1. Univ. of TehranComputer Network1 Special Topics on Wireless Ad-hoc Networks University of Tehran Dept. of EE and Computer Engineering By: Dr. Nasser Yazdani Wireless LANs Lecture 3: Wireless LANs

2. Univ. of TehranComputer Network2 Covered topic How to build a small wireless network? considerations Media access issues References Chapter 3 of the book “Wireless Medium Access control protocols” a survey “MACAW: A Media Access Protocol for Wireless LAN’s” “Design alternative for Wireless local area networks”, “Bluetooth” SSCH: Slotted Seeded Channel Hopping for Capacity … ECHOS: Enhanced Capacity 802.11 Hotspots A backoff Algorithm for Improving Saturation Throughput in IEEE 802.11 DCF A wireless MAC protocol Using Implicit Pipelining

3. Univ. of TehranComputer Network3 Outlines Why wireless LANs? Applications? Wireless LAN’s issues 802.11 standard Mac protocols. Bluetooth ZigBee

4. Univ. of TehranComputer Network4 What is special on wireless? Channel characteristics Half-Duplex Location dependency Very noisy channel, fading effects, etc., Resource limitation Bandwidth Frequency Battery, power. Wireless problems are usually optimization problems.

5. Univ. of TehranComputer Network5 Why wireless networks? Mobility: to support mobile applications Costs: reductions in infrastructure and operating costs: no cabling or cable replacement Special situations: No cabling is possible or it is very expensive. Reduce downtime: Moisture or hazards may cut connections.

6. Univ. of TehranComputer Network6 Applications ? Pervasive computing or nomadic access. Ad hoc networking: Where it is difficult or impossible to set infrastructure. LAN extensions: Robots or industrial equipment communicate each others. Sensor network where elements are two many and they can not be wired!.

7. Univ. of TehranComputer Network7 Ideal Wireless LAN? Wish List High speed Low cost No use/minimal use of the mobile equipment battery Can work in the presence of other WLAN Easy to install and use Etc

8. Univ. of TehranComputer Network8 Wireless LAN Design Alternatives Wireless LAN Design Goals Portable product: Different countries have different regulations concerning RF band usage. Low power consumption License free operation Multiple networks should co-exist Design Choices Physical Layer: IR or RF? Radio Technology: Direct-Sequence or Frequency-Hopping? Which frequency range to use? Which MAC protocol to use. Peer-Peer architecture or Base-Station approach?

9. Univ. of TehranComputer Network9 Physical Layer Alternatives IR Simple circuitry, cost-effective, no regulatory constraints, no Rayleigh fading (waves are small), also nice for micro-cellular networks... (multiple cells can exist in a room providing more bandwidth) RF more complicated circuitry, regulatory constraints (ISM bands) in the U.S.

10. Univ. of TehranComputer Network10 Physical Layer Alternatives IRRF Cost<$10<$20 RegulationNoneNo license on ISM bands InterferenceAmbient LightRadiators coverageSpotWide Area PerformanceModerateDepends on Bandwidth Multiple networks LimitedPossible

11. Univ. of TehranComputer Network11 Radio Technology Spread Spectrum Technologies Frequency Hopping: The sender keeps changing the carrier wave frequency at which its sending its data. Receiver must be in synch with transmitter, and know the ordering of frequencies. Direct-Sequence: The receiver listens to a set of frequencies at the same time. The subset of frequencies that actually contain data from the sender is determined by spreading code, which both the sender and receiver must know. This subset of frequencies changes during transmission. Non-Spread Spectrum requires licensing

12. Univ. of TehranComputer Network12 Frequency Hopping versus Direct Sequence DS advantages Lower cost FH advantages Higher capacity Interference avoidance capability: If some frequency has interference on it, simply don't hop there. Multiple networks can co-exist: Just use a different frequency hopping pattern.

13. Univ. of TehranComputer Network13 LAN Industry WANs are offered as service Cost of infrastructure Coverage area LANs are sold as “end products” You own, no service charge Analogy with PSTN/PBX WLAN vs. WAN Cellular Networks Data rate (2 Mbps vs. 54 Mbps) Frequency band regulation (Licensing) Method of data delivery (Service vs. own)

14. Univ. of TehranComputer Network14 Growth of Home wireless

15. Univ. of TehranComputer Network15 LAN standard IEEE 802 Standards 802.3, 802.4, 802.5 are wired LANs 802.9: ISO Ethernet 802.6: MAN 802.11, 802.15, 802.16: Wireless local net 802.14 Cable modem 802.10 Security management

16. Univ. of TehranComputer Network16 LAN standard

17. Univ. of TehranComputer Network17 Early Experiences IBM Switzerland,Late 1970 Factories and manufacturing floors Diffused IR technology Could not get 1 Mbps HP Labs, Palo Alto, 1980 100 Kbps DSSS around 900 Mhz CSMA as MAC Experimental licensing from FCC Frequency administration was problematic, thus abandoned Motorola, ~1985 1.73 GHz Abandoned after FCC difficulties

18. Univ. of TehranComputer Network18 Architectures Distributed wireless Networks: also called Ad-hoc networks Centralized wireless Networks: also called last hop networks. They are extension to wired networks.

19. Univ. of TehranComputer Network19 Base-Station Approach Advantages over Peer-Peer No hidden terminal: base station hears all mobile terminals, are relays their information to ever mobile terminal in cell. Higher transmission range Easy expansion Better approach to security Problem? Point of failure, Feasibility?

20. Univ. of TehranComputer Network20 Wireless LAN Architecture Server PDA Laptop Access Point Ad Hoc Pager DS

21. Univ. of TehranComputer Network21 Access Point Functions Access point has three components Wireless LAN interface to communicate with nodes in its service area Wireline interface card to connect to the backbone network MAC layer bridge to filter traffic between sub-networks. This function is essential to use the radio links efficiently

22. Univ. of TehranComputer Network22 Medium Access Control Wireless channel is a shared medium Need access control mechanism to avoid interference MAC protocol design has been an active area of research for many years. See Survey.

23. Univ. of TehranComputer Network23 MAC: A Simple Classification Wireless MAC CentralizedDistributed Guaranteed or controlled access Random access Our focus SDMA, FDMA, TDMA, Polling On Demand MACs, Polling

24. Univ. of TehranComputer Network24 Wireless MAC issues Half duplex operations: difficult to receive data while sending Time varying channel: Multipath propagation, fading Burst Channel error: BER is as high as 10 -3. We need a better strategy to overcome noises. Location dependant carrier sensing: signal decays with path length. Hidden nodes Exposed nodes Capture: when a receiver can cleanly receive data from two sources simultaneously, the farther one sounds a noise.

25. Univ. of TehranComputer Network25 Performance Metrics Delay: ave time on the MAC queue Throughput: fraction used for data transmission. Fairness: Not preference any node Stability: handle instantaneous loads greater than its max. capacity. Robust against channel fading Power consumption: or power saving Support for multimedia

26. Univ. of TehranComputer Network26 Wireless LAN Architecture, Cont… Logical Link Control Layer MAC Layer: Consist of two sub layer, physical Layer and physical convergence layer  Physical convergence layer, shields LLC from the specifics of the physical medium. Together with LLC it constitutes equivalent of Link Layer of OSI

27. Univ. of TehranComputer Network27 Multi-Channel MAC: A simple approach Divide bandwidth into multiple channels Choose any one of the idle channels Use a single-channel protocol on the chosen channel ALOHA MACA

28. Univ. of TehranComputer Network28 Multiple Channels Multiple channels in ad hoc networks: typically defined by a particular code (CDMA) or frequency band (FDMA) TDMA requires time synchronization among hosts in ad hoc network Difficult Many MAC protocols have been proposed

29. Univ. of TehranComputer Network29 MAC & Network Topology CDMA: Not beneficial under current regulations - difficult to get good spreading codes FDMA: Inefficient spectrum utilization for bursty traffic CSMA: Suitable for Peer-to Peer architecture TDMA: favors Base-Station/Remote-Station architecture

30. Univ. of TehranComputer Network30 CSMA versus TDMA CSMA Advantages Can be implemented on an Ethernet chipset TDMA advantages simple remote stations isochronous traffic supported (low-latency, consistent throughput for such things as voice) high power saving potential (only need to listen at certain times)

31. Univ. of TehranComputer Network31 Integrated CSMA/TDMA MAC Protocol Supports guaranteed bandwidth traffic and random access traffic The bandwidth is divided into a random part and a reserved part. Random part is LBT, reserved part During high traffic all bandwidth can be used for reserved traffic (like wireless telephony) H1 Reserved-1H2 Reserved-2H3 LBT

32. Univ. of TehranComputer Network32 Reservation/Polling MAC Protocol Works only with AP Fair and slow. First-in-First-Out Wireless station send a request. All requests are queued. Wireless stations are polled in the same order that the requests have arrive. All data reception is acknowledged.

33. Univ. of TehranComputer Network33 Power Management Battery life of mobile computers/PDAs are very short. Need to save The additional usage for wireless should be minimal Wireless stations have three states Sleep Awake Transmit

34. Univ. of TehranComputer Network34 Power Management, Cont… AP knows the power management of each node AP buffers packets to the sleeping nodes AP send Traffic Delivery Information Message (TDIM) that contains the list of nodes that will receive data in that frame, how much data and when? The node is awake only when it is sending data, receiving data or listening to TDIM.

35. Univ. of TehranComputer Network35 IEEE 802.11 WLAN, History 1997 IEEE 802.11 working group developed standard for inter-working wireless LAN products for 1 and 2 Mbps data rates in 2.4 GHz ISM (industrial, scientific, and medical) band (2400-2483 MHz) Required that mobile station should communicate with any wired or mobile station transparently (802.11 should appear like any other 802 LAN above MAC layer), so 802.11 MAC layer attempts to hide nature of wireless layer (eg, responsible for data retransmission)

36. Univ. of TehranComputer Network36 802.11 WLAN History, Cont.. 1999 IEEE 802.11a amendment for 5 GHz band operation and 802.11b amendment to support up to 11 Mbps data rate at 24 GHz Different standards: a, b, e, etc., differ in physical link properties, services, etc. MAC sub layer uses CSMA/CA (carrier sense multiple access with collision avoidance)

37. Univ. of TehranComputer Network37 802.11 Features Power management: NICs to switch to lower-power standby modes periodically when not transmitting, reducing the drain on the battery. Put to sleep, etc. Bandwidth: To compress data Security: Addressing: destination address does not always correspond to location.

38. Univ. of TehranComputer Network38 IEEE 802.11 Topology Independent basic service set (IBSS) networks (Ad-hoc) Basic service set (BSS), associated node with an AP Extended service set (ESS) BSS networks Distribution system (DS) as an element that interconnects BSSs within the ESS via APs.

39. Univ. of TehranComputer Network39 Starting an IBSS One station is configured to be “initiating station,” and is given a service set ID (SSID); Starter sends beacons; Other stations in the IBSS will search the medium for a service set with SSID that matches their desired SSID and act on the beacons and obtain the information needed to communicate; There can be more stations configured as “starter.”

40. Univ. of TehranComputer Network40 ESS topology connectivity between multiple BSSs, They use a common DS

41. Univ. of TehranComputer Network41 Starting an ESS The infrastructure network is identified by its extended service set ID (ESSID); All APs will have been set according to this ESSID; On power up, stations will issue probe requests and will locate the AP that they will associate with.

42. Univ. of TehranComputer Network42 802.11 Logical Architecture PLCP: Physical Layer Convergence Procedure PMD: Physical Medium Dependent MAC provides asynchronous, connectionless service Single MAC and one of multiple PHYs like DSSS, OFDM, IR and FHSS.

43. Univ. of TehranComputer Network43 802.11 MAC Frame Format Frame Control DurationAddr 1 Protocol Version TypeSub typeTo DS From DS RetryLast Fragment RSVDEPPower Mgt CRCSequence Control User Data Address 4 Addr 2 Addr 3 MAC Header Encrypted to WEP Preamble PLCP header MPDU Bytes 32 6 34~2346 2 2 6 6 Bytes 2 6 6 4 2 Bits 2 4 1 1 1

44. Univ. of TehranComputer Network44 802.11 MAC Frame Format Address Fields contains Source address Destination address AP address Transmitting station address DS = Distribution System User Data, up to 2304 bytes long

45. Univ. of TehranComputer Network45 IEEE 802.11 LLC Layer Provides three type of service for exchanging data between (mobile) devices connected to the same LAN Acknowledged connectionless Un-acknowledged connectionless, useful for broadcasting or multicasting. Connection oriented Higher layers expect error free transmission

46. Univ. of TehranComputer Network46 IEEE 802.11 LLC Layer, Cont.. Each SAP (Service Access Point) address is 7 bits. One bit is added to it to indicate whether it is order or response. Control has three values Information, carry user data Supervisory, for error control and flow control Unnumbered, other type of control packet Destination SAP Source SAP Data Control

47. Univ. of TehranComputer Network47 IEEE 802.11 LLC MAC Primitives Four types of primitives are exchanged between LLC and MAC Layer Request: order to perform a function Confirm: response to Request Indication: inform an event Response: inform completion of process began by Indication

48. Univ. of TehranComputer Network48 Reception of packets AP Buffer traffic to sleeping nodes Sleeping nodes wake up to listen to TIM (Traffic Indication Map) in the Beacon AP send a DTIM (Delivery TIM) followed by the data for that station. Beacon contains, time stamp, beacon interval, DTIM period, DTIM count, sync info, TIM broadcast indicator

49. Univ. of TehranComputer Network49 Frame type and subtypes Three type of frames Management Control Asynchronous data Each type has subtypes Control RTS CTS ACK

50. Univ. of TehranComputer Network50 Frame type and subtypes, Cont.. Management Association request/ response Re-association request/ response: transfer from AP to another. Probe request/ response privacy request/ response: encrypting content Authentication: to establish identity Beacon (Time stamp, beacon interval, channels sync info, etc.)

51. Univ. of TehranComputer Network51 Frame type and subtypes, Cont.. Management… TIM (Traffic Indication Map) indicates traffic to a dozing node dissociation

52. Univ. of TehranComputer Network52 802.11 Management Operations Scanning Association/Reassociation Time synchronization Power management

53. Univ. of TehranComputer Network53 Scanning in 802.11 Goal: find networks in the area Passive scanning Not require transmission Move to each channel, and listen for Beacon frames Active scanning Require transmission Move to each channel, and send Probe Request frames to solicit Probe Responses from a network

54. Univ. of TehranComputer Network54 Association in 802.11 AP 1: Association request 2: Association response 3: Data traffic Client

55. Univ. of TehranComputer Network55 Reassociation in 802.11 New AP 1: Reassociation request 3: Reassociation response 5: Send buffered frames Old AP 2: verify previous association 4: send buffered frames Client 6: Data traffic

56. Univ. of TehranComputer Network56 Time Synchronization in 802.11 Timing synchronization function (TSF) AP controls timing in infrastructure networks All stations maintain a local timer TSF keeps timer from all stations in sync Periodic Beacons convey timing Beacons are sent at well known intervals Timestamp from Beacons used to calibrate local clocks Local TSF timer mitigates loss of Beacons

57. Univ. of TehranComputer Network57 Power Management in 802.11 A station is in one of the three states Transmitter on Receiver on Both transmitter and receiver off (dozing) AP buffers packets for dozing stations AP announces which stations have frames buffered in its Beacon frames Dozing stations wake up to listen to the beacons If there is data buffered for it, it sends a poll frame to get the buffered data

58. Univ. of TehranComputer Network58 Authentication Three levels of authentication Open: AP does not challenge the identity of the node. Password: upon association, the AP demands a password from the node. Public Key: Each node has a public key. Upon association, the AP sends an encrypted message using the nodes public key. The node needs to respond correctly using it private key.

59. Univ. of TehranComputer Network59 IEEE 802.11 Wireless MAC Distributed and centralized MAC components Distributed Coordination Function (DCF) Point Coordination Function (PCF) DCF suitable for multi-hop and ad hoc networking DCF is a Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) protocol

60. Univ. of TehranComputer Network60 IEEE 802.11 DCF Uses RTS-CTS exchange to avoid hidden terminal problem Any node overhearing a CTS cannot transmit for the duration of the transfer Uses ACK to achieve reliability Any node receiving the RTS cannot transmit for the duration of the transfer To prevent collision with ACK when it arrives at the sender When B is sending data to C, node A will keep quite ABC

61. Univ. of TehranComputer Network61 ABC Hidden Terminal Problem [Tobagi75] Node B can communicate with A and C both A and C cannot hear each other When A transmits to B, C cannot detect the transmission using the carrier sense mechanism If C transmits, collision will occur at node B

62. Univ. of TehranComputer Network62 MACA Solution for Hidden Terminal Problem [Karn90] When node A wants to send a packet to node B, node A first sends a Request-to-Send (RTS) to A On receiving RTS, node A responds by sending Clear-to-Send (CTS), provided node A is able to receive the packet When a node (such as C) overhears a CTS, it keeps quiet for the duration of the transfer Transfer duration is included in RTS and CTS both ABC

63. Univ. of TehranComputer Network63 IEEE 802.11 CFABED RTS RTS = Request-to-Send

64. Univ. of TehranComputer Network64 IEEE 802.11 CFABED RTS RTS = Request-to-Send NAV = 10 NAV = remaining duration to keep quiet

65. Univ. of TehranComputer Network65 IEEE 802.11 CFABED CTS CTS = Clear-to-Send

66. Univ. of TehranComputer Network66 IEEE 802.11 CFABED CTS CTS = Clear-to-Send NAV = 8 DATA packet follows CTS. Successful data reception acknowledged using ACK.

67. Univ. of TehranComputer Network67 IEEE 802.11 CFABED DATA

68. Univ. of TehranComputer Network68 CFABED ACK IEEE 802.11 Reserved area

69. Univ. of TehranComputer Network69 IEEE 802.11 CFABED DATA Transmit range Interference range Carrier sense range FA

70. Univ. of TehranComputer Network70 IEEE 802.11 CFABED ACK

71. Univ. of TehranComputer Network71 CSMA/CA Carrier sense in 802.11 Physical carrier sense Virtual carrier sense using Network Allocation Vector (NAV) NAV is updated based on overheard RTS/CTS/DATA/ACK packets, each of which specified duration of a pending transmission Collision avoidance Nodes stay silent when carrier sensed (physical/virtual) Backoff intervals used to reduce collision probability

72. Univ. of TehranComputer Network72 Backoff Interval When transmitting a packet, choose a backoff interval in the range [0,cw] cw is contention window Count down the backoff interval when medium is idle Count-down is suspended if medium becomes busy When backoff interval reaches 0, transmit RTS

73. Univ. of TehranComputer Network73 DCF Example data wait B1 = 5 B2 = 15 B1 = 25 B2 = 20 data wait B1 and B2 are backoff intervals at nodes 1 and 2 cw = 31 B2 = 10

74. Univ. of TehranComputer Network74 Backoff Interval The time spent counting down backoff intervals is a part of MAC overhead Choosing a large cw leads to large backoff intervals and can result in larger overhead Choosing a small cw leads to a larger number of collisions (when two nodes count down to 0 simultaneously)

75. Univ. of TehranComputer Network75 Backoff Interval (cont) Since the number of nodes attempting to transmit simultaneously may change with time, some mechanism to manage contention is needed IEEE 802.11 DCF: contention window cw is chosen dynamically depending on collision occurrence

76. Univ. of TehranComputer Network76 Binary Exponential Backoff in DCF When a node fails to receive CTS in response to its RTS, it increases the contention window cw is doubled (up to an upper bound) When a node successfully completes a data transfer, it restores cw to Cw min cw follows a sawtooth curve 802.11 has large room for improvement Random backoff Data Transmission/ACK RTS/CTS

77. Univ. of TehranComputer Network77 Inter Frame Spacing SIFS = Short inter frame space = dependent on PHY PIFS = point coordination function (PCF) inter frame space = SIFS + slot time DIFS = distributed coordination function (DCF) inter frame space = PIFS + slot time The back-off timer is expressed in terms of number of time slots.

78. Univ. of TehranComputer Network78 802.11 Frame Priorities Short interframe space (SIFS) For highest priority frames (e.g., RTS/CTS, ACK) PCF interframe space (PIFS) Used by PCF during contention free operation DCF interframe space (DIFS) Minimum medium idle time for contention-based services Time Busy SIFS PIFS DIFS content window Frame transmission

79. Univ. of TehranComputer Network79 SIFS/DIFS SIFS makes RTS/CTS/Data/ACK atomic RTS CTS Data ACK SIFS DIFS Time Sender1 Receiver1 RTS TimeSender2 DIFS

80. Univ. of TehranComputer Network80 MACA protocol Key observation: in CSMA/CA any node hearing RTS or CTS differ communication. This is to avoid collision with ACKs. We can leave ACKs, Reliability to upper layer. Any node hearing RTS, not CTS, only need to differ the RTS sender to receive CTS. Then, that node can start communication. No exposed node.

81. Univ. of TehranComputer Network81 MACAW Based on MACA Design based on 4 key observations: Contention is at receiver, not the sender Congestion is location dependent To allocate media fairly, learning about congestion levels should be a collective enterprise Media access protocol should propagate synchronization information about contention periods, so that all devices can contend effectively

82. Univ. of TehranComputer Network82 MILD Algorithm in MACAW When a node successfully completes a transfer, reduces cw by 1 In 802.11 cw is restored to cw min In 802.11, cw reduces much faster than it increases MACAW: cw reduces slower than it increases Exponential Increase Linear Decrease MACAW can avoid wild oscillations of cw when large number of nodes contend for the channel

83. Univ. of TehranComputer Network83 Receive-Initiated Mechanism In most protocols, sender initiates a transfer Alternatively, a receiver may send a Ready-To-Receive (RTR) message to a sender requesting it to being a packet transfer Sender node on receiving the RTR transmits data How does a receiver determine when to poll a sender with RTR? Based on history, and prediction of traffic from the sender

84. Univ. of TehranComputer Network84 Reliability Wireless links are prone to errors. High packet loss rate detrimental to transport-layer performance. Mechanisms needed to reduce packet loss rate experienced by upper layers When node B receives a data packet from node A, node B sends an Acknowledgement (Ack). This approach adopted in many protocols If node A fails to receive an Ack, it will retransmit the packet ABC

85. Univ. of TehranComputer Network85 Fairness Issue Assume that initially, A and B both choose a backoff interval in range [0,31] but their RTSs collide Nodes A and B then choose from range [0,63] Node A chooses 4 slots and B choose 60 slots After A transmits a packet, it next chooses from range [0,31] It is possible that A may transmit several packets before B transmits its first packet AB CD Two flows

86. Univ. of TehranComputer Network86 MACAW Solution for Fairness When a node transmits a packet, it appends the cw value to the packet, all nodes hearing that cw value use it for their future transmission attempts Since cw is an indication of the level of congestion in the vicinity of a specific receiver node, MACAW proposes maintaining cw independently for each receiver Using per-receiver cw is particularly useful in multi- hop environments, since congestion level at different receivers can be very different

87. Univ. of TehranComputer Network87 Another MACAW Proposal For the scenario below, when node A sends an RTS to B, while node C is receiving from D, node B cannot reply with a CTS, since B knows that D is sending to C When the transfer from C to D is complete, node B can send a Request-to-send-RTS to node A. Node A may then immediately send RTS to node B This approach, however, does not work in the scenario below Node B may not receive the RTS from A at all, due to interference with transmission from C A B C D

88. Univ. of TehranComputer Network88 Priorities in 802.11 CTS and ACK have priority over RTS After channel becomes idle If a node wants to send CTS/ACK, it transmits SIFS duration after channel goes idle If a node wants to send RTS, it waits for DIFS > SIFS

89. Univ. of TehranComputer Network89 SIFS and DIFS DATA1 ACK1 SIFS backoff DIFS RTS SIFS

90. Univ. of TehranComputer Network90 Energy Conservation Since many mobile hosts are operated by batteries, MAC protocols which conserve energy are of interest Two approaches to reduce energy consumption Power save: Turn off wireless interface when desirable Power control: Reduce transmit power

91. Univ. of TehranComputer Network91 Power Control with 802.11 Transmit RTS/CTS/DATA/ACK at least power level needed to communicate with the receiver A/B do not receive RTS/CTS from C/D. Also do not sense D’s data transmission B’s transmission to A at high power interferes with reception of ACK at C BCDA

92. Univ. of TehranComputer Network92 A Plausible Solution RTS/CTS at highest power, and DATA/ACK at smallest necessary power level A cannot sense C’s data transmission, and may transmit DATA to some other host This DATA will interfere at C This situation unlikely if DATA transmitted at highest power level Interference range ~ sensing range BCDA RTS Data Interference range Ack Data sensed

93. Univ. of TehranComputer Network93 Transmitting RTS at the highest power level also reduces spatial reuse Nodes receiving RTS/CTS have to defer transmissions

94. Univ. of TehranComputer Network94 Bridge Functions Speed conversion between different devices, results in buffering. Frame format adaptation between different incompatible LANs Adding or deleting fields in the frame to convert between different LAN standards

95. Univ. of TehranComputer Network95 Wireless Capacity Wireless channel is inefficient due to MAC backoff procedure RTS/CTS mechanism Frequency interference. Possible solutions: Use better backoff mechanisms. Exploit more physical resources: more spectrum Cell mechanism Exploit diversity, use different frequencies. Parallel control with data

96. Univ. of TehranComputer Network96 Improve Spatial Reuse Power/Rate Control ABCD A BCD

97. Univ. of TehranComputer Network97 Exploit Infrastructure Infrastructure provides a tunnel to forward packets E A BC D BS1BS2 X Z infrastructure Ad hoc connectivity

98. Univ. of TehranComputer Network98 Exploit Antennas Diversity antenna Steered beam directional antenna

99. Univ. of TehranComputer Network99 Path Diversity Multiple paths to a destination  Multiple next-hops to a destination

100. Univ. of TehranComputer Network100 Inefficiency of IEEE 802.11 Backoff interval should be chosen appropriately for efficiency Backoff interval with 802.11 far from optimum Ms. Khalaj thesis

101. Univ. of TehranComputer Network101 Proposed Method The current method used in DCF seems to lead to high jitter and wasted bandwidth When CW is reset to its minimum after a large value, the next packet delays will be too low in compare with delays before CW size reduction Collision => Network busy Transmission => low load. These rapid changes in CW size cause high variations in delay or jitter In real conditions these assumptions are not always true. A packet being transmitted successfully does not necessarily mean the network is not congested Unfair access to the medium. Hence resetting CW to CWmin may cause more collisions and lead to wasting bandwidth

102. Univ. of TehranComputer Network102 Proposed Method (Cont.) We attempt to know how much reduction in CW will give better performance Scheme 1 is the method used in DCF, resetting CW to its minimum size After a successful transmission: In scheme 2, CW will be set to CWmin + (CWcurrent - CWmin) / 4 In scheme 3, CW will be set to CWmin + (CWcurrent - CWmin) / 2 In scheme 4, CW will be set to CWmin + 3(CWcurrent - CWmin) / 4 By comparing the results of these schemes we can see how reduction of CW size will influence the performance

103. Univ. of TehranComputer Network103 Simulation Model We used NS-2 (Network Simulator-2) for simulation Three types of traffics were generated in our simulation: audio, video and data Audio traffics have the highest priority and data traffics the lowest All of the stations are in direct access range of each other All stations send their flows to a common receiver We have considered throughput, delay, and jitter to evaluate the performance of different schemes

104. Univ. of TehranComputer Network104 The parameters of our simulation AudioVideoData CWmin71531 CWmax2555111024 IFS50us70us90us Packet Size160 bytes1280 bytes1500 bytes Packet Interval20 ms10 ms12.5 ms Flow Rate8 KBps128 KBps120 KBps

105. Univ. of TehranComputer Network105 Results Throughput, delay and jitter of audio traffic

106. Univ. of TehranComputer Network106 Results (Cont.) Throughput, delay and jitter of video traffic

107. Univ. of TehranComputer Network107 Results (Cont.) Throughput and delay of data traffic

108. Univ. of TehranComputer Network108 Results (Cont.) Throughput of three classes in scheme 1

109. Univ. of TehranComputer Network109 Results (Cont.) Throughput of three classes in scheme 2

110. Univ. of TehranComputer Network110 Results (Cont.) Throughput of three classes in scheme 3

111. Univ. of TehranComputer Network111 Results (Cont.) Throughput of three classes in scheme 4

112. Univ. of TehranComputer Network112 Observation Backoff and RTS/CTS handshake are unproductive: Do not contribute to goodput Random backoff Data Transmission/ACK RTS/CTS Unproductive

113. Univ. of TehranComputer Network113 Pipelining Two stage pipeline: 1.Random backoff and RTS/CTS handshake 2.Data transmission and ACK “Total” pipelining: Resolve contention completely in stage 1 Random backoff Data Transmission/ACK RTS/CTS Stage1Stage2

114. Univ. of TehranComputer Network114 How to pipeline? Use two channels  Control Channel: Random backoff and RTS/CTS handshake  Data Channel: Data transmission and ACK Data Transmission/ACK Random backoff RTS/CTS Random backoff RTS/CTS Random backoff Data Transmission/ACK

115. Univ. of TehranComputer Network115 Pipelining works well only if two stages are balanced! Data Transmission/ACK Random backoff RTS/CTS Random backoff RTS/CTS Random backoff Data Transmission/ACK Control Channel Data Channel

116. Univ. of TehranComputer Network116 Difficult to keep the two stages balanced Length of stage 1 depends on:  Control channel bandwidth  The random backoff duration  The number of collisions occurred Length of stage 2 depends on:  Data channel bandwidth  The data packet size

117. Univ. of TehranComputer Network117 How much bandwidth does control channel require? If small, then RTS/CTS takes very long time. Collision detection is slow If large, then The portion of channel bandwidth used for productive data packet transmission is reduced Total bandwidth is fixed!

118. Univ. of TehranComputer Network118 Difficulty with Total Pipelining The optimum division of channel bandwidth varies with contention level and data packet size Performance with inappropriate bandwidth division could be even worse than 802.11 DCF How to get around the issue of bandwidth division ?

119. Univ. of TehranComputer Network119 Partial Pipelining Only partially resolve channel contention in stage 1 Since no need to completely resolve contention, the length of stage 1 can be elastic to match the length of stage 2

120. Univ. of TehranComputer Network120 Modified Two Stage Pipeline Backoff phase 1 Data/ACK Stage1Stage2 RTS/CTS Backoff phase 2  Stage 1: Random backoff phase 1  Stage 2: Random backoff phase 2, RTS/CTS handshake and Data/ACK transmission

121. Univ. of TehranComputer Network121 How to pipeline? Random backoff phase 1 Still use two channels  Narrow Band Busy Tone Channel: Random backoff phase 1  Data Channel: Random backoff phase 2, RTS/CTS handshake and Data/ACK Data/ACK RTS/CTS Backoff phase 2 Data/ACK RTS/CTS Backoff phase 2

122. Univ. of TehranComputer Network122 Random Backoff Phase 1 Each Station maintains a counter for random backoff phase 1 The stations, which count to zero first, send a busy tone to claim win in stage 1 Multiple winners are possible Other stations know they lost on sensing a busy tone

123. Univ. of TehranComputer Network123 Gain over total pipelining? No packets transmitted on busy tone channel  bandwidth can be small  the difficulty of deciding optimum bandwidth division in “total pipelining” is avoided Length of stage 1 is elastic so the two stages can be kept balanced

124. Univ. of TehranComputer Network124 Benefits of Partial Pipeline Only winners of stage 1 can contend channel in stage 2 reduces the data channel contention reduces collision probability on the data channel Stage 1Stage 2

125. Univ. of TehranComputer Network125 Sounds like HIPERLAN/1? Elimination Stage Data Transmission Yield Stage HIPERLAN / 1 (no pipelining) Random backoff phase 1 Data/ACK RTS/CTS Backoff phase 2 Data/ACK RTS/CTS Backoff phase 2 Partial Pipelining

126. Univ. of TehranComputer Network126 Benefits of Partial Pipeline Random backoff phase 1 Data/ACK RTS/CTS Backoff phase 2 Data/ACK RTS/CTS Backoff phase 2 Partial Pipelining Because of pipelining, stages 1 and 2 proceed in parallel. Stage 1 costs little except for a narrow band busy tone channel

127. Univ. of TehranComputer Network127 Benefits of Partial Pipeline By migrating most of the backoff to busy tone channel, bandwidth cost of random backoff is reduced  Cost of backoff = Channel bandwidth * backoff duration Data Channel Bandwidth Busy Tone Channel Bandwidth Backoff Duration Area = cost of backoff Using IEEE 802.11 DSSS, the backoff duration could be several milliseconds

128. Univ. of TehranComputer Network128 Results of Partial Pipelining Improved throughput and stability over 802.11 DCF 802.11 DCF Partial Pipelining

129. Univ. of TehranComputer Network129 Can we avoid using busy tone channel?

130. Univ. of TehranComputer Network130 Observation Busy tone may not always be sensed Narrow-band channel for busy tone

131. Univ. of TehranComputer Network131 Observation Taking this into account did not make the performance much worse Sensing probability 0 as well ! Suggests the “implicit” pipelining scheme

132. Univ. of TehranComputer Network132 Implicit Pipeline Backoff phase 1 Data/ACK Stage1Stage2 RTS/CTS Backoff phase 2  Stage 1: Random backoff phase 1  Stage 2: Random backoff phase 2, RTS/CTS handshake and Data/ACK transmission

133. Univ. of TehranComputer Network133 Still two stages, but with single channel Random backoff phase 1 Data/ACK RTS/CTS Backoff phase 2 Data/ACK RTS/CTS Backoff phase 2 Similar to busy tone probability = 0

134. Univ. of TehranComputer Network134 Random backoff phase 1 Data/ACK RTS/CTS Backoff phase 2 Data/ACK RTS/CTS Backoff phase 2 Channel usage Implicit stage 1 Stations do not know when a station counts to 0 Effectively, all stations may count down till the end of phase 1 (as marked by end of pipelined data transmission)

135. Univ. of TehranComputer Network135 Backoff Phase 1 During the random backoff phase 1, the stations counting down the backoff counter to zero win stage 1. Only the winners of stage 1 contend channel in stage 2 Difference from partial pipelining: With busy tone, only stations counting down to 0 first win stage 1. Multiple winners are possible only if they count down to 0 together Without busy tone sensing, no way for a station to claim channel explicitly more stations can win stage 1

136. Univ. of TehranComputer Network136 Backoff Phase 1 Nodes can count down number of slots = duration of on-going data transmission Generalize Ignore data packet size Each node reduces backoff interval by an “arbitrary” (reasonably chosen) amount at the end of current busy channel period

137. Univ. of TehranComputer Network137 Implicit Pipeline (Dual-Stage) Choose backoff such that number of winners from stage 1 (entering stage 2) is non-zero but small at the end of each busy period Backoff increased aggressively (on failure to win phase 2, not just on collision) Backoff decreased faster for nodes that have been waiting longer

138. Univ. of TehranComputer Network138 Implicit Pipeline Two stages as in Hiperlan/1, but no need to use busy tone

139. Univ. of TehranComputer Network139 Average number of stations in stage 2

140. Univ. of TehranComputer Network140 Implicit Pipelining Inherites benefits of partial pipelining Reduces channel contention by reducing the number of contending stations. Backoff phase 1 proceeds in parallel with other channel activities

141. Univ. of TehranComputer Network141 Contention Window 1

142. Univ. of TehranComputer Network142 Implicit Pipelining Advantages compared with “partial pipelining” No busy tone channel is needed Can be applied to multi-hop ad hoc networks Disadvantage compared with partial pipelining More stations may win stage 1, which leads to degraded stability in large networks

143. Univ. of TehranComputer Network143 Simulation results for Implicit Pipelining Obtained via modified ns-2 simulator Constant Bit Rate (CBR) traffic Channel bit rate 11 Mbps Active stations are always backlogged Various packet sizes Simulated both in wireless LANs and multi-hop ad hoc networks

144. Univ. of TehranComputer Network144 Wireles LANs with RTS/CTS Handshake packet size: 256 bytes 802.11 DCF Implicit Pipelining 53% improvement Normalized throughput

145. Univ. of TehranComputer Network145 Wireless LANs with RTS/CTS Handshake packet size: 512 bytes 46% improvement Normalized throughput Implicit Pipelining 802.11 DCF

146. Univ. of TehranComputer Network146 Wireless LANs with RTS/CTS Handshake packet size: 2048 bytes Implicit Pipelining 26% improvement 802.11 DCF Normalized throughput

147. Univ. of TehranComputer Network147 Wireless LANs NO RTS/CTS Handshake packet size: 512 bytes Implicit Pipelining 802.11 DCF 87% improvement Normalized throughput

148. Univ. of TehranComputer Network148 Fairness Comparable to 802.11 Fairness Index Implicit Pipelining 802.11 DCF

149. Univ. of TehranComputer Network149 Fairness Comparable to 802.11 Max/Min Throughput Ratio Implicit Pipelining 802.11 DCF

150. Univ. of TehranComputer Network150 Simulation results for multi-hop Ad hoc networks Simulated in 30 1000m*1000m random networks with 80 active stations Throughput Ratio of “implicit pipelining” over 802.11

151. Univ. of TehranComputer Network151 Simulation results for multi-hop Ad hoc networks Simulated in 30 1000m*1000m random networks with 80 active stations Number of collisions Implicit Pipelining 802.11 DCF

152. Univ. of TehranComputer Network152 SSCH: Slotted Seeded Channel Hopping – Overview A dynamic assignment algorithm divides the time into equal sized slots (e.g. 10 ms) and switches each radio across multiple orthogonal channels on the boundary of slots in a distributed manner Main aspect of SSCH channel scheduling self-computation of tentative schedule communication of schedules synchronization with other nodes

153. Univ. of TehranComputer Network153 SSCH – Desired Properties No Logical Partition: Ensure all nodes come into contact occasionally so that they can communicate their tentative schedule Synchronization: Allow nodes that need to communicate to synchronize De-synchronization: Infrequently overlap between nodes with no communication

154. Univ. of TehranComputer Network154 Channel Scheduling -Self-Computation Each node use (channel, seed) pairs to represent its tentative schedule for the next slot Seed: [1, number of channels -1] Initialized randomly Focus on the simple case of using one pair Update rule: new channel = (old channel + seed) mod (number of channels) 10210210 A: Seed = 2 01201201 B: Seed = 1 Example: 3 channels, 2 seeds

155. Univ. of TehranComputer Network155 Channel Scheduling – Logical Partition 12012012 A: Seed = 1 01201201 B: Seed = 1 Are nodes guaranteed to overlap? same init channel, same seed (always overlap) same init channel, different seeds (overlap occasionally) different init channels, different seeds (overlap occasionally) Special case: Nodes may never overlap if they have the same seed but different channels

156. Univ. of TehranComputer Network156 Channel Scheduling – Solution to Logical Partition Parity slot every (number of channels) slots, add a parity slot in parity slot, the channel number is the seed do not allow the seed to change until the parity slot A: Seed = 1 B: Seed = 1 1201201211 0120120111 Parity Slot

157. Univ. of TehranComputer Network157 Channel Scheduling - Communication of Schedules Each node broadcasts its tentative schedule (represented by the pair) once per slot

158. Univ. of TehranComputer Network158 Channel Scheduling - Synchronization If node B needs to send data to node A, it adjusts its (channel, seed) pair to be the same as A. A B 1201201211 0211201221 111111111 Seed 222111112 Flow starts Sync starts upon the parity slot

159. Univ. of TehranComputer Network159 Channel Scheduling – Channel Congestion It is likely various nodes will converge to the same (channel, seed) pair and communicate infrequently after that. (1,2)

160. Univ. of TehranComputer Network160 Channel Scheduling – Solution to Channel Congestion De-synchronization To identify channel congestion: compare the number of the synchronized nodes and the number of the nodes sending data. De- synchronize when the ratio >= 2 To de-synchronize, simply choose a new (channel, seed) pair for each synchronized and non-sending nodes

161. Univ. of TehranComputer Network161 Channel Scheduling – Synchronizing with Multiple Nodes Examples a sender with multiple receivers a forwarding node in a multi-hop network Solution: Use multiple seeds per node use one seed to synchronize with one node add a parity slot every cycle ( = number of channels * number of seeds); the channel number of the parity slot is the first seed. 221011022100 Green slots are generated by seed 1 Yellow slots are generated by seed 2 1

162. Univ. of TehranComputer Network162 Channel Scheduling – Partial Synchronization 22101102210012012110201021 A B Seed 1211211222112 2122222222222 Flow starts Partial Sync Sync the second seed only

163. Univ. of TehranComputer Network163 Evaluations of SSCH Simulate in QualNet 802.11a, 54Mbps, (used) 13 orthogonal channels Slot switch time = 80 µ s 4 seeds per node, slot duration = 10 ms UDP flows: CBR flows of 512 bytes sent every 50 µ s (enough to saturate the channel)

164. Univ. of TehranComputer Network164 Evaluation – Throughput (UDP)

165. Univ. of TehranComputer Network165 Evaluation – Multi-hop Mobile Networks

166. Univ. of TehranComputer Network166 The Problem  Situation The total number of hotspot users around the world is expected to to 30 million by the end of 2004 according to researcher Gartner. Given the explosive growth in hotspot wireless usage, enhancing capacity of 802.11-based hotspot wireless networks is an important problem.

167. Univ. of TehranComputer Network167 The ECHOS Solution AP – CST algorithm Dynamically adjusts the CST in order to allow more flows to co-exist in the same channel in current 802.11 architectures. RNC – SC algorithm Allows each cell or AP access to all available channels. RNC algorithm executes in a centralized radio network controller Uses one channel as primary & the other two as secondary channels Allows to improve Hotspot performance beyond AP- CST.

168. Univ. of TehranComputer Network168 Abilities of the Algorithms Dynamically allocate channels to stations Flexibly adopts parameters such as CST and/or transmit power THE CLAIM ! Performance of 802.11-based hotspots can be improved by both these algorithms by up to 195% per-cell and 70% overall.

169. Univ. of TehranComputer Network169 Related Work Different techniques for parallelism in 802.11 to form ad- hoc networks Involve either modifications to the 802.11 MAC protocol or using out-of-band tones and thus, cannot be used to enhance the performance of the hundreds of millions of already deployed 802.11 cards and access points. Very recently, they have discovered that varying CST can help boost performance. Use of multiple channels for throughput enhancement has been proposed for ad hoc multi-hop wireless networks, BUT these solutions rely on each node making decisions based on its locally perceived medium characteristics and there is little scope for centralized coordination.

170. Univ. of TehranComputer Network170 Related Work Cont… Centralized coordination of APs in PCF mode by allocating channels & time slots to APs Through graph coloring & centralized scheduling However these & most of the work in this area assume that each AP is capable of using only a single channel at a given time.

171. Univ. of TehranComputer Network171 Observations on Carrier Sensing in 802.11 Qualnet simulator transmission at 2Mbps with a CST of -93dBm & transmit power of 15dBm How to calculate the ranges?

172. Univ. of TehranComputer Network172 Range Calculation Suppose T & T’ are two transmitters at distance d t & d i from the receiver. T’ is the interferer to the transmission from T. Then, SNR at the receiver is assuming that both the transmitters transmit with the same power Strength of the received signal falls off as Where, K is a suitable constant is the transmission power d is the distance from the signal source For successful reception, the requirement is that the SNR be above a threshold This yields the requirement: Range

173. Univ. of TehranComputer Network173 Observation 1 How to chose the optimum value of CST ? - Dynamic

174. Univ. of TehranComputer Network174 Observation 2 The value of CST needed at T to sense the carrier of any interfering source I at or within a distance 2.78 d from T is given by Where, P o = transmit power SS[T,R] = Received signal strength from T at R Is the optimum carrier sense threshold required at T

175. Univ. of TehranComputer Network175 Architecture & Algorithms Principle Dynamically identify flows that can coexist Allow them to coexist by setting optimum CST values (Observation 2) Note: All clients report load & signal conditions to AP & in RNC-SC the AP reports to the RNC

176. Univ. of TehranComputer Network176 Algorithm AP - CST The only issue is of distinguishing between inside and outside cell transmissions. This is solved by identifying the data frame RTS or CTS Basic idea: If, by reducing the CST, we can allow additional flows to operated without causing interference beyond the available tolerance of existing flows, we have improved the performance for those flows. Else CST[AP]=infinity For each station s CST[AP] = min(CST[AP],SS[AP,s]/alpha – epsilon)

177. Univ. of TehranComputer Network177 Algorithm RNC - SC Algorithm RNC-SC: has two main steps Determine if a cell is overloaded. Choose and switch a client to a secondary channel in overloaded cell, if possible. Measuring load and overload: MAC service time (i.e., the time between the instant a frame is submitted to the MAC for transmission and the time instant the ACK is received) seen by a node as the measure of load. This value is smoothed using an exponential filter and averaged over all members of the cell. Where, is the threshold providing hystersis

178. Univ. of TehranComputer Network178 Choosing Client & Secondary Channel To create a secondary cell that has no impact on the primary cell, we need any AP/station of the secondary cell should not interfere with the primary the throughput in primary should not decrease because of this change.

179. Univ. of TehranComputer Network179 Get Client Algorithm Has three main steps: Compute maximum tolerated interference on each secondary channel k Reduce the transmit powers of secondary AP and clients on each secondary channel k Choose the client,channel pair such that the client observes minimum interference from outside the cell on that channel

180. Univ. of TehranComputer Network180 Performance Evaluation Topology 1000 * 1000m divided into 4 cells. Each AP covers 250m approx. 11Mbps Each simulation run lasted 100sec & results averaged over 10 runs Homogeneous user/load distribution Each cell has 15 clients, half the max no. of clients allowed in current practice Each client station has an HTTP client with a think time of 1sec Each cell has an FTP client Both upstream & downstream traffic present

181. Univ. of TehranComputer Network181 HIPERLAN 1995 ETSI technical group RES 10 (Radio Equipment and Systems) developed HIPERLAN/1 wireless LAN standards using 5 channels in 5.15-5.3 GHz frequency range Technical group BRAN (Broadband Radio Access Network) is standardizing HIPERLAN/2 for wireless ATM ETSI URL for Hiperlan information http://www.etsi.org/frameset/home.htm? /technicalactiv/Hiperlan/hiperlan2.htm http://www.etsi.org/frameset/home.htm

182. Univ. of TehranComputer Network182 HIPERLAN Characteristics HIPERLANs with same radio frequencies might overlap Stations have unique node identifiers (NID) Stations belonging to same HIPERLAN share a common HIPERLAN identifier (HID) Stations of different HIPERLANs using same frequencies cause interference and reduce data transmission capacity of each HIPERLAN Packets with different HIDs are rejected to avoid confusion of data

183. Univ. of TehranComputer Network183 HIPERLAN Protocol Layers Data link layer = logical link control (LLC) sub layer + MAC sub layer + channel access control (CAC) sub layer data link physical LLC MAC network CAC

184. Univ. of TehranComputer Network184 HIPERLAN Protocol Layers, Cont.. MAC sub layer: Keeps track of HIPERLAN addresses (HID + NID) in overlapping HIPERLANs Provides lookup service between network names and HIDs Converts IEEE-style MAC addresses to HIPERLAN addresses Provides encryption of data for security

185. Univ. of TehranComputer Network185 HIPERLAN Protocol Layers, Cont.. MAC sub layer: Provides “multi hop routing” – certain stations can perform store-and- forwarding of frames Recognizes user priority indication (for time-sensitive frames)

186. Univ. of TehranComputer Network186 HIPERLAN Protocol Layers, Cont.. CAC sub layer: Non-preemptive priority multiple access (NPMA) gives high priority traffic preference over low priority Stations gain access to channel through channel access cycles consisting of 3 phases:

187. Univ. of TehranComputer Network187 HIPERLAN CAC Protocol CAC sub layer: 1 2 3 4 AP 1 2 345 Prioritization Phase Contention Phase Transmission Phase Time Data ACK Cycle

188. Univ. of TehranComputer Network188 HIPERLAN Protocol Layers, Cont… CAC is designed to give each station (of same priority) equal chance to access the channel First stations with highest priority data are chosen. The rest will back off until all higher priority data is transmitted. Stations with the same priority level data, compete according to a given rule to choose “survivors” Survivors wait a random number of time slots and then listen to see if the channel is idle

189. Univ. of TehranComputer Network189 HIPERLAN Protocol Layers, Cont… If the channel is idle then it starts transmitting. Those who could not transmit wait until next period

190. Univ. of TehranComputer Network190 HIPERLAN/2 To support QoS, Handoff and integrate WLAN with next generation Cellular sys. Supporting IP& ATM at 54Mbps Use TDMA as MAC DLC (Data Link Control) layer constitutes a logical link Between AP and MT to ensure a connection oriented Communication.

191. Univ. of TehranComputer Network191 Bluetooth Goals Ad-hoc wireless connectivity for everything! Original goal Low-cost replacement for annoying wire between cellphone and headset Result: Two modes of operation Point to point (serial wire replacement) Point to multipoint (ad-hoc networking)

192. Univ. of TehranComputer Network192 Bluetooth devices Cellphones Headsets PDAs Laptops Two-way pagers Pads, tabs, etc…

193. Univ. of TehranComputer Network193 Bluetooth design Specs Price: single chip $15-20 today, <$5 in volume Frequency: 2.4 GHz ISM band Power Transmit: 1 mW (0 dBm) 30 uA sleep, 60 uA hold, 200 uA standby Range: 10 meters Hybrid DS and FH spread spectrum 1600 hops/second! Rate: 721 + 56 Kbit/s per picocell Picocells: 8 devices per picocell (3 voice or 7 data max) 10 piconets in coverage area (w/ graceful degradation) Simple link layer security (encryption, authentication)

194. Univ. of TehranComputer Network194 Bluetooth Reality: Frequencies ISM band is not the same everywhere! Smaller band in Japan Defense band in France! How does radio know where it is and local laws? Airplanes and FAA Conflicts with 802.11 More powerful 802.11 stomps on Bluetooth

195. Univ. of TehranComputer Network195 More Bluetooth Realities Cost Hard to produce cheap single-chip radio Mix of analog and digital circuits Not meeting noise margin requirements Currently requires two chips Total redesign of boards/products! Ad-hoc networking is hard Still lots of issues about networking protocols First Bluetooth deployments will be P-to-P

196. Univ. of TehranComputer Network196 More Bluetooth Realities Encryption Bluetooth devices use short keys for link layer encryption (export issues) Authentication How do two Bluetooth devices exchange keys? Push a button on both simultaneously Small window of vulnerability What about ceiling mounted base stations?

197. Univ. of TehranComputer Network197 Bluetooth summary Will be very cool when it arrives Will enable low-cost ad-hoc wireless networking Lots of problems to be worked out first

198. Univ. of TehranComputer Network198 Related Standards Activities IEEE 802.11 http://grouper.ieee.org/groups/802/11/ Hiperlan/2 http://www.etsi.org/technicalactiv/hiperlan2.htm BlueTooth http://www.bluetooth.com IETF manet (Mobile Ad-hoc Networks) working group http://www.ietf.org/html.charters/manet-charter.html