Scaling API-first – The story of a global engineering organization
Demand Assigned Multiple Access
1. INTERNATIONAL INSTITUTE OF PROFESSIONAL STUDIES DAVV INDORE
Mobile and Wireless Computing
Internal Test III
Name - Anushka Shastri
Roll No - IT-2K17-09
Batch - MTech 2k17
Semester - VIII
Guided By - Ms. Manju Sachdeo Ma'am
Date - 24/05/2021
3. Multiple Access:
We do multiple access to enable satellite to
take or give signals from different stations at
time without any interference between them.
4.
5. Multiple Access
Sometimes a satellite’s service
is present at a particular location
on the earth station and
sometimes it is not present. That
means, a satellite may have
different service stations of its
own located at different places
on the earth. They send carrier
signal for the satellite.
In this situation, we do multiple
access to enable satellite to take
or give signals from different
stations at time without any
interference between them.
FDMA
(Frequency Division Multiple Access)
TDMA
(Time Division Multiple Access)
CDMA
(Code Division Multiple Access)
6. What is DAMA ?
● Full form - Demand Assigned Multiple Access
● Channel Allocation Technique
● There are two channel allocation techniques -
○ PAMA - Permanent Assigned Multiple Access
○ DAMA - Demand Assigned Multiple Access
7.
8. DAMA
DAMA is a technique used to
assign satellite channels to on
an as request basis.
The most multiple-access
systems use DAMA in which
the available channels are
allocated on an as required
basis to users.
9. DAMA
Demand Assigned Multiple Access (DAMA) is a technology used
to assign a 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 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.
10. How DAMA works ?
● Demand access systems require two types of a channel:
○ a common signaling channel (CSC) and
○ a communication channel.
● A user wishing to enter the communication network
○ first calls the controlling earth station using the CSC,
○ and the controller then allocates a pair of channels to that user.
● The CSC are located at the ends of the transponder bandwidth.
● When earth station wants to access the satellite, it transmits a control packet to satellite
on the CSC Frequency & waits for a reply.
11. How DAMA works ?
● The control packet is received by the hub earth station
and decoded.
● The control packet contains source address & destination
address also it includes cyclic redundancy check (CRC).
● The control station measures duration of the connection.
12. Advantages of DAMA
Prior
Reservation
A sender reserves
a future time-slot
Increased
Efficiency
Less
Collision
Reservation can
increase
efficiency to 80%
Sending within this
reserved time-slot is
possible without
collision
14. Access method DAMA: Explicit Reservation
● Two modes:
○ ALOHA mode for reservation:
■ competition for small reservation slots, collisions possible
○ reserved mode for data transmission within successful
reserved slots (no collisions possible)
It is important for all stations to keep the reservation list consistent at
any point in time and, therefore, all stations have to synchronize from
time to time.
16. PRMA
Packet Reservation
Multiple Access
● a certain number of slots form a
frame
● frames are repeated
● stations compete for empty slots
according to the slotted aloha
principle
● once a station reserves a slot
successfully, this slot is
automatically assigned to this
station in all following frames as
long as the station has data to
send
● competition for this slots starts
again as soon as the slot was
empty in the last frame
18. Reservation-TDMA
every frame
consists of N
mini-slots and x
data-slots
every station has
its own mini-slot
and can reserve
up to k data-slots
using this mini-
slot (i.e. x = N *
k).
other stations can
send data in
unused data-slots
according to a
round-robin
sending scheme
(best-effort
traffic)
19.
20. Uses of DAMA
Military for satellite
communications
(SATCOM)
Remote location Internet
access and mobile
maritime communications.
VSAT systems for point of
sale (POS) transactions
such as credit card, polling
or radio frequency
identification
21. How DAMA differs from Multiplexing?
Multiplexing
Divides a single
communication channel
into multiple channels
DAMA
Assigns a pair of
frequencies to a user
terminal
Multiplexing
Technical
process
DAMA
Administrative
process
22. Conclusion
DAMA assigns a pair of
frequencies to a user
terminal.
Then, the frequencies
are returned to a list, or
central pool, of
frequencies available to
other terminal users.
The number of transient
clients that use DAMA
network terminals
increases according to
efficient user
sequencing at specific
frequencies and
different timeslots.
Thus, DAMA is used
for infrequently-
used networks.
DAMA does not
require continuous
connection from
user terminals to a
network control
system.
