Local Area Network

Descriptions of LAN (Local Area Network) development andhistory, including the different existing typologies and their

characteristics.

ContentsLAN (Local Area Network)...........................................................................................3

History........................................................................................................................ 3

OSI Model................................................................................................................... 4

Layer 1: Physical layer............................................................................................4

Layer 2: Data link layer...........................................................................................4

Layer 3: Network layer............................................................................................4

Layer 4: Transport layer..........................................................................................4

Layer 5: Session layer............................................................................................4

Layer 6: Presentation layer.....................................................................................4

Layer 7: Application layer........................................................................................4

Elements of LAN.........................................................................................................5

HUB......................................................................................................................... 5

Switch...................................................................................................................... 5

Router......................................................................................................................5

LAN adapter............................................................................................................5

Server...................................................................................................................... 5

Bridge......................................................................................................................5

LAN Services...............................................................................................................6

Printing....................................................................................................................6

File........................................................................................................................... 6

Internet Connection.................................................................................................6

Wi-Fi............................................................................................................................ 6

Wireless access point..............................................................................................6

Speeds (bandwidth)................................................................................................6

Numbering.................................................................................................................. 6

IP Address................................................................................................................6

MAC Address...........................................................................................................7

LAN Topology..............................................................................................................7

Physical bus topology..............................................................................................8

Physical star topology.............................................................................................8

Physical ring topology.............................................................................................8

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Physical mesh topology...........................................................................................9

Physical hybrid topology.........................................................................................9

Star-bus................................................................................................................9

Star-ring...............................................................................................................9

Hierarchical topology..............................................................................................9

Tree topology...........................................................................................................9

Logical LAN topology.............................................................................................10

Ethernet.............................................................................................................10

Token ring...........................................................................................................10

FDDI................................................................................................................... 10

IEEE Standards......................................................................................................11

IEEE 802.3..........................................................................................................11

IEEE 802.5..........................................................................................................11

IEEE 802.4..........................................................................................................11

IEEE 802.22........................................................................................................11

Bibliography.............................................................................................................12

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LAN (Local Area Network)LAN (Local Area Network) refers to a groupof computers which are connected togetherand share some characteristics. Thisconnection is used for computers that arefound on the same room or building andtheir specific arrangement depends on thetype of connection done.

LAN connection appeared due to theincreasing demand and use of computers inuniversities and research labs in the late1960s, which generated the need toprovide high-speed interconnectionsbetween computer systems.

HistoryA number of experimental and early commercial LAN technologies were developedin the 1970s. One of the first LAN was called Cambridge Ring, and it was developedat Cambridge University in 1974. Ethernet was developed at Xerox PARC in 1973–1975. In 1976, after the system was deployed at PARC, Robert Metcalfe and DavidBoggs published a seminal paper. ARCNET was developed by Datapoint Corporationin 1976 and announced in 1977. It had the first commercial installation in December1977 in New York.

The development and proliferation of personal computers using the CP/M operatingsystem in the late 1970s, and later DOS-based systems starting in 1981, meant thatmany sites grew to dozens or even hundreds of computers. The initial driving forcefor networking was generally to share storage and printers, which were bothexpensive at the time. There was much enthusiasm for the concept and for severalyears, from about 1983 onward, computer industry pundits would regularly declarethe coming year to be, “The year of the LAN”. Typically, each vendor would have itsown type of network card, cabling, protocol, and network operating system. Asolution appeared with the advent of Novell NetWare which provided even-handedsupport for dozens of competing card/cable types, and a much more sophisticatedoperating system than most of its competitors.

During the same period, UNIX workstations were using TCP/IP based networking.Although this market segment is now much reduced, the technologies developed in

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this area continue to be influential on the Internet and in both Linux and Apple MacOS X networking—and the TCP/IP protocol has now almost completely replaced IPX,AppleTalk, NBF, and other protocols used by the early PC LANs.

OSI ModelOSI Model is a conceptual model that characterizesand standardizes the communication functions of atelecommunication or computing system withoutregard to their underlying internal structure andtechnologies; the model partitions acommunication system into abstraction layers. Theoriginal version of the model defined seven layers.

Layer 1: Physical layerThe physical layer defines the electrical andphysical specifications of the data connection. Itdefines the relationship between a device and aphysical transmission medium.

Layer 2: Data link layerThe data link layer provides node-to-node data transfer a link between two directlyconnected nodes. The node-to-node data transfer is the movement of data from onenode of a network to the next.

Layer 3: Network layerThe network layer provides the functional and procedural means of transferringvariable length data sequences from one node to another connected to the samenetwork.

Layer 4: Transport layerThe transport layer provides the functional and procedural means of transferringvariable-length data sequences from a source to a destination host via one or morenetworks, while maintaining the quality of service functions.

Layer 5: Session layerThe session layer controls the dialogues between computers. It establishes,manages and terminates the connections between the local and remote application.

Layer 6: Presentation layerThe presentation layer establishes context between application-layer entities, inwhich the application-layer entities may use different syntax and semantics if thepresentation service provides a mapping between them.

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Layer 7: Application layerThe application layer is the OSI layer closest to the end user, which means both theOSI application layer and the user interact directly with the software application.This layer interacts with software applications that implement a communicatingcomponent.

Elements of LAN

HUBThe term HUB refers to the technological device which has the capacity ofcentralizing all the connections in a certain network, especially in the case of LAN.The objective of the HUB is to expand the network to other ports using the sameprotocol, which is repeated and extended successively, in this way, all of thecomponents connected to it, can access to the information at the same time.

SwitchLAN switching is a form of packet switching used in local area networks (LAN).Switching technologies are crucial to network design, as they allow traffic to be sentonly where it is needed in most cases, using fast and hardware-based methods. LANswitching uses different kinds of network switches. A network switch is thecomponent to which all cables are connected, and it is responsible of the properfunctioning and interaction among them.

RouterA router is a networking device that forwards data packets between computernetworks. Routers perform the traffic directing functions on the Internet, for thisreason router are essential in order to provide the internet connection used in allnetworks.

LAN adapterA network interface controller is a computer hardware component that connects acomputer to a computer network. Early network interface controllers werecommonly implemented on expansion cards that plugged into a computer bus. Thelow cost and ubiquity of the Ethernet standard means that most new computershave a network interface built into the motherboard.

ServerA local area network (LAN) server is a program (and by implication usually thecomputer it runs in) that "serves" the resources (files, storage, applicationprograms, printers, and other devices) for a number of attached workstations.

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BridgeA network bridge is a computer networking device that creates a single aggregatenetwork from multiple communication networks or network segments. This functionis called network bridging. Bridging is distinct from routing, which allows multipledifferent networks to communicate independently while remaining separate.

LAN ServicesLAN connections offer main advantages to computers, as this are all connected tothe same network, some of the facilities that this offers are:

PrintingIf the Local Area Network includes an output device, such as a printer, all thecomputers connected to the network have the possibility to the access of thisservice and printing pictures or documents directly from the computer.

File Thanks to file interaction within a LAN, all of the computers can easily access to thefiles shared by the center computer. As well, each of the computers can share fileswhich can be seen by the rest of the members of the connection.

Internet ConnectionInternet connection or internet access is the process that lets to the individuals andthe organizations to connect to the Internet using computers and mobile devices,sometimes through computer networks. Once connected to the Internet, users canaccess to Internet.

Wi-FiWI-FI is a technology for wireless local area networking with devices based on theIEEE 802.11 standards. Devices that can use Wi-Fi technology include personalcomputers, video-game consoles, smartphones, digital cameras, tablet computers,digital audio players and modern printers. Wi-Fi can be connected to the internetthrough a WLAN network or a wireless access point.

Wireless access pointWireless access point is a networking hardware device that allows a Wi-Fi device toconnect to a wired network. The WAP usually connects to a router as anindependent device.

Speeds (bandwidth)Speeds (bandwidth) is the velocity which can be achieved through the internet connection in a computer. It depends on the amount of megabytes used by the computers and can be tested online thanks to various applications.

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Numbering

IP Address It’s a number that it’s named to each device, participating in a computer networkthat uses the Internet Protocol for communication. An IP address serves twoprincipal functions: host the network interface identification and locationaddressing.

MAC AddressA media access control address of a computer is a unique identifier assigned tonetwork interfaces for communications at the data link layer of a network segment.MAC addresses are used as a network address for most IEEE 802 networktechnologies, including Ethernet and Wi-Fi.

LAN TopologyThere are two types of topologies: Physical and Logical. The physical topology of anetwork refers to the layout of cables, computers and other peripherals. Forinstance, is like being in a room with a small network, so that one can see networkcables coming out of every computer that is part of the network, then those cablesplug into a hub or switch. Therefore, this is what can be considered as the physicaltopology of that network. In the other way, Logical topology is the method used topass the information between the computers. In other words, looking at that sameroom is like trying to see how the network works with all the computers (generatingtraffic and packets of data going everywhere on the network). The way thecomputers will be connected to each other and the direction of the traffic iscontrolled by the various protocols. If it is being used a token ring, then the physicaltopology would have to change to meet the requirements of the way the token ringprotocol works (logically). The physical topology describes the layout of thenetwork, just like a map shows the layout of various roads, and the logical topologydescribes how the data is sent across the network or how the cars are able to travel(the direction and speed) at every road on the map. The most common types ofphysical topologies are: Bus, Star, Mesh, Ring, Hybrid, Hierarchical and Treetopologies.

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Physical bus topologyBus topology is considered one of the first topologies designed for LAN connection,even though it was revolutionary and spread quite fast some years ago; nowadaysits presence is decreasing as new topologies, usually with better capacities, havesubstituted them. With the Bus topology, all workstations are connecting directly tothe main backbone that carries the data. Traffic generated by any computer willtravel across the backbone and be received by all workstations. This works well in asmall network of 2-5 computers, but as the number of computers increases so willsthe network traffic and this can greatly decrease the performance and availablebandwidth of the network. All computers are attached to a continuous cable whichconnects them in a straight line. The arrows clearly indicate that the packetgenerated by one of the computer is transmitted to all computers on the network,regardless the destination of this packet. Also, because of the way the electricalsignals are transmitted over this cable, its ends must be terminated by specialterminators that work as "shock absorbers", absorbing the signal so it won't reflectback to where it came from. The value of 50Ohms has been selected after carefullytaking in consideration all the electrical characteristics of the cable used, thevoltage that the signal which runs through the cables, the maximum and minimumlength of the bus and a few more. If the bus (the long yellow cable) is damagedanywhere in its path, then it will most certainly cause the network to stop workingor, at the very least, cause big communication problems between the workstations.

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Physical star topologyThe Star or Hub topology is one of the most common network topologies found inmost offices and home networks. It has become very popular in contrast to the bustype because of the cost and the ease of troubleshooting. The advantage of the startopology is that if one computer on the star topology fails, then only the failedcomputer is unable to send or receive data, while the rest of the computerbelonging to the network continue to be able of both sending and receiving data.The remainder of the network functions normally. The disadvantage of using thistopology is that because each computer is connected to a central hub or switch, ifthis device fails, the entire network fails. There is a different type of Star topologyknown as Extended Star topology, which basically works in the same way as Startopology but connecting more than one network at the same time. Therefore, Startopology offers the advantage of the dependence in only one computer, instead ofin every single one.

Physical ring topologyIn the ring topology, computers are connected on a single circle of cable. Unlike thebus topology, there are no terminated ends. The signals travel around the loop inone direction and pass through each computer, which acts as a repeater to boostthe signal and send it to the next computer. On a larger scale, multiple LANs can beconnected to each other in a ring topology by using Thicknet coaxial or fiber-opticcable. The method by which the data is transmitted around the ring is called tokenpassing. IBM's token ring uses this method. A token is a special series of bits thatcontains control information. Possession of the token allows a network device totransmit data to the network. Each network has only one token. However, Ringtopology is quite more expensive than the rest of the topologies.

Physical mesh topologyIn a mesh topology, each computer is connected to every other computer by aseparate cable. This configuration provides redundant paths through the new work,so if one computer blows up, the network is not lost. On a large scale, can beconnected multiple LANs using mesh topology with leased telephone lines, Thicknetcoaxial cable or fiber optic cable. The big advantage of this topology is its backupcapabilities by providing multiple paths through the network. In a few words, datatransmission works in a more useful way in Mesh topology, even though there canbe different preferences.

Physical hybrid topologyWith the hybrid topology, two or more topologies are combined to form a completenetwork. For example, a hybrid topology could be the combination of a star and bustopology. These are also the most common in use. Hybrid topology works as acombination of different topologies, offering the advantages that each of thesepossess. The most common type of Hybrid topology is that which combines Star onewith Bus and Ring, respectively.

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Star-busIn a star-bus topology, several star topology networks are linked to a busconnection. So, this connection avoids the disadvantage of Bus topology (if onecomputer fails, the whole network collapses) in a way that, if a computer fails, it willnot affect the rest of the network. However, if the central component, or hub, thatattaches all computers in a star, fails (as happens in Star topology) the wholenetwork will go down.

Star-ringIn the Star-Ring topology, the computers are connected to a central component asin a star network. These components, however, are wired to form a ring network.Like the star-bus topology, if a single computer fails, it will not affect the rest of thenetwork. By using token passing, each computer in a star-ring topology has anequal chance of communicating. This allows for greater network traffic betweensegments than in a star-bus topology.

Hierarchical topologyThe Hierarchical topology works in a similar way as Extended Star topology but,instead of connecting switches, the system is connected to a computer whichcontrols the whole process of traffic of data inside of the topology. This structure isused in most of the Local Area Networks nowadays.

Tree topologyAlternatively referred to as a Star-Bus topology, Tree topology is one of the mostcommon network setups that is similar to a Bus topology and a Star topology. A Treetopology connects one-star network to other star networks. Below is a visualexample of a Tree topology, with a simple computer set up on a network using theStar topology connected to another network using the Star topology.

In the picture above, if the main cable or trunk between each of the two-startopology networks was to fail, those networks would be unable to communicate witheach other. However, computers on the same Star topology would still be able tocommunicate with each other.

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Logical LAN topologyLogical topology, or signal topology, is the arrangement of devices on a computernetwork and how they communicate with one another. Logical topologies describehow signals act on the network. In contraposition to physical LAN topology, which isthe cables and nodes that connect the local area network’s components, logicalones are responsible for the proper functioning of the LAN. For instance, logical LANtopology is as the software of a computer, while physical, would be like thehardware.

Ethernet Ethernet was first introduced in 1980, and started being used around 1983, sincethat moment it has been improving its performance in LAN connections tosubstitute other logical LAN topology components such as the Token ring. FirstEthernet cables used a coaxial connection, in the course of the years it has beenreplaced by a twisted pair; finally, last innovations in Ethernet had allowed it afaster connection in a more easily and comfortable way thanks to the fiber optic’sintroduction. Ethernet is commonly used to connect both Star and Bus topologies.

Token ringToken ring was introduced by IBM in 1984 and was fairly successful, particularly incorporate environments, but gradually eclipsed by the later versions of Ethernet.Token ring technology is logical LAN topology connection for local area networks. Ituses a special three-byte frame called a "token" that travels around a "ring" ofworkstations or servers. This token passing is a channel access method providingfair access for all stations, and eliminating the collisions of contention-based accessmethods. While Ethernet was the connection for Star and Bus topologies, Tokenring, as its name indicates, is used for Ring topologies.

FDDIFiber Distributed Data Interface (FDDI) is a standard for data transmission in a localarea network. In this case, the connection is neither made through Ethernet norToken ring, but it uses optical fiber as its standard underlying physical medium,although it was also later specified to use copper cable, in which case it may becalled CDDI (Copper Distributed Data Interface).

IEEE Standards The Institute of Electrical and Electronics Engineers Standards Association (IEEE-SA)is an organization within IEEE that develops global standards in a broad range ofindustries, including: power and energy, biomedical and health care, informationtechnology and robotics, telecommunication and home automation, transportation,nanotechnology, information assurance, and many more. IEEE-SA is not a bodyformally authorized by any government, but rather a community. In the case ofLocal Area Network, IEEE has introduced the following standards, this projectbecame known within the company and internationally as IEEE 802.

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IEEE 802.3 This standard corresponds to Ethernet connection. Its first version was introduced inmarket in 1978 and it was connected through a coaxial cable; periodically, newupdates have been created, the last one being likely to be introduced in thesummer of 2017, therefore is a connection that is currently in progress in stillexpanding.

IEEE 802.5This standard belongs to Token Ring connection. The design of Token Ring Networkwas presented by E. E. Newhall in 1969, being firstly launched into the market byIBM in 1982, receiving its official standard in 1985.

IEEE 802.4This standard is for Token Bus connection, which is based on a logical LAN Ringtopology and works thanks to the action of a coaxial cable.

IEEE 802.22This last standard belongs to WLAN (Wireless Local Area Network), which works as acommon LAN, but taking into a count the connection without the requirement ofwires.

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