Lesson 4: Other Common Protocols

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This lesson provides a summary of several of the lesser, yet most commonly used, protocols.

After this lesson, you will be able to:

• Identify several of the more common protocols.
• Determine which protocol is best suited for the network scenario.

Estimated lesson time: 15 minutes

Network Basic Input/Output System (NetBIOS)

Most of the services and applications that run within the Windows operating system use the NetBIOS interface or interprocess communication (IPC). NetBIOS was developed on LANs and has evolved into a standard interface for applications to use to access networking protocols in the transport layer for both connection-oriented and nonconnection-oriented communications. NetBIOS interfaces exist for NetBEUI, NWLink, and TCP/IP. NetBIOS requires an IP address and a NetBIOS name to uniquely identify a computer.

NetBIOS performs four primary functions:

• NetBIOS name resolution Each workstation on a network has one or more names. NetBIOS maintains a table of the names and any aliases. The first name in the table is the unique name of the NIC. Optional user names can be added to provide a user-friendly identification system. NetBIOS then cross-references the names as required.
• NetBIOS Datagram service This function allows a message to be sent to any name, group of names, or to all users on the network. However, because this does not use point-to-point connections, there is no guarantee that the message will arrive at its destination.
• NetBIOS Session service This service opens a point-to-point connection between two workstations on the network. One workstation initiates a call to another and opens the connection. Because both workstations are peers, they both can send and receive data concurrently.
• NetBIOS NIC/session status This function makes information about the local NIC, other NICs, and any currently active sessions available to any application software using NetBIOS.

Originally, IBM offered NetBIOS as a separate product, implemented as a terminate-and-stay-resident (TSR) program. This TSR program is now obsolete; if you should encounter one of these systems, you should replace it with the Windows NetBIOS interface.

NetBEUI

NetBEUI is the acronym for NetBIOS Extended User Interface. Originally, NetBIOS and NetBEUI were tightly tied together and considered one protocol. However, several network manufacturers separated out NetBIOS, the session-layer protocol, so that it could be used with other routable transport protocols. NetBIOS (network basic input/output system) is an IBM session-layer LAN interface that acts as an application interface to the network. NetBIOS provides the tools for a program to establish a session with another program over the network and, because so many application programs support it, it is very popular.

NetBEUI is a small, fast, and efficient transport-layer protocol that is supplied with all Microsoft network products. It has been available since the mid-1980s and was supplied with the first networking product from Microsoft: MS-NET.

Advantages of NetBEUI include its small stack size (important for computers running MS-DOS), its speed of data transfer on the network medium, and its compatibility with all Microsoft-based networks.

The major disadvantage of NetBEUI is that it does not support routing. It is also limited to Microsoft-based networks. NetBEUI is a good and economical solution for a small peer-to-peer network where all workstations use Microsoft operating systems.

X.25 Packet Switching

A set of WAN protocols, X.25 is incorporated in a packet-switching network made up of switching services. The switching services were originally established to connect remote terminals to mainframe host systems. The network breaks up each transmission into multiple packets and places them on the network. The pathway between nodes is a virtual circuit that looks like a single, continuous, logical connection to the upper layers. Each packet can take different routes from the source to the destination. After the packets arrive, they are reassembled into their original data message.

A typical packet includes 128 bytes of data; however, the source and destination can negotiate a different packet size after making the virtual connection. The X.25 protocol can support a theoretical maximum of 4095 concurrent virtual circuits across a physical link between a node and the X.25 network. Typical data-transmission speed for X.25 is 64 Kbps.

The X.25 protocol works in the physical, data-link and network layers of the OSI reference model. It has been around since the mid-1970s and has been well debugged; therefore, it is a stable network environment. It does, however, have two shortcomings:

• The store-and-forward mechanism causes delays. Typically, the delay is about .06 second and has no effect on large blocks of data. However, in a flip-flop type of transmission, the delay might be noticeable.

NOTE

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A "flip-flop" is a circuit that alternates between two possible states when a pulse is received at the input. For example, if the output of a flip-flop is high and a pulse is received at the input, the output "flips" to low; a second input pulse "flops" the output back to high, and so on.

• A large amount of buffering is required to support the store-and-forward data transfer.

X.25 and TCP/IP are similar in that they both use packet-switched protocols. However, there are several differences between the two:

• TCP/IP has only end-to-end error checking and flow control; X.25 has error checking from node to node.
• To compensate for the fact that a TCP/IP network is completely passive, TCP/IP has a more complicated flow control and window mechanism than X.25 has.
• X.25 has tightly specified the electrical and link levels; TCP/IP is designed to travel over many different kinds of media, with many different types of link service.

Xerox Network System (XNS)

Xerox developed Xerox Network System (XNS) for its Ethernet LANs. XNS became widely used in the 1980s, but has been slowly replaced by TCP/IP. It is a large, slow protocol, but produces more broadcasts, causing more network traffic.

Advanced Program-to-Program Communication (APPC)

Advanced Program-to-Program Communication (APPC ) is IBM's transport protocol developed as part of its Systems Network Architecture (SNA). It was designed to enable application programs running on different computers to communicate and exchange data directly.

AppleTalk

AppleTalk is Apple Computer's proprietary protocol stack designed to enable Apple Macintosh computers to share files and printers in a networked environment. It was introduced in 1984 as a self-configuring LAN technology. AppleTalk is also available on many UNIX systems that use third-party freeware and commercial packages. The AppleTalk protocol suite encompasses high-level file sharing using AppleShare, LaserWriter printing services and print spoolers, along with lower-level data streams and simple datagram delivery. Table 6.4 illustrates AppleTalk features.

Table 6.4 AppleTalk Protocols

AppleTalk Type	Description
AppleTalk	A collection of protocols that correspond to the OSI reference model. It supports LocalTalk, EtherTalk, and TokenTalk.
LocalTalk	Describes the simple, shielded, twisted-pair cable used to connect Macintoshes to other Macintoshes or printers. A LocalTalk segment supports a maximum of 32 devices and operates at a speed of 230 Kbps.
EtherTalk	AppleTalk over Ethernet. It operates at a speed of 10 Mbps. Fast EtherTalk operates at a speed of 100 Mbps.
TokenTalk	AppleTalk over Token-Ring. Depending on its hardware, TokenTalk operates at either 4 Mbps or 16 Mbps.

Figure 6.6 shows a typical AppleTalk network including an Ethernet connection.

Figure 6.6 AppleTalk network

OSI Protocol Suite

The OSI protocol suite is a complete protocol stack. Each protocol maps directly to a single layer of the OSI reference model. The OSI protocol suite includes routing and transport protocols, IEEE 802 series protocols, a session-layer protocol, a presentation-layer protocol, and several application-layer protocols designed to provide full networking functionality, including file access, printing, and terminal emulation.

DECnet

DECnet is Digital Equipment Corporation's proprietary protocol stack. It is a set of hardware and software products that implement the Digital Network Architecture (DNA). It defines communication networks over Ethernet LANs, Fiber Distributed Data Interface metropolitan area networks (FDDI MANs), and WANs that use private or public data-transmission facilities. DECnet can also use TCP/IP and OSI protocols as well as its own protocols. It is a routable protocol.

DECnet has been updated several times; each update is called a "phase." The current revision is DECnet Phase V, and the protocols used are both proprietary to Digital and offer a fairly complete implementation of the OSI protocol suite.

Lesson Summary

The following points summarize the main elements of this lesson:

• Many protocols are used for networking; each has unique advantages and disadvantages.
• NetBIOS and NetBEUI are commonly used for Microsoft-based, peer-to-peer networks.
• NetBIOS and NetBEUI are nonroutable protocols.
• X.25 is a protocol for packet switching.
• AppleTalk is the protocol developed for Macintosh networks.
• DECnet is Digital Equipment Corporation's proprietary protocol stack.

Exercise 6.4: Protocol Matching Problem

Along with the better-known protocols, many other lesser, but still common, protocols exist. Five such protocols are listed below. In this exercise, you will be matching each of the protocols in the list that follows with the feature that describes what it does.

Five common protocols

1. AppleTalk
2. DECnet
3. NetBEUI
4. NetBIOS
5. X.25

In each blank space on the left, fill in the letter of the protocol that uses the feature listed on the right. Note that more than one protocol can be matched to a particular feature.

______________ A protocol that is commonly used for Microsoft-based, peer-to-peer networks

______________ A protocol used for packet switching

______________ A protocol that is commonly used for Macintosh networks

______________ A protocol designed by Digital Equipment Corporation (DEC)

______________ A protocol originally offered by IBM

______________ A small, fast, transport-layer protocol

______________ A protocol that is nonroutable

Answers