TRANSPORT LAYER
This is the fourth layer of the OSI Model. I like to call it the heart of the OSI Model. This is where much attention is required.
It is responsible for the transmission of data segments between points on a network, including segmentation, acknowledgment and multiplexing. It provides a reliable means of transferring data of variable length from one host to another across a network, while every other functionality is not affected. This protocol can be connection-oriented or connectionless. Most times, this usually requires the breaking down of data into segments (smaller lengths), because the network layer has a maximum number of data lengths it accepts.
The most common protocol used in this layer of the Internet originated in the development of TCP/IP. The best-known transport protocol of the Internet protocol suite is the Transmission Control Protocol (TCP), it is used for connection-oriented transmissions, whereas the connectionless User Datagram Protocol (UDP) is used for simpler messaging transmissions. The TCP is a more complex protocol, due to its design incorporating reliable transmission and data stream services.
A few functions of the Transport Layer are:
Connection-Oriented Communication
Reliability
Flow Control: This is to improve efficiency and the rate of data transmission between nodes.
Multiplexing, etc.
The transport layer is said to be responsible for delivering data to the appropriate application process on the host computer. With a source and the destination IP address, the port numbers are set to constitute an identification address of the process-to-process communication.
Below are some lists of protocols that are in the Transport Layer;
NORM, NACK-Oriented Reliable Multicast
RDP, Reliable Data Protocol
RUDP, Reliable User Datagram Protocol
SCTP, Stream Control Transmission Protocol
SPX, Sequenced Packet Exchange
SST, Structured Stream Transport
TCP, Transmission Control Protocol
UDP, User Datagram Protocol, etc.