Different Types of Communication Devices

The objective of this comprehensive article is to highlight the communication devices and its  importance:-

1. Repeater

A repeater connects two segments of your network cable. It re-times and regenerates the signals to proper amplitudes and sends them to the other segments. When talking about, Ethernet topology you are probably talking about using a hub as a repeater.

Repeater require a small amount of time to regenerate the signal. This can be cause a propagation delay which can affect network communication when there are several repeaters in a row. Repeaters work only at the physical layer of the Open System Interconnection (OSI) network model.

2. Bridge

A bridge is a device that connects one local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or Token ring). If a data unit on one LAN is intended for a destination on an interconnected LAN, the bridge forwards the data unit to the LAN; otherwise, it passes it long on the same LAN. A router connects a network to one or more other networks that are usually parts of a wide area network  (WAN) and may offer a number of paths out to destinations on those networks.

A router therefore needs to have more information than a bridge about the interconnected networks. It consists a routing table for this information. Since a given outgoing data unit or packet from a computer may be intended fro an address on the local network, on an interconnected LAN or the wide area network. It makes sense to have a single unit that the examines all data units and forwards them appropriately.

3. Router

In packet-switched network such as the internet, a router is a device or in some cases, software in a computer, that determines the next network point to which a packet should be forwarded towards its destination. The router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to.  A router is located at any gateway where one network meets another, including each point of presence on the internet. A router is often included as part of a network switch.

A router may create or maintain a table of the available routes on their conditions and use this information along with distance and cost algorithms to determine the best route for a given packet. Typically, a packet may travel through a number of network  points with routes before arriving at its destination. Routing is a function associated with the Network layer (layer 3) in the standard model of network programming, the Open System Interconnection (OSI) model. A layer-3 switch is a switch that can perform routing functions.

An edge router is a route than interface with an asynchronous transfer mode (ATM) network. A router is a network bridge combined with a router. For home and business computer users who have high speed internet connections such as cable satellite or DSL, a router can act as a hardware firewall. This is true even if the home or business has only one computer. Many engineers believe that the use of a router provides better protection against hacking than a software firewall, because no computer internet protocol address are directly exposed to the internet. This makes port scans (a technique fro exploring weaknesses) essentially impossible. In addition, a router does not consume computer resources as a software firewall does.  Commercially manufactured routers are easy to install, reasonably priced and available for hard wired or wireless networks.

4. Gateway

A gateway is a network point that acts as an entrance to another network. On the internet, a node or stopping point can be either a gateway node or a host (end point) node. Both the computers of internet users and the computers that serve page to users are host nodes. The computers that control traffic within your company’s network or at your local internet service provider (ISP) are gateway nodes.

In the network for an enterprise, a computer serve acting as a gateway node is often also acting as a proxy server and a firewall server. A gateway is often associated with both a router, which knows where to direct a given packet of data that arrives at the gateway and a switch, which furnishes the actual path in and out of the gateway for a given packet.

5. Hub

A network hub is a device which is used to connect multiple twisted pair or fire optic Ethernet devices together and makes them act as a single network segment. Hub work at the physical layer i.e., layer 1 of the   Open System Interconnection (OSI) model. Therefore, this device is a form of multi-port repeater. Repeater hubs also participate in collision detection, by sending a jam signal to all ports at the time detection of a collision. Hubs also often come with a BNC or AUI connector to allow connection to legacy 10BASE2 or 10BASE5 network segments. In the present scenario, network switches are replacing hubs but hubs are still seen in older installations and more specialized applications.

6. Server

A server itself a computer that provides services or resources to other computer connected with it by some networking mechanism. It is designated for running specific server application. A computer that is designated for only one server application is often named for that application. Server applications can be divided among server computers over an extreme range, depending upon the workload. Every server application can run concurrently under light loading, but multiple server computers may be required for each application under a heavy load. Under medium loading, it is common to use one server computer per server application, in order to limit the amount of damage caused by failure of any single server computer or security breach of any single server application. Any server computer can also be used as a workstation, but it is avoided in practice, again to contain risk.

When a server starts, it opens the door for incoming requests from its clients, but it never initiates a service until it is requested to do so. ( A client is a program running on the local machine requesting service from a server. A client is a finite program which means it is started by the users or some another application program and terminates when the service is complete.) When server starts, it runs infinitely unless a problem arises. It waits for incoming requests from clients and when a request arises, it responds to the request.

7. Switch

When we have multiple devices we face a problem to connect them to make one-on-one communication possible. The number and length of the links required for connecting them needs too much infrastructure. Majority of the links remain idle for most of the time. A network switch is a computer networking device that connect network segments.

A switched network consists of a series of interlinked nodes called switches. A switch may be hardware or a software device capable of creating temporary connection between two or more devices linked to the switch but not to each other.

8. LAN Card

A Local Area Network (LAN) card is used to provide access to computers and servers on network. It work by exchanging signals with a router, which transmits the signals over a physically wired line. A LAN card communicates with the router. The computer converts data into binary form and sends it to the LAN card, which in turn broadcasts the signal to be picked up by the router. The router sends the information on in the form of packets of information and bundles information for return to the computer via the LAN card in the same way.

Multiple users can maintain a connection to the router on different bands, to avoid interference and are assigned unique identities by the router in the form of an IP address. Each user attempting to access the network will need a LAN card, which is either available  built into the computer or as an external attachment which can be connected through a Universal Serial Bus port or PC card slot in laptop.

9. Modem

The word MODEM consists of MO+DEM MO stands of Modulator and DEM stands of Demodulator. The conversion of digital signals to analog signals is called modulation and the reverse process is called demodulation. Modems are connected both at sending and receiving ends. The modulator of sender changes the bit pattern to analog signals. The modem is connected between a terminal and telephone line. The signal is sent through telephone line and the modem at receiving end demodulates the wave pattern into digital signals and these signals are converted into output or stored in computer.

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