VoIP: fundamentals of SIP and related topics — part #2: the basic SIP headers

Thanks to undraw.co

Here we are with the third appointment with the mini-series about VoIP.
You can find the last here:

VoIP: fundamentals of SIP and related topics — part #1 basic concepts of SIP

In this episode I’ll talk about the basic SIP headers:

1. Request-URI
2. From & To
3. Call-ID
4. Via & Contact
5. Record-route & Route
6. P-Asserted-Identity Remote-Party-ID e P-Preferred-Identity

Request-URI

The Request-URI indicates the URI (the address) of the UAS to which the packet is to be sent.

The initial Request-URI (of an INVITE not in dialog) must be equal to the URI present in the To field (except for REGISTERS).

How to write a R-URI? The Request-URI of requests in dialog must follow this rule:

• if there are NO Record-Route header, the Request-URI must be equal to the URI present in the Contact of the response.