Michael Procter wrote:
Some SIP servers implement special features using special character, such as sipphone.com, dial "*0" to know if your ATA is behind a NAT router.
In an interoperability test. One of the the server failed to interoperate with ATA. We find it's because the contact field in the 200 OK message (Contact: *30 <sip: [EMAIL PROTECTED]:5080> ). Since there is the special character *, the "*" in "contact" header has some special meanning in some SIP messages .
Looking in RFC3261 section 25 shows that this contact header is valid, so should be parseable by the receiver. RFC3261 also permits a Contact header consisting of only a *. But section 10.2.2 includes the phrase:
The REGISTER-specific Contact header field value of "*" [...]
Which suggests to me that 'Contact: *' only has meaning inside a REGISTER transaction. Indeed, there are no semantics defined for this in other transactions that I can find.
You should also note that the special case for * exists when it is the only item on the header line, not when it simply prefixes other items.
The "*" used in register is syntactically distinct from all of the use cases discussed here. It takes the place of the entire url in the contact - there is no sip: or tel:. So it is irrelevant to this discussion.
Paul
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