Cheat code
Call-flow cheat sheet
- REGISTER, 401, REGISTER, 200. No media.
- INVITE, 100 from each hop, 180, 200, ACK. RTP can skip the proxy.
- Hold is a re-INVITE with sendonly or inactive, then the matching answer.
- Blind REFER gets 202. 202 is not answer. Read NOTIFY.
- Early media is 183 with SDP, not a confirmed dialog.
Source: RFC 3261. Ladder pages in this lab expand each line.
Sources and go deeper
Opened 2026-10. A row marked confirm has no link, because that page was not verified.
- RFC. RFC 3261, SIP last checked 2026-10
- RFC. RFC 3264, offer/answer last checked 2026-10
- RFC. RFC 3515, SIP REFER last checked 2026-10
- RFC. RFC 3550, RTP last checked 2026-10
- RFC. RFC 4566, SDP last checked 2026-10
- Protocol and ports. CUCM 15 TCP and UDP port usage last checked 2026-10
- Protocol and ports. IANA SIP parameters last checked 2026-10
- Community. Cisco Community, Collaboration knowledge base last checked 2026-10
- Wikipedia. Session Initiation Protocol (Wikipedia) last checked 2026-10
- Cisco. Collaboration 12 SRND book. confirm. The historical Collaboration 12 SRND path opened as a product listing, not the design book. Use the Preferred Architecture index, which was opened. last checked 2026-10