# A ladder you are allowed to draw

Study notes. Not vendor documentation and not legal advice.

- A ladder is a drawing of messages between named boxes.
- Draw a message only if a page you opened names that job.
- SIP can create, modify, and terminate a session. Registration is a separate function in RFC 3261.
- Early media, transfer, and conference methods are not copied here unless the section was read.
- Vendor call-flow posters were not opened.

Draw caller, SIP proxy, called party. Add one dashed RTP line that does not have to pass through the proxy. Title the drawing teaching sketch, not a packet capture.