> From: sip-implementors On Behalf Of Brez Borland [[email protected]]
> 
>    sip:alice;[email protected]
> 
>    The last sample URI above has a user field value of
> "alice;day=tuesday".  The escaping rules defined above allow a
> semicolon to appear unescaped in this field.  For the purposes of
> this protocol, the field is opaque.  The structure of that value is
> only useful to the SIP element responsible for the resource.
> 
> ==========================
> 
> The last URI example, I would treat "alice" as the hostname, and
> "[email protected]" as a parameter pair.

As others have pointed out, "@" may not appear in a uri-parameter, and
";" may appear in 'user' so the user must be "alice;day=tuesday".

> With the URI like "sip:alice;[email protected]", I would expect
> semicolon to be escaped in the user part, or the address to be enclosed in
> the angle brackets.

Be careful interpreting the syntax rules.  There are actually *3*
syntax contexts.  One context is where the text must be a URI, which
is also named "addr-spec", and never contains <...>.  One context is
where the text must be a "name-addr", which is a URI surrounded with
<...>, possibly preceeded by a display name and ofllowed by "field
parameters".  The third context may be followed by a comma admits
"addr-spec / name-addr", and can only be disambiguated by the rule at
the end of section 20:

   The Contact, From, and To header fields contain a URI.  If the URI
   contains a comma, question mark or semicolon, the URI MUST be
   enclosed in angle brackets (< and >).  Any URI parameters are
   contained within these brackets.  If the URI is not enclosed in angle
   brackets, any semicolon-delimited parameters are header-parameters,
   not URI parameters.

*As you've asked the question*, we are discussing URIs, and so <...>
is not admissible.  If this was the third context (e.g., in many SIP
headers), then <...> would be requires to "protect" the semicolon in
the URI.

Dale

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