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Wireless networks

Wireless networks. Philippe Jacquet. Link layer: protocols in local area networks. Couche 5. MAC/link address: 6 octets Starts with 1: unicast Starts with 0: multicast Internet address: 4 octets (IPv4) First octets subnet address 16 octets (IPv6). Couche 4. Couche 3. Couche 2: Lien.

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Wireless networks

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  1. Wireless networks Philippe Jacquet

  2. Link layer: protocols in local area networks Couche 5 • MAC/link address: • 6 octets • Starts with 1: unicast • Starts with 0: multicast • Internet address: • 4 octets (IPv4) • First octets subnet address • 16 octets (IPv6) Couche 4 Couche 3 Couche 2: Lien Couche 1: Physique

  3. Encapsulation IP packet IP destination IP source data MAC receiver MAC emitter MAC packet

  4. Local protocol gateway • if IP address out of subnet • Toward gateway • Otherwise address resolution protocol (ARP) • Get MAC address in correspondance address • Otherwise launch an ARP request

  5. Protocole ARP émetteur requête • ARP Request • ARP Reply MAC FFFFFF MAC emitter IP destination MAC receiver MAC emitter IP destination emitter reply: correspondance

  6. ARPprotocol

  7. Reverse ARP • MAC → IP

  8. DHCP • IP addresses for mobile nodes (Dynamic Host Configuration Protocol)

  9. Link/MAC: Multiple access protocols • In wireless networks, medium channel is unique and must be shared • One or several of frequencies

  10. Wireless Communication Architecture • Access point architecture • Wifi infrastructure mode • GSM, UMTS • Wimax • Ad hoc architecture • Mesh networks • Mobile ad hoc • Sensor networks

  11. Multiple access protocols • Frequency Division Multiple Access • Frequency set is split between users • Time Division Multiple Access (TDMA) frequencies time time

  12. Wireless Access Protocols • Periodic TDMA • Time slot periodically allocated to terminal in round robin. • Examples: GSM, bluetooth. time slot

  13. Wireless Access Protocols • Random access protocols • More than two transmitters over one slot→ collision • Collision detection (no ACK) • Collision resolution algorithm. time slot

  14. Models of wireless reception 5 1 • Signal attenuation • Minimal SNR for reception 2 4 3

  15. Wireless ALOHA • Transmitters come as a space-time Poisson process of rate per time unit and per area unit • Poisson rate is in • In dimension D it is in • In wired network D=0 (classic ALOHA)

  16. Wireless ALOHA • Signal level map

  17. Wireless Aloha • Reception areas

  18. Reception area in urban environment

  19. Area of correct reception • Area where SNR>K around an emitter X • Average size of order (homothetic principle) X

  20. Paradox of wireless Aloha: • When D>0 average sum of correct reception remains the same for all • Not true for D=0: classic unstable ALOHA X X X X

  21. Consequence on MANET theoretical performance • N nodes on an area A, density • Per node traffic rate • Average neighbor size

  22. Paradox of space capacity • Average number of hops • Net per node capacity • Total network transport capacity

  23. MANET Capacity limit • But the network must be connected • Total transport capacity

  24. Capacity paradox • Transport Capacity increases with space and density when N increases. • In D=0 (wired net) • Transport Capacity is constant

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