Need For Protocol Architecture
When computers, terminals, and/or other data processing devices exchange data, the procedures involved can be quite complex. eg. file transfer. There must be a data path between the two computers. But also need:
- Source to activate communications Path or inform network of destination
- Source must check destination is prepared to receive
- File transfer application on source must check destination file management system will accept and store file for his user
- May need file format translation
Instead of implementing the complex logic for this as a single module, the task is broken up into subtasks, implemented separately. In a protocol architecture, the modules are arranged in a vertical stack, each layer in the stack performs a related subset of the functions. It relies on the next lower layer to perform more primitive functions. It provides services to the next higher layer. The peer layers communicate using a set of rules or conventions known as a protocol.
Key Elements of a Protocol
Communication is achieved by having the corresponding, or peer, layers in two systems communicate. The peer layers communicate by means of formatted blocks of data that obey a set of rules or conventions known as a protocol. The key features of a protocol are:
- Syntax: Concerns the format of the data blocks
- Semantics: Includes control information for coordination and error handling
- Timing: Includes speed matching and sequencing
TCP/IP Protocol Architecture
The TCP/IP protocol architecture is a result of protocol research and development conducted on the experimental packet-switched network, ARPANET, funded by the Defense Advanced Research Projects Agency (DARPA), and is generally referred to as the TCP/IP protocol suite. This protocol suite consists of a large collection of protocols that have been issued as Internet standards by the Internet Activities Board (IAB).
Simplified Network Architecture
In general terms, communications can be said to involve three agents: applications (eg. file transfer), computers (eg. PCs & servers), and networks. These applications, and others, execute on computers that can often support multiple simultaneous applications. Computers are connected to networks, and the data to be exchanged are transferred by the network from one computer to another. Thus, data transfer involves first getting the data to the computer in which the application resides and then getting the data to the intended application within the computer. Can think of partitioning these tasks into 3 layers as shown.