[sr-dev] outbound rfc question

[Juha Heinanen]

in section 4.3. Sending Non-REGISTER Requests of outbound rfc 5626:

   If the UAC is using a Globally
   Routable UA URI (GRUU) [RFC5627] that was instantiated using a
   Contact header field value that included an "ob" parameter, the UAC
   sends the request over the flow used for registration, and subsequent
   requests will arrive over that same flow.

what does 'that was instantiated using a Contact header field value that
included an "ob" parameter' mean?  which request the referred Contact
header belongs to?

-- juha