Allied Telesis AT-S62 - Manual (Page 237)

AT-S62 Management Software Menus Interface User’s Guide
Section II: Advanced Operations 237
Observe the following guidelines when using this variable:
ˆ This variable must be left blank or set to IP when setting a Layer3 or
Layer 4 variable.
ˆ To specify a protocol by its number, you can enter the value in decimal
or hexadecimal format. If you choose hexadecimal, precede the
number with the prefix “0x”.
IP ToS (Type of Service) (Layer 3)
Type of Service (ToS) is a standard field in IP packets. It is used by
applications to indicate the priority and Quality of Service for a frame. The
range of the value is 0 to 7. The location of the field is shown in Figure 66.
Figure 66. ToS field in an IP Header
Observe these guidelines when using this criterion:
ˆ The Protocol variable must be left blank or set to IP.
ˆ You cannot specify both an IP ToS value and an IP DSCP value in the
same classifier.
IP DSCP (DiffServ Code Point) (ToS) (Layer 3)
The Differentiated Services Code Point (DSCP) tag indicates the class of
service to which packets belong. The DSCP value is written into the TOS
field of the IP header, as shown in Figure 66 on page 237. Routers within
the network use this DSCP value to classify packets, and assign QoS
appropriately. When a packet leaves the DiffServ domain, the DSCP value
can be replaced with a value appropriate for the next DiffServ domain.The
range of the value is 0 to 63.
0
ver IHL
0
3 7
ToS total length
15 31
. . .
1 2 3 4 5 6 7
DSCP value
Precedence