Are you expected to bring poster presentations to academic conferences?
Usually if you are presenting a poster, it's because you 


submit a poster abstract to a call for posters, and it is accepted, or
submit a paper, and you are informed that it is accepted for a poster presentation instead of a talk, or
are otherwise informed by the organizers to bring a poster.


If you don't fall in any of the categories above, then in my experience, you aren't presenting a poster.