Simple Sensor Interface protocol
Overview
SSI (Simple Sensor Interface) protocol is a simple communications protocol designed for data transfer between computers or user terminals and smart sensors. SSI protocol is an Application layer protocol as in OSI model.
SSI protocol has been developed jointly by Nokia, Vaisala, Suunto, Ionific, Mermit and University of Oulu. Currently SSI is being developed within Mimosa project which is a part of European Union Framework Programmes on Research.
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 criterion for SSI protocol development are:
- general purpose
- simple – minimal overhead
- small footprint on the server (sensor) side
Sample implementation of SSI protocol for MSP430 microcontrollers will be published as open source during August 2006 by Nokia.
SSI message structure
An SSI message is formed of a 2-byte header and n-byte payload. The header consists of one byte address (wildcard is '?', 0x3F in ASCII) and one byte message/command type. The different possible values for message/command type are presented in SSI v1.2 command base.
SSI v1.2 command base
| Command byte | Direction | Description |
|---|---|---|
| Q,q (0x51,0x71) | C-> | Query |
| A,a (0x41,0x61) | <-S | Query reply |
| C,c (0x43,0x63) | C-> | Discover sensors |
| N,n (0x4E,0x6E) | <-S | Discovery reply |
| Z,z (0x5A,0x7A) | C-> | Reset sensor device |
| G,g (0x47,0x67) | C-> | Get configuration data for a sensor. |
| X,x (0x58,0x78) | <-S | Configuration data response |
| S,s (0x53,0x73) | C-> | Set configuration data for a sensor |
| R,r (0x52,0x72) | C-> | Request sensor data |
| V,v (0x56,0x76) | <-S | Sensor data response |
| D,d (0x44,0x64) | <-S | Sensor response with one byte status field |
| M,m (0x4D, 0x6D) | <-S | Sensor response with many data points |
| O,o (0x4F,0x6F) | C-> | Create sensor observer |
| Y,y (0x59,0x79) | <-S | Observer created |
| K,k (0x4B,0x6B) | <-> | Delete sensor observer / listener |
| U,u (0x55,0x75) | <-> | Observer / listener finished |
| L,l (0x4C,0x6C) | <-S | Request sensor listener |
| J,j (0x4A,0x6A) | C-> | Sensor listener created |
| E,e (0x45, 0x65) | <-> | Error |
| F,f (0x46, 0x66) | <-> | Free data for custom purposes |
History
- 0.1 March 14, 2003
- 0.2 April 29, 2003
- 0.3 May 20, 2003
- 0.4 October 2, 2003
- 0.5 December 5, 2003, not compatible with previous
- 0.6 November 3, 2004
- 0.7 December 22, 2004
- 0.8 January 14, 2005
- 1.0 April 11, 2005
- 1.1 October 27, 2005
- 1.2 May 27, 2006, not compatible with previous