Why does a wireless switch replace a hub?

What is a wireless switch and a hub? As the main connection device of the local area network, vswitches have many obvious advantages over hubs.

We have learned that the data packet transmission mode of the hub is broadcast. Because only one broadcast exists in the hub, only one data packet can be transmitted at the same time, low channel utilization. For wireless switches.

It can "recognize" every computer connected to itself. Why? It is based on the physical address of each network card, also known as "MAC address ". The vswitch also provides the MAC address learning function. It remembers the MAC addresses connected to itself to form a table corresponding to the nodes and MAC addresses.

With such a table, it does not have to broadcast any more. The data sent from a port contains the MAC address of the destination, in the MAC address table saved in the cache, find the node corresponding to the destination MAC address contained in the data package, A temporary dedicated data transmission channel is established between the two nodes, so that the two nodes can communicate without interference.

Note that the lower the switch grade, the smaller the switch cache, that is, the smaller the space prepared to save the MAC address, the corresponding number of MAC addresses is smaller. Generally, a vswitch has 1024 MAC address memories, which can meet actual needs.

From the above analysis, we know that the data transmission carried out by the switch has a clear direction, rather than disorderly transmission, rather than the hub broadcast mode, as shown in transfer 3. At the same time, because the switch can perform full duplex transmission, the switch can establish temporary Dedicated channels between multiple pairs of nodes at the same time, forming a three-dimensional cross data transmission channel structure.

The Data Transmission Principle of a vswitch is described as follows:

After receiving an Ethernet frame from a node, the switch immediately searches for the address table port number-MAC address in its memory, to confirm the node on which the NIC of the target MAC is connected, and then forward the frame to the node. If the MAC address is not found in the address table, that is, the target MAC address is displayed for the first time, the switch broadcasts the packets to all nodes.

After the NIC that owns the MAC address receives the broadcast frame, it immediately responds, so that the switch can add the "MAC address" of its node to the MAC address table. In other words, when the switch receives a frame from a node, the broadcast frame is excluded.) Two actions are performed on the address table.

First, check whether the source MAC address of the frame is already in the address table. If not, add the MAC address to the address table so that you can know the node on which the MAC address is located; second, check whether the target MAC address of the frame is in the address table.

If the MAC address is already in the address table, send the frame to the corresponding node, instead of sending the frame to all nodes as the hub, you only need to send the frame to the corresponding node so that the nodes that are neither the source node nor the target node can still communicate with each other, this provides a higher transmission rate than the hub. If the MAC address is not in the address table, the frame will be sent to all other node source nodes), which is equivalent to a broadcast frame.

When talking about this, we need to understand the fact that the switch cannot know the address of each node in your network when it is just bought. That is to say, when the switch is powered on, its MAC address table is blank. How is the vswitch Address Table created?

Learning! The wireless switch updates the address table based on the source MAC address in the Ethernet frame. When a computer is powered on, the NIC installed in the system regularly sends out idle packets or signals, and the switch can learn about its existence and its MAC address. This is called automatic address learning.

Because the switch can automatically update the address table based on the source MAC address in the received Ethernet frame, the longer the switch is used, the more MAC addresses it learns, the fewer unknown MAC addresses, the smaller the number of broadcast packets, and the faster the speed.

So, will the wireless switch always remember the relationship between all port numbers-MAC addresses? No. Because the memory in the switch is limited, the number of MAC addresses that can be remembered is also limited. Since we can't remember all the MAC addresses endlessly, we must give them a corresponding mechanism to forget the MAC addresses, so as to get rid of the new MAC addresses.

In fact, engineers set an Auto-aging time for the switch. If a MAC address is set to 300 seconds by default within a certain period of time, the switch automatically clears the MAC address from the address table. When this MAC address is re-displayed, it will be processed as a new address.

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To sum up, as the main connection device of the current LAN, the wireless switch has many obvious advantages over the hub. At present, it is replacing the hub in an all-round way. With the continuous development of the exchange technology, the price of Ethernet switches drops sharply, and switching to the desktop is the trend of the times. If the network has a large number of users, busy applications and a variety of servers, and you have not made any adjustments to the network structure.

The performance of the entire network may be very low. The most effective solution is to replace the original hub with a vswitch. Of course, the price of the vswitch is more expensive than that of the hub, but it should be acceptable at present. Moreover, the performance is not as simple as "a little bit!