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QoS or Quality of service is the most important factor that
determines how effectively the available enterprise bandwidth is being
used in the WAN. It is also an index of the overall User Experience of
the available Bandwidth.
DSCP
The DSCP Groups can be viewed by clicking on the View DSCP Group link. If no DSCP Groups have been created earlier, then an appropriate message is displayed and the user is prompted to create a DSCP group. The bottom of the page lists the Top DSCP IN Traffic as a Pie Distribution.
The time period for which the report is shown can be
controlled by using the time selection bar at the top.
TOS
Because the Internet by itself has no direct knowledge of optimizing the path for a particular application or user, the IP protocol provides a facility for upper layer protocols to convey hints to the Internet Layer about how the tradeoffs should be made for a particular packet. This facility is the "Type of Service" facility, abbreviated as the "TOS facility".
Specification of the TOS Field
The semantics of the TOS field values (expressed as binary
numbers):
1000 | minimize delay |
0100 | maximize throughput |
0010 | maximize reliability |
0001 | minimize monetary cost |
0000 | normal service |
The values used in the TOS field are referred to as "TOS values",
and the value of the TOS field of an IP packet is referred to as
the "requested TOS". The TOS field value 0000 is referred
to "default TOS." Because this specification redefines TOS values to be
integers rather than sets of bits, computing the logical OR of two TOS
values is no longer meaningful. For example, it would be a
serious error for a router to choose a low delay path for a
packet whose requested TOS was 1110 simply because the router
noted that the former "delay bit" was set.
Although the semantics of values other than the five listed above
are not defined , they are perfectly legal TOS values, and
hosts and routers must not preclude their use in any way. Only the
default TOS is in any way special. A host or router need not make any
distinction between TOS values
For example, setting the TOS field to 1000 (minimize delay) does
not guarantee that the path taken by the datagram will have a
delay that the user considers "low". The network will
attempt to choose the lowest delay path available, based on its
(often imperfect) information about path delay. The network
will not discard the datagram simply because it believes that the
delay of the available paths is "too high" (actually, the network
manager can override this behavior through creative use of
routing metrics, but this is strongly discouraged: setting the
TOS field is intended to give better service when it is
available, rather than to deny service when it is not).
Use of the TOS Field in Routing
The most important of all the inherent limitations is that the TOS facility is strictly an advisory mechanism. It is not an appropriate mechanism for requesting service guarantees.There are two reasons why this is so:
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