Distinguish between Pure ALOHA and Slotted ALOHA
Pure ALOHA
Pure ALOHA is an unslotted, fully-decentralized protocol. It is extremely easy and trivial
to execute. The basic form is - "when you want to talk, just talk!" So, a node that wants
to transmit will go ahead and send the packet on its communication channel, with no
consideration whatsoever as to whether anybody else is transmitting or not.
Slotted ALOHA
In the slotted ALOHA, stations are enabled to send frames in slots only. If longer than one
station transmits in a similar slot, it will generate a collision. This reduces the appearance
of collisions in the network system. Here, every station has to maintain the record of the
time slot. The process of transmission will be initiated by any station at the beginning of
the time slot only.
Comparison
The major differences between Pure ALOHA and Slotted ALOHA are as follows−
| Pure ALOHA | Slotted ALOHA |
|---|
| Pure ALOHA was introduced by Norman
and his associates at the University of
Hawaii in 1970. | Slotted ALOHA was introduced by Roberts
in 1972. |
| In pure ALOHA, whenever a station has
data to send, it transmits it without
waiting. | In slotted ALOHA, a user waits till the next
time slot begins to transmit the data. |
| The frames are transmitted at arbitrary
times. | The time is divided up into discrete slots,
and the frame is sent at the start of the
slot. |
| The performance is given by S = Ge−2G | The performance is given by S = Ge−G |
| Due to the very low utilization factor, it
cannot be used for satellites. | It is used in broadcast satellites. |
| It does not require global time. | It requires global time synchronization, as
it is divided up into discrete slots. |
| The maximum utilization is about 18%. | The maximum utilization is about double
that of Pure ALOHA, i.e., 37%. |
| The implementation is very simple. | The implementation is complex due to the
synchronization of all the stations. |
Published on 05-May-2021 10:50:40
