Assigning precedence values will ideally occur by loose consensus within the Internet community. We do not advocate tying a precedence value directly to an application type (or TCP port), or more abstract qualifiers that lack scalability in the global infrastructure, but rather to the qualities of the individual flow, as judged by the user and system administrators of the end systems.
Because the IP Precedence field is largely unused at this time, most packets today contain a default value of zero. Packets with this zero value would receive lowest priority, whether they have that value because they are not participating in the scheme or because they choose the lowest priority. The default priority for bulk traffic would be 1. We propose discouraging use of the highest precedence value, 7, reserving it for traffic surrounding issues of network management, routing or other traffic considered critical.
Software developers should set default priority levels for the IP precedence field as they develop and distribute their applications, based on some general guidelines. Users of the applications would then be able to modify the priority, either on a per session basis or permanently. Criteria to modulate priorities could include:
One could use this
table to easily classify more than 35% of traffic as low priority.
Although one could simply have the routers
assign priorities according to Table 1,
we do not advocate a situation where a
network owner would dictate what traffic
travels on its network.
Developers and users will implement use of the precedence field only as they so desire. As described earlier, the current default setting for IP Precedence is typically 0, which is the lowest priority defined in the IP specification. If users encounter no problems with their priority 0 traffic, they will see no reason to change. End users who want better service will be able to obtain new versions of applications that default to a higher IP Precedence value, and perhaps allow the end user to modify the value further.
Table 1: Example stratification of
traffic into precedence levels
Obviously, skilled system users will be able to rewrite or override the priority set to any value by their applications. In the future, however, most users of Internet will not have the necessary expertise to do this themselves. Moreover in some cases (such as netnews) the application operator will have little or no incentive to cheat by assigning their own outgoing packets a higher priority. We will discuss more elaborate methods of fostering compliance with priority guidelines in Section 3.3.