In Chapter 4, we learned that Novell's NetWare is one of the leading network architectures. In this lesson, we explore the protocols used by NetWare and how they relate to the OSI reference model.
After this lesson, you will be able to:
- Define the protocols that make up the NetWare protocol suite.
- Relate the NetWare protocols to the OSI reference model.
Estimated lesson time: 15 minutes
Like TCP/IP, Novell provides a suite of protocols developed specifically for NetWare. The five main protocols used by NetWare are:
Because these protocols were defined well before the finalization of the OSI reference model, they do not exactly match OSI. Figure 6.5 provides mapping of the NetWare protocols to the OSI reference model. In actuality, no direct correlation to the layer boundaries of the two architectures exists. These protocols follow an enveloping pattern. More specifically, the upper-lever protocols (NCP, SAP, and RIP) are enveloped by IPX/SPX. A Media Access Protocol header and trailer then envelop IPX/SPX.
Figure 6.5 Comparing NetWare and OSI reference models
Media Access Protocols define the addressing that distinguishes each node on a NetWare network. The addressing is implemented on the hardware or NIC. The most common implementations are:
This protocol is responsible for placing the header on the packet. Each header includes the source and destination code. After the packet has been transmitted and is on the media, each network card checks the address; if their address matches the destination address on the packet, or, if the packet is a broadcast message, the NIC copies the packet and sends it up the protocol stack.
In addition to addressing, this protocol provides bit-level error checking in the form of a cyclical redundancy check (CRC). With the CRC appended to the packet, it is virtually certain that all the packets will be free of corruption.
CRC error checking uses a complex calculation to generate a number based on the data transmitted. The sending device performs the calculation before transmission and includes it in the packet that it sends to the receiving device. The receiving device repeats the same calculation after transmission. If both devices obtain the same result, it is assumed that the transmission was error-free. The procedure is known as a redundancy check because each transmission includes not only data but extra (redundant) error-checking values.
Internetwork Packet Exchange (IPX) defines the addressing schemes used on a NetWare network, and Sequenced Packet Exchange (SPX) provides security and reliability to the IPX protocol. IPX is a datagram-based, connectionless, unreliable, network-layer protocol that is equivalent to the IP. It does not require an acknowledgement for each packet sent. Any acknowledgement control or connection control must be provided by the protocols above IPX. SPX provides connection-oriented, reliable servers at the transport layer.
Using the Xerox Network System (XNS) Internet Datagram Protocol, Novell adopted IPX protocol. IPX defines two kinds of addressing:
IPX protocols are used only on networks with NetWare servers and are often installed along with another protocol suite such as TCP/IP. Even NetWare is moving toward using TCP/IP as a standard.
Facilitating the exchange of routing information on a NetWare network, RIP, like IPX, was developed from XNS. However, in RIP, an extra field of data was added to the packet to improve the decision criteria for selecting the fastest route to a destination. The broadcast of an RIP packet allows several things to occur:
The Service Advertising Protocol (SAP) allows service-providing nodes (including file servers, printer servers, gateway servers, and application servers) to advertise their services and addresses. Clients on the network are able to obtain the internetwork address of any servers they can access. With SAP, the adding and removing of services on the network becomes dynamic. By default, a SAP server broadcasts its presence every 60 seconds. A SAP packet contains:
The NetWare Core Protocol (NCP) defines the connection control and service request encoding that make it possible for clients and servers to interact. This is the protocol that provides transport and session services. NetWare security is also provided within this protocol.
This exercise is designed to help you understand the relationship between the OSI reference model and NetWare protocols. NetWare was developed earlier than the OSI reference model and, therefore, does not precisely match the seven layers. In this exercise, you will be mapping the various components of NetWare protocols to the seven layers of the OSI reference model.
In the table that follows, the column on the left lists the seven layers of the OSI reference model. The blank columns on the right represent various components of the NetWare protocol. In the blank columns, map the following NetWare protocol components to the OSI reference model.
Comparison of OSI Reference Model with NetWare Protocols
|OSI Layers||NetWare Protocols|
The following points summarize the main elements of this lesson: