# Glossary of common SMPP API terms This glossary explains common SMPP terms and those specific to the SMPP API. Understanding these will help you with the SMPP API integration process. | **Term** | **Description** | | ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | SMPP | The Short Message Peer-to-Peer (SMPP) protocol is an open, industry standard protocol designed to provide a flexible data communications interface for the transfer of short message data. It comprises a limited set of commands to support mobile terminated (MT) messages, mobile originated (MO) messages, and delivery receipts (DLR). | | SMSC | The Short Message Service Center (SMSC) refers to Twilio's SMPP 'server' entity, to which an SMPP 'client', called an External Short Message Entity (ESME), can connect. | | ESME | External Short Message Entity (ESME) serves as the customer's SMPP client, allowing connectivity to Twilio's SMPP server. | | MO | Mobile originated messages (MO) are messages sent from a mobile device to a Twilio customer. | | MT | Mobile terminated messages (MT) are messages sent from a Twilio customer to a mobile device. | | DLR | Delivery receipts (DLR) are notifications provided by Twilio to customers, detailing the final delivery status of a mobile terminated (MT) message. | | TLS | Transport Layer Security (TLS) is a cryptographic protocol that encrypts data to secure communications over computer networks, such as the internet. All connections with Twilio must use TLS version 1.2 or higher. | | command | SMPP commands are a defined set of actions that allow ESMEs and SMSCs to establish, maintain, or terminate connections, as well as send and receive short messages and delivery receipts. | | `command_status` | The `command_status` field in an SMPP command response indicates whether an SMPP command request has succeeded or failed. | | smpp credential | SMPP credentials consist of the `system_id`, which identifies the ESME (client) to the SMSC (server), and the `password` used by the SMSC (server) to authenticate the ESME (client). These credentials are used during the binding process. | | `system_id` | The `system_id` is used to identify the customer's ESME to the Twilio SMSC during the binding process. It works similarly to a username within the SMPP credentials. The number of allowed binds are controlled at Twilio at the `system_id` level. | | bind | A bind is the persistent connection between the customer's ESME and Twilio's SMSC over which mobile terminated (MT) messages, mobile originated (MO) messages, and delivery receipts (DLR) are exchanged. | | TX | A Transmitter (TX) bind is authorized to send short messages to the SMSC and to receive the corresponding SMPP responses from the SMSC. Transmitter binds aren't able to receive mobile originated messages or delivery receipts. A transmitter bind is established when an ESME issues a `bind_transmitter` command request and an SMSC returns a `command_status` of 0 ESME\_ROK in the corresponding `bind_transmitter_resp` command response. | | TRX | A Transceiver (TRX) bind is authorized to send short messages to the SMSC and receive mobile originated messages or delivery receipts from the SMSC. Transceiver binds must send and receive the corresponding SMPP responses to and from the SMSC. A transceiver bind is established when an ESME issues a `bind_transceiver` command request and an SMSC returns a `command_status` of 0 ESME\_ROK in the corresponding `bind_transceiver_resp` command response. | | RX | A Receiver (RX) bind is authorized to receive short messages and delivery receipts sent from the SMSC and is required to send the corresponding SMPP responses back to the SMSC. Receiver binds can't send mobile terminated messages. A receiver bind is established when an ESME issues a `bind_receiver` command request and an SMSC returns a `command_status` of 0 ESME\_ROK in the corresponding `bind_receiver_resp` command response. | | `submit_sm` | This command allows a customer ESME to submit a mobile terminated message to Twilio's SMSC for delivery to a mobile device. The corresponding command response is the `submit_sm_resp` which will contain the `command_status` that provides the information on the outcome of the request to the customer. | | `deliver_sm` | This is used by the Twilio SMSC to submit either a mobile originated message or a delivery receipt to a customer ESME. The corresponding command response is the `deliver_sm_resp`. | | `enquire_sm` | This command request is used by a customer ESME or by Twilio's SMSC to validate that a bind is still active. The corresponding command response is the `enquire_sm_resp`. | | `unbind` | A command issued by either the Twilio SMSC server or customer ESME client to terminate the SMPP session. | | Encoding | Encoding is the process of converting data into a format required for transmission. Twilio supports the following encoding formats: GSM7, UCS2, Latin 1, and (IA5/Latin 9/ASCII). | | segmentSID | Twilio-spefic message ID. Each segment sent by the customer's ESME and received at Twilio's SMSC will be assigned a unique segmentSID in the `submit_sm_resp`. Twilio segmentSIDs are 34-character alphanumeric strings that begin with 'YV'. | ## Next steps Now that you are familiar with some of the Twilio SMPP API terms, you can either explore the [key concepts of the SMPP API](/docs/smpp/key-concepts) or learn [how to connect your application with SMPP API](/docs/smpp/initial-setup-and-connection).