Rebuild an instance for a small Internet cafe

Seeing that the Internet cafes around him were so hot, Lao Zhang also made an investment. So we have the following story:

Lao Zhang borrowed money to open an Internet cafe!

I bought a new computer!

The network composition is not smooth, silly!

......

Time is money! What should we do? Lao Zhang quickly found this "world-class man ". I did not live up to the title of "Prawn", and it was done in less than an hour. Maybe you will ask, where is the reason? How can this problem be solved? Don't be busy, and listen slowly.

　　Lao Zhang's network is like this.

In order to save the initial investment to the maximum extent, Lao Zhang uses cheap hubs (also known as hubs). This networking method is theoretically referred to as shared networks. A shared network is a network in which all computers in the network share the network bandwidth. For example, if the port speed of the hub is 10 Mbps and 24 ports are connected to a computer, the transmission rate of each port is only 1/24 of 10 Mbps. Lao Zhang's Internet cafe has more than 40 computers, making it reasonable that the Internet access speed is slow and the connection performance between computers is relatively poor.

Figure 1 The connection rate between hub A and hub C is only 1/256 of 10 Mbps!

It is worth noting that the connection between the hubs of the Internet cafe is also faulty (1 ). When the port number of the hub is 16, the connection rate between hub A and hub B is only 1/16 of 10 Mbps, and the connection rate between hub B and hub C is also 1/16 of 10 Mbps, the connection rate between hub A and hub C is only 1/256 of 10 Mbps! When hub C communicates with the computer of hub A, it's not too slow! In addition, because the proxy server used to share Internet access is also located in hub A, it makes sense that computers on the hub C are intolerable to access the Internet. To improve network performance, you must use the connection method shown in 2 to ensure that the connection speed between any two hubs is 1/16 of 10 Mbps, in addition, the connection between all computers and proxy servers can be ensured at a high rate.

Figure 2 the connection method required to improve network performance.

Guaranteed to some extent

Computers and troubles

The slow speed problem is basically solved. But why can't I connect to each other after I add some computers?

Figure 3 incorrect connection method.

The reason is simple. To connect an added computer to the network, a new set line device must be added. Unfortunately, Lao Zhang still uses a hub and connects 4th hubs in cascade mode (as shown in 3). This violates the 5-4-3 rule of 10Base-T, network Communication fails. The so-called 10Base-T refers to the international standard for building 10 Mbps twisted pair Ethernet. However, it is often used to refer to 10 Mbps twisted pair network. 10Base-T specifies the maximum transmission distance of twisted pair wires to 100 meters.

The 10Base-T 5-4-3 rule means a maximum of five lines between any two computers (including the connection cable from the hub to the hub and the connection cable from the hub to the computer) and four hubs, and only three hubs can be directly connected to network devices such as computers. 4 shows the maximum topology allowed by the 10Base-T network and the number of layers of the hub connected by the energy level. The middle hub is the only hub in the network that cannot be directly connected to the computer. The use of rules is related to the maximum latency allowed by the network. After the computer sends data, if no response is received within a certain period of time, it will be deemed that the data fails to be sent and will be repeatedly sent, but the other party will never receive it. The transmission delay of data in the network is affected by the length of the network cable and the collection line equipment. Therefore, the twisted pair cable network not only limits the transmission distance of the cable, the number of hubs is also limited.

Figure 4 maximum topology allowed by the 10Base-T network and the number of hub layers connected by the energy level.

In the connection mode of Lao Zhang, although there are no more than five lines and no more than four hubs between computers, the four hubs are connected to the computer, it still violates rules 5-4-3. Therefore, communication between computers becomes inevitable. It is impossible to access the Internet through a proxy server.

Figure 5 connect multiple hubs in this way.

Can't the network be expanded? Of course. You only need to connect the other three hubs to the same hub, as shown in Figure 5. In this way, not only do we strictly abide by the 5-4-3 rules, but also ensure the network communication efficiency to some extent.

Better networking solutions

Through the above description, we can see that the communication efficiency of the shared network is relatively poor. The larger the network, the smaller the Effective Bandwidth allocated to each computer, and the inability to build large-scale or ultra-large scale networks. So, is there no effective remedy? Of course.

1. Improve the hub transmission rate

From the perspective of available network bandwidth, in addition to 10 Mbps hubs, there are also 10/100 Mbps and Mbps adaptive hubs available. Of course, the network card transmission rate can also adapt to it, otherwise it will be futile. However, since bandwidth is shared in the shared network, the improvement of the hub transmission rate cannot significantly improve the transmission efficiency caused by the excessive number of networks. Therefore, simply increasing the transmission rate of a hub is only applicable to networks with a small number of users.

Ii. upgrade to a switched network

When the number of computers in the network is large and the communication efficiency is significantly reduced, you can consider using switches to upgrade the network. If the network transmission rate requirement is not too high, you can add only one vswitch and connect the hub and server to the vswitch (6 ), the hubs connected to different ports can communicate with each other at the same time to improve network transmission efficiency. Of course, if conditions are met, you can replace all the hubs with switches, and the network communication efficiency will soar!

Figure 6 vswitch Networking Solution.

The transmission mechanism of a vswitch is completely different from that of a hub. The transmission rate provided by each port in a switched network is the nominal bandwidth of the network. If we compare a shared-bandwidth network to a country path, the exchange network is like an overlay. No matter where the data comes from and where it goes, it can be passed through at a high speed at the same time.

Currently, the mainstream switch brands on the market include Cisco, 3Com, Huawei, Digital China, all-round, Shida, and TP-Link, these manufacturers' 8-port 10/100 M switches have hundreds of Yuan of products and thousands of yuan of products. The 24-port 10/100/6000 m switch with the most application in the network can be roughly divided into three grades. The prices of Cisco and 3Com are generally about yuan, and the prices of Intel products are between and ~ 8000 yuan, while the prices of domestic brands are generally less than 4000 yuan, such as digital China, omnidirectional, Shida, TP-Link, etc. Enterprises or public institutions that are generally used can focus more on products of domestic brands when the price level is obvious.