The ToS/DSCP Configuration window allows you to configure a ToS (Type of Service) or DSCP (Diffserv Codepoint) value to automatically generate 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.
ToS/DSCP Rewrite
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 ToS section of the Create Class of Service window or 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 General tab.
| 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. |
|---|
Click the graphic for more information.
- 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 one of the Value fields to generate a DSCP hexadecimal value.
- Well-Known 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.
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