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Q
Q Bit
The Q
bit is a bit in an X.25 packet that indicates whether or not a packet
contains control information or user data.
Quality of Service (QOS)
In
general quality of service is the measure of how well service is provided
to a subscriber of a service such as a telephone service or a computer
network service. In the context of the OSI reference model, the users of
the Transport Layer specify and quantify the quality of service required.
This is done by providing QOS parameters along with the request to
establish a communication channel.
The
QOS parameters support different levels of service based on the
requirements of an application. For example, an interactive application
used for inquiries to a text database might specify very high QOS parameter
values for connection establishment delay, throughput, transit delay, and
connection priority, to get good response time. While specifying a lower
QOS value for residual error rate/probability, because the impact of errors
on the user is relatively low (the user just requests a retransmission). A
file transfer application used to move updated data around a network at
night, on the other hand, can accept slower response, but must have reliable,
error free transfer of data, so correspondingly different values might be
specified.
Queuing
In the telephony
world, queuing is a feature that allows calls to be held or delayed at the
origination switch while waiting for a trunk to become available. In
computer processes, queuing refers to the storing of commands or operations
until the appropriate time.
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