Two Media Access Control Protocols (MAC) for Wireless Networks

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

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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)

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Graphical Representation of IPRMA
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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.

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Determining Ps and Pd

• Authors determine optimal Ps by plotting max
  number of speech users supported under the
  condition Pdroplt0.01 for various values of Ps.
  They found Ps0.35 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 Pd0.08.
• 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.

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Throughput of IPRMA and PRMA
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Average speech packet delay of IPRMA and PRMA
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Average data packet delay of IPRMA and PRMA
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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.

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Frame Format of PRMA/DA protocol
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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.

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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.

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Dynamic allocation of available slots

• Second term is there so as not to degrade the QoS
  of reserving stations.

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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 dont need all their slots they
  grant them to VBR users.

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Throughput of PRMA/DA and PRMA/FA
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CBR access delay of PRMA/DA and PRMA/FA
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VBR cell transmission delay of PRMA/DA and PRMA/FA