HUB (multi-port forwarder)

HUB is a multi-port transponder. When HUB is the central device, even if a certain line in the network fails, it will not affect the work of other lines. Therefore, HUB has been widely used in local area networks. Most of the time, it is used in star and tree network topologies. It is connected to each host with an RJ45 interface (also has a BNC interface). There are many types of HUB according to different statements. HUB can be divided into passive HUB, active HUB, and intelligent HUB according to the way of processing the input signal.

Classification

Passive HUB is the lowest level. It does not do any processing on the signal, does not extend the transmission distance of the medium, and has a certain influence on the signal. Each computer connected to this HUB can receive signals from all other computers on the same HUB;

The difference between an active HUB and a passive HUB is that it can amplify or regenerate the signal, so that it extends the effective transmission distance between the two hosts;

Smart HUB

Smart HUB

In addition to all the functions of an active HUB, the intelligent HUB also has network management and routing functions. In the intelligent HUB network, not every machine can receive the signal, only the computer with the same address as the signal destination address can receive it. Some smart HUBs can choose the best path by themselves, which can manage the network well.

According to other methods, there are many types, such as 10M, 100M, 10/100M adaptive HUB, etc., which will not be introduced here. In short, the market price is not that expensive, so try to buy a better one.

If we are often in touch 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?

"USB HUB" is divided into two parts: "USB" and "hub". First, USB is the abbreviation of Universal SerialBus in English, and "Universal Serial Bus" in Chinese, also known as Universal Serial Interface. Second, HUB is a hub that everyone often calls, it is used in a network that uses a star topology to connect multiple computers or network devices. USB HUB, a device that can expand one USB interface to multiple (usually 4) and use these interfaces at the same time.

A hub (HUB) is a basic device in a data communication system. Like a transmission medium such as a twisted pair cable, 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 and is applied to the first layer of the OSI reference model, so it is also called a physical layer device. The hub uses 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 respect, the hub functions as a multi-port repeater. In fact, a hub is actually a kind of repeater. The difference is only that the hub can provide more port services, so the hub is also called a multi-port repeater.

The external board structure of the ordinary hub is very simple. For example, D-Link's simplest 10BASE~T EthernetHub hub is a rectangular parallelepiped, with AC power sockets and switches, an AUI interface and a BNC interface on the back, and a row of 17 RJ-45 interfaces on most of the front. There are LED interface indicators and LED status indicators corresponding to each RJ-45 interface on the right side of the front. High-end hubs look no different from modern routers or switching routers. In particular, modern dual-speed adaptive Ethernet hubs generally have built-in switching modules that can communicate between internal 10Mb/s and 100Mb/s network segments, so that this type of hub can completely be in the network segment with the hub as the node. , To realize the communication exchange between various nodes, and sometimes people simply call this type of switching hub a switch, which makes it difficult for users who use the hub for the first time to correctly distinguish them. But it is a relatively simple method to distinguish the hub based on the type of backplane interface.

Work characteristics

According to the IEEE 802.2 protocol, the hub function is to randomly select a port's 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 at work.

The first is that the Hub is just a multi-port signal amplification device. When a port receives a data signal during work, the signal has been attenuated during the transmission from the source port to the Hub, so the Hub will shape and amplify the signal. Regenerate (restore) the attenuated signal to the state when it was sent, and then forward it to all other ports that are in working state. It can be seen from the working mode of Hub that 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 ability to transmit signals. It is a standard shared device. So some people call hubs "silly Hub" or "dumb Hub".

The second is that Hub only communicates with its uplink devices (such as upper-level Hubs, switches, or servers). The ports on the same layer do not communicate directly, but broadcast information to all ports through the uplink devices. It can be seen that even if it is to communicate between two different ports of the same Hub, it must 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 composed of Hub is a shared network, and Hub can only work in half-duplex.

Hub is mainly used for the formation of shared networks, and it is the most economical solution from the server to the desktop. In a switched network, the Hub is directly connected to the switch and sends data on the switch port to the desktop. The Hub is flexible in networking. It is located at a star-shaped node in the network, and centrally manages the workstations connected to the node, so that the workstations that have problems will not affect the normal operation of the entire network, and users are also free to join and exit.

Basic classification

Classified by structure

Classified by structure and function, hubs can be divided into three types: unmanaged hubs, stacked hubs and chassis hubs.

Unmanaged hub

The simplest hub provides a central network connection through the Ethernet bus, which is connected in the form of a star. This is called an unmanaged hub and is only used in very small networks of up to 12 nodes (in a few cases, more can be used). 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.

Stacked hub

Stacked hubs are slightly more complicated hubs. The most notable feature of a stacking 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 already installed hub. This method is not only low-cost, but also simple and easy to implement.

Chassis hub

Chassis hub is a modular device, and multiple types of modules can be inserted on its backplane circuit board. Some hubs have redundant backplanes and power supplies. At the same time, some modules allow users to replace failed modules without shutting down the entire hub. The backplane of the hub prepares multiple buses for 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 (Asynchronous Transfer Mode). , ATM). Some hubs also contain bridges, routers or switching modules. Active chassis hubs may also have retiming modules to associate with amplified data signals.

Classified by LAN perspective

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

Single trunk network segment hub

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

Multi-segment hub

Derived directly from the single trunk network segment hub, using the hub backplane, this kind of hub has multiple trunk network segments. Its 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.

Port switching hub

The integrator is based on a multi-segment hub that automates the connection process between user ports and multiple backplane network segments, and is realized 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.

Network interconnection hub

Port switching hubs focus on port switching, while network interconnection hubs can provide some types of integrated connections between multiple network segments on the backplane. This function is completed by a comprehensive bridge, router or LAN switch. Such hubs usually adopt the form of a chassis.

Switching hub

The boundaries between hubs and switches have become blurred. The switching hub has a core switching backplane, which uses a pure switching system to replace the traditional shared media relay network segment. Such products are already on the market, and hybrid (relay/switching) 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 this type of hub and switch.

Selection criteria

With the development of technology, in local area networks, especially in some large and medium-sized local area networks, hubs have gradually withdrawn from application and replaced by switches. Hubs are mainly used in the edge of some small and medium-sized networks or large and medium-sized networks. The following describes the selection method with the application of small and medium LAN as the characteristic.

Speed standard

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

Uplink device bandwidth

If the uplink device allows 100Mbit/s to run, you can naturally buy a 100Mbit/s hub; otherwise, a 10Mbit/s hub should be an ideal choice, because it is for a network with a small number of network connected devices and a small communication traffic, 10Mbit The /s hub can meet application needs.

Number of connection ports provided

Since all stations connected to the hub compete for the same uplink bus, the more ports connected, the easier it is to cause conflicts. At the same time, 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 of the equipment. According to practical experience, the number of computers managed by a 10Mbit/s hub should not exceed 15, and that of 100Mbit/s should not exceed 25. If it exceeds, a switch should be used instead of a hub.

Application requirements

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

Can it meet the expansion?

When a hub provides insufficient ports, there are generally two ways to expand the number of users.

Stack

Stacking is a way to solve the problem of insufficient ports of a single hub, but because multiple hubs stacked together still work in the same environment, the number of stacked layers cannot be too many. However, many hubs on the market have more stacked layers than other brands as a selling point. If you encounter this situation, you must treat them differently: on the one hand, the more stackable layers, the higher the stability of the hub; On the one hand, the more layers that can be stacked, the smaller the bandwidth that each user can actually enjoy.

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 dedicated port is provided and cascading is necessary, the twisted pair connecting the two hubs must be miswired during production.

Whether to provide network management function

The early Hub was a low-end product and was not manageable. In recent years, with the development of technology, some hubs have introduced the function of a switch technically, and the simple management (SNMP) of the hub can be realized by adding a network management module to facilitate use. But it needs to be pointed out that although the same provides support for SNMP, modules of different manufacturers cannot be mixed, and modules of different products of the same manufacturer are also different. At present, the price of Hub that provides SNMP function is higher. For example, the price of D-Link's DEl824 non-intelligent 24-port 10Base-T is about 1,000 yuan cheaper than DEl8241 with network management module.

Dimensions

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

Brand and price

Like network cards, Hubs on the market are basically dominated by American brands and Taiwanese brands. Recently, several mainland companies have also launched hub products. Among them, high-end Hubs are mainly occupied by American brands, such as 3COM, Intel, Bay, etc. They are unique in design, usually several or even one processor per port, of course, the price is also higher. D-Link and Accton in Taiwan of China accounted for the main share of the low-end Hub. Mainland companies such as Lenovo, Shida, TPLink and others have launched their own products to the market with strong strength. These middle and low-end products all use single-processor technology, and the design ideas of their peripheral circuits are similar. The welding process methods to realize these ideas are basically the same, and the prices are similar. Mainland products are relatively cheaper and are increasingly occupying a larger market share. Recently, as the price of switch products has been declining, the hub market has shrunk day by day. However, on certain occasions, hubs can bring higher efficiency with lower investment due to their low latency. The switch cannot completely replace the hub.

Failure analysis

For the most common and most commonly used star topology, the hub (HUB) is the heart part. Once it has a problem, the entire network cannot work, so its quality is very important to the entire network.

The hub (HUB) or switch (Switch) is the most popular device in the local area network. 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 on, you can judge whether the network connection is normal. For 10/100/s adaptive HUB (or Switch), it is also possible to judge whether the connected computer is working under 10Mb/s or 100Mb/s through the different colors of the connection port indicator. Therefore, in most applications, the use of HUB (or Switch) is beneficial to network maintenance. However, because of improper use of HUB (or Switch) or its own damage, it will bring problems to the network connection.

Application failure of hub in 100Mb/s network

Failure 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 through the cascade connection between HUBs. Up to three levels can be cascaded in a 10Mb/s network, so that the maximum transmission distance of the network can reach 500m. But when the network is upgraded from 10Mb/s to 100Mb/s or a new 100Mb/s local area network is created, if the normal method is used to connect 100MHUB, the local area network will not work normally. As we all know, only two 100Mb/s HUBs are allowed to be cascaded in a 100Mb/s network, and the connection distance between two 100Mb/sHUBs cannot be greater than 5m, so the maximum distance of a 100Mb/s LAN when using a HUB is 205m . If the actual connection distance does not meet the above requirements, the network will not be able to connect. Enough attention should be paid to this point, otherwise it is easy to cause serious errors when users plan the network.

Application failure of hub during cascading

Failure phenomenon

An organization built a local area network by itself, using two 16-port (and a cascade port) 10M shared hub, and all computers were connected to the HUB in the main computer room through the HUB. Among them, HUB-A is connected to the 16th port of HUB-B through the cascade port, HUB-B is connected to the HUB in 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 of which are 192.168.0.2, 192.168.0.3...and so on, 192.168.0.1 is allocated to the NT server, and each computer (including the server The subnet masks of) are all 255.255.255.0. Before formally connecting to the server, each workstation is set up and tested using the Ping command. The results are all connected, and all the workstations connected to HUB-A can also use the Ping command to communicate with the workstations connected to HUB-B. However, when the server is connected, only the workstation connected to HUB-B can log in to the server, but the workstation connected to HUB-A cannot log in.

Fault analysis and processing

By observing the indicator light of the computer network card and the indicators of each port on the two HUBs, except for the indicator light corresponding to the 16th port of HUB-B and the HUB-A cascade port is not bright, all network cards and other ports The indicators light up evenly, indicating that the connection between the computer and the HUB is normal, so the problem is most likely to be the cascade port of HUB-A and the 16th port of HUB-B. According to this situation, it is suspected that at least one of the cascade ports of HUB-A and the 16th port of HUB-B is broken. In order to further confirm whether a certain port is broken, the positions of the two HUBs can be exchanged, and the result is still the same. Next, I tried to plug the twisted-pair cable connected to the HUB-A cascade port to an ordinary port elsewhere on HUB-B. As a result, the problem was solved. All workstations in the network can communicate with the server, and two HUBs All connected workstations can respond to each other. It can be seen that the cascade port of some HUBs and a port next to it are not two independent 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 is omitted in the subsequent products, but if one of the ports is used as a cascade port, the other One port will be invalid.

HUB often burns out

Failure phenomenon

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

Fault analysis and processing

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

Working principle

We know that there is only one physical signal transmission channel in a ring network, all of which are transmitted through one transmission medium. In this way, there is a contradiction between each node competing for the channel, and the transmission efficiency is low. After the introduction of the hub, a network concentrating device, each station is connected to the hub with its own dedicated transmission medium. There is no longer only one transmission channel between each node. The signals sent back by each node are concentrated through the hub, and the hub then transmits the signal After being reshaped and amplified, it is sent to all nodes, so that at least there will be no collisions on the uplink channel. However, the hub-based network is still a local area network with shared media. The "sharing" here is actually the internal bus of the hub, so when the upstream channel communicates with the downstream.

There will still be signal collisions when the channels send data at the same time. When the hub detects a collision from its internal port, it generates a collision enhancement signal (Jam) and transmits it to the target port connected to the hub. At this time, all data will not be able to be sent successfully, forming a "big traffic jam" on the network. The emergence of this kind of network phenomenon can be illustrated by an image of reality, that is, cars coming in two directions on a single lane at the same time.

We know that a single-lane lane usually only allows cars in one direction to pass, but in small towns, there are usually no such regulations when conditions are limited. A single-lane lane may also allow vehicles in two directions, but they must pass at different times. . The same is true in hubs. Although the connection between each node and the hub has its own independent channel, there is only one common channel inside the hub. Uplink and downlink data must be sent and received through this shared channel. This may be like Like a single lane, traffic jams may occur when data is sent from the uplink and downlink channels at the same time. Is it easy to understand?

Because of this shortcoming of the hub, it cannot be used alone in a larger network (usually to share a small part of the network communication load with switches and other equipment), just like there cannot be a single lane in a large city center, because The larger the network, the greater the chance of network collision. For this reason, the data transmission efficiency of the hub is relatively low, because it can only transmit data in one direction at the same time, which is the so-called "simple" method. If the hub is to be used as a single hub device in the hub network, the network size should be less than 10, and the hub bandwidth should be 10/100Mbps or more.

In addition to the inadequacies of the hub sharing bandwidth, there is another aspect that must be considered when choosing a hub, and that is its broadcasting method. Because the hub is a pure hardware network bottom device, it basically has no "intelligent memory" ability, let alone "learning" ability. It does not have the MAC address table that the switch has, so it is not targeted when sending data, but is sent by broadcast. That is to say, when it wants to send data to a node, it does not directly send the data to the destination node, but sends the data packet to all nodes connected to the hub.

There are two shortcomings in this way of sending data by broadcast: Firstly, user data packets are sent to all nodes, which may cause insecure factors in data communication. Some people with ulterior motives can easily intercept other people's data packets illegally; Secondly, since all data packets are sent to all nodes at the same time, coupled with the shared bandwidth method introduced above, it is more likely to cause network traffic jams and further reduce the efficiency of network execution.

Common ports

After understanding the working principle of the hub, let's take a look at the installation and connection method of the hub in the local area network.

The most important thing about an access device is its interface technology. Different interfaces are used in different application environments, and different applications correspond to corresponding interfaces. Not only hubs, but also switches and routers that will be discussed later. The interface of the hub is relatively simple. In order to make you master the various application connections of the hub, it is necessary for us to understand some of the main interfaces of the hub.

Hubs usually provide three types of ports, namely RJ-45 ports, BNC ports and AUI ports, which are suitable for connecting different types of cables to build networks. Some high-end hubs also provide fiber ports and other types of ports.

RJ-45 interface

The RJ-45 interface can be used to connect to the RJ-45 connector, which is suitable for networks constructed by twisted-pair cables. This type of port is the most common. Generally, Ethernet hubs will provide this type of port. The number of hubs we usually talk about refers to the number of RJ-45 ports.

The RJ-45 port of the hub can be directly connected to terminal devices such as computers and network printers, and can also be connected to other switches, hubs and other hub devices and routers. It should be noted that when connecting to different devices, the jumper method of the twisted pair cable used is different. For details, please refer to the introduction of the network cable production section introduced above.

BNC port

The BNC port is the interface used to connect with the thin coaxial cable. It is generally connected through a BNC T-type connector.

Most 10Mbit/s hubs have a BNC port. When the hub has both BNC and RJ-45 ports, it can be connected to a twisted-pair network through the RJ-45 port, and can be connected to a thin-cable network through a BNC interface, so twisted-pair and thin coaxial cables can be realized The connection between two networks that use different communication transmission media. This dual-interface feature can be used to be compatible with the original thin coaxial cable network (10Base-2), and can realize the gradual transition to the mainstream twisted pair network (10Base-T), and of course, it can also realize the same as the remote Connection between shaft cable networks (less than 185 meters).

Similarly, if the distance between the two networks is greater than 100 meters, and the connection between the two networks cannot be achieved using twisted pair cables, then the two transmission networks can also be connected through the BNC port of the hub using thin coaxial cable transmission. However, both networks can still use twisted-pair cables, a cheap and common transmission medium. However, it should be noted that the distance between these two networks still cannot be greater than 185m.

AUI port

The AUI port can be used to connect the AUI connector of the thick coaxial cable, so this interface is used to connect to the thick coaxial cable network. At present, there are few hubs with this interface, mainly in some backbone-level hubs. Due to the high cost of networks using thick coaxial cables as the transmission medium and the difficulty of wiring, it is very rare in practice to actually use thick coaxial cables for wiring. However, since the transmission distance supported by a single section of thick coaxial cable (10Base-5) is as high as 500 meters, it is completely possible to use thick coaxial cables as the communication cable for the connection between the longer-distance networks. Therefore, it can also be used as a cheap remote connection solution.

With the aid of the transceiver, the AUI port can also be connected to the RJ-45 interface, BNC interface and even optical fiber interface. Of course, there are many types of such transceivers, such as RJ-45 to RS-232, RJ-45 to BNC and so on. But don’t underestimate this little gadget. Guess its price. I think in most cases, you’ll look down upon it. I couldn’t figure out the price when I first bought it, but I asked After many homes (really hard to find), I realized that I had to accept the price. Generally speaking, this kind of product costs about 130 yuan for a genuine product. Is this unexpected? The main brands of this kind of interface transceiver are: D-Link, HP, etc. This product acts as an interface type conversion (of course it is not as simple as a cable connection, which needs to be completed through a certain circuit), so it is usually called an "adapter".

Stack port

This kind of port is of course only available for stackable hubs, and its role is as its name is used to connect two stackable hubs. Generally speaking, a stackable hub has two ports with similar appearance: one is marked as "UP" and the other is marked as "DOWN". When connecting, a cable is used to connect the "UP" port of one hub to another. On the "DOWN" port of a stackable hub, there are "female" headers, so the cable ends must be "male", but this kind of cable is provided by the manufacturer when you purchase a stackable hub If it is damaged or lost, you can also make one directly in the Computer City, as long as you explain the purpose to the merchant.

Installation steps

Overview

The installation of the hub is relatively simple, especially the fool hub, as long as it is fixed in the wiring cabinet and plugged in the power cord. Which twisted pair needs to be connected, just insert the RJ-45 head of which twisted pair into the hub port. Although the smart hub is fixed and ready for use, if you want to realize remote management, you must perform the necessary configuration and specify the IP address information for the hub. In addition, rack-mounted hubs are generally used in some large networks, which involves rack installation of the hub.

There are two types of hubs in terms of structure: rack type and desktop type. The hub used in general departments is desktop type; enterprise computer rooms usually use rack type. Rack-mounted hubs are easy to fix in a fixed place, usually with other hubs, switches, and some with servers in a cabinet, which is convenient for network connection and management, and also saves equipment The space occupied. If you choose a rack-mounted hub when purchasing, you can choose a hub rack (generally provided by the manufacturer). Let's take a look at the installation of rack hubs.

Rack-mounted hubs are generally installed in cabinets together with other equipment. Of course, these cabinets have corresponding structural standards in the industry, especially in terms of size (such as width, 1U (unit) height, etc.). ), so that all devices can be installed together conveniently and beautifully. This is why the hub is empty but must be made the same size. Of course, a large chassis has another advantage, that is, better heat dissipation. .

The international standard cabinets can be roughly divided into three types, 19 inches, 23 inches and 24 inches in width, which are mainly determined according to the requirements of server cabinets. Depending on the number of installed devices, cabinets of different heights can also be selected. The height of the cabinet is usually "U" as the unit. "U" actually means "Unit", which means "one unit" in Chinese, and 1U=1.75 inches. The installation of this kind of cabinet is usually carried out in the following steps.

Step 1

Fixed mounting bracket

Before installing the hub to the cabinet, you should first install the fixing bracket on the specified position of the hub (refer to the operation manual). This is to prepare for installing the hub on the rack in the future. Different hubs have big differences in the brackets installed, but the installation principles are basically the same.

Step 2

After the fixed device mounting bracket is fixed, the next thing to do is to put the hub device with the bracket installed in the corresponding position of the cabinet and fix it in the cabinet. In fact, this installation method is very easy, in fact, it only needs to fix a few screws.

Step 3

Fixed wire guide

After the hub is installed in the cabinet, it is necessary to connect the network cables. Generally speaking, there are several network devices together in a cabinet, so that there are many network cables concentrated in this cabinet. If these network cables are not clear, please Network management will bring great inconvenience, for this we need to bundle, install and organize the network cables. At this time, it is generally necessary to install a wire guide for the network cable, so that the bundled network cable becomes neat and beautiful, and easy to manage.

Above we introduced the method of installing rack-mounted hubs in cabinets. This is generally applicable to larger networks. For small offices, there is usually no cabinet, and the hub can only be installed on the desktop or on the wall.

To install the hub on the desktop, you can first fix the mounting bracket on the desktop. This installation method should pay attention to two different installation directions: one is the horizontal installation method where the hub is placed horizontally; the other is to make the hub vertical place.

There are also two ways to install the hub on the wall: one is to fix the hub horizontally on the wall; the other is to install the hub vertically on the wall.

Connection principle

Although the connection of the hub is simple and basically does not require any configuration, through the understanding of its connection principle, the hub can be better utilized to meet the needs of medium and small network applications. Before formally introducing the connection method of the hub, let's first understand the signal forwarding principle of the hub.

The signal forwarding principle of the hub

The hub works on the physical layer of the OSI/RM reference model and the MAC (Media Access Control) sublayer of the data link layer. The physical layer defines electrical signals, symbols, line status and clock requirements, connectors for data encoding and data transmission. Because the hub only reshapes and amplifies the signal and then retransmits it without coding, it is a physical layer device. The 10M hub has 4 standard interfaces available at the physical layer, namely: 10BASE-5, 10BASE-2, 10BASE-T, and 10BASE-F. The 10BASE-5 (AUI) port of the 10M hub is used to connect layer 1 and layer 2.

The hub uses the CSMA/CD (Carrier Frame Listening Multiple Access/Conflict Detection) protocol. CSMA/CD is the MAC layer protocol, so the hub also contains the content of the data link layer.

As a special multi-port repeater, the 10M hub must follow the 5-4-3 rule in the network relay expansion, that is: a network segment can only be divided into 5 sub-network segments; a network segment can only be There are 4 repeaters; a network segment can only have up to three subnet segments containing PCs.

The working process of a hub is very simple. It can be described simply as follows: First, the node sends a signal to the line, and the hub receives the signal. Because the signal is attenuated during cable transmission, the hub will shape and amplify the attenuated signal after receiving the signal. The hub broadcasts the amplified signal and forwards it to all other ports.

Stacking of hubs

In order to make hubs meet the number of ports required by large networks, the stacking or cascading method of hubs is generally used in larger networks. However, the main application scenarios of the two methods are different. The stacking method will be introduced first.

The stacking method refers to connecting several hubs with cables through stacking ports to achieve the expansion of the number of ports of a single hub. It should be noted that only stackable hubs have this kind of port. A stackable hub generally has "UP" at the same time. "And "DOWN" stacking ports.

The hub stack is connected directly from the "UP" stack port of one to the "DOWN" stack port of another hub through a dedicated connection cable provided by the manufacturer. All the hubs in the stack can be regarded as a whole hub for management, that is, all the hubs in the stack can be regarded as one hub from the topological structure. This kind of connection between hubs usually does not occupy the original ordinary ports on the hub, and the stack port has intelligent identification performance, so the stacked hubs can be treated as a hub for unified management. Hub stacking technology uses a dedicated management module and stack connection cables, which can establish a wider broadband link between hubs, so that the bandwidth of each user actually used may be wider (only when not all ports are Use case).

The port expansion method of a stacked hub is limited by the type and separation distance of the hub. The first condition is that the stacked hub must be stackable; another such stack connection is generally the connection between the station hubs that are very close to each other ( The stack connection cable provided by the manufacturer is generally 1m), so this kind of hub port expansion connection method is too limited by the distance.

The wireless HUB is the access point for wireless workstations to enter the wired Ethernet, and is responsible for managing the information flow within its coverage area (wireless unit). AP-550 supports IEEE802.1D bridging protocol. A group of wireless HUBs covering overlapping areas, supporting continuous roaming of wireless workstations in a larger area, and always maintaining network connection. Multiple wireless HUBs placed in the same place can achieve higher overall throughput. Superb antenna Diversity technology and Modem based on digital signal processing technology eliminate multipath propagation and spatial fading. For some special applications, high-gain full/directional antennas can be used. AP-550 has a compact appearance and can be easily installed on shelves, desktops, ceilings and walls. It is also the only access point device based on ISA/PCI/PCMCIA interface card specially developed in the industry.