[SIPForum-discussion] sending UA capabilities

[Ayyanar PK]

Hi all,This is regarding expressing sip capabilities. The aim is to make others know the capability of a SIP UA. I need to send my UA's capabilities in REGISTER's contact header. I went through the RFC3840 and I am not sure to understand the following passage from the RFC< From RFC38406 Expressing Capabilities in a Registration When a UA registers, it can choose to indicate a feature setassociated with a registered contact.Whether or not a UA does sodepends on what the registered URI represents.If the registered URIrepresents a UA instance (the common case in registrations), a UAcompliant to this specification SHOULD indicate a feature set usingthe mechanisms described here.If, however, the registered URIrepresents an addressofrecord, or some other resource that is notrepresentable by a single feature set, it SHOULD NOT include afeature set.As an example, if a user wishes to forward calls fromsip:user1 at example.com to sip:user2 at example.org, it could generate aregistration that
  looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:user1 at example.com Contact: sip:user2 at example.org In this case, the registered contact is not identifying a UA, butrather, another addressofrecord.In such a case, the registeredcontact would not indicate a feature set. From RFC 3840> My understanding of the above passage is that, since the Contact header has contact information about some other UA (i.e sip:user2 at example.org ) it is not recommended to add the feature tags to the Contact header of the REGISTER message. Is my understanding right?Can someone please clarify on what the above passage from the RFC is trying to convey?Regards,AyyanarDear discussion ! Get Yourself a cool, short @in.com Email ID now!
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