DOWNLOAD MY Ph.D Thesis - UNAM

Chapter 3The DVB/DAVIC protocol p5) If the request was transmitted successfully, wait until the INA grants the request totransmit the data packet.6) Finally, after transmitting the current data packet in the reserved slots assigned bythe INA, if there are more data packets to transmit repeat the process starting in 1).In the following sections, a description of the operation and dynamic that eachcontention resolution algorithm uses to resolve collisions is presented.3.5.2 Exponential backoff algorithm overviewIn this sub-section we present a review of the operation of the exponential backoffalgorithm adopted by the DVB/DAVIC protocol. Furthermore, in Section 6.3 weapproach a performance analysis and optimisation of this algorithm.When an NIU wants to transmit a reservation request in a contention slot, it choosesarbitrarily one contention slot in the next group of contention slots described by thesignalling information field, as depicted in Figure 3.4. In case of collision, thisalgorithm defines how many cells a station needs to let pass before it can transmit. Thisnumber of cells is computed as a uniform random integer variable in the range of [0-2 backoff ].P k A r r iv a lS t a r t C o n t e n t io nP r o c e s sT x . R e q . i n a R N D C SC SR e qT xR N D= C n t e n t i o n S l o t= R e q u e s t= T r a n s m it= R a n d o mi = in it ia l b a c k o f f e x p .t = t r u n c a t e d b a c k o f f e x p .C o lli s i o n ?N OS u c c e s s f u l R e q . T xW a it f o r g r a n t a n d t h e nt r a n s m it d a t a s l o t sY E Si = i + 1 , u n t il i < = tb = R N D ( 2i)b a c k o f f ( b - 1 ) C S &T x . R e q . I n t h e b t h C SE n dFigure 3.4 – Block diagram of the exponential backoff algorithm.3-8