A Local Area Network (LAN) is a high-speed data network that covers a relatively small geographic area. It typically connects workstations, personal computers, printers, servers, and other devices. LANs offer computer users many advantages, including shared access to devices and applications, file exchange between connected users, and communication between users via electronic mail and other applications. It's introduces the various media access methods, transmission methods, topologies, and devices used in a local area network (LAN) or LAN's are used to interconnect distributed communities of computer based DTEs located within a single building or localized group of buildings. The focus is on understanding the methods and devices used in Ethernet/IEEE 802.3, Token Ring/IEEE 802.5, and Fiber Distributed Data Interface (FDDI).
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Figure 1:- Three LAN Implementations that is commonly used
This network introduces the various protocols and technologies used in wide-area network (WAN) environments. The summary here includes point to point links, circuit switching, packet switching, virtual circuits, dialup services, and WAN devices.
Objective
Local Area Network (LAN)
Local Area Network (LAN) is usually refers to a local computer network for communication usually in a common office area, physically linked together by a common file server. Example a school or office will have all of their computers linked through one network, creating their own LAN. Nevertheless, given that all the equipment is situated within a single founding, LAN's are normally installed and maintained by the organization. This assortment of devices requires simplified connectivity tailored to the demands of each device. For example, devices such as IP telephones or cameras may be powered via the LAN switch, automatically assigned an IP address, and be placed in a virtual LAN (VLAN) to securely segment them from the other devices. Wireless access points may be used to provide secure mobile access for laptop computers, scanning devices, wireless IP phones, or kiosks. Therefore they are also referred to as private data networks. Many LAN are divided into logical groups called subnets. An internet protocol ( IP) "class A" LAN can in the theory accommodate more than 10 million devices.
Wide Area Network (WAN)
Wide Area Network (WAN) is a communications network that spans a wider area than does a local area network. A system that includes computers spread across large geographical locations that are connected, usually involving several cities, states or countries. Communications connections in a WAN are typically done over modems, or satellite hookups.
Explanation of research area
Local Area Network (LAN)
LAN's are introduced to provide a private communications facility, services over a relatively limited geographic area, high data rate for computer communications, and common access to a wide range of devices and services. Security issues pertinent to LAN's are discussed. For example, LAN's share many security problems and approaches for their solutions with point-to-point conventional communications systems.
In addition, LAN's have some unique problems of their own such as:-
Universal data availability
Passive and active wiretap threats,
End-to-end access control
Security group control
Countermeasures include physical protection, and separation by physical, logical, and encryption methods. Trusted Network Interface Units, encryption, and key distribution are also discussed. Examples are discussed to illustrate the different approaches to LAN security. The examples in this study are a composite of several existing product features, selected to demonstrate the use of encryption for confidentiality, and trusted system technology for a local area network. In a typical LAN's configuration, one computer is designated as the file server. It stores all of the software that controls the network, as well as the software that can be shared by the computers attached to the network. Computers connected to the file server are called workstations. The workstations can be less powerful than the file server, and they may have additional software on their hard drives. On most LAN's, cables are used to connect the network interface cards in each computer.
A LAN's is a communications mechanism using a transmission technology suitable for relatively short distances (typically a few kilometers) at relatively high bit-per-second rates (typically greater than a few hundred kilobits per second) with relatively low error rates, which exists primarily to support data communication among suitably attached computer systems and terminals (collectively, Data terminal equipment DTE). The Data terminal equipment (DTE) are, at least in principle, heterogeneous; that is, they are not merely multiple instances of the same product. The Data terminal equipment (DTE) is assumed to communicate by means of layered protocols. Note that no assumptions are made about the particular transmission medium or the particular topology in play. LAN's media can be twisted pair wires, CATV or other coaxial-type cables, optical fibers, wireless, or whatever. LAN topologies can be "bus," "ring," "star", or "tree." The significant properties of a LAN's are the high bit transmission capacity and the good error properties.
LAN Topologies
LAN topologies define the manner in which network devices are organized. Four common LAN topologies exist: bus, ring, star, and tree. These topologies are logical architectures, but the actual devices need not be physically organized in these configurations. Logical bus and ring topologies, for example, are commonly organized physically as a star.
Bus Topology
A bus topology is a linear LAN architecture in which transmissions from network stations propagate the length of the medium and are received by all other stations. Of the three most widely used LAN implementations, Ethernet/IEEE 802.3 networks-including 100BaseT-implement a bus topology, which is illustrated in Figure 2
Figure 2:- Some Networks Implement a Local Bus Topology
Ring Topology
A ring topology is a LAN architecture that consists of a series of devices connected to one another by unidirectional transmission links to form a single closed loop. Both Token Ring/IEEE 802.5 and FDDI networks implement a ring topology. Figure 3 depicts a logical ring topology.
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Figure 3:-Some Networks Implement a Logical Ring Topology
Star Topology
A star topology is a LAN architecture in which the endpoints on a network are connected to a common central hub, or switch, by dedicated links. Logical bus and ring topologies are often implemented physically in a star topology, which is illustrated in Figure 4.
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Figure 4:- Some Networks Implement physically in a star topology
Tree Topology
A tree topology is a LAN architecture that is identical to the bus topology, except that branches with multiple nodes are possible in this case. Figure 5 illustrates a logical tree topology.
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Figure 5 illustrates a logical tree topology.
SUMMARY OF NETWORK TOPOLOGY
RING TOPOLOGY
BUS TOPLOGY
STAR TOPOLOGY
Structure
All computes and other devices are connected in a circle
There is a single central cable (backbone ) and all computers and other devices connect to it
There is a central host and all nodes connect to it
Host Existence
Depends on network needs
Depends on network needs
Yes
Connection Between Nodes
Yes
It has no connection between the nodes
No
Host Failure
Network will fail
Network still can run
Network will fail
Node Failure
Network will fail
Network still can run
Network can still run
Ease Of Troubleshooting
Depends on backbone. If there is a backbone, troubleshooting is difficult. If there is no backbone , the focus is on the two nodes not communicating
Difficult. Need to search for the problematic node one by one
Depends on the host. It is easier to repair the problematic host. However, if the nodes fail, then each node has to be searched
Ease of Adding or Removing Nodes
Difficult
Easy
Average
Number Of Nodes When Extending Network
Limited
Many
Limited
Wide Area Network (WAN)
Wide Area Network (WAN) is a geographically dispersed telecommunications network. It's generally defined as a network created to connect two or more local area networks (LAN's). wide area network (WAN) often connects multiple smaller networks, such as local area networks (LANs) or metro area networks (MAN's). The world's most popular wide area network (WAN) is the Internet. Some segments of the Internet are also wide area network (WAN) in themselves. Wide area network (WAN) is used to connect the computers in the one part of the world with the other part of the world. So the users and computers from the different parts of the world can communicate with each other. Many wide area networks (WAN's) are generally built for one organization. Other type of wide area network (WAN) networking is the Internet service providers that connect the LAN's or individual computers to the Internet. Wide area network (WAN), networks are built using the leased lines and a router is connected to the one end of the wide area Network (WAN) and a hub is connected to the other end. In order for communication to take place between the computers the mediums must be used. These mediums can be cables, Routers, Repeaters, Ethernet, Protocols and switches etc. These different mediums make the data communication possible in different scenarios. Over time, through the advent of the Internet and those companies providing services, the "carrier" who previously may only have been connecting the lowest layers, have taken on the name of "Service Provider". Today the terms "carrier" and "service provider" or "Internet Service Provider" (ISP) are sometimes used interchangeably. The ISP can provide basic local connectivity to them, and then further connectivity into the Internet. Over the past few years there has also been a blending of terms to the point that some technologies once considered Metropolitan Area Network (MAN) are now included in some wide area Network (WAN) discussions. The wide area network (WAN) of choice between carriers must of necessity be of much greater speed and capacity since it serves as the "core" of all the customer networks. Figure 6 illustrates the relationship between the common wide area network (WAN) technologies and the Open System Interconnection (OSI) model.
OSI Layers WAN Specificationhttp://www.cisco.com/en/US/i/Other/cpress_ill/CT_-_Mar_2002/CT840301.jpg
Figure 6: illustrates the relationship between the common wide area network (WAN) technologies and the Open System Interconnection (OSI) model.
Point-to-Point Links
A point-to-point link provides a single, pre-established wide area network (WAN) communications path from the customer premises through a carrier network, such as a telephone company, to a remote network. Point-to-point lines are usually leased from a carrier and thus are often called leased lines because its established path is permanent and fixed for each remote network reached through the carrier facilities. Point-to-point links are generally more expensive than shared services such as Frame Relay. Figure 7 illustrates a typical point-to-point link through a wide area network (WAN).
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Figure 7: illustrates a typical point-to-point link through a wide area network (WAN).
Circuit Switching
Switched circuits allow data connections that can be initiated when needed and terminated when communication is complete. This works much like a normal telephone line works for voice communication. Integrated Services Digital Network (ISDN) is a good example of circuit switching. When a router has data for a remote site, the switched circuit is initiated with the circuit number of the remote network. In the case of Integrated Services Digital Network (ISDN) circuits, the device actually places a call to the telephone number of the remote Integrated Services Digital Network (ISDN) circuit. When the two networks are connected and authenticated, they can transfer data. When the data transmission is complete, the call can be terminated. Figure 8 illustrates an example of this type of circuit.
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Figure 8: illustrates an example of this type of circuit.
Packet Switching
Packet switching is a wide area network (WAN) switching method in which network devices share a single point-to-point link to transport packets from a source to a destination across a carrier network. Statistical multiplexing is used to enable devices to share these circuits. Asynchronous Transfer Mode (ATM), Frame Relay, Switched Multimegabit Data Service (SMDS), and X.25 are examples of packet-switched wide area network (WAN) technologies. Figure 9 shows an example packet-switched circuit.
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Figure 9: shows an example packet-switched circuit.
Advantage
Disadvantage
Workstations do not necessarily need their own hard disk or CD-ROM drives which make them cheaper to buy than stand-alone PCs.
Special security measures are needed to stop users from using programs and data that they should not have access to.
Users can communicate with each other and transfer data between workstations very easily.
Networks are difficult to set up and need to be maintained by skilled technicians.
Workstations can share peripheral devices like printers. This is cheaper than buying a printer for every workstation.
If the file server develops a serious fault, all the users are affected, rather than just one user in the case of a stand-alone machine.
Advantage and Disadvantage of WAN
Advantage
Disadvantage
Messages can be sent very quickly to anyone else on the network. These messages can have pictures, sounds, or data included with them (called attachments).
Setting up a network can be an expensive and complicated experience. The bigger the network the more expensive it is.
Expensive things (such as printers or phone lines to the internet) can be shared by all the computers on the network without having to buy a different peripheral for each computer.
Security is a real issue when many different people have the ability to use information from other computers. Protection against hackers and viruses adds more complexity and expense.
Share information/files over a larger area.
Information may not meet local needs or interests.
Advantage and Disadvantage of LAN
