Hey folks,
I've been looking into caller preferences and callee capabilities, and more
specifically the "Priority" feature tag and how it should be
encoded/interpreted.
The definition according to RFC3840 says:
Summary of the media feature indicated by this tag: The sip.priority
feature tag indicates the call priorities the device is willing to
handle. A value of X means that the device is willing to take
requests with priority X and higher. This does not imply that a
phone has to reject calls of lower priority. As always, the
decision on handling of such calls is a matter of local policy.
Values appropriate for use with this feature tag: An integer. Each
integral value corresponds to one of the possible values of the
Priority header field as specified in SIP [1].
At the same time, the BNF, indicates possible "data-types" as:
feature-param = enc-feature-tag [EQUAL LDQUOT (tag-value-list
/ string-value ) RDQUOT]
enc-feature-tag = base-tags / other-tags
base-tags = "audio" / "automata" /
"class" / "duplex" / "data" /
"control" / "mobility" / "description" /
"events" / "priority" / "methods" /
"schemes" / "application" / "video" /
"language" / "type" / "isfocus" /
"actor" / "text" / "extensions"
tag-value-list = tag-value *("," tag-value)
tag-value = ["!"] (token-nobang / boolean / numeric)
token-nobang = 1*(alphanum / "-" / "." / "%" / "*"
/ "_" / "+" / "`" / "'" / "~" )
boolean = "TRUE" / "FALSE"
numeric = "#" numeric-relation number
numeric-relation = ">=" / "<=" / "=" / (number ":")
number = [ "+" / "-" ] 1*DIGIT ["." 0*DIGIT]
The ambiguity I am trying to resolve, is that "values appropriate" says
*integer*, which would at first glance tell me to use the "numeric" construct
for tag-value. This would give me the possibility to use values such as
;priority="#<=10" or similar for describing intervals/ranges of priority.
But that collides with the summary description which says: "A value of X
means....priority X and higher"...which would make the ">=;<=;=" operators
redundant.
At the same time, RFC3841 indicates that the matching process:
The matching
rules in RFC 2533 only require an implementation to know whether the
feature tag is a numeric, token, or quoted string (booleans can be
treated as tokens).
Where the presence of param="#" indicates numeric. Without the "#",
;priority="10" becomes a token, and would be compared case-insensitive.
"Priority X and higher" indicates numeric analysis, wheras token comparison
does not.
So, which is it?
How is everyone else interpreting this?
Regards
Taisto Qvist
IP-Solutions.se
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