SIP registration
Flows
42 ladders with a moving packet. Reduced motion keeps every step visible in the SVG.
Basic INVITE
Early offer
Delayed offer
Early media and PRACK
Hold
Blind transfer
Attended transfer
Session refresh
OPTIONS keepalive
CUBE two legs
Dial-peer hunt
SRST fallback
CSS search order
Route list
Called-party transform
SIP trunk OPTIONS
Traversal zone
MRA registration
QoS trust
One-way audio
SRTP with SDES
Fax re-INVITE
Ad-hoc conference
Call park
Single number reach
No answer to voicemail
Emergency callback identity
UCCE comprehensive path
Queue until an agent
CUCM and UCCE
Local gateway call
Dual-run one number
Survivability gateway
Shared line
Hunt pilot
Emergency call and PSAP callback
Phone on a switch CER does not know
Phone built-in bridge fork
CUBE as a recording client
SIP trunk to another PBX
Browser media across a gateway
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 3550, RTP last checked 2026-10
- RFC. RFC 4566, SDP last checked 2026-10
- RFC. RFC 3711, SRTP last checked 2026-10
- Cisco. Cisco Unified Communications Manager product support last checked 2026-10
- Cisco. System Configuration Guide for CUCM, Release 15 last checked 2026-10
- Cisco. Cisco Collaboration Preferred Architectures last checked 2026-10
- Cisco. Preferred Architecture for Cisco Collaboration 15, design overview (PDF) last checked 2026-10
- Cisco. Cisco Unified Border Element product support last checked 2026-10
- Protocol and ports. CUCM 15 TCP and UDP port usage last checked 2026-10
- Protocol and ports. Cisco Expressway IP port usage (X14.3 and X15.0) last checked 2026-10
- Protocol and ports. Port reference for Webex Calling last checked 2026-10
- Protocol and ports. IANA SIP parameters last checked 2026-10
- Protocol and ports. IANA RTP parameters last checked 2026-10
- Protocol and ports. IANA service names and port numbers last checked 2026-10
- Community. Cisco Community, Collaboration knowledge base last checked 2026-10
- Wikipedia. Session Initiation Protocol (Wikipedia) last checked 2026-10
- Wikipedia. Real-time Transport Protocol (Wikipedia) last checked 2026-10
- Wikipedia. Session Description Protocol (Wikipedia) last checked 2026-10
- Wikipedia. Voice over IP (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
- Cisco. Enterprise QoS SRND book. confirm. The Enterprise QoS SRND path returned HTTP 404. last checked 2026-10
- Wikipedia. English Wikipedia article for Cisco Unified Communications Manager. confirm. That title returned HTTP 404. The CUCM disambiguation page is the Wikipedia page that opened. last checked 2026-10