Author: Neftaly Malatjie

A bridge is very similar in functionality to a repeater, but operates at Layer 2 of the OSI model. Therefore, a bridge actually filters traffic transmitted over the network based on the Layer 2, or MAC, address. Bridges dynamically update their routing tables with source addresses as they receive packet traffic. They determine the MAC address for each machine on the basis of the contents of packets (the MAC addresses of both the source and destination hosts) sent over the network. The destination MAC address of each packet is then used to selectively filter traffic packets in the following manner:

• Packets with unidentified destinations are sent on to every network segment to which the bridge is connected.
• Packets with identified destinations on other network segments to which the bridge is connected are sent on to the segment on which the destination machine resides.
• Packets in which the source and destination address are both within the same network segment are not sent to any other network segment.

Bridges are both good and bad in terms of their contribution to the problem of managing networks. An advantage of bridges (at least compared to repeaters) is that the former are not as passive; they can at least send traffic to other network segments or, if appropriate, keep traffic within a particular local segment. They can also selectively filter traffic on the basis of each packet’s destination MAC address. A disadvantage is that bridges cannot filter broadcasts (transmissions from hosts that are intended to reach other computers independently of the computers’ addresses).

In the most basic sense, networks work by sending electrical signals across cables. These signals, however, attenuate as they traverse each cable; at some point along a cable, the signal may fail to carry any further. Devices called repeaters are used in digital networks to regenerate signals as they go down cables so that they can reach destination hosts. Repeaters are often used to increase the physical size of LANs, allowing additional systems and peripherals to connect to a preexisting LAN. Note, however, that Ethernet does not need repeaters, because of the limited distances over which traffic to segments travels.

Contrasted with other types of network components, repeaters are in many respects more passive in their functionality. In the most elementary sense, they simply take signals, magnify them, and then send them along a network cable without the capacity to selectively filter, in any way, what is sent. A potential problem in connection with repeaters, therefore, is that a repeater can potentially overwhelm a network with volumes of traffic. Hosts in any part of a network in which repeaters are present can produce an enormous amount of traffic volume even though some, much, or all of this traffic may be superfluous to the systems along the way.

You might think, therefore, that repeaters would be frequent targets of network attacks in the Windows NT or any other networking environment. Gaining unauthorized access to a repeater or sending network traffic to a repeater in a manner that causes the repeater to fail or other possible attack scenarios could conceivably lead to widespread denial-of-service. Attacks against other components of networks (for example, routers and firewalls) are, however, generally not only easier to remotely perpetrate, but they are also more likely to subvert higher-level network functionality, such as routing.

A modem enables you to connect your computer to the available internet connection over the existing telephone line. Like NIC, Modem is not integrated with a computer motherboard. It comes as separate part which can be installed on the PCI slots found on motherboard.

A modem is not necessary for LAN, but required for internet connection such as dial-up and DSL.

There are some types of modems, which differs in speed and transmission rate. Standard PC modem or Dial-up modems (56Kb data transmission speed), Cellular modem (used in a laptop that enables to connect while on the go), cable modem (500 times faster than standard modem) and DSL Modems are the most popular.

When we talk about computer network components, the other device that used to connect a LAN with an internet connection is called Router. When you have two distinct networks (LANs) or want to share a single internet connection to multiple computers, we use a Router.

In most cases, recent routers also include a switch which in other words can be used as a switch. You don’t need to buy both switch and router, particularly if you are installing small business and home networks.

There are two types of Router: wired and wireless. The choice depends on your physical office/home setting, speed and cost.

It is a high-speed cable which transmits data using light beams through a glass bound fibers. Fiber-optic cable is high data transmission cable comparing to the other cable types. But the cost of fibre optics is very expensive which can only be purchased and installed on governmental level.