Integrating Siebel CRM - WSDL & JMS

Hi Experts,

We are planning to integrate ECC & Siebel CRM using PI. what would be the best adapter for processing Synchronous and Asynchronous transactions.

My idea is to use the below ,

PI <-> Siebel:

1.SOAP for Synchronous communication from PI to Siebel or Siebel to PI.

2.JMS for Asynchronous communication from PI to Siebel.

PI <-> ECC:

1. PROXY for Synchronous and Asynchronous communication from PI to ECC.

Can we use HTTP.

Please correct me if i am wrong, need your inputs on this.

Note: data transfer would be huge.

Thanks,

Baskar