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Iridium Services at a glance

A common reference for the Iridium and cellular transport types used by Ground Control IoT and tracking products, and how they compare.

Products, transceivers and supported transports​

ProductIridium moduleIMTIP dataSBDA-PNTCellular
RockBLOCK 9704Iridium Certus 9704✓
RockBLOCK ProIridium Certus 9704✓
RockFLEET AssuredIridium Certus 9704✓✓
RockREMOTEIridium Certus 9770✓✓✓
RockREMOTE MiniIridium Certus 9770✓✓
RockBLOCK APNTIridium PNT ASIC (receive only)✓
RockBLOCK 9602/9603/PlusIridium 9602/9603✓
RockBLOCK 9604Iridium 9604✓✓
RockBLOCK RTUIridium SBD transceiver✓✓
RockFLEETIridium 9603✓✓
RockAIRIridium 9603N✓✓
RockSTARIridium SBD transceiver✓

Transport types​

IMT (Iridium Messaging Transport)IP data (Iridium Certus 100)SBD (Short Burst Data)
ModelBi-directional messagesBi-directional IP packetsBi-directional short messages
SizeUp to 100 kB per messageStandard IP packetsMO up to 340 bytes, MT up to 270 bytes
ThroughputSee Data ratesSee Data ratesNo quoted data rate
LatencyTypically under 10 seconds for small messages, measured to Cloudloop. See Latency and cold starts.IP latency, measured per packet to the IP destination. See Latency and cold starts.Approximately 10–30 seconds per message, depending on the antenna's view of the sky and the message size.

Interfaces and protocols​

IMTIP dataSBD
Device interfaceRockBLOCK 9704: serial (UART or USB) with the RockBLOCK 9704 library
RockBLOCK Pro and RockREMOTE Mini: AT commands over serial
RockREMOTE: MQTT IoT Gateway and REST API over the LAN		Ethernet LAN: see RockREMOTE LAN and the RockREMOTE Mini IP interfaceRockBLOCK 9602/9603/Plus and 9604: Iridium AT commands over serial
RockBLOCK RTU: GPIO and RS232, configured with the RockCONNECT app
RockFLEET and RockAIR: GPIO, RS232 and the Serial API, configured with the RockCONNECT apps
RockSTAR: RockCONNECT apps
End destinationCloudloop, on Ground Control airtimeThe IP destination. Traffic without an individual public IP originates from the Ground Control source IPs.Cloudloop, on Ground Control airtime
Onward deliveryCloudloop Data: REST API (poll/pull), HTTP webhook, FTP and MQTT (push)Not applicable. Traffic can be routed through a public IP or VPN.Cloudloop Data: REST API (poll/pull), HTTP webhook, FTP and MQTT (push)

Signal strength​

Do not check signal strength before sending

The Iridium Certus 9704 and 9770 transceivers in RockBLOCK and RockREMOTE products are configured in firmware to transmit only when signal strength is at least 1 bar. Do not duplicate this check in your application. Do not delay, block or skip a transmission based on a signal reading; send the data and the transceiver will transmit it when conditions allow.

Signal readings remain useful for diagnostics, installation checks and monitoring.

Latency and cold starts​

Latency is defined as the time taken for a transmission to be sent from the Iridium transceiver to the end destination.

  • IMT messages: on Ground Control airtime, the end destination is Cloudloop. From there, messages can be API pulled or pushed/forwarded to your own systems.
  • IP data: Latency for IP data is measured per packet between the transceiver and the IP destination.

End-to-end latency of an Iridium transmission, whether an IMT message or IP data, consists of three stages:

  1. Session ramp-up: approximately 5 seconds to establish a session with the satellite network.
  2. Transmission: the time taken to send the data, which increases with the amount of data.
  3. Gateway to cloud: the time taken for the data to travel from the Iridium gateway to its destination.
Session ramp-up in practice

Approximately 5 seconds is the average session ramp-up time quoted by Iridium. In practice it depends heavily on signal strength and the antenna's view of the sky. Ground Control regularly observes ramp-up times of 5 to 12 seconds, and occasionally longer.

Session ramp-up applies only to the first transmission in a session. Further transmissions while the session is active are sent without this delay.

If no data is transmitted for approximately 15 seconds or longer, the satellite link closes. The next transmission then requires a new session (a cold start) and incurs the full session ramp-up time.

On Iridium Certus 9770 products, an active IP data session also reduces IMT delivery time. Where ring alerts are used, MT delivery takes approximately 2 seconds longer.

Latency in an active session and after a cold startThree bars of equal length, each divided into stages. Single transmission: a short session ramp-up, a long transmission, then a short gateway-to-cloud stage. Consecutive transmissions in an active session: one session ramp-up, then transmissions 1, 2 and 3 in sequence, then gateway to cloud; transmissions 2 and 3 are sent without session ramp-up. Cold start: session ramp-up, transmission 1 and gateway to cloud, then a period of approximately 15 seconds or more without transmission during which the link closes, followed by a new session ramp-up, transmission 2 and gateway to cloud.Session ramp-up (typically 5–12 s)TransmissionGateway to cloudLink closedSingle transmissionRamp-upTransmissionConsecutive transmissions in an active sessionRamp-upTransmission 1Transmission 2Transmission 3Transmissions 2 and 3 are sent without session ramp-upCold start after approximately 15 seconds without transmissionRamp-upTransmission 1Link closedRamp-upTransmission 2Transmission 2 requires a new session ramp-up
Source: Iridium partner proprietary document, from which valid information has been taken to be shared with the public.

Data rates​

TransceiverMax transmitMax receiveGround Control products
Iridium Certus 97044.8 kbps4.8 kbpsRockBLOCK 9704, RockBLOCK Pro
Iridium Certus 977022 kbps88 kbpsRockREMOTE, RockREMOTE Mini

Transmission time increases with the amount of data: 100 kB takes approximately 170 seconds to transmit at 4.8 kbps, or approximately 36 seconds at 22 kbps.

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