1.
Both
frequency and time-division multiplexing would have been inefficient for the
application because of the unpredictable nature of communications. Both types
of multiplexing are made to handle separate channels, but even so, it might not
provide enough channels for the data requested.
2.
If
there were thousands of remote stations, instead of the few that truly exist,
polling would not be a feasible option. The time that it takes to poll each
station and check to see if that station has a request to make it too lengthy
to go through thousands of stations.
3.
If
there we no obstacles between the remote stations and all of the stations could
hear each other’s communications, the CSMA/CD access control would definitely
improve the situation. The way that the CSMA/CD checks the station for idleness
and transmits only if the station is idle makes it feasible for a system where
communications are heard through all stations.
4.
If
the system was synchronized in time slots that were a little longer than the
maximum packet transmission time and no transmission could start except at the
beginning of a slot, the time is broken up and there are only certain times
that each transmission is allowed to transmit. By dividing up the time the
packets are transmitted in this way, there is less of a chance of overlapping,
or colliding, the packets.
5.
To
gain flexibility of Aloha random access while still using the channel
efficiently the channel should be split. Multiplexing provides for a
significant increase in the number of potential users. The book gives the
example of GSM using FDM to divide for mobile subscribers. Because the message
from a mobile subscriber announcing its presence it quite short and infrequent,
poor utilization of Aloha channels is not a problem. This might be the basis of
an option to utilize the channel more efficiently.