Zhao Yazhi _java Network Programming (4) Differences between TCP/IP, HTTP, and sockets

Programming via Java Network (1) network architecture and communication Protocols I know that the IP protocol corresponds to the network layer, the TCP protocol corresponds to the transport layer, and the HTTP protocol corresponds to the application layer,

The three are inherently not comparable

• The TPC/IP protocol is a transport layer protocol that mainly addresses how data is transmitted over the network,
• HTTP is an application-layer protocol that primarily addresses how data is packaged.
• Sockets are the encapsulation and application of the TCP/IP protocol (at the programmer level).

The three relationships in general

• The TCP of the transport layer is based on the IP protocol of the network layer.
• The HTTP protocol of the application layer is also the TCP protocol based on the transport layer.
• The socket itself is not a protocol, it simply provides an interface for TCP or UDP programming

Socket

• Socket is the encapsulation of TCP/IP protocol, the socket itself is not a protocol, but a calling interface (API).
• With the socket, we can use the TCP/IP protocol.
• In fact, the socket is not necessarily associated with the TCP/IP protocol.
• The socket programming interface is designed to adapt to other network protocols as well.

So, the advent of sockets just makes it easier for programmers to use the TCP/IP protocol stack, which is an abstraction of the TCP/IP protocol, thus forming some of the most basic function interfaces we know, such as Create, listen, connect, accept, send, Read and write, and so on.

The relationship between TCP/IP and HTTP protocols

• When we transmit data, we can use only the (Transport Layer) TCP/IP protocol, but in that case, the data content cannot be recognized without the application layer.
• If you want to make the transferred data meaningful, you must use the application-layer protocol.
• There are many application layer protocols, such as HTTP, FTP, Telnet, etc., and you can define the application layer protocol yourself.
• The web uses the HTTP protocol as an application-layer protocol to encapsulate HTTP text information and then send it to the network using TCP/IP as the Transport layer protocol.

Socket and TCP/IP protocol relationships

• TCP/IP is just a protocol stack, just like operating system operation mechanism, must be implemented specifically, but also to provide external operating interface.
• This is like the operating system will provide standard programming interfaces, such as the Win32 programming interface,
• TCP/IP also provides the interface for programmers to do network development, which is the socket programming interface. ”

CSDN has a comparative image of the description: HTTP is a sedan, providing a specific form of encapsulation or display data; the socket is the engine that provides the ability to communicate on the network.

Want to learn more about the TCP/IP protocol knowledge to find Niang.

A detailed knowledge point

TCP connections

To understand the socket connection, you need to understand the TCP connection first. Mobile phone can use the network function is because the bottom of the mobile phone implementation of TCP/IP protocol, you can make the mobile phone terminal through the wireless network to establish a TCP connection. TCP protocol can provide an interface to the upper network, so that the transmission of the upper network data is based on the "No Difference" network.

Setting up a TCP connection requires a "three-time handshake":

1. First handshake: The client sends a SYN packet (SYN=J) to the server and enters the Syn_send state, waiting for the server to confirm;
2. Second handshake: The server receives the SYN packet, it must confirm the customer's SYN (ACK=J+1), and also send itself a SYN packet (syn=k), that is, the Syn+ack packet, when the server enters the SYN_RECV state;
3. Third handshake: The client receives the server's Syn+ack packet, sends the acknowledgment packet ack (ACK=K+1) to the server, the packet is sent, the client and the server enter the established state, and the handshake is completed three times.

The data is not included in the packets that are delivered during the handshake, and the client and server formally begin transmitting the data after the three handshake is complete.

Ideally, once a TCP connection is established, the TCP connection is maintained until either side of the communication actively closes the connection.

When disconnected, both the server and client can proactively initiate a request to disconnect a TCP connection, which requires a "four-time handshake" between the server and the client, eventually determining the disconnection

HTTP connection

The HTTP protocol, the Hypertext Transfer Protocol (hypertext Transfer Protocol), is the foundation of Web networking and one of the most commonly used protocols for mobile networking, an application built on the TCP protocol.

The most notable feature of an HTTP connection is that each request sent by the client requires a server loopback response, and the connection is actively released after the request has ended . The process from establishing a connection to closing a connection is called a "one-time connection."

1. In HTTP 1.0, each request from the client requires a separate connection to be established, and the connection is automatically freed after the request is processed.
2. In HTTP 1.1, multiple requests can be processed in a single connection, and multiple requests can overlap, without waiting for a request to end before sending the next request.

Because HTTP is actively releasing the connection after each request ends, the HTTP connection is a "short connection", which requires constant connection requests to the server to maintain the client program's online status. As a general practice, there is no need to obtain any data immediately, and the client will keep a "keep-connected" request to the server at regular intervals, and the server responds to the client after receiving the request, indicating that the client is "online". If the server can not receive the client's request for a long time, it is considered that the client "offline", if the client cannot receive a reply from the server for a long time, it is considered that the network has been disconnected.

Socket principle

Socket (socket) concept

Socket (socket) is the cornerstone of communication and is the basic operating unit of network communication supporting TCP/IP protocol .

It is an abstract representation of the endpoint in the network communication process and contains five kinds of information that must be made for network communication:

1. protocol used by the connection
2. IP address of the local host
3. Protocol port for Local processes
4. IP address of the remote host
5. Protocol port of the remote process.

When the application layer communicates data through the transport layer, TCP encounters a problem that provides concurrent services for multiple application processes at the same time.

Multiple TCP connections or multiple application processes may require data to be transmitted over the same TCP protocol port.

To differentiate between different application processes and connections, many computer operating systems provide a socket (socket) interface for applications interacting with the TCP/IP protocol.

The application layer can communicate with the transport layer through the socket interface, differentiate the communication from different application processes or network connections, and realize the concurrent service of data transmission.

Establish a socket connection to establish a socket connection requires at least one pair of sockets, one running on the client, called Clientsocket, and the other running on the server side, called ServerSocket.

The connection process between sockets is divided into three steps:

1. Server monitoring: Server-side sockets do not locate specific client sockets, but are waiting for the status of the connection, real-time monitoring network status, waiting for the client connection request.
2. Client request: Refers to the client's socket to make a connection request, to connect to the target is the server-side socket. To do this, the client's socket must first describe the socket of the server it is connecting to, indicate the address and port number of the server-side socket, and then make a connection request to the server-side socket.
3. Connection confirmation: When a server-side socket hears or receives a connection request from a client socket, it responds to a client socket request, establishes a new thread, sends a description of the server-side socket to the client, and once the client confirms the description, the two sides formally establish the connection. While the server-side socket continues to be in the listening state, it continues to receive connection requests from other client sockets.

Socket connection and TCP connection

When you create a socket connection, you can specify the transport layer protocol used, which can support different transport layer protocols (TCP or UDP), which is a TCP connection when a connection is made using the TCP protocol.

Socket connection and HTTP connection

Since the socket connection is usually a TCP connection, once the socket connection is established, the communication parties can start sending data content to each other until the two sides are disconnected.

However, in real network applications, the client-to-server communication often needs to traverse multiple intermediary nodes, such as routers, gateways, firewalls, and so on, most firewalls will turn off long inactive connections and cause the Socket connection to be disconnected, so it needs to be polled to tell the network that the connection is active.

The HTTP connection uses a "request-response" approach, not only to establish a connection at the time of the request, but also to be able to reply to the server after the client has made a request to the server.

In many cases, the server side is required to proactively push data to the client, keeping the client and server data in real time and in sync.

• If a socket connection is established, the server can transmit the data directly to the client
• If an HTTP connection is established, the server needs to wait until the client sends a request before the data can be passed back to the client

Therefore, the client periodically sends a connection request to the server, not only to remain online, but also to "ask" the server if there is new data, and if so, pass the data to the client.

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Zhao Yazhi _java Network Programming (4) Differences between TCP/IP, HTTP, and sockets