What is ECI?

External Call Interface 

ECI calls are the way of communication between CICS and Web Services which uses TCP IP connections.

Client Side or Web Service need not use BMI setups to connect to CICS online transactions.

ECI calls are set up and linked the CICS default transaction. And on the client side or Web Service side can be set up in a way where it can run on mirror transactions

Read Blog for more reference  : TCPIP CONNECTION BETWEEN CICS AND WEB SERVICES

Establishing TCP IP service between Web Services and CICS via CIEP Default transactions

                    TCPIP Connection between CICS and Web Services

If you have any Java front end connected to CICS via Web Services following parameters needs to be taken care of:

Currently, I have tested with the Web Services using WSDL objects. There are Web services use the standard web protocols HTTP, XML, SOAP, WSDL, and UDDI. WSDL (Web Services Description Language) is an XML-based language used to define web services and to describe how to access them. 

- Connection between CICS and Web Method Serivces via TCP IP protocols

- Define TCP IP Service and link it to the port number

Command in CICS