Abstract

Data Communications Protocols

The data industry borrowed the protocol term, an apt metaphor, from the world of diplomacy.
Layer1-Physical
Layer 1 transfers bits across a circuit, which can be any transmission medium including wire, fiber optics, coaxial cable, or wireless.
Layer2-Datalink
Datalink protocols provide link integrity to transmit frames of data between endpoints.
Layer 3—Network
The network layer routes packets between endpoints on a network. A packet is a frame with a header that contains addressing and other information.
Layer 4—Transport
The transport layer assures integrity between endpoints. Transport protocols
establish and terminate connections, segment data into manageable PDUs, and reassemble them at the receiving end.
Layer 5—Session
Session service is an optional function that may be embedded in the application as opposed to employing a separate protocol.
Layer 6—Presentation
This layer provides the syntax for the session. For example, it might translate between ASCII and EBDIC if the two systems use a different format.
Layer 7—Application
Examples of application layer functions now in use are ITU-T’s X.400 Electronic Mail Protocol and its companion X.500 Directory Services Protocol.
ETHERNET: IEEE 802.3
Standards work began with modest objectives of sharing facilities: files, expensive peripherals such as printers and plotters, and software applications. Stations can detect other transmissions in a wired network, but a finite time known as the collision window is required for a pulse to traverse the length of the medium.
TRANSMISSION CONTROL PROTOCOL/INTERNET PROTOCOL (TCP/IP)
In the 1970s, the Department of Defense commissioned the development of the TCP/IP suite of protocols to provide interoperability among computers.
User Datagram Protocol (UDP)
Error correction delays packet flow. To a data application, delay is either invisible or appears as a longer response time, which may be annoying but does not affect integrity.
Internet Protocol (IP)
Routers at IP nodes usually have multiple paths for delivering packets. An IP data gram contains a header that is 20 octets or more in length plus a data field that can be up to 65,535 octets long.