4) Transport Layer
• To provide reliable end-to-end message delivery and error recovery.
• Responsible for source to destination delivery for entire message.
• Network layer oversees source-to-destination delivery of the entire packets but it does not recognize any relationship b/w those packets.
• Responsible for source –to-destination.
• Dl Layer oversees the delivery of data between 2 systems on the same network.
• Network Layer ensures that each packet gets from its point of origin to its final destination.
2) Data link layer
• Transforms Physical layer which is transmission facility to a reliable link
• Responsible for Node to Node delivery.
• Make Physical layer look error free to the upper layer.
• Coordinates the functions required to transmit a bit stream over a physical medium.
• Deals with electronic and mechanical specification.
• Also defines and function that physical devices and interfaces need to perform for TX.