Excise,Service Tax

This is not a Conversion arrangement. Two seperate units of the same company situated in two different states want to exchange processed materials. Unit A in UP State will be sending semi processed goods to Unit B in Bihar and in turn Bihar Unit will process the same and return the finished product to Unit A for further downstream finished products. What are tax implications (Excise,Service Tax,CST etc).Please enlighten me.

Thanks.

J Bnerjee