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WIFI Goes to Town - An article summary presentation
- 1. WIFI Goes to Town Rapid Picocell Switching for Wireless Transit Networks Directed by : Belasker Adel Ismail Yaich
- 2. •Every day Millions of daily traveler in urban centers that use different means of transports : by train , light rail , underground rail , vehicles .. are using wireless networks to keep them connected outdoor and along the way . •This number of traveler is increasing hugely which implies a great demand for high-capacity wireless networks serving transportation that allows users to surf the web , watch videos , make audio calls .. all while traveling .
- 3. •A solution used by Wireless networks operators in order to support this demand of high- capacity is to decrease cells size .
- 4. •But moving to smaller cells needs a performant « Handover« technique to serve the client roaming (moving) from an Access Point AP to another .
- 5. •The standard Roaming WIFI Protocol used nowadays is 802.11r Fast Roaming, it allows clients switch to a nearby AP without loosing connection .
- 6. •That’s why the WIFI standard 802.11r is unable to handle efficiently vehicular clients . •But we tested this current Handover solution (802.11r) on a client that drives from AP1 to AP2 at a speed of 25 mph and it shows that the handover fails and the link quality is decreasing significantly because switching decision is too slow .
- 7. Solution •As an alternative to 802.11r protocol a research team from Princeton University introduced the WIFI Goes To Town solution which is the first WIFI roadside hotspot networks designed to operate in vehicular speeds .
- 8. •It is a deployment of an inexpensive array of WIFI APs , called Pico Cells , along a roadside with a central controller that controls tightly the Pico Cells array . •It enables APs to make delivery decisions to the vehicular clients at millisecond level . •It introduces a quick method on how to decide which AP should delivers the packet to the client .
- 9. •In order to accomplish this goals WIFI Goes To Town team worked on writing some advanced algorithms and techniques then implementing it into kernel level .
- 10. WGTT : Quand passe-on d’un AP à un autre? Comment passer d’un AP à un autre?
- 11. Fonctionnement du Système • WGTT Association uplink Downlink
- 12. • Association Fonctionnement du Système association AP1 AP3 AP2 controler association association
- 13. Fonctionnement du Système • Uplink AP1 AP2 AP3 Controler (deduplicates data) Même BSSID (@ MAC) Packages to send
- 14. Fonctionnement du Système • Uplink problem: AP1 AP2 data ack ack Solution: Block ACK forwarding, AP2 envoie un pacquet Block ACK à AP1 pour que AP1 ne renvoie pas les données au client. Block ack
- 15. Fonctionnement du Système • Downlink Qui va envoyer? AP3 AP2 controler pacquets pacquets pacquets Le contrôleur décide qui est le routeur qui va envoyer en se basant sur un algorithme de switching. On calcule à chaque fois le SNR d’un pacquet émis par le client vers les APs pour savoir la qualité du signal reçue et puis on choisie le taux le plus élevé ainsi le routeur adéquat. SNR = signal / bruit (db)
- 16. Fonctionnement du Système • Downlink example AP3 AP2 controler pacquets switch start ACK Lorsque un client en mouvement et reçoie des pacquets de AP2 et puis le controleur décide de faire un switch vers AP3 suivant notre algorithme, AP2 envoie un pacquet start vers AP3 et puis AP3 envoie un ack vers le controler. Finalement AP2 indique à AP3 les pacquets blocqués pour qu’il sache quels pacquets il doit continuer à envoyer vers le client.
- 17. Performance Evaluation WGTT solution is more performant than 802.11r when the client moves at different speeds .
- 20. Web browsing