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COMPUTERNETWORKINGBy,SAVIN SHETTYBHARAT SHETTYANKITA SHETTYPOOJA SHETTYNIKITA RAI
INDEX TOPICS                COVERED BY  INTRODUCTION        SAVIN SHETTY  TYPES OF TOPOLOGY   ANKITA SHETTY  TYPES OF S...
What is Computer networking?Networking is the word basically relating to computers and their connectivity. Itis very often...
For this connection a Local area network card or the LAN card is requiredwhich enables the connection of the computers in ...
BUS TOPOLOGY :Bus Topology is the simplest of network topologies. In this type of topology, allthe nodes (computers as wel...
Advantages of Linear Bus Topology :1) It is easy to set-up and extend bus network.2) Cable length required for this topolo...
STAR TOPOLOGY: In Star topology, all the components of network are connected to the centraldevice called nodes were connec...
Advantages of Star Topology :1) As compared to Bus topology it gives far much better performance,   signals don’t necessar...
RING TOPOLOGY:In Ring Topology, all the nodes are connected to each-other in such a way thatthey make a closed loop. Each ...
Advantages of Ring Topology :1) This type of network topology is very organized. Each node gets tosend the data when it re...
MESH TOPOLOGY:In a mesh network topology, each of the network node, computer and otherdevices, are interconnected with one...
Advantages of Mesh topology:1) Data can be transmitted from different devices simultaneously. Thistopology can withstand h...
SERVERSWhat are Servers?     Server is a computer or a device that manages network resources such     as file, printer, an...
Servers in a data center. Several servers are mounted on a rack and connectedto a KVM switch.Servers often provide essenti...
2.) Catalog Server:     A catalog server provides a single point of access that allows users to     centrally search for i...
3.) Communications servers:Communications servers are open, standards-based computing systems thatoperate as a carrier-gra...
5.) Fax Server:A fax server is a system installed in a local area network (LAN) server thatallows computer users whose com...
6.) File Server:In computing, a file server is a computer attached to a network that has theprimary purpose of providing a...
7.) Game Server:A game server (sometimes host or shard) is a server which is the authoritativesource of events in a multip...
9. Print server:A print server, or printer server, is a device that connects printers to clientcomputers over a network. I...
10.) Proxy Server:A proxy server is a server (a computer system or an application) that acts asan intermediary for request...
TYPES OF NETWORKS:A computer network, or simply a network, is a collection of computers andother hardware components inter...
Typical library network, in a branching tree topology and controlled access toresourcesA sample LAN is depicted in the acc...
A local area network (LAN) supplies networking capability to a group ofcomputers in close proximity to each other such as ...
(a)Advantages of LANs     1.   expensive hardware can be shared e.g. laser printer     2.   network software is cheaper th...
Characteristics of MAN’S : The network size falls intermediate between LANs and WANs. A MANtypically covers an area of be...
Disadvantages of MANs    The key disadvantage of MANs is the cost of the cutting-edge technology    employed. Also, this e...
Characteristics of WAN:Followings are the major characteristics of WAN.1.Communication Facility: For a big company spannin...
Advantages Of WAN-Messages can be sent very quickly to anyone else on the network. Thesemessages can have pictures, sounds...
What is networking?Networking is the word basically relating to computers and their connectivity. Itis very often used in ...
With the increasing use of the computers and the networking the local areanetwork of the LAN is one such network type whic...
Network switchA network switch or switching hub is a computer networking device thatconnects network segments or network d...
which the message was meant. This makes the switch a more intelligent devicethan a hub (which receives a message and then ...
Hubs, Bridges, Switches and Routers are used to build networks. If you aretrying to design your own LAN (Local Area Networ...
the source segment. If the destination is same as the source, frame isdiscarded.Switches have built-in hardware chips sole...
Routers use NAT (Network Address Translation) in conjunction with IPMasquerading to provide the internet to multiple nodes...
possible to find new products in the market combining two or more of thesedevices into one.Examples are:- Brouter: Works a...
Types of routersThe earliest types of EDA routers were "manual routers" -- the drafter clicked amouse on the endpoint of e...
ModemA modem (modulator-demodulator) is a device that modulates an analogcarrier signal to encode digital information, and...
These days the modems area great benefit to be used in the telecommunicationsystems with the launch of the radio modems. T...
OSI MODELVirtually all networks in use today are based in some fashion on the OpenSystems Interconnection (OSI) standard. ...
Layer 1: Physical - This is the level of the actual hardware. It defines thephysical characteristics of the network such a...
and flow control                                             Path determination and logical          Packet/Datagram 3. Ne...
local-area networks, such as token ring, FDDI, ITU-T G.hn and IEEE 802.11,as well as personal area networks such as Blueto...
1. Subnetwork access – that considers protocols that deal with the interface      to networks, such as X.25;   2. Subnetwo...
Feature Name                     TP0 TP1 TP2 TP3 TP4Connection oriented network                               Yes Yes Yes ...
encapsulation of the payload takes place only at endpoint, GRE becomes closerto a transport protocol that uses IP headers ...
communication partners, determining resource availability, and synchronizingcommunication. When identifying communication ...
BIBLIOGRAPHYWWW.GOOGLE.COMWWW.WIKIPEDIA.COMhttp://computer.howstuffworks.com
Networking  hard copy (1)
Networking  hard copy (1)
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Networking hard copy (1)

  1. 1. COMPUTERNETWORKINGBy,SAVIN SHETTYBHARAT SHETTYANKITA SHETTYPOOJA SHETTYNIKITA RAI
  2. 2. INDEX TOPICS COVERED BY  INTRODUCTION SAVIN SHETTY  TYPES OF TOPOLOGY ANKITA SHETTY  TYPES OF SERVES NIKITA RAI  TYPES OF NETWORKS BHARAT SHETTY  COMPONENTS OF POOJA SHETTY NETWORKS  OSI MODEL SAVIN SHETTY  BIBLIOGRAPHY -
  3. 3. What is Computer networking?Networking is the word basically relating to computers and their connectivity. Itis very often used in the world of computers and their use in differentconnections. The term networking implies the link between two or morecomputers and their devices, with the soul purpose of sharing the data storedin the computers, with each other. The networks between the computingdevices are very common these days due to the launch of various hardware andcomputer software which aid in making the activity much more convenient tobuild and use. Networking is the word basically relating to computers and theirconnectivity. It is very often used in the world of computers and their use indifferent connections. The term networking implies the link between two ormore computers and their devices, with the soul purpose of sharing the datastored in the computers, with each other. The networks between the computingdevices are very common these days due to the launch of various hardware andcomputer software which aid in making the activity much more convenient tobuild and use.Computer networking is then categorized into several different areas and uses,such as the most common ones like LAN and WAN.Computer networking is also based on different network designs. The two basicclassification categories of the network design are the client-server and peer-to-peer. The client-server networking refers to the computer servers that arecentralized, which are mainly used in storing emails, web pages, files andapplications. The peer-to-peer network is the most commonly used and all thecomputers mainly support its functions. The Client server is used extensivelyin the business functions, whereas the peer-to-peer server is for home use.Every network requires a topology to work through which the data flows andthe computers can communicate with each other. The most common types oftopologies are bus, star, ring, and mesh.Networking also involves a special communication language used by thecomputer devices. These languages are called network protocols, and most ofthe computers use a range of protocols which they support. The most commonnetwork in the Internet and home networks is the TCP/IP.Networking can be either wired or wireless. The most common wired networkslike Ethernet cables were extensively used but now wireless networking haveemerged and the new computer networks mainly support this feature.With the increasing use of the computers and the networking the local areanetwork of the LAN is one such network type which links the two computers ina connection.
  4. 4. For this connection a Local area network card or the LAN card is requiredwhich enables the connection of the computers in a network. It is a piece ofhardware which is connected inside the PC linking the computer network.What is Network Topology?Computer network topology is the way various components of a network (likenodes, links, peripherals, etc) are arranged. Network topologies define thelayout, virtual shape or structure of network, not only physically but alsologically. The way in which different systems and nodes are connected andcommunicate with each other is determined by topology of the network.Topology can be physical or logical.Physical Topology is the physical layoutof nodes, workstations and cables in the network; while logical topology is theway information flows between different components.Types of Physical Network Topologies Bus Topology Star Topology Ring Topology Mesh Topology
  5. 5. BUS TOPOLOGY :Bus Topology is the simplest of network topologies. In this type of topology, allthe nodes (computers as well as servers) are connected to the single cable(called bus), by the help of interface connectors. This central cable is thebackbone of the network and is known as Bus (thus the name). Everyworkstation communicates with the other device through this Bus.A signal from the source is broadcasted and it travels to all workstationsconnected to bus cable. Although the message is broadcasted but only theintended recipient, whose MAC address or IP address matches, accepts it. If theMAC /IP address of machine doesn’t match with the intended address,machine discards the signal.A terminator is added at ends of the central cable, to prevent bouncing ofsignals. A barrel connector can be used to extend it.
  6. 6. Advantages of Linear Bus Topology :1) It is easy to set-up and extend bus network.2) Cable length required for this topology is the least compared to othernetworks.3) Bus topology costs very less.4) Linear Bus network is mostly used in small networks. Good for LAN.Disadvantages of Linear Bus Topology : 1) There is a limit on central cable length and number of nodes that can be connected. 2) Dependency on central cable in this topology has its disadvantages. If the main cable (i.e. bus ) encounters some problem, whole network breaks down. 3) Proper termination is required to dump signals. Use of terminators is must. 4) It is difficult to detect and troubleshoot fault at individual station. 5) Maintenance costs can go higher with time. 6) Efficiency of Bus network reduces as the number of devices connected to it increases. 7) It is not suitable for networks with heavy traffic. 8) Security is very low because all the computers receive the sent signal from the source.
  7. 7. STAR TOPOLOGY: In Star topology, all the components of network are connected to the centraldevice called nodes were connected to central cable, here all the workstationsare connected to central device with a point-to-point connection. So it can besaid that every computer is indirectly connected to every other node by the helpof “hub”.All the data on the star topology passes through the central device beforereaching the intended destination. Hub acts as a junction to connect differentnodes present in Star Network, and at the same time it manages and controlswhole of the network. Depending on which central device is used, “hub” can actas repeater or signal booster. Central device can also communicate with otherhubs of different network. Unshielded Twisted Pair (UTP) Ethernet cable isused to connect workstations to central node.
  8. 8. Advantages of Star Topology :1) As compared to Bus topology it gives far much better performance, signals don’t necessarily get transmitted to all the workstations. A sent signal reaches the intended destination after passing through no more than 3-4 devices and 2-3 links. Performance of the network is dependent on the capacity of central hub.2) Easy to connect new nodes or devices. In star topology new nodes can be added easily without affecting rest of the network. Similarly components can also be removed easily3) Centralized management. It helps in monitoring the network.4) Failure of one node or link doesn’t affect the rest of network. At the same time it’s easy to detect the failure and troubleshoot it.Disadvantages of Star Topology :1) Too much dependency on central device has its own drawbacks. If it fails whole network goes down.2) The use of hub, a router or a switch as central device increases theoverall cost of the network.3) Performance and as well number of nodes which can be added insuch topology is depended on capacity of central device.
  9. 9. RING TOPOLOGY:In Ring Topology, all the nodes are connected to each-other in such a way thatthey make a closed loop. Each workstation is connected to two othercomponents on either side, and it communicates with these two adjacentneighbors. Data travels around the network, in one direction. Sending andreceiving of data takes place by the help of TOKEN.Token Passing: Token contains a piece of information which along with data issent by the source computer. This token then passes to next node, whichchecks if the signal is intended to it. If yes, it receives it and passes the emptyto into the network, otherwise passes token along with the data to next node.This process continues until the signal reaches its intended destination.The nodes with token are the ones only allowed to send data. Other nodes haveto wait for an empty token to reach them. This network is usually found inoffices, schools and small buildings.
  10. 10. Advantages of Ring Topology :1) This type of network topology is very organized. Each node gets tosend the data when it receives an empty token. This helps to reduceschances of collision. Also in ring topology all the traffic flows in only one direction at very high speed.2) Even when the load on the network increases, its performance isbetter than that of Bus topology.3) There is no need for network server to control the connectivitybetween workstations.4) Additional components do not affect the performance of network.5) Each computer has equal access to resources.Disadvantages of Ring Topology:1) Each packet of data must pass through all the computers betweensource and destination. This makes it slower than Star topology.2) If one workstation or port goes down, the entire network getsaffected.3) Network is highly dependent on the wire which connects differentcomponents.4) Multistation Access Unit, and network cards are expensive ascompared to Ethernet cards and hubs.
  11. 11. MESH TOPOLOGY:In a mesh network topology, each of the network node, computer and otherdevices, are interconnected with one another. Every node not only sends itsown signals but also relays data from other nodes. In fact a true mesh topologyis the one where every node is connected to every other node in the network.This type of topology is very expensive as there are many redundantconnections, thus it is not mostly used in computer networks. It is commonlyused in wireless networks. Flooding or routing technique is used in meshtopology.
  12. 12. Advantages of Mesh topology:1) Data can be transmitted from different devices simultaneously. Thistopology can withstand high traffic.2) Even if one of the components fails there is always an alternativepresent,So data transfer doesn’t get affected.3)Expansion and modification in topology can be done withoutdisrupting other nodes.Disadvantages of Mesh topology1) There are high chances of redundancy in many of the networkconnections.2) Overall cost of this network is way too high as compared to othernetwork topologies.3) Set-up and maintenance of this topology is very difficult. Evenadministration of the network is tough.
  13. 13. SERVERSWhat are Servers? Server is a computer or a device that manages network resources such as file, printer, and user group as well as network traffic on the network. During the server selection two parameter are very important to consider that is server specification and processor specification. There are also some more specification to be consider are memory, storage, connectivity, operating system support specifications.
  14. 14. Servers in a data center. Several servers are mounted on a rack and connectedto a KVM switch.Servers often provide essential services across a network, either to privateusers inside a large organization or to public users via the Internet.Types of serversIn a general network environment the following types of servers may be found.1.)Application Server: An application server is a server that provides software applications withservices such as security, data services, transaction support, load balancing,and management of large distributed systems.The term is often used for web servers that support the Java Platform,Enterprise Edition; however its use isnt restricted to Java.
  15. 15. 2.) Catalog Server: A catalog server provides a single point of access that allows users to centrally search for information across a distributed network. In other words, it indexes databases, files and information across large network and allows keywords, Boolean and other searches.
  16. 16. 3.) Communications servers:Communications servers are open, standards-based computing systems thatoperate as a carrier-grade common platform for a wide range ofcommunications applications and allow equipment providers to add value atmany levels of the system architecture.4.) Database servers:A database server is a computer program that provides database services toother computer programs or computers, as defined by the client–servermodel.The term may also refer to a computer dedicated to running such a program.Database management systems frequently provide database serverfunctionality.Such a server is accessed either through a "front end" running on the user’scomputer which displays requested data or the "back end" which runs on theserver and handles tasks such as data analysis and storage.
  17. 17. 5.) Fax Server:A fax server is a system installed in a local area network (LAN) server thatallows computer users whose computers are attached to the LAN to send andreceive fax messages.Alternatively the term fax server is sometimes used to describe a program thatenables a computer to send and receive fax messages, set of software runningon a server computer which is equipped with one or more fax-capable modems(or dedicated fax boards) attached to telephone lines or, more recently, softwaremodem emulators which use T.38 ("Fax over IP") technology to transmit thesignal over an IP network. Its function is to accept documents from users,convert them into faxes, and transmit them, as well as to receive fax calls andeither store the incoming documents or pass them on to users. Users maycommunicate with the server in several ways, through either a local network orthe Internet. In a big organization with heavy fax traffic, the computer hostingthe fax server may be dedicated to that function, in which case the computeritself may also be known as a fax server.
  18. 18. 6.) File Server:In computing, a file server is a computer attached to a network that has theprimary purpose of providing a location for shared disk access, i.e. sharedstorage of computer files (such as documents, sound files, photographs,movies, images, databases, etc.) that can be accessed by the workstations thatare attached to the same computer network. The term server highlights the roleof the machine in the client–server scheme, where the clients are theworkstations using the storage. A file server is not intended to performcomputational tasks, and does not run programs on behalf of its clients.It is designed primarily to enable the storage and retrieval of data while thecomputation is carried out by the workstations.File servers are commonly found in schools and offices, where users use a LANto connect their client computers.
  19. 19. 7.) Game Server:A game server (sometimes host or shard) is a server which is the authoritativesource of events in a multiplayer video game. The server transmits enough dataabout its internal state to allow its connected clients to maintain their ownaccurate version of the game world for display to players. They also receive andprocess each players input.8.) Home Server: A home server is a server located in a private residence providing services to other devices inside and/or outside the household through a home network and/or the Internet. Such services may include file and/or printer serving, media center serving, web serving (on the network or internet), web caching, account authentication and backup services. Because of the relatively low number of computers on a typical home network, a home server commonly does not require significant computing power.
  20. 20. 9. Print server:A print server, or printer server, is a device that connects printers to clientcomputers over a network. It accepts print jobs from the computers and sendsthe jobs to the appropriate printers.Print servers may support a variety of industry-standard or proprietary printingprotocols including Internet Printing Protocol, Line Printer Daemon protocol,Microsoft Network Printing protocol, NetWare, NetBIOS/NetBEUI, or Jet Direct.A print server may be a networked computer with one or more shared printers.Alternatively a print server may be a dedicated device on the network, withconnections to the LAN and one or more printers. Dedicated server appliancestend to be fairly simple in both configuration and features. Print serverfunctionality may be integrated with other devices such as a wireless router, afirewall, or both. A printer may have a built-in print server. A wireless print server
  21. 21. 10.) Proxy Server:A proxy server is a server (a computer system or an application) that acts asan intermediary for requests from clients seeking resources from other servers.A client connects to the proxy server, requesting some service, such as a file,connection, web page, or other resource available from a different server andthe proxy server evaluates the request as a way to simplify and control theircomplexity. Today, most proxies are web proxies, facilitating access to contenton the World Wide Web. Communication between two computers (shown in grey) connected through a third computer (shown in red) acting as a proxy.
  22. 22. TYPES OF NETWORKS:A computer network, or simply a network, is a collection of computers andother hardware components interconnected by communication channels thatallow sharing of resources and information.[1] Where at least one process in onedevice is able to send/receive data to/from at least one process residing in aremote device, then the two devices are said to be in a network. Simply, morethan one computer interconnected through a communication medium forinformation interchange is called a computer network.Networks may be classified according to a wide variety of characteristics, suchas the medium used to transport the data, communications protocol used,scale, topology, and organizational scope.A local area network (LAN) is a network that connects computers and devicesin a limited geographical area such as home, school, computer laboratory,office building, or closely positioned group of buildings. Each computer ordevice on the network is a node. Current wired LANs are most likely to bebased on Ethernet technology, although new standards like ITU-T G.hn alsoprovide a way to create a wired LAN using existing home wires (coaxial cables,phone lines and power lines).
  23. 23. Typical library network, in a branching tree topology and controlled access toresourcesA sample LAN is depicted in the accompanying diagram. All interconnecteddevices must understand the network layer (layer 3), because they are handlingmultiple subnets (the different colors). Those inside the library, which haveonly 10/100 Mbit/s Ethernet connections to the user device and a GigabitEthernet connection to the central router, could be called "layer 3 switches"because they only have Ethernet interfaces and must understand IP. It wouldbe more correct to call them access routers, where the router at the top is adistribution router that connects to the Internet and academic networkscustomer access routers.The defining characteristics of LANs, in contrast to WANs (Wide AreaNetworks), include their higher data transfer rates, smaller geographic range,and no need for leased telecommunication lines. Current Ethernet orother IEEE 802.3 LAN technologies operate at data transfer rates up to 10Gbit/s. IEEE has projects investigating the standardization of 40 and 100Gbit/s.[14] LANs can be connected to Wide area network by using routers.A LAN is a computer network that spans a relatively small area. Most LANs areconfined to a single building or group of buildings, however, one LAN can beconnected to other LANs over any distance via telephone lines and radio waves.A system of LANs connected in this way is called a wide-area network (WAN).Most LANs connect workstations and personal computers.Each node(individual computer ) in a LAN has its own CPU with whichit executes programs, but it also is able to access data and devices anywhereon the LAN. This means that many users can share expensive devices, such aslaser, as well as data. Users can also use the LAN to communicate with eachother, by sending e-mail or engaging in chat sessions.LANs are capable of transmitting data at very fast rates, much faster than datacan be transmitted over a telephone line; but the distances are limited, andthere is also a limit on the number of computers that can be attached to asingle LAN.
  24. 24. A local area network (LAN) supplies networking capability to a group ofcomputers in close proximity to each other such as in an office building, aschool, or a home. A LAN is useful for sharing resources like files, printers,games or other applications. A LAN in turn often connects to other LANs, andto the Internet or other WAN.Most local area networks are built with relatively inexpensive hardware suchas Ethernet cables, network adapters, and hubs. Wireless LAN and other moreadvanced LAN hardware options also exist.FEATURES OF LANA LAN is designed for a small area. Generally it spans a single office, workgroup floor in a building, or in a campus etc. LAN uses different protocols orrules lor information transmission.Limited No. of Users: - Most LAN supports I number of users usually aroundfive or ten. More users can be supported by connecting different LANs together,which gives better results than making one; by network of the nature of MAN.Reliability & Stability: - LANS tend to be very reliable failures on a LAN aremostly due to wrong or improper installation and monitoring. Software thatcomes along with a LAN provides a number of useful programs like error-detection, prevention of transmission loss and excellent security features.Flexibility: - Major development in LANs today is flexibility they offer. Earlierversions would support only one type of desktop computers. Todays advancedLANs however can support different types of computers. The flexibility alsoextends to operating systems & storage media.
  25. 25. (a)Advantages of LANs 1. expensive hardware can be shared e.g. laser printer 2. network software is cheaper than buying individual packages 3. users can access the same files 4. messages can be sent between users 5. a single Internet connection can be shared among many users (b) Disadvantages of LANs 1. quite expensive to set up and maintain 2. a virus can spread to all the computers on the network 3. more prone to hacking because of multiple points of access 4. if the file server goes down, the entire network may go down (star network)MAN :A metropolitan area network (MAN) is a computer network that usuallyspans a city or a large campus. A MAN usually interconnects a number of localarea networks (LANs) using a high-capacity backbone technology, such asfiber-optical links, and provides up-link services to wide area networks (orWAN) and the Internet.The IEEE 802-2002 standard describes a MAN as being:[1]“ A MAN is optimized for a larger geographical area than a LAN, ranging from several blocks of buildings to entire cities. MANs can also depend on communications channels of moderate-to-high data rates. A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations. MANs might also be owned and operated as public utilities. They will often provide means for internetworking of local networks.
  26. 26. Characteristics of MAN’S : The network size falls intermediate between LANs and WANs. A MANtypically covers an area of between 5 and 50 km diameter. Many MANscover an area the size of a city, although in some cases MANs may be assmall as a group of buildings or as large as the North of Scotland. A MAN (like a WAN) is not generally owned by a single organisation. TheMAN, its communications links and equipment are generally owned byeither a consortium of users or by a single network provider who sells theservice to the users. This level of service provided to each user musttherefore be negotiated with the MAN operator, and some performanceguarantees are normally specified. A MAN often acts as a high speed network to allow sharing of regionalresources (similar to a large LAN). It is also frequently used to provide ashared connection to other networks using a link to a WAN.Advantages of MANsThe biggest advantage of MANs is the bandwidth (potential speed) of theconnecting links.This means that resources (such as databases and files) shared on thenetwork can be accessed extremely quickly.Some installations allow multiple users to share the same high-speedInternet connection, thereby sharing the cost of the service and securing abetter quality of service through collective bargaining and economies ofscale.
  27. 27. Disadvantages of MANs The key disadvantage of MANs is the cost of the cutting-edge technology employed. Also, this equipment generally has to be installed for the first time, as the copper traditionally used for the phone network is generally considered to be too slow to be annexed for this purpose. The cost is what inhibits the geographical reach of MANs, which is also another drawback.WAN:A Wide Area Network (WAN) is a network that covers a broad area (i.e., anynetwork that links across metropolitan, regional, or national boundaries). TheInternet is the most popular WAN, and is used by businesses, governments,non-profit organizations, individual consumers, artists, entertainers, andnumerous others for almost any purpose imaginable.[1]Related terms for other types of networks are personal areanetworks (PANs), local area networks (LANs), campus area networks (CANs),or metropolitan area networks (MANs) which are usually limited to a room,building, campus or specific metropolitan area (e.g., a city) respectively.A computer network that spans a relatively large geographical area. Typically, aWAN consists of two or more local-area networks (LANs).Computers connected to a wide-area network are often connected throughpublic networks, such as the telephone system. They can also be connectedthrough leased lines or satellites. The largest WAN in existence is theInternet.
  28. 28. Characteristics of WAN:Followings are the major characteristics of WAN.1.Communication Facility: For a big company spanning over different partsof the country the employees can save long distance phone calls and itovercomes the time lag in overseas communications. Computer conferencing isanother use of WAN where users communicate with each other through theircomputer system.2.Remote Data Entry: Remote data entry is possible in WAN. It means sittingat any location you can enter data, update data and query other information ofany computer attached to the WAN but located in other cities. For example,suppose you are sitting at Madras and want to see some data of a computerlocated at Delhi, you can do it through WAN.3.Centralised Information: In modern computerised environment you will findthat big organisations go for centralised data storage. This means if theorganisation is spread over many cities, they keep their important businessdata in a single place. As the data are generated at different sites, WAN permitscollection of this data from different sites and save at a single site.Examples of WAN1.Ethernet: Ethernet developed by Xerox Corporation is a famous example ofWAN. This network uses coaxial cables for data transmission. Specialintegrated circuit chips called controllers are used to connect equipment to thecable.2.Aparnet: The Aparnet is another example of WAN. It was developed atAdvanced Research Projects Agency of U. S. Department. This Networkconnects more than 40 universities and institutions throughout USA andEurope.
  29. 29. Advantages Of WAN-Messages can be sent very quickly to anyone else on the network. Thesemessages can have pictures, sounds, or data included with them (calledattachments).-Expensive things (such as printers or phone lines to the internet) can beshared by all the computers on the network without having to buy a differentperipheral for each computer.-Everyone on the network can use the same data. This avoids problems wheresome users may have older information than others.-Share information/files over a larger areaDisadvantages Of WAN-Setting up a network can be an expensive and complicated experience. Thebigger the network the more expensive it is.-Security is a real issue when many different people have the ability to useinformation from other computers. Protection against hackers and viruses addsmore complexity and expense.-Once set up, maintaining a network is a full-time job which requires networksupervisors and technicians to be employed.-Information may not meet local needs or interests
  30. 30. What is networking?Networking is the word basically relating to computers and their connectivity. Itis very often used in the world of computers and their use in differentconnections. The term networking implies the link between two or morecomputers and their devices, with the soul purpose of sharing the data storedin the computers, with each other. The networks between the computingdevices are very common these days due to the launch of various hardware andcomputer software which aid in making the activity much more convenient tobuild and use. Networking is the word basically relating to computers and theirconnectivity. It is very often used in the world of computers and their use indifferent connections. The term networking implies the link between two ormore computers and their devices, with the soul purpose of sharing the datastored in the computers, with each other. The networks between the computingdevices are very common these days due to the launch of various hardware andcomputer software which aid in making the activity much more convenient tobuild and use.Computer networking is then categorized into several different areas and uses,such as the most common ones like LAN and WAN.Computer networking is also based on different network designs. The two basicclassification categories of the network design are the client-server and peer-to-peer. The client-server networking refers to the computer servers that arecentralized, which are mainly used in storing emails, web pages, files andapplications. The peer-to-peer network is the most commonly used and all thecomputers mainly support its functions. The Client server is used extensivelyin the business functions, whereas the peer-to-peer server is for home use.Every network requires a topology to work through which the data flows andthe computers can communicate with each other. The most common types oftopologies are bus, star, ring, and mesh.Networking also involves a special communication language used by thecomputer devices. These languages are called network protocols, and most ofthe computers use a range of protocols which they support. The most commonnetwork in the Internet and home networks is the TCP/IP.Networking can be either wired or wireless. The most common wired networkslike Ethernet cables were extensively used but now wireless networking haveemerged and the new computer networks mainly support this feature.
  31. 31. With the increasing use of the computers and the networking the local areanetwork of the LAN is one such network type which links the two computers ina connection.For this connection a Local area network card or the LAN card is requiredwhich enables the connection of the computers in a network. It is a piece ofhardware which is connected inside the PC linking the computer network.The LAN Card is of both the common types which are the OSI layer 1 and 2,dealing with the physical as well as the data link layer respectively. It uses thecorrectly entered MAC addresses for the network to work. This then allows thecomputers to connect using cables or even wirelessly which then requires aspecial type of LAN card called the WLAN card.What is LAN CARD?With the increase in the development and technology, the local area network ofthe wireless type is now mostly preferred. Therefore a Wireless LAN Card isrequired for this purpose. The computers with the wireless LAN Card cantransmit and receive data via radio waves using the special technology of SSTor the Spread-Spectrum technology.The wireless LANs are available in four basic types which include the 802.11,followed by type a, b and also g.Any sort of LAN card you use will have some of the typical features of anetwork card which includes the twisted pair, the AUI socket and also theBNC. It is at the AUI socket that the network cable has to be connected. TheLAN cards usually are designed to support the rate transfer to be ranging from10 to 1000 megabits per second.HUBA common connection point for devices in a network. Hubs are commonly usedto connect segments of a LAN. A hub contains multiple ports. When apacket arrives at one port, it is copied to the other ports so that all segments ofthe LAN can see all packets.A passive hub serves simply as a conduit for the data, enabling it to go fromone device (or segment) to another. So-called intelligent hubs include additionalfeatures that enables an administrator to monitor the traffic passing throughthe hub and to configure each port in the hub. Intelligent hubs are alsocalled manageable hubs.A third type of hub, called a switching hub, actually reads the destinationaddress of each packet and then forwards the packet to the correct port.
  32. 32. Network switchA network switch or switching hub is a computer networking device thatconnects network segments or network devices. The term commonly refers to amulti-port network bridge that processes and routes data at the data linklayer (layer 2) of the OSI model. Switches that additionally process data atthe network layer (layer 3) and above are often referred to as layer-3switches or multilayer switches.The first Ethernet switch was introduced by Kalpana in 1990Definition: A network switch is a small hardware device that joins multiplecomputers together within one local area network (LAN). Technically, networkswitches operate at layer two (Data Link Layer) of the OSI model.Network switches appear nearly identical to network hubs, but a switchgenerally contains more intelligence (and a slightly higher price tag) than ahub. Unlike hubs, network switches are capable of inspecting data packets asthey are received, determining the source and destination device of eachpacket, and forwarding them appropriately. By delivering messages only to theconnected device intended, a network switch conserves network bandwidth andoffers generally better performance than a hub.As with hubs, Ethernet implementations of network switches are the mostcommon. Mainstream Ethernet network switches support either10/100Mbps Fast Ethernet or Gigabit Ethernet(10/100/1000) standards.Different models of network switches support differing numbers of connecteddevices. Most consumer-grade network switches provide either four or eightconnections for Ethernet devices. Switches can be connected to each other, aso-called daisy chaining method to add progressivelyFunctionA switch is a telecommunication device which receives a message from anydevice connected to it and then transmits the message only to the device for
  33. 33. which the message was meant. This makes the switch a more intelligent devicethan a hub (which receives a message and then transmits it to all the otherdevices on its network). The network switch plays an integral part in mostmodern Ethernet local area networks (LANs). Mid-to-large sized LANs contain anumber of linked managed switches. Small office/home office (SOHO)applications typically use a single switch, or an all-purpose convergeddevice such as a residential gateway to access smalloffice/home broadband services such asDSL or cable Internet. In most of thesecases, the end-user device contains a router and components that interface tothe particular physical broadband technology. User devices may also include atelephone interface for VoIP.An Ethernet switch operates at the data link layer of the OSI model to create aseparate collision domain for each switch port. With 4 computers (e.g., A, B, C,and D) on 4 switch ports, any pair (e.g. A and B) can transfer data back andforth while the other pair (e.g. C and D) also do so simultaneously, and the twoconversations will not interfere with one another. In full duplex mode, thesepairs can also overlap (e.g. A transmits to B, simultaneously B to C, and so on).In the case of a repeater hub, they would all share the bandwidth and runin half duplex, resulting in collisions, which would then necessitateretransmissions.Role of switches in a networkSwitches may operate at one or more layers of the OSI model, including datalink and network. A device that operates simultaneously at more than one ofthese layers is known as a multilayer switch.In switches intended for commercial use, built-in or modular interfaces make itpossible to connect different types of networks, including Ethernet, FibreChannel, ATM, ITU-T G.hn and 802.11. This connectivity can be at any of thelayers mentioned. While layer-2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies suchas Ethernet and token ring is easier at layer 3.Devices that interconnect at layer 3 are traditionally called routers, so layer-3switches can also be regarded as (relatively primitive) routers.Where there is a need for a great deal of analysis of network performance andsecurity, switches may be connected between WAN routers as places foranalytic modules. Some vendors provide firewall,[2][3] network intrusiondetection,[4]and performance analysis modules that can plug into switch ports.Some of these functions may be on combined modules.[5]In other cases, the switch is used to create a mirror image of data that can goto an external device. Since most switch port mirroring provides only onemirrored stream, network hubs can be useful for fanning out data to severalread-only analyzers, such as intrusion detection systems and packet sniffers.
  34. 34. Hubs, Bridges, Switches and Routers are used to build networks. If you aretrying to design your own LAN (Local Area Network) at home, then youprobably need to know what they do and the main differences between them. Iwill try to cover all that in addition to some networking details to cultivate thearticle and provide better understanding of how the internet works. After all,always remember that the internet as you know it is nothing more than anetwork of networks!Hubs are used to build a LAN by connecting different computers in astar/hierarchal network topology, the most common type on LANs now a day. Ahub is a very simple (or dumb) device, once it gets bits of data sent fromcomputer A to B, it does not check the destination, instead, it forwards thatsignal to all other computers (B, C, D…) within the network. B will then pick itup while other nodes discard it. This amplifies that the traffic is shared.There are mainly two types of hubs:1. Passive: The signal is forwarded as it is (so it doesn’t need power supply).2. Active: The signal is amplified, so they work as repeaters. In fact they havebeen called multiport repeaters. (use power supply)Hubs can be connected to other hubs using an uplink port to extend thenetwork.OSI Model: Hubs work on the physical layer (lowest layer). That’s the reasonthey can’t deal with addressing or data filtering.Switches on the other hand are more advanced. Instead of broadcasting theframes everywhere, a switch actually checks for the destination MAC addressand forward it to the relevant port to reach that computer only. This way,switches reduce traffic and divide the collision domain into segments, this isvery sufficient for busy LANs and it also protects frames from being sniffed byother computers sharing the same segment.They build a table of which MAC address belongs to which segment. If adestination MAC address is not in the table it forwards to all segments except
  35. 35. the source segment. If the destination is same as the source, frame isdiscarded.Switches have built-in hardware chips solely designed to perform switchingcapabilities, therefore they are fast and come with many ports. Sometimes theyare referred to as intelligent bridges or multiport bridges.Different speed levels are supported. They can be 10 Mb/s, 100 Mb/s, 1 Gb/sor more.Most common switching methods are:1. Cut-through: Directly forward what the switch gets.2. Store and forward: receive the full frame before retransmitting it.OSI: Switches are on the data link layer (just above physical layer) that’s whythey deal with frames instead of bits and filter them based on MAC addresses.Switches are known to be used for their filtering capabilities.VLANs (Virtual LANs) and broadcast domains: Switches do not controlbroadcast domains by default, however, if a VLAN is configured in a switch itwill has its own broadcast domain.*VLAN is a logical group of network devices located on different LAN physicalsegments. However they are logically treated as if they were located on a singlesegment.Bridges are used to extend networks by maintaining signals and traffic.OSI: Bridges are on the data link layer so in principle they are capable to dowhat switches do like data filtering and separating the collision domain, butthey are less advanced. They are known to be used to extend distancecapabilities of networks.In a comparison with switches, they are slower because they use software toperform switching. They do not control broadcast domains and usually comewith less number of ports.Routers are used to connect different LANs or a LAN with a WAN (e.g. theinternet). Routers control both collision domains and broadcast domains. If thepacket’s destination is on a different network, a router is used to pass it theright way, so without routers the internet could not functions.
  36. 36. Routers use NAT (Network Address Translation) in conjunction with IPMasquerading to provide the internet to multiple nodes in the LAN under asingle IP address.Now a day, routers come with hub or switch technology to connect computersdirectly.OSI: Routers work on the network layer so they can filter data based on IPaddresses. They have route tables to store network addresses and forwardpackets to the right port.Gateways are very intelligent devices or else can be a computer running theappropriate software to connect and translate data between networks withdifferent protocols or architecture, so their work is much more complex than anormal router. For instance, allowing communication between TCP/IP clientsand IPX/SPX or AppleTalk.OSI: Gateways operate at the network layer and above, but most of them at theapplication layer.P.S. The term Gateway is used to refer to routers in some articles so beware. Inthis case, the router has gateway software. And Default Gateway is used torefer to the node (e.g. router) connecting the LAN to the outside (e.g. internet).Repeaters are simple devices that work at the physical layer of the OSI. Theyregenerate signals (active hubs does that too).There is an important rule to obey while using repeaters/hubs to extend a localnetwork and is called the 5-4-3 rule or the IEEE way. The rule forces that in asingle collision domain there shouldn’t be more than 5 segments, 4 repeatersbetween any two hosts in the network and only 3 of the segments can bepopulated (contain user connections).This rule ensures that a signal sent over the network will reach every part of itwithin an acceptable length of time.If the network is bigger, the collision domain can be divided into two parts ormore using a switch or a bridge.ConclusionWhat have been introduced so far are the main traditional devices used tobuild networks, understanding how they work helps to understand the logicbehind networks designing, however, now that technology advance quickly, it is
  37. 37. possible to find new products in the market combining two or more of thesedevices into one.Examples are:- Brouter: Works as a Bridge and as a Router.- IP Switch or MultiLayer Switch (MLS): New switches with routing capabilities,they forward data based on IP addresses, work at the network layer too.Router (computing)A Cisco ASM/2-32EM router deployed atCERN in 1987A router is a device that forwards data packets between computer networks,creating an overlay internetwork. A router is connected to two or more datalines from different networks. When a data packet comes in one of the lines,the router reads the address information in the packet to determine itsultimate destination. Then, using information in its routing table or routingpolicy, it directs the packet to the next network on its journey. Routers performthe "traffic directing" functions on the Internet. A data packet is typicallyforwarded from one router to another through the networks that constitute theinternetwork until it gets to its destination node.[1]The most familiar type of routers are home and small office routers that simplypass data, such as web pages and email, between the home computers and theowners cable or DSL modem, which connects to the Internet through an ISP.More sophisticated routers, such as enterprise routers, connect large businessor ISP networks up to the powerful core routers that forward data at high speedalong the optical fiber lines of the Internet backbone.
  38. 38. Types of routersThe earliest types of EDA routers were "manual routers" -- the drafter clicked amouse on the endpoint of each line segment of each net. Modern PCB designsoftware typically provides "interactive routers" -- the drafter selects a pad andclicks a few places to give the EDA tool an idea of where to go, and the EDAtool tries to place wires as close to that path as possible without violating DRC.Some more advanced interactive routers have "push and shove" features in aninteractive router; the EDA tool pushes other nets out of the way, if possible, inorder to place a new wire where the drafter wants it and still avoid violatingDRC. Modern PCB design software also typically provides "autorouters" thatroute all remaining unrouted connections without human intervention.The five main types of autorouters are: Maze router[1] Line probe router[2] Channel router[3] Area routers Switchbox routingBridge - network bridgesDefinition: A bridge device filters data traffic at a network boundary. Bridgesreduce the amount of traffic on a LAN by dividing it into two segments.Bridges operate at the data link layer (Layer 2) of the OSI model. Bridgesinspect incoming traffic and decide whether to forward or discard it. AnEthernet bridge, for example, inspects each incoming Ethernet frame -including the source and destination MAC addresses, and sometimes the framesize - in making individual forwarding decisions.Bridges serve a similar function as switches, that also operate at Layer 2.Traditional bridges, though, support one network boundary, whereas switchesusually offer four or more hardware ports. Switches are sometimes called"multi-port bridges" for this reason.
  39. 39. ModemA modem (modulator-demodulator) is a device that modulates an analogcarrier signal to encode digital information, and also demodulates such acarrier signal to decode the transmitted information. The goal is to producea signal that can be transmitted easily and decoded to reproduce the originaldigital data. Modems can be used over any means of transmitting analogsignals, from light emitting diodes to radio. The most familiar example isa voice band modem that turns the digital data of a personal computer intomodulated electrical signals in the voice frequency range ofa telephone channel. These signals can be transmitted over telephone lines anddemodulated by another modem at the receiver side to recover the digital data.Modems are generally classified by the amount of data they can send in agiven unit of time, usually expressed in bits per second (bit/s, or bps), or bytesper second (B/s). Modems can alternatively be classified by their symbol rate,measured in baud. The baud unit denotes symbols per second, or the numberof times per second the modem sends a new signal. For example, the ITU V.21standard used audio frequency-shift keying, that is to say, tones of differentfrequencies, with two possible frequencies corresponding to two distinctsymbols (or one bit per symbol), to carry 300 bits per second using 300 baud.By contrast, the original ITU V.22 standard, which was able to transmit andreceive four distinct symbols (two bits per symbol), handled 1,200 bit/s bysending 600 symbols per second (600 baud) using phase shift keying.What is Modem and its benefits?Modem is actually one of the most important hardware devices used in thecomputer especially for the purpose of networking of the internet. Modems areused to modulate signals of analog types so as to be able to encode the digitalinformation from it. Modems are also used for demodulation of the signals soas to decode the information transmitted.Therefore it is for the soul purpose of transmission of the signal easily so that itcan be decoded to reproduce the digital information.The classification of modems is done on the basis of the information that cantransferred in a given time period by them which is usually measured in bps,or bits per second. Modems are now used by the internet users, whichpreferably run faster than such as the cable and the ADSL modems.
  40. 40. These days the modems area great benefit to be used in the telecommunicationsystems with the launch of the radio modems. These modems are themicrowave modems and can transmit even more than a hundred million bitsper second, which is a very high speed for any modem to work on. The launchof the optical fibers has given rise to the optical modems which are now usedfor the purpose of transmission of data over undersea optical fibers. Thesemodems have unbelievably high rate of transmission, which can reach up toabout a billion bits per second.Although modem internet connection has been replaced over the recent yearswith broadband, modems still hold a vital position is certain other aspects ofthe modern world such as the space telecommunications and of course in thetelephone communications.
  41. 41. OSI MODELVirtually all networks in use today are based in some fashion on the OpenSystems Interconnection (OSI) standard. OSI was developed in 1984 bytheInternational Organization for Standardization (ISO), a global federation ofnational standards organizations representing approximately 130 countries.The core of this standard is the OSI Reference Model, a set of seven layersthat define the different stages that data must go through to travel from onedevice to another over a network. In this article, youll find out all about theOSI standard.Description of OSI layersAt each layer, certain things happen to the data that prepare it for the nextlayer. The seven layers, which separate into two sets, are:Application SetLayer 7: Application - This is the layer that actually interacts withthe operating system or application whenever the user chooses to transfer files,read messages or perform other network-related activities.Layer 6: Presentation - Layer 6 takes the data provided by the Applicationlayer and converts it into a standard format that the other layers canunderstand.Layer 5: Session - Layer 5 establishes, maintains and ends communicationwith the receiving device.Transport SetLayer 4: Transport - This layer maintains flow control of data and providesfor error checking and recovery of data between the devices. Flow controlmeans that the Transport layer looks to see if data is coming from more thanone application and integrates each applications data into a single stream forthe physical network.Layer 3: Network - The way that the data will be sent to the recipient device isdetermined in this layer. Logical protocols, routing and addressing are handledhere.Layer 2: Data - In this layer, the appropriate physical protocol is assigned tothe data. Also, the type of network and the packet sequencing is defined.
  42. 42. Layer 1: Physical - This is the level of the actual hardware. It defines thephysical characteristics of the network such as connections, voltage levels andtiming.The OSI Reference Model is really just a guideline. Actual protocolstacks often combine one or more of the OSI layers into a single layer.According to recommendation X.200, there are seven layers, labeled 1 to 7,with layer 1 at the bottom. Each layer is generically known as an N layer. An"N+1 entity" (at layer N+1) requests services from an "N entity" (at layer N).At each level, two entities (N-entity peers) interact by means of the N protocolby transmitting protocol data units (PDU).A Service Data Unit (SDU) is a specific unit of data that has been passed downfrom an OSI layer to a lower layer, and which the lower layer has not yetencapsulated into a protocol data unit (PDU). An SDU is a set of data that issent by a user of the services of a given layer, and is transmitted semanticallyunchanged to a peer service user.The PDU at a layer N is the SDU of layer N-1. In effect the SDU is the payloadof a given PDU. That is, the process of changing an SDU to a PDU, consists ofan encapsulation process, performed by the lower layer. All the data containedin the SDU becomes encapsulated within the PDU. The layer N-1 adds headersor footers, or both, to the SDU, transforming it into a PDU of layer N. Theadded headers or footers are part of the process used to make it possible to getdata from a source to a destination. OSI Model Data unit Layer Function 7. Application Network process to application Data representation, encryption and decryption, convert machine 6. Presentation dependent data to machine Data Host independent data layers Interhost communication, 5. Session managing sessions between applications Segments 4. Transport End-to-end connections, reliability
  43. 43. and flow control Path determination and logical Packet/Datagram 3. Network addressing Media Frame 2. Data link Physical addressing layers Media, signal and binary Bit 1. Physical transmissionSome orthogonal aspects, such as management and security, involve everylayer.Security services are not related to a specific layer: they can be related by anumber of layers, as defined by ITU-TX.800 Recommendation.[3]These services are aimed to improve theCIA triad (confidentiality, integrity,andavailability) of transmitted data. Actually the availability of communicationservice is determined by network design and/ornetworkmanagement protocols. Appropriate choices for these are needed to protectagainst denial of service.Layer 1: physical layerThe physical layer defines electrical and physical specifications for devices. Inparticular, it defines the relationship between a device and a transmissionmedium, such as a copper or fiber optical cable. This includes the layoutof pins, voltages, line impedance, cable specifications, signaltiming, hubs, repeaters, network adapters, host bus adapters (HBA usedin storage area networks) and more.The major functions and services performed by the physical layer are: Establishment and termination of a connection to a communications medium. Participation in the process whereby the communication resources are effectively shared among multiple users. For example, contention resolution and flow control. Modulation or conversion between the representation of digital data in user equipment and the corresponding signals transmitted over a communications channel. These are signals operating over the physical cabling (such as copper and optical fiber) or over a radio link.Parallel SCSI buses operate in this layer, although it must be remembered thatthe logical SCSI protocol is a transport layer protocol that runs over this bus.Various physical-layer Ethernet standards are also in this layer; Ethernetincorporates both this layer and the data link layer. The same applies to other
  44. 44. local-area networks, such as token ring, FDDI, ITU-T G.hn and IEEE 802.11,as well as personal area networks such as Bluetooth and IEEE 802.15.4.Layer 2: data link layerThe data link layer provides the functional and procedural means to transferdata between network entities and to detect and possibly correct errors thatmay occur in the physical layer. Originally, this layer was intended for point-to-point and point-to-multipoint media, characteristic of wide area media in thetelephone system. Local area network architecture, which included broadcast-capable multi-access media, was developed independently of the ISO workin IEEE Project 802. IEEE work assumed sublayer-ing and managementfunctions not required for WAN use. In modern practice, only error detection,not flow control using sliding window, is present in data link protocols suchas Point-to-Point Protocol(PPP), and, on local area networks, the IEEE802.2 LLC layer is not used for most protocols on the Ethernet, and on otherlocal area networks, its flow control and acknowledgment mechanisms arerarely used. Sliding window flow control and acknowledgment is used at thetransport layer by protocols such as TCP, but is still used in nicheswhere X.25 offers performance advantages.The ITU-T G.hn standard, which provides high-speed local area networkingover existing wires (power lines, phone lines and coaxial cables), includes acomplete data link layerwhich provides both error correction and flow controlby means of a selective repeat Sliding Window Protocol.Both WAN and LAN service arrange bits, from the physical layer, into logicalsequences called frames. Not all physical layer bits necessarily go into frames,as some of these bits are purely intended for physical layer functions. Forexample, every fifth bit of the FDDI bit stream is not used by the layer.Layer 3: network layerThe network layer provides the functional and procedural means of transferringvariable length data sequences from a source host on one network to adestination host on a different network (in contrast to the data link layer whichconnects hosts within the same network), while maintaining the quality ofservice requested by the transport layer. The network layer performsnetwork routing functions, and might also perform fragmentation andreassembly, and report delivery errors. Routers operate at this layer, sendingdata throughout the extended network and making the Internet possible. Thisis a logical addressing scheme – values are chosen by the network engineer.The addressing scheme is not hierarchical.The network layer may be divided into three sublayers:
  45. 45. 1. Subnetwork access – that considers protocols that deal with the interface to networks, such as X.25; 2. Subnetwork-dependent convergence – when it is necessary to bring the level of a transit network up to the level of networks on either side 3. Subnetwork-independent convergence – handles transfer across multiple networks.An example of this latter case is CLNP, or IPv6 ISO 8473. It managesthe connectionless transfer of data one hop at a time, from end systemto ingress router, router to router, and from egress router to destination endsystem. It is not responsible for reliable delivery to a next hop, but only for thedetection of erroneous packets so they may be discarded. In this scheme, IPv4and IPv6 would have to be classed with X.25 as subnet access protocolsbecause they carry interface addresses rather than node addresses.A number of layer-management protocols, a function defined in theManagement Annex, ISO 7498/4, belong to the network layer. These includerouting protocols, multicast group management, network-layer information anderror, and network-layer address assignment. It is the function of the payloadthat makes these belong to the network layer, not the protocol that carriesthem.Layer 4: transport layerThe transport layer provides transparent transfer of data between end users,providing reliable data transfer services to the upper layers. The transport layercontrols the reliability of a given link through flow control,segmentation/desegmentation, and error control. Some protocols are state-and connection-oriented. This means that the transport layer can keep track ofthe segments and retransmit those thafail. The transport layer also providesthe acknowledgement of the successful data transmission and sends the nextdata if no errors occurred.OSI defines five classes of connection-mode transport protocols ranging fromclass 0 (which is also known as TP0 and provides the least features) to class 4(TP4, designed for less reliable networks, similar to the Internet). Class 0contains no error recovery, and was designed for use on network layers thatprovide error-free connections. Class 4 is closest to TCP, although TCPcontains functions, such as the graceful close, which OSI assigns to thesession layer. Also, all OSI TP connection-mode protocol classes provideexpedited data and preservation of record boundaries. Detailed characteristicsof TP0-4 classes are shown in the following table
  46. 46. Feature Name TP0 TP1 TP2 TP3 TP4Connection oriented network Yes Yes Yes Yes YesConnectionless network No No No No YesConcatenation and separation No Yes Yes Yes YesSegmentation and reassembly Yes Yes Yes Yes YesError Recovery No Yes Yes Yes YesReinitiate connection (if an excessive number No Yes No Yes Noof PDUs are unacknowledged)Multiplexing and demultiplexing over a single virtual No No Yes Yes YescircuitExplicit flow control No No Yes Yes YesRetransmission on timeout No No No No YesReliable Transport Service No Yes No Yes YesAn easy way to visualize the transport layer is to compare it with a Post Office,which deals with the dispatch and classification of mail and parcels sent. Doremember, however, that a post office manages the outer envelope of mail.Higher layers may have the equivalent of double envelopes, such ascryptographic presentation services that can be read by the addressee only.Roughly speaking, tunneling protocols operate at the transport layer, such ascarrying non-IP protocols such as IBMs SNA or Novells IPX over an IPnetwork, or end-to-end encryption with IPsec. While Generic RoutingEncapsulation (GRE) might seem to be a network-layer protocol, if the
  47. 47. encapsulation of the payload takes place only at endpoint, GRE becomes closerto a transport protocol that uses IP headers but contains complete frames orpackets to deliver to an endpoint. L2TP carries PPP frames inside transportpacket.Although not developed under the OSI Reference Model and not strictlyconforming to the OSI definition of the transport layer, the TransmissionControl Protocol (TCP) and the User Datagram Protocol (UDP) of the InternetProtocol Suite are commonly categorized as layer-4 protocols within OSI.Layer 5: session layerThe session layer controls the dialogues (connections) between computers. Itestablishes, manages and terminates the connections between the local andremote application. It provides for full-duplex, half-duplex,or simplex operation, and establishes checkpointing, adjournment,termination, and restart procedures. The OSI model made this layerresponsible for graceful close of sessions, which is a property ofthe Transmission Control Protocol, and also for session checkpointing andrecovery, which is not usually used in the Internet Protocol Suite. The sessionlayer is commonly implemented explicitly in application environments thatuse remote procedure calls. On this level, Inter-Processcommunication happen(SIGHUP, SIGKILL, End Process, etc.).Layer 6: presentation layerThe presentation layer establishes context between application-layer entities, inwhich the higher-layer entities may use different syntax and semantics if thepresentation service provides a mapping between them. If a mapping isavailable, presentation service data units are encapsulated into sessionprotocol data units, and passed down the stack.This layer provides independence from data representation (e.g., encryption) bytranslating between application and network formats. The presentation layertransforms data into the form that the application accepts. This layer formatsand encrypts data to be sent across a network. It is sometimes called thesyntax layer.[5]The original presentation structure used the basic encoding rules of AbstractSyntax Notation One (ASN.1), with capabilities such as converting an EBCDIC-coded text file to anASCII-coded file, or serialization of objects and other datastructures from aLayer 7: application layerThe application layer is the OSI layer closest to the end user, which means thatboth the OSI application layer and the user interact directly with the softwareapplication. This layer interacts with software applications that implement acommunicating component. Such application programs fall outside the scopeof the OSI model. Application-layer functions typically include identifying
  48. 48. communication partners, determining resource availability, and synchronizingcommunication. When identifying communication partners, the applicationlayer determines the identity and availability of communication partners for anapplication with data to transmit. When determining resource availability, theapplication layer must decide whether sufficient network or the requestedcommunication exists. In synchronizing communication, all communicationbetween applications requires cooperation that is managed by the applicationlayer.
  49. 49. BIBLIOGRAPHYWWW.GOOGLE.COMWWW.WIKIPEDIA.COMhttp://computer.howstuffworks.com

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