The difference between the transport layer and the network layer

In the protocol stack, the transport layer is above the network layer, the Transport Layer protocol provides logical communication for the processes running on different hosts, and the Network layer protocol provides logical communication for different hosts. The difference is subtle, but it's very important. Let's use a family analogy to illustrate the difference.

Imagine two houses, one on the east Coast and the other on the West Coast, where 12 children live in each house. The children in the East Coast House and the children in the West Coast house are cousins. The children in the two houses like to communicate with each other-every week each child writes a letter to every sibling, and each letter is mailed by an old post office in an envelope. In this way, every week there are 144 of letters to be sent to another family (these kids can save a lot of money if they can email them!) In every house. A child, Ann of the West Coast House and bili--in the East Coast House. Responsible for the collection and distribution of mail. Every week Ann collects letters from her siblings and sends them to the mail attendant every day. When the letter arrives at the West Coast House, Ann distributes the letters to her siblings. Bili has the same job on the east coast.

In this case, the mail service provides a logical communication between the two houses-postal services deliver mail between the two houses, rather than services for everyone. Ann and Bili, on the other hand, provide logical communication between cousins--ann and Bili collect mail from their siblings and deliver them to them. Note that from these cousins ' perspective, Ann and Bili are mail service providers, although they are only part of the End-to-end delivery service (the Terminal Systems Section). This example is an image metaphor of the relationship between the transport layer and the network layer:

Host (also known as terminal system) = House
Process = Cousins
Application message = letter in envelope
Network Layer protocol = Mail Service (including postman)
Transport layer protocol =ann and Bill