The Transport Layer
An Introduction
Prof. David Bernstein
James Madison University
Computer Science Department
bernstdh@jmu.edu
A Review
Application Layer:
Involves user requests
Transport Layer:
Responsible for between processes/applications on different hosts
Network/Internetwork Layer:
Responsible for routing and delivering frames/datagrams
The Abstraction
Processes/applications use the services provided by the transport layer without worrying about the details of the lower levels.
Implementation of Transport Layer Protocols
Where is the code?
It resides on the host computers,
not
on routers
The Sender:
Process/application sends messages to the transport layer
Transport-layer software creates segments (each with a header)
Transport-layer gives the segments to the network-layer software which transmits them
The Receiver:
The network-layer software receives the datagrams
The network-layer software gives the segments contained in the datagrams to the transport-layer software
The transport-layer software gives the segments to the appropriate process/application
An Analogy
The Situation:
You want to send a letter to a friend at another university
The address includes a postal code that is specific to the University and your friend's box number
The Network Layer:
The U.S. postal service delivers the letter from your university to your friend's university (through a variety of intermediate points)
The Transport Layer:
Your university's mail system gave the letter to the U.S. postal service
Your friend's university's mail system got the letter from the U.S. postal service and delivered it to your friend
There's Always More to Learn