1 / 32

WiFi, Bluetooth & Layers

WiFi, Bluetooth & Layers. Emmanuel Baccelli. Last week. Medium Access Control Basic example : Aloha. Wifi, Bluetooth: wireless LANs. Wifi, Bluetooth, Ethernet. Protocol layers 1 et 2 Transfer packets over a link Standardization body: IEEE Standards: 802.11, 803.2, 802.15… . Couche 5.

rangle
Download Presentation

WiFi, Bluetooth & Layers

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. WiFi, Bluetooth & Layers Emmanuel Baccelli

  2. Last week • Medium Access Control • Basic example : Aloha • Wifi, Bluetooth: wireless LANs

  3. Wifi, Bluetooth, Ethernet • Protocol layers 1 et 2 • Transfer packets over a link • Standardization body: IEEE • Standards: 802.11, 803.2, 802.15… Couche 5 Couche 4 Couche 3 Couche 2: Lien Couche 1: Physique

  4. = la norme IEEE 802.11 • Norme = règles, techniques, formats communs à respecter • Protocole = norme de communication entre machines • IEEE = Institute of Electrical and Electronics Engineering • IEEE 803.2 • IEEE 1394 • IEEE 802.15.1

  5. IEEE 802.11 standard • Communication between terminals and access point • Direct communication between terminals

  6. Infrastructure mode in urban situation

  7. IEEE 802.11 basic • Emission power 100 mW (1/10 of GSM) • Bursty packet emissions 2-5-10-..54 Mbits/s • Range: 100 m outdoor several ten meters • European ETS 300328

  8. Frequencies • 52 MHz bandwidth around 2.4 GHz • 11 channels with partial overlaps

  9. coding IEEE 802.11b • Spread spectrum • Spread of 11MHz (11 bits Barker sequence) 1 Msymbols/s • 1 Mbps: modulation PSK 1, 1 bit/ symbol (DSSS IEEE 802.11) • 2 Mbps: mod QPSK, 2 bits/ symbol • Spread of 11 MHz (séquence 8 bits CCK), 1,375 Msymbol/s • 5,5 Mbps: 4 bits/symbole • 11 Mbps: 8 bits/symbole

  10. IEEE 802.11b,a,g,n • IEEE 802.11b (1-2-5,5-11 Mbps) • Bandwidth 2,4 GHz • Modulation Direct Sequence Spread Spectrum (DSSS) • No Forward Error Control (FEC) • IEEE 802.11a (6-54 Mbps) • Bande 5,2 GHz • Mod. Orthogonal Frequency Division Multiplexing (OFDM) • FEC rate ½, 2/3, 3/4 (convolutive code) • IEEE 802.11g (ERP-OFDM), IEEE 802.11n (MIMO)

  11. Carrier SenseMultiple Access

  12. Basic CSMA:listen before talk • node withdraws over signal detection DIFS packet emitter ack destination forbidden period forbidden zone

  13. Hidden nodes collisionsavoidance • Node withdraws over hidden nodes detection RTS packet emitter CTS ack forbidden period destination

  14. Collision management • CSMA/CA Carrier Sense Multiple Access with Collision Avoidance

  15. Retransmissions packet RTS packet DIFS • Random backoff of transmission over forbidden periods • Evite les collisions répétées • The node selects a random backoff: a number of mini-slots between 0 and Cmax-1 (8) • Mini-slots are not decremented during forbidden periods • Cmax double at each collision (lack of CTS or ACK) • Retry number limited to max_retry (7-16). • Slot<DIFS (Distributed Inter Frame Space) ack CTS ack forbidden period Forbidden Period Forbidden period slot slot Forbid. period slot Example: time for a backoff of 3 slots

  16. Terminology Distribution system IBSS • Infrastructure mode ESS AP terminal • ad hoc mode BSS AP: Access Point BSS: Basic Set Service ESS: Extended Set Service IBSS: Independent Basic Set Service

  17. Formats (packets) • IEEE 802.11 packet • Packet emission preamble MAC header Data part (IP packet) Check sum Emitter node packet SISF Intended Receiver node ACK

  18. Format (Preamble)

  19. Formats (MAC header) • Four addresses in infrastructure mode • Only two in ad hoc mode • Control field contains length and mode • Sequence field for fragmentation control Address 1 Address 2 Address 3 sequence Address 4

  20. WEP security • Authentification and encryption (secret key K, symmetric) • The terminal requires the access point authentification • The access point sends a challenge of 128 random bits • The terminal returns the 128 bits xored by K • The access point confirms authentification • Default: James Bond overhear the key K via direct comparison between challenge and terminal reply! • Packet encryption (algorithm RC4) • pseudo random sequence seed=K*IV (Initialisation Vector in packet header) • Integrity check via an internal check sum • RC4 is linear (RC4(xy)=RC4(x)RC4(y))! • WEP is very weak and only address unvolontary earsdropping.

  21. improved security • WEP improvement with IEEE 802.11i • Introduction of IEEE 802.1x to manage the secret keys K (Extensible Authentification Protocol- Transport Layer Security, EAP-TLS). • Authentification made indépendant of encryption • Introduction of more sophisticated function : (K,IV)RC4 seed. Authentification agent IEEE 802.1x IEEE 802.11

  22. = IEEE 802.15.1 • Communication between personnal devices • Architecture piconet master slave: • 7 slaves max per piconet • Exclusive links slave-master • Slotted time master slaves piconet

  23. IEEE 802.15.1 • Wide area architecture : scatternet • Several tiled piconets • Frequency hopings differ • certains nodes switch status master-slave esclaves

  24. IEEE 802.15.1 • Limited emission power • Class 1: 100 mW • class 2: 2,5 mW • class 3: 1 mW (1/1000 GSM) • Minimal signal processing • Periodic TDMA • Throughput 1 Mbps max • Few meters range. • Profiles • Standadized applications

  25. IEEE 802.15.1 • Slotted system managed by the master node over a single frequence • Adaptative FEC, rate: 1 (no correction), 2/3, 1/3 • Frequency hopping (1600/sec) • One hop per slot over 79 channels (2,4 GHz) • Throughput 1 Mbps, extensions for10 Mbps. From master From slave

  26. Bluetooh + WiFi

  27. Formats • Format du paquet • Access Code (AC): synchro, pagination (slot #). Channel AC, Device AC, Inquiry AC. • Header: address, sequence number, flow control, acquittement

  28. frequency hoping Periodic change of frequencies. Predetermined sequence fixed in standard. Goal: use uncongested frequencies.

  29. Connection • Connection establishment • Inquiry for destination terminal identification (source, destination) • paging for synchronization of emissions (source, master, destination) • polling, the master prompts each slave emission. • Out of connection, the slave can be in wake mode or in sleed mode, otherwise it looses its MAC address.

  30. Sécurity • Authentification (E1 algorithm) • Secret shared key (link key) (128 bits) • Encryption (algorithms KG, E0) • Secret key Kc (deduced from link key par KG) from 8 to 128 bits (negociated) • Use of slot number in E0 (indicated in paging) • E1 and E0 differ. • Default of Bluetooth security • Keys are too short • link key and Kc are both function of device PIN (4 bits).

  31. Authentification • Authentification of B byA • B sends its address (48 bits) • A returns rand(A) to B (challenge 128 bits) • E1(addr B, link key, rand(A))=(SRES,ACO) (32 bits, 96 bits) • B returns SRES.

  32. Encryption • mode 2 • Packets are encrypted via individual keys Kc(B)=KG(…,ACO(B)) • Broadcast packets are not encrypted • mode 3 • All packets are encrypted via the key of the master Kc=KG(…,ACO(A)) • encryption • Kc depends on link key, ACO and EN_RAND • The pseudo random word Kstr depends on slot number and the addess of the master • In packet crypted code=dataKstr

More Related