How to use Median Fillter 2D

I suggest tyou to have a look at

http://www.altera.com/literature/hb/qts/qts_qii54021.pdf?gsa_pos=3&wt.oss_r=1&wt.oss=avalon%20st

and

http://www.altera.com/literature/fs/fs_avalon_streaming.pdf?gsa_pos=6&wt.oss_r=1&wt.oss=avalon%20st

with those documents you will easily understand the properties of the Avalon Streaming interface and how the components should be connected to thet interface. A source and a sink are simply components that, in your processing chain, are connected just before and just after your filter.