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Table Of Contents  CertiGuide to Network+
 9  Chapter 0011:  Network Hardware
      9  III  Layer 1 – Physical Layer

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NIC (Network Interface Card)
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Repeater
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Hub

Effectively, the hub is the electronic center of the network for 10nBaseT networks. All signals come to the center where they are repeated on all active (in-use) ports. As you can see from the illustration below, multiple cables, each leading to a device on the network, plug into a single hub, which takes care of transmitting signals among all devices plugged into the hub, allowing the devices to communicate with each other. You can stack hubs to expand the network. In most cases, PC’s connect to the hub via patch cables using the RJ-45 connector that is plugged in to the PC’s NIC. In classic hubs, there are limits to how many can be stacked, and performance degrades quickly when stacking.

[spacer]About Hubs

RJ means Registered Jack.

When stacking hubs, the hub counts as one repeater hop in the stack.


Figure 34: Hub

 


When you stack hubs you send the signal received from one hub and it is transmitted to the other, even if the intended receiver is not on the second hub. All stations must listen anyway. This means you have only one collision domain. To stack two hubs, connect a cable from the specially-marked port (normally called uplink, cascade, repeater or sometimes just X) on one hub, to a standard port on the other. This allows the signals to pass between both hubs.

Fast Ethernet

In Fast Ethernet, (100Mbit – 100BaseTX) you can only stack two hubs, total!


Note that all hubs are not created equal. Different models of hubs have different capabilities in terms of network error isolation, statistics reporting, port management and expandability. In general, smart hubs cost more, and have more functions built in to their hardware, than do other types of hubs. Some smart hubs can even report their status to monitoring software, and be controlled by that software, for ease in detecting and correcting network issues without physical access to the hardware.

Hubs

Hubs
function on Layer 1, have a single collision domain, and do not segment network traffic, as a switch does. Use a switch to improve performance and segment subnets. The switch is discussed in the section on Layer 2 hardware.



Previous Topic/Section
NIC (Network Interface Card)
Previous Page
Pages in Current Topic/Section
1
Next Page
Repeater
Next Topic/Section

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