NETWORKING CONCEPTS

COMPARISON OF OSI AND TCP/IP Common features Both are based on the concept of stack of independent protocols Functionality of layers is roughly similar In both models the layers up through and including the transport layer are there to provide an end-to-end, network- independent transport service to processes wishing to communicate in both models, the layers above transport are application-oriented users of the transport service

COMPARISON OF OSI AND TCP/IP Differences 1. Three concepts are central to the OSI model: 1. Services. 2. Interfaces. 3. Protocols. Services. The service definition tells what the layer does, not how entities above it access it or how the layer works Interface tells the processes above it how to access it

COMPARISON OF OSI AND TCP/IP The TCP/IP model did not originally clearly distinguish between services, interfaces, and protocols protocols in the OSI model are better hidden than in the TCP/IP model and can be replaced relatively easily as the technology changes 2. The OSI reference model was devised before the corresponding protocols were invented With TCP/IP the reverse was true: the protocols came first, and the model was really just a description of the existing protocols

COMPARISON OF OSI AND TCP/IP 3. Difference between the two models is the number of layers: the OSI model has seven layers and the TCP/IP model has four. 4. The OSI model supports both connectionless and connection oriented communication in the network layer, but only connection-oriented communication in the transport layer The TCP/IP model supports only one mode in the network layer (connectionless) but both in the transport layer

A CRITIQUE OF OSI OSI model never became a popular one Reasons are 1. Bad timing. 2. Bad technology. 3. Bad implementations. Bad timing. The time at which a standard is established is absolutely critical to its success.

A CRITIQUE OF OSI This figure shows the amount of activity surrounding a new subject.

A CRITIQUE OF OSI When the subject is first discovered, there is a burst of research activity in the form of discussions, papers, and meetings. After a while this activity subsides(less intense), corporations discover the subject, and the billion- dollar wave of investment hits. standards be written in the trough in between these two If they are written too early (before the research results are well established), the subject may still be poorly understood; the result is a bad standard.

A CRITIQUE OF OSI If they are written too late, so many companies may have already made major investments in different ways of doing things that the standards are effectively ignored. If the interval between the two is very short (because everyone is in a hurry to get started), the people developing the standards may get crushed(deform). It now appears that the standard OSI protocols got crushed The competing TCP/IP protocols were already in widespread use by research universities by the time the OSI protocols appeared.

A CRITIQUE OF OSI Bad Technology The OSI model, along with its associated service definitions and protocols, is extraordinarily complex. They are difficult to implement and ineffient in operation. Problem with OSI is that some functions, such as addressing, flow control, and error control, reappear again and again in each layer. Bad implementation Because of complexity of models and protocols initial implementations were huge, unwidely and slow. In contrast, one of the implementation of TCP/IP was good and people began using it quickly which led to a large user community

Bad politics OSI was widely thought to be the creature of the European telecommunication ministries, the European Community, and later the U.S. Government. This belief was only partly true, but the very idea of a bunch of government bureaucrats trying to shove(push roughly) a technically inferior {lower in quality)standard down the throats of the poor researchers and programmers down in the trenches (channel)actually developing computer networks did not help much.

A CRITIQUE OF TCP/IP First, the model does not clearly distinguish the concepts of services, interfaces, and protocols. Second, the TCP/IP model is not at all general and is poorly suited to describing any protocol stack other than TCP/IP. Trying to use the TCP/IP model to describe Bluetooth, for example, is completely impossible. Third,the host-to-network layer is not really a layer in the normal sense of the term used in the context of layered protocols. Fourth, TCP/IP model does not distinguish between the physical and data link layers. A proper model should include both as separate layers. The TCP/IP model does not do this.

NOVEL NETWARE Novell NetWare is the most popular network system in the PC world. It provides transparent remote file access and numerous other distributed network services, including printer sharing and support for various applications such as electronic mail transfer. NetWare was developed by Novell, Inc., and introduced in the early 1980s. Novell Networks are based on the client/server model in which at least one computer functions as a network file server, which runs all of the NetWare protocols and maintains the networks shared data on one or more disk drives

NOVEL NETWARE PROTOCOL SUITE Novell provides a suite of protocols developed specifically for NetWare. The five main protocols used by NetWare are Media Access Protocol. Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX). Routing Information Protocol (RIP). Service Advertising Protocol (SAP). NetWare Core Protocol (NCP).

Media Access Protocols: The NetWare suite of protocols supports several media-access protocols, including Ethernet/IEEE 802.3, Token Ring/IEEE 802.5, Fiber Distributed Data Interface (FDDI), and Point-to-Point Protocol (PPP)

IPX(Internetwork Packet Exchange protocol): Routing and networking protocol at Network layer. When a device to be communicated whith is located on a different network, IPX routes the information to the destination through any intermediate networks. It datagram-based, connectionless, unreliable protocol that is equivalent to the IP

SPX(Sequenced Packet Exchange protocol): Control protocol at the transport layer (layer 3) for reliable, connection-oriented datagram transmission. SPX is similar to TCP in the TCP/IP suite

Routing Information Protocol (RIP): Facilitate the exchange of routing information on a NetWare network. 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

Service Advertisement Protocol (SAP): It is an IPX protocol through which network resources, such as file servers and print servers, advertise their addresses and the services they provide. Advertisements are sent via SAP every 60 seconds. This SAP packet contains information regarding the servers which provide services. Using these SAP packets, clients on the network are able to obtain the internetwork address of any servers they can access

NetWare Core Protocol (NCP): It 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.