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Understanding Wireless Network Protocols in Local Area Networks

Learn about the protocols and layers involved in wireless networks, including MAC addressing, IP addressing, data transmission, and access methods. Explore multiple access protocols, access point architectures, and wireless communication models for improved network understanding. Discover the challenges and paradoxes in wireless reception models and network capacities.

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Understanding Wireless Network Protocols in Local Area 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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