The ToS/DSCP Configuration window allows you to automatically configure a ToS
(Type of Service) or
DSCP (Diffserv Codepoint) value defined by a hexadecimal number between 0 and
FF. The ToS/DSCP field contained in the IP header of a frame is used by
applications to indicate the priority and Quality of Service for each frame.
(For an explanation of the ToS/DSCP field and the service parameters, see IP
Type of Service.)
In Policy Manager, you can configure a ToS/DSCP value in two different
situations, as follows:
IP Type of Service Classification
An IP Type of Service classification rule causes the one-byte ToS/DSCP
field in the IP header of incoming packets to be read. If a value is
found in this field and it matches the ToS/DSCP value specified in the
classification rule, the packet is classified accordingly. You can access the
ToS/DSCP Configuration window during the creation
of the classification rule by clicking the Select button in the Rule
Wizard's or Traffic Description
Wizard's IP Type of Service window.
Some IP rules allow a ToS/DSCP value to be
written to the ToS/DSCP field in the IP header of incoming packets. If the packet's
ToS/DSCP
field is blank, the value specified in the rule is entered, or if the value
is already present, it is replaced with the new value. The traffic is then
classified accordingly. In Policy Manager, you specify the ToS/DSCP rewrite value by creating a
CoS (class of service)
and associating the appropriate ToS/DSCP value with it. You then select
this CoS action for the classification rule. You can access the ToS/DSCP Configuration window during the creation
of the class of service by clicking the Select button in the Enable ToS
area of the Class of Service General tab. You
then select this CoS action for the classification rule in the Rule
Wizard or on the rule's Actions tab.
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NOTE: |
The ToS/DSCP Rewrite feature works only for the appropriate
classification rules. It does not work at the role level. If you select a CoS
that is associated with a ToS/DSCP value as the default CoS for a role, the ToS/DSCP
value will be ignored.
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Click the graphic for more information.
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- Type of Service (ToS)
- Select this option to generate a ToS hexadecimal value. Type of Service
is used by applications to indicate priority and Quality of Service for
each frame.
- Precedence
- Use the drop-down list to select the desired precedence. Precedence
specifies the importance or priority of the traffic.
0 -- Routine
1 -- Priority
2 -- Immediate
3 -- Flash
4 -- Flash Override
5 -- CRITIC/ECP
6 -- Internetwork Control
7 -- Network Control
The Internetwork Control designation is
intended for use by gateway originators only. The Network Control precedence designation is intended to be used within a network only. The actual
use and control of that designation is up to each network.
- Delay Sensitive
- Select this check box to generate a Low Delay service parameter that
will minimize delay.
- High Throughput
- Select this check box to generate a High Throughput service parameter
that will maximize throughput.
- High Reliability
- Select this check box to generate a High Reliability service parameter
that will maximize reliability.
- Explicit Congestion Notification
- Select this check box to generate an Explicit Congestion Notification service
parameter that will minimize monetary cost.
- Diffserv Codepoint (DSCP)
- Select this option and use the Value drop-down list to generate a DSCP hexadecimal value.
- Value
- The drop-down list presents recommended codepoints
for three Differentiated Services (DS) Per-Hop-Behavior (PHB) groups
called Assured Forwarding (AF), Class-Selector (CS), and Expedited
Forwarding (EF). For more
information on these PHB groups, refer to RFC 2474, RFC 2597 and RFC 2598.
For information on related concepts:
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