Are you expected to bring poster presentations to academic conferences? BACKGROUND

I am attending an academic (engineering) conference where I am schedule to speak for my paper which was accepted, using MS PowerPoint/videos to assist my talk.  This is my first conference.  Currently I'm only bringing nice clothes and my lap top and the basics.  Due to lack of money, I'm only arriving on the day I'm scheduled to speak, then leaving immediately (cheapest roundtrip available).

QUESTION

Am I expected to bring a poster presentation to the conference?  Or is it typical to only give a talk (with a powerpoint, etc)?  I've checked the website and it says nothing about posters - but I don't want to be embarrassed and not have one.  I tried calling but couldn't reach an informed person.  Am I expected to be at the conference the entire time, or just for my talk?
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.