Allied Telesis AT-S63 - Manual (Page 115)

AT-S63 Management Software Features Guide
Section II: Advanced Operations 115
Observe the following guidelines when using this variable:
ˆ When selecting a Layer 3 or Layer 4 variable, this variable must be left
blank or set to IP.
ˆ If you choose to specify a protocol by its number, you can enter the
value in decimal or hexadecimal format. If you choose the latter,
precede the number with the prefix “0x”.
ˆ The range for the protocol number is 1536 (0x600) to 65535 (0xFFFF).
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 5.
Figure 5. 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 5 on page 115. 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