Komunikasi Data dan Jaringan Komputer (Bagian 3)

1. Komunikasi Data dan Jaringan Komputer(Bagian 3) Dr. Tb. Maulana Kusuma mkusuma@staff.gunadarma.ac.id http://staffsite.gunadarma.ac.id/mkusuma Magister Teknik Elektro

2. LAN Generation • First • Carrier Sense Multiple Access (CSMA) / Collision Detection (CD) and Token Ring • Terminal to host and client server • Moderate data rates • Second • Fiber Distributed Data Interface (FDDI) • Backbone • High performance workstations • Third • Asynchronous Transfer Mode (ATM) • Aggregate throughput and real time support for multimedia applications Magister Teknik Elektro

3. Third Generation LAN • Support for multiple guaranteed classes of service • Live video may need 2Mbps • File transfer can use background class • Scalable throughput • Both aggregate and per host • Facilitate LAN / WAN internetworking Magister Teknik Elektro

4. LAN Applications (1) • Personal computer LANs • Low cost • Limited data rate • Back end networks and storage area networks • Interconnecting large systems (mainframes and large storage devices) • High data rate • High speed interface • Distributed access • Limited distance • Limited number of devices Magister Teknik Elektro

5. LAN Applications (2) • High speed office networks • Desktop image processing • High capacity local storage • Backbone LANs • Interconnect low speed local LANs • Reliability • Capacity • Cost Magister Teknik Elektro

6. LAN Architecture • Protocol architecture • Topologies • Media Access Control (MAC) • Logical Link Control (LLC) Magister Teknik Elektro

7. Protocol Architecture • Lower layers of OSI model • IEEE 802 reference model • Physical • LLC • MAC Magister Teknik Elektro

8. IEEE 802 v OSI Magister Teknik Elektro

9. 802 Layers - Physical • Encoding/decoding • Preamble generation/removal • Bit transmission/reception • Transmission medium and topology Magister Teknik Elektro

10. 802 Layers -Logical Link Control • Interface to higher levels • Flow and error control Magister Teknik Elektro

11. 802 Layers -Media Access Control • Assembly of data into frame with address and error detection fields • Disassembly of frame • Address recognition • Error detection • Govern access to transmission medium • Not found in traditional layer 2 data link control • For the same LLC, several MAC options may be available Magister Teknik Elektro

12. LAN Protocols in Context Magister Teknik Elektro

13. Topologies • Tree • Bus • Special case of tree • One trunk, no branches • Ring • Star Magister Teknik Elektro

14. LAN Topologies Magister Teknik Elektro

15. Bus and Tree • Multipoint medium • Transmission propagates throughout medium • Heard by all stations • Need to identify target station • Each station has unique address • Full duplex connection between station and tap • Allows for transmission and reception • Need to regulate transmission • To avoid collisions • To avoid hogging • Data in small blocks - frames • Terminator absorbs frames at end of medium Magister Teknik Elektro

16. Frame Transmission - Bus LAN Magister Teknik Elektro

17. Ring Topology • Repeaters joined by point to point links in closed loop • Receive data on one link and retransmit on another • Links unidirectional • Stations attach to repeaters • Data in frames • Circulate past all stations • Destination recognizes address and copies frame • Frame circulates back to source where it is removed • Media access control determines when station can insert frame Magister Teknik Elektro

18. Frame TransmissionRing LAN Magister Teknik Elektro

19. Star Topology • Each station connected directly to central node • Usually via two point to point links • Central node can broadcast • Physical star, logical bus • Only one station can transmit at a time • Central node can act as frame switch Magister Teknik Elektro

20. Media Access Control • Where • Central • Greater control • Simple access logic at station • Avoids problems of co-ordination • Single point of failure • Potential bottleneck • Distributed • How • Synchronous • Specific capacity dedicated to connection • Asynchronous • In response to demand Magister Teknik Elektro

21. Asynchronous Systems • Round robin • Good if many stations have data to transmit over extended period • Reservation • Good for stream traffic • Contention • Good for bursty traffic • All stations contend for time • Distributed • Simple to implement • Efficient under moderate load • Tend to collapse under heavy load Magister Teknik Elektro

22. Logical Link Control • Transmission of link level PDUs between two stations • Must support multiaccess, shared medium • Relieved of some link access details by MAC layer • Addressing involves specifying source and destination LLC users • Referred to as service access points (SAP) • Typically higher level protocol Magister Teknik Elektro

23. Bus LAN • Signal balancing • Signal must be strong enough to meet receiver’s minimum signal strength requirements • Give adequate signal to noise ration • Not so strong that it overloads transmitter • Must satisfy these for all combinations of sending and receiving station on bus • Usual to divide network into small segments • Link segments with amplifies or repeaters Magister Teknik Elektro

24. Transmission Media • Twisted pair • Not practical in shared bus at higher data rates • Baseband coaxial cable • Used by Ethernet • Broadband coaxial cable • Included in 802.3 specification but no longer made • Optical fiber • Expensive • Difficulty with availability • Not used • Few new installations • Replaced by star based twisted pair and optical fiber Magister Teknik Elektro

25. Baseband Coaxial Cable • Uses digital signaling • Manchester or Differential Manchester encoding • Entire frequency spectrum of cable used • Single channel on cable • Bi-directional • Few kilometer range • Ethernet (basis for 802.3) at 10Mbps • 50 ohm cable Magister Teknik Elektro

26. 10Base5 • Ethernet and 802.3 originally used 0.4 inch diameter cable at 10Mbps • Max cable length 500m • Distance between taps a multiple of 2.5m • Ensures that reflections from taps do not add in phase • Max 100 taps • 10Base5 Magister Teknik Elektro

27. 10Base2 • Cheaper • 0.25 inch cable • More flexible • Easier to bring to workstation • Cheaper electronics • Greater attenuation • Lower noise resistance • Fewer taps (30) • Shorter distance (185m) Magister Teknik Elektro

28. Repeaters • Transmits in both directions • Joins two segments of cable • No buffering • No logical isolation of segments • If two stations on different segments send at the same time, packets will collide • Only one path of segments and repeaters between any two stations Magister Teknik Elektro

29. Baseband Configuration Magister Teknik Elektro

30. Ring LAN • Each repeater connects to two others via unidirectional transmission links • Single closed path • Data transferred bit by bit from one repeater to the next • Repeater regenerates and retransmits each bit • Repeater performs data insertion, data reception, data removal • Repeater acts as attachment point • Packet removed by transmitter after one trip round ring Magister Teknik Elektro

31. Ring Repeater States Magister Teknik Elektro

32. Listen State Functions • Scan passing bit stream for patterns • Address of attached station • Token permission to transmit • Copy incoming bit and send to attached station • Whilst forwarding each bit • Modify bit as it passes • e.g. to indicate a packet has been copied (ACK) Magister Teknik Elektro

33. Transmit State Functions • Station has data • Repeater has permission • May receive incoming bits • If ring bit length shorter than packet • Pass back to station for checking (ACK) • May be more than one packet on ring • Buffer for retransmission later Magister Teknik Elektro

34. Bypass State • Signals propagate past repeater with no delay (other than propagation delay) • Partial solution to reliability problem (see later) • Improved performance Magister Teknik Elektro

35. Star LAN • Use unshielded twisted pair wire (telephone) • Minimal installation cost • May already be an installed base • All locations in building covered by existing installation • Attach to a central active hub • Two links • Transmit and receive • Hub repeats incoming signal on all outgoing lines • Link lengths limited to about 100m • Fiber optic - up to 500m • Logical bus - with collisions Magister Teknik Elektro

36. Hubs and Switches • Shared medium hub • Central hub • Hub retransmits incoming signal to all outgoing lines • Only one station can transmit at a time • With a 10Mbps LAN, total capacity is 10Mbps • Switched LAN hub • Hub acts as switch • Incoming frame switches to appropriate outgoing line • Unused lines can also be used to switch other traffic • With two pairs of lines in use, overall capacity is now 20Mbps Magister Teknik Elektro

37. Switched Hubs • No change to software or hardware of devices • Each device has dedicated capacity • Scales well • Store and forward switch • Accept input, buffer it briefly, then output • Cut through switch • Take advantage of the destination address being at the start of the frame • Begin repeating incoming frame onto output line as soon as address recognized • May propagate some bad frames Magister Teknik Elektro

38. Hubs and Switches Magister Teknik Elektro

39. Wireless LAN • Wireless LANs are growing in popularity because they eliminate cabling and facilitate network access from a variety of locations. • The most common wireless networking standard is IEEE 802.11, often called Wireless Ethernet or Wireless LAN. • Broadband wireless (IEEE 802.16) is now growing in popularity Magister Teknik Elektro

40. Wireless Communications • In wireless communications signals travel through space instead of through a physical cable. • Two general types of wireless communications are: • Radio transmission • Infrared transmission Magister Teknik Elektro

41. Why Wireless LAN? • Mobility • Flexibility • Hard to wire areas • Reduced cost of wireless systems • Improved performance of wireless systems Magister Teknik Elektro

42. Types of Wireless LANs • IEEE 802.11a • IEEE 802.11b • IEEE 802.11g • Infrared • Bluetooth Magister Teknik Elektro

43. IEEE 802.11b Two forms of the IEEE 802.11b standard currently exist: • Direct Sequence Spread Spectrum (DSSS) systems transmit signals through a wide range of frequencies simultaneously. The signal is divided into many different parts and sent on different frequencies simultaneously. Data rate: ~ 11Mbps. • Frequency Hopping Spread Spectrum (FHSS) divides the frequency band into a series of channels and then use each frequency in turn. FHSS changes its frequency channel about every half a second, using a pseudorandom sequence. Magister Teknik Elektro

44. FHSS is more secure, but is only capable of data rates of 1 or 2 Mbps. • IEEE 802.11a is another Wireless LAN standard developed around the same time as 802.11b. It operates in the 5 GHz band and is capable of data rates of up to 54 Mbps. • IEEE 802.11gcombines the best of both 802.11a and 802.11b. 802.11g supports bandwidth up to 54 Mbps, and it uses the 2.4 Ghz frequency for greater range. 802.11g is backwards compatible with 802.11b, meaning that 802.11g access points will work with 802.11b wireless network adapters and vice versa. Magister Teknik Elektro

45. IEEE 802.11a vs802.11bvs802.11g • 802.11a is the most expensive. It fits predominately in the business market, whereas 802.11b better serves the home market. • 802.11a supports bandwidth up to 54 Mbps and signals in a regulated 5 GHz range. Compared to 802.11b, this higher frequency limits the range of 802.11a. The higher frequency also means 802.11a signals have more difficulty penetrating walls and other obstructions. Magister Teknik Elektro

46. Although slower than 802.11a, the range of 802.11b is about 7 times greater than that of 802.11a. • Because 802.11a and 802.11b utilize different frequencies, the two technologies are incompatible with each other. • Some vendors offer hybrid 802.11a/b network gear, but these products simply implement the two standards side by side. • 802.11g offers the best of both worlds and allow for greater flexibility. Magister Teknik Elektro

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49. Wireless LAN Applications • LAN Extension • Cross building interconnection • Nomadic access • Ad hoc networks Magister Teknik Elektro

50. LAN Extension • Buildings with large open areas • Manufacturing plants • Warehouses • Historical buildings • Small offices • May be mixed with fixed wiring system Magister Teknik Elektro