Two Media Access Control Protocols (MAC) for Wireless Networks

Technical University of Crete2 PRMA is essentially a slotted ALOHA protocol. Designed under the assumption that only speech users are present. If a speech user has a packet to transmit and there is an idle slot he transmits his packet with probability P s If he succeeds(no collision), he reserves this slot for the corresponding frames until he enters silence(vertical reservation). If not, he repeats until successful. The Packet Reservation Multiple Access (PRMA) protocol

Technical University of Crete3 IPRMA is a variant of PRMA trying to integrate speech and data users. In IPRMA, data users can reserve multiple slots in a frame(horizontal reservation) but not more than k-M slots (k = free slots) The Integrated PRMA (IPRMA) protocol

Technical University of Crete4 Graphical Representation of IPRMA

Technical University of Crete5 Under low loading conditions significant improvements because a data user can transmit many packets, thus making more efficient use of the medium. But the speech users are hampered by this scheme. Setting M 0 is a mechanism to protect the speech users. On the other hand, when k = M and there are no speech users but data users exist, we are wasting our resources. Also M should be dependent on the speech traffic present, but a fixed value(M = 2) is assumed in all experiments. Pros and Cons of IPRMA

Technical University of Crete6 Authors determine optimal P s by plotting max number of speech users supported under the condition P drop <0.01 for various values of P s. They found P s =0.35 for 36 speech users. P d is determined by making a plot of max data rate per user assuming 20 data users in the system and so they find P d =0.08. But the optimal values of P s and P d will be different when mixed load is applied in the channel. But now we have to make more calculations to find them. Determining P s and P d

Technical University of Crete7 Throughput of IPRMA and PRMA

Technical University of Crete8 Average speech packet delay of IPRMA and PRMA

Technical University of Crete9 Average data packet delay of IPRMA and PRMA

Technical University of Crete10 This variant of PRMA is more suitable when we have speech, video and data users on the same channel (multimedia wireless networks). Each frame is divided into available and reservation slots(unlike IPRMA). Available slots are used to make declarations about the traffic characteristics of each source. Reservation slots are used to transmit the actual information. Available slots enable Call Admission Control policy. The PRMA with Dynamic Allocation of available slots (PRMA/DA) protocol

Technical University of Crete11 Frame Format of PRMA/DA protocol

Technical University of Crete12 In PRMA/FA(Fixed Allocation) each MS takes the reservation slots it needs and the rest are available slots. In PRMA/DA we first allocate available slots and then distribute reservation slots in each MS. Number of available slots depends on the intensity of demand to access the network. Number of reservation slots assigned to each MS is dependent on its statistical properties of traffic. More on available and reservation slots

Technical University of Crete13 Number of available slots should be equal to the number of contending stations, unless it affects the QoS of reserving stations. In practice, we cannot have perfect knowledge of number of contending stations so an algorithm to estimate them is needed. Allocating available slots

Technical University of Crete14 Dynamic allocation of available slots Second term is there so as not to degrade the QoS of reserving stations.

Technical University of Crete15 Once the number of available slots has been determined we allocate the reservation slots dynamically for each MS. If ABR users don’t need all their slots they grant them to VBR users. Dynamic allocation of reservation slots

Technical University of Crete16 Throughput of PRMA/DA and PRMA/FA

Technical University of Crete17 CBR access delay of PRMA/DA and PRMA/FA

Technical University of Crete18 VBR cell transmission delay of PRMA/DA and PRMA/FA