Learning notes-transmission of TCP/IP protocol, learning notes-tcpip Protocol

Learning notes-transmission of TCP/IP protocol, learning notes-tcpip Protocol
1. Data Transmission over the network can be divided into two types: connection-oriented and connection-free:1.For connectionless protocols, such as Ethernet, IP, and UDP. 2. For connected protocols, such as ATM, frame relay, and TCP. See the following figure:

• Connection Oriented

In connection-oriented mode, before sending data, you must connect a communication line between the receiving and receiving hosts.

The connection-oriented model is like making calls. After the phone number of the other party is set out, only the peer can pick up the phone number to make the call. After the call is over, the telephone will be deducted as if the power is cut off. Therefore, in connection-oriented mode, you must establish and disconnect connections before and after communication transmission. If you cannot communicate with the peer end, you can avoid sending unnecessary data.

• Connectionless

Connection is not required for connectionless models. The sender can send data freely at any time.,On the contrary, the receiving end never knows where to receive the data. Therefore, when there is no connection, the receiving end must always confirm whether the data is received.

This is just like sending parcels to the post office. The salesperson responsible for processing the mail business does not need to confirm whether the recipient's detailed address exists or whether the recipient can receive the package, as long as the sender has a mail address, the mail package business can be handled. For non-connection communication, unlike telephone communication, it does not need to call or stop the phone, but is free to send the data you want to transmit by the sender. Therefore, in connection-free communication, you do not need to check whether the peer end exists. Even if the receiver does not exist or cannot receive data, the sender can send the data.

(Original link: http://blog.csdn.net/yelangjueqi/article/details/38276203, welcome to reprint, reprint please indicate the source !!)

Ii. Circuit Switching and group Switching

Currently, network communication methods are roughly divided into two types: Circuit Switching and group switching. Circuit Switching technology has a long history and is mainly used in telephone networks in the past. The group exchange technology is a new communication method.20Century60The second half of the year was gradually recognized by people. This book focuses on introducingTCP/IP,Group exchange technology is adopted.

In circuit switching, switches are mainly responsible for data transfer. The computer is first connected to a vswitch, while the vswitch and the vswitch are connected by multiple communication lines. Therefore, when sending data between computers, a communication circuit must be established between the switches and the target host. We call the connection circuit establish a connection. After the connection is established, the user can continue to use this circuit until the connection is disconnected.

If a circuit is only used to connect the communication lines of the two computers, it means that only the two computers need to communicate with each other. Therefore, the two computers can transmit data over an exclusive line. However, if a circuit is connected to multiple computers that need to transmit data to each other, a new problem may occur. Since a computer excludes the entire circuit when sending and receiving information, other computers can only use this circuit to send and receive data after the computer completes processing. And in this process,No one can predict the start and end of data transmission on a computer. If the number of concurrent users exceeds the number of communication lines between vswitches, the communication is impossible. To this end, people think of a new method, that is, let the computer connected to the communication circuit divide the data to be sent into multiple data packets, arranged in a certain order and then sent separately. This isGroup exchange. With group exchange, after data is subdivided, all computers can send and receive data together, which improves the utilization of communication lines. Because the sender and acceptor addresses have been written to the header of each group during the grouping process, even if the same line is used to provide services for multiple users at the same time, you can also clearly distinguish the destination where each group of data is sent and the computer on which it communicates.

In a group switch, a group switch (vro) connects to a communication line. The general process of group exchange is that the sending computer sends the data group to the router. After receiving the group data, the router caches the data in its own buffer zone and forwards the data to the target computer. Therefore, the group exchange has another name: accumulation exchange.

After receiving the data, the router caches the data to the corresponding queue in sequence, and then sends them one by one in the FIFO order.

In group exchange, there is usually only one communication line between the computer and the router, and between the router and the router. Therefore, this line is actually a shared line. In circuit switching, the transmission speed between computers remains unchanged. However, in group switching, the speed of the communication line may be different. Depending on network congestion, the time for data to reach the target address is long or short. In addition, when the vro cache is saturated or overflows, the group data may be lost and cannot be sent to the peer end.

The features of circuit switching and group switching have been demonstrated.








The TCP/IP protocol implements communication between hosts.

TCP/IP is the basic communication protocol used in the network. Although TCP/IP includes two protocols, Transport Control Protocol (TCP) and Internet Protocol (IP), TCP/IP is actually a group of protocols, it includes TCP, IP, UDP, ICMP, RIP, TELNET, FTP, SMTP, ARP, TFTP, and many other protocols. These protocols are collectively referred to as TCP/IP protocols.
TCP/IP consists of four layers: data link layer, network layer, transmission layer, and application layer.
1. Data Link Layer
This is the lowest layer of TCP/IP software. It is responsible for receiving IP data packets and sending them over the network, or receiving physical frames from the network, extracting IP data packets, and handing them over to the IP layer.
2 Network Layer
Responsible for communication between adjacent computers. Its functions include:
1. process the packet sending request from the transport layer. After receiving the request, load the packet into an IP datagram, fill in the header, select the path to the sink, and then send the datagram to the appropriate network interface.
2. process the input datagram: first check its validity, and then perform a path-if the datagram has arrived at the sink, remove the header and hand over the remaining part to the appropriate transmission protocol; if the datagram has not reached the destination, it is forwarded.
3. handle problems such as path, traffic control, and congestion.
Three transport layers
Provides communication between applications. Its functions include:
1. format the information stream;
2. reliable transmission. To implement the latter, the transport layer protocol requires the receiving end to send back for confirmation, and if the group is lost, it must be resend.
4 Application Layer
Provides users with a set of common applications, such as email, file transfer access, and remote logon. Remote logon TELNET provides interfaces registered on other hosts in the network using the TELNET protocol. The TELNET session provides a character-based virtual terminal. File Transfer access FTP uses the FTP protocol to provide the file copy function between machines in the network.

TCP/IP communication

Group exchange