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T3 · T3-R08 · Numbers and trunks

Two domains and a SIP trunk

Draw two clouds before you draw a price. Private is the PBX side. Public is the telephone network side. The trunk is the interconnection the article requires between them. Twilio and Telnyx are two providers whose trunk pages opened. Their field names are not the same.

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Counts on this page

4boxes
4opened sources
2confirm rows
5study lines

Opened sources

Confirm rows, no URL

Learn it in 5 minutes

  • Wikipedia says SIP trunking is how Internet telephony service providers deliver telephone services to customers with a SIP-based IP-PBX.
  • The article splits the network into a private domain, connected to a PBX or unified communications server, and a public domain, toward the PSTN or PLMN.
  • It says the interconnection between those domains must occur through a SIP trunk.
  • Twilio's Elastic SIP Trunking docs opened, including emergency calling, codecs, and calls per second as page names.
  • Telnyx's SIP trunking guide says inbound traffic and authentication use SIP connections, and outbound routing uses outbound voice profiles.

Visual

Two domains and a SIP trunk Trunk. Teaching sketch. Confirm a live system. Private Trunk Public PSTN Names come from pages opened in 2026-10. A missing name stays confirm.

Count the boxes: 4. Each label is a name from a page or a study label marked on the drawing.

Flow

Two domains and a SIP trunk Caller SIP Called session setup session setup RTP, not required to hairpin Teaching sketch from RFC 3261 and RFC 3550. Not a packet capture.

What is going on

Draw two clouds before you draw a price. Private is the PBX side. Public is the telephone network side. The trunk is the interconnection the article requires between them. Twilio and Telnyx are two providers whose trunk pages opened. Their field names are not the same.

Telnyx authenticates a SIP connection with credentials, an IP address, or an FQDN, and it names an anchorsite as the regional point of presence for media. A daily spend limit is a component on that page. The amount was not a number in the text that opened, so the cap stays confirm.

Worked example

Label a PBX as private and the PSTN as public. Put Twilio or Telnyx on the trunk, and write the authentication method only if you copied it from the Telnyx guide: credentials, IP address, or FQDN.

Quiz

1. The SIP trunking article says the private and public domains meet through a SIP trunk.

2. The Telnyx guide publishes a numeric daily spend cap in the overview that opened.

Ecosystem

Sister pieces sit on the ecosystem page: the glossary, the mind map, the integration map, and the bridges.

  • Private domain — The SIP trunking article's name for the part of the network connected to a PBX or unified communications server.
  • SIP connection — The Telnyx object for inbound traffic and authentication. Outbound voice profiles are the other object, for outbound routing.

Config. Write private, trunk, and public. Then write the provider's object name, not a generic one.

Troubleshooting. If inbound rings and outbound fails, Telnyx's split is the first check: connection versus outbound voice profile. Twilio's trunk page is a different menu.

Bridge. RFC 7092's back-to-back user agent is one way a platform can sit in the signaling path. A trunk is the service Wikipedia describes. Do not use the words as synonyms without saying which page you mean.

Mind map, sister technologies, and future hooks live on the ecosystem page.

Sources and go deeper

Opened 2026-10. A row marked confirm has no link, because that page was not verified.

sources.json Markdown