UDP message structure and precautions

Catalog

The original situation of the network  

The transport layer UDP

UDP Header structure

UDP buffer

Summary

---

The original situation of the network  

The original situation of the network ： Data in the network , Between routers , Jumping 、 Like a relay , To the target host , There are two problems :
1. Network transmission is unreliable
        1) The data you sent , The other party does not guarantee to receive

        2) There is no guarantee that the other party will receive it strictly in the order in which it was sent

Because the road may be different , It is difficult to guarantee that the data will arrive in the order of departure .

2. The Internet is not secure
        1) All the data you send , The routers along the way can be checked or modified （ hacking 、 Tampering ）

        2) Others can fake the data you send

The transport layer UDP

User Datagram Protocol User message protocol
UDP Is a very simple transport layer protocol , It just fulfills the most basic responsibilities of the transport layer ( stay host to host Together with the case , Realization process to process).
The network layer itself is unreliable ,UDP I haven't done any treatment , therefore ,UDP It's not reliable .

It's not reliable here , Not at all UDP What did you do , Just become unreliable , It is UDP You've done nothing at all? , Therefore, the unreliability of the network layer is directly expressed to the application layer , So from the perspective of application layer , We just said UDP It's not reliable .

UDP What has been done ( Mechanism )

UDP The head of the newspaper (header） What does it look like , The contents of these headers , It's all cooperation UDP The agreement fulfills its duties .
1. Responsibilities in the header of all network protocols :

How to unpack ( How to put header and payload Separate )

byte[]data = {12345}
2. The problem of distribution , stay UDP in , The problem of distribution is actually process to process The problem of .

UDP Public praise of (UDP Characteristics ） From the perspective of application layer :

shortcoming ： unreliable

advantage ： There is no connection 、 Data oriented message 、 The cost is low ( cheap )

UDP Header structure

How can the recipient be based on header Unpack the data in . because header The length of is fixed （ Fixed length ), front 8 Bytes must be header, The rest must be payload.

UDP length ： The length of the whole message .64kb

16 position (bit) = 2 byte (byte) = 2^16-1=65535——>65535 / 1024 = 64kb

How to make it for distribution , Which process of the application layer should the data be handed over ?

Use the destination port . At the same time, it can support reply , Also bring the source port .

The checksum

UDP buffer

buffer

UDP No send buffer

UDP There's a receive buffer

Summary