2. Demand Assigned Multiple Access
• Demand Assigned Multiple Access (DAMA) is a name for a
central allocation of network resources. it is an operation process
that lies above multiple access processes, because it is an
administrative, not a technical function.
•Demand Assigned Multiple Access (DAMA) is a name for a
central allocation of network resources. DAMA is one of the two
main techniques for allocating channels to users.
• The most multiple-access systems use DAMA in which the
available channels are allocated on an as required basis to users.
• DAMA is a technique used to assign satellite channels to on an as
request basis.
3. Demand Assigned Multiple Access (DAMA) is a
technology used to assign a channel to clients that don't
need to use it constantly. DAMA systems assign
communication channels based on news issued from user
terminals to a network security system.
Channels are typically a pair of carrier frequencies (one
for transmit and one for receive), but can be other fixed
bandwidth resources such as timeslots in a TDMA burst
plan or even physical party line channels.
Once a channel is allocated to a given pair of nodes, it is
not available to other users in the network until their
session is finished.
4. A. Packet Reservation Multiple Access (PRMA)
refers to a multiple access strategy with frames of
a fixed number of slots.
B. In case a terminal contains a set of data packets or
speech segments to deliver, it competes to gain
access in any free slot.
C. In PRMA, adjacent cells make use of distinct
carrier frequencies in line with a cellular reuse
plan. The fundamental process of PRMA includes
occupying a time slot only at the time of speech
talkspurts and releasing the channel at the time of
silence periods.
5. PRMA facts:
TDMA with slotted ALOHA reservation system
Source rates are 32 kbit/sec
Frame Duration is 16 msec ( 62.5 frames/sec)
20 slots per frame
Channel bit rate is 720 kbit/sec and bandwidth is 720
khz
576 bits per slot (contains 64 bit overhead)
Packet dropping rate is 1%
Supports data and voice
6. Medium Access Control (MAC) Protocols
The role of the MAC protocol [1] is to determine when
a node is allowed to transmit its packets. It typically
controls all access to the medium.
Wireless MAC protocols have been studied extensively
since the 1970s. The initial protocols were developed for
data and satellite communications.
The two major objectives of a multiple access protocol
are maximization of the channel capacity utilization and
minimization of latency between a station deciding to
transmit and able to transmit.
7. High throughput- A high network throughput, or high efficiency, is
achieved when the protocol has low overhead and low collision probability.
It is also equivalent to low frame delay.
Scalability- The network throughput should be unaffected by increases in
number of nodes. Naturally, the per-node throughput decreases as the
number of active nodes increases but ideally, this should follow a linear
decrease.
Topology independence- The network throughput should be transparent to
network topology changes. In high mobility scenarios, where the rate of
nodes joining and leaving the network is high, as well as node velocity, the
protocol should be able to maintain a high network throughput.
Fairness- The protocol should not give priority to particular nodes over the
others.
Quality of Service (QoS) - When multiple traffic classes are defined, the
protocol should be able to manage the bandwidth resources in order to
assign different priorities to real-time and besteffort nodes.
9. CDMA/PRMA
Joint Code Division Multiple Access Packet
Reservation Multiple Access (CDMA/PRMA)
protocol was introduced as a candidate for an
uplink protocol for third generation mobile
communication.
Packet CDMA the time axis is unslotted and
packets are granted random access to the
channel, in Joint CDMA/PRMA the time axis
is slotted, with the slots grouped into frames
(as in PRMA) and the access of packets to the
channel
