Lesson 3

Selecting Network/Transport Layer Protocols

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Lesson 3: Selecting Network/Transport Layer Protocols

Once you have selected a data-link layer protocol for your network, your concerns for

the physical infrastructure are finished. It is now time to move upward in the OSI ref-

erence model and select the protocols for the network and transport layers and above.

There is no need to be concerned about protocol compatibility at this point, because

all the data-link layer protocols in current use can function with any network/transport

layer protocol combination.

After this lesson, you will be able to

■ Describe the circumstances under which you should use the three network/transport

layer protocol options supported by Microsoft Windows operating systems

Estimated lesson time: 15 minutes

Windows Server 2003 (like all current Windows operating systems) includes support

for three network/transport layer protocol combinations: TCP/IP, Internetwork Packet

Exchange (IPX), and the NetBIOS Extended User Interface (NetBEUI). The operating

systems can function with any or all of these protocols installed at the same time. TCP/

IP and IPX are both collections of protocols (called protocol suites) that function

together to provide services that span several layers of the OSI reference model. Both

TCP/IP and IPX include network and transport layer protocols, and depending on the

functions a computer is performing, the services provided by the protocol suite can at

times run all the way up to the application layer. NetBEUI is a monolithic protocol that

provides basic network functionality but is not nearly as flexible as TCP/IP or IPX.

Using TCP/IP

TCP/IP is a large collection of protocols that provides a comprehensive array of net-

working services in addition to basic Windows file sharing. For most network design-

ers, the process of selecting protocols for the network and transport layers is a brief

one, because TCP/IP is the only logical selection. Only TCP/IP provides the flexibil-

ity, expandability, and Internet compatibility that most networks require. The TCP/IP

protocols were designed in the 1970s to support the experimental packet-switching

network that eventually became the Internet. Because this network consisted of

many different types of computers, the protocols were designed to be completely

hardware-independent. This is why the TCP/IP protocols have their own indepen-

dent addressing system.

The two primary protocols in the TCP/IP suite are the Internet Protocol (IP), which

operates at the network layer, and the Transmission Control Protocol (TCP), which

operates at the transport layer. There is a second transport-layer protocol called the User

Datagram Protocol (UDP). Virtually all TCP/IP communications use the IP protocol at