pub fn with_ob(contact: &str) -> StringExpand description
Add the ob URI parameter to a contact for a dialog-forming request (§4.3).
§4.3: a UA sending a dialog-forming request “MUST include the ‘ob’ parameter in its Contact header field” when it has no GRUU. It marks the contact as one that is only reachable back down this flow, so a mid-dialog request is sent over the flow rather than to the address — which, behind a NAT, is the difference between a re-INVITE arriving and vanishing.
ob is a URI parameter, so it goes inside the angle brackets, unlike reg-id.