1. Algoritmi de rutare bazați pe informațiile de poziție ale nodurilor într-o rețea ad-hoc
Proiect realizat în cadrul cursului “Rețele de Calculatoare și Internet"
Petruș Andrei
An 2 – Master IISC

2. Cuprins Introducere in retele de senzori wireless / ad-hoc
Algoritmi de rutare
Generalitati
Parametrii critici
Algoritmul A: LAR
Algoritmul B: DREAM

3. 1. Introducere in WSN/WAN
Ce este un senzor wireless?
SoC compus din:
Procesor consum redus
Putere de procesare limitata
Memorie
Capacitate redusa
Modul radio
Rata de transfer mica
Raza de acoperire redusa
Senzori
Scalari
Camere de captura, microfoane
Sursa energie P O W E R
Sensors
Storage
Processor
Radio
Fig. 1 – modulele componente ale unui nod
Fig. 2 – exemple de noduri WSN (incapsulat si SMD)

4. 1. Introducere in WSN/WAN
Ce este o retea de senzori wireless?
Este compusa din mai multi senzori wireless (noduri)
Proprietati:
Puternic limitate dpdv energetic
(compromis performanta/autonomie)
Self-management, Self-organizing
Scalabile (numar mare de noduri)
Heterogene (noduri organizateierarhic,
dispozitive cu diferite capabilitati)
Adaptabile
Securitate sporita
Fig. 3 – retea WSN cu senzori distribuiti aleator

5. 1. Introducere in WSN/WAN
Diferente intre WSN / WAN
Retelele de senzori sunt mai dense
Retelele de senzori sunt predispuse la erori/failures
Topologia retelelor de senzori de schimba foarte des
WSN trimite mesajele broadcast, pe cand in retelele ad-hoc comunicarea este point-to-point
Nodurile din WSN pot sau nu sa aiba identificator unic global

6. 1. Introducere in WSN/WAN
Aplicatii ale retelelor de senzori wireless
Monitorizare
Scop stiintific, aplicatii in ecologie.
Informatii spatio-temporale in timp real
Accesul la zone restrictionate
Supraveghere si urmarire
Recunoastere
Controlul perimetrului
Medii “inteligente”
Agricultura
Procese industriale

7. 1. Introducere in WSN/WAN
Aplicatii ale retelelor de senzori wireless
Monitorizare
Fig. 4 – o implementare WSN in scop de monitorizare a unui obiectiv

8. 1. Introducere in WSN/WAN
Aplicatii ale retelelor de senzori wireless
Supraveghere si urmarire
Fig. 5 – o implementare WSN in scop militar, de recunoastere

9. 1. Introducere in WSN/WAN
Aplicatii ale retelelor de senzori wireless
Fig. 6 – implementari WSN in aplicatii consumer

10. 2. Algoritmi de rutare Algoritm de rutare -> serviciu Funcții:
Defineste procedurile si infrastructura pentru transmiterea mesajelor/datelor intre nodurile retelei
Asigura flexibilitate si adaptabilitate retelei
Un algoritm de rutare eficient va contribui semnificativ la: autonomia generala a sistemului, confidentialitatea datelor transmise
Fig. 7 – frame-ul pachetului intr-o retea TDMA
Fig. 8 – o retea WSN

11. 2. Algoritmi de rutare
Ce folosesc informatiile de pozitie ale nodurilor in retea:
GPSR – Greedy Perimeter Stateless Routing
Location-aware long-lived route selection
DREAM – Distance Routing Algorithm for Mobility
LAR – Location Aided Routing
Fig. 9 – GPSR
(rutare geografica)
Fig. 10 – retea WAN
Fig. 11 – LAR (rutarea asistata
de localizare)

12. 2a. Parametrii critici Parametrii critici pentru algoritmii de rutare:
Eficienta de rutare (correct destination high hit rate)
Evitarea buclelor de rutare
Alegerea rutelor optime
Viteza de rutare
Perioada mica de convergenta a retelei
Rata ridicata de transfer a pachetelor in retea
Eficienta energetica
Complexitatea implementarii

13. 2b. Protocolul de rutare LAR
Foloseste doar informatii geo pentru descoperirea rutelor si se bazeaza pe un protocol de rutare on-deman (gen Ad-hoc on demand distance-vector routing)
Daca emitorul cunoaste o pozitie anterioara a receptorului cat si viteza acestuia de deplasare, el va calcula o arie unde este posibil sa se afle receptorul in momentul actual (expected zone)
Astfel, se va minimiza efectul de flood a pachetelor menite sa identifice rutele
Pachetele sunt trimise doar in ‘expected zone’
Daca un nod din exteriorul acestei zone primeste un astfel de pachet, il ignora
Daca nodul destinatie primeste pachetul, acesta raspunde cu pozitia sa curenta si viteza de deplasare
Atunci cand un nod intra in retea, acesta nu cunoaste informatiile de pozitie a celorlalte noduri, motiv pentru care nodul face fall-back si va folosi protocolul fundamental de rutare (flood the entire network)
The Location Aided Routing Protocol (LAR, [Ko00]) only uses geographical information for route discovery. It is based on an on-demand protocol, like AODV. If the sender knows where the destination was at some time and it knows its speed, it can determine in which area the destination is now. This area is called the expected zone. LAR uses this to limit the flooding of route discovery packets. Packets are flooded within an defined area containing both the source and the expected zone. When a node outside this area recieves a packet, it ignores it. When the destination receives the route discovery packet, it returns it with its current location and speed, which can assist in future route discoveries.
When a node enters the network, it has no information about the geographical position of other nodes. LAR will then fall back to the underlying protocol, which floods the route discovery packet. For LAR to be an improvement over flooding, the network has to be stable. LAR will perform well for moving nodes and disappearing nodes, but not when a lot of new nodes are added to the network. Furthermore, connections in the network has to be stable. If nodes connect to many other nodes for a short time, location information will not be available or accurate enough to make use of LAR.
Fig. 13 – LAR (rutarea asistata
de localizare)

14. 2b. Protocolul de rutare LAR
Pentru ca LAR sa aduca un beneficiu peste traditionalul flood, reteaua trebuie sa fie stabila! LAR va fi eficient in cadrul retelelor dinamice (si/sau) cu noduri care dispar, insa eficienta va fi scazuta atunci cand apar noduri noi.
Avantaje:
Se evita floodarea inutila a intregii retele
Performante ridicate chiar si in retele puternic dinamice
Dezavantaje
Daca reteaua nu este stabila, algoritmul este ineficient
Performantele sunt scazute in retelele in care fluxul de intrare a nodurilor noi este ridicat
For LAR to be an improvement over flooding, the network has to be stable. LAR will perform well for moving nodes and disappearing nodes, but not when a lot of new nodes are added to the network. Furthermore, connections in the network has to be stable. If nodes connect to many other nodes for a short time, location information will not be available or accurate enough to make use of LAR.

15. 2c. Protocolul de rutare DREAM
Fiecare nod isi cunoaste pozitia
Fiecare nod isi comunica adresa si pozitia in retea
Cand se trimite un pachet, acesta este inaintat numai pe directia nodului receptor
Apare “efectul de distanta”:
Nodurile apropiate intre ele isi trimit informatii unul celuilalt mai des decat nodurile intre care exista o distanta mai mare
Cand un pachet este transmis de la nodul A catre nodul mai departat B, informatiile despre pozitia nodului B se detaliaza pe masura ce pachetul se propaga in retea
Cand un nod isi schimba pozitia dez, acesta trimite mai frecvent informatii vecinilor sai
The DREAM protocol was proposed in [Bas98]. It assumes that each node knows its own location. Each node then communicates its address and location through the network. When a packet is sent, it is sent to the direction of the receiving node.
DREAM makes use of what is called the distance effect: the greater the distance separating two nodes, the slower they appear to be moving with respect to each other. Neighbours close by are frequently informed of the location of a node; nodes which are farther away only occasionally receive this information. The further a packet travels to its destination, the more detailed the position of the destination becomes.
Furthermore, DREAM takes into account the mobility of the nodes. When a node travels fast, it frequently sends its location information to its neighbours.
DREAM is similar to HSLS in that the update frequency is dependant on the distance to a node, only it uses coordinates instead of routing paths. This makes it very well scalable, but introduces the problem of determining the location for each node.
Fig. 12 – GPSR
(rutare geografica)

16. 2c. Protocolul de rutare DREAM
Frecventa de actualizare/notificare a informatiilor de pozitie a unui nod A catre nodul B este dependenta de distanta dintre aceste noduri. Informatiile de pozitie constau in coordonate, ci nu in cai de rutare!
Avantaje:
Permite o scalabilitate ridicata a retelei
Algoritmul are o eficienta de rutare buna
Dezavantaje
Trebuie rezolvata problema achizitiei informatiilor de pozitie pentru fiecare nod (prin GPS = cost ridicat dpdv al eficientei energetice)
DREAM is similar to HSLS in that the update frequency is dependant on the distance to a node, only it uses coordinates instead of routing paths. This makes it very well scalable, but introduces the problem of determining the location for each node.

17. Bibliografie
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18. Algoritmi de rutare bazați pe informațiile de poziție ale nodurilor într-o rețea ad-hoc
Proiect realizat în cadrul cursului “Rețele de Calculatoare și Internet"
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