Computer Network Basics (5) hub ?Hub of the English language as &quot;Hub&quot; (the &quot;Center&quot; means), the hub of the main function is to regenerate the received signal shaping to enlarge, to expand the network of transmission distance, while all nodes concentrated in It is the center node. Hub (HUB) is the basis of data communication systems equipment, transmission media such as twisted pair it as a software without any support or management of software management with minimal hardware. Hub is actually a repeater, the difference only lies in the hub ports can provide more services, so called multi-mouth following the device hub. ?Hub Features: ?1. To provide a central unit that can connect multiple nodes to the network. Allow a large number of computers connected to one or more LAN. ?2. Through the centralized network design to reduce network congestion, to provide multi-protocol service. ?3. To improve the network communication speed, to provide links to different types of media, such as: coaxial cable, twisted pair, fiber. ?4. To meet the centralized network management. ?5. Intelligent hub can also filter the data or provide diagnostic information on the web. ?The basic working principle of the hub ?We know that in the ring network, there is only one physical signal transmission channel, is to transfer through a transmission medium, so that each node on the existence of the contradiction between fighting for the channel, transmission efficiency is low. Into the hub of this network device assembly line, each station is its own dedicated transmission medium connected to the hub, all nodes not only a transmission channel, each node signal comes back through the hub focus, hub, then the signal shaping, amplification and sent to all nodes, so that at least no longer appear in the upstream channel collisions. However, the hub of the network is still based on a shared media LAN, where &quot;sharing&quot; is actually a hub internal bus, so when the uplink channel and downlink channel to send data at the same time there would still be the signal collisions. When the hub from its internal port to detect a collision, a collision reinforcement signal (Jam) hub connected to the destination port for delivery. At this time all data will not be sent successfully to form a network of &quot;big traffic jam.&quot; This phenomenon occurs we can use a network image to show the reality of the situation, that is, bicycle lane in both directions simultaneously to cars Chi. ?Because of the inadequacies of this hub, so it alone can not apply to a larger network (usually together with the switches and other devices to share a small part of the network traffic load), as in large urban centers can not have the same cycle paths because the network becomes busy, the network appears the greater the chance of collisions. Hub of the data transmission efficiency is relatively low, since it at the same time only one direction of data transmission, that is, the so-called &quot;simplex&quot; mode. ?Hub Type: 1. According to the functions and structure of the points: (1) stand-alone hub. As its name suggests, it serves the working group on a computer, other equipment and network isolation. Stand-alone hub for smaller independent departments, homes, offices or laboratories. It can be passive, it can be intelligent type. (2) Stackable hubs. As the name suggests, is to actually stack a few stand-alone hub stack together. It exists to avoid stand-alone single point of failure shortcomings. Generally stacked four or five hubs can be stacked. (3) modular hub. Modular construction site provided by a large number of optional interface options, making it use than stand-alone and stacked more convenient and flexible. The hub has motherboard and socket, most people are smart, it can be with the router, WAN connected, also install the redundant parts, so it&#39;s the highest reliability. (4) intelligent hub. It can process data, monitor data transmission and provides troubleshooting information. As can be anywhere in the network management of its implementation, it is called managed hub. Has the processing power of stand-alone, stacked, modular hub can be called intelligent hubs. Although the hub technology has been improved, but in essence were added to the switch (SWITCH) technology, developed today, and some also have a smart switch function of the hub. Can be said to have been in the technology hub to switch product technology transition, with a certain degree of intelligence and data exchange capabilities. But with prices falling switch, only the price advantage is no longer obvious, the hub of the market getting smaller and smaller, the edge is eliminated. However, the hub for the home or small businesses, the economy still has a bit tempting, especially for the family a few machines as a branch network or networks of small and medium company. 2. From the point of view to distinguish between local area network: (1) single repeater hub segment. Simple hub, is a kind of relay for the simplest type LAN segment of the hub, and Ethernet hub or stack multi-station token ring network access components (MAU) and the like. (2) Multi-segment hub. Segments from a single relay hub derived directly, using the hub backplane, this hub with multiple relay network segment. Its main advantage is that users can be distributed in multiple relay segment in order to reduce the load of each segment of information flow, information flow between the segments generally require a separate bridge or router. (3) port switching hub. The hub is a hub in a multi-segment, based on the user port and the connection between the number of backplane segments automate the process, and by increasing the port switching matrix (PSM) to implement the hub. PSM provides an automated tool for any external users to connect to a hub port on any relay backplane segment. Port switching hub of the main advantages is that enables mobile, additions and modifications to the automated features. (4) networking hub. Port switching hub port-oriented exchange, and networking hub in the back between the various segments can be integrated to provide some type of connection, this feature integrated by a bridge, router or LAN switch to complete. Currently, these hubs are usually housed in chassis form. (5) switching hub. Currently, the boundaries between hubs and switches have become blurred. Switching hubs have a core switching backplane, using a pure share-exchange system instead of the traditional media relay network segment. Such products have been listed, and mixed (relay / switching) hub is likely to control the market in the next few years. It should be noted that such hubs and switches is almost no difference between the characteristics. Work hub features: Hub function is a port of the device were randomly selected, and make it exclusive full bandwidth, and the hub of the joint devices (switches, routers or servers, etc.) to communicate. It can be seen, the hub at work with the following two characteristics. The first is a multi-port Hub is the signal amplification equipment, work when a port receives data signals, as signals from the transmission source port to the Hub has been a process of decay, the Hub will be shaping the signal amplification, to be attenuation of signal regeneration (recovery) to send when the state, followed by forwarding to all other ports are in working condition. From the Hub&#39;s work, it was evident only in the network play the role of signal amplification and retransmission, which aims to expand the network&#39;s transmission range, but not with the directional signal transmission capacity, is - the standard of shared equipment. Therefore called a hub for the &quot;stupid Hub&quot; or &quot;dumb Hub&quot;. Second, the Hub is only associated with its equipment (such as the upper Hub, switch or server) to communicate with the layer between the port will not communicate directly, but by then the information broadcast on the associated equipment to all ports. Thus, even in the same Hub port different between the two to communicate, must go through two steps: The first step is to upload information to the joint equipment; second step is to further the information on the associated equipment broadcast to all ports. However, as technology and needs change, many of the Hub was broadened in function, not by the mechanism of such work. Hub network is formed by a shared network, while only able to half-duplex Hub to work. Hub is mainly used for sharing network formation, is directly to the desktop from the server to resolve the most economical option. In switched networks, Hub and switches directly connected to switch port data sent to the desktop. Hub network using flexible, it is in a star network node, the node connected to a centralized management station, to prevent problems affect the entire network of workstations running, and users are also free to join and exit. LAN hub options: As technology advances, especially in the local area network - some medium and large local area network, the hub has been excluded from the application of the switch was replaced. At present, the hub is mainly used for small to medium sized networks or edge of the network. Following the application of small and medium local area network, characterized introduced its selection. 1. Speed as standard Hub speed choice, mainly on the following three factors. ?(1) on the bandwidth associated equipment. If the joint device allowing to run 100Mbit / s, Nature can be purchased lOOMbit / s hub; otherwise lOMbit / s hub should be the ideal choice, because it is less for the number of network connection devices, and network traffic is not great speaking, lOMbit / s hub is enough to meet application needs. ?(2) the number of available ports. Since all connected to the hub sites are competing for the same upstream bus, so the number of ports to connect, the more easily lead to conflict. At the same time, sent to the hub port of any data will be sent to all connected with the hub port, the port will reduce the number of excess equipment and effective utilization. The basis of experience, a lOMbit / s hub managed by the number of not more than 15 computers, lOOMbit / s of not more than 25. If exceeded, the switch should be used instead of hubs. ?(3) applications. Did not involve the transmission of voice, images, transmission is relatively small, select 10Mbit / s can be. If you transfer large quantities, and may involve multi-media applications (note the time sensitivity of the hub is not suitable for transmission signals such as voice signals), it should choose 100Mbit / s or 10/100Mbit/s adaptive hub. 10/100Mbit/s adaptive hub prices generally than 100Mbit / s high. ?2. Can expand to meet the standard ?When a hub port is not enough to provide, generally there are two ways to expand the number of users. ?(1) stack. Stack is a single hub port insufficient to resolve a method, but because many hubs or stacks of work in the same environment, it can not be too stacked layer. However, many hubs on the market than other brands with its stacked multi-layers and as a selling point, if this happens, we should distinguish between: on the one hand stacked layers of the more general description of the stability of the hub higher; the other hand, the more layers can be stacked, each user can enjoy the actual bandwidth is smaller. ?(2) cascade. Cascade is to increase the number of users in the network another way, but the use of this feature - as is conditional, that Hub can be cascaded to provide the port, the port often labeled &quot;Uplink&quot; or &quot;MDI &quot;message, use this port to cascade to other Hub. If no specific port and have to be level with, the twisted pair connecting the two hubs of production must be carried out in the wrong line. 3. To whether to provide network management capabilities as standard. The Hub is a kind of early low-end products, and not management. In recent years, with the technology, part of the hub in the technical introduction of the function switches can be realized by increasing the network hub module simple management (SNMP), to facilitate use. However be pointed out that, although the same is SNMP support modules from different vendors can not be mixed, and while the same manufacturer are different modules for different products. 4. Reference to external dimensions. If the network is relatively simple, there is no cabling between buildings, but relatively few users within the network, such as a family, one or several adjacent office, there is no need to reconsider the Hub of the form factor. But sometimes not the case, for example, to facilitate centralized management of multiple Hub, the purchase of Hub has been acquired before the cabinet, this time in the purchase Hub must be considered when its dimensions, or Hub can not be installed in the rack on. The cabinet is now available in the market generally followed in the design industry standard 19-inch, it can be installed most of the 5, 8, 16 and 24 of the Hub. However, in order to prevent accidents, in the purchase must pay attention to whether it meets the standard 19-inch work, in order to secure the cabinet to focus to manage. Common Trouble-shooting of Hub: ?General the most common star topology, the hub (HUB) is the heart of the problem if it is, the network will not work, so it&#39;s good or bad for the whole network is very important. ?1. Hub in the 100Mb / s network of faults The network from 10Mb / s upgrade to 100Mb / s, the network does not work. Fault analysis: In the LAN, when the network connection to a larger extent, it can cascade through the HUB to expand network between the transmission distance. In the 10Mb / s network cascade up to four, the maximum transmission distance of the network to reach 600m. But when the network from 10Mb / s upgrade to 100Mb / s, or create a 100Mb / s LAN, if the ordinary method 100MHUB to connect local area network will not work correctly. As we all know, the 100Mb / s network, allowing only two 100Mb / s of the HUB to cascade, and the connection between the two 10Mb/sHUB distance not greater than 5m, so 100Mb / s LAN using HUB maximum distance 205m. If the actual link distance does not meet the above requirements, the network will not connect. This is to pay sufficient attention to planning the network or the user can easily cause serious errors. 2. Hub during the time of application failure cascade A unit of their own to form a local area network, using two 16 (also with a cascade port) and 10M shared hub, all computers through the HUB HUB is connected with the overall room. One HUBA through cascade port to connect to the HUBB the first 16 ports, HUBB through the cascading port to connect to the exchange room of the HUB, the other ports are connected to the workstation. Use a static IP address the workstation, and its value as 192.168.0.2,192.168.0.3 ... ... and so on, 192.168.0.1 assigned to the NT server, each PC (including servers ) all the subnet mask 255.255.255.0. Formal connection to the server before each set to a workstation, use the Ping command to test, the results are all connected, and the HUB A workstation connected to all the Ping command can be used also connected with the HUB B connected workstations. However, when connected to the server, only the HUB B is connected workstation to log on the server, but HUBA connected workstations can not log on. ?Fault analysis: a computer network card by looking at light, and two HUB indicator on each port, except the first 16 found HUBB HUB A cascade port and the port corresponding to the indicator is off, all the cards and Other ports are uniformly bright light, indicating a connection between the computer and the HUB are normal, so the problem most likely lies in the HUBA HUB B cascade port and the first 16 ports. In this situation, began to wonder at the HUB A HUB B cascade port and the first 16 ports in at least one port is bad. To further confirm the port is bad, could be the location of two HUB&#39;s exchange, but the result remains the same. Then try to connect the twisted pair port HUB A cascade inserted elsewhere in the HUB B of a common port, the results of problem solving, and network all of the workstations and servers can be connected, and connected the two HUB The workstation can be to respond to each other. It can be seen, some with HUB cascade port and a port close to the two ports are not independent, but should belong to the same port (although there are two separate physical ports). Before many of the HUB is the use of a toggle switch between the two ports the choice of the cascade port, and in the subsequent launch of the product has saved the switch, but if you one of these ports as a cascade port to use, and the other A port will not work. 3. HUB often burn ?One linking the two buildings with the HUB often burn, sometimes three or four times a month among the necessary bad. ?Fault analysis: The test, in which A building power system is aging, the absolute zero line voltage is 30V, FireWire absolute voltage is 250V, while the amount of voltage with a multimeter or 220V; HUB to the B Building HUB, the HUB to bear two 30V electrical potential difference, is likely to be damaged. The solution is simple, just switch in the A building housing a ground wire can be connected. Common Port Hub Hubs usually provide three types of port, RJ-45 port that is, BNC port and AUI port, to apply to different types of cables built to connect the network. Some high-end hub also offers other types of fiber optic ports and port. Hub installation Hub installation is relatively simple and particularly stupid hub, as long as the cabinet will be fixed in the wiring and plug in the power cable. Which need to connect the root twisted pair, which took root in the RJ-45 twisted pair to the hub port you can plug into. Although the intelligent hub is secured to be able to use, but if you want to remote management, we must make the necessary configuration, specify the IP address information for the hub. Also in some large networks, has opted to rack hubs, thus involving the hub rack installed. Hub from the structure in terms of a rack and two tables machine type, the general department of the hub is used with a desktop; business room usually rack. Rack hub secured in a fixed place, usually with other hubs, switches, and others with the server installation in a cabinet, which, like the one an easy connection and management of the network, while also saves the space occupied by equipment. If you buy when purchasing a hub is the rack, you can rack optional hub (usually manufacturers provide). Here we look at the rack hub installation. Rack of the hub are generally together with other equipment installed in the cabinet, the cabinet of course, have corresponding structure in the industry standard, especially in size have strict rules (such as width, 1U (unit 4.445cm ) height, etc.), so that all devices can be conveniently installed with the beautiful, which is why the hub empty inside, but insisted the reason for doing as great as, of course, there are other benefits of a large box, then that can better heat dissipation. In the international standard rack width from roughly divided into 19-inch, 23 inch and 24-inch categories, which are mainly based on the requirements of the server cabinet set. According to the different number of devices installed, you can also choose a different height cabinets. Cabinet height is usually &quot;U&quot; as a unit, &quot;U&quot; is actually &quot;Unit&quot; means, in Chinese means &quot;a unit&quot;, 1U = 1.75 英寸. The installation of this cabinet is usually carried out mainly by the following steps. Step 1: Fixed mounting bracket In the hub to the cabinet before installation should be provided first in the hub position fixed bracket (This reference to the operation manual), which is the hub for the future will be installed in the rack as a preparation. Different hub, the installation of the stent have a larger difference, but the principles are basically the same installation. Step 2: Fixed Equipment After the mounting bracket securely, you need to do is to support the hub device installed into the rack corresponding position, and fixed in the cabinet. In fact, this installation method is easy, in fact only a few Luo screw can be fixed. Step 3: fixed-wire device After installing the hub to the cabinet, it is necessary to connect the network cable in a cabinet in general, there are several network devices together, so there are many articles cable also concentrated in the cabinet, if the network cable ignore the clear words of the network management will bring a great inconvenience, for which we need to install the cable bundle, order. At this time, we should install wire devices for the cable so that cable into the beam to become neat and attractive, and easy to manage.