Presented by:
MAHESH.P.DESAI,
SACHIN.G.KADADEVAR

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Introduction
NetWare, made by Novell, introduced in the early 1980s. Is a widely-installed network server operating system. Initially very successful in installing its products in large and small office local area networks (LANs), Novell redesigned (or at least refeatured) NetWare to work successfully as part of larger and heterogeneous networks, including the Internet. An early - and primary competitor was the Microsoft Windows NT operating system
NetWare Communications Processes
Protocols
Most computer networks require that information transferred between two nodes be broken up into blocks, called packets. This packetizing makes the information more manageable for the sending and receiving nodes, and any intermediate nodes (bridge or routers). In addition to the information, or data, that is being transferred, each packet contains control information used for error checking, addressing, and other purposes. The protocols being used on the network define the content of this control information. In most cases multiple protocols exist within a packet and the control information for each protocol serves a different purpose. When multiple protocols are used, the control information for the highest level protocol is first placed around the data, then the control information for each subsequent protocol in the protocol stack is added to the beginning and/or end of the packet. This is called enveloping. (See Figure 1.)
The enveloping pattern illustrated in Figure 1 is common in the computer communications industry but the tasks assigned to each protocol in the packet differs for different vendor's implementations. In an effort to standardize the definition of protocols--and therefore make the networking implementations of different vendors interoperable--several standards organizations have been formed by governments and corporations. One of these, the International Standards Organization (ISO), has developed a model, called the Open Systems Interconnection (OSI) model, that specifies how protocols should be defined in the future. The OSI model separates the functions required for effective computer communications (such as error checking and addressing) into seven categories, or layers. These layers are the Application, Presentation, Session, Transport, Network, Data-Link and Physical layers..
Having been defined prior to the finalization of the OSI model, the protocols used by NetWare do not all correspond exactly to the OSI model's definitions? NetWare uses a variety of protocols. Some of these protocols were developed specifically for NetWare; some are used throughout the networking industry. The protocols required for communications between NetWare workstations and file servers are the following:
Medium-access Protocols
Internet work Packet Exchange (IPX)
Routing Information Protocol (RIP)
Service Advertising Protocol (SAP)
NetWare Core Protocol (NCP)
Medium-Access Protocol Implementations
A number of medium-access protocols have been defined, many of which are used with NetWare. The focus within this document is on the implementations of medium-access protocols, the most common of which are 802.5 Token-Ring, 802.3 Ethernet, Ethernet v2.0, and Arcnet. The 802.x protocols have been defined by the Institute of Electrical and Electronic Engineers (IEEE). Ethernet v2.0 was co-developed by Xerox and Digital Equipment Corporation, and Arcnet was developed by Datapoint, Inc. These medium-access protocol implementations are primarily concerned with the transport of packets from one node to another on a single network segment.
Medium-access protocols provide bit-level error checking in the form of a cyclic redundancy check (CRC). This CRC, which is appended to every packet that is transmitted, assures that 99.9999 percent of the packets successfully received will be free of corruption. In view of this level of integrity, NetWare does not provide any additional bit-level error checking within any of its upper-level protocols. (Note that bit-level error checking checks to make sure that bits within a packet have not been corrupted. The packet-level error checking discussed later checks that complete packets are not lost.)
Medium-access protocol implementations define the addressing that distinguishes each mode on a NetWare network. This addressing is implemented within the hardware of each network interface card (NIC). To move a packet to the proper node on a network, a medium-access control (MAC) header is placed at the beginning of every packet. This header contains source and destination node address fields to indicate where the packet originated and where it is going. Each NIC checks the destination address in the MAC header of each packet sent on the network segment it is attached to. If the destination address matches the NIC's own address, or if the packet is a broadcast packet intended for all nodes, the NIC will copy the packet.
Bit-level error checking and node addressing are provided by the majority of medium-access protocol implementations. IBM's Token- Ring (802.5) implementation defines a method of routing called source routing. Source routing allows ring segments to be interconnected by bridges, allowing administrators to segment network traffic. This requries that each workstation maintain a table of routes to the nodes it is communicating with. Furthermore, routing information must be included in the MAC header of each packet it sends. This information instructs bridges how to properly forward each packet to its destination. Source routing can be used instead of or in conjunction with NetWare routing.
Internet work Packet Exchange (IPX)
The IPX protocol was adopted by Novell from Xerox Network System's (XNS) Internet Datagram Protocol. IPX is a datagram, connectionless protocol that does not require an acknowledgement for each packet sent. This packet acknowledgement, or connection control, must be provided by protocols above IPX. IPX defines internet work and intranode addressing schemes, while relying on the network hardware for the definition of node addressing.
The network number assigned in NETGEN (NetWare 2.1x) is the basis of IPX's internet work addressing. Each network segment on a NetWare internet work must be assigned a unique network number. This network number is used by routers to forward packets to their final destination segment.
The IPX intranode address comes in the form of socket numbers. Since several processes are normally operating within a node, socket numbers provide a sort of mail slot so that each process can distinguish itself to IPX. As a process needs to communicate on the network, it requests that a socket number be assigned to it. Any packets that IPX receives that are addressed to that socket are passed on to the process. Hence, socket numbers provide a quick method of routing packets within a node.
Novell has reserved several socket numbers for specific purposes. These are shown in Figure 3. Since socket numbers are internal to each node, several workstations can use the same socket number at one time without any fear of confusion. All NCP requests from workstations must be addressed to socket 451h..
The network, node, and socket addresses for both the desetination and the source are held within the packet's IPX header. The IPX header is placed after the MAC header and before the packet data. (Packet data is usually the header of a higher-level protocol.) Figure 4 illustrates the structure of an IPX packet on an 802.3 network