NetWare IPX/SPX

NetWare IPX/SPX

The protocols utilized with NetWare are summarized in Figure 5.4. The NetWare protocols have been designed with a high degree of modularity. This modularity makes the NetWare protocols adaptable to different hardware and simplifies the task of incorporating other protocols into the suite. Windows NT doesn’t use the IPX/SPX suite to communicate with NetWare resources. Microsoft instead developed a clone of IPX/SPX called NWLink IPX/SPX Compatible Transport. IPX/SPX is generally smaller and faster than TCP/IP and, like TCP/IP, it is routable.

The Internetwork Packet Exchange Protocol (IPX) is a Network layer protocol that provides connectionless (datagram) service. (IPX was developed from the XNS protocol originated by Xerox.) As a Network layer protocol, IPX is responsible for internetwork routing and maintaining network logical addresses. Routing uses the RIP protocol (described later in this section) to make route selections.

IPX relies on hardware physical addresses found at lower layers to provide network device addressing. IPX also uses sockets, or upper-layer service addresses, to deliver packets to their ultimate destinations. On the client, IPX support is provided as a component of the older DOS shell and the current DOS NetWare requester.

The Router Information Protocol (RIP) uses the distance-vector route discover method to determine hop counts to other devices. Like IPX, RIP was developed from a similar protocol in the XNS protocol suite. RIP is implemented as an upper-layer service and is assigned a socket (service address). RIP is based directly on IPX and performs Network layer functions.

Sequenced Packet Exchange (SPX) is a Transport layer protocol that extends IPX to provide connection-oriented service with reliable delivery. Reliable delivery is ensured by retransmitting packets in the event of an error. SPX is derived from a similar SPX protocol in the XNS network protocol suite.

SPX establishes virtual circuits called connections. The connection ID for each connection appears in the SPX header. A given upper-layer process can be associated with multiple-connection IDs.

SPX is used in situations where reliable transmission of data is needed. SPX sequences the packets of data. Missing packets or packets that don’t arrive in the order in which they were sent are detected immediately. In addition, SPX offers connection multiplexing, which is used in the printing environment. Many accounting programs, for example, call upon the services of SPX to ensure that data is sent accurately. On the client, SPX support is provided as a component of the older DOS shell and of the current NetWare requester.

The NetWare Core Protocol (NCP) provides numerous function calls that support network services, such as file service, printing, name management, file locking, and synchronization. NetWare client software interfaces with NCP to access NetWare services.

NCP is a high-level protocol built into the NetWare operating system kernel. NCP covers aspects of the Session, Presentation, and Application layers of the OSI reference model and has its own miniature language that programmers use when writing applications for the NetWare environment. The commands that NCP understands are associated primarily with access to files and directories on a file server.