Layer Four - Transport Layer

the transport layer is responsible for the accuracy of the data transmission. it maintains overall management and control responsibilities. this fourth layer is what provides LAN network operating systems the intelligence to measure traffic performance that was not available with x.25 and other early packet-switching technologies. specifically being able to view in real-time the files a network user was accessing was a network management coup.

as an extra protective measure, a copy of the original message is archived at this layer until the succesful and of trasmission signal is received. if data retransmission is necessar, the message is retransmitted without returning ot the orginal applicaion.

if you think of layer 4 as a highway, the transport alyer is the same as to speed recognition devies that relay the current recorded speed of your car.

transport layer is a reliable connection oriented and its used for management and control for accuracy
where as layer 3 is connectionless

Transport Examples:
TCP
SPX
NetBIOS