The access control industry moves to OSDP communication protocol. After decades of adopting the wiegand protocol. OSDP stands for Open Supervised Device Protocol. Developed by the SIA to improve interoperability among access control and security products.
Actually, it comes to overcome the wiegand drawbacks and to make communication more secure.
Wiegand VS OSDP
| wiegand | OSDP | |
| Encryption | No | 128 bits AES encryption |
| Bidirectional communication | No | Yes |
| Supervised cable | No | Yes |
| Packet size limit | 26, 32, 37 bits | Up to 128 bytes, doesn’t exceed 1440 bytes |
| Biometric devices | No | Yes |
While the wiegand protocol is sending the facility code and the ID card number. OSDP establishes continuous communication between the reader and the controller, which are called respectively Peripheral Devices (PD) and Control Panel (CP).
The CP and DP are constantly communicating. The CP sends command messages to the PD. So the PD must reply.
Timing
A CP message contains a reply delay. Therefore, the DP must send a reply within this delay. If it can’t. For example, because it is busy or overwhelmed, it sends an acknowledgement or a busy message.
The reply should not exceed 50 milliseconds.
Somme OSDP messages
- SOM: Start of a message: begins each message header.
- ADDR: The address of the PD to which the message is directed or the address of the responding PD.
- OSDP_DATA: Data transfer command.
- OSDP_BUZ: Reader buzzer control command.
- OSDP_BIOREAD: Scan and read biometric template.
Wiring OSDP based system
OSDP communication protocol uses RS-485 wiring. It is supervised with 120-ohm end of line resistor
Why OSDP protocol?
- OSDP guarantees complete security data transmition through 128-bit AES encryption. Consequently, no chance for hackers to intercept transmissions between readers and controllers.
- OSDP uses RS-485 wiring; it is supervised with 120-ohm end of line resistor. So if a cable is broken, a system would be alerted.
- A communication is bidirectional. As a result, configuration changes & firmware updates are managed directly at the reader.
- Interoperability features, meaning that communication among different manufacturers’ devices is guaranteed. So, no restrictions to choose a single supplier.
