DATA COMMUNICATIONS. Computer network

Transcription

1 UNIT I DATA COMMUNICATIONS Cmpnents Directin f Data flw netwrks Cmpnents and Categries Types f Cnnectins Tplgies Prtcls and Standards ISO / OSI Mdel Transmissin Media Caxial Cable Fiber Optics Line Cding Mdems RS232 Interfacing sequences. Cmputer netwrk A cllectin f cmputing devices cnnected in rder t cmmunicate and share resurces. Cnnectins between cmputing devices can be physical using wires r cables r wireless using radi waves r infrared signals Data cmmunicatin - electrnic transmissin f infrmatin that has been encded digitally (as fr strage and prcessing by cmputers) Basic Cmpnents fr a Cmmunicatin System All cmmunicatin systems require 5 things: 1. Data Surce: This is where the data being transferred riginates. 2. A Transmitter: encdes data int a signal fr transmissin. 3. A Transmissin Medium: This is the physical channel by which the data signal is transmitted. It may be cable r nn cable. 4. A Receiver: This decdes the transmitted data back int a useable frm. 5. The Destinatin: The final destinatin fr where the transmitted data is required.

2 Directin f Data flw 1. Simplex: Cmmunicatin can take place nly in ne directin. eg. T.V bradcasting. 2. Half-duplex: Cmmunicatin can take place in ne directin at a time. Suppse nde A and B are cnnected then half-duplex cmmunicatin means that at a time data can flw frm A t B r frm B t A, but nt simultaneusly. eg. Tw persns talking t each ther such that when speaks the ther listens and vice versa. 3. Full-duplex: Cmmunicatin can take place simultaneusly in bth directins. eg. A discussin in a grup withut discipline. Types f Netwrks Lcal-area netwrk (LAN) A netwrk that cnnects a relatively small number f machines in a relatively clse gegraphical area Ring tplgy directin cnnects all ndes in a clsed lp n which messages travel in ne Star tplgy centers arund ne nde t which all thers are cnnected and thrugh which all messages are sent Bus tplgy ndes are cnnected t a single cmmunicatin line that carries messages in bth directins

3 Wide-area netwrk (WAN) A netwrk that cnnects lcal-area netwrks ver a ptentially large gegraphic distance Metrplitan-area netwrk (MAN) The cmmunicatin infrastructures that have been develped in and arund large cities What is a Tplgy? The physical tplgy f a netwrk refers t the cnfiguratin f cables, cmputers, and ther peripherals. Physical tplgy shuld nt be cnfused with lgical tplgy which is the methd used t pass infrmatin between wrkstatins. Netwrk Tplgies A netwrk tplgy is the basic design f a cmputer netwrk. It is very much like a map f a rad. It details hw key netwrk cmpnents such as ndes and links are intercnnected. There are three primary types f netwrk tplgies which refer t the physical and lgical layut f the Netwrk cabling. They are: 1. Star Tplgy: All devices cnnected with a Star setup cmmunicate thrugh a central Hub by cable segments. Signals are transmitted and received thrugh the Hub. It is the simplest and the ldest and all the telephne switches are based n this. In a star tplgy, each netwrk device has a hme run f cabling back t a netwrk hub, giving each device a separate cnnectin t the netwrk. S, there can be multiple cnnectins in parallel.

4 Advantages Netwrk administratin and errr detectin is easier because prblem is islated t central nde Netwrks runs even if ne hst fails Expansin becmes easier and scalability f the netwrk increases Mre suited fr larger netwrks Disadvantages Bradcasting and multicasting is nt easy because sme extra functinality needs t be prvided t the central hub If the central nde fails, the whle netwrk ges dwn; thus making the switch sme kind f a bttleneck Installatin csts are high because each nde needs t be cnnected t the central switch 2. Bus Tplgy: The simplest and ne f the mst cmmn f all tplgies, Bus cnsists f a single cable, called a Backbne that cnnects all wrkstatins n the netwrk using a single line. All transmissins must pass thrugh each f the cnnected devices t cmplete the desired request. Each wrkstatin has its wn individual signal that identifies it and allws fr the requested data t be returned t the crrect riginatr. In the Bus Netwrk, messages are sent in bth directins frm a single pint and are read by the nde (cmputer r peripheral n the netwrk) identified by the cde with the message. Mst Lcal Area Netwrks (LANs) are Bus Netwrks because the netwrk will cntinue t functin even if ne cmputer is dwn. This tplgy wrks equally well fr either peer t peer r client server.

5 The purpse f the terminatrs at either end f the netwrk is t stp the signal being reflected back. Advantages Bradcasting and multicasting is much simpler Netwrk is redundant in the sense that failure f ne nde desn't affect the netwrk. The ther part may still functin prperly Least expensive since less amunt f cabling is required and n netwrk switches are required Gd fr smaller netwrks nt requiring higher speeds Disadvantages Truble shting and errr detectin becmes a prblem because, lgically, all ndes are equal Less secure because sniffing is easier Limited in size and speed 3. Ring Tplgy: All the ndes in a Ring Netwrk are cnnected in a clsed circle f cable. Messages that are transmitted travel arund the ring until they reach the cmputer that they are addressed t, the signal being refreshed by each nde. In a ring tplgy, the netwrk signal is passed thrugh each netwrk card f each device and passed n t the next device. Each device prcesses and retransmits the signal, s it is capable f supprting many devices in a smewhat slw but very rderly fashin. There is a very nice feature that everybdy gets a chance t send a packet and it is guaranteed that every nde gets t send a packet in a finite amunt f time.

6 Advantages Bradcasting and multicasting is simple since yu just need t send ut ne message Less expensive since less cable ftage is required It is guaranteed that each hst will be able t transmit within a finite time interval Very rderly netwrk where every device has access t the tken and the pprtunity t transmit Perfrms better than a star netwrk under heavy netwrk lad Disadvantages Failure f ne nde brings the whle netwrk dwn Errr detectin and netwrk administratin becmes difficult Mves, adds and changes f devices can effect the netwrk It is slwer than star tplgy under nrmal lad Generally, BUS architecture is preferred ver the ther tplgies - f curse, this is a very subjective pinin and the final design depends n the requirements f the netwrk mre than anything else. Lately, mst netwrks are shifting twards the STAR tplgy. Ideally we wuld like t design netwrks, which physically resemble the STAR tplgy, but behave like BUS r RING tplgy.basic types f tplgies Cnsideratins When Chsing a Tplgy: Mney. A linear bus netwrk may be the least expensive way t install a netwrk; yu d nt have t purchase cncentratrs. Length f cable needed. The linear bus netwrk uses shrter lengths f cable. Future grwth. With a star tplgy, expanding a netwrk is easily dne by adding anther cncentratr. Cable type. The mst cmmn cable in schls is unshielded twisted pair, which is mst ften used with star tplgies.

7 Summary Chart: Physical Tplgy Cmmn Cable Cmmn Prtcl Linear Bus Star Twisted Pair Caxial Fiber Twisted Pair Fiber Ethernet LcalTalk Ethernet LcalTalk Star-Wired Ring Twisted Pair Tken Ring Tree Twisted Pair Caxial Fiber Ethernet Layer 7 - Applicatin: OSI MODEL The Applicatin layer prvides services t the sftware thrugh which the user requests netwrk services. This layer is nt nr des it cntain any applicatins, and yur cmputer applicatin sftware is nt n this layer. In ther wrds, a prgram like Micrsft Wrd des nt exist at this layer, but brwsers, FTP clients and mail clients d. Layer 6 - Presentatin: This layer is cncerned with data representatin and cde frmatting. Layer 5 - Sessin: The Sessin layer establishes, maintains, and manages the cmmunicatin sessin between cmputers. Layer 4 - Transprt: The functins defined in this layer prvide fr the reliable transmissin f data segments as well as the disassembly and assembly f the data befre and after transmissin. Layer 3 - Netwrk:

8 This is the layer n which ruting takes place. The Netwrk layer defines the prcesses used t rute data acrss the netwrk and the structure and use f lgical addressing. Layer 2 - Data Link: As its name suggests, this layer is cncerned with the linkages and mechanisms used t mve data abut the netwrk, including the tplgy, such as Ethernet r Tken Ring, and als deals with the ways in which data is reliably transmitted. Layer 1 - Physical: The Physical layer's name says it all. This layer defines the electrical and physical specificatins fr the netwrking media that carry the data bits acrss a netwrk. ISO-OSI 7-Layer Netwrk Architecture This lecture intrduces the ISO-OSI layered architecture f Netwrks. We will first list the layers as defined by the standard in the increasing rder f functin cmplexity: 1. Physical Layer 2. Data Link Layer 3. Netwrk Layer 4. Transprt Layer 5. Sessin Layer 6. Presentatin Layer 7. Applicatin Layer Physical Layer This layer is the lwest layer in the OSI mdel. It helps in the transmissin f data between tw machines that are cmmunicating thrugh a physical medium, which can be ptical fibers, cpper wire r wireless etc. The fllwing are the main functins f the physical layer: 1. Hardware Specificatin: The details f the physical cables, netwrk interface cards, wireless radis, etc are a part f this layer. Caxial Cable Hybrid Cable Wireless Card Netwrk Card

9 2. Encding and Signaling: Hw are the bits encded in the medium is als decided by this layer. Fr example, n the cpper wire medium, we can use different vltage levels fr a certain time interval t represent '0' and '1'. We may use +5mV fr 1nsec t represent '1' and -5mV fr 1nsec t represent '0'. All the issues f mdulatin is dealt with in this layer. e.g., we may use Binary phase shift keying fr the representatin f '1' and '0' rather than using different vltage levels if we have t transfer in RF waves. Binary Phase Shift Keying 3. Data Transmissin and Receptin: The transfer f each bit f data is the respnsibility f this layer. This layer assures the transmissin f each bit with a high prbability. The transmissin f the bits is nt cmpletely reliable as their is n errr crrectin in this layer. 4. Tplgy and Netwrk Design: The netwrk design is the integral part f the physical layer. Which part f the netwrk is the ruter ging t be placed, where the switches will be used, where we will put the hubs and hw many machines is each switch ging t handle, what server is ging t be placed where, and many such cncerns are t be taken care f by the physical layer. The varius kinds f entmlgies that we decide t use may be ring, bus, star r a hybrid f these tplgies depending n ur requirements.

10 Data Link Layer This layer prvides reliable transmissin f a packet by using the services f the physical layer which transmits bits ver the medium in an unreliable fashin. This layer is cncerned with: 1. Framing: Breaking input data int frames (typically a few hundred bytes) and caring abut the frame bundaries and the size f each frame. 2. Acknwledgment: Sent by the receiving end t infrm the surce that the frame was received withut any errr. 3. Sequence Numbering: T acknwledge which frame was received. 4. Errr Detectin: The frames may be damaged, lst r duplicated leading t errrs. The errr cntrl is n link t link basis. 5. Retransmissin: The packet is retransmitted if the surce fails t receive acknwledgment. 6. Flw Cntrl: Necessary fr a fast transmitter t keep pace with a slw receiver.

11 Data Link Layer Netwrk Layer Its basic functins are ruting and cngestin cntrl. Ruting: This deals with determining hw packets will be ruted (transferred) frm surce t destinatin. It can be f three types : Static: Rutes are based n static tables that are "wired int" the netwrk and are rarely changed. Dynamic: All packets f ne applicatin can fllw different rutes depending upn the tplgy f the netwrk, the shrtest path and the current netwrk lad. Semi-Dynamic: A rute is chsen at the start f each cnversatin and then all the packets f the applicatin fllw the same rute. Ruting

12 The services prvided by the netwrk can be f tw types: Cnnectin less service: Each packet f an applicatin is treated as an independent entity. On each packet f the applicatin the destinatin address is prvided and the packet is ruted. Cnnectin riented service: Here, first a cnnectin is established and then all packets f the applicatin fllw the same rute. T understand the abve cncept, we can als draw an analgy frm the real life. Cnnectin riented service is mdeled after the telephne system. All vice packets g n the same path after the cnnectin is established till the cnnectin is hung up. It acts like a tube ; the sender pushes the bjects in at ne end and the receiver takes them ut in the same rder at the ther end. Cnnectin less service is mdeled after the pstal system. Each letter carries the destinatin address and is ruted independent f all the thers. Cngestin Cntrl: A ruter can be cnnected t 4-5 netwrks. If all the netwrks send packet at the same time with maximum rate pssible then the ruter may nt be able t handle all the packets and may drp sme/all packets. In this cntext the drpping f the packets shuld be minimized and the surce whse packet was drpped shuld be infrmed. The cntrl f such cngestin is als a functin f the netwrk layer. Other issues related with this layer are transmitting time, delays, jittering. Internetwrking: Internet wrks are multiple netwrks that are cnnected in such a way that they act as ne large netwrk, cnnecting multiple ffice r department netwrks. Internet wrks are cnnected by netwrking hardware such as ruters, switches, and bridges. Internetwrking is a slutin brn f three netwrking prblems: islated LANs, duplicatin f resurces, and the lack f a centralized netwrk management system. With cnnected LANs, cmpanies n lnger have t duplicate prgrams r resurces n each netwrk. This in turn gives way t managing the netwrk frm ne central lcatin instead f trying t manage each separate LAN. We shuld be able t transmit any packet frm ne netwrk t any ther netwrk even if they fllw different prtcls r use different addressing mdes. Inter-Netwrking

13 Netwrk Layer des nt guarantee that the packet will reach its intended destinatin. There are n reliability guarantees. Transprt Layer Its functins are: Multiplexing / Demultiplexing: Nrmally the transprt layer will create distinct netwrk cnnectin fr each transprt cnnectin required by the sessin layer. The transprt layer may either create multiple netwrk cnnectins (t imprve thrughput) r it may multiplex several transprt cnnectins nt the same netwrk cnnectin (because creating and maintaining netwrks may be expensive). Demultiplexing will be required at the receiving end. A pint t nte here is that cmmunicatin is always carried ut between tw prcesses and nt between tw machines. This is als knwn as prcess-t-prcess cmmunicatin. Fragmentatin and Re-assembly: The data accepted by the transprt layer frm the sessin layer is split up int smaller units (fragmentatin) if needed and then passed t the netwrk layer. Crrespndingly, the data prvided by the netwrk layer t the transprt layer n the receiving side is re-assembled. Fragmentatin Reassembly Types f service: The transprt layer als decides the type f service that shuld be prvided t the sessin layer. The service may be perfectly reliable, r may be reliable within certain tlerances r may nt be reliable at all. The message may r may nt be received in the rder in which it was sent. The decisin regarding

14 the type f service t be prvided is taken at the time when the cnnectin is established. Errr Cntrl: If reliable service is prvided then errr detectin and errr recvery peratins are als perfrmed. It prvides errr cntrl mechanism n end t end basis. Flw Cntrl: A fast hst cannt keep pace with a slw ne. Hence, this is a mechanism t regulate the flw f infrmatin. Cnnectin Establishment / Release: The transprt layer als establishes and releases the cnnectin acrss the netwrk. This requires sme srt f naming mechanism s that a prcess n ne machine can indicate with whm it wants t cmmunicate. Sessin Layer It deals with the cncept f Sessins i.e. when a user lgins t a remte server he shuld be authenticated befre getting access t the files and applicatin prgrams. Anther jb f sessin layer is t establish and maintain sessins. If during the transfer f data between tw machines the sessin breaks dwn, it is the sessin layer which re-establishes the cnnectin. It als ensures that the data transfer starts frm where it breaks keeping it transparent t the end user. e.g. In case f a sessin with a database server, this layer intrduces check pints at varius places s that in case the cnnectin is brken and reestablished, the transitin running n the database is nt lst even if the user has nt cmmitted. This activity is called Synchrnizatin. Anther functin f this layer is Dialgue Cntrl which determines whse turn is it t speak in a sessin. It is useful in vide cnferencing. Presentatin Layer This layer is cncerned with the syntax and semantics f the infrmatin transmitted. In rder t make it pssible fr cmputers with different data representatins t cmmunicate data structures t be exchanged can be defined in abstract way alng with standard encding. It als manages these abstract data structures and allws higher level f data structures t be defined an exchange. It encdes the data in standard agreed way(netwrk frmat). Suppse there are tw machines A and B ne fllws 'Big Endian' and ther 'Little Endian' fr data representatin. This layer ensures that the data transmitted by ne gets cnverted in the frm cmpatible t ther machine. This layer is cncerned with the syntax and semantics f the

15 infrmatin transmitted. In rder t make it pssible fr cmputers with different data representatins t cmmunicate data structures t be exchanged can be defined in abstract way alng with standard encding. It als manages these abstract data structures and allws higher level f data structures t be defined an exchange. Other functins include cmpressin, encryptin etc. Applicatin Layer The seventh layer cntains the applicatin prtcls with which the user gains access t the netwrk. The chice f which specific prtcls and their assciated functins are t be used at the applicatin level is up t the individual user. Thus the bundary between the presentatin layer and the applicatin layer represents a separatin f the prtcls impsed by the netwrk designers frm thse being selected and implemented by the netwrk users.fr example cmmnly used prtcls are HTTP(fr web brwsing), FTP(fr file transfer) etc. Netwrk Layers as in Practice The functinality f Applicatin layer and Presentatin layer is merged int ne and is called as the Applicatin Layer. Functinalities f Sessin Layer is nt implemented in mst netwrks tday. Als, the Data Link layer is split theretically int MAC (Medium Access Cntrl) Layer and LLC (Link Layer Cntrl). But again in practice, the LLC layer is nt implemented by mst netwrks. S as f tday, the netwrk architecture is f 5 layers nly. Netwrk Layers in Internet Tday

16 Physical Layer Physical layer is cncerned with transmitting raw bits ver a cmmunicatin channel. The design issues have t d with making sure that when ne side sends a 1 bit, it is recieved by the ther side as 1 bit and nt as 0 bit. In physical layer we deal with the cmmunicatin medium used fr transmissin. Types f Medium Medium can be classified int 2 categries. 1. Guided Media: Guided media means that signals is guided by the presence f physical media i.e. signals are under cntrl and remains in the physical wire. Fr eg. Cpper wire. 2. Unguided Media: Unguided Media means that there is n physical path fr the signal t prpagate. Unguided media are essentially electr-magnetic waves. There is n cntrl n flw f signal. Fr eg. Radi waves. Cmmunicatin Links In a netwrk ndes are cnnected thrugh links. The cmmunicatin thrugh links can be classified as 4. Simplex: Cmmunicatin can take place nly in ne directin. eg. T.V bradcasting. 5. Half-duplex: Cmmunicatin can take place in ne directin at a time. Suppse nde A and B are cnnected then half-duplex cmmunicatin means that at a time data can flw frm A t B r frm B t A but nt simultaneusly. eg. tw persns talking t each ther such that when speaks the ther listens and vice versa. 6. Full-duplex: Cmmunicatin can take place simultaneusly in bth directins. eg. A discussin in a grup withut discipline. Links can be further classified as 1. Pint t Pint: In this cmmunicatin nly tw ndes are cnnected t each ther. When a nde sends a packet then it can be received nly by the nde n the ther side and nne else. 2. Multipint: It is a kind f sharing cmmunicatin, in which signal can be received by all ndes. This is als called bradcast.

17 Generally tw kind f prblems are assciated in transmissin f signals. 1. Attenuatin: When a signal transmits in a netwrk then the quality f signal degrades as the signal travels lnger distances in the wire. This is called attenuatin. T imprve quality f signal amplifiers are used at regular distances. 2. Nise: In a cmmunicatin channel many signals transmit simultaneusly, certain randm signals are als present in the medium. Due t interference f these signals ur signal gets disrupted a bit. Bandwidth Bandwidth simply means hw many bits can be transmitted per secnd in the cmmunicatin channel. In technical terms it indicates the width f frequency spectrum. Transmissin Media Guided Transmissin Media In Guided transmissin media generally tw kind f materials are used. 1. Cpper Caxial Cable Twisted Pair 2. Optical Fiber 1. Caxial Cable: Caxial cable cnsists f an inner cnductr and an uter cnductr which are separated by an insulatr. The inner cnductr is usually cpper. The uter cnductr is cvered by a plastic jacket. It is named caxial because the tw cnductrs are caxial. Typical diameter f caxial cable lies in between 0.4 inch t 1 inch. The mst applicatin f caxial cable is cable T.V. The caxial cable has high bandwidth, attenuatin is less.

18 2. Twisted Pair: A Twisted pair cnsists f tw insulated cpper wires, typically 1mm thick. The wires are twisted tgether in a helical frm the purpse f twisting is t reduce crss talk interference between several pairs. Twisted Pair is much cheaper then caxial cable but it is susceptible t nise and electrmagnetic interference and attenuatin is large. Twisted Pair can be further classified in tw categries: Unshielded twisted pair: In this n insulatin is prvided, hence they are susceptible t interference. Shielded twisted pair: In this a prtective thick insulatin is prvided but shielded twisted pair is expensive and nt cmmnly used. The mst cmmn applicatin f twisted pair is the telephne system. Nearly all telephnes are cnnected t the telephne cmpany ffice by a twisted pair. Twisted pair can run several kilmeters withut amplificatin, but fr lnger distances repeaters are needed. Twisted pairs can be used fr bth analg and digital transmissin. The bandwidth depends n the thickness f wire and the distance traveled. Twisted pairs are generally limited in distance, bandwidth and data rate. 3. Optical Fiber: In ptical fiber light is used t send data. In general terms presence f light is taken as bit 1 and its absence as bit 0. Optical fiber cnsists f inner cre f either glass r plastic. Cre is surrunded by cladding f the same material but f different refractive index. This cladding is surrunded by a plastic jacket which prevents ptical fiber frm electrmagnetic interference and harshly envirnments. It uses the principle f ttal internal reflectin t transfer data ver ptical fibers. Optical fiber is much better in bandwidth as cmpared t cpper wire, since there is hardly any attenuatin r electrmagnetic interference in ptical wires.

19 Hence there are fewer requirements t imprve quality f signal, in lng distance transmissin. Disadvantage f ptical fiber is that end pints are fairly expensive. (eg. switches) 4. Differences between different kinds f ptical fibers: 1. Depending n material Made f glass Made f plastic. 2. Depending n radius Thin ptical fiber Thick ptical fiber 3. Depending n light surce LED (fr lw bandwidth) Injectin lased dide (fr high bandwidth) Wireless Transmissin 1. Radi: Radi is a general term that is used fr any kind f frequency. But higher frequencies are usually termed as micrwave and the lwer frequency band cmes under radi frequency. There are many applicatin f radi. Fr eg. Crdless keybard, wireless LAN, wireless Ethernet. But it is limited in range t nly a few hundred meters. Depending n frequency radi ffers different bandwidths.

20 2. Terrestrial micrwave: In terrestrial micrwave tw antennas are used fr cmmunicatin. A fcused beam emerges frm an antenna and is received by the ther antenna, prvided that antennas shuld be facing each ther with n bstacle in between. Fr this reasn antennas are situated n high twers. Due t curvature f earth terrestrial micrwave can be used fr lng distance cmmunicatin with high bandwidth. Telecm department is als using this fr lng distance cmmunicatin. An advantage f wireless cmmunicatin is that it is nt required t lay dwn wires in the city hence n permissins are required. 3. Satellite cmmunicatin: Satellite acts as a switch in sky. On earth VSAT (Very Small Aperture Terminal) are used t transmit and receive data frm satellite. Generally ne statin n earth transmitts signal t satellite and it is received by many statins n earth. Satellite cmmunicatin is generally used in thse places where it is very difficult t btain line f sight i.e. in highly irregular terrestrial regins. In terms f nise wireless media is nt as gd as the wired media. There are frequency band in wireless cmmunicatin and tw statins shuld nt be allwed t transmit simultaneusly in a frequency band. The mst prmising advantage f satellite is bradcasting. If satellites are used fr pint t pint cmmunicatin then they are expensive as cmpared t wired media. Objective type questins 1. A hub is similar t a switch in which f the fllwing ways: a. size and appearance f bx b. supprt fr file sharing c. similar prt cnfiguratins d. all f the abve e. nne f the abve 2. Hubs are manufactured with varying numbers f available prts. What are the mst cmmn prt cnfiguratins available in hubs tday? a. 2-, 4-, 6-, r 8-prt b. 3-, 5-, 7-, r 9-prt c. 4-, 5-, 8-, r 16-prt d. 5-, 10-, 15-, r 20-prt e. Nne f the abve

21 3. The cnnectin pints that cmputers use t netwrk with the hub are called a. buses b. jacks c. prts d. sckets e. Nne f the abve 4. What is a hub, physically speaking? a. a small bx with multiple cnnectin pints n the frnt r back b. a type f netwrk cable c. a special cmputer that has n mnitr, keybard, r pinting device d. a sftware prgram e. Nne f the abve 5. One imprtant benefit a hub brings t the hme netwrk is a. prtectin against viruses and added security while n the Internet b. shared (netwrk-attached) strage c. ability t share files amng tw, three, r mre cmputers d. Nne f the abve 6. Fr hubs and switches, the term chaining refers t a. the ability t cnnect hubs/switches t ther hubs/switches t increase the verall size f the netwrk b. the act f securing a hub r switch with cable tiedwns s that it cannt be stlen c. cnnecting mre than ne cmputer t the same hub r switch d. nne f the abve 7. Many hubs and switches include a special built-in in prt fr chaining purpses. This prt is called an a. chain prt b. uplink prt c. WAN prt d. parallel prt 8. Hubs and switches exist fr ther types f data links besides Ethernet a. True b. False 9. The Wrld Wide Web (WWW) is assciated with which Internet prtcl? a. FTP b. HTTP c. POP d. WWWP 10. In the early 1960s, the American RAND crpratin develped an experimental netwrk called

22 a. AARNET b. ARPANET c. INTERNET d. MILNET e. RANDNET 11. On the Internet, which prtcl is used t verify the crrect delivery f packets frm ne machine t anther? a. FTP b. HTTP c. IP d. TCP e. POP 12. Telnet is: a. a mechanism fr establishing a text based cnnectin t a remte server b. a methd fr dialing up a cmputer using a mdem c. a methd f cnverting a telephne netwrk t a packet switched netwrk d. a prtcl fr transmitting files frm ne cmputer t anther e. the methd that dumb terminals use fr cmmunicating with a server 13. CmpuServe is a cmputer netwrk a. develped in the last tw years t prvide faster access t the internet b. that gives advice n playing tennis c. that is privately run, but linked t the rest f the internet d. that is used fr mail, but is nt linked t the rest f the internet e. that was used prir t the Internet 14. A listerv is a: a. cmputer prgram fr distributing b. list f addresses t which shuld be sent c. way f distributing where each user passes the message t the next user alng the list d. additinal feature fund n newer cmputers and perating systems e. nne f the abve 15. Which f these prtcls prvide fast cnnectinless cmmunicatins that relies n upper layers f the OSI mdel fr errr crrectin? a. TCP (Transmissin Cntrl Prtcl) b. UDP (User Datagram Prtcl) c. SPX d. nne f the abve 16. The Micrsft versin f Nvell's IPX/SPX prtcl? a. ODI b. NWLink c. DLC

23 d. Nne f the abve 17. Utility used t run applicatins n a cmputer at a remte lcatin? a. ODI b. ARP (Address Reslutin Prtcl) c. Telnet d. Nne f the abve 18. A packet in a TCP/IP netwrk whse destinatin is utside the lcal netwrk ges t the a. TCP transceiver b. default gateway c. IP subnet d. Nne f the abve 19. OSI layer respnsible fr mail and file transfers? a. transprt layer b. data link layer c. applicatin layer d. Nne f the abve 20. Using the TCP/IP prtcl when is a subnet mask required? a. nly when cnnecting utside the LAN b. fr bth intranet and internet usage c. nly when using TCP/IP d. nne f the abve 21. Which f the fllwing prtcls need t be installed n yur client's NT system befre DHCP and DNS can be enabled? a. TCP/IP b. IPX/SPX c. NetBEUI d. Nne f the abve 22. The OSI layer respnsible fr name recgnitin, security lgins, and synchrnizatin f the cnnectin? a. presentatin b. applicatin c. sessin d. Nne f the abve 23. What must be cnfigured in TCP/IP fr tw cmputers n the same segment t cmmunicate with each ther? a. IP address and subnet mask b. default gateway c. all f the abve

24 d. Nne f the abve 24. The IEEE 802 standards perate at these layers f the OSI mdel? a. netwrk and transprt b. sessin and presentatin c. physical and data link d. Nne f the abve 25. PPP is part f which OSI Layer? a. physical b. data link c. netwrk d. Nne f the abve 26. OSI level respnsible fr cmpressin and encryptin f data? a. sessin b. applicatin c. presentatin d. nne f the abve 27. A prtcl that functins at the transprt layer f the OSI mdel? a. IP b. IPX c. SPX d. Nne f the abve 28. OSI level that ensures errr-free delivery f packets? a. transprt b. netwrk c. data link d. Nne f the abve 29. The TCP/IP prtcl used n the internet allws apprximately hw much billin unique IP addresses? a. 1 b. 4 c. 10 d. 6 e. Nne f the abve Review questins 1. What are varius types f netwrks? 2. Explain pint t pint Netwrk system. 3. What are the differences between data rate and bandwidth? 4. Cmpare fiber ptic and cpper wire transmissin media. 5. What are the uses f Cmputer netwrk?

25 6. What is the Principal difference between cnnectinless and cnnectin riented cmmunicatin? 7. What is the similarity and difference between cngestin cntrl and flw cntrl? 8. Enumerate any fur reasns fr using layered prtcls. 9. What are the types f transmissin? 10. What is meant by Cmputer netwrk? 11. What is meant by Data cmmunicatin? 12. What are the Basic Cmpnents fr a Cmmunicatin System 13. What is meant by Directin f Data flw? 14. What is meant by Simplex? 15. What is meant by Half-duplex? 16. What is meant by Full-duplex? 17. What is meant by Lcal-area netwrk (LAN)? 18. What is meant by Wide-area netwrk (WAN)? 19. What is meant by Metrplitan-area netwrk (MAN)? 20. What is a Tplgy? 21. What are Netwrk Tplgies? 22. What is meant by Star Tplgy? 23. What are Advantages and disadvantages star tplgies? 24. What is Bus Tplgy? 25. What is Advantages & Disadvantages bus Tplgy? 26. What is meant by Ring Tplgy? 27. What are the Advantages& disadvantages f Ring Tplgy? 28. What is meant by acknwledgement? 29. What is meant by Framing? 30. What is meant by Flw cntrl? Part B Questins 1. Explain with a neat sketch, the functins f the prtcls used in each layer f the OSI mdel and illustrate hw cmmunicatin is taking place between tw end systems. 2. Distinguish between OSI Reference Mdel and TCP Reference mdel. 3. Name all the basic netwrk tplgies and describe advantages f each. Draw Prper diagram fr each tplgy 4. (ii) Explain the fllwing terms : a) Bandwidth b) Channel capacity c) Multiplexing d) Quality f Service (QS) e) Full duplex transmissin 5. Explain abut Transmissin Media.

26 REFERENCE BOOKS 1. Behruz A. Fruzan, Data cmmunicatin and Netwrking, Tata McGraw-Hill, James F. Kurse and Keith W. Rss, Cmputer Netwrking: A Tp-Dwn Apprach Featuring the Internet, Pearsn Educatin, Andrew S. Tanenbaum, Cmputer Netwrks, PHI, Furth Editin, William Stallings, Data and Cmputer Cmmunicatin, Sixth Editin, Pearsn Educatin,