1. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 1 Chapter 4 The Medium Access Control Sublayer 4.3 Etherent IEEE 802 Group

2. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 2 Chapter 4 The Medium Access Control Sublayer 4.3 Etherent

3. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 3 Chapter 4 The Medium Access Control Sublayer IEEE 802.3: 1-persistent CSMA/CD 4.3 Etherent Classical Ethernet Switched Ethernet Fast Ethernet (100Mbps), Gigabit Ethernet, 10G Ethernet

4. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 4 Chapter 4 The Medium Access Control Sublayer 4.3.1 Classical Ethernet Physical Layer MIT->Harvard->Hawaii->Xerox PARC (Palo Alto Research Center)->Ethernet ->3COM

5. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 5 Chapter 4 The Medium Access Control Sublayer 4.3.1 Classical Ethernet Physical Layer The Xerox Ethernet was so successful that DEC, Intel, and Xerox drew up a standard in 1978 for a 10-Mbps Ethernet, called DIX standard. DIX became IEEE 802.3 in 1983.

6. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 6 Chapter 4 The Medium Access Control Sublayer 4.3.1 Classical Ethernet Physical Layer

7. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 7 Chapter 4 The Medium Access Control Sublayer Cable topologies. (a) Linear, (b) Spine, (c) Tree, (d) Segmented 4.3.1 Classical Ethernet Physical Layer

8. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 8 Chapter 4 The Medium Access Control Sublayer To allow larger networks, multiple cables can be connected by repeaters. A repeater is a physical layer device. It receives, amplifies, and retransmits signals in both directions. As far as the software is concerned, a series of cable segments connected by repeaters is no different than a single cable. 4.3.1 Classical Ethernet Physical Layer

9. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 9 Chapter 4 The Medium Access Control Sublayer 10BASE5 10BASE2 1BASE5 10BROAD36 10BASE-T Ethernet Cheaper net StarLAN Broadband Twisted-pair medium coaxial cable 50ohm-10mm coaxial cable 50ohms-5mm twisted-pair unshielded coaxial cable 75ohms 2 simplex TP unshielded signals maximum segment nodes per segment collision detection Notes 10Mbps Manch 10Mbps Manch 1Mbps Manch 10Mbps DPSK 10Mbps Manch 500m185m500m1800m100m maximum distance 2.5km0.925km2.5km3.6km1km 10030 2 excess current 2 active hub inputs transmission =reception activity on receiver and transmitter slot time=512 bits; gap time=96 bits; jam=32 to 48 bits

10. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 10 Chapter 4 The Medium Access Control Sublayer Manchester Encoding 4.3.1 Classical Ethernet Physical Layer

11. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 11 Chapter 4 The Medium Access Control Sublayer 4.3.2 Classical Ethernet MAC Sublayer Protocol Frame formats. (a) Ethernet (DIX). (b) IEEE 802.3. >1500 is type, otherwise interprets as length

12. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 12 Chapter 4 The Medium Access Control Sublayer 802.3 frame format single address group address local address global address 0 1 0 1 multicast (all 1's for broadcast) No significance outside one of 2 46 unique address 4.3.2 Classical Ethernet MAC Sublayer Protocol The first 3 bytes are OUI (Organizationally Unique Identifier) (Manufacturer)

13. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 13 Chapter 4 The Medium Access Control Sublayer 802.3 frame format Minimum frame length: 64 bytes (6+6+2+46+4) 4.3.2 Classical Ethernet MAC Sublayer Protocol

14. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 14 Chapter 4 The Medium Access Control Sublayer 4.3.2 Classical Ethernet MAC Sublayer Protocol For a 10 Mbps LAN with a maximum length of 2500 meters (with 4 repeaters), the round-trip time is 50 sec in the worst case. (10M)x(50 sec) =500 bits~512 bits=64 bytes Checksum= 32-bit CRC= x 32 +x 26 +x 23 +x 22 +x 16 +x 12 +x 11 +x 10 +x 8 +x 7 +x 5 +x 4 +x 2 +x+1

15. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 15 Chapter 4 The Medium Access Control Sublayer 802.3 frame format As the network speed goes up, the minimum frame length must go up or the maximum cable length must come down proportionally. For a 2500-meter LAN operating at 1 Gbps, the minimum frame size would have to be 6400 bytes. Alternatively, the minimum frame size could be 64 bytes and the maximum distance between any two stations 250 meters. 4.3.2 Classical Ethernet MAC Sublayer Protocol

16. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 16 Chapter 4 The Medium Access Control Sublayer Ethernet Frame Structure v2 (or DIX Ethernet, for DEC, Intel, Xerox) preamble SFD DA SA type CRC synchronize the receiver 7 1 6 6 2 4 60 to 1514 bytes start frame delimiter Cyclic Redundancy Check Type>0x0600=1536 Data 0800: IPv4 datagram 0806: ARP request/reply 8035: RARP request/reply 86DD: IPv6 4.3.2 Classical Ethernet MAC Sublayer Protocol

17. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 17 Chapter 4 The Medium Access Control Sublayer The Binary Exponential Backoff Algorithm If a frame has collided n successive times, where n<16, then the node chooses a random number K with equal probability from the set {0,1,2,3,...,2 m -1} where m=min{10,n}. The node then waits for bit times. (slot time=512 bit time) after first collision after second collision after third collision select one to start transmission 4.3.2 Classical Ethernet MAC Sublayer Protocol

18. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 18 Chapter 4 The Medium Access Control Sublayer Acknowledgements As far as CSMA/CD is concerned, an acknowledgement would be just another frame and would have to fight for channel time just like a data frame. (What is the problem?) A simple modification would allow speedy confirmation of frame receipt. All that would be needed is to reserve the first contention slot following successful transmission for the destination station. 4.3.2 Classical Ethernet MAC Sublayer Protocol

19. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 19 Chapter 4 The Medium Access Control Sublayer Performance Assume k stations are always ready to transmit and a constant retransmission probability in each slot. (A rigorous analysis of the binary exponential backoff algorithm is complicated.) If each station transmits during a contention slot with probability p, the probability A that some station acquires the channel in that slot is 4.3.3 Ethernet Performance

20. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 20 Chapter 4 The Medium Access Control Sublayer Performance The probability that the contention interval has exactly j slots in it is A(1-A) j-1, so the mean number of slots per contention is given by Since each slot has a duration 2, the mean contention interval, w, is 2 /A. Assuming optimal p, the mean number of contention slots is never more than e, so w is at most 2 e 5.4. 4.3.3 Ethernet Performance

21. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 21 Chapter 4 The Medium Access Control Sublayer Performance If the mean frame takes P sec to transmit, when many stations have frames to send, channel efficiency= Here we see where the maximum cable distance between any two stations enters into the performance figures. The longer the cable, the longer the contention interval. By allowing no more than 2.5km of cable and four repeaters between any two transceivers, the round-trip time can be bounded to 51.2 sec, which at 10Mbps corresponds to 512 bits or 64 bytes, the minimum frame size. 4.3.3 Ethernet Performance

22. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 22 Chapter 4 The Medium Access Control Sublayer Performance Let P=F/B (frame_length/bandwidth) and =L/C (cable_length/signal_propagation_speed). For the optimal case of e contention slots per frame, channel efficiency= Increasing network bandwidth or distance (the BL product) reduces efficiency for a given frame size. Unfortunately, much research on network hardware is aimed precisely at increasing this product. People want high bandwidth over long distances, which suggests that 802.3 may not be the best system for these applications. 4.3.3 Ethernet Performance

23. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 23 Chapter 4 The Medium Access Control Sublayer 4.3.3 Ethernet Performance

24. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 24 Chapter 4 The Medium Access Control Sublayer Many theoretical analysis assume the input traffic is Poisson. It now appears that network traffic is rarely Poisson, but self- similar. What this means is that averaging over long periods of time does not smooth out the traffic. The average number of packets in each minute of an hour has as much variance as the average number of packets in each second of s minute. The consequence of this discovery is that most models of network traffic do not apply to the real world and should be taken with a grain of salt. 4.3.3 Ethernet Performance

25. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 25 Chapter 4 The Medium Access Control Sublayer 4.3.4 Switched Ethernet (a) Hub. (b) Switch. Not necessarily this kind of wiring Must know which station is in which port Just like a single cable Ethernet

26. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 26 Chapter 4 The Medium Access Control Sublayer 4.3.4 Switched Ethernet An Ethernet switch.

27. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 27 Chapter 4 The Medium Access Control Sublayer The three primary reasons that the 803 committee decided to go with a souped-up 802.3 LAN (instead of a totally new one) were: 1. The need to be backward compatible with thousands of existing LANs. 2. The fear that a new protocol might have unforeseen problems. 3. The desire to get the job done before the technology changed. Fast Ethernet 4.3.5 Fast Ethernet

28. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 28 Chapter 4 The Medium Access Control Sublayer The basic idea behind fast Ethernet was simple: keep all the old packet formats, interfaces, and procedural rules, but just reduce the bit time form 100 nsec to 10 nsec. Technically, it would have been possible to copy 10Base5 or 10Base2 and still detect collisions on time by just reducing the maximum cable length by a factor of ten. However, the advantages of 10BaseT wiring were so overwhelming that fast Ethernet is based entirely on this design. Thus all fast Ethernet systems use hubs and switches. Fast Ethernet 4.3.5 Fast Ethernet

29. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 29 Chapter 4 The Medium Access Control Sublayer The category 3 UTP scheme, called 100Base-T4, uses a signaling speed of 25 MHz, only 25 percent faster than standard 802.3s 20 MHz. To achieve the necessary bandwidth, 100BaseT4 requires four twisted pairs. Fast Ethernet 4.3.5 Fast Ethernet

30. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 30 Chapter 4 The Medium Access Control Sublayer Of the four twisted pairs, one is always to the hub, one is always from the hub, and the other two are switchable to the current transmission direction. To get the necessary bandwidth, Manchester encoding is not used, but with modern clocks and such short distances, it is no longer needed. Fast Ethernet 4.3.5 Fast Ethernet

31. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 31 Chapter 4 The Medium Access Control Sublayer Ternary signals are sent, so that during a single clock period the wire can contain a 0, a 1, or a 2. With three twisted pairs going in the forward direction and ternary signaling, any one of the 27 possible symbols can be transmitted, making it possible to send 4 bits with some redundancy. Transmitting 4 bits in each of the 25 million clock cycles per second gives the necessary 100 Mbps. In addition, there is always a 33.3 Mbps (100/3) reverse channel using the remaining twisted pair. Fast Ethernet 4.3.5 Fast Ethernet

32. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 32 Chapter 4 The Medium Access Control Sublayer For category 5 wiring, the design, 100Base-TX, is simpler because the wires can handle clock rates up to 125 MHz and beyond. Only two twisted pairs per station are used, one to the hub and one from it. Rather than just use straight binary coding, a scheme called 4B5B is used at 125 MHz. Every group of 5 clock periods is used to send 4 bits in order to give some redundancy, provide enough transitions to allow easy clock synchronization, create unique patterns for frame delimiting, and be compatible with FDDI in the physical layer. Fast Ethernet 4.3.5 Fast Ethernet

33. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 33 Chapter 4 The Medium Access Control Sublayer Consequently, 100Base-TX is a full-duplex system; stations can transmit at 100 Mbps and receive at 100 Mbps at the same time. Often 100Base-TX and 100Base-T4 are collectively referred as 100Base-T. The last option, 100Base-FX, uses two strands of multimode fiber, one for each direction, so it, too, is full duplex with 100 Mbps in each direction. In addition, the distance between a station and the hub can be up to 2 km. Fast Ethernet 4.3.5 Fast Ethernet

34. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 34 Chapter 4 The Medium Access Control Sublayer Gigabit Ethernet The ink was barely dry on the fast Ethernet standard when the 802 committee bagan working on a yet faster Ethernet. It was quickly dubbed gigabit Ethernet and was ratified by IEEE in 1999 under the name 802.3ab. An important design goal: remain backward compatibility 4.3.6 Gigabit Ethernet

35. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 35 Chapter 4 The Medium Access Control Sublayer Gigabit Ethernet All configurations of gigabit Ethernet are point-to-point. Each individual Ethernet cable has exactly two devices on it, no more and no fewer. 4.3.6 Gigabit Ethernet

36. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 36 Chapter 4 The Medium Access Control SublayerChapter 4 The Medium Access Sublayer Gigabit Ethernet Two different modes of operation: full duplex and half duplex The normal mode is full-duplex used when computers are connected to a switch. The sender does not have to sense the channel to see if anybody else is using it because contention is impossible. So CSMA/CD protocol is not used. So the maximum length of the cable is determined by signal strength issues rather than by the collision detection issue. 4.3.6 Gigabit Ethernet

37. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 37 Chapter 4 The Medium Access Control Sublayer Gigabit Ethernet Half-duplex is used when the computers are connected to a hub. A hub does not buffer incoming frames. So collisions are possible and CSMA/CD is required. But now the transmission time for a 64-byte frame is 100 times faster. So the distance is 100 times less than Ethernet. That is, only 25 meters. The 802.3ab committee considered a radius of 25 meters to be unacceptable and added two features to the standard to increase the radius. 4.3.6 Gigabit Ethernet

38. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 38 Chapter 4 The Medium Access Control Sublayer Gigabit Ethernet The first feature, called carrier extension, essentially tells the hardware to add its own padding to extend the frame to 512 bytes. Of course, using 512 bytes to transmit 64 bytes of data has a line efficiency of 9%. The second feature, called frame bursting, allows a sender to transmit a concatenated sequence of multiple frames in a single transmission. If the total length is less than 512 bytes, the hardware pads it again. Just for backward compatibility. Most will use switches. 4.3.6 Gigabit Ethernet

39. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 39 Chapter 4 The Medium Access Control Sublayer Gigabit Ethernet Cabling Gigabit Ethernet uses new encoding rules on the fiber. Manchester encoding at 1Gbps would require 2G baud signal, too difficult and too wasteful. 4.3.6 Gigabit Ethernet

40. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 40 Chapter 4 The Medium Access Control Sublayer Gigabit Ethernet 8B/10B is used. Each 8-bit byte is encoded as 10 bits. 256 out of 1024. Two rules are used: 1.No codeword may have more than four identical bits in a row. 2.No codeword may have more than six 0s or six 1s. In addition, many input bytes have two possible codewords assigned to them. When there is a choice, the encoder always chooses the one that tries to equalize the number of 0s and 1s transmitted so far. 4.3.6 Gigabit Ethernet

41. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 41 Chapter 4 The Medium Access Control Sublayer Gigabit Ethernet 1000Base-T uses a different encoding scheme since clocking data onto copper wire in 1 nsec is too difficult. The solution uses four category 5 twisted pairs to allow four symbols to be transmitted in parallel. Each symbol is encoded using one of five voltage levels. This scheme allows a single symbol to encode 00, 01, 10, 11, or a special value for control purposes. The clock runs at 125MHz, allowing 1-Gbps operation. 4.3.6 Gigabit Ethernet

42. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 42 Chapter 4 The Medium Access Control Sublayer Gigabit Ethernet Gigabit Ethernet supports flow control which consists of one end sending a special control frame to the other end telling it to pause for some period of time. For gigabit Ethernet, the time unit for pause is 512 nsec. The maximum is 33.6 msec. 4.3.6 Gigabit Ethernet

43. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 43 Chapter 4 The Medium Access Control Sublayer 4.3.7 10-Gigabit Ethernet 10 Gigabit Ethernet cabling

44. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 44 Chapter 4 The Medium Access Control Sublayer 4.3.8 Retrospective on Ethernet Ethernet has been around for over 30 years and has no serious competitions. Few CPU architectures, operating systems, or programming languages have been king of the mountain for three decades going on strong. Clearly, Ethernet did something right. What?

45. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 45 Chapter 4 The Medium Access Control Sublayer 4.3.8 Retrospective on Ethernet Simple and Flexible Simple translates into reliable, cheap, and easy to maintain. Ethernet interworks easily with TCP/IP, which has become dominant. (Both are connectionless) Lastly and perhaps the most importantly, Ethernet has been able to evolve in certain crucial ways

46. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 46 Chapter 4 The Medium Access Control Sublayer In anyway, 4.3.8 Retrospective on Ethernet

47. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 47 Chapter 4 The Medium Access Control Sublayer What I see in the Korea Customs: Korea Immigration Smart Service 4.3.8 Retrospective on Ethernet

48. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 48 Chapter 4 The Medium Access Control Sublayer 4.4 Wireless LANS

49. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 49 Chapter 4 The Medium Access Control Sublayer 4.4.1 The 802.11 Architecture and Protocol Stack 802.11 architecture – infrastructure mode Access Point Client To Network

50. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 50 Chapter 4 The Medium Access Control Sublayer 4.4.1 The 802.11 Architecture and Protocol Stack 802.11 architecture – ad-hoc mode

51. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 51 Chapter 4 The Medium Access Control Sublayer 4.4.1 The 802.11 Architecture and Protocol Stack Part of the 802.11 protocol stack.

52. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 52 Chapter 4 The Medium Access Control Sublayer 4.4.1 The 802.11 Architecture and Protocol Stack

53. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 53 Chapter 4 The Medium Access Control Sublayer 4.4.2 The 802.11 Physical Layer Rate adaptation: Reduce rate if signal is bad OFDM (Orthogonal Frequency Division Multiplexing)

54. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 54 Chapter 4 The Medium Access Control Sublayer 4.4.2 The 802.11 Physical Layer MIMO (Multiple Input Multiple Output) Note that the terms input and output refer to the radio channel carrying the signal, not to the devices having antennas.

55. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 55 Chapter 4 The Medium Access Control Sublayer 4.4.3 The 802.11 MAC Sublayer Protocol CSMA/CA: CSMA with Collision Avoidance DCF: Distributed Coordination Function

56. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 56 Chapter 4 The Medium Access Control Sublayer Two modes of operation: DCF: distributed coordination function, no central control PCF: point coordination function, the base station controls all activity in its cell All implementations must support DCF but PCF is optional. 4.4.3 The 802.11 MAC Sublayer Protocol CSMA/CA: CSMA with Collision Avoidance

57. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 57 Chapter 4 The Medium Access Control Sublayer When DCF is employed, 802.11 uses a protocol called CSMA/CA (CSMA with Collision Avoidance). Two methods of operation are supported by CSMA/CA. In the first method: 1.When a station wants to transmit, it senses the channel. If it is idle, it just starts transmitting. 2.If the channel is busy, the sender defers until it is idle and then starts transmitting. 3.It does not sense the channel while transmitting. 4.If a collision occurs, the colliding stations wait a random time, using Ethernet binary exponential backoff algorithm, and try again later. 4.4.3 The 802.11 MAC Sublayer Protocol CSMA/CA: CSMA with Collision Avoidance

58. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 58 Chapter 4 The Medium Access Control Sublayer (a) The hidden station problem (b) The exposed station problem 4.4.3 The 802.11 MAC Sublayer Protocol CSMA/CA: CSMA with Collision Avoidance

59. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 59 Chapter 4 The Medium Access Control Sublayer Virtual channel sensing. A wants to send to B. C is within range of A. D is within range of B, but not A. (NAV: network allocation vector) 4.4.3 The 802.11 MAC Sublayer Protocol CSMA/CA: CSMA with Collision Avoidance

60. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 60 Chapter 4 The Medium Access Control Sublayer Wireless networks are noisy and unreliable. If a frame is too long, it has very little chance of getting through undamaged. So 802.11 allows frames to be fragmented into smaller pieces, each with its own checksum. Stop and Wait is used. 4.4.3 The 802.11 MAC Sublayer Protocol CSMA/CA: CSMA with Collision Avoidance

61. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 61 Chapter 4 The Medium Access Control Sublayer In PCF, the base stations polls the other stations, asking them if they have any frames to send. The basic mechanism is for the base station to broadcast a beacon frame periodically (10 to 100 times per second). Battery life is always an issue with mobile devices, so in 802.11, the base station can direct a mobile station to go into sleep until explicitly awakened by the base station or the user. 4.4.3 The 802.11 MAC Sublayer Protocol CSMA/CA: CSMA with Collision Avoidance

62. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 62 Chapter 4 The Medium Access Control Sublayer PCF and DCF can coexist within one cell. SIFS: Short InterFrame Spacing, PIFS: PCF IFS, DIFS: DCF IFS, EIFS: Extended IFS 4.4.3 The 802.11 MAC Sublayer Protocol CSMA/CA: CSMA with Collision Avoidance

63. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 63 Chapter 4 The Medium Access Control Sublayer 4.4.3 The 802.11 MAC Sublayer Protocol CSMA/CA: CSMA with Collision Avoidance

64. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 64 Chapter 4 The Medium Access Control Sublayer 802.11 Frame Structure 4.4.4 The 802.11 Frame Structure Format of the 802.11 data frame

65. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 65 Chapter 4 The Medium Access Control Sublayer Frame Control Field : –Retry: Indicates that the frame is a retransmission of an earlier frame. –To DS, From DS (DS=Distribution System, meaning AP) –More Fragment, More Data –Power Management : Active Mode, PS Mode (Power Save) –Protected: Data are encypted –Order: Frame must arrive in order Duration: how long the frame and ack will control the channel (NAV) Address 3: the distant endpoint 802.11 Frame Structure 4.4.4 The 802.11 Frame Structure

66. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 66 Chapter 4 The Medium Access Control Sublayer 802.11 Frame Structure 4.4.4 The 802.11 Frame Structure Frame Control Duration RA TA FCS MAC Header RTS Frame Frame Control Duration RA FCS MAC Header CTS Frame

67. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 67 Chapter 4 The Medium Access Control Sublayer Five distribution services and four station services Five distribution services: 1. Association: connect to a base station 2. Disassociation: break the association either by the base station or the station 3. Reassociation: change preferred base station 4. Distribution: how to route frames sent to the base station 5. Integration: translate from 802.11 to non-802.11 (in address scheme or frame format) 4.4.5 The 802.11 Services

68. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 68 Chapter 4 The Medium Access Control Sublayer Four intercell station services 1.Authentication: a station proves its knowledge of the secret key by encrypting the challenge frame and sending it back to the base station 2.Deauthentication 3.Privacy: manage the encryption and decryption using RC4 4.Data delivery 4.4.5 The 802.11 Services

69. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 69 Chapter 4 The Medium Access Control Sublayer 4.5 Broadband Wireless 802.16: Broadband Wireless Access Running fiber, coaxial, or even category 5 twisted pair to millions of homes and businesses is prohibitively expensive! What is a competitor can do? The wireless local loop The wireless last mile The wireless MAN (metropolitan area network)

70. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 70 Chapter 4 The Medium Access Control Sublayer WiMAX, the Worldwide Interoperability for Microwave Access, is a telecommunications technology aimed at providing wireless data over long distances in a variety of ways, from point-to-point links to full mobile cellular type access. It is based on the IEEE 802.16 standard, which is also called Wireless MAN. The name WiMAX was created by the WiMAX Forum, which was formed in June 2001 to promote conformance and interoperability of the standard. The forum describes WiMAX as "a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL." 4.5 Broadband Wireless

71. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 71 Chapter 4 The Medium Access Control Sublayer 4.5 Broadband Wireless The 802.16 architecture

72. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 72 Chapter 4 The Medium Access Control Sublayer 4.5 Broadband Wireless Comparison of 802.11 with 802.16 1.802.16 provides service to buildings, and buildings are not mobile. 2.Buildings can have more than one computer in them. 3.Better radios are available for buildings. So 802.16 can use full-duplex communications. 4.In 802.16, the distances involved can be several kilometers, affect signal-to-noise ratio and need security and privacy. 5.More bandwidth is needed. Hence 802.16 has to operate in higher 10-66 GHz band, thus require a completely different physical layer. 6.Error handling is much more important in 802.16. 7.802.16 should support QoS.

73. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 73 Chapter 4 The Medium Access Control Sublayer 4.5 Broadband Wireless Comparison of 3G with 802.16 The next step of 3G is 4G, using LTE (Long Term Evolution). It appears that LTE has prevailed over WiMax.

74. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 74 Chapter 4 The Medium Access Control Sublayer 4.5 Broadband Wireless The 802.16 protocol stack

75. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 75 Chapter 4 The Medium Access Control Sublayer 4.5 Broadband Wireless The 802.16 physical layer Frames and time slots for time division duplexing.

76. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 76 Chapter 4 The Medium Access Control Sublayer 4.5 Broadband Wireless The 802.16 MAC layer All connection-oriented services 4 Service Classes: Constant bit rate service Real-time variable bit rate service Non-real-time variable bit rate service Best efforts service

77. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 77 Chapter 4 The Medium Access Control Sublayer 4.5 Broadband Wireless The 802.16 frame structure (a) A generic frame. (b) A bandwidth request frame. Encrypted or notFinal checksum present or not Encryption key

78. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 78 Chapter 4 The Medium Access Control Sublayer 4.6 Bluetooth Bluetooth is an industrial specification for wireless personal area networks (PANs). Bluetooth provides a way to connect and exchange information between devices such as mobile phones, laptops, PCs, printers, digital cameras, and video game consoles over a secure, globally unlicensed short-range radio frequency. The Bluetooth specifications are developed and licensed by the Bluetooth Special Interest Group.

79. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 79 Chapter 4 The Medium Access Control Sublayer 4.6 Bluetooth Architecture Piconets can be connected to form a scatternet. 10 meters 7 active slaves and 255 parked nodes

80. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 80 Chapter 4 The Medium Access Control SublayerChapter 4 The Medium Access Sublayer 4.6 Bluetooth Profiles

81. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 81 Chapter 4 The Medium Access Control Sublayer 4.6 Bluetooth Protocol stack The Bluetooth protocol architecture. Logical Link Control Adaptation Protocol

82. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 82 Chapter 4 The Medium Access Control Sublayer 4.6 Bluetooth SCO (synchronous connection oriented) –fixed-bandwidth channel between a master and a slave –slots spaced by regular intervals –up to 3 SCO links per master –SCO packets are never retransmitted! bandwidth-guaranteed, but not error-free-guaranteed

83. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 83 Chapter 4 The Medium Access Control Sublayer 4.6 Bluetooth ACL (asynchronous connectionless) –a point-to-multipoint link between a master and ALL its slaves –only on slots NOT reserved for SCO links but the communication can include a slave already involves in a SCO link –packet retransmission is applicable. packet-switched style –a slave can send only when it is addressed in the previous master-initiated slot

84. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 84 Chapter 4 The Medium Access Control Sublayer 4.6 Bluetooth Detailed Connecting Steps inquiry: –used by master to find the identities of devices within range inquiry scan: –listening for an inquiry message page: –used by master to send PAGE message to connect to a slave by transmitting slaves device address code (DAC) page scan: –slave listening for a paging packet with its DAC

85. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 85 Chapter 4 The Medium Access Control Sublayer Slaves Four Mode in Connection State 4.6 Bluetooth Active: –actively participates in the piconet by listening, transmitting, and receiving packets. –the master periodically transmits to the slave to maintain synchronization Sniff: –only wake up in specific slots, and go to reduced-power mode in the rest of slots

86. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 86 Chapter 4 The Medium Access Control Sublayer Slaves Four Mode in Connection State 4.6 Bluetooth Hold: –goes to reduced-power mode and does not support ACL link any more may still participate in SCO exchanges –while in reduced-power mode, the slave may participate in another piconet

87. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 87 Chapter 4 The Medium Access Control Sublayer Slaves Four Mode in Connection State 4.6 Bluetooth Park: –does not participate in the piconet but still wants to remain as a member and remain time-synchronized –the slave gets a parking member address (PM_ADDR), and loses its AM_ADDR –by so doing, a piconet can have > 7 slaves

88. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 88 Chapter 4 The Medium Access Control Sublayer 4.6 Bluetooth Typical Bluetooth data frame at (a) basic, and (b) enhanced, data rates. Flow control (slave buffer full) Piggyback ack Stop-and-wait sequence number

89. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 89 Chapter 4 The Medium Access Control Sublayer 4.7 RFID (Radio Frequency Identification) A means of storing and retrieving data through electromagnetic transmission to an RF compatible integrated circuit. Basic components: –RFID readers: read data emitted from RFID tags –RFID tags: use a defined radio frequency and protocol to transmit and receive data Passive: without a battery, reflect the RF signal transmitted to them from a reader and add information by modulating the reflected signal, replace barcode, less expensive, unlimited operational lifetime, but read ranges are limited Active: contain both a radio transceiver and a button- cell battery to power the transceiver, longer range

90. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 90 Chapter 4 The Medium Access Control Sublayer 4.7 RFID (Radio Frequency Identification)

91. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 91 Chapter 4 The Medium Access Control Sublayer 4.7 RFID (Radio Frequency Identification)

92. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 92 Chapter 4 The Medium Access Control Sublayer 4.7 RFID (Radio Frequency Identification)

93. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 93 Chapter 4 The Medium Access Control Sublayer 4.7 RFID (Radio Frequency Identification)

94. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 94 Chapter 4 The Medium Access Control Sublayer 4.7 RFID (Radio Frequency Identification) An Electronic Product Code (EPC) is one common type of data stored in a tag

95. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 95 Chapter 4 The Medium Access Control Sublayer 4.7 RFID (Radio Frequency Identification)

96. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 96 Chapter 4 The Medium Access Control Sublayer 4.7 RFID (Radio Frequency Identification)

97. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 97 Chapter 4 The Medium Access Control Sublayer 4.7 RFID (Radio Frequency Identification) Example message exchange to identify a tag

98. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 98 Chapter 4 The Medium Access Control Sublayer 4.7 RFID (Radio Frequency Identification) Format of the Query message Define the range of slots over which tags will respond, from 0 to 2 Q -1

99. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 99 Chapter 4 The Medium Access Control Sublayer A Bridge C LANs can be connected by devices called bridges, which operate in the data link layer. Bridges do not examine the network layer header. 4.8 Datalink Layer Switching

100. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 100 Chapter 4 The Medium Access Control Sublayer A Router C In contrast, a router examines network layer headers. 4.8 Datalink Layer Switching

101. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 101 Chapter 4 The Medium Access Control Sublayer 4.8 Datalink Layer Switching Multiple LANs connected by a backbone to handle a total load higher than the capacity of a single LAN.

102. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 102 Chapter 4 The Medium Access Control Sublayer Why a single organization may end up with multiple LANs? (to need bridges) 1. Autonomy of departments to choose their own types of LANs 2. Cheaper to have separate LANs than to run a single large LANs 3. Load splitting 4. Physical distance is too great. (For example, >2.5km in 802.3) 5. More reliable 6. More secure 4.8 Datalink Layer Switching

103. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 103 Chapter 4 The Medium Access Control Sublayer 4.8 Datalink Layer Switching Bridge connecting two multidrop LANs Cut-through switching (wormhole routing)

104. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 104 Chapter 4 The Medium Access Control Sublayer 4.8 Datalink Layer Switching Bridges (and a hub) connecting seven point-to- point stations Backward learning algorithm: learn and forget

105. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 105 Chapter 4 The Medium Access Control Sublayer 4.8 Datalink Layer Switching Operation of a LAN bridge from 802.11 to 802.3.

106. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 106 Chapter 4 The Medium Access Control Sublayer 4.8 Datalink Layer Switching Bridges with two parallel links

107. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 107 Chapter 4 The Medium Access Control Sublayer 4.8 Datalink Layer Switching A spanning tree connecting five bridges. The dotted lines are links that are not part of the spanning tree

108. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 108 Chapter 4 The Medium Access Control Sublayer 4.8 Datalink Layer Switching (a) Which device is in which layer. (b) Frames, packets, and headers

109. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 109 Chapter 4 The Medium Access Control Sublayer 4.8 Datalink Layer Switching A building with centralized wiring using hubs and a switch

110. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 110 Chapter 4 The Medium Access Control Sublayer 4.8 Datalink Layer Switching Two VLANs, gray and white, on a bridged LAN

111. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 111 Chapter 4 The Medium Access Control Sublayer 4.8 Datalink Layer Switching The IEEE 802.1Q Standard Bridged LAN that is only partly VLAN-aware. The shaded symbols are VLAN aware. The empty ones are not

112. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 112 Chapter 4 The Medium Access Control Sublayer 4.8 Datalink Layer Switching The IEEE 802.1Q Standard The 802.3 (legacy) and 802.1Q Ethernet frame formats

113. Local Area Networks by R.S. Chang, Dept. CSIE, NDHU 113 Chapter 4 The Medium Access Control Sublayer Exercises: Page 368: Problem1 Page 369: Problems 4, 9, 11 Page 370: Problems 15, 25 Page 371: Problems 35, 39