There are several other network protocols that may be involved in a network environment. We'll mention them here, but we won't go into detail about them as they are not as common in UNIX environments as IP networks are. If you are curious about these other network protocols, we suggest that you consult a good book on networks and protocols; several are listed in Appendix D. Several of these protocols can share the same physical network as an IP-based network, thus allowing more economical use of existing facilities, but they also make traffic more available to eavesdroppers and saboteurs.
Novell Netware networks use a proprietary protocol known as Internet Packet eXchange protocol (IPX). It does not scale well to large networks such as the Internet, although RFC1234 describes a system for connecting IPX networks together using IP networks and a technique known as tunneling.
IPX is commonly found in PC-based networks. Some UNIX vendors support IPX-based services and connections with their products.
The System Network Architecture (SNA) is an old protocol used by IBM to link mainframes together. It is seldom found elsewhere. These days, IBM machines are in the process of transitioning to IP or IPX. We expect that SNA will be extinct before too long.
The DECnet protocol was developed at Digital Equipment Corporation to link together machines and is based on Digital's proprietary operating systems. DECnet provides many of the same basic functions as IP, including mail, virtual terminals, file sharing, and network time. During its heyday, many third parties also built peripherals to support DECnet. Many large DECnet networks have been built, but the trend within Digital has been to migrate to open standards such as IP.
The Open System Interconnection (OSI) protocols, developed by the International Standards Organization (ISO), are an incredibly complex and complete set of protocols for every kind of network implementation. OSI was developed after TCP/IP, and supports many of the same kinds of services.
OSI is a classic example of what happens when a committee is asked to develop a complex specification without the benefit of first developing working code. Although many organizations have stated that they intend to switch from IP to OSI standards, this has not happened except for a few high-level services, such as X.500 directory service and cryptographic certificates. On matters such as data transmission, the OSI standards have in general proven to be too cumbersome and complex to fully implement efficiently.
We are clearly not big fans of OSI, but if you are interested in pursuing all the gory details, an excellent book on the topic (which will give you a fairer treatment of OSI than we do here) is The Open Book: A Practical Perspective on OSI by Marshall T. Rose (Prentice Hall, 1990).
The Xerox Network Systems (XNS) protocol family was developed by Xerox. These were supported by a few other computer manufacturers, but few people use them now. Development inside Xerox has largely switched over to IP as well.