NetWare is a network operating system (NOS) and related support services environment created by Novell.
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It was introduced to the market in the early 1980s.
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NetWare's networking technology was derived from Xerox Networks Systems (XNS), a networking system developed by the Xerox Corporation in the late 1970s.
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Today, NetWare is used worldwide.
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As internetwork connections increase, NetWare and its supporting protocols often operate on the same physical channel as other popular protocols such as

• TCP/IP
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• DECnet
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• AppleTalk
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As a NOS environment, NetWare provides support for

• file sharing
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• printer sharing
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• electronic mail transfer
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• database access
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NetWare is based on a client-server architecture.
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Clients or workstations request services such as file and printer access from servers.
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NetWare clients and servers can be represented by virtually any kind of computer system, from PCs to mainframes.
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In the client-server system remote network access is transparent to the user.
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This is accomplished through remote procedure calls.
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A server receives a procedure call from a local computer program running on a client or workstation.
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The server then executes the remote procedure call and returns the requested information to the local computer client.
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Novell's Internetwork Packet Exchange (IPX) is a proprietary protocol derived from the Xerox Network Systems (XNS) protocol.
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Novell Internetwork Packet Exchange (IPX) - functioning at the heart of the NetWare protocol suite - is the original network layer protocol used to route packets through an internetwork.
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IPX is a connectionless datagram-based network protocol and as such is similar to the Internet Protocol (IP) found in Transmission Control Protocols (TCP/IP) networks.
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The Novell/IPX protocol stack corresponds loosely to the OSI model but does not map exactly onto it.
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NetWare protocol designers wanted to provide a high level of functionality rather than adhering strictly to existing standards.
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As a NOS environment, NetWare specifies the upper five layers of the OSI reference model.
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The Novell/NetWare protocols can be grouped as shown.
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The NetWare Core Protocol (NCP) corresponds roughly to the OSI application, presentation, and session layers.
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The Network Basic Input/Output System (NetBIOS) emulator corresponds roughly to the session and transport layers, although it is usually known as a session layer interface specification.
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Servers and routers use the Service Advertisement Protocol (SAP) to advertise their services and network addresses.
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So SAP corresponds to the OSI transport and network layers as well as the upper layers.
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Sequenced Packet Exchange (SPX) is a transport layer protocol.
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Internet Packet Exchange (IPX), Routing Information Protocol (RIP) and Novell Link Services Protocol (NLSP) are network layer protocols.
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At the lower layer are the media access control (MAC) protocols on which Novell IPX can run.
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These are

• Ethernet/IEEE 802.3
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• Token Ring/IEEE 802.5
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• Fiber Distributed Data
  Interface (FDDI)
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• ARCnet
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• Point-to-Point protocol (PPP)
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The higher level protocols such as NetBIOS, SAP, NCP, SPX, NLSP, and RIP rely on the MAC protocols and IPX to handle lower level communications, for example, node addressing.
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Novell IPX is a network layer/Transport layer protocol.
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It defines internetwork and internode addresses, and routes packets in an IPX internetwork.
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To communicate with devices on different networks, IPX routes the information through intermediate networks.
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IPX uses the physical device address of the underlying hardware and its socket, that is, a service address, to address the packet to its final node destination.
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Novell IPX is also a datagram connectionless protocol.
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A datagram is a logical grouping of information sent as a network layer unit over a transmission medium without prior establishment of a virtual circuit.
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So when processes running on two separate nodes use IPX to communicate, no connection is established between the nodes before data is transmitted.
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Because it is a connectionless protocol, IPX does not require an acknowledgment for each packet sent.
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IPX uses the services of the dynamic distance vector routing protocol, Routing Information Protocol (RIP), or the link state routing protocol, NetWare Link Services Protocol (NLSP).
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RIP is used by Novell IPX to route packets in an internetwork.
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RIP uses IPX and the Media Access Control (MAC) protocols for its transport.
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The IPX RIP metrics used for making decisions on the optimal path are

• ticks (a time measure)
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• hop count
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The tick metric, in principle is the delay expected when using a particular path length.
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One tick is 1/18th of a second.
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In the case of two paths with an equal tick count, IPX RIP uses the hop count, the passage of a packet through a router, as the tie breaker.
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Routing updates are sent at 60-second intervals.
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The high frequency of updates can cause excessive overhead traffic on some internetworks.
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For more on IPX RIP and NLSP see the CBT Systems course ^RImplementing IPX RIP and NLSP on Cisco Routers^r.
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Novell IPX uses the proprietary Service Advertisement Protocol (SAP) to advertise network services.
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SAP allows nodes such as file servers or print servers to advertise both their addresses and the services they provide.
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Servers running SAP identify themselves and advertise their services by broadcasting a service identification packet.
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Advertisements are sent via SAP every 60 seconds.
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Services are identified by a hexadecimal number which is called a SAP identifier, for example 4=file server and 7=printer server.
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Routers gather this information and share it with other routers.
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Workstations on the network can utilize SAP to determine which services are available on the network.
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This information is obtained by using a service query packet.
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Workstations can reference information in the IPX header to find a service address with which to initiate a session.
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Novell has introduced a link-state protocol called Novell Link Services Protocol (NLSP) intended to replace RIP and SAP.
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NLSP was derived from ISO's Intermediate System-to-Intermediate System (IS-IS) protocol.
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NLSP routers exchange information to maintain a logical map of the internetwork.
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This information includes

• connectivity states
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• path costs
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• maximum transmission unit size
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• media types
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The Sequenced Packet Exchange (SPX) is a reliable connection-oriented protocol that supplements the datagram service provided by IPX, NetWare's network layer protocol.
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Under a connection-oriented protocol, data transfer must occur over a virtual circuit.
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So SPX supplements the datagram service provided by network layer protocols and provides the packet verification lacking in IPX routing.
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The upper layer NetWare Core Protocol (NCP) is used by IPX to provide client-to-server connections and applications.
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Services provided by NCP include

• file access
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• printer access
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• name management
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• accounting
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• security
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• file synchronization
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As well as having its own protocol suite, Novell IPX supports a number of other upper layer protocols and applications.
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For example Novell IPX supports the Network Basic Input/Output System (NetBIOS) session-layer interface specification from IBM and Microsoft.
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Novell's NetBIOS emulation software allows programs written to the industry-standard NetBIOS interface to run within the NetWare system.
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Novell IPX can run on any of the following lower layer media access control (MAC) protocols

• Ethernet/IEEE 802.3
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• Token Ring/IEEE 802.5
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• Fiber Distributed Data
  Interface (FDDI)
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• ARCnet
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• Point-to-Point Protocol (PPP)
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Ethernet and IEEE 802.3 specify similar technologies.
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They are both carrier-sense multiple access/collision detection (CSMA/CD) LANs.
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CSMA/CD stations are those that can detect transmission collisions occurring when two stations simultaneously transmit over a network.

So CSMA/CD stations know when data should be retransmitted.
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Today the term Ethernet is applied to all CSMA/CD LANs, including IEEE 802.3, that generally conform to Ethernet specifications.
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Ethernet itself provides services which correspond to the physical and data-link layers of the OSI model.
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The data-link layer in the OSI model corresponds to two sublayers, logical link control (LLC) and media access control (MAC), in IEEE architecture.
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IEEE 802.3 specifies the physical layer and the media-access portion of the OSI data-link layer.
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However it does not define a logical link control protocol.
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So there are very slight differences between Ethernet and IEEE 802.3 in relation to the OSI model as modified by IEEE.
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The term Token Ring is generally used to refer to IBM's Token Ring network and IEEE 802.5 networks.
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The associated protocols use the token passing media access method.
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A small frame called a token is moved around the network.
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Token Ring specifies the physical layer and the MAC, but not the LLC section of the data link layer.
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FDDI is similar to Token Ring/IEEE 802.5 as it also uses the token passing media access method.
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It is based on the structure of two rings, one to move data and one to perform backup and other services.
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The FDDI ANSI standard consists of four parts.
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The Physical Media Dependent (PMD) and the Physical layer (PHY) correspond to the physical layer of the OSI model.
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The Media Access Control (MAC) corresponds to the lower half of the OSI data-link layer.
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The fourth part is Station Management which fixes faults on the ring, gets data on and off the ring, and generates data.
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Attached Resource Computer Network (ARCnet) is a simple network system that supports twisted pair, coaxial, and fiber-optic cable types.
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It combines the token-passing element of Token Ring with the bus and star topologies.
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ARCnet functions map evenly to the physical and data-link layers of the OSI model.
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The Point-to-Point Protocol (PPP) also maps exactly to the data-link and physical layers of the OSI model.
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PPP provides router-to-router and host-to-host connections.
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At the data link layer it uses the Logical Link Control protocol to manage point-to-point connections.
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It also uses the High Level Data Link (HLDL) protocol as the basis of encapsulating datagrams over point-to-point links.
