In Part 4 we discussed about the top three layers (Application, Presentation, and Session), in this part we will discuss the lower 4 layers of the OSI Model (Transport, Network, Data Link, and the Physical).
The lower layers, or the Transport Set, are for the transportation of the segments, packets, frames, and bits.
Transport Layer (Layer 4) provides for reliable or unreliable delivery and performs error correction before retransmit. This layer segments and reassembles data into data stream by providing end-to-end data transport service which creates a logical connection between the sending and destination hosts.
Network Layer (Layer 3) provides for logical addressing, which the routers use for path determination. This layer manages device addressing, tracks the location of devices on the internetwork, and determines the best path available.
Data Link Layer (Layer 2) combines packets into bytes and bytes into frames, provides access to media using MAC address, performs error detection – not correction. This layer provides for the transmission of data and handles error notification, topology of the network, and flow control.
Physical Layer (Layer 1) moves the bits between devices, specifies wire speed, voltage, and the pin-out of cable. Sends and receives bits, some use tones, and others can use variations of voltage or signals
Data integrity is maintained through flow control whose purpose is to govern the amount of data sent by the sender.
Connection-Oriented Communication is where the transmitting device first creates a session with its peer system through a call setup, or three-way handshake. The three-way handshake is a series of synchronization, negotiation, synchronization, acknowledgement, connection, and finally data transfer.