The working principle of the network card

Network card fault does not only affect the workstation itself, but also often affect the normal operation of the entire network, must arouse the attention of network management personnel. In Ethernet, the network card is used to connect the access media and control the access to the media, and the carrier interception multi-channel access/Conflict detection method (CSMA/CD) adopted by Ethernet is realized in the network card.

At the same time, the NIC is also responsible for the upper layer protocol formed by the Protocol Data Unit (PDU) into the Ethernet data frame sent to the network, and is responsible for receiving the processing network from the Ethernet frame.

First, the network card working principle

When sending data, the NIC first listens for carriers on the media (the carrier is indicated by the voltage), and if so, the other site is believed to be transmitting information and continues to listen for the media. Once the communication medium in a certain period of time (called the gap between the frames ifg=9.6 microseconds) is quiet, that is not occupied by other sites, then start to send frame data, while continuing to listen to communication media to detect conflicts. During the sending of data. Http://www.woaidiannao.com

If a conflict is detected, immediately stops the send and sends a "blocking" signal to the media informing the other site that there has been a conflict, discarding the corrupted frame data that might have been received, and waiting for a random time (CSMA/CD the algorithm for determining the wait time is the binary exponential avoidance algorithm). After waiting for a random time, a new send is made. If there is still a conflict after the retransmission multiple times (greater than 16 times), the send is discarded.

When received, the NIC browses each frame transmitted on the media and is considered a conflict fragment if its length is less than 64 bytes. If the received frame is not a conflict fragment and the destination address is a local address, the frame is checked for integrity, and if the frame length is greater than 1518 bytes (called an extra long frame, may be caused by an incorrect LAN driver or interference) or fails to pass the CRC checksum, the frame is considered distorted. By verifying that the frame is considered valid, the NIC receives it for local processing. Basic knowledge of the computer

Factors affecting the work of network card

Whether the NIC works correctly depends on the network card and its connected switching device settings and the interference caused by the network card working environment. such as signal interference, grounding interference, power interference, radiation interference, etc. can have a greater impact on the performance of the network card, and some interference may directly cause network card damage. Computer

PC power failure often causes the NIC to work abnormally. The power supply failure occurs when the discharge interference signal may be channeling to the NIC output port, after entering the network will occupy a large amount of network bandwidth, destroy the normal data packets of other workstations, forming numerous FCS frame checksum error packets, resulting in a large number of reset frames and invalid frames, the proportion with the actual flow of each workstation increased and increase, Seriously interfere with the operation of the entire network system.

The grounding interference also often affects the network card work, the grounding is not good, static because of nowhere to release and constantly accumulate on the chassis, so that the grounding of the network card (through the top of the network card directly connected to the chassis) voltage is not normal, resulting in network card work is not normal, this situation will even breakdown of the network card on the control chip caused by the network card damage.

The interference situation is very easy to appear, sometimes the network card and the video card because too close also can cause interference. When the interference is not serious, the network card can barely work, the data communication quantity is not very often when the user does not feel, but in the large amount of data communication, under the WINDOWS98 will appear "network resources insufficient" prompts, causing machine crash phenomenon.

The network card settings will also directly affect the speed of the workstation. The computer network card can work in full duplex and Half-duplex mode, when the server, switch, workstation working state does not match, such as server, workstation network card is set to Full-duplex state, and switches, hubs, etc. are working in Half-duplex state, will produce a large number of collision frames and some FCS checksum error frames, The access speed will be very slow, and it may take 5-10 minutes to copy a 20MB file from the server.

This error is often due to the negligence of network maintenance personnel, most of the time they use the default settings, and do not verify the actual state.