Subject: [Sip] Priority request-header values

From: [email-masked]
Date: Tue, 23 Oct 2001 15:48:26 EDT

To all,

The current 2543bis defines the Priority request-header field as follows:

Priority = "Priority" ":" priority-value
Priority-value = "emergency" | "urgent" | "normal" | "non-urgent" | 
other-priority
other-priority = token

(It isn't explained what "other-priority=token" means, but I suppose those 
deeply involved in the protocol understand this.)

I find no explicit statement about the ordering of these values, although one 
might infer the order from the meaning of the (English) words. But I really 
can't decide the relationship between "routine" and "non-urgent". They sound 
synonomous to me.

This does not satisfy the requirement of the US military networks for 
possible use of SIP for mission critical traffic. The requirement for the US 
military, based on long-standing national and international 
telecommunications standards, is for five levels of precedence, namely: 
"Flash Override", "Flash", "Immediate", "Priority", and "Routine" (in 
English). Of course, other countires which use the same standard might use 
different words to represent the levels (to a human).

The machine, and the network elements, do not need to know or deal with these 
English words. They only need to know the relationship between the values.

We require the definition of a field to carry the precedence (often called 
priority) level in the form of a number from 0-4, with an explicit definition 
that 0 is the highest priority. Its association with the local language or 
the words used for the specific network is not a matter for the standard. The 
preferable solution would be to define a 4 bit field and assign 5 values, 
exactly as is defined in draft-ietf-mpls-cr-ldp-05 of March 2001.

Since it is probable that most would not agree to changing the present 
(RFC2543) definitions, it would then seem appropriate to make the change in 
2543bis to add five new values to the current four, as follows:

"level0" | "level1" | "level2" | "level3" | "level4"

and to add the following statement:

When the values "level0" through "level4" are used, they must be interpreted 
as an ordered set such that level0 > level1 > level2 > level3 > level4 (in 
relation to their treatment to prioritize call handling operations). No 
explicit ordering of "emergency", "urgent", "normal", and "non-urgent" or 
their relation to level0 through level4 is defined.

This constant use of specific English words rather than numeric values is 
causing the protocol and its processing to become less efficient and is 
leading to complications in the definition, as in the recent spate of e-mails 
regarding the meaning of the ANI-II digits. It is also causing difficulties 
in attempts to internationalize (or rather de-Americanize) the definitions of 
the Internet Protocol. I think it is time for a major change in the approach 
being used to define such protocols.

Mike Pierce

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