Comprehensive interpretation of the hub

Comprehensive interpretation of the hub

If we are in constant contact with the network, we should not be unfamiliar with the hub as the basic equipment for building a local area network, but how much do we know about the knowledge behind the hub?

1. Definition of hub

The hub (HUB) belongs to the basic equipment in the data communication system. It is a hardware device that does not require any software support or requires little management software management. It is widely used in various occasions. The hub works in a local area network (LAN) environment. Like a network card, it is applied to the first layer of the OSI reference model, so it is also called a physical layer device. The hub uses internal electrical interconnection. When the LAN maintenance environment is a logical bus or ring structure, the hub can be used to establish a physical star or tree network structure. In this regard, the hub acts as a multi-port repeater. In fact, the hub is actually a type of repeater. The difference is that the hub can provide more port services, so the hub is also called a multi-port repeater.

The structure of the external board surface of a common hub is very simple. For example, D-Link's simplest 10BASE ~ T EthernetHub hub is a rectangular parallelepiped, with AC power sockets and switches on the back, an AUI interface and a BNC interface, and a row of 17 RJ-45 interfaces are distributed in most places on the front. On the right side of the front there are LED interface indicators and LED status indicators corresponding to each RJ-45 interface. From the appearance, high-end hubs are not much different from modern routers or switched routers. Especially for modern dual-speed adaptive Ethernet hubs, because of the universal built-in switching modules that can communicate with each other between internal 10Mb / s and 100Mb / s network segments, such hubs can be completely used in the network segment with the hub as a node In order to achieve communication exchange between nodes, sometimes people will simply call this type of switching hub as a switch, which makes it difficult for users who use the hub for the first time to correctly identify them. But it is a relatively simple method to identify the hub according to the type of the backplane interface.

Second, the working characteristics of the hub

According to the IEEE 802.3 protocol, the hub function is to randomly select a certain port of the device and let it monopolize the entire bandwidth to communicate with the hub's uplink device (switch, router or server, etc.). It can be seen from this that the hub has the following two characteristics during operation.

The first is that the Hub is just a multi-port signal amplification device. When a port receives a data signal during operation, because the signal has been attenuated during the transmission from the source port to the Hub, the Hub will shape and amplify the signal. Regenerate (restore) the attenuated signal to the state at the time of transmission, and then forward it to all other ports in working state. As can be seen from the working method of Hub, it only plays the role of signal amplification and retransmission in the network. Its purpose is to expand the transmission range of the network without the directional transmission capability of the signal. It is a standard shared device. Therefore, some people call the hub "silly Hub" or "dumb Hub".

Secondly, the Hub only communicates with its upstream devices (such as upper-level Hubs, switches, or servers). The ports on the same layer do not communicate directly, but broadcast the information to all ports through the upstream devices. It can be seen that even when communicating between two different ports of the same Hub, it is necessary to go through two steps: the first step is to upload the information to the uplink device; the second step is to upload the information to the uplink device Broadcast to all ports.

However, with the development of technology and changes in demand, many Hubs have expanded their functions and are no longer affected by this working mechanism. The network formed by Hub is a shared network, and Hub can only work under half-duplex.

Hub is mainly used for the establishment of a shared network, which is the most economical solution from the server to the desktop. In a switched network, Hub is directly connected to the switch and sends the data from the switch port to the desktop. The Hub networking is flexible. It is located in a star-shaped node of the network. It centrally manages the workstations connected to the nodes. It does not allow the problematic workstations to affect the normal operation of the entire network, and users are free to join and exit.

Three, hub classification

There are many types of hubs.

1. Classification by structure and function

According to the structure and function, hubs can be divided into three types: unmanaged hubs, stacked hubs and chassis hubs.

(1) Unmanaged hub

The simplest hub provides a central network connection via an Ethernet bus, connected in a star form. This is called an unmanaged hub and is only used in very small networks with up to 12 nodes (in a few cases, it can be more). Unmanaged hubs do not have management software or protocols to provide network management functions. Such hubs can be passive or active. Active hubs are used more often.

(2) Stacked hub

Stacked hubs are slightly more complicated hubs. The most notable feature of the stacked hub is that 8 repeaters can be directly connected to each other. In this way, the network can be expanded by simply adding a hub and connecting it to an installed hub. This method is not only low-cost, but also simple and easy.

(3) Chassis hub

Chassis hub is a modular device, which can be inserted into many types of modules on its backplane circuit board. Some hubs have redundant backplanes and power supplies. At the same time, some modules allow users to replace those failed modules without shutting down the entire hub. The backplane of the hub prepares multiple buses for the plug-in modules. These plug-in modules can adapt to different segments, such as Ethernet, Fast Ethernet, Fiber Distributed Data Interface (FDDl) and Asynchronous Transfer Mode , ATM). Some hubs also contain bridges, routers, or switching modules. Active chassis hubs may also have retimed modules to associate with amplified data signals.

2. According to the type of LAN

From the perspective of LAN, hubs can be divided into five different types.

(1) Single-relay hub

The simplest hub is a type of hub used in the simplest trunking LAN segment, similar to a stacked Ethernet hub or token ring network multi-station access unit (MAU).

(2) Multi-segment hub

Derived directly from the hub of a single trunk network segment, using a hub backplane, this hub has multiple trunk network segments. The main advantage is that users can be distributed on multiple relay network segments to reduce the information traffic load of each network segment. The information traffic between network segments generally requires an independent bridge or router.

(3) Port switching hub

The integrator is based on a multi-segment hub, which automates the connection process between user ports and multiple backplane segments, and is implemented by adding a port switch matrix (PSM). PSM can provide an automatic tool for connecting any external user port to any trunk network segment on the hub backplane. The main advantage of the port-switching hub is that it can realize the automatic features of movement, addition and modification.

(4) Network interconnection hub

Port switching hubs focus on port switching, and network interconnect hubs can provide some types of integrated connections between multiple network segments on the backplane. This function is accomplished through an integrated bridge, router, or LAN switch. At present, such hubs are usually in the form of chassis. (5) Switching hub

At present, the line between the hub and the switch has become blurred. The switching hub has a core switching backplane and uses a pure switching system to replace the traditional shared media trunk network segment. Such products are already on the market, and hybrid (trunk / switch) hubs are likely to control this market in the next few years. It should be noted that there is almost no difference in the characteristics between such hubs and switches.

Fourth, the choice of LAN hubs With the development of technology, in LANs, especially in some large and medium-sized LANs, hubs have gradually withdrawn from application and replaced by switches. At present, the hub is mainly used in the edge of some small and medium-sized networks or large and medium-sized networks. The characteristics of the application of small and medium-sized local area networks are introduced below, and their selection methods are introduced.

1. Speed ​​as standard

The choice of hub speed is mainly determined by the following three factors.

(1) Bandwidth of uplink device

If the uplink equipment allows to run 100Mbit / s, you can naturally buy a 100Mbit / s hub; otherwise, lOMbit / s hub should be an ideal choice, because it is a network with a small number of connected devices and the communication traffic is not very large / S hub can meet the application needs.

(2) Number of connection ports provided

Since all stations connected to the hub are competing for the same upstream bus, the greater the number of connected ports, the easier it is to cause conflicts. At the same time, the data sent to any port of the hub will be sent to all ports connected to the hub. Too many ports will reduce the effective utilization rate of the device. According to practical experience, the number of computers managed by a lOMbit / s hub should not exceed 15 and the number of lOOMbit / s should not exceed 25. If it exceeds, you should use a switch instead of a hub.

(3) Application requirements

The transmitted content does not involve voice or image. When the transmission volume is relatively small, select 10Mbit / s. If the transmission volume is large, and it may involve multimedia applications (note that the hub is not suitable for transmitting time-sensitive signals, such as voice signals), you should choose 100Mbit / s or 10 / 100Mbit / s adaptive hub. The price of 10 / 100Mbit / s adaptive hub is generally higher than 100Mbit / s.

2. Based on whether expansion can be met

When the ports provided by a hub are not enough, there are generally the following two methods to expand the number of users.

(1) Stack

Stacking is a method to solve the shortage of a single hub port, but because multiple hubs stacked together still work in the same environment, the number of stacked layers can not be too much. However, many hubs on the market have more stacking layers than other brands as a selling point. If you encounter this situation, you should treat them differently: on the one hand, the more stackable layers, the higher the stability of the hub. On the one hand, the more stackable layers, the less bandwidth each user can actually enjoy.

(2) Cascade

Cascading is another way to increase the number of users in the network, but the use of this function is generally conditional, that is, the Hub must provide a cascadable port, which is often marked as "Uplink" or "MDI" "", Use this port to cascade with other Hubs. If no special port is provided and cascading is necessary, the twisted pair connecting the two hubs must be miswired during production.

3. Based on whether to provide network management functions

The early Hub was a low-end product and was not manageable. In recent years, with the development of technology, some hubs have technically introduced the function of a switch, and a simple management (SNMP) of the hub can be realized by adding a network management module for convenient use. However, it should be pointed out that, although the same supports SNMP, modules of different manufacturers cannot be mixed, and modules of different products of the same manufacturer are also different. At present, the Hub that provides SNMP function has a higher price. For example, the price of DE-824 non-intelligent 24-port 10Base-T from D-Link is about 1,000 yuan cheaper than that of DEl8241 after the installation of network management module.

4. Take the external dimensions as reference

If the network system is relatively simple, there is no integrated wiring between buildings, and there are fewer users in the network, such as a family, one or several adjacent offices, there is no need to consider the size of the Hub. But sometimes this is not the case. For example, to facilitate centralized management of multiple Hubs, the cabinet has been purchased before the Hub is purchased. At this time, the size of the Hub must be considered when purchasing the Hub, otherwise the Hub cannot be installed in the rack on. Now the cabinets on the market generally follow the 19-inch industrial specifications when designing, and it can install most of the 5-, 8-, 16-, and 24-port Hubs. However, in order to prevent accidents, be sure to pay attention to whether it meets the 19-inch working specification when purchasing, so that it can be safely and centrally managed in the cabinet.

5. Due consideration of brand and price

Like network cards, Hub currently on the market is basically occupied by American brands and Chinese Taiwanese brands. Recently, several companies in the mainland have also launched hub products. Among them, high-end Hubs are mainly occupied by American brands, such as 3COM, Intel, Bay, etc. They are relatively unique in design. Generally, several or even each port is equipped with a processor. Of course, the price is also higher. D-Link and Accton in Taiwan of our country occupy the main share of the low-end Hub. Lenovo, Shida, TPLink and other companies in the mainland have introduced their products to the market with strong strength. These mid-range and low-end products all use single-processor technology, and the design ideas of their peripheral circuits are similar. The welding process to achieve these ideas is basically the same. The prices are similar. The mainland products are relatively cheaper and are increasingly occupying a larger market share. Recently, with the decreasing price of switch products, the hub market is shrinking. However, in certain occasions, the hub can bring higher efficiency with lower investment due to its low latency characteristics. It is impossible for a switch to completely replace a hub.

V. Analysis and processing of common failures of the hub For the most common and commonly used star topology, the hub (HUB) is the heart. Once it fails, the entire network will not work, so its quality is for the entire network Both are quite important.

Hub (HUB) or switch (Switch) is the most popular equipment in LAN. In general, they provide convenience for users to find network faults. For example, by observing whether the indicator light of the port connected to the HUB (or Switch) is lit, you can determine whether the network connection is normal. For lO / lOOMb / s adaptive HUB (or Switch), you can also judge whether the connected computer is working in the 10Mb / s state or the lOOMb / s state through the different colors of the port indicator lights. Therefore, in most applications, the use of HUB (or Switch) is conducive to network maintenance. However, improper use of HUB (or Switch) or damage to itself will cause problems for the network connection.

1. Application failure of hub in 100Mb / s network

[Fault phenomenon]

After upgrading the network from 10Mb / s to 100Mb / s, the network cannot work normally.

[Fault analysis and processing]

In a local area network, when the connection range of the network is large, the transmission distance of the network can be expanded by cascading between HUBs. In the 10Mb / s network, up to four levels can be cascaded, so that the maximum transmission distance of the network can reach 600m. But when the network is upgraded from 10Mb / s to 100Mb / s or a new 100Mb / s local area network is established, if the ordinary method is used to connect to 100MHUB, the local area network will not work properly. As we all know, in a 100Mb / s network, only two 100Mb / s HUBs are allowed to be cascaded, and the connection distance between two 10Mb / sHUBs cannot be greater than 5m, so the maximum distance of a 100Mb / s LAN when using HUB is 205m . If the actual connection distance does not meet the above requirements, the network will not be able to connect. This should be paid enough attention, otherwise it is easy to cause serious errors when users plan the network.

2. Application failure of the hub when cascading

[Fault phenomenon]

A unit set up a local area network by itself, using two 16-port (with a cascade port) 10M shared hub, all computers are connected to the HUB of the main computer room through the HUB. Among them, HUBA is connected to the 16th port of HUBB through the cascade port, HUBB is connected to the HUB of the main computer room through the cascade port, and the other ports are respectively connected to the workstation. The entire workstation uses a static IP address, the values ​​are, ... and so on, is assigned to the NT server, each computer (including the server ) Subnet masks are all Before setting up a workstation before connecting to the server, use the Ping command to test, the results are all connected, and all the workstations connected to HUB A can also use the Ping command to communicate with the workstation connected to HUB B. However, when connected to the server, only the workstation connected to HUB B can log in to the server, but the workstation connected to HUBA cannot log in.

[Fault analysis and processing]

By observing the indicators of the computer's network card and the indicators of the ports on the two HUBs, all the indicators of the network cards and other ports are found except that the indicators corresponding to the 16th port of HUBB and the cascade port of HUB A are not lit. The lights are evenly lit, indicating that the connection between the computer and the HUB is normal, so the problem is most likely caused by the cascade port of HUBA and the 16th port of HUB B. According to this situation, it began to suspect that at least one of the cascading ports of HUB A and the 16th port of HUB B is bad. In order to further confirm that its port is bad, the position of the two HUBs can be changed, but the result is still the same. Next, try to plug the twisted pair connecting the HUB A cascade port to a common port elsewhere on HUB B. As a result, the problem is solved. All the workstations in the network can communicate with the server, and the two HUBs are connected. All workstations can respond to each other. It can be seen from this that some HUB cascade ports and a port next to them are not independent two ports, but should belong to the same port (although there are two independent physical ports). Many previous HUBs used a toggle switch to select the cascade port between the two ports, but this switch was omitted in subsequent products, but if one of the ports is used as a cascade port, the other One port will be invalid.

3. HUB often burns out

[Fault phenomenon]

A HUB connecting two buildings is often burned out, sometimes three or four times a month.

[Fault analysis and processing]

After testing, the power system in Building A has been aged, the absolute voltage of the neutral line is 30V, the absolute voltage of the live line is 250V, and the voltage of the multimeter is still 220V; UB to the HUB of the B building, the two HUBs must bear the 30V potential difference, very It may be damaged. The solution is simple, just connect a ground wire to the switch room in Building A.

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