Archive for the ‘Cables’ Category

Hubs and switches are similar in many ways. Both contain connection ports into which twisted-pair RJ-45 connectors (similar to phone RJ-11 jacks) plug. They can be administered remotely. Either can be used to create a LAN, and they funnel messages to the network backbones.

 

There are salient differences between hubs and switches, however:

 

  • Shared or dedicated bandwidth —The main distinction is how they operate. Hosts in a hub-based network share the full bandwidth, but a switch is capable of creating independent full-speed connections for any two devices on the LAN that must communicate. Each connection operates at the full switch bandwidth.
  • How they handle signals —A hub acts like a repeater. It takes an incoming frame and retransmits it to all other attached hosts. Each hub port has a single host connected to it. Hubs are dumb devices and cannot learn. Switches examine incoming frames and immediately transmit them to one or more other ports. This process is very fast. Each switch port can have a single host or a LAN segment connected to it. Switches learn media access control (MAC) addresses and build a contentaddressable memory (CAM) table.
  •  Cost —Switches are more expensive than hubs for the same number of ports because they have more powerful hardware and software capabilities. Switches have more memory, a CPU, and a complete suite of software tools to manage them. Hubs have a trimmed-down version of the firmware code.

 

Like switches, bridges are also layer 2 devices. They learn MAC addresses, filter and forward frames, and can be used to segment LANs. However, they usually have 16 or fewer ports. Much of the functionality of bridges has been moved to routers.

 

Just as routers have replaced bridges at layer 3, switches (as their cost continues to fall) may eventually replace hubs at layer 2, but that has not happened yet. Hubs, it must be pointed out, have become smarter, less expensive, and easier to set up and manage. As more and more LANs are being set up, network managers continue to deploy hubs as an easy and inexpensive way to connect printers, low-traffic servers, PCs, and management consoles. The number of installed hubs is increasing mainly because of cost and simplicity.


From a distance, crossover cables look identical to regular network cables. To help you identify them,

many crossover cables come with a label such as “CROSS” taped to them. If you don’t see such a label, I suggest you add your own so that you can keep the two types of cable separate. If you didn’t do that and now you’re not sure which of your cables is a crossover, there’s a way to tell. Take the connectors on each end of the cable and place them side by side so that you have a good view of the colour wires inside. (A clear plastic covering helps here.) Make sure you hold the connectors

with the same orientation (it’s usually best to have the plastic tabs facing down). If the layout of the wires is identical on both connectors, then you’ve got a regular network cable. If you see, instead, that two of the wires—specifically, the red and the green— have switched positions, then you’ve got a crossover cable.