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Two Media Access Control Protocols (MAC) for Wireless Networks

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galena
18 diapositives · 384 Views · Sep 23, 2014

Two Media Access Control Protocols (MAC) for Wireless Networks. The Packet Reservation Multiple Access (PRMA) protocol. PRMA is essentially a slotted ALOHA protocol. Designed under the assumption that only speech users are present.

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Two Media Access Control Protocols (MAC) for Wireless Networks
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  1. Two Media Access Control Protocols (MAC) for Wireless Networks

  2. The Packet Reservation Multiple Access (PRMA) protocol • 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 Ps • 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. Technical University of Crete

  3. The Integrated PRMA (IPRMA) protocol • 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) Technical University of Crete

  4. Graphical Representation of IPRMA Technical University of Crete

  5. Pros and Cons of IPRMA • 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. Technical University of Crete

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

  7. Throughput of IPRMA and PRMA Technical University of Crete

  8. Average speech packet delay of IPRMA and PRMA Technical University of Crete

  9. Average data packet delay of IPRMA and PRMA Technical University of Crete

  10. The PRMA with Dynamic Allocation of available slots (PRMA/DA) protocol • 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. Technical University of Crete

  11. Frame Format of PRMA/DA protocol Technical University of Crete

  12. More on available and reservation slots • 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. Technical University of Crete

  13. Allocating available slots • 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. Technical University of Crete

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

  15. Dynamic allocation of reservation slots • 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. Technical University of Crete

  16. Throughput of PRMA/DA and PRMA/FA Technical University of Crete

  17. CBR access delay of PRMA/DA and PRMA/FA Technical University of Crete

  18. VBR cell transmission delay of PRMA/DA and PRMA/FA Technical University of Crete