Ethernet switch router HUB (1)

It is not a specific network, but a technical specification.

Ethernet is the most common communication protocol standard used by local area networks. This standard defines the cable type and signal processing method used in LAN. Ethernet is 10 ~ 10 Base T Ethernet is the most widely used Ethernet technology because of its low cost, high reliability and 10 Mbps speed. The direct expansion of wireless Ethernet can reach 11 Mbps. Many manufacturing suppliers can use common software protocols for communication, which is the best open.

Ethernet connection

Topology

Bus Type: the required cables are few, the price is low, and the management cost is high. It is not easy to isolate fault points, and the shared access mechanism is used, which may cause network congestion. In the early days, Ethernet mostly used bus-type topology, and adopted coaxial cables as the transmission medium. The connection was simple. dedicated network equipment was usually not needed in small-scale networks, however, due to its inherent defects, it has been gradually replaced by star networks with hubs and switches as the core.

Star: easy to manage, easy to expand, dedicated network devices are required as the core node of the network, more network cables are required, and high reliability requirements on core settings are required. A dedicated network device, such as a hub or vswitch, is used as the core node. Each host in the LAN is connected to the core node through twisted pair wires, forming a star structure. Although the star network requires more cables than the bus type, the wiring and connectors are cheaper than the bus type. In addition, the star topology can be easily expanded to a large scale by means of cascade, so it is widely used and used by most Ethernet networks.

Transmission Media

Ethernet can use a variety of connection media, including coaxial cables, twisted pair wires, and optical fiber cables. The twisted pair wires are mostly used for connection from the host to the hub or switch, while the optical fiber cables are mainly used for cascading between switches and the point-to-point link between switches and routers. As the main early connection medium, coaxial cables have gradually become obsolete.

Interface Working Mode

An Ethernet Card can work in two modes: half-duplex and full-duplex.

Half-duplex: the half-duplex transmission mode realizes multi-channel access conflict detection for Ethernet carrier monitoring. The traditional shared LAN works in half duplex mode and can only transmit data in one direction at a time. When data in both directions is transmitted at the same time, conflicts occur, which reduces the efficiency of Ethernet.

Full Duplex: Full Duplex Transmission uses point-to-point connections. This arrangement does not conflict because they use two independent lines in the twisted pair. This means that the bandwidth is increased without installing new media. For example, a parallel track is added between the stations in the preceding example, and two trains can be used for two-way access at the same time. In dual-work mode, the conflict detection circuit is unavailable. Therefore, each dual-work connection only uses one port for point-to-point connection. The transmission efficiency of standard Ethernet can reach 50% ~ With a bandwidth of 60%, the dual-network provides 100% efficiency in both directions.

Working principle of Ethernet

Ethernet adopts the CSMA/CD mechanism with Multi-Channel Access to the carrier frame with conflict detection. Nodes in the Ethernet can see all the information sent in the network. Therefore, we say that Ethernet is a broadcast network.

The Ethernet process is as follows:

To transmit data to a host over Ethernet, perform the following steps:

1. Is there any signal transmitted on the frame receiving channel. If there is any, it indicates that the channel is in the busy state, and the frame listening continues until the channel is idle.

2. If no frame hears any signal, data will be transmitted.

3. Frame listening continues during transmission. if a conflict is found, the backoff algorithm is executed. After a random wait period, the system re-executes Step 1. When a conflict occurs, computers involved in the conflict will return to the frame listening channel status.

Note: Each computer can send only one packet and one congestion sequence at a time to warn all nodes)

4. If no conflict is found, the message is sent successfully. Before all computers attempt to send data again, they must wait 9.6 microseconds to run at 10 Mbps after the last sending ).