Hi David,
The tag sessions are defined by the EPC Gen 2 standard for an RFID tag. All compliant tags will support this feature. The tag sessions are used for two things, specify how long after a read a tag will respond to another inventory request by a reader, and the second is to allow multiple readers to inventory a tag at the same time.
Each session has two inventory states: A, and B. When a tag is inventoried by a reader the selected tag session will switch from the default state, A to the inventoried state, B. It will stay in the B state for the EPC defined length of time for that session, and in general will not respond to a reader again for the defined length of time for that session. Here is the list:
- Session 0: Instructs the tag to reset the state to A every time it is inventoried. This is required if you want to read the tag numerous times, and is not optimal for inventorying a large number of tags because all of the tags will be responding continuously.
- Session 1: Instructs the tag to stay in state B for a maximum of 5 seconds. This will reduce the amount of reads of a single tag as an inventory is in progress.
- Session 2 and 3: These two sessions have the same definition. The tag is instructed to stay in the B state for at least 2 seconds. These two sessions are optimal for larger number of tags when you want to keep them 'quiet' after they have responded to the inventory.
The main thing to take away from the different tag sessions is that it is useful for optimizing the RFID read performance based on your environment and how you are attempting to read the tags. This will need to be accounted for as you are implementing your RFID system. It's important to note that these are the EPC Gen 2 specifications for the tag states and depending on the manufacturer of the tag you may see some slightly different characteristics.
Thanks David, and let us know if you have any further questions on this.
