Basic Hardware and HUBS These days there is a plethora of networking products to consider when planning network infrastructure. There are devices for everything from connecting computer systems to the network to extend a Topology’s specifications to controlling network traffic. Sometimes your choices are limited. For example, to connect an office computer to the network, you must have a network card. Many of these devices, when used correctly, can also help to improve network security. Following Network devices are explained.
(a) Repeaters Repeaters are simple two-port signal amplifiers. They are used in a bus topology to extend the maximum distance that can be spanned on a cable run. The strength of the signal is boosted as it travels down the wire. A Repeater will receive a digital signal on one of its ports, amplify it, and transmit it out the other side. A repeater is like a typical home stereo amplifier. The Amp takes the signal it receives from CD or Tape deck, amplify the signal, and sends it on its way to the speakers. Repeaters function similarly to a stereo amplifier, they simply boost whatever they receive and send it on its way.
(b) HUBS One network component that is becoming standard equipment in more and more networks is the hub. A hub is the central component in a star topology. There are three types of Hubs.
(i) Active Hubs Most hubs are active in that they regenerate and retransmit the signals the same way a repeater does. Active hubs require electrical power to run.
(ii) Passive Hubs Some types of hubs are passive. They act as connection points and do not amplify or regenerate the signal, the signal passes through the hub. Passive hubs do not require electrical power to run.
(iii) Hybrid Hubs Advanced hubs that will accommodate several different types of cables are called hybrid hubs. A hub-based network can be expanded by connecting more than one hub.
(c) Bridges
(i) The first device in this group is the bridge, which operates at layer 2 or the data link layer of the OSI model.
(ii) Bridges are devices with two or more ports that are used as intelligent repeaters in that they are designed to connect two or more networks together in one common broadcast domain.
(iii) Depending on the type of bridge employed, this connectivity can take place in a local area or wide area environment.
(iv) Essentially, during this process the bridge watches network traffic on all interfaces, and creates a table of which hosts reside on what ports.
(v) To ensure that information contained in the table remains current, the bridge will expire or remove entries once a specified period of time elapses with no traffic seen to or from a particular host. The information collected and maintained in the table is used by a second process, called forwarding.
(vi) As noted earlier, when a bridge receives a frame on one of its interface, the bridge compares the destination address of the frame to the forwarding table built with the learning process. Assuming a match for the destination is found, the bridge forwards the packet to the appropriate interface.
(vii) No match be found, the bridge uses a third process called flooding, in which the bridge sends the frame to all ports and waits to receive a reply from the frame’s destination.
(viii) The last process, called filtering, allows for the minimization of unnecessary traffic within or between network segments. For example, on a basic level a bridge employs filtering to ensure that communications between any two given hosts on the same segment are not forwarded or flooded to other bridge ports. In an advanced implementation, filtering can be used to limit communication between hosts on different network segments as well.
(d) Switches
(i) Switch is a device that could support creating separate virtual or physical networking segments. It has the ability to create separate collision domains either physically or virtually.
(ii) They operate at the data link layer (or layer 2 in the OSI model), and higher in cases of a multilayer switch. When operating at layer 2, a device has the ability to make intelligent decisions on how to handle a given packet of data based on the source and destination MAC (Media Access Control).
(iii) A MAC address is essentially a unique identifier that is hard-coded into every network device at the time of production.
(iv) Ethernet switches are switch frames of data between ports Other network switches do exist for example, frame relay switches are used largely
by telecommunication carriers, as are Asynchronous Transfer Mode (ATM) switches. ATM switches are differ greatly from Ethernet switches in that they switch in cells and not frames.
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