Data communication and network Chapter - 2


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Data communication and network Chapter - 2

  1. 1. Copyright revised for Zafar Ayub Data Communication and Network ( Chapter - 2 Compile by Zafar Ayub1
  2. 2. Network Protocol A protocol is a set of rules that governs the communications between computers on a network. In order for two computers to talk to each other, they must be speaking the same language. These rules include guidelines that regulate the following characteristics of a network; access method, allowed physical topologies, types of cabling, and speed of data transfer. Many different types of network protocols and standards are required to ensure that your computer (no matter which operating system, network card, or application you are using) can communicate with another computer located on the next desk or half-way around the world.2 Copyright revised for Zafar Ayub (
  3. 3. Types of Network Protocols¢ Network protocols also known as Network Technologies, the most common network protocols are; ¢ Ethernet (LAN protocol; architecture developed by Xerox, DEC, and Intel in 1976) ¢ Local Talk ( network protocol that was developed by Apple Computer, Inc. for Macintosh computers) ¢ Token Ring ( patented by IBM in 1981, is a network protocol that employs token-passing between computers arranged in a logical ring network) ¢ FDDI (set of ANSI and ISO standards for data transmission on fiber optic lines in a local area network (LAN) that can extend in range up to 200 km (124 miles). ¢ ATM (ATM is a high-speed networking standard designed to support both voice and data communications. ATM is normally utilized by Internet service providers on their private long- distance networks) 3 Copyright revised for Zafar Ayub (
  4. 4. Ethernet Protocol¢ The Ethernet protocol is by far the most widely used. Ethernet uses an access method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection).¢ This is a system where each computer listens to the cable before sending anything through the network. If the network is clear, the computer will transmit.¢ If some other node is already transmitting on the cable, the computer 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 off and waits a random amount of time before attempting to retransmit.¢ With this access method, it is normal to have collisions. However, the delay caused by collisions and retransmitting is very small and does not normally effect the speed of transmission on the network. ring network) 4 Copyright revised for Zafar Ayub (
  5. 5. Types of Ethernet¢ 10 Base 5 Coaxial cable (10Base5) Thicknet. (Bus Topology)¢ 10 Base 2 Thin 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 wires 100BASE-T4: four pairs of normal-quality twisted-pair wires 100BASE-FX: fiber optic cables 100 Mbps speed on Star Topologies on HUBs (Twisted pair CAT-6 cable) 5 Copyright revised for Zafar Ayub (
  6. 6. ¢ Giga Base T / 1000 Base X High speed Ethernet on layer 3 switches with twisted pair and 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: 10 km 1,490 nm downstream 1,310 nm upstream 1000BASE-T Twisted-pair cabling (Cat-5, Cat-5e, Cat-6, or 100 meters Cat-7) 1000BASE-TX Twisted-pair cabling (Cat-6, Cat-7) 100 meters 6 Copyright revised for Zafar Ayub (
  7. 7. ¢ 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 7 Copyright revised for Zafar Ayub (
  8. 8. Standard of Ethernet¢ 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 8 Copyright revised for Zafar Ayub (
  9. 9. CSMA / CD¢ 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’s signal interferes – back off and try again later. 9 Copyright revised for Zafar Ayub (
  10. 10. CSMA / CD - Transmitting10 Copyright revised for Zafar Ayub (
  11. 11. ¢ When Ethernet network determine transmission of data, data broken into packet, and packed into frames.¢ Maintain queued for transmission, usually this process occur on NIC.¢ Before transmission, transceiver listen on medium is used or not, if free 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, and began transmitting, cable medium is shared medium; so possibly two or more transmission frames collapse with each other.¢ Collapse known as collision.¢ When transmission began, sender station continuously monitor the medium, 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 of time. 11 Copyright revised for Zafar Ayub (
  12. 12. ¢ If collision occurs: wait a random time t1 - 0< t1<d. D depends on transmission speed – time for frame width or 512 bits.¢ 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. 12 Copyright revised for Zafar Ayub (
  13. 13. CSMA / CD - Receiving13 Copyright revised for Zafar Ayub (
  14. 14. ¢ Each station on the medium, listen incoming frames and check for fragments; fragments are partial frame (faulty or collision occur frames).¢ In first step, check frame size, valid Ethernet frame has approximately size is 64 bytes.¢ If frame is shooter, then assumed that collision may occur, then not further process, and try again.¢ In second step, station also check MAC address of destination frame, if this address is not match, then start receiving again.¢ And if address match, then check series of various elements, like receiving frame not too long, conditionally length is 1518 bytes, if exceed assumed that frame is faulty, and transmission terminate due to over size of frame.¢ If over size test is clear, then check CRC formula, and comparing result value with receiving frame value.¢ if comprising value checked then, and result is match then disassemble frame, and successful receiving. 14 Copyright revised for Zafar Ayub (
  15. 15. ¢ If length field is not match, then aboard receiving.¢ And CRC not match, then check extra bit (check sum), if no extra bit then end of receiving due to CRC error.¢ And If add extra value in CRC, then again aboard receiving due to alignment error. 15 Copyright revised for Zafar Ayub (
  16. 16. Token Ring Protocol¢ Initially used only in IBM computers in 1981, it was eventually standardized with protocol IEEE 802.5.¢ Token ring technology is a local area network protocol which resides 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 around the 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. 16 Copyright revised for Zafar Ayub (
  17. 17. Token Ring Topology¢ Ring topology is used for token ring protocol; but actually physically star topology and logically ring topology are used. 17 Copyright revised for Zafar Ayub (
  18. 18. ¢ 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 every computer linked with two UTP / STP cables, one for received and second for transmit.¢ These short cable which are attached with computer to MSAU, is called Lobe.¢ There are two types of computers on token ring topology, only one at ring is active monitor, and all other reaming are standby monitor.¢ Active monitor responsible for generating token and passing through on network in clock wise.¢ Standby monitors just like clients which are directly connected on ring , waiting for token for data transmission at its own parity.¢ Active monitor selection is done by automatically by an election method, and if within 10 millisecond, active monitor is out of response, automatically election generated and new computer active monitor. 18 Copyright revised for Zafar Ayub (
  19. 19. Token Passing¢ The first computer set its NIC default value.¢ In second perform lobe test, transmit and receive cables initially connected with MSAU, in this test computer send single on their transmit cable and listening back same signal at its receiving cable.¢ If successful communication occur then other process shall be start, other wise computer goes to fail for ring attachment; this test called loopback test.¢ In next stage computer place current (phantom current) on cable ring, which cause this lobe is active on MSAU, otherwise MSAU assume this computer is going switch off.¢ After this network adapter now checks to insure that its MAC address is unique on network; for this its send special signal (destination its own MAN address) if no computer set an indicator flag on this frame, then its assume its address is unique, otherwise remove from network until anyone reconfigure its MAC address.¢ Within seven second, a ring poll occur, by this every computer get know its upstream neighbor address. 19 Copyright revised for Zafar Ayub (
  20. 20. ¢ Ring poll: ring polling occur every seven second, by this process every computer aware of its next upstream neighbor MAC address. All of this value also be save at active, and in every seven second every computer listen that active monitor is present or not other wise 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 a active monitor.¢ Computer A is automatically elected by an election, now B required to send data to E, then when token is pass through at B computer, its check if token is empty then he copy their data into empty token.¢ Token is now moving forward C; again C check that this token is for its or not, forward it, token forward to D; again this process happened, and when this token at E, this computer NIC check that destination MAC is match, if yes then copy all data and copied flagged is down means off. 20 Copyright revised for Zafar Ayub (
  21. 21. ¢ Again token forwarding back to A, after reaching A computer check if copy flag is down or off then again up this flag and assume that data has been copied other wise again transmit in ring.¢ When this happen means data has been copied, A also up all reaming flags; like token is empty, data copy, and if any error then remove from frame.¢ Then A again transmit this token on ring, when its pass through by B, computer B check and if token empty flag is up then computer B able to copy their data on this token, and computer B copy their data on exiting pervious computer A data.¢ Token priority / flag: There are 8 priority / flags on token ring transmission; from 0-7, every flag represent any one operation like token is empty, data has been copied or error, etc. 21 Copyright revised for Zafar Ayub (
  22. 22. 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 on the ring. •a particular timer on an end station expires such as the case when a station hasnt 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. 22 Copyright revised for Zafar Ayub (
  23. 23. The active monitor performs a number of ringadministration functions. •The first function is to operate as the master clock for the ring in order to provide synchronization of the signal for stations on the wire. •Another function of the AM is to insert a 24-bit delay into the ring, to ensure that there is always sufficient buffering in the ring for the token to circulate. •A third function for the AM is to ensure that exactly one token circulates whenever there is no frame being transmitted, and to detect a broken ring. •Lastly, the AM is responsible for removing circulating frames from the ring. 23 Copyright revised for Zafar Ayub (
  24. 24. 24 Copyright revised for Zafar Ayub (
  25. 25. FDDI Protocol¢ Fiber Distributed Data Interface (FDDI) provides a 100 Mbps optical standard for data transmission in a local area network that can extend in range up to 200 kilometers (120 mi).¢ Although FDDI logical topology is a ring-based token network, it does 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 token protocol.¢ In addition to covering large geographical areas, FDDI local area networks can support thousands of users. As a standard underlying medium it uses optical fiber, although it can use copper cable, in which case it may be referred to as CDDI (Copper Distributed Data 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 25 Copyright revised for Zafar Ayub (
  26. 26. Network Topologies A Network Topology is the layout pattern of interconnections of the various elements (links, cables, devices, etc) of a computer system. In network arrangement of computers or flow of network traffic, known as Network Topology. Means arrangement of device on network with structural (physical) or virtual (logical) is Network Topology.26 Copyright revised for Zafar Ayub (
  27. 27. Types of Network Topologies¢ Network topologies may be physical or logical with respect to their functionality.¢ Physical topology refers to the physical design of a network including the devices, location and cable installation. The shape of the cabling layout used to link devices is called the physical topology of the network.This refers to the layout of cabling the locations of nodes the interconnections between the nodes and the cabling The physical topology of a network is determined by; the capabilities of the network access devices and media the level of control fault tolerance desired the cost associated with cabling or telecommunications circuits. 27 Copyright revised for Zafar Ayub (
  28. 28. ¢ Logical topology refers to how data is actually transferred in a network as opposed to its physical design. The logical topology is define; is the way that the signals act on the network media the way that the data passes through the network from one device to the next without regard to the physical interconnection of the devices. A networks logical topology is not necessarily the same as its physical topology. For example; the original UTP Ethernet using hubs / switches, but logically connected bus topology layout. Token Ring is a logical ring topology, but is wired a physical star from the MSAU (Media Station Access Unit).¢ In general physical topology relates to a core network whereas logical topology relates to basic network. 28 Copyright revised for Zafar Ayub (
  29. 29. BUS Topology¢ A bus network topology is a network architecture in which a set of clients are connected via a shared communications line / medium, called a BUS topology.¢ The bus topology is often referred to as a linear bus because the computers are connected in a straight line. This is the simplest and most common method of networking computers.Advantages : Easy to connect a computer or peripheral to a linear bus. Easy to implement and extend Well suited for temporary networks (quick setup) Typically the cheapest topology to implement Faster than a ring network. If any node on the bus network fails, the bus its self is not effected. Requires less cable length than a star topology. 29 Copyright revised for Zafar Ayub (
  30. 30. Disadvantages : Difficult to administer/troubleshoot Limited cable length and number of stations A cable break can disable the entire network Maintenance costs may be higher in the long run Performance degrades as additional computers are added or onheavy traffic Low security (all computers on the bus can see all datatransmissions) One virus in the network will affect all of them (but not as badly as astar or ring network) Proper termination is required.(loop must be in closed path) Significant Capacitive Load (each bus transaction must be able tostretch to most distant link). 30 Copyright revised for Zafar Ayub (
  31. 31. How it’s work?¢ A Bus networks are the simplest way to connect multiple clients, but may have problems when two clients want to transmit at the same time on the same bus.¢ The Ethernet is common protocol for bus topology.¢ Thus systems which use bus network architectures normally have some scheme of collision handling or collision avoidance for communication on the bus, quite often using CSMA / CD(Carrier Sense 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(British Naval Connector) / Transverse (DB-15) and at last of both cables ends T-Connector or open loop must be closed.¢ Bus topology has two basic types 10Base-2 and 10Base-5. 31 Copyright revised for Zafar Ayub (
  32. 32. 10Base-2¢ 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 not highly susceptible to noise interference.¢ It transmits at 10Mbps megabits per second and can support up to 30 nodes per segment.¢ This is a type of coax cable you can use for networks it’s a thinner cable, like the one you find on your cable television. 32 Copyright revised for Zafar Ayub (
  33. 33. ¢ Thinnet cabling components include; ¢ BNC barrel connectors ¢ BNC T connectors ¢ BNC terminator 33 Copyright revised for Zafar Ayub (
  34. 34. ¢ 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) 34 Copyright revised for Zafar Ayub (
  35. 35. 5-4-3 Rule: A thinnet network can combine as many as five cable segments connected by four repeaters; but only three segments can have stations attached. Thus, two segments are untapped and are often referred to as "inter-repeater links." This is known as the 5-4-3 rule. 35 Copyright revised for Zafar Ayub (
  36. 36. ¢ 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 of the network and to allow the computers on trunk segments 1 and 5 to be on the same network.¢ Because normal Ethernet limits are too confining for a large business, repeaters can be used to join Ethernet segments and extend 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 36 Copyright revised for Zafar Ayub (
  37. 37. Advantages: Relatively inexpensive Easy to install Easy to configureDisadvantages: Limitation of computer till max 90 computers 37 Copyright revised for Zafar Ayub (
  38. 38. 10Base-5¢ In 10Base-5 coax cable used Thicknet cable (RG-59) 50 ohm.¢ Thick-net cable is often used as backbone in local area network environment.¢ It transmit data speed of 10Mbps covers distances of up to 1640 feet / 500 meters and accommodates up to 100 nodes per segments. 38 Copyright revised for Zafar Ayub (
  39. 39. ¢ Thicknet cabling components include; ¢ Transceivers These are devices that can both transmit and receive, provide communications between the computer and the main LAN cable, and are located in the vampire taps attached to the cable ¢ Transceiver cables The transceiver cable (drop cable) connects the transceiver to the NIC. 39 Copyright revised for Zafar Ayub (
  40. 40. ¢ DIX (or AUI) connectors These are the connectors on the transceiver cable.40 Copyright revised for Zafar Ayub (
  41. 41. ¢ N-series connectors, including N-series barrel connectors, and N-series terminators41 Copyright revised for Zafar Ayub (
  42. 42. ¢ 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 42 Copyright revised for Zafar Ayub (
  43. 43. 5-4-3 Rule: One thicknet Ethernet network can have a maximum of five backbone segments connected using repeaters , of which up to three can accommodate computers. Figure shows how the 5-4-3 rules are applied to thicknet. 43 Copyright revised for Zafar Ayub (
  44. 44. ¢ The length of the transceiver cables is not used to measure the distance supported on the thicknet cable; only the end-to-end length of the thicknet cable segment itself is used.¢ Between connections, the minimum thicknet cable segment is 2.5 meters (about 8 feet).¢ This measurement excludes transceiver cables. Thicknet was designed to support a backbone for a large department or an entire building.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 44 Copyright revised for Zafar Ayub (
  45. 45. Advantages: Backbone cable Covers distances of up to 1640 feet or 500 meters Accommodates up to 100 nodes per segmentDisadvantages: it’s very difficult to work it transmits data at speeds of 10Mbps A loose connection or missing terminator could cause erraticnetwork performance. This will lead to reduced speed, error counts in high-frametransmission or even a lack of network connectivity. When using thin-net, a malfunction transceiver could alsocause excessive packet transmission or frame transmissionerrors. 45 Copyright revised for Zafar Ayub (