1. SPU Information Science Institute of Sripatum University Sripatum University 1 IS516 Computer Communication and Networks การสื่อสารคอมพิวเตอร์และเครือข่าย Asst.Dr.Surasak Mungsing surasak.mu@spu.ac.th mungsing@gmail.com http://www.spu.ac.th/teacher/surasak.mu

2. 2 Lecture 06 Switching and Routing

3. 3 IS516 การสื่อสารคอมพิวเตอร์และเครือข่าย Switching Techniques

4. SPU Information Science Institute of Sripatum University 4 Switching Networks Data sent to a long distant receiver through switched nodes Nodes are not interested in contents Computer, terminal, phone, etc. communications network Data route assigned by switch from one node to another

5. SPU Information Science Institute of Sripatum University 5 Simple Switched Network

6. SPU Information Science Institute of Sripatum University 6 Circuit Switching Dedicated to communication channel to two communication stations 3 phases of operation Establish Transfer Disconnect switching capacity and channel capacity for connection establishment Manage data route intelligently

7. SPU Information Science Institute of Sripatum University 7 Circuit Switching - Applications Inefficient Dedicated channel Still connected even no data communication Connection establishment requires time After the establishment, data communication can be done as if the two communicator are directly connected Developed for voice communication (telephone )

8. SPU Information Science Institute of Sripatum University 8 Public Circuit Switched Network

9. SPU Information Science Institute of Sripatum University 9 Telecomms Components Subscriber Devices connected to network Subscriber line Local Loop or Subscriber loop Connection to network Distance no longer than 10 KM Exchange Switching centers End office - supports subscribers Trunks Branches between exchanges Multiplexed

10. SPU Information Science Institute of Sripatum University 10 Circuit Establishment

11. SPU Information Science Institute of Sripatum University 11 Circuit Switch Elements

12. SPU Information Science Institute of Sripatum University 12 Circuit Switching Concepts Digital Switch Network Interface Control Unit Establish connections Maintain connection Disconnect

13. SPU Information Science Institute of Sripatum University 13 Blocking or Non-blocking Blocking Cannot connect if network capacity is fully utilized Only available in blocking network Use in voice communication system Occur during a short period of time Non-blocking Allow connection at any time use for data communication

14. SPU Information Science Institute of Sripatum University 14 Space Division Switching Developed for analog communication Separate physical communication paths Crossbar switch Number of crosspoints grows as square of number of stations Loss of crosspoint prevents connection Inefficient use of crosspoints All stations connected, only a few crosspoints in use Non-blocking

15. SPU Information Science Institute of Sripatum University 15 Multistage Switch Reduce number of crosspoints Many communication paths in network Complex control May be blocking Three-stage Space Division Switch

16. SPU Information Science Institute of Sripatum University 16 Time Division Switching Modern digital systems depend on intelligent control of devices and time management Time allocation technique required for establishing and maintaining connection of virtual circuit Partition low speed stream of bits and send each portion with high speed stream of bits on the common high speed channel

17. SPU Information Science Institute of Sripatum University 17 Circuit-Switching Stages Circuit establishment Data transfer point-to-point from endpoints to node internal switching/multiplexing among nodes Circuit disconnect

18. SPU Information Science Institute of Sripatum University 18 Circuit Establishment Station request connection to node Node defines best data path then sends data to the next link each next node defines next data path After connection establishment, test message will be sent to test whether receiver is ready to receive data

19. SPU Information Science Institute of Sripatum University 19 Data Transfer Point-to-point data sending from sender station to node Internal switching and multiplexed from node to node Point-to-point data sending from node to receiver station Normally is full-duplex during communication period

20. SPU Information Science Institute of Sripatum University 20 Circuit Disconnect A station disconnects when communication ended Must broadcast signal to all nodes involve data communication to release resources to the system

21. SPU Information Science Institute of Sripatum University 21 Operation of Packet Switching Data sent in small packets Normal packet size is 1000 octets Long message will be divide in to packets Each packet consists of user data and control data Control info Routing information (network addresses) Store and forward

22. SPU Information Science Institute of Sripatum University 22 Use of Packets

23. SPU Information Science Institute of Sripatum University 23 Advantages of Packet Switching Better Line efficiency Data rate conversion All packets will be received even toght the network is busy data rate may be lower Capable of prioritizing data

24. SPU Information Science Institute of Sripatum University 24 Packet Switching Technique Long message divided into small packets Packets are sent one by one through network Two types of packet sending Datagram Virtual circuit

25. SPU Information Science Institute of Sripatum University 25 Datagram Each packets sent independently Packets takes any route to destination Packets may reach destination not in order Packets may be lost along the way Receiver reordering packets arrived and mannage to solve lost packet problem

26. SPU Information Science Institute of Sripatum University 26 Datagram Diagram

27. SPU Information Science Institute of Sripatum University 27 Virtual Circuit Established prepared connection path before sending packets Perform handshaking Each packet has virtual circuit identifier No decision on selecting data path Cancellation of request and circuit Not a dedicated path

28. SPU Information Science Institute of Sripatum University 28 Virtual Circuit Diagram

29. SPU Information Science Institute of Sripatum University 29 Virtual Circuits vs Datagram Virtual circuits Maintain ordering of packets and error control Sending packets fast No decision making on data path Low reliablity If a node along the path fails, all path include that node will fail Datagram No connection establishment process Better performance for small amount of packets More flexible Routing path avoids heavy data traffic portion of network

30. SPU Information Science Institute of Sripatum University 30 Packet Size

31. SPU Information Science Institute of Sripatum University 31 Circuit vs Packet Switching Performance Propagation delay Transmission time Node delay

32. SPU Information Science Institute of Sripatum University 32 Event Timing

33. SPU Information Science Institute of Sripatum University 33 Packet-Switched Congestion Control If line utilization is more than 80% of its capacity, queue length increase quickly Limitation of queue length used for congestion problem Congestion status exchanged between nodes Used flow control as of X.25

34. SPU Information Science Institute of Sripatum University 34

35. 35 Routing Algorithms

36. SPU Information Science Institute of Sripatum University 36 Store-and-Forward Packet Switching The environment of the network layer protocols.  Packet is stored until it completely arrived  Router examine for correctness before forwarding to next router

37. SPU Information Science Institute of Sripatum University 37 Connectionless and Connection- oriented Services Two types of services in network layer Connectionless Service Each packet has independent route Data unit is datagram Subnetwork is called datagram subnet Connection-oriented Service Data path from source router to destination router must be prepared Establish connection as virtual circuit Subnetwork is called virtual circuit subnet

38. SPU Information Science Institute of Sripatum University 38 Implementation of Connectionless Service Routing within a diagram subnet

39. SPU Information Science Institute of Sripatum University 39 Implementation of Connection-Oriented Service Routing within a virtual-circuit subnet

40. SPU Information Science Institute of Sripatum University 40 Comparison of Virtual-Circuit and Datagram Subnets 5-4

41. SPU Information Science Institute of Sripatum University 41 Routing Algorithms Shortest Path Routing Flooding Distance Vector Routing Link State Routing Hierarchical Routing Broadcast Routing Multicast Routing Routing for Mobile Hosts Routing in Ad Hoc Networks

42. SPU Information Science Institute of Sripatum University 42 Routing Algorithms (2) Conflict between fairness and optimality. If amount of data transfer from A to A’, from B to B’ and from C to C’ are large enough then the horizontal bus may be saturate and data transfer from X และ X’ must be suspended for the network to work efficiently

43. SPU Information Science Institute of Sripatum University 43 Shortest Path Routing The first 5 steps used in computing the shortest path from A to D. The arrows indicate the working node. Dijkstra (1959) ได้นำเสนอ algorithm สำหรับการค้นหาเส้นทางที่สั้น ที่สุดระหว่างจุด 2 จุด

44. SPU Information Science Institute of Sripatum University 44 Flooding Non adaptive technique to system Router sends packets to all of its connected routers except the router that it receives packets from This technique quickly creates large amount of same data in network Requires technique to avoid creating huge amount of data in network Counter included in header Keep record of packets received so that they will not be sent to same router again

45. SPU Information Science Institute of Sripatum University 45 Distance Vector Routing algorithm for dynamic route selection Router must have routing table of distance best route for forwarding packets to other routers Always updating routing table by exchange information between adjacent routers Measures are number of routers in the route, amount of packets waiting for forwarding, and time to wait along the route, etc.

46. SPU Information Science Institute of Sripatum University 46 Distance Vector Routing (a) A subnet. (b) Input from A, I, H, K, and the new routing table for J. ถ้า Router J ต้องการคำนวนเวลาส่งข้อมูลไปยัง Router G: 1) ส่งข้อมูล ผ่าน Router Aใช้เวลา 8 มิลลิวินาที 2) จาก A ไปยัง G ใช้เวลา 18 มิลลิวินา ที่ เวลารวม = 8+18=28 มิลลิวินาที ในทำนองเดียวกัน ถ้าส่งผ่าน I, H, และ K จะใช้เวลารวม (10+31=41), (12+6=18), และ (6+31=37) ตามลำดับ เวลาที่ดีที่สุดคือ18 ดังนั้น J บันทึกเวลา18 ผ่าน H

47. SPU Information Science Institute of Sripatum University 47 Link State Routing  Dynamic algorithm for high speed transmission line  Each router must do the followings Learn to know adjacent routers and their network addresses Compute waiting time or cost in communicating with adjacent routers Create packets for sending its own routing information Send packets of routing information to all routers Compute shortest distance for each router communication

48. SPU Information Science Institute of Sripatum University 48 Hierarchical Routing Consequence of having more and more routers in network Algorithm use for partitioning routers into small group, called region Routers in the same region knows routes for communication to each other, but have no information of routers in other reegion

49. SPU Information Science Institute of Sripatum University 49 Hierarchical Routing Hierarchical routing. ตัวอย่างการจัดแบ่งกลุ่มข้อมูลออกเป็น 2 ระดับ ประกอบด้วย 5 region: การจัด แบบเดิม router 1A ต้องมีข้อมูลถึง 17 รายการ เมื่อจัดแบบ 2 ระดับ router 1A จะมีรายการเหลือเพียง 7 รายการ ดังนั้นเมื่อจำนวน router เพิ่มมากขึ้นเท่าใด วิธีการนี้จะช่วยลดจำนวนรายการในตารางข้อมูลได้มากยิ่งขึ้น

50. SPU Information Science Institute of Sripatum University 50 Broadcast Routing Same messages are sent to many or all hosts in the system  Direct sending Create copies of packets as many as number of in the system Each copy of packets defines address of each node  Send by Flooding - there will ne large amount of copies of packets hence reduce the overall performance of the  Send by Multi-destination routing Each packet contains all destination addresses intended to send to Router examines all receiver list to select transmission line to be used and duplicates packets as many as number of selected transmission lines then update each pakets with correct destination address  Apply sink tree and spanning tree

51. SPU Information Science Institute of Sripatum University 51 Broadcast Routing Reverse path forwarding. (a) A subnet. (b) a Sink tree. (c) The tree built by reverse path forwarding.

52. SPU Information Science Institute of Sripatum University 52 Multicast Routing Setup group receiver– create, destroy, join, resign membership to be used for routing consideration Each router build its own spanning tree When packets are distributed to group receiver, the first router that receives message examines spanning tree. All unable to contact hosts will be ignored.

53. SPU Information Science Institute of Sripatum University 53 Multicast Routing (a) A network. (b) A spanning tree for the leftmost router. (c) A multicast tree for group 1. (d) A multicast tree for group 2.

54. 54 Congestion Control

55. SPU Information Science Institute of Sripatum University 55 Congestion Control Algorithms General Principles of Congestion Control Congestion Prevention Policies Congestion Control in Virtual-Circuit Subnets Congestion Control in Datagram Subnets Load Shedding Jitter Control

56. SPU Information Science Institute of Sripatum University 56 Congestion When too much traffic is offered, congestion sets in and performance degrades sharply.

57. SPU Information Science Institute of Sripatum University 57 General Principles of Congestion Control Monitoring system for congestion problem Send message to department that is responsible for congestion problem solving Reconfigure working operation to solve the problem

58. SPU Information Science Institute of Sripatum University 58 Policies that affect congestion 5-26

59. SPU Information Science Institute of Sripatum University 59 Congestion Control in Virtual-Circuit Subnets (a) A congested subnet. (b) A redrawn subnet, eliminates congestion and a virtual circuit from A to B.

60. SPU Information Science Institute of Sripatum University 60 Hop-by-Hop Choke Packets (a) A choke packet that affects only the source. (b) A choke packet that affects each hop it passes through.

61. SPU Information Science Institute of Sripatum University 61 Jitter Control ( a) High jitter. (b) Low jitter. Jitter: delay of packet delivery

62. 62 Quality of Service

63. SPU Information Science Institute of Sripatum University 63 Quality of Service Requirements Techniques for Achieving Good Quality of Service Integrated Services Differentiated Services Label Switching and MPLS

64. SPU Information Science Institute of Sripatum University 64 Requirements How stringent the quality-of-service requirements are. 5-30

65. SPU Information Science Institute of Sripatum University 65 Buffering การทำให้การนำส่งแพ็กเกตราบรื่นด้วยการใช้ Buffer

66. SPU Information Science Institute of Sripatum University 66 The Leaky Bucket Algorithm (a) A leaky bucket with water (b) a leaky bucket with packets

67. SPU Information Science Institute of Sripatum University 67 The Token Bucket Algorithm (a) Before (b) After 5-34

68. SPU Information Science Institute of Sripatum University 68 Admission Control An example of flow specification. 5-34

69. SPU Information Science Institute of Sripatum University 69 Packet Scheduling (a) A router with five packets queued for line O. (b) Finishing times for the five packets.

70. SPU Information Science Institute of Sripatum University 70 Integrated Services Architecture that support multimedia data stream Flow-based algorithm Use for both unicast and Multicast applications Resource reServation Protocol (RSVP) Developed by Zhang et al., 1993 Many senders can send data to many receivers Each receiver can switch to receive data from any sender Efficient use of bandwidth while trying to eliminate congestion problem

71. SPU Information Science Institute of Sripatum University 71 RSVP-The ReSerVation Protocol (a) A network (b) The multicast spanning tree for host 1 (c) The multicast spanning tree for host 2

72. SPU Information Science Institute of Sripatum University 72 RSVP-The ReSerVation Protocol (2) (a) Host 3 requests a channel to host 1 (b) Host 3 then requests a second channel, to host 2 (c) Host 5 requests a channel to host 1

73. SPU Information Science Institute of Sripatum University 73 Expedited Forwarding Expedited packets experience a traffic-free network. การจัดส่งข้อมูลเร่งด่วน (มาตรฐาน RFC 3246) กำหนดโดย IETF

74. SPU Information Science Institute of Sripatum University 74 Assured Forwarding A possible implementation of the data flow for assured forwarding

75. SPU Information Science Institute of Sripatum University 75 Label Switching and MPLS Transmitting a TCP segment using IP, MPLS, and PPP  Developed by a group of router manufacturers  Label, instead of receiver address, is added to the front of header and quickly compute data route by information from the label.  Resources are reserved for the whole data route

76. SPU Information Science Institute of Sripatum University 76 Next Lecture: Switching and Routing