1. The most common communication model in the network layer: (reliable two-way byte stream)
World Wide Web: c/s model
BitTorrent: point-to-point model a large number of clients open to connect with each client, other exchange data
SkyType: relay server (eg WeChat chat)
2. Two main advantages of packet exchange
1. It makes the exchange very simple because they don’t need to understand the packet flow
2. It allows us to share the effective sharing capacity between the many streams of the link
3. Hierarchical significance
simple steps through the code c:
source -> compiler (lexical analysis and interpretation of the code and the code generation preprocessing statement optimization) -> linker (object files and libraries linked together to form an executable file)
points The layer solves the overall problem of writing programs to be executed on the hardware. It is divided into modules and functional components. Each module or functional component has a clear role and provides a defined service for the upper layer, with clear separation of concerns, eg: linker You can focus on effectively splicing objects together,
(breaking the layering): we need some special operations that only the processor can complete, eg: you need to run on a new processor, the developer needs to write new assembly code eg : (NAT and network) Address translator, very useful equipment, but it is almost impossible to add a new transmission protocol like internet
1. Modularity : break down the system into smaller and more manageable modules
2. Clearly defined services : each layer provides clear services for the upper layer
3. Reuse : the upper layer can be realized by all the hard work of others This layer
4. Light points separation
5. Continuous improvement
6. Peer-to-peer communication (specific to hierarchical communication systems)
encapsulation and architecture principles:
1. If you use wifi to open a web page process:
your web browser will Generate an HTTP Get request. The HTTP GET request is the payload of the TCP segment, the TCP segment that encapsulates the HTTP GET is the payload of the IP data packet, and the IP data packet of the
crazy TCP segment and the HTTP GET segment is the payload of the wifi.
2. Use encapsulation to recursively layer the protocol layers
eg: (used in the enterprise) Virtual Private Network Transport Layer Security (TLS) When you communicate with the Internet and send IP packets instead of sending them normally, you can Send them in the connection, the office router can route them normally, so that you can access the protected private network resources in the office, allowing people to log in to the network service through the virtual private network, and you can pass the gateway (receive from allowed customers Connected computer) to perform this operation
**3.**
字节顺序：如何在内存中布置多字节值的方式称为字节顺序，并且有两个选项，Little endian, the least significant byte is at the lowest address (more meaningful to computers), Big endian, the most significant byte is the lowest address (more meaningful to humans)
