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  • 1. CS455 Introduction to Computer Networks Dr. Wenzhan Song Assistant Professor, Computer Science WSU Vancouver
  • 2. Course roadmap
    • Introduction
    • Application Layer: WWW, FTP, email, DNS, multimedia
    • Transport Layer: reliable end-end data transfer principles, UDP, TCP
    • Network Layer: IP addressing, routing and other issues
    • Data Link Layer: framing, error control, flow control
      • Medium Access Control (MAC) Layer: multiple-access, channel allocation
    • Physical Layer: wired, wireless, satellite
    • Other Topics: network security, social issues, hot topics, research directions
  • 3. Data Link Layer Road Map
    • Data link layer design issues
      • Framing
      • Error Control
      • Reliable data transfer and flow control
    • Example data link protocols
      • HDLC and PPP
    • Multiple Access Protocols
      • Static channel allocation
      • Dynamic channel allocation
    • LAN technologies and their MAC protocols
      • Ethernet
      • WiFi and WiMax
  • 4. Ethernet
    • MAC addressing
    • MAC protocol: CSMA/CD
    • Ethernet interconnection
  • 5. Ethernet
    • “ dominant” wired LAN technology:
    • cheap $20 for 100Mbs!
    • first widely used LAN technology
    • Simpler, cheaper than token LANs and ATM
    • Kept up with speed race: 10 Mbps – 10 Gbps
    Metcalfe’s Ethernet Sketch [mid-1970’s] Ethernet 10Base2 Bus topology
  • 6. Manchester encoding
    • Used in 10BaseT
    • Each bit has a transition
    • Allows clocks in sending and receiving nodes to synchronize to each other
      • no need for a centralized, global clock among nodes!
    • Hey, this is physical-layer stuff!
  • 7. MAC Addresses Each adapter on LAN has unique MAC address Broadcast address = FF-FF-FF-FF-FF-FF = adapter 1A-2F-BB-76-09-AD 58-23-D7-FA-20-B0 0C-C4-11-6F-E3-98 71-65-F7-2B-08-53 LAN (wired or wireless)
  • 8. ARP: Address Resolution Protocol
    • Each IP node (Host, Router) on LAN has ARP table
    • ARP Table: IP/MAC address mappings for some LAN nodes
    • < IP address; MAC address; TTL>
      • TTL (Time To Live): time after which address mapping will be forgotten (typically 20 min)
    1A-2F-BB-76-09-AD 58-23-D7-FA-20-B0 0C-C4-11-6F-E3-98 71-65-F7-2B-08-53 LAN Question: how to determine MAC address of B knowing B’s IP address?
  • 9. Ethernet
    • Frame format and addressing
    • MAC protocol: CSMA/CD
    • Interconnecting issues
  • 10. Ethernet uses CSMA/CD
    • No slots
    • adapter doesn’t transmit if it senses that some other adapter is transmitting, that is, carrier sense
    • transmitting adapter aborts when it senses that another adapter is transmitting, that is, collision detection
    • Before attempting a retransmission, adapter waits a random time, that is, random access
  • 11. CSMA/CD (Collision Detection)
    • CSMA/CD: carrier sensing, deferral as in CSMA
      • collisions detected within short time
      • colliding transmissions aborted, reducing channel wastage
    • collision detection:
      • easy in wired LANs: measure signal strengths, compare transmitted, received signals
      • difficult in wireless LANs: receiver shut off while transmitting
  • 12. Ethernet CSMA/CD algorithm
    • 1. Adaptor receives datagram from net layer & creates frame
    • 2. If adapter senses channel idle, it starts to transmit frame. If it senses channel busy, waits until channel idle and then transmits
    • 3. If adapter transmits entire frame without detecting another transmission, the adapter is done with frame !
    • 4. If adapter detects another transmission while transmitting, aborts and sends jam signal
    • 5. After aborting, adapter enters exponential backoff : after the mth collision, adapter chooses a K at random from {0,1,2,…,2 m -1}. Adapter waits K · 512 bit times and returns to Step 2
  • 13. Ethernet’s CSMA/CD (more)
    • Jam Signal: make sure all other transmitters are aware of collision; 48 bits
    • Bit time: .1 microsec for 10 Mbps Ethernet ; for K=1023, wait time is about 50 msec
    • Exponential Backoff:
    • Goal: adapt retransmission attempts to estimated current load
      • heavy load: random wait will be longer
    • first collision: choose K from {0,1}; delay is K · 512 bit transmission times
    • after second collision: choose K from {0,1,2,3}…
    • after ten collisions, choose K from {0,1,2,3,4,…,1023}
  • 14. CSMA/CD (Collision Detection)
    • CSMA/CD can be in one of three states: contention, transmission, or idle.
  • 15. CSMA/CD efficiency
    • See equation on textbook page 280
    • Much better than ALOHA, also decentralized, simple, and cheap
  • 16. Ethernet services
    • Connectionless: No handshaking between sending and receiving adapter.
    • Unreliable: receiving adapter doesn’t send acks or nacks to sending adapter
      • stream of datagrams passed to network layer can have gaps
      • gaps will be filled if app is using TCP
      • otherwise, app will see the gaps
  • 17. IEEE 802.2: Logical Link Control
    • (a) Position of LLC. (b) Protocol formats.
    Ethernet and other 802 protocol offer a best-efforts datagram service. LLC can be added to provides 3 service options: unreliable datagram service, acked datagram service, reliable connection-oriented service
  • 18. Ethernet
    • Frame addressing
    • MAC protocol: CSMA/CD
    • Interconnecting issues
  • 19. Hubs
    • Hubs are essentially physical-layer repeaters:
      • bits coming from one link go out all other links
      • at the same rate
      • no frame buffering
      • no CSMA/CD at hub: adapters detect collisions
      • provides net management functionality
    twisted pair hub
  • 20. Interconnecting with hubs
    • Backbone hub interconnects LAN segments
    • Extends max distance between nodes
    • But individual segment collision domains become one large collision domain
    • Can’t interconnect 10BaseT & 100BaseT, because hubs can not buffer frames for different rates
    hub hub hub hub
  • 21. Switch
    • Link layer device
      • stores and forwards Ethernet frames
      • examines frame header and selectively forwards frame based on MAC dest address
      • when frame is to be forwarded on segment, uses CSMA/CD to access segment
    • transparent
      • hosts are unaware of presence of switches
    • plug-and-play, self-learning
      • switches do not need to be configured
  • 22. Forwarding
    • How to determine onto which LAN segment to forward frame?
    • Looks like a routing problem...
    1 2 3 hub hub hub switch
  • 23. Self learning
    • A switch has a switch table
    • entry in switch table:
      • (MAC Address, Interface, Time Stamp)
      • stale entries in table dropped (TTL can be 60 min)
    • switch learns which hosts can be reached through which interfaces
      • when frame received, switch “learns” location of sender: incoming LAN segment
      • records sender/location pair in switch table
  • 24. Filtering/Forwarding
    • When switch receives a frame:
    • index switch table using MAC dest address
    • if entry found for destination then{
    • if dest on segment from which frame arrived then drop the frame
    • else forward the frame on interface indicated
    • }
    • else flood
    forward on all but the interface on which the frame arrived
  • 25. Switch example
    • Suppose C sends frame to D
    • Switch receives frame from C
      • notes in bridge table that C is on interface 1
      • because D is not in table, switch forwards frame into interfaces 2 and 3
    • frame received by D
    hub hub hub switch A B C D E F G H I address interface A B E G C 1 1 2 3 1 1 2 3 insert
  • 26. Switch example
    • Suppose D replies back with frame to C.
    • Switch receives frame from D
      • notes in bridge table that D is on interface 2
      • because C is in table, switch forwards frame only to interface 1
    • frame received by C
    hub hub hub switch A B C D E F G H I address interface A B E G C 1 1 2 3 1
  • 27. Switch: traffic isolation
    • switch installation breaks subnet into LAN segments
    • switch filters packets:
      • same-LAN-segment frames not usually forwarded onto other LAN segments
      • segments become separate collision domains
    collision domain collision domain collision domain hub hub hub switch
  • 28. Switches: dedicated access
    • Switch with many interfaces
    • Hosts have direct connection to switch
    • No collisions; full duplex
    • Switching: A-to-A’ and B-to-B’ simultaneously, no collisions
    switch A A’ B B’ C C’
  • 29. More on Switches
    • cut-through switching: frame forwarded from input to output port without first collecting entire frame
      • slight reduction in latency
    • combinations of shared/dedicated, 10/100/1000 Mbps interfaces
  • 30. Institutional network hub hub hub switch to external network router IP subnet mail server web server
  • 31. Switches vs. Routers
    • both store-and-forward devices
      • routers: network layer devices (examine network layer headers)
      • switches are link layer devices
    • routers maintain routing tables, implement routing algorithms
    • switches maintain switch tables, implement filtering, learning algorithms
  • 32. Summary comparison
  • 33. Repeaters, Hubs, Bridges, Switches, Routers and Gateways
    • (a) Which device is in which layer.
    • (b) Frames, packets, and headers.
  • 34. Data Link Layer Road Map
    • Data link layer design issues
      • Framing
      • Error Control
      • Reliable data transfer and flow control
    • Example data link protocols
      • HDLC and PPP
    • Multiple Access Protocols
      • Static channel allocation
      • Dynamic channel allocation
    • LAN technologies and their MAC protocols
      • Ethernet
      • WiFi and WiMax
  • 35. Elements of a wireless network network infrastructure
    • wireless hosts
    • laptop, PDA, IP phone
    • run applications
    • may be stationary (non-mobile) or mobile
      • wireless does not always mean mobility
  • 36. Elements of a wireless network network infrastructure
    • base station
    • typically connected to wired network
    • relay - responsible for sending packets between wired network and wireless host(s) in its “area”
      • e.g., cell towers 802.11 access points
  • 37. Elements of a wireless network
    • wireless link
    • typically used to connect mobile(s) to base station
    • also used as backbone link
    • multiple access protocol coordinates link access
    • various data rates, transmission distance
    network infrastructure
  • 38. Elements of a wireless network network infrastructure
    • infrastructure mode
    • base station connects mobiles into wired network
    • handoff: mobile changes base station providing connection into wired network
  • 39. Elements of a wireless network
    • Ad hoc mode
    • no base stations
    • nodes can only transmit to other nodes within link coverage
    • nodes organize themselves into a network: route among themselves
  • 40. Wireless Link Characteristics
    • Differences from wired link ….
      • decreased signal strength: radio signal attenuates as it propagates through matter (path loss)
      • interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well
      • multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times
    • … . make communication across (even a point to point) wireless link much more “difficult”
  • 41. Wireless network characteristics
    • Multiple wireless senders and receivers create additional problems (beyond multiple access):
    • Hidden terminal problem
    • B, A hear each other
    • B, C hear each other
    • A, C can not hear each other
    • means A, C unaware of their interference at B
    • Signal fading:
    • B, A hear each other
    • B, C hear each other
    • A, C can not hear each other interferring at B
    A B C A B C A’s signal strength space C’s signal strength
  • 42. Characteristics of selected wireless link standards 384 Kbps 56 Kbps 54 Mbps 5-11 Mbps 1 Mbps 802.15 802.11b 802.11{a,g} IS-95 CDMA, GSM UMTS/WCDMA, CDMA2000 .11 p-to-p link 2G 3G 802.16 802.16 10-66GHz 802.11a 5GHz ISM band 802.11b,g 2.4GHz ISM band 802.15 2.4GHz ISM band Indoor 10 – 30m Outdoor 50 – 200m Mid range outdoor 200m – 4Km Long range outdoor 5Km – 20Km
  • 43. IEEE 802.11 Wireless LAN
    • 802.11b
      • 2.4-2.485 GHz unlicensed radio spectrum
      • up to 11 Mbps
      • direct sequence spread spectrum (DSSS) in physical layer
        • all hosts use same chipping code
      • widely deployed, using base stations
    • 802.11a
      • 5-5.8 GHz range
      • up to 54 Mbps
    • 802.11g
      • 2.4-2.485 GHz range
      • up to 54 Mbps
    • All use CSMA/CA for multiple access
    • All have base-station and ad-hoc network versions
  • 44. 802.11 LAN architecture
    • wireless host communicates with base station
      • base station = access point (AP)
    • Basic Service Set (BSS) (aka “cell”) in infrastructure mode contains:
      • wireless hosts
      • access point (AP): base station
      • ad hoc mode: hosts only
    BSS 1 BSS 2 hub, switch or router Internet AP AP
  • 45. 802.11: Channels, association
    • 802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at different frequencies
      • AP admin chooses frequency for AP
      • interference possible: channel can be same as that chosen by neighboring AP!
    • host: must associate with an AP
      • scans channels, listening for beacon frames containing AP’s name (SSID) and MAC address
      • selects AP to associate with
      • may perform authentication [Chapter 8]
      • will typically run DHCP to get IP address in AP’s subnet
  • 46. 802.11 Wireless LANs
    • MAC protocols
      • DCF: CSMA/CA
    • 802.11 Frame format and addressing
    • Physical layer issues
  • 47. IEEE 802.11 Protocol Architecture Point Coordination Function (PCF) OFDM
  • 48. Media Access Control
    • Distributed wireless foundation MAC (DWFMAC)
      • Distributed access control mechanism
      • Optional centralized control on top
    • Lower sublayer is distributed coordination function (DCF)
      • Contention algorithm to provide access to all traffic
      • Asynchronous traffic
    • Point coordination function (PCF)
      • Centralized MAC algorithm
      • Contention free
      • Built on top of DCF
  • 49. Distributed Coordination Function (DCF)
    • DCF sublayer uses CSMA/CA
      • Uses both physical and virtual carrier sensing.
        • MACAW(Multiple Access with Collision Avoidance for Wireless) with virtual carrier sensing.
        • 1-persistent physical carrier sensing.
      • No collision detection
        • Not practical on wireless network
        • Dynamic range of signals very large
        • Transmitting station cannot distinguish incoming weak signals from noise and effects of own transmission
    • DCF includes delays
      • Amounts to priority scheme
        • Interframe space
  • 50. CSMA/CA
    • 802.11 sender
    • 1 if sense channel idle for DIFS then
      • transmit entire frame (no CD)
    • 2 if sense channel busy then
      • start random backoff time
      • timer counts down while channel idle
      • transmit when timer expires
      • if no ACK, increase random backoff interval, repeat 2
    • 802.11 receiver
    • - if frame received OK
    • return ACK after SIFS (ACK needed due to hidden terminal problem)
    sender receiver DIFS data SIFS ACK
  • 51. Avoiding collisions in CSMA/CA
    • idea: allow sender to “reserve” channel rather than random access of data frames: avoid collisions of long data frames
    • sender first transmits small request-to-send (RTS) packets to BS using CSMA
      • RTSs may still collide with each other (but they’re short)
    • BS broadcasts clear-to-send CTS in response to RTS
    • RTS heard by all nodes
      • sender transmits data frame
      • other stations defer transmissions
    Avoid data frame collisions completely using small reservation packets!
  • 52. Collision Avoidance: RTS-CTS exchange AP A B time defer RTS(A) RTS(B) RTS(A) CTS(A) CTS(A) DATA (A) ACK(A) ACK(A) reservation collision
  • 53. virtual channel sensing in CSMA/CA
    • The use of virtual channel sensing in CSMA/CA.
    A B C D
  • 54. Point Coordination Function (PCF)
    • Alternative access method implemented on top of DCF
    • Polling by centralized polling master (point coordinator)
    • Uses PIFS when issuing polls
      • PIFS smaller than DIFS
      • Can seize medium and lock out all asynchronous traffic while it issues polls and receives responses
    • E.g. wireless network configured so number of stations with time-sensitive traffic controlled by point coordinator
      • Remaining traffic contends for access using CSMA
    • Point coordinator polls to stations asking if any frames to send
    • When poll issued, polled station may respond using SIFS
    • Once a station has signed up for polling service at a certain rate, it is effectively guaranteed a certain fraction of the bandwidth
  • 55. IEEE 802.11 MAC Logic
  • 56. IEEE 802.11 MAC Logic
    • Single delay known as interframe space (IFS)
    • Using IFS, rules for CSMA :
    • Station with frame senses medium
      • If idle, wait to see if remains idle for one IFS. If so, may transmit immediately
      • If busy (either initially or becomes busy during IFS ) station defers transmission
        • Continue to monitor until current transmission is over
        • Once current transmission over, delay another IFS
          • If remains idle , back off random time and again sense
            • If medium still idle, station may transmit
            • During backoff time, if becomes busy, backoff timer is halted and resumes when medium becomes idle
    • To ensure stability, binary exponential backoff used
  • 57. IEEE 802.11 MAC Timing Basic Access Method
  • 58. Priority: Interframe Space Values
    • Use three values for IFS
    • SIFS (short IFS):
      • Shortest IFS
      • For all immediate response actions
        • Acknowledgment (ACK)
        • Clear to send (CTS)
        • Poll response
    • PIFS (point coordination function IFS):
      • Midlength IFS
      • Used by the centralized controller in PCF scheme when issuing polls
        • Takes precedence over normal contention traffic, e.g., DCF
        • Frames using SIFS have precedence over PCF poll
    • DIFS (distributed coordination function IFS):
      • Longest IFS
      • Used as minimum delay for asynchronous frames contending for access
  • 59. 802.11 Wireless LANs
    • MAC protocols
      • DCF: CSMA/CA
    • 802.11 Frame format and addressing
    • Physical layer issues
  • 60. IEEE 802.11 Protocol Architecture Point Coordination Function (PCF) OFDM
  • 61. Wireless Physical Layer
    • Physical layer conforms to OSI (five options)
      • 1997: 802.11 infrared, FHSS, DHSS
      • 1999: 802.11a OFDM and 802.11b HR-DSSS
      • 2001: 802.11g OFDM
    • 802.11 Infrared
      • Two capacities 1 Mbps or 2 Mbps.
      • Range is 10 to 20 meters and cannot penetrate walls.
      • Does not work outdoors.
    • 802.11 FHSS ( Frequence Hopping Spread Spectrum )
      • Offers good resistance to multipath fading.
      • 79 non-overlapping channels, each 1 Mhz wide at low end of 2.4 GHz ISM band.
      • Same pseudo-random number generator used by all stations.
      • Dwell time: min. time on channel before hopping (400msec).
    Multipath Fading The deflection of a radio signal off obstacles which can cause interference during signal reception. Multipath occurs when a radio signal is received directly by an antenna and later the same signal is received again, reflected from a building or mountain. &quot;Ghosting&quot; of a TV signal is a form of muiltipath. Under certain conditions, two or more of the signals can interfere with each other and create &quot;fading&quot; (a loss of signal) in the communications link.
  • 62. Wireless Physical Layer
    • 802.11 DSSS ( Direct Sequence Spread Spectrum )
      • Spreads signal over entire spectrum using pseudo-random sequence (similar to CDMA see Tanenbaum sec. 2.6.2).
      • Each bit transmitted using an 11 chips Barker sequence, PSK at 1Mbaud.
      • 1 or 2 Mbps.
    • 802.11a OFDM (Orthogonal Frequency Divisional Multiplexing)
      • Compatible with European HiperLan2.
      • Good immunity to multipath fading
      • 54Mbps in wider 5.5 GHz band  transmission range is limited.
      • Uses 52 FDM channels (48 for data; 4 for synchronization).
      • Encoding is complex ( PSM up to 18 Mbps and QAM above this capacity).
      • E.g., at 54Mbps 216 data bits encoded into into 288-bit symbols.
      • More difficulty penetrating walls.
  • 63. Wireless Physical Layer
    • 802.11b HR-DSSS ( High Rate Direct Sequence Spread Spectrum )
      • 11a and 11b shows a split in the standards committee.
      • 11b approved and hit the market before 11a.
      • Up to 11 Mbps in 2.4 GHz band using 11 million chips/sec.
      • Note in this bandwidth all these protocols have to deal with interference from microwave ovens, cordless phones and garage door openers.
      • Range is 7 times greater than 11a.
      • 11b and 11a are incompatible!!
  • 64. Wireless Physical Layer
    • 802.11g OFDM ( Orthogonal Frequency Division Multiplexing )
      • An attempt to combine the best of both 802.11a and 802.11b.
      • Supports bandwidths up to 54 Mbps.
      • Uses 2.4 GHz frequency for greater range.
      • Is backward compatible with 802.11b.
  • 65. Data Link Layer Road Map
    • Data link layer design issues
      • Framing
      • Error Control
      • Reliable data transfer and flow control
    • Example data link protocols
      • HDLC and PPP
    • Multiple Access Protocols
      • Static channel allocation
      • Dynamic channel allocation
    • LAN technologies and their MAC protocols
      • Ethernet
      • WiFi and WiMax and WPAN
  • 66. Broadband Wireless
    • Wireless MAN or Wi-Max
    • IEEE 802.16 standard for bridging the “last mile” between ISPs and their customers as replacement for costly-todeploy fiber optic/DSL/cable modem links (Broadband Wireless Access, BWA)
    • Original PHY-Layer
      • 10-66 GHz; line-of-sight connections with fixed, directed outdoor antennas; single-carrier, TDD or FDD with TDMA in the uplink
    • In 802.16a a second PHY-layer was added to make the standard suitable for residential applications (no line-of-sight, more multi-path propagation)
      • 2-11 GHz, both licensed and license-exempt; non-line-of-sight operation possible; support for advanced antenna systems; three air interfaces: single carrier, OFDM with TDMA, or OFDMA
  • 67. Comparison of 802.11 and 802.16a License-exempt or licensed License-exempt (ISM) Spectrum Triple-DES (128-bit) and RSA (1024-bit) WPA/WEP Security Yes None Service Levels Thousands Hundreds Users Outdoor Opt. Indoor Opt. Coverage Yes None QoS 40 km 100 m Range 70 Mbps 54 Mbps (11a & g) Max Speed IEEE 802.16a IEEE 802.11
  • 68. The 802.16 Protocol Stack
    • The 802.16 Protocol Stack.
  • 69. The 802.16 Physical Layer
    • The 802.16 transmission environment.
    Use error-correction code: Hamming code
  • 70. The 802.16 Physical Layer (2)
    • FDD + TDD
    • Example: Frames and time slots for time division duplexing(TDD)
  • 71. The 802.16 MAC Sublayer Protocol
    • Downstream channel
      • Base station decide
    • Upstream channel
      • Competing uncoordinated subscribers
      • Related to QoS issues
      • Four Connection-Oriented Service Classes
        • Constant bit rate service (uncompressed voice)
        • Real-time variable bit rate service (compressed multimedia)
        • Non-real-time variable bit rate service (not real time heavy transmissions, large file transfers)
        • Best efforts service (everything else)
      • Decided when connection is set up
  • 72.
    • less than 10 m diameter
    • replacement for cables (mouse, keyboard, headphones)
    • ad hoc: no infrastructure
    • master/slaves:
      • slaves request permission to send (to master)
      • master grants requests
    • 802.15: evolved from Bluetooth specification
      • 2.4-2.5 GHz radio band
      • up to 721 kbps
    radius of coverage 802.15: personal area network M S S S P P P P M S Master device Slave device Parked device (inactive) P
  • 73. Unlicensed Radio Spectrum 902 Mhz 928 Mhz 26 Mhz 83.5 Mhz 125 Mhz 2.4 Ghz 2.4835 Ghz 5.725 Ghz 5.785 Ghz cordless phones baby monitors Wireless LANs 802.11 Bluetooth Microwave oven 802.11a HyperLan  33cm 12cm 5cm
  • 74. Frequency Hopping
    • Total bandwidth divided into 1MHz physical channels
    • FH occurs by jumping from one channel to another in pseudorandom sequence
    • Hopping sequence shared with all devices on piconet
  • 75. Frequency Hopping
    • frequency hopping spread spectrum
      • 2.402 GHz + k MHz, k=0, …, 78
      • 1,600 hops per second
    . . . 1Mhz 1 2 3 79 83.5 Mhz
  • 76. Radio Specification
    • Low Power Consumption
      • Three power classes defined with max output power from 1 mW (Class 3 ) to 100 mW (Class 1 ).
        • Class 1: Outputs 100 mW for maximum range
          • Power control mandatory
          • Provides greatest distance
        • Class 2: Outputs 2.4 mW at maximum
          • Power control optional
        • Class 3: Nominal output is 1 mW
          • Lowest power
    • Short Range 10-100 Meter
        • Class 1 – 100 meter (300 feet)
        • Class 2 – 20 meter (60 feet)
        • Class 3 – 10 meter (30 feet)
  • 77. Baseband Layer
    • MAC sublayer + some elements of physical layer
    • Deal with how the master controls time slots and how these slots are grouped into frames
    • Piconet access:
      • Bluetooth devices use time division duplex (TDD)
      • Access technique is TDMA
  • 78. Reading Assignment
    • Chapter 2
      • 2.1 - must
    • Chapter 8