For M2M, Telemetry and Tracking applications, the Iridium Short Burst Data (SBD) service is an effective way to use small portable satellite modems to relay important information back to SCADA host or tracking applications.
Iridium’s Short Burst Data Service (SBD) is a simple and efficient satellite network service for transmitting short data messages between field equipment and a centralized host computing system. The primary elements of an end-to-end SBD architecture consist of your Field Application (FA), the Iridium Subscriber Unit or satellite transceiver/modem (ISU), the Iridium satellite constellation, the Gateway SBD Subsystem (GSS) located at the Iridium gateway, the Internet, and your host Application such as a tracking or SCADA host application.
The Field Application represents the hardware and software that is configured for specific applications such as collecting and transmitting equipment health parameters or GPS location information. The ISU is an Iridium L-Band Transceiver (LBT) with the SBD feature available in firmware and the service activated on the Iridium network. The GSS is responsible for storing and forwarding messages from the ISU to the Host VA Application and storing messages from the VA Application to forward to the ISU. The ISU communicates with the GSS via the Iridium satellite constellation.
The interface between the Host Application and the GSS uses either standard Internet mail protocols or an IP Socket type interface to send and receive messages. Mobile terminated messages are sent to the GSS using a common email or IP address, identifying the specific ISU by encoding the unique ISU IMEI in the subject line of the email or as part of the IP Socket payload. For email, the data message itself is transported as a binary attachment to the email. For IP Socket, the data message is part of the payload. Messages sent to the Host Application are delivered to a specific email or IP address that is configured when the IMEI is provisioned. The delivery address for each IMEI can be changed on-line by Network Innovations.
It is also possible for one ISU to send a message direct to another ISU(s) without the message passing to the Host Application. The second ISU destination IMEI must be programmed on-line by Network Innovations. However, only one delivery type (email or ISU-ISU) is permitted. Up to five email addresses or five ISU IMEIs or one IP Socket address can be provisioned as destinations for MO- SBD messages.
The interface between the Field Application and the ISU is a serial connection with extended proprietary AT commands. This interface is used to load and retrieve messages between the ISU and the Field Application.
For a Mobile Originated SBD Message (MO-SBD) the message is loaded into the MO buffer in the ISU, then a message transfer session between the ISU and the GSS is initiated. For a Mobile Terminated SBD Message (MT-SBD) the ISU can either initiate a Mailbox Check to see whether a MT message is queued at the GSS; or the ISU can use the “SBD RingAlert” capability to be told when a MT message is queued at the GSS. The ISU must then retrieve the MT-SBD message from the GSS. When the message is received from the GSS it can be retrieved from the MT buffer in the ISU by the Field Application. Additionally a MT-SBD message can also be retrieved in the same network transaction by the ISU when a MO-SBD message is sent from the ISU.
Messages are transferred between the ISU and the GSS using a reliable transport mechanism that ensures the message is delivered error free. If the ISU was not able to send or receive messages, an indication is passed to the Field Application via the serial interface.
The MO and MT message buffers in the ISU will maintain messages as long as the ISU is powered on. Once a message is transferred from the Field Application to the MO buffer in the ISU, it will remain there even after it is successfully sent to the GSS. If a MT message is received at the ISU from the GSS, it will remain in the MT buffer even after the FA reads it. The buffers in the ISU will be cleared only when either given an explicit command or when the ISU is power cycled, or is overwritten with new data.
All MO and MT messages between the Host Application and the GSS are routed to the Internet by default. Iridium offers additional options for Virtual Private Network (VPN) and leased line routing of email or IP Socket messages to provide additional security, capacity and/or redundancy if required for the application. ISU-ISU SBD messages remain entirely within the Iridium network infrastructure.
The maximum length of a MO-SBD message is 1960 bytes. The maximum length of a MT-SBD message is 1890 bytes. Global network transmit latency for message delivery ranges from 5 seconds for messages of 70 bytes to approximately 20 seconds for maximum length messages. (Additional latency may occur across the Internet.)