# SMPP SMSC trunk settings reference

This reference describes the fields available when creating or editing an SMPP
SMSC trunk. With this trunk type, DIDWW connects and binds to your SMSC as an
ESME. The settings are grouped by the sections of the trunk form in the DIDWW
User Panel.

For configuration steps, see [Create an SMPP SMSC trunk](how-to-guides/create-smpp-smsc-trunk.html) or [Manage SMPP SMSC
trunks](how-to-guides/manage-smpp-smsc-trunk.html). This page covers trunk settings only.
For protocol details, see the [SMPP specification](../technical-data/smpp-specification.html#service-incoming-sms).

## General settings

The **General** section identifies the trunk, selects the DIDWW SMPP server
that binds to your SMSC, and defines the connection details and credentials of
your SMSC. DIDWW uses these values when it binds to your SMSC. See
[Mandatory SMPP SMSC bind parameters](how-to-guides/accept-smpp-smsc-bind-requests.html#smpp-smsc-bind-parameters).

| Field | Availability | Description |
| --- | --- | --- |
| Friendly name | Required | Unique name used to identify the trunk. For example, `My SMPP SMSC SMS Trunk`. |
| System type | Optional | Value that categorizes the type of ESME that binds to your SMSC. For example, `VMS` (voice mail system) or `OTA` (over-the-air activation system). DIDWW sends this value as the `system_type` bind parameter. |
| Server location | Required | DIDWW SMPP server that connects and binds to your SMSC: **US, NY** or **NL, AMS**. Your firewall must accept connections from the IP address of the selected location. See [Server locations and IP addresses](../technical-data/smpp-specification.html#smpp-endpoints). When you change the location, DIDWW binds to your SMSC from the new location. Your SMSC connection details stay the same. |
| Password | Required | Password that your SMSC requires to authenticate the ESME during the bind. DIDWW sends this value as the `password` bind parameter. |
| System ID | Required | System ID that your SMSC requires to identify the ESME during the bind. DIDWW sends this value as the `system_id` bind parameter. |
| Host | Required | Public hostname or IP address of your SMSC. For example, `smsc.example.com`. |
| Use SSL | Optional | When on, DIDWW connects to your SMSC over TLS and establishes TLS before it sends the bind request. When off, DIDWW binds over plain TCP. TLS applies to the session on the **TX port**, and to the session on the **RX port** when **Transceiver mode** is off. **Use SSL** does not change the ports. Your SMSC must accept TLS connections on the ports you enter. Default: off. |
| Connection timeout | Optional | Time between TCP connection retries, in seconds. Range: `0` to `32767`. Default: `20`. |
| TX port | Optional | Port of your SMSC for the transmitter session, or for the single transceiver session when **Transceiver mode** is on. Range: `1` to `65535`. Default: `2775`. |
| RX port | Optional | Port of your SMSC for the receiver session when **Transceiver mode** is off. It is ignored when **Transceiver mode** is on. Range: `1` to `65535`. Default: `2776`. The default value is unrelated to TLS. |
| Transceiver mode | Optional | Defines how messages are exchanged between DIDWW and your SMSC.   - Off: DIDWW uses separate transmitter and receiver sessions. It sends   `bind_transmitter` on the **TX port** and `bind_receiver` on the   **RX port**. - On: DIDWW uses a single transceiver session for two-way   communication. It sends one `bind_transceiver` on the **TX port**.   Default: off. |

## Source address settings

The **Source Address Settings** section controls which DID numbers can be used
as the sender ID for outbound SMS.

| Field | Availability | Description |
| --- | --- | --- |
| Allow any DID(s) for SMS OUT | Optional | Controls how sender IDs are assigned. When the toggle is on, all DIDs with Outbound P2P SMS enabled in your account can be used as the sender ID. When the toggle is off, only the numbers in **Allowed source addresses** can be used. Default: on. |
| Available source addresses | Optional | DIDs that you can add to **Allowed source addresses** when **Allow any DID(s) for SMS OUT** is off. The list shows only DIDs that support outbound P2P SMS, with their **Country**, **Number**, and **Description**. Filters: **Source address**, **Description**, **Country**, and **Region**. |
| Allowed source addresses | Optional | DIDs that can be used as the sender ID when **Allow any DID(s) for SMS OUT** is off. Only the numbers in this list are available as sender IDs. |

## Trunk group settings

The optional **Trunk Group Configuration** section assigns the trunk to an
existing [SMS trunk group](../trunk-groups/sms-trunk-groups.html).

| Field | Availability | Description |
| --- | --- | --- |
| Assign to trunk group | Optional | Existing SMS trunk group to which the trunk is assigned. |
| Priority | Optional | Priority of the trunk within the selected trunk group. It determines the order in which trunks are used. The system attempts to contact the target SMS trunk with the highest-numbered priority first. Trunks with the same priority are tried in a random order. Range: `0` to `32767`. Default: `1`. |

## Related resources

- [Create an SMPP SMSC trunk](how-to-guides/create-smpp-smsc-trunk.html) -
  Create a trunk and configure the settings described on this page.
- [Manage SMPP SMSC trunks](how-to-guides/manage-smpp-smsc-trunk.html) - Edit
  or delete an existing trunk.
- [Accept SMPP SMSC bind requests](how-to-guides/accept-smpp-smsc-bind-requests.html) - Prepare your SMSC to
  accept the bind parameters defined by these settings.
- [SMPP SMSC trunk](smpp-smsc-trunk.html) - Understand how DIDWW connects
  and binds to your SMSC.
- [Assign an SMS trunk](../../../phone-numbers/my-numbers/how-to-guides/assign-sms-trunk.html#assigning-sms-trunk) - Assign the trunk to one
  or more DID numbers to receive inbound SMS.
- [SMPP specification](../technical-data/smpp-specification.html#service-incoming-sms) - Review protocol details,
  including encoding, concatenation, and all available DIDWW endpoints.