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Outbound, reg-id, and keepalives

RFC 5626 binds a UA instance to one or more flows with reg-id and +sip.instance, and keepalives hold those flows open.

Learn in 5 minutes

  1. Read reg-id and +sip.instance on Contact
  2. Tell a second flow from a refresh of the first
  3. Name the keepalive used on TCP and on UDP

Visual

Two flows, one instance · study drawing · cyphermonkeylabs.com UAEdge REGISTER 200 REGISTER 200

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The instance URN stays. reg-id changes when the flow changes.

Worked example

Count the flows Dissect the second 200 OK. Two Contact headers share an instance and differ by reg-id.

  1. Dissect the 200.
  2. Compare +sip.instance on each Contact.
  3. Compare reg-id.

Fault

The UA registers reg-id 2 for redundancy. The registrar drops reg-id 1. An outage on the second path leaves the UA unreachable.

A refresh reuses reg-id. A new reg-id is an additional flow.

Quiz

reg-id identifies


+sip.instance is


Same instance and a new reg-id means


The TCP keepalive in RFC 5626 is


Outbound is specified in


A later request to the UA is sent


Ecosystem

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

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Glossary · Ecosystem map · Ports · Troubleshooting

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