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1.5 TCP/IP Protocols by Name and Function

In this chapter we already looked briefly at some TCP/IP protocols. It is, however, worth summarizing each protocol formally in terms of its name and the RFC that describes it. Some of these protocols will be explored in later chapters as indicated in Table 1.6.

The following list of RFCs and protocols is not definitive. Listed are the most useful RFCs, but not all RFCs that relate to the subject, as the list is extensive for the more complex protocols. The RFC column of the table lists the chapter of this book that covers the protocol where applicable. We work down the stack from the Application layer (5), again, taking the journey that application data takes.

The Application layer has literally hundreds of applications and many protocols that the applications at this layer use. They are listed in Table 1.6 by relevant RFC, protocol name, and a brief description.

Table 1.6 Application Layer Protocol Descriptions





Chapter 11


Domain Name Service is a text-based, distributed host-to-IP address (and IP address-to-host) mapping solution based on Berkeley Internet Name Domain (BIND) library routines. It also provides, through mail exchanger (MX) information, the IP addresses and names of servers that accept inbound e-mail for given domain names.



File Transfer Protocol transfers a file by copying a complete file from one system to another system.



This service provides a remote connection and login facility, which runs over any TCP/IP network.



This service, offered by UNIX systems, enables users of one machine to connect to other UNIX systems across the Internet and to interact as though their terminals were connected directly to the machines.


Chapter 9


Dynamic Host Configuration Protocol automates the assignment of IP addresses in an organization's network.



Simple Mail Transfer Protocol transfers electronic mail messages from one machine to another.



Simple Network Management Protocol is the language that allows for the monitoring and control of network entities.



Post Office Protocol lets users collect e-mail from a POP server over any TCP/IP network. The user's host runs a POP client application, and the server runs the POP server software, which gives the user authenticated access to his or her mailbox.



Internet Message Access Protocol, like POP, lets users collect e-mail from an IMAP server over a TCP/IP network. The user's host runs an IMAP client application, and the server runs the IMAP server software, which gives the user authenticated access to his or her mailbox. IMAP4 is more powerful and offers more features than POP3.



HyperText Transfer Protocol is used by the World Wide Web to display text, pictures, sounds, and other multimedia information with a Web browser.

Table 1.7 lists the important Transport layer protocols. Chapter 7 explores these in detail.

Table 1.7 Transport Layer (4) Protocol Descriptions





Chapter 7


Transmission Control Protocol is a connection-oriented protocol that provides the full-duplex, stream service on which many application protocols depend. It is encapsulated in IP.


Chapter 7


User Datagram Protocol provides a datagram delivery to application and is encapsulated in IP.

Table 1.8 describes the protocols of the Internet layer. Chapter 4 covers ARP/RARP, and Chapters 5 and 13 cover IPv4 and IPv6, respectively.

Table 1.9 shows the Network layer protocols, with many technologies to choose from. Ethernet is by far the most important LAN technology to understand. Alternatives such as Token Ring and Token Bus exist, but they are far less important than Ethernet.

Table 1.8 Internet Layer (3) Protocol Descriptions





Chapter 4


Address Resolution Protocol defines the method used to map a 32-bit IP address to a 48-bit Ethernet address.


Chapter 4


Reverse Address Resolution Protocol is the reverse of ARP. It maps a 48-bit Ethernet address to a 32-bit IP address.



Chapters 5 and 13


Internet Protocol determines the path a datagram must take, based on the destination host's IP address.


Chapter 5


Internet Control Message Protocol communicates error messages and other controls within IP datagrams.

Table 1.9 Network Layer (2) Protocol Descriptions






Serial Line IP encapsulates IP datagrams on serial lines.


826, 894

Chapter 3



Point-to-Point Protocol transmits datagrams over serial point-to-point links.

Ethernet is a broadcast-based, contention-bus LAN technology.


Key Learning Points

  • The OSI/ISO 7-layer reference model is a generic network model.

  • The DoD 5-layer model is specifically for the TCP/IP protocol family.

  • TCP and UDP are transport protocols that provide a delivery service to the Application layer.

  • IP is an Internet layer protocol that offers a datagram-based routing service to the Transport and Application layers.

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