More inefficiency is created when single messages are broken into separate frames because it makes the transmission longer.
[4] A method of flow control in which a receiver gives a transmitter permission to transmit data until a window is full.
[5] Sliding-window flow control is best utilized when the buffer size is limited and pre-established.
For example, in a wireless environment if data rates are low and noise level is very high, waiting for an acknowledgement for every packet that is transferred is not very feasible.
The value of N is usually chosen such that the time taken to transmit the N words is less than the round trip delay from transmitter to receiver and back again.
[6] Selective repeat is a connection oriented protocol in which both transmitter and receiver have a window of sequence numbers.
If this window becomes full, the protocol is blocked until an acknowledgement is received for the earliest outstanding message.
[7] This section is geared towards the idea of comparing stop-and-wait, sliding window with the subsets of go back N and selective repeat.
It is more convenient to calculate the average number of transmissions necessary to communicate a block, a quantity we denote by 0, and then to determine T from the equation
In this case, the controlling software in the modem and computer may be written to give priority to incoming radio signals such that outgoing data from the computer is paused by lowering CTS if the modem detects a reception.
The open-loop flow control mechanism is characterized by having no feedback between the receiver and the transmitter.
Open-loop flow control has inherent problems with maximizing the utilization of network resources.
An open-loop system has no feedback or feed forward mechanism, so the input and output signals are not directly related and there is increased traffic variability.
This information is then used by the transmitter in various ways to adapt its activity to existing network conditions.
The controller examines the information with respect to a desired value and initiates a correction action if required.
The controller then communicates to the regulator what action is needed to ensure that the output variable value is matching the desired value.
Therefore, there is a high degree of assurance that the output variable can be maintained at the desired level.
The feed-back mechanism monitors the output variable and determines if additional correction is required.
The output variable value that is fed backward is used to initiate that corrective action on a regulator.
The closed-loop model produces lower loss rate and queuing delays, as well as it results in congestion-responsive traffic.