SIP trunks#
An inbound SIP trunk is a logical connection that delivers calls from DIDWW to a SIP endpoint, such as an IP PBX, session border controller (SBC), communications platform, or application server, using the Session Initiation Protocol (SIP). Use an inbound SIP trunk when calls to DID numbers on your DIDWW account must be delivered to a SIP endpoint. The trunk defines how DIDWW routes SIP signaling to the destination and provides settings for controlling signaling, media, and call handling.
How SIP trunks work#
When a caller dials a DID number, the public telephone network routes the call
to DIDWW. DIDWW uses the trunk assigned to the DID number to determine how the
call should be delivered. For an inbound SIP trunk, DIDWW determines the SIP
destination from the trunk configuration and sends a SIP INVITE to the SIP
endpoint.
When the call is answered, RTP carries the media between DIDWW and the SIP endpoint.
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flowchart LR
caller["Caller"] --> |dials DID| did["DID number"]
did --> |assigned trunk| trunk["Inbound SIP trunk"]
trunk --> |SIP INVITE| endpoint["Customer SIP endpoint"]
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classDef process fill:#ccfbf1,stroke:#2dd4bf,color:#1f2d3d,stroke-width:1.5px
class caller,endpoint endpoint
class did,trunk process
linkStyle default stroke:#0066cc,stroke-width:1.5px
SIP trunks and DID numbers#
A DID number and an inbound SIP trunk serve different purposes in DIDWW. The DID number receives inbound calls, while the SIP trunk defines how DIDWW delivers those calls to your SIP endpoint.
A DID number must be assigned to an inbound trunk before calls can be delivered through that trunk. Multiple DID numbers can be assigned to the same SIP trunk, allowing calls to those numbers to use the same SIP configuration.
The DID number must have sufficient Capacity to receive concurrent calls. The trunk’s Capacity Limit setting can further restrict the number of simultaneous calls delivered through that trunk, but it cannot add DID Capacity.
Routing methods#
The routing method determines how DIDWW obtains the SIP destination for calls delivered through the trunk. Each inbound SIP trunk uses one of the following routing methods:
Static Endpoint — DIDWW sends calls to a SIP destination configured on the trunk. Use this method when your SIP endpoint has a stable, publicly reachable address.
Dynamic Registration — Your SIP system registers with DIDWW, and DIDWW sends calls to a destination learned through the registration. Use this method when your system uses registration-based connectivity, such as when its public address can change or it operates behind NAT.
For a detailed comparison and information about destination selection, see SIP routing methods.
Failover and redundancy#
Inbound SIP delivery can use several mechanisms to improve redundancy at different stages of the routing process:
Preferred Server controls the DIDWW Point of Presence (PoP) used to deliver calls to the SIP endpoint. The default Auto option allows DIDWW to select the appropriate PoP for call delivery.
DNS SRV can provide multiple SIP destinations for the hostname configured for a Static Endpoint.
Trunk Groups combine multiple SIP or PSTN trunks and provide failover and load balancing between separate routing destinations.
These mechanisms serve different purposes and can be used together as part of a resilient inbound routing configuration. For SIP destination selection, see SIP routing methods. For detailed failover and load-balancing behavior, see Service Failover and Load Balancing.
Get started#
Create a trunk and prepare your SIP endpoint for inbound calls.
Create and initially configure an inbound SIP trunk in the DIDWW User Panel.
Compare Static Endpoint and Dynamic Registration and how each determines the call destination.
Understand signaling, media, authentication, and firewall requirements for your SIP endpoint.
Manage trunks and routing#
View and update existing trunks and routing settings.
View, edit, or delete SIP trunks and enable CNAM lookup.
Choose which DIDWW Points of Presence are available for trunks using Auto.
Dynamic Registration#
These guides apply only to trunks using Dynamic Registration.
Find the username, password, and registrar endpoint needed to register your SIP system.
Review successful registration intervals and the endpoints registered to your trunk.
Call handling and delivery#
Explore optional features for resilient delivery, transfers, and fax.
Configure your trunks and SIP platform to redirect or transfer inbound calls through an outbound SIP trunk.
Understand DIDWW network redundancy and delivery through DNS SRV and trunk groups.
Check the requirements for receiving fax calls over SIP using T.38.
Call information#
Learn what caller information DIDWW can deliver to your SIP endpoint.
Review caller-name delivery for U.S. caller IDs, availability, and lookup charges.
Understand the caller authentication headers DIDWW delivers to your SIP endpoint.
Identify the caller’s network or device category using information delivered in SIP requests.
Technical references#
Look up configuration fields and connectivity specifications.
Find field definitions, defaults, supported values, and limits for SIP trunk settings.
Find signaling and media addresses, ports, codecs, DTMF modes, and encryption options.