Principles of Network Applications

• The application architecture, on the other hand, is designed by the application developer and dictates how the application is structured over the various end systems. Two predominant architectural paradigms used in modern network applications: the client-server architecture or the peer-to-peer (P2P) architecture.
• In the jargon of operating systems, it is not actually programs but processes that communicate.
• A process is analogous to a house and its socket is analogous to its door. A socket is the interface between the application layer and the transport layer within a host. It is also referred to as the Application Program Interface (API) between the application and the network.
• To identify the receiving process two pieces of information need to be specified: (1) the address of the host (IP address); (2) an identifier that specifies the receiving socket (A destination port number).
• What are the services that transport-layer protocol can offer to applications invoking it? We can broadly classify the possible services along four dimensions: reliable data transfer, throughput, timing, and security.
• The Internet makes two transport-layer protocols available to applications, UDP and TCP.
• The TCP services model includes a connection-oriented service and a reliable data transfer service.
• TCP has the client and server exchange transport-layer control information with each other before the application-level messages begin to flow. After the handshaking phase, a TCP connection is said to exist between the sockets of the two processes(full-duplex).
• Secure Sockets Layer (SSL) is an enhancement of TCP, with the enhancements being implemented in the application layer. SSL has its own socket API that is similar to the traditional TCP socket API.