UUCP (UNIX-to-UNIX Copy Protocol)
UUCP (UNIX-to-UNIX Copy Protocol) is a set of UNIX programs for copying (sending) files between different UNIX systems and for sending commands to be executed on another system. The main UUCP commands (each supported by a UUCP program) are:
- uucp, which requests the copying of a specific file to another specified system
- uux, which sends a UNIX command to another system where it is queued for execution
- uucico, which runs on a UNIX system as the program that carries out the copying and initiates execution of the commands that have been sent. Typically, this program is run at various times of day; meanwhile, the copy (uucp) and command (uux) requests are queued until the uucico program is run.
- uuxqt, which executes the commands sent by uux, usually after being started by the uucico program
The uucico programs are the programs that actually communicate across a network. There are several network protocols (variations on packet size and error-checking) that can be used by uucico programs, depending on the kinds of carrier networks being used.
Xerox Network Systems (XNS) and the OSI Model
We need to take a brief look at the Xerox Network Systems XNS model developed at Palo Alto Research Center (Parc), because several of the major LAN vendors (notably Novell and Banyan) have based portions of their NOS on the XNS model. See the Xerox Network Systems (XNS) and the OSI Model diagram below.
Figure 6-6. Xerox Network Systems (XNS) and the OSI Model
XNS Applications
XNS also defines standards for application level functions. These include the following services:
 | clearinghouse for data network resources (such as addresses) |
| authentication and security services |
| time stamping information |
| character code standards |
| document management and interchange |
| print, file and mail standards |
IPX and SPX
IPX and SPX are derived from Xerox Network Systems' IDP and SPP protocols, respectively. IPX is a network layer protocol (layer 3 of the OSI Model), while SPX is a transport layerprotocol (layer 4 of the OSI Model). The SPX layer sits on top of the IPX layer and provides connection-oriented services between two nodes on the network. SPX is used primarily byclient–server applications.
IPX and SPX both provide connection services similar to TCP/IP, with the IPX protocol having similarities to IP, and SPX having similarities to TCP. IPX/SPX was primarily designed forlocal area networks (LANs), and is a very efficient protocol for this purpose (typically SPX's performance exceeds that of TCP on a small LAN,[citation needed] as in place of congestion windows and confirmatory acknowledgements, SPX uses simple NAKs). TCP/IP has, however, become the de facto standard protocol. This is in part due to its superior performance overwide area networks and the Internet (which uses TCP/IP exclusively), and also because TCP/IP is a more mature protocol[citation needed], designed specifically with this purpose in mind.
Despite the protocols' association with NetWare, they are neither required for NetWare communication (as of NetWare 5.x), nor exclusively used on NetWare networks. NetWare communication requires an NCP implementation, which can use IPX/SPX, TCP/IP, or both, as a transport.