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Roles a trace is actually showing

A trace shows a user agent, a proxy, a registrar, a redirect server, or a B2BUA, and products often combine those roles.

Learn in 5 minutes

  1. Separate UAC and UAS from the box name
  2. Predict what a redirect server leaves behind
  3. Recognize a B2BUA by the second dialog

Visual

Redirect steps out, proxy stays · study drawing · cyphermonkeylabs.com UARedirectProxyPeer INVITE 302 ACK INVITE 100 INVITE 200

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The location service is a database the proxy consults. It is not a request method.

Worked example

Who is still on the ladder? After the ACK of the 302, which role is finished?

  1. Step through the 302 and its ACK.
  2. Start the second INVITE.
  3. Name the role that does not appear again.

Fault

The ladder is documented as a pure proxy, but the outgoing INVITE has a different Call-ID and a different From tag.

A proxy preserves Call-ID, From tag, and To tag. A new Call-ID means a new dialog created by a UAC inside a B2BUA.

Quiz

The UAC is


A redirect server


A stateful proxy


Registrar and proxy in RFC 3261 are


A strong sign of a B2BUA is


The location service


Ecosystem

Glossary, sister systems, and the integration seam for this room.

Workforce management WFM forecasts volume and builds schedules. It consumes contact-center events. It does not parse Via headers. When a forecast is wrong, the SIP symptom is usually queue delay and 480 or carrier congestion, not a broken dialog ID.

Glossary · Ecosystem map · Ports · Troubleshooting

Sources and go deeper