Dpi refers to the number of pixels per unit area, which is the scanning accuracy. At present, the number of pixels in an inch area is calculated internationally. The smaller the dpi, the lower the definition of scanning. Due to the influence of network transmission speed, all the pictures used on the web page are 72dpi, but this parameter cannot be used for developing photos, and it must be 300dpi or 350dpi higher. For example, to develop a 4*6 inch photo, the scanning accuracy must reach 300, so the file size should be (4*300)*(6*300)= 1200 pixels * 1800 pixels.

DPI (Deep Packet Inspection) Deep Packet Inspection Technology

DPI technology is a traffic detection and control technology based on application layer. When IP packets, TCP or UDP data streams pass through the bandwidth management system based on DPI technology, the system deeply reads the contents of IP packets, reorganizes the application layer information in the OSI seven-layer protocol, thus obtaining the contents of the whole application program, and then shapes the traffic according to the management strategy defined by the system.

The bandwidth management solution based on DPI technology is similar to the well-known antivirus software system in some respects, that is, the application type it can identify must be known to the system. Take BT, which users are familiar with, as an example, and its handshake protocol feature word is ". BitTorrent protocol "; In other words, the anti-virus system should have a huge virus feature library in the background, and the bandwidth management system based on DPI technology should also maintain an application feature library. When the traffic passes, the application type can be determined by comparing the unpacked application information with the background feature database. When new applications appear, the background application feature database should be updated to have the ability to identify and control new applications.