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1 Introduction
Protocol - a set of rules and conventions between the communicating participants. The client and the server communicate with each other using some protocol. Eg: Let the web client like browser make a HTTP request to the HTTP server. The client initiating connection with server is called synchronous. If server makes connection with client is called asynchronous callback communication.
Network application: client and server.
Multiple clients communicating with same server
Multiple clients can communicate with the same server at the same time. Eg: Opening multiple browser windows and requesting the same webpage from the same server.
If the client and the servers are on the different LAN’s, they are connected through WAN. Routers are building blocks of WAN. The largest WAN today is the Internet.
OSI Model
Layer 7: The application layer...This is the layer at which communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. (This layer is not the application itself, although some applications may perform application layer functions.)
Layer 6: The presentation layer...This is a layer, usually part of an operating system, that converts incoming and outgoing data from one presentation format to another (for example, from a text stream into a popup window with the newly arrived text). Sometimes called the syntax layer.
Layer 5: The session layer...This layer sets up, coordinates, and terminates conversations, exchanges, and dialogs between the applications at each end. It deals with session and connection coordination.
Layer 4: The transport layer...This layer manages the end-to-end control (for example, determining whether all packets have arrived) and error-checking. It ensures complete data transfer.
Layer 3: The network layer...This layer handles the routing of the data (sending it in the right direction to the right destination on outgoing transmissions and receiving incoming transmissions at the packet level). The network layer does routing and forwarding.
Layer 2: The data-link layer...This layer provides synchronization for the physical level and does bit-stuffing for strings of 1's in excess of 5. It furnishes transmission protocol knowledge and management.
Layer 1: The physical layer...This layer conveys the bit stream through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier.