Patton electronic SmartNode 4110 Series manual Specifying the precedence field

SmartWare Software Configuration Guide 13 • Link scheduler configuration

The type-of-service (TOS) byte in an IP header specifies precedence (priority) and type of service (RFC791, RFC1349). The precedence field is defined by the first three bits and supports eight levels of priority. The next four bits—which are set by the set ip tos command—determine the type-of-service (TOS).

		Table 5. TOS values and their meaning
TOS Value	SmartWare Value	Meaning
1000	8	Minimize delay.
0100	4	Maximize throughput.
0010	2	Maximizes reliability.
0001	1	Minimize monetary costs.
0000	0	All bits are cleared, normal service, “default TOS.”

Historically those bits had distinct meanings but since they were never consistently applied routers will ignore them by default. Nevertheless you can configure your routers to handle specific TOS values and SmartWare allows you to inspect the TOS value in the ACL rules and to modify the TOS value with the link scheduler set ip tos command.

Mode: Source

Command	Purpose
node(src)[name]#set ip tos value	Defines the type-of-service (TOS) value applied to packets of for the
	selected class or policy name. Standard ToT values are 0, 1, 2, 4,
	and 8, as given in table 5 on page 163, but any number from 0 to
	15 can be configured.

Specifying the precedence field

The set ip precedence command specifies the precedence marking applied to packets of the class name. Pre- cedence and DSCP markings cannot be used at the same time.

The type-of-service (TOS) byte in an IP header specifies precedence (priority) and type of service (RFC791, RFC1349). The precedence field is defined by the first three bits and supports eight levels of priority. The low- est priority is assigned to 0 and the highest priority is 7.

The no form of this command disables precedence marking.

Mode: Source

Command	Purpose
node(src)[name]#set ip precedence value	Defines the precedence marking value applied to pack-
	ets of for the selected class or policy name. The range
	for value is from 0 to 7, but only values from 0 to 5
	should be used.

Specifying differentiated services codepoint (DSCP) marking

Differentiated services enhancements to the Internet protocol are intended to enable the handling of “traffic- classes” throughout the Internet. In this context the IP header TOS field is interpreted as something like a

Link scheduler configuration task list 163