. None of the above
20. Which of the following best describes one function of Layer 3, the network layer,
in the OSI model?
A. It is responsible for reliable network communication between nodes.
B. It is concerned with physical addressing and network topology.

C. It determines which is the best path for traffic to take through the network.
D. It manages data exchange between presentation layer entities.
21. What function allows routers to evaluate available routes to a destination and to
establish the preferred handling of a packet?
A. Data linkage
B. Path determination
C. SDLC interface protocol
D. Frame Relay
1102.book Page 473 Tuesday, May 20, 2003 2:53 PM
474 Chapter 8: Routing Fundamentals and Subnets
22. How does the network layer forward packets from the source to the destination?
A. By using an IP routing table
B. By using ARP responses
C. By referring to a name server
D. By referring to the bridge
23. What are the two parts of a network layer address that routers use to forward
traffic through a network?
A. Network address and host address
B. Network address and MAC address
C. Host address and MAC address
D. MAC address and subnet mask
1102.book Page 474 Tuesday, May 20, 2003 2:53 PM
1102.book Page 475 Tuesday, May 20, 2003 2:53 PM
Objectives
Upon completion of this chapter, you will be able to
■ Describe the functions of the TCP/IP transport layer
■ Describe flow control
■ Describe the processes of establishing a connection between peer systems
■ Describe windowing
■ Describe acknowledgment

■ Identify and describe transport layer protocols
■ Describe the Transmission Control Protocol (TCP) header format and
port numbers
■ Describe the User Datagram Protocol (UDP) header format and port numbers
1102.book Page 476 Tuesday, May 20, 2003 2:53 PM
Chapter 9
TCP/IP Transport and
Application Layer
The transport layer uses the services provided by the network layer, such as best-path
selection and logical addressing, to provide end-to-end communication between source
and destination. This chapter describes how the transport layer regulates the flow of
information from source to destination reliably and accurately. The primary characteristics
of the transport layer are discussed, including the following:
■ The transport layer data stream is a logical connection between the endpoints of a
network.
■ End-to-end control and reliability are provided by sliding windows, sequencing
numbers, and acknowledgments.
■ Layer 4 protocols TCP and UDP use port numbers to keep track of different conver-
sations that cross the network at the same time, and to pass information to the
upper layers.
The primary characteristics of the TCP/IP application layer include the following:
■ End-user applications reside at this layer.
■ Commonly used applications include NFS, DNS, ARP, rlogin, talk, FTP, NTP, and
traceroute.
Please be sure to look at this chapter’s associated e-Lab Activities, Videos, and Photo-
Zooms that you will find on the CD-ROM accompanying this book. These CD elements
are designed to supplement the material and reinforce the concepts introduced in this
chapter.
1102.book Page 477 Tuesday, May 20, 2003 2:53 PM
478 Chapter 9: TCP/IP Transport and Application Layer

Understanding the TCP/IP Transport Layer
The phrase “quality of service” often is used to describe the purpose of Layer 4, the
transport layer. UDP, which is covered later, also operates at Layer 4 and provides con-
nectionless transport services. However, the primary protocol operating at this layer
is connection-oriented TCP. Its main function is to transport and regulate the flow of
information from source to destination reliably and accurately. The primary duties of
the transport layer are to provide end-to-end control, to provide flow control via slid-
ing windows, and to ensure reliability via sequencing numbers and acknowledgments.
To understand reliability and flow control, think of a person who speaks really fast. In
conversation, the listener might need to ask this person to repeat some words if they
are not understood (for reliability) and to speak slowly, so the listener can catch the
words (flow control), as shown in Figure 9-1.
Figure 9-1 Transport Layer Analogies
The transport layer provides transport services from the source host to the destina-
tion host. It constitutes a logical connection between the endpoints of the network.
Transport services segment and reassemble data that is sent by several upper-layer
applications onto the same transport layer data stream. This transport layer data
stream provides end-to-end transport services.
The transport layer data stream is a logical connection between the endpoints of a net-
work. The transport layer defines end-to-end connectivity between host applications.
Figure 9-2 illustrates the transport layer.
1102.book Page 478 Tuesday, May 20, 2003 2:53 PM