Signaling agrees the session
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Diagram atlas
142 custom SVGs. 140 use a moving packet. Count each file once.
Drawings
OPTIONS across two transports
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user=phone, then a redirect
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Each arrow has a chapter
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The map names the document
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The m= line is not a license
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Walk the first transaction
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Redirect steps out, proxy stays
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Busy is final
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Compact request, long response
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Retransmit, then a new ACK branch
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Early, then confirmed, then BYE
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Retransmit until 100, then wait
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UDP in, TCP out
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Hop-by-hop ACK of a 603
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Two proxies stay on the dialog
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183, then PRACK
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Answer the INVITE, then UPDATE
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422, then a longer interval
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CANCEL, then 487
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REFER with Replaces
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Challenge, then a binding
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SIP after the lookup
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BYE with two loose routes
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Two flows, one instance
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Learn both vectors, then call
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Register a GRUU, then invite it
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Two early dialogs
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SDP rides inside the INVITE
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Two streams, one refused
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96 and 111 are both opus
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re-INVITE to sendonly
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Second stream refused
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183 with SDP, then 180 without it
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Delayed offer, then the ACK answer
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SIP finishes, then RTP starts
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Static types need no guess
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Pick a shared name
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Reports follow the answer
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Digits in RTP, named in SDP
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ptime sits in the offer
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Answer says sendonly
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407 first, then a 401
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INVITE over TLS
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Two legs, two methods
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PAI stops at the edge
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No Identity header, no STIR result
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A REGISTER that should have been challenged
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Policy on one INVITE
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Offer with a documentation address
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Response follows the source port
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Binding request, then a SIP offer
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Allocate, then media via the relay
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Gather, offer, check, nominate
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UDP rewritten, TLS not rewritten
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First packet, not c=
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Requirements do not change the ladder
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Two Call-IDs for one conversation
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Hide the caller address
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Anchored answer SDP
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OPTIONS before the next INVITE
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INVITE refused at the budget
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The standby is not a SIP hop
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CUBE between the phone and the carrier
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session target becomes the Request-URI host
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Diversion present, then removed on the copy you test
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Delayed inbound, early outbound
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CUCM trunk to CUBE
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CUCM forwards to the Unity SIP peer
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The messages the debug is showing
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Two sides of one Oracle SBC
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Server removed on the way out
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SIP still looks like SIP on either family
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Remove Server toward the carrier
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One header, removed only by the grammar that is loaded
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PAI arrives from the carrier
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TLS INVITE with an FQDN Contact
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INVITE to the primary proxy
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Healthy OPTIONS, then a call
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TLS and SRTP toward the Webex peer
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This ladder is premises-based PSTN only
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SIPREC toward the analytics connector
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Request-URI matches the termination URI
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BYOC Cloud signaling in the synthetic
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Match this dialog, then the 2xx ACK
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CANCEL, then 487
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A capture of one answered call
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Synthetic ccsip, then the response
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422, then a taller session interval
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OPTIONS to Teams after TLS
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Each hop has a document
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An intended path among lab addresses
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Listed sources only
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Synthetic emergency request
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Fork to a disclosed SRS
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SIP sets up the call. EF applies to the voice.
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OPTIONS, then 503
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Baseline OPTIONS, then one INVITE
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Roles on a single call
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The ladder stays SIP
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Assistance is not a hop
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The call the exams still expect you to read
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Which page owns the hop
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PSTN lands on CUBE, then CUCM
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Premises PSTN through Local Gateway
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The ladder the interview is about
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A 488, named correctly
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Two legs, two Call-IDs possible
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Silence after a completed ladder
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Checklist mapped onto one call
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CUCM to CUBE to Teams
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Which number is on which hop
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The application picks SIP. The socket is only the transport.
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Register on WSS, with the example's .invalid host
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Gather, then signal the result in SDP
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SIP offers the description. DTLS keys the packets.
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Browser softphone, study sequence
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SIP hits Kamailio. Media can be anchored in rtpengine.
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A phone registers to Asterisk. The dialplan is a separate file.
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SIP profile accepts the call. The dialplan routes it.
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Edge proxy in front of a PBX
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SIP on Kamailio, RTP toward rtpengine
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A successful call is not a compliance result
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Identity is a header on the INVITE, not a second call
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An emergency study call still needs location, not just SIP
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Two paths. Do not merge them in one ladder.
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Four checks, one call trace
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From a word to a document
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The session completes. A neighbor hears an event.
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Decide the plane, then the page
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CUCM trunk toward an open SIP server
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A control event is not the SIP call
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User agent, proxy, registrar
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Offer then answer
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Signaling beside media
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ICE candidate checklist
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SBC as a back-to-back user agent
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STIR identity on the INVITE
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Troubleshooting tree
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Trunk cutover
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Browser media and a SIP trunk
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Emergency call path, protocol level
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Sources and go deeper
- RFC 3261 — last checked 2026-10