Describes the concept and basic functions of a hub in detail.

I. Overview　

As its name implies, Hub is the activity center. In network terms, the Hub or Concentrator is a wiring point based on a star topology. Arcnet, 10Base-T, 10Base-F, and many other dedicated networks rely on hubs to connect each segment of cables and distribute data to each segment. The basic function of a hub is information distribution, which distributes all signals received by a port to all ports. Some hubs regenerate weak signals before distribution, and some hubs sort the signal timing to provide synchronous data communication between all ports. A hub with multiple 10Base-F interfaces uses a mirror to distribute light to each port.

Figure 1 shows the basic 10 base-2 network. Pay attention to the connection mode between machines and the processing and transmission of data between the source and target devices.

Figure 1

Figure 2 is the same network as Figure 1, but it is only 10Base-T. You can see how different topologies and hubs are embedded in this network.

Figure 2

In the 10Base-T network, all devices need to be connected to one or more hubs with unshielded twisted pair wires. The hub should have multiple ports or even multiple types of ports. Sometimes you need to connect multiple hubs. In this case, you may want to use a high-speed port to establish a network trunk. The hubs and servers should be directly connected to the high-speed trunk. Because most of the main LAN communication is between the workstation and the master server, the master is of great significance to the overall performance of the network.

Figure 3 is a complex 10Base-T network. note how the trunk connects to multiple hubs and servers. The trunk should be high-speed connections, such as fast Ethernet or FDDI.

Figure 3

A device can also be called a hub in the ring net. MSAU (Multi-Station Access Unit) can be considered as a hub because its function is similar to that of an Ethernet Hub, however, MSAU routes packets serially to various devices, Unlike Ethernet hubs. In order not to be confused, the Ring Network MSAU is not discussed as a hub.

2. Who needs a hub?

The method to determine whether your LAN needs a hub is simple: if you want to build a star network with at least two hosts, you need a hub. There is only one exception to this rule, that is, only two 10Base-T networks of the host can be directly connected, but a cable that requires a special transmitter to cross-connect with the acceptor is very common, if you really can not find, you can also do one, it is easy and cheap, the required items for a small pair of twisted pair, two RJ-45 connectors and tools, according to the following table to connect.

RJ-45 connector 1 RJ-45 connector 2

PIN number Function

1 send + <-> 3 receive +

2 send-<-> 6 receive-

3 receive + <-> 1 send +

6 receive-<-> 2 send-

Iii. Hub type　

We know that hubs play an important role in the network of a star topology. There are multiple types of hubs with specific functions and different levels of services. The following describes the differences between some standard features and passive, active, and smart hubs of most hubs, as well as some additional features of high-performance hubs.

Basic specifications

All hubs have some basic features based on the connectable cable type. A hub can provide additional services except interfaces to a network, but it must also comply with IEEE's requirements on media.

Most of the hub's main connection is RJ-45 socket, which is based on a variety of twisted pair Ethernet standard connector type, from 10Base-T to 100Base-T, LAN workstations, printers and other equipment is usually a pair of twisted pair wire to connect to the Hub, the two ends of the RJ-45 connector.

The length of each cable to the hub is determined by the media used. See the following table ).

Ethernet distance

10Base-2 185 meters

10Base-5 500 meters

10Base-T 100 meters

10Base-F 2 km

10broad-36 3,600 meters

The above is the maximum length of the Ethernet specification, most of which can be extended using repeater. Of course there are other requirements.

A hub is an electronic device and therefore requires a power supply. Most hubs also have LEDs that indicate various states. The two common indicators are power supply and port status indicators, some hubs also have indicator lights that monitor port communication status and conflict.

2. Passive Hub

As the name suggests, the passive hub is relatively static. They do not have specific actions to improve network performance, nor can they help you detect hardware errors or performance bottlenecks. They simply receive data from a port and distribute data through all ports, this is the simplest thing a hub can do. A passive hub is an entry-level device for Ethernet in a star topology.

A passive hub usually has a 10Base-2 port and some RJ-45 connectors. We know that 10Base-5 uses the Ethernet of the crude cable. This 10Base-2 connector can be used to connect the trunk. Some hubs also have AUI ports that can be connected to the transceiver to create a trunk.

3. Active Hub

The active hub has all the performance of the passive hub and can monitor data. They are important roles in implementing storage and forwarding technology over Ethernet. They check data before forwarding. They do not prioritize, but correct corrupt groups and adjust the timing.

If the signal is weak but still readable, the active hub restores it to a strong state before forwarding. This makes some devices with poor performance can be used normally. If the signal sent by a device is not strong enough to make the passive hub unidentifiable, the signal amplifier of the active hub can make the device continue to work normally. In addition, the active hub can report that those devices are invalid, providing a certain degree of diagnostic capability.

Some cables may have electromagnetic interference, so that the Group cannot arrive at The Hub according to the normal sequence. The active hub can re-Synchronize the forwarded groups. Sometimes the data cannot reach the destination. The active hub resends the group on a single port to compensate for data loss. The active hub can adjust the timing to adapt to slow connections with a high error rate. Of course, this will reduce the overall network speed of the device connected to the hub, but sometimes this is better than the loss of data. In addition, time sequence adjustment can reduce the number of conflicts in the LAN. The LAN can transmit new data without repeated broadcasts. Active hubs provide optimized performance and diagnostic capabilities. They are more expensive than simple passive hubs and can be configured with multiple or multiple ports.

4. Smart Hub 　

Smart hubs provide more benefits than the first two, allowing users to share resources more effectively. Its technology has emerged in recent years, and many places have no chance to enjoy its benefits. In addition to the features of the active hub, the smart hub provides a centralized management function. If something goes wrong with the device connected to the smart hub, you can easily identify, diagnose, and fix it. This is a huge improvement. In a large network, if there is no centralized management tool, you often need to run it one by one in a line box to find the faulty device.

Another outstanding feature of smart hub is its ability to provide flexible transmission rates for different devices. In addition to ports connected to the high-speed trunk, the smart Hub also supports 10, 16, and Mbit/s speeds to the desktop, that is, Ethernet, licensing ring, and FDDI.

5. Advanced features

The high-end Hub also provides other features, such as redundant AC power supply, built-in DC power supply, redundant fan, automatic disconnection of cable connections, hot swapping of modules, and polarity adjustment of 10Base-T connectors, for example, redundant storage and clock configurations, some hubs also integrate routing and bridging functions.

1. Procedure for configuring Cisco switches and hubs for Network Management