# phone.systems(TM) trunks

An inbound **phone.systems(TM) trunk** delivers calls received on your DIDWW DID
numbers to the phone.systems(TM) PBX associated with your DIDWW account. Use this
trunk type to send incoming calls to the PBX rather than directly to an
external SIP endpoint or PSTN phone number.

The trunk settings control the format of the caller's number, an optional
caller ID prefix, and optional [CNAM lookup](../sip-trunks/call-information/cnam-in.html) for U.S. caller IDs. Configure
how
calls are answered and routed separately in phone.systems(TM), using
[call flows](../../../phone-systems/Call-flows/control-panel.html#ps3-call-flows), [users](../../../phone-systems/Users/index.html#ps3-users-index), and
[contact methods](../../../phone-systems/Contact-methods/index.html#ps3-contact-methods).

## How phone.systems(TM) trunks work

When a caller dials a DID number, the public telephone network routes the call
to DIDWW. DIDWW delivers the call through the phone.systems(TM) trunk assigned to
that DID number. The PBX then applies the routing configured for the number
to determine where the call goes.

```
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    "fontSize": "14px",
    "primaryColor": "#e0f2fe",
    "primaryBorderColor": "#38bdf8",
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}}%%

flowchart LR
    caller["Caller"] --> |dials DID| did["DID number"]
    did --> |assigned trunk| trunk["phone.systems(TM) trunk"]
    trunk --> pbx["phone.systems(TM) PBX"]
    pbx --> |configured routing| destination["Call destination"]

    classDef endpoint fill:#e0f2fe,stroke:#0066cc,color:#1f2d3d,stroke-width:1.5px
    classDef process fill:#ccfbf1,stroke:#2dd4bf,color:#1f2d3d,stroke-width:1.5px

    class caller,destination endpoint
    class did,trunk,pbx process

    linkStyle default stroke:#0066cc,stroke-width:1.5px
```

The DIDWW phone.systems(TM) trunk is separate from [Inbound Trunks in
phone.systems(TM)](../../../phone-systems/Trunks/inbound-trunks.html#ps3-inbound-trunks), which configure how the PBX
receives SIP
traffic from VoIP providers.

## phone.systems(TM) trunks and DID numbers

To route a DID number's incoming calls to phone.systems(TM), [assign a
phone.systems(TM) trunk to that
number](../../../phone-numbers/my-numbers/how-to-guides/assign-voice-trunk.html#user-panel-assign-trunk) in the DIDWW
User Panel. Multiple DID numbers can use the same trunk and its caller ID
and CNAM lookup settings.

Assigned DID numbers automatically appear under **Numbers > Phone Numbers**
in phone.systems(TM). These DIDWW number records cannot be edited or deleted
from that list. Manage their trunk assignment in the DIDWW User Panel and
their PBX routing in phone.systems(TM). See [phone.systems(TM) Phone
Numbers](../../../phone-systems/Numbers/phone-numbers.html) for details about the number records.

The DID number must have sufficient [Capacity](../../../phone-numbers/capacity/how-capacity-works.html) for concurrent
inbound calls.
The phone.systems(TM) trunk configuration does not include a separate
**Capacity Limit** field.

---

## Get started

An active phone.systems(TM) subscription and at least one DID number are
required. A trunk named **phone.systems** is created automatically with
your subscription. Assign it to your DID numbers, then configure the PBX.

**Subscribe to phone.systems(TM)**

Start a subscription and choose the number of seats for your PBX.

[Subscribe to phone.systems(TM)](../../../phone-systems/subscription-details/subscribe.html)

**Assign a voice trunk**

Assign the phone.systems(TM) trunk to one or more DID numbers.

[Assign a voice trunk](../../../phone-numbers/my-numbers/how-to-guides/assign-voice-trunk.html#user-panel-assign-trunk)

**Launch and configure phone.systems(TM)**

Open the PBX and prepare your app or softphone to receive calls.

[Launch and Configure phone.systems(TM)](../../../phone-systems/Getting-started/index.html#ps3-launch-and-configure)

## Configure and manage trunks

Create an additional trunk only when some DID numbers need different
caller ID or CNAM settings. Editing an existing trunk changes the settings
used by all DID numbers assigned to it.

**Create a phone.systems(TM) trunk**

Create an additional trunk with its own caller ID and CNAM settings.

[Create a phone.systems(TM) trunk](how-to-guides/create-phone-systems-trunk.html)

**Manage phone.systems(TM) trunks**

View, edit, or delete existing trunks.

[Manage phone.systems(TM) trunks](how-to-guides/manage-phone-systems-trunks.html)

## Caller information

Configure the caller number and optional caller name delivered to the PBX.

**Configure caller ID**

Choose the caller ID format and an optional prefix.

[Number Translations](how-to-guides/create-phone-systems-trunk.html#create-phone-systems-trunk-number-translations)

**Enable CNAM lookup**

Enable caller-name lookup for U.S. caller IDs. Additional per-call
charges apply.

[Enable CNAM lookup](how-to-guides/manage-phone-systems-trunks.html#inbound-phone-systems-trunks-enable-cnam)

## Configure PBX call routing

Configure how phone.systems(TM) answers and routes calls after they arrive
through the trunk.

**Call flows**

Build call flows to direct incoming calls through the PBX.

[Call Flows](../../../phone-systems/Call-flows/control-panel.html#ps3-call-flows)

**Users**

Create users and configure their application lines and access.

[Users](../../../phone-systems/Users/users.html)

**Contact methods**

Configure apps, SIP devices, and forwarding destinations for
incoming calls.

[Contact Methods](../../../phone-systems/Contact-methods/index.html#ps3-contact-methods)

## Monitor calls and troubleshoot

Review delivery to the PBX and how phone.systems(TM) handles each call.

**Inbound Call Logs**

Review DIDWW call records for delivery attempts to the PBX.

[Inbound Call Logs](../../../logs-analytics/call-logs/inbound-logs.html#inbound-cdr-logs)

**phone.systems(TM) Call History**

Review call destinations, statuses, and end codes inside the PBX.

[Call History](../../../phone-systems/Call-analytics/call-history.html)

**Inbound troubleshooting**

Identify failed inbound calls and investigate delivery problems.

[Troubleshooting](../troubleshooting.html)

## References and related resources

Look up trunk settings and the DID Capacity required for incoming calls.

**phone.systems(TM) trunk settings reference**

Find field definitions, defaults, supported values, and limits.

[phone.systems(TM) trunk settings reference](phone-systems-trunk-settings-reference.html)

**DID Capacity**

Understand the capacity needed to receive simultaneous calls on
your DID numbers.

[How capacity works](../../../phone-numbers/capacity/how-capacity-works.html)

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