Simple Sensor Interface protocol: Difference between revisions

Revision as of 01:05, 29 September 2010

Revision as of 01:38, 29 September 2010

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The SSI (Simple Sensor Interface) protocol is a simple communications protocol designed for data transfer between computers or user terminals and smart sensors. The SSI protocol is an [[Application layer]] protocol as in the [[OSI model]].

The SSI protocol has been developed jointly by [[Nokia]], [[Vaisala]], [[Suunto]], Ionific, Mermit and [[University of Oulu]]. Currently SSI is being developed within the [http://www.mimosa-fp6.com/ Mimosa project] which is a part of [[European Union Framework Programmes on Research]].

The SSI protocol is used in point-to-point communications over [[UART]] and networking [[nanoIP]] applications. SSI also provides polling sensors and streaming sensor data. For [[RFID]] sensor tags SSI specifies memory map for sensor data.

The criteria for SSI protocol development are:

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* small footprint on the server (sensor) side

Sample implementation of the SSI protocol for [[MSP430]] [[microcontrollers]] will be published as [[open source]] during August 2006 by Nokia.

== SSI message structure ==

An SSI message is formedconsists of a 2-byte header and an n-byte payload. The header consists of a one byte address (wildcard is '?', 0x3F in [[ASCII]]) and a one byte message/command type. The different possible values for the message/command type are presented in SSI v1.2 command base.

=== SSI v1.2 command base ===

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*S – set sensor configuration

are used to find and configure sensor units utilizing the SSI-protocol.

The group of commands

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are used to read sensor data infrequently.

For data streaming purposes are defined commands are

*O – create sensor observer

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=== Point-to-point SSI ===

Point-to-point messaging with SSI can be done with SSI/UART. An SSI UART message consists of a 3-byte UART header, an SSI message as the payload and an optional [[CRC|Cyclic redundancy check]] [[checksum]]. The use of a checksum is defined by the SSI message/command type, with lower case commands indicating the use of CRC. The header consists of a start byte (0xFE), a 2-byte (total) length of the message and a 2-byte [[bitwise]] [[NOT|Negation]] of length bytes to help identifyingidentify the frame start.

=== Networking SSI ===

SSI networking in a variable environment is done e.g. using [[nanoIP]]. In a typical case for using SSI, an individual message is not important, and so nanoUDP (simplified [[User Datagram Protocol|UDP]] defined by nanoIP) is used as the message format. If individual messages are important, nanoTCP can be used, as it provides flow control and retransmission, withat thea cost of message size and increase in network traffic.

A nanoUDP message consists of a 5-byte nanoUDP header, an n-byte message payload and an optional 2-byte CRC checksum. The header consists of one protocol byte, a 2-byte message length (total length, including header and CRC), a 1-byte source port and a 1-byte destination port number. The destination port number should be 0x28 for SSI messages.

== Version history ==