# Outbound trunks

An outbound SIP trunk connects your customer system to DIDWW termination
routes so you can place calls to local and international destinations. Each
trunk controls authentication, media, Caller ID, allowed destinations,
capacity, and spending.

Important

Outbound trunks are not enabled automatically.
[Request access](get-access.html) before creating a trunk or placing
outbound calls.

## Key features

- Control simultaneous call capacity and rolling 24-hour spending limits.
- Choose from supported authentication methods and restrict signaling and
  media by IP address where applicable.
- Configure Caller ID numbers and allow or block destination prefixes.
- Use SIP over UDP, TCP, or TLS, with optional encrypted media.
- Place calls through local or global routes and use emergency calling in
  supported countries.
- Review per-trunk call records, statistics, and reports.
- Use redundant network infrastructure and customer-side failover options.

## How outbound calls work

Your customer system sends a SIP `INVITE` to DIDWW. DIDWW identifies and
authenticates the outbound trunk according to its configured authentication
method, applies Caller ID and dialing rules, and routes the call to the
destination network for delivery to the called party.

```
        %%{init: {
  "theme": "base",
  "themeVariables": {
    "fontSize": "14px",
    "actorBkg": "#e0f2fe",
    "actorBorder": "#38bdf8",
    "actorTextColor": "#1f2d3d",
    "actorLineColor": "#38bdf8",
    "signalColor": "#0f766e",
    "signalTextColor": "#1f2d3d",
    "labelBoxBkgColor": "#ccfbf1",
    "labelBoxBorderColor": "#14b8a6",
    "labelTextColor": "#1f2d3d",
    "noteBkgColor": "#fef3c7",
    "noteBorderColor": "#f59e0b",
    "noteTextColor": "#1f2d3d",
    "sequenceNumberColor": "#ffffff"
  }
}}%%

sequenceDiagram
   autonumber
   participant system as Customer System
   participant trunk as DIDWW
   participant network as Destination network
   participant callee as Called party

   system->>trunk: SIP INVITE
   Note over trunk: Authenticate the trunk<br/>Apply Caller ID and dialing rules
   trunk->>network: Route call
   network->>callee: Deliver call
```

See [Authentication and security](authentication-security.html) for
authentication methods. See [Call-flow examples](routing-dialing/call-flow-examples.html) for complete Credentials &
IP-Based and
IP-Only SIP exchanges.

Reliability and failover details

Outbound call delivery uses several layers of redundancy across the DIDWW
network and your customer system's connection:

- DIDWW provides [network redundancy](outbound-sip-information.html#voice-out-network-redundancy) across multiple Points of Presence
  (PoPs), termination carriers, load balancers, and session border
  controllers (SBCs).
- DIDWW maintains resilient connectivity through multi-homed IP transit and
  [direct interconnections](../../presence/index.html#network-interconnection) at major Internet
  Exchanges.
- Use [DNS SRV](outbound-sip-information.html#voice-out-dns-srv) or
  [BGP Anycast](outbound-sip-information.html#voice-out-bgp-anycast) for customer-side failover, or
  [create multiple outbound trunks](how-to-guides/create-outbound-trunk.html) to distribute traffic.

For signaling, network architecture, and failover details, see
[Outbound SIP information](outbound-sip-information.html).

## Get started

Choose the path that matches your account:

**Get access to outbound trunks**

Start here if outbound trunks are not enabled on your account.

[Get access to outbound trunks](get-access.html)

**Create an outbound trunk**

Create your first trunk after outbound trunk access is enabled.

[Create an outbound trunk](how-to-guides/create-outbound-trunk.html)

## Configure, manage, and monitor outbound calling

**How-to guides**

Edit, enable, disable, or delete trunks, and manage trunk credentials.

[How-to guides](how-to-guides/index.html)

**Authentication and security**

Understand authentication methods and controls that reduce unauthorized
use and toll fraud.

[Authentication and security](authentication-security.html)

**Routing and dialing**

Configure number formats, local routes, call forwarding, and destination
restrictions.

[Routing and dialing](routing-dialing/index.html)

**Caller ID and CNAM OUT**

Configure the calling number and Caller Name Delivery (CNAM OUT).

[Caller ID and CNAM OUT](caller-id-cnam-out.html)

**Analytics and troubleshooting**

Review outbound call logs, statistics, and reports, and isolate common
configuration problems.

[Analytics and troubleshooting](analytics-troubleshooting.html)

## Trust and compliance

**STIR/SHAKEN for outbound trunks**

Understand DIDWW attestation and customer-generated Identity header
relay.

[STIR/SHAKEN for outbound trunks](stir-shaken-outbound.html)

**Robocall mitigation and call labeling**

Understand call labeling and applicable US robocall compliance
requirements.

[Robocall mitigation and call labeling](robocall-mitigation/index.html)

## Technical references

**Outbound SIP information**

Find signaling endpoints, transports, media networks, codecs,
encryption, registration, and SIP header details.

[Outbound SIP information](outbound-sip-information.html)

**Outbound trunk reference**

Find definitions, values, and status behavior for every field on the
Outbound Trunks page and in the trunk creation and edit forms.

[Outbound trunk reference](outbound-trunk-reference.html)

## Related resources

**Emergency calling**

Register an eligible DID for emergency calling and activate the service
required for outbound emergency calls.

[Emergency Calling](../emergency-calling/index.html)

**Inbound trunks**

Create and manage inbound voice trunks for call routing.

[Inbound Trunks](../inbound-trunks/index.html)

**My numbers**

Manage the DID numbers assigned to your account and their trunks.

[My Numbers](../../phone-numbers/my-numbers/index.html)

**Download pricelists**

Download public or account-specific SIP trunking pricelists.

[Download pricelists](../../phone-numbers/buy-numbers/download-pricelists.html#services-coverage-pricing-access-pricelists)

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