[ASM][DDoS][TPS-Based Detection]- TPS description and User Agents requests rate limit

Hello,

I am new to the DDoS protection on ASM and therefore I have been reading some KBs, but still did not hit (or might have missed) what can help me solve my points

1. In TPS-Based Detection, what is a Transaction : single packet or single session ?
2. Can I perform a TPS-Based Detection (without an iRule) on User Agent only and not By Device ID? E.g. 10req/s max sent by a specific User Agent (e.g. "Mozilla...") connecting to my site.

Thank you for your quick reactions.

Regards