TCP/IP (1)-Protocol origin, hierarchy and basic knowledge

TCP/IP explanation (1) -- the origin, layering, and basic knowledge of the Protocol. Why does the TCP/IP protocol www.2cto.com exist all over the world, various computers run different operating systems to serve everyone. These computers use different methods to express the same information. It is as if God in the Bible had disrupted the accents of people everywhere and made them unable to cooperate. Computer users realize that computers only work for individual soldiers and will not play a major role. Only by associating them can a computer realize its maximum potential. As a result, people tried to connect computers with wires. However, simple interconnection is far from enough. It is like two people with different languages have met each other and cannot communicate with each other. Therefore, they need to define something in common for communication, and TCP/IP is born for this. TCP/IP is not a protocol, but a collective name of a protocol family. It includes the IP protocol, IMCP protocol, TCP protocol, and more familiar http, ftp, pop3 protocol and so on. Computers can communicate freely with other computer terminals as if they have learned a foreign language. TCP/IP protocol layer mentioned protocol layer, we can easily think of the classic architecture of the ISO-OSI layer-7 protocol, but the structure of the TCP/IP protocol family is slightly different. TCP/IP protocol families are packaged in layers from top to bottom. The top layer is the application layer, which includes http, ftp, and other familiar protocols. The second layer is the transport layer. The famous TCP and UDP protocols are at this layer (do not tell me that you have never used udp to play interstellar games ). The third layer is the network layer. The IP protocol is here. It is responsible for adding IP addresses and other data to the data (which will be discussed later) to determine the transmission target. The fourth layer is the data link layer. This layer adds an Ethernet protocol header to the data to be transmitted and performs CRC encoding to prepare for the final data transmission. The next step is the hardware level, responsible for network transmission. The definition of this level includes the network cable standard and the definition of the network card. (We Don't Need To care about this. We don't need to do it either ), therefore, some books do not place this level in the TCP/IP protocol family, because it has almost no relationship with the TCP/IP protocol writers. The sending protocol host encapsulates the data according to the protocol from the top to the bottom, and the host receiving the data unpacks the data packet according to the protocol, and finally obtains the required data. This structure is very stack-like, so some articles also refer to the TCP/IP protocol family as the TCP/IP protocol stack. Some basic knowledge www.2cto.com should have some basic knowledge before learning the protocol. · Each node on an Internet address (IP address) must have an independent Internet address (also called an IP address ). Currently, the IP address is usually a 32bit number, which is also known as the IPv4 standard. The 32bit number is divided into four groups, that is, the common rule 255.255.255.255 format. According to IPv4 standards, addresses are classified into five categories. We usually use Class B addresses. For specific categories, see other documents. Note that IP addresses are a combination of network numbers and host numbers, which is very important. · The Domain Name System is a distributed database that provides the service of converting the Host Name (that is, the website address) into an IP address. · What is RFCRFC? RFC is the standard document of TCP/IP protocol. Here we can see the long definition list of RFC. Now it has over 4000 protocol definitions. Of course, what we want to learn is, that is, more than a dozen protocols. · Port Note: This number is a logical number used on TCP and UDP. It is not a hardware port. We usually say that port XX has been closed, it's just that the IP packet with this number is filtered out at the IP level. · Application programming interfaces currently commonly used programming interfaces include socket and TLI. The previous section is also called "Berkeley socket", which shows how much contribution Berkeley has made to the development of the network.