Allied Telesis AT-S63 - Manual (Page 255)

AT-S63 Management Software Menus Interface User’s Guide
Section II: Advanced Operations 255
ˆ When selecting a Layer3 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”.
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 81.
Figure 81. 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 81 on page 255. 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.
Observe these guidelines when using this criterion:
ˆ The Protocol variable must be left blank or set to IP.
0
ver IHL
0
3 7
ToS total length
15 31
. . .
1 2 3 4 5 6 7
DSCP value
Precedence