Principles of Network Applications
Last updated
Last updated
Client and Server Processes: When there’s no confusion, we’ll sometimes also use the terminology “client side and server side of an application". An application has client and server side.
The Interface Between the Process and the Computer Network: A process sends messages into, and receives messages from, the network through a software interface called a socket.
A socket is the interface between the application layer and the transport layer within a host. It is also referred to as the Application Programming Interface (API) between the application and the network, since the socket is the programming interface with which network applications are built. A socket is uniquely identified by IP address and port number.
Addressing Processes
To identify the receiving process, two pieces of information need to be specified:
the address of the host (IP address)
an identifier that specifies the receiving process in the destination host (port number)
Only one program can bind a socket to a particular port at any given time.
Four dimensions of services a transport-layer protocol can offer to applications:
reliable data transfer
throughput
timing
security
Reliable data transfer: Some multimedia applications are loss-tolerant applications while some other applications requires reliable data transfer.
Throughout: a guaranteed throughput of r bits/sec. Applications that have throughput requirements are said to be bandwidth-sensitive applications. WeChat video call.
Timing: An example guarantee might be that every bit that the sender pumps into the socket arrives at the receiver’s socket no more than 100 ms later.
The Internet (and, more generally, TCP/IP networks) makes two transport protocols available to applications, UDP and TCP. When you (as an application developer) create a new network application for the Internet, one of the first decisions you have to make is whether to use UDP or TCP. Each of these protocols offers a different set of services to the invoking applications.
TCP Services
The TCP service model includes a connection-oriented service and a reliable data transfer service.
Connection-oriented services
Handshaking TCP connection
The connection is a full-duplex connection in that the two processes can send messages to each other over the connection at the same time. When the application finishes sending messages, it must tear down the connection.
Reliable data transfer
No missing or duplicate bytes
TCP congestion control also attempts to limit each TCP connection to its fair share of network bandwidth.
UDP Services
UDP is a no-frills, lightweight transport protocol, providing minimal services. Connectionless, no handshaking. No congestion.
Today’s Internet can often provide satisfactory service to time-sensitive applications, but it cannot provide any timing or throughput guarantees.
Internet telephony applications usually prefer to run their applications over UDP, thereby circumventing TCP’s congestion control mechanism and packet overheads. But because many firewalls are configured to block (most types of) UDP traffic, TCP serves as a backup if UDP communication fails.
RFC vs Proprietary application protocols
