Data communication and network Chapter - 2

Data Communication and Network

Chapter - 2

Compile by Zafar Ayub

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Network Protocol

Copyright revised for Zafar Ayub ([email protected])

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� A protocol is a set of rules that governs the communicationsbetween computers on a network. In order for two computers totalk to each other, they must be speaking the same language.

� These rules include guidelines that regulate the followingcharacteristics of a network; access method, allowed physicaltopologies, types of cabling, and speed of data transfer.

� Many different types of network protocols and standards arerequired to ensure that your computer (no matter which operatingsystem, network card, or application you are using) cancommunicate with another computer located on the next desk orhalf-way around the world.

Types of Network Protocols


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¢ Network protocols also known as Network Technologies, the mostcommon network protocols are;

¢ Ethernet (LAN protocol; architecture developed by Xerox,DEC, and Intel in 1976)

¢ Local Talk ( network protocol that was developed by AppleComputer, Inc. for Macintosh computers)

¢ Token Ring ( patented by IBM in 1981, is a network protocolthat employs token-passing between computers arranged in alogical ring network)

¢ FDDI (set of ANSI and ISO standards for data transmission onfiber optic lines in a local area network (LAN) that can extendin range up to 200 km (124 miles).

¢ ATM (ATM is a high-speed networking standard designed tosupport both voice and data communications. ATM is normallyutilized by Internet service providers on their private long-distance networks)

Ethernet Protocol


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¢ The Ethernet protocol is by far the most widely used. Ethernet usesan access method called CSMA/CD (Carrier Sense MultipleAccess/Collision Detection).

¢ This is a system where each computer listens to the cable beforesending anything through the network. If the network is clear, thecomputer will transmit.

¢ If some other node is already transmitting on the cable, thecomputer will wait and try again when the line is clear.

¢ Sometimes, two computers attempt to transmit at the same instant.When this happens a collision occurs. Each computer then backs offand waits a random amount of time before attempting toretransmit.

¢ With this access method, it is normal to have collisions. However,the delay caused by collisions and retransmitting is very small anddoes not normally effect the speed of transmission on the network.ring network)

Types of Ethernet


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¢ 10 Base 5Coaxial cable (10Base5)Thicknet. (Bus Topology)

¢ 10 Base 2Thin coax cable (10Base2)Thinnet. (Bus Topology)

¢ 10 Base T

Twisted pair Ethernet (10BaseT)

Star Topology on HUBs

¢ 100 Base T (Fast Ethernet)100BASE-TX: two pairs of high-quality twisted-pair wires100BASE-T4: four pairs of normal-quality twisted-pair wires100BASE-FX: fiber optic cables

100 Mbps speed on Star Topologies on HUBs (Twisted pair CAT-6cable)


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¢ Giga Base T / 1000 Base X

High speed Ethernet on layer 3 switches with twisted pairand fiber cable

Name Medium Specified distance

1000BASE-CX Twinaxial cabling 25 meters

1000BASE-SX Multi-mode fiber 220 to 550 meters dependent on fiber

diameter and bandwidth

1000BASE-LX Multi-mode fiber 550 meters

1000BASE-LX Single-mode fiber 5 km

1000BASE-LX10 Single-mode fiber using 1,310 nm wavelength 10 km

1000BASE-ZX Single-mode fiber at 1,550 nm wavelength ~ 70 km

1000BASE-BX10 Single-mode fiber, over single-strand fiber:

1,490 nm downstream 1,310 nm upstream

10 km

1000BASE-T Twisted-pair cabling (Cat-5, Cat-5e, Cat-6, or

Cat-7)

100 meters

1000BASE-TX Twisted-pair cabling (Cat-6, Cat-7) 100 meters


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¢ 10G Base Ethernet

For core network backbone and submarine cables

Name Medium Specified distance

10GBASE-SR Multi-mode fiber 100 meters

10GBASE-LR Single-mode fiber 10 km

10GBASE-LRM Multi-mode fiber 300 meters

10GBASE-ER Single-mode fiber 40 Km

10GBASE-ZR Single – mode fiber 80 km

10GBASE-LX4 Single-mode fiber at 1,550 nm wavelength 10 km

10GBASE-T Twisted pair 100 m

Standard of Ethernet


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¢ 10 Base T

10 Mbps (Half Duplex)

IEEE 802.3 at Data Link Layer / Layer 2

¢ 100 Base T (Fast Ethernet)

100 Mbps (Half Duplex / Full Duplex)

IEEE 802.3u at Data Link Layer / Layer 2

¢ Giga Ethernet

1000 Mbps (Full Duplex )

IEEE 802.3z at Data Link Layer / Layer 2

¢ 10 Giga Ethernet

10000 Mbps (Full Duplex)

IEEE 802.3ae at Data Link Layer / Layer 2

CSMA / CD


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¢ Carrier Sense: wait till medium is idle before sending frame.

¢ Multiple Access: multiple computers use the same shared media.Each uses same access algorithm.

¢ Collision Detection: Listen to medium – detect if another station’ssignal interferes – back off and try again later.

CSMA / CD - Transmitting


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¢ When Ethernet network determine transmission of data, databroken into packet, and packed into frames.

¢ Maintain queued for transmission, usually this process occur onNIC.

¢ Before transmission, transceiver listen on medium is used or not, iffree then start transmission, other wise wait for an algorithm.

¢ The listing process through out whole cable transceivers.

¢ It is possible that two or more of them sense simultaneously, andbegan transmitting, cable medium is shared medium; so possibly twoor more transmission frames collapse with each other.

¢ Collapse known as collision.

¢ When transmission began, sender station continuously monitor themedium, and when collision is occur, then transmit “Jam Signal”.

¢ At this stage all station which are involved in this collision, began“evasive action”, is an algorithm for waiting of random period oftime.


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¢ If collision occurs: wait a random time t1 - 0< t1<d.

D depends on transmission speed – time for frame width or 512bits.

¢ If second collision occurs, wait a random time t2 - 0< t2<2d.

Double range for each successive collision.

¢ If collision occur its maximum value, transmission aboard.

¢ And if no collision, then again listen cable that is busy or not.

CSMA / CD - Receiving


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¢ Each station on the medium, listen incoming frames and check forfragments; fragments are partial frame (faulty or collision occurframes).

¢ In first step, check frame size, valid Ethernet frame hasapproximately size is 64 bytes.

¢ If frame is shooter, then assumed that collision may occur, then notfurther process, and try again.

¢ In second step, station also check MAC address of destinationframe, if this address is not match, then start receiving again.

¢ And if address match, then check series of various elements, likereceiving frame not too long, conditionally length is 1518 bytes, ifexceed assumed that frame is faulty, and transmission terminate dueto over size of frame.

¢ If over size test is clear, then check CRC formula, and comparingresult value with receiving frame value.

¢ if comprising value checked then, and result is match thendisassemble frame, and successful receiving.


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¢ If length field is not match, then aboard receiving.

¢ And CRC not match, then check extra bit (check sum), if no extrabit then end of receiving due to CRC error.

¢ And If add extra value in CRC, then again aboard receiving due toalignment error.

Token Ring Protocol


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¢ Initially used only in IBM computers in 1981, it was eventuallystandardized with protocol IEEE 802.5.

¢ Token ring technology is a local area network protocol whichresides at the data link layer (DLL 2 layer) of the OSI model.

o It uses a special three-byte frame called a token that travels aroundthe ring.

o Active monitor grants the possessor permission to transmit on themedium.o Token ring frames travel completely around the loop.o Like Ethernet any computer start transmitting at every time; notpossible, either wait for special frame “token”, and when it get onwire and if is token is empty then copy their data on it, and passingthrough forward.o This token traveling method is clockwise and called as token passingmethod.

Token Ring Topology


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¢ Ring topology is used for token ring protocol; but actually physicallystar topology and logically ring topology are used.


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¢ In token ring protocol, ring topology used MSAU as central device,CAT-3 (4Mbps to16Mbps), and IBM token ring adapter.

¢ MSAU (Multi Station Access Unit) just like Ethernet hub, but everycomputer linked with two UTP / STP cables, one for received andsecond for transmit.

¢ These short cable which are attached with computer to MSAU, iscalled Lobe.

¢ There are two types of computers on token ring topology, only oneat ring is active monitor, and all other reaming are standby monitor.

¢ Active monitor responsible for generating token and passingthrough on network in clock wise.

¢ Standby monitors just like clients which are directly connected onring , waiting for token for data transmission at its own parity.

¢ Active monitor selection is done by automatically by an electionmethod, and if within 10 millisecond, active monitor is out ofresponse, automatically election generated and new computeractive monitor.

Token Passing


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¢ The first computer set its NIC default value.

¢ In second perform lobe test, transmit and receive cables initiallyconnected with MSAU, in this test computer send single on theirtransmit cable and listening back same signal at its receiving cable.

¢ If successful communication occur then other process shall bestart, other wise computer goes to fail for ring attachment; this testcalled loopback test.

¢ In next stage computer place current (phantom current) on cablering, which cause this lobe is active on MSAU, otherwise MSAUassume this computer is going switch off.

¢ After this network adapter now checks to insure that its MACaddress is unique on network; for this its send special signal(destination its own MAN address) if no computer set an indicatorflag on this frame, then its assume its address is unique, otherwiseremove from network until anyone reconfigure its MAC address.

¢ Within seven second, a ring poll occur, by this every computer getknow its upstream neighbor address.


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¢ Ring poll: ring polling occur every seven second, by this processevery computer aware of its next upstream neighbor MAC address.All of this value also be save at active, and in every seven secondevery computer listen that active monitor is present or not otherwise again election shall be occur.

¢ By clearing all test computer become full flag member of ring.

¢ Lets start a ring which have five computer A to E, where A is aactive monitor.

¢ Computer A is automatically elected by an election, now Brequired to send data to E, then when token is pass through at Bcomputer, its check if token is empty then he copy their data intoempty token.

¢ Token is now moving forward C; again C check that this token isfor its or not, forward it, token forward to D; again this processhappened, and when this token at E, this computer NIC check thatdestination MAC is match, if yes then copy all data and copiedflagged is down means off.


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¢ Again token forwarding back to A, after reaching A computer checkif copy flag is down or off then again up this flag and assume thatdata has been copied other wise again transmit in ring.

¢ When this happen means data has been copied, A also up allreaming flags; like token is empty, data copy, and if any error thenremove from frame.

¢ Then A again transmit this token on ring, when its pass through byB, computer B check and if token empty flag is up then computer Bable to copy their data on this token, and computer B copy theirdata on exiting pervious computer A data.

¢ Token priority / flag: There are 8 priority / flags on token ringtransmission; from 0-7, every flag represent any one operation liketoken is empty, data has been copied or error, etc.


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Active Monitor: Every station in a token ring network is either anactive monitor (AM) or standby monitor (SM) station. However, therecan be only one active monitor on a ring at a time. The active monitoris chosen through an election or monitor contention process.The monitor contention process is initiated when

•a loss of signal on the ring is detected.•an active monitor station is not detected by other stations onthe ring.•a particular timer on an end station expires such as the casewhen a station hasn't seen a token frame in the past 7 seconds.

When any of the above conditions take place and a station decidesthat a new monitor is needed, it will transmit a "claim token" frame,announcing that it wants to become the new monitor. If that tokenreturns back to the sender, it is OK for it to become the monitor. Ifsome other station tries to become the monitor at the same timethen the station with the highest MAC address will win the electionprocess. Every other station becomes a standby monitor. All stationsmust be capable of becoming an active monitor station if necessary.


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The active monitor performs a number of ringadministration functions.

•The first function is to operate as the master clockfor the ring in order to provide synchronization of thesignal for stations on the wire.•Another function of the AM is to insert a 24-bit delayinto the ring, to ensure that there is always sufficientbuffering in the ring for the token to circulate.•A third function for the AM is to ensure that exactlyone token circulates whenever there is no frame beingtransmitted, and to detect a broken ring.•Lastly, the AM is responsible for removing circulatingframes from the ring.


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FDDI Protocol


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¢ Fiber Distributed Data Interface (FDDI) provides a 100 Mbpsoptical standard for data transmission in a local area network thatcan extend in range up to 200 kilometers (120 mi).

¢ Although FDDI logical topology is a ring-based token network, itdoes not use the IEEE 802.5 token ring protocol as its basis; instead,its protocol is derived from the IEEE 802.4 token bus timed tokenprotocol.

¢ In addition to covering large geographical areas, FDDI local areanetworks can support thousands of users. As a standard underlyingmedium it uses optical fiber, although it can use copper cable, inwhich case it may be referred to as CDDI (Copper DistributedData Interface). FDDI offers both a Dual-Attached Station (DAS),counter-rotating token ring topology and a Single-Attached Station(SAS), token bus passing ring topology

http://en.wikipedia.org/wiki/Token_ring

http://en.wikipedia.org/wiki/Communications_protocol

http://en.wikipedia.org/wiki/Token_bus

http://en.wikipedia.org/wiki/Optical_fiber

http://en.wikipedia.org/wiki/Copper

Network Topologies


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� A Network Topology is the layout pattern of interconnections of thevarious elements (links, cables, devices, etc) of a computer system.

� In network arrangement of computers or flow of network traffic,known as NetworkTopology.

� Means arrangement of device on network with structural (physical)or virtual (logical) is NetworkTopology.

Types of Network Topologies


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¢ Network topologies may be physical or logical with respect to theirfunctionality.

¢ Physical topology refers to the physical design of a networkincluding the devices, location and cable installation.

The shape of the cabling layout used to link devices is called thephysical topology of the network.This refers to

ü the layout of cabling

ü the locations of nodes

ü the interconnections between the nodes and the cabling

The physical topology of a network is determined by;

ü the capabilities of the network access devices and media

ü the level of control

ü fault tolerance desired

ü the cost associated with cabling or telecommunicationscircuits.


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¢ Logical topology refers to how data is actually transferred in anetwork as opposed to its physical design.

The logical topology is define;

ü is the way that the signals act on the network media

ü the way that the data passes through the network from onedevice to the next without regard to the physical interconnection ofthe devices.

A network's logical topology is not necessarily the same as itsphysical topology. For example;

ü the original UTP Ethernet using hubs / switches, but logicallyconnected bus topology layout.

ü Token Ring is a logical ring topology, but is wired a physicalstar from the MSAU (Media Station Access Unit).

¢ In general physical topology relates to a core network whereaslogical topology relates to basic network.

BUS Topology


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¢ A bus network topology is a network architecture in which a set ofclients are connected via a shared communications line / medium,called a BUS topology.

¢ The bus topology is often referred to as a linear bus because thecomputers are connected in a straight line. This is the simplest andmost common method of networking computers.

Advantages :ü Easy to connect a computer or peripheral to a linear bus.ü Easy to implement and extendüWell suited for temporary networks (quick setup)ü Typically the cheapest topology to implementü Faster than a ring network.ü If any node on the bus network fails, the bus its self is not effected.ü Requires less cable length than a star topology.


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Disadvantages :üDifficult to administer/troubleshootü Limited cable length and number of stationsüA cable break can disable the entire networküMaintenance costs may be higher in the long runü Performance degrades as additional computers are added or onheavy trafficü Low security (all computers on the bus can see all datatransmissions)üOne virus in the network will affect all of them (but not as badly as astar or ring network)ü Proper termination is required.(loop must be in closed path)ü Significant Capacitive Load (each bus transaction must be able tostretch to most distant link).

How it’s work?


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¢ A Bus networks are the simplest way to connect multiple clients,but may have problems when two clients want to transmit at thesame time on the same bus.

¢ The Ethernet is common protocol for bus topology.

¢ Thus systems which use bus network architectures normally havesome scheme of collision handling or collision avoidance forcommunication on the bus, quite often using CSMA / CD(CarrierSense Multiple Access / Collision Detection).

¢ In Bus topology computers are connected with each other via cable,called coax cable (thick net / thin net) with their NIC.

¢ NIC connect with cable via passive device called BNC -T(BritishNaval Connector) / Transverse (DB-15) and at last of both cablesends T-Connector or open loop must be closed.

¢ Bus topology has two basic types 10Base-2 and 10Base-5.

10Base-2


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¢ In 10Base-2 coax cable used Thinnet cable (RG-58) 50 ohm.

¢ It is capable of covering up to 590 feet (180 meters) and is nothighly susceptible to noise interference.

¢ It transmits at 10Mbps megabits per second and can support up to30 nodes per segment.

¢ This is a type of coax cable you can use for networks it’s a thinnercable, like the one you find on your cable television.


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¢ Thinnet cabling components include;

¢ BNC barrel connectors

¢ BNC T connectors

¢ BNC terminator


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¢ 10Base-2 specification;

Category Notes

Maximum segment length 185 meters (607 feet)

Connection to network interface card BNC T connector

Trunk segments and repeaters Five segments can be joined using four repeaters

Computers per segment 30 computers per segment by specification

Segments that can have computers Three of the five segments can be populated

Total number of computers 90 computers

Maximum total network length 925 meters (3035 feet)


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5-4-3 Rule:

A thinnet network can combine as many as five cable segmentsconnected by four repeaters; but only three segments can havestations attached.

Thus, two segments are untapped and are often referred to as"inter-repeater links." This is known as the 5-4-3 rule.


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¢ There are five segments, four repeaters, and trunk segments 1, 2,and 5 are populated (have computers attached to them).

¢ Trunk segments 3 and 4 exist only to increase the total length ofthe network and to allow the computers on trunk segments 1 and5 to be on the same network.

¢ Because normal Ethernet limits are too confining for a largebusiness, repeaters can be used to join Ethernet segments andextend the network to a total length of 925 meters (3035 feet).

Note:The 5-4-3-2-1 rule limits the range of a collision domain by limiting thepropagation delay to a "reasonable" amount of time. The rule breaksdown as follows:5 - The number of network segments4 - the number of repeaters needed to join the segments into onecollision domain3 - the number of network segments that have active (transmitting)devices attached2 - the number of segments that do not have active devices attached1 - the number of collision domains


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Advantages:

ü Relatively inexpensive ü Easy to installü Easy to configure

Disadvantages:

ü Limitation of computer till max 90 computers

10Base-5


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¢ In 10Base-5 coax cable used Thicknet cable (RG-59) 50 ohm.

¢ Thick-net cable is often used as backbone in local area networkenvironment.

¢ It transmit data speed of 10Mbps covers distances of up to 1640feet / 500 meters and accommodates up to 100 nodes persegments.


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¢ Thicknet cabling components include;

¢ Transceivers These are devices that can both transmit and receive,provide communications between the computer and the main LANcable, and are located in the vampire taps attached to the cable

¢ Transceiver cables The transceiver cable (drop cable) connects thetransceiver to the NIC.


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¢ DIX (or AUI) connectors These are the connectors on thetransceiver cable.


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¢ N-series connectors, including N-series barrelconnectors, and N-series terminators


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¢ 10Base-5 specification;

Category Notes

Maximum segment length 500 meters (1640 feet).

Transceivers Connected to the segment (in the tap).

Maximum computer-to-transceiver distance 50 meters (164 feet).

Minimum distance between transceivers 2.5 meters (8 feet).

Trunk segments and repeaters Five segments can be joined using four repeaters.

Segments that can have computers Three of the five segments can be populated.

Maximum total length of joined segments 2500 meters (8200 feet).

Maximum number of computers per segment 100 by specification.

Total number of computers 300 computers


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5-4-3 Rule:

One thicknet Ethernet network can have a maximum of fivebackbone segments connected using repeaters , of which up tothree can accommodate computers.

Figure shows how the 5-4-3 rules are applied to thicknet.


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¢ The length of the transceiver cables is not used to measure thedistance supported on the thicknet cable; only the end-to-endlength of the thicknet cable segment itself is used.

¢ Between connections, the minimum thicknet cable segment is 2.5meters (about 8 feet).

¢ This measurement excludes transceiver cables. Thicknet wasdesigned to support a backbone for a large department or an entirebuilding.

Note:The 5-4-3-2-1 rule limits the range of a collision domain by limiting thepropagation delay to a "reasonable" amount of time. The rule breaksdown as follows:5 - The number of network segments4 - the number of repeaters needed to join the segments into onecollision domain3 - the number of network segments that have active (transmitting)devices attached2 - the number of segments that do not have active devices attached1 - the number of collision domains


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Advantages:ü Backbone cableüCovers distances of up to 1640 feet or 500 metersüAccommodates up to 100 nodes per segment

Disadvantages:ü it’s very difficult to workü it transmits data at speeds of 10MbpsüA loose connection or missing terminator could cause erraticnetwork performance.ü This will lead to reduced speed, error counts in high-frametransmission or even a lack of network connectivity.üWhen using thin-net, a malfunction transceiver could alsocause excessive packet transmission or frame transmissionerrors.

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Data communication and network Chapter - 2