reuse info from lower lever protocol epl

Hello,

i'm having problems for creating a dissector under powerlink (epl) protocol. My protocol will dissect the unprocessed datas. The problem is that i need to get the source displayed in the epl protocol. Is there a solution to get this value ? It seems I can't analyse previous bits which are dissected by the epl protocol. I absolutely need this information. Thanks in advance for answers.

Sylvain