(20 marks) Question 2. Fundamental concepts and mechanisms (a) Middleware provides a convenient programming model to application programmers. Describe some of the limitations of middleware and com- pare the following middleware products and standards: CORBA, Java RMI, and web services. (b) Outline and explain three main limitations of IPv4. (c) Describe how Network Address Translation works (NAT) and what prob- lem does it solve. (d) TCP/IP functionality is divided into five layers, cach of which includes specific protocols. Briefly describe the work done by each of the five layers of the TCP/IP model and list some of the most important protocols at each layer