A transport layer and a network distinction:
The network layer provides a logical communication between hosts, the transport layer is between processes running on different hosts provides a logical communication
Second, the example shows:
Consider two families, one in the east coast of the United States, one in the US West Coast, each family has 12 children. East Coast family home on the west coast of the children are the children of cousins. These two families of kids like to communicate with each other, each person each week to write each other a letter, each letter in a separate envelope through the traditional postal service delivery. Therefore, each family every week to send 144 letters to another. Each family has a child who receives mail, the west coast is home sim, while the east coast is bi. Each week sim to all his brothers and sisters to collect letters and handed them letters home every day in front of the postal service of the car. When the mail to reach the West Coast family, bi is also responsible for distributing letters to his brother and sister on hand, but also this kind of work in the sim East Coast.
--------------- In this case, the postal service is to provide logical communication between two families, the postal service letters from one house to another, rather than one person to another A person. sim and bi is the mail service
Application layer packets = character on the envelope
Cousins process =
Host (also called end system) = Home
Operation and bi-layer protocol = sim
Network layer protocol = postal service (including the coach)
Two, UDP, TCP:
1, UDP: User Datagram Protocol, which provides an unreliable to invoke its application, connectionless service
2, TCP: Transmission Control Protocol, provides a reliable application to call it, connection-oriented services