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SPU Information Science Institute of Sripatum University Sripatum University 1 IS516 Computer Communication and Networks การสื่อสารคอมพิวเตอร์และเครือข่าย.

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งานนำเสนอเรื่อง: "SPU Information Science Institute of Sripatum University Sripatum University 1 IS516 Computer Communication and Networks การสื่อสารคอมพิวเตอร์และเครือข่าย."— ใบสำเนางานนำเสนอ:

1 SPU Information Science Institute of Sripatum University Sripatum University 1 IS516 Computer Communication and Networks การสื่อสารคอมพิวเตอร์และเครือข่าย Asst.Dr.Surasak Mungsing

2 2 Lecture 05: Guided Networks

3 3 LAN

4 SPU Information Science Institute of Sripatum University 4 Line Configuration Computers are connected for data communication through transmission Medium, which may be either Guided Media or Unguided Media Two types of connection configuration, point- to-point and multipoint

5 SPU Information Science Institute of Sripatum University 5 Point-to-Point Line Configuration A pair of computers or network devices have specific connection points for connecting only those pairs of computers or devices Communication capacity dedicated to the two connected computers or devices Transmission media may be either guided or unguided medium

6 SPU Information Science Institute of Sripatum University 6 Multipoint Line Configuration Use common medium for two or more computers and devices

7 SPU Information Science Institute of Sripatum University 7 Topology Connection structure of computer network(computers or network devices) Five types of topology: Mesh, Star, Tree, Bus and Ring

8 SPU Information Science Institute of Sripatum University 8 Mesh Topology  All nodes are directly connected (linked) to other nodes in the network  Number of connection lines n(n-1) / 2 where n is number of computers in the network  Each node must have (n-1) I/O ports

9 SPU Information Science Institute of Sripatum University 9 Mesh Topology Advantages: - better transmission rate and system reliability - easy to detect errors - better security and privacy Disadvantages: - many connection point and I/O ports required e.g. 100 nodes requires 4950 connection lines

10 SPU Information Science Institute of Sripatum University 10 Star Topology Each node directly connects to the center device, called “hup”, which a node must send data to other nodes through the hub Saves a lot of connection lines in comparison with mesh topology In star topology, as well as the mesh, if a line fails only the two connected nodes fails to communicate. But if the hub fails the whole network fails to work.

11 SPU Information Science Institute of Sripatum University 11 Tree Topology  Based on star from star topology, in such a way that each node connects to a hub, either active hub or passive hub  The center of the network structure is an active hub and repeaters are used to extend signal distance  Passive Hub is directly connected to nodes  Longer distance network than star topology

12 SPU Information Science Institute of Sripatum University 12 Bus Topology  Bus is Multipoint connection, but the previous (Mesh, Star, and Tree) are point-to-point connection  All node are connected to a cable, which acts as a backbone for the network, so that all nodes can communicates to each other through this cable

13 SPU Information Science Institute of Sripatum University 13 Bus Topology Use less connection lines and connection ports than Mesh, Star, and Tree Cable Terminators required at the two ends and all nodes in the network tap to the cable Disadvantage: - if the cable fails, then the network fails - Adding new node is more difficult than Mesh, Star, and Tree topologies - low data transmission rate due to sharing of a common cable

14 SPU Information Science Institute of Sripatum University 14 Ring Topology Is a point-to-point connection between two nodes (a node and its predecessor node) Communication between nodes takes place from one node to another in one direction until the intended received is reached while each node in the ring acts as a repeater to relay data to the next node

15 SPU Information Science Institute of Sripatum University 15 Ring Topology Easy to install and change, e.g. adding a node only requires two connections Requires longer time for sending data from a node to another due the moving is in one direction, in particular when there are many nodes in the ring

16 SPU Information Science Institute of Sripatum University 16 Hybrid Topology Connection in a network may be a hybrid of more than one topology

17 SPU Information Science Institute of Sripatum University 17 IEEE 802 LAN The Institute of Electrical and Electronics Engineers or IEEE (read eye-triple-ee) is an international non-profit, professional organization for the advancement of technology related to electricity. It has the most members of any technical professional organization in the world, with more than 395,000 members in around 150 countries The services and protocols specified in IEEE 802 map to the lower two layers (Data Link and Physical) of the seven-layer OSI networking reference model IEEE 802 describes CSMA/CD (Carrier Sense Multiple Access with Collision Detection), (Token Bus) and Token Ring LAN, which are different in Physical and MACsublayer

18 SPU Information Science Institute of Sripatum University 18 IEEE 802

19 SPU Information Science Institute of Sripatum University 19 Project 802

20 SPU Information Science Institute of Sripatum University 20 IEEE Ethernet (1) IEEE began from 100-nodes set up at Xerox that can send data as far as 1 km. at the rate of 2.94 Mbps, called Ethernet Follows by cooperation of Xerox, DEC and Intel in developing Ethernet standard that can operate at the rate of 10 Mbps, the IEEE 802.3

21 SPU Information Science Institute of Sripatum University 21 IEEE Ethernet (2) The describes LANs that use the principle of CSMA/CD (Carrier Sense Multiple Access with Collision Detection), which operates at the data rate of 1 ถึง 100 Mbps and on variety of transmission media IEEE and Ethernet have some different information in the Header (IEEE field length is used to identify type of Packet in the Ethernet standard ) Therefore IEEE describes LAN that use CSMA/CD but Ethernet means a product of IEEE LAN

22 SPU Information Science Institute of Sripatum University 22 IEEE Ethernet (3) วิธีการรับส่งข้อมูลของแลน IEEE ซึ่งเป็นแบบ CSMA/CD ก็ทำงานในลักษณะเดียวกัน คือโหนดใดที่ ต้องการส่งข้อมูลลงในสื่อกลางการส่งข้อมูล จะตรวจสอบ ดูสัญญาณในสื่อกลาง ถ้าหากสื่อกลางในการส่งข้อมูลว่าง ก็จะทำการส่งข้อมูลได้ทันที แต่หากโนดตั้งแต่ 2 โนดขึ้น ไปส่งข้อมูลลงไปในสื่อกลางพร้อมๆกัน สัญญาณข้อมูลจะ เกิดการชนกันขึ้น ทุกๆสถานีจะต้องหยุดการส่งข้อมูลแล้ว รอเวลา ซึ่งช่วงเวลาของการรอแต่ละครั้งจะทำการสุ่ม ขึ้นมา (Random Time) หลังจากหมดเวลารอแล้วก็จะทำ การตรวจสอบสัญญาณในสื่อกลางเพื่อส่งข้อมูลลงไปใหม่ อีก

23 SPU Information Science Institute of Sripatum University 23 Collision Detection (1) เมื่อเกิดการชนกันของสัญญาณข้อมูลแล้ว เวลาจะถูก แบ่งออกเป็นช่องๆ (slots) แต่ละช่องมีช่วงเวลา 51.2 ไมโครวินาที (นั่นคือเวลาสถานีที่ส่งข้อมูลรู้ว่าเกิดการ ชนกันของข้อมูลหรือไม่ สำหรับความยาวของแลน 2,500 เมตร อัตราการส่งข้อมูล 10 Mbps) หลังจากการ ชนกันครั้งแรก แต่ละสถานีจะสร้างตัวเลขสุ่ม (Random) ที่มีค่า 0 หรือ 1 (เลขสุ่ม 2^1 ค่า) สถานีที่ได้ค่า 0 จะส่งข้อมูลออกไปในช่องเวลา 0 และ สถานีที่ได้ค่า 1 จะส่งข้อมูลในช่องเวลาที่ 1 หากสอง สถานีได้ค่าเลขสุ่มเดียวกันและส่งข้อมูลภายในช่องเวลา เดียวกัน จะเกิดการชนกันอีกครั้ง

24 SPU Information Science Institute of Sripatum University 24 Collision Detection (2) หลังจากการชนกันครั้งที่ 2 แต่ละสถานีจะสร้าง ตัวเลขสุ่มที่มีค่า 0,1,2, หรือ 3 (นั่นคือเลขสุ่ม 2^2 ค่า) แล้วส่งข้อมูลภายในช่องเวลาของตนเอง หากชนกันอีกก็จะสร้างเลขสุ่มจำนวน 2^3 ค่า กล่าวคือหลังจากการชนกัน i ครั้ง แต่ละสถานีก็จะมี การสร้างเลขสุ่มตั้งแต่ค่า 0 ถึง 2^i-1 ค่า และสถานีก็ จะส่งข้อมูลภายในช่องเวลาของตนเอง กระบวนการใน การแก้ไขการชนกันของข้อมูลแบบนี้เรียกว่า Binary Exponential Back off ซึ่งจะเห็นได้ว่ากระบวนการ นี้ทำให้โอกาสในการที่จะเกิดการชนกันของข้อมูลมี น้อยลง เมื่อจำนวนครั้งของการชนกันของข้อมูลมาก ขึ้น

25 SPU Information Science Institute of Sripatum University 25

26 SPU Information Science Institute of Sripatum University 26

27 SPU Information Science Institute of Sripatum University 27 TypeCableLength of Segme nt Number of nodes per Segment Advantage 10Base 5 Thick Coaxial 500 meters 100Use as Backbone 10Base 2 Thick Coaxial 200 meters 30Least expensive 10Base T Twisted Pair 100 meters 1,024Easy to maintain 10Base F Fiber Optic 2,000 meters 1,024Connection between buildings Cable for IEEE802.3 LAN

28 SPU Information Science Institute of Sripatum University 28 Figure 12-9-continued 10BASE5

29 SPU Information Science Institute of Sripatum University 29 Ethernet Segments

30 SPU Information Science Institute of Sripatum University 30 10BASE2

31 SPU Information Science Institute of Sripatum University 31 10BASET

32 SPU Information Science Institute of Sripatum University 32 Fast Ethernet High speed demand due to multimedia applications IEEE decided to improve standard to 803.2u, called Fast Ethernet Fast Ethernet operates at the speed of 100 Mbps, with no change in frame structure and collision detection and control but reduce time of transmission of each bit from 100 nanoseconds to 10 nanoseconds to obtain 10 time faster

33 SPU Information Science Institute of Sripatum University 33 Gigabit Ethernet Gigabit Ethernet operates at the speed of 1000 Mbps or 1 Gbps by improving data encoding and data transmission technique and using Fiber Optic media instead of Twisted Pairs

34 SPU Information Science Institute of Sripatum University 34 IEEE LAN Token Bus is IEEE standard, which cannot guarantee whether a node can send data at the time it wants Physical topology is Bus but operation is logical ring Each node knows the addresses of node on its left and node on its right

35 SPU Information Science Institute of Sripatum University 35 IEEE LAN When ring is established, a token will be send from one node to another in the same direction The node that wants to send data will have to wait for the token with available flag to have the right to send data therefore there will be only one sender at a time

36 SPU Information Science Institute of Sripatum University 36 IEEE LAN Each node in IEEE LAN or Token Ring LAN connects to the ring (which is different from Ethernet and Token Bus) Signals move in one direction from sender passing other nodes to the receiver

37 SPU Information Science Institute of Sripatum University 37 A ส่งข้อมูล ถึง C Token Ring

38 SPU Information Science Institute of Sripatum University 38

39 39 WAN

40 SPU Information Science Institute of Sripatum University 40 Wide Area Networks Relation between hosts on LANs and the subnet.

41 SPU Information Science Institute of Sripatum University 41 Switching Techniques  Circuit switching  Packet switching

42 SPU Information Science Institute of Sripatum University 42 Circuit Switching Characteristics Channel capacity dedicates to the sender and receiver, even through there is no data sending Once communication line connected, users feel like they have direct connection with no more delays Was developed for voice communication, but now also used for data communication

43 SPU Information Science Institute of Sripatum University 43 Circuit Switching Applications Public Telephone Network (PSTN) Private Branch Exchanges (PBX) Private Wide Area Networks (often used to interconnect PBXs in a single organization) Data Switch

44 SPU Information Science Institute of Sripatum University 44 Traditional Circuit Switching Illustration

45 SPU Information Science Institute of Sripatum University 45 Packet-Switching Networks Developed in 1970s for long distance data communication due to the limitations of circuit switching  During communication with circuit-switching, data traffic on the transmission line is rather light, so inefficiently use of data transmission line  sender and receiver must communicate at the same data rate

46 SPU Information Science Institute of Sripatum University 46 Packet Switching Operation Data are arranged into small pieces called packets, which can be sent to the destination in different routes Advantage: more efficiently use of transmission line, signals can be transmitted on different line, and priority can be arranged Disadvantage: delays of data at nodes, each data packets arrive at different time (jitter), and all packets have extra information, e.g. addresses

47 SPU Information Science Institute of Sripatum University 47 Packet Switching Illustration

48 SPU Information Science Institute of Sripatum University 48 Integrated network access using dedicated channels

49 SPU Information Science Institute of Sripatum University 49 Integrated network access using public switched WAN

50 SPU Information Science Institute of Sripatum University 50 X.25 The first public data network developed in 1970s Is connection-oriented network Support switched virtual circuit and permanent virtual circuitม similar to Leased Line Replaced by newer network, the Frame Relay, in 1980s How to use X.25 network First establish connection between sender and receiver by dial telephone number: connection number for data communication Each data packet consists of 3-byte header and not more than 128 bytes of data Header consists of 12-bit connection number, packet sequence number, acknowledgement number and 2-3 bits for other

51 SPU Information Science Institute of Sripatum University 51 Frame Relay Designed to reduce overhead of X.25 Use simple protocol with no flow control and error control between point-to-point communication Use “permanent virtual circuit” (like virtual leased line) between points of communication Packet size of 1,600 bytes Data rate of 1.5 Mbps, which is 23 times faster than that of X.25

52 SPU Information Science Institute of Sripatum University 52 Frame Relay protocol vs. X.25 protocol Reliability  Frame relay looses capability in flow control and error control and error control for point-to-point communication  X.25 has connection protocol for reliability point-to-point communication  No advantage on this point due to more reliability of transmission and switching devices Streamlining  Frame relay reduce user interface connection protocols requirements and processing requirements within network  Better throughput than that of X.25, at least an order of magnitude

53 SPU Information Science Institute of Sripatum University 53 Asynchronous Transfer Mode (ATM) Technology used in B-ISDN network, called cell relay faster than X.25 Sending data continuously faster than frame relay in many order of magnitude Packets are small, called “cell” Cell size is 53 bytes (5 byte for header and 48 bytes for data) No link-by-link error control or flow control

54 SPU Information Science Institute of Sripatum University 54 ATM Cell Format

55 SPU Information Science Institute of Sripatum University 55 ATM Virtual Circuits

56 SPU Information Science Institute of Sripatum University 56 Cell-switching vs Circuit switching Cell-switching is more flexible and effective for services with both data of almost constant size, e.g. multimedia data, and variable data such as data from database Data transmission at rate of Gbps, using Cell- switching technique, which more efficient than using multiplexor รื Circuit- switching, especially on fiber cable Cell-switching supports information broadcasting, such as television broadcasting, while circuit- switching does not directly support

57 SPU Information Science Institute of Sripatum University 57 Next Lecture: Switching and routing


ดาวน์โหลด ppt SPU Information Science Institute of Sripatum University Sripatum University 1 IS516 Computer Communication and Networks การสื่อสารคอมพิวเตอร์และเครือข่าย.

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