# SMPP Specifications The SMPP specification defines how to exchange SMS messages with DIDWW using the Short Message Peer-to-Peer protocol. It is fully compliant with the [SMPP v3.4 Specifications](https://smpp.org/SMPP_v3_4_Issue1_2.pdf) and supports both outbound messages sent from an External Short Messaging Entity (ESME) to an SMSC and inbound messages delivered from an SMSC to an ESME. > - **External Short Messaging Entity (ESME)** is an external application that connects to a Short Message Service Center (SMSC) to engage in the sending and/or receiving SMS messages > - **Short Message Service Center (SMSC)** is a network element in the mobile telephone network. Its purpose is to store, forward, convert and deliver SMS messages. --- ## P2P and A2P Messaging The SMPP protocol is used for both Person-to-Person (P2P) and Application-to-Person (A2P) messaging. > - **P2P** - Low-volume, two-way exchange of SMS between end-users. Typically handled through either ESME or SMSC trunks, depending on direction. > - **A2P** - High-volume SMS generated by applications and sent to subscribers. Usually sent over an ESME trunk, where your application connects directly to the SMSC. Important A2P traffic requires a sender ID registered through an active [Sender ID Verification](../../sender-id-verifications/index.html#user-panel-sms-campaign). --- ## Bind Parameters for SMPP ESME Trunks When your application connects to the DIDWW SMSC (using an [ESME trunk](../create-smpp-esme-trunk.html#sms-esme)), it must perform a bind with the following parameters. | Parameter | Description | | --- | --- | | **system\_id** | The **System ID** from the trunk's [Credentials](../create-smpp-esme-trunk.html#user-panel-sms-smpp-esme-credentials). Identifies your ESME during the bind request. | | **password** | The **Password** from the trunk's [Credentials](../create-smpp-esme-trunk.html#user-panel-sms-smpp-esme-credentials). Used with the system\_id for authentication. | | **system\_type** | Optional field set when [creating the SMPP trunk](../create-smpp-esme-trunk.html#user-panel-sms-smpp-esme-create). Categorizes the bind (e.g., `VMS` for voicemail, `OTA` for over-the-air updates). | | **host** | The **Host** from the trunk's [Credentials](../create-smpp-esme-trunk.html#user-panel-sms-smpp-esme-credentials). It depends on the trunk's **Server location**. See [Server locations and IP addresses](#smpp-endpoints). | | **port** | `2775` (default SMPP port). | Important - For [SMPP SMSC trunks](../create-smpp-smsc-trunk.html#sms-smsc), DIDWW performs the bind to your system automatically using the credentials you provide in the trunk settings. - Your SMSC must be configured to **accept incoming bind\_transmitter or bind\_transceiver requests** on the specified host/port, and validate them using the system\_id and password you defined in the trunk. - Your firewall must **accept connections from the IP address** of the trunk's **Server location**. See [Server locations and IP addresses](#smpp-endpoints). --- ## SMPP Message Flow In SMPP, the SMS payload and control are exchanged using **Protocol Data Units (PDUs)**. The key PDUs for message delivery are: > - **submit\_sm** - Sent by an ESME to submit an outbound SMS. It typically carries fields like `source_addr`, `destination_addr`, and the `short_message` text. > - **deliver\_sm** - Sent by an SMSC to deliver an inbound (MO) SMS to an ESME, or to return a delivery receipt (DLR). It may carry either message text or status information. Message flow depends on the SMPP trunk type: > - **ESME** - Your application binds as the ESME to DIDWW's SMSC. You send SMS using `submit_sm` and receive inbound SMS or DLRs via `deliver_sm`. > - **SMSC** - DIDWW binds as an ESME to your SMSC. DIDWW submits SMS with `submit_sm`, and your SMSC can send inbound messages or receipts with `deliver_sm`. When [creating an SMSC trunk](../create-smpp-smsc-trunk.html#user-panel-sms-smpp-smsc-create), you can choose the SMPP connection mode: > - **Transmitter** - The ESME (DIDWW) can only send outbound messages to your SMSC. Uses the **TX (Transmitter) port**, while the RX port is ignored. > - **Transceiver** - The ESME (DIDWW) can both send and receive messages on the same bind session. Uses the **Transceiver port** (TX/RX combined). Note - The SMS text is normally carried in the `short_message` field. - Concatenated messages use a User Data Header (UDH) within `short_message` to split and reassemble long SMS. - Delivery receipts (DLR) are also sent in `deliver_sm` and typically contain status information. - Each PDU requires an acknowledgement: `submit_sm` ↔ `submit_sm_resp`, `deliver_sm` ↔ `deliver_sm_resp`. --- ## Data Coding Scheme (DCS) The `data_coding` parameter, also known as **DCS (Data Coding Scheme)**, specifies the character set for an SMS message. The encoding you use directly impacts how many characters can fit into a single SMS part. | DCS Value | Encoding | Max characters per SMS | | --- | --- | --- | | `0` | GSM-7 (Default). | 160 | | `1` | US-ASCII. | 160 | | `3` | Latin1 ([ISO-8859-1](https://www.iso.org/standard/28245.html)). | 160 | | `8` | Unicode / UCS-2 ([ISO/IEC-10646](https://www.iso.org/standard/76835.html)). | 70 | Note - GSM-7 is the standard encoding for most SMS. - UCS-2 is required for non-Latin scripts (e.g., Chinese, Arabic, Cyrillic) but reduces the per-SMS character limit. --- ## Concatenated Messages To overcome the 160-character limit of a single SMS, long texts are split into smaller fragments and reassembled at the recipient's device. This creates a multi-part SMS, known as a concatenated message. A User Data Header (UDH) is added to each part, which slightly reduces the character capacity. Note - Up to **255 parts** can be combined to form one long message. - Each part is billed as a separate SMS. | Encoding | Bit Size | Max Chars (Single SMS) | Max Chars (per Part in Concatenated SMS) | | --- | --- | --- | --- | | **GSM-7 & Latin-1/9** | 7-bit | 160 | 153 | | **UCS-2 (Unicode)** | 16-bit | 70 | 67 | --- ## Server Locations and IP Addresses Each SMPP trunk uses the DIDWW SMPP server defined in its **Server location** setting: **US, NY** or **NL, AMS**. - **SMPP ESME Trunk:** Your application connects and binds to the DIDWW SMPP server of the trunk's **Server location**, using the host shown in the trunk's [Credentials](../create-smpp-esme-trunk.html#user-panel-sms-smpp-esme-credentials). Your firewall must allow your application to open connections to that server's IP address. - **SMPP SMSC Trunk:** DIDWW connects and binds to your SMSC from the DIDWW SMPP server of the trunk's **Server location**, using the **Host** and ports defined in the trunk settings. Your firewall must accept connections from that server's IP address on the **TX port** of your SMSC, and on the **RX port** when **Transceiver mode** is off. | Hostname | Server location | IP Address | | --- | --- | --- | | `us.sms-out.didww.com` | US, NY | `46.19.209.214` | | `eu.sms-out.didww.com` | NL, AMS | `185.238.173.74` | | `sms-out.didww.com` | - | `46.19.209.214` | | `nyc.us.sms-out.didww.com` | US, NY | `46.19.209.214` | | `mia.us.sms-out.didww.com` | US, MIA | `46.19.209.214` | | `lac.us.sms-out.didww.com` | US, LA | `46.19.209.214` | | `sg.sms-out.didww.com` | SG | `46.19.209.214` | On this page