CRM to ECC via PI

Hi

I have a CRM web UI....where i can enter some data and i want that to go to ECC ( proxy) though PI and get some response back in web UI..

1. Will the CRM web UI internally call standard proxies on CRM so that it will be like a CRM ( proxy ) to ECC ( proxy ) synchronous scenraio,

OR

2. Will it be a SOAP to Proxy synchronous ....so that i will need to provide a wsdl to the CRM team ??