How to connect an Allenbradley or any PLC?

Hi

Can anybody give expertise advise on how to connect PLC.

We have two PLC's to connect . One is Allenbradley and another one is Siemens. ( i dont know model number's yet )

So , What is the process of connecting those PLC's for two scenarios ( OPC compliant and Not ).

What is the role of xMII OPC DA UDS xMII UDS roles in connecting that plc.

What is the easiest,good and recommended approach ?

Please Advice.

Thanks in advance.

--Hari