Open Systems Interconnection (OSI)

OSI (Open Systems Interconnection) model

Brief of History
Open Systems Interconnection (OSI). OSI model was introduced in the late 1970s which was proposed by British Standards Institute to the International Organization for Standardization (ISO) that to define communication infrastructure for distributed processing a standard architecture was needed. Most the design of OSI was done by a group at Honeywell Information Systems, headed by Mike Canepa, with Charlie Bachman as the principal technical member.
Introduction
OSI model served for the purpose to show there is a way to communicate different type of systems with different logic of underlying hardware and software through without the need to change the systems specifications. OSI model

Data link layer act as transmission protocol that support error handling in the physical layer, flow control, frame synchronization and the data corruption through check summing. Data link layer itself is divided to two sub-layers which are the Media Access Control (MAC) and Logical Link Control (LLC). Mac help in the control the flow of the data that been send across network on how to send, receive and give permission to do it. While LLC works to control the frame synchronization, flow control and error checking. Example of data link layer includes PPP, FDDI, ATM, IEEE 802.5/ 802.2, IEEE 802.3/802.2, HDLC, Frame Relay.
Network layer
The network layer provides the protocol for routing the data through the configured network nodes. This layer provides switching and routing technologies that enable data to be transmitted, both of the technologies create a virtual circuits or logical paths that is use to transmit the data across network from the one node to another targeted node. Routing and forwarding are functions of this layer with addition of other functions of this layer includes addressing, internetworking, error handling, congestion control and finally packet sequencing. Example of network layer is AppleTalk DDP, IP, IPX.
Transport

OSI provides layer functioning and the functions of all the layers while TCP/IP model is more based on protocols where the protocol are not flexible with other layers.
2. In OSI model the transport layer guarantees the delivery of packets while TCP/IP model the transport layer does not guarantees delivery of packets.
3. OSI model follows horizontal |approach while TCP/IP model follows vertical approach.
4. OSI model has a separate presentation layer while TCP/IP |does not have a separate presentation layer
5. OSI is a general model where it can be use in other application while TCP/IP model cannot be used in any other application.
6. OSI model is a reference model while TCP/IP is an implementation of OSI model
7. OSI model can fit some protocol but it have a problem of fitting the protocols in the model while TCP/IP model does not fit any protocol
8. OSI model have hidden protocols and where it can be replace easily as the changes in technology while replacing protocol TCP/IP is not