Thursday 28 January 2021

Networking Devices : Repeater, Hub, Bridge, Router, Brouter and Modem

 

NETWORKING DEVICES:

 

A] Repeaters:

 

o   Repeaters are physical hardware devices that have a primary function to re generate the electric signal by:

1.    Reshaping the waveform

2.    Amplifying the waveform

3.    Retiming the signal

 

o   The purpose of a repeater is to extend the line segment beyond its physical limits.

 

o   A line segment is a logical path such as the logical was used by all 802.3 Ethernet types.

 

o   A line segment is given an identification number called a segment number or network number to differentiate it from other segments.

 

o   Typically repeaters are used to connect two physically close buildings together that are too far apart to just extend the segment.

 

o   They can be used to connect floors of a building together that would surface the maximum allowable segment length.


Repeater

Wi-Fi Repeater


B] Hubs:

 

o   A hub is basically a multiport repeater. A hub connects multiple wires coming from different branches, for example, the connector in star topology which connects different stations.

 

o   Hub is a small box that connects together the signal from each individual device, optionally amplifies each signal, and then sends the signal out to all other connected devices.

 

o   Amplification helps to ensure that devices on the network receive reliable information.

 

o   Hubs are also called concentrators or repeaters.

 

o   They come in various sizes the most common being 12 port or 24 port.

 

o   There are three main points to remember about hubs:

 

1.     Many kinds of nodes can be connected to the hub with the networking cables.

2.     All Hubs can be uplink together, either with straight cable or crossover cable depending on whether or not the hub has a uplink port

3.     Performance will decrease as the number of users is increased.

 

o   Hubs cannot filter data, so data packets are sent to all connected devices.

 

o   Also, they do not have intelligence to find out best path for data packets which leads to inefficiencies and wastage.

 

o   When choosing a hub, the main consideration should be performance. Always remember that the network may expand in the future.  Try to buy a hub that has enough ports to allow for expansion without more hardware purchases.

 

Types of Hub:

1.    Active Hub: - These are the hubs which have their own power supply and can clean, boost and relay the signal along the network. It serves both as a repeater as well as wiring center. These are used to extend maximum distance between nodes.

2.    Passive Hub: - These are the hubs which collect wiring from nodes and power supply from active hub. These hubs relay signals onto the network without cleaning and boosting them and can’t be used to extend distance between nodes.


Hub

C] Bridges:

 

o   Bridges are both hardware and software devices.

 

o   They can be standalone devices - separate boxes specifically designed for bridging applications or they can be dedicated PCs with two NIC and bridging software.

 

o   A bridge operates at data link layer. A bridge is a repeater; with add on functionality of filtering content by reading the MAC addresses of source and destination.

o   It is also used for interconnecting two LANs working on the same protocol. It has a single input and single output port, thus making it a 2 port device.

Types of Bridges:

1.    Transparent Bridges: - These are the bridge in which the stations are completely unaware of the bridge’s existence. That is, whether or not a bridge is added or deleted from the network, reconfiguration of the stations is unnecessary. These bridges make use of two processes i.e. bridge forwarding and bridge learning.

2.    Source Routing Bridges: - In these bridges, routing operation is performed by source station and the frame specifies which route to follow. The host can discover frame by sending a special frame called discovery frame, which spreads through the entire network using all possible paths to destination.


Working of Bridge

Bridge


D] Router:

 

o   A router is a device that forwards data packets along networks.

 

o   A router is connected to at least two networks, two LANs or WANs, or a LAN and its ISP’s network.

 

o   Routers are located at gateways, the places where two or more networks connect and are the critical device that keeps data flowing between networks and keep the networks connected to the internet.

 

o   When data is sent between locations on one network or from one network to a second network the data is always seen and directed to the correct location by the router.

 

o   They complete this by using headers and forwarding tables to determine the best path for forwarding data packets and they use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.

 

o   Routers are physical devices that join multiple wired or wireless networks together.

 

o   By maintaining configuration information in the routing table, wired or wireless routers also have the ability to filter traffic either incoming or outgoing based on the IP addresses of the senders and receivers.

 

o   Router translates information from one network to another; it is similar to a super intelligent bridge. 

 

o   Routers select the best path to route a message, based on the destination address and origin.

 

o   The router can direct traffic to prevent head on collision and is smart enough to know when to direct traffic along back roads and shortcuts.

 


Router

E] Brouter:

 

o   They are protocol dependent devices.

 

o   When brouter receives a frame to be forwarded to the remote segment, it checks to see if it recognizes the network layer protocol.

 

o   If the brouter does, it acts like a router and finds the shortest path.

 

o   If it doesn't recognize the network layer protocol all it acts like a bridge and forwards the frame to the next segment.

 

o   The key advantage of them is that they have the ability to act as both a bridge and a router.

 

o   It can replace separator bridges and routers, thus, saving money.


Brouter


F] Modem:

 

o   A modem (modulator-demodulator) is a hardware device that converts data into a format suitable for a transmission medium so that it can be transmitted from computer to computer (over telephone wires).

 

o   A modem modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information.

 

o   The goal is to produce a signal that can be transmitted easily and decoded reliably to reproduce the original digital data.

 

o   A common type of modem is one that turns the digital data of a computer into modulated electrical signal for transmission over telephone lines and demodulated by another modem at the receiver side to recover the digital data.


Modulation-Demodulation


o   Modems are generally classified by the maximum amount of data they can send in a given unit of time, usually expressed in bits per second (symbol bit(s), sometimes abbreviated "bps") or rarely in bytes per second (symbol B(s)).

 

o   Modems can also be classified by their symbol rate, measured in baud. The baud unit denotes symbols per second, or the number of times per second the modem sends a new signal.

 

o   There is one standard interface for connecting external modems to computers called RS-232. Consequently, any external modem can be attached to any computer that has an RS-232 port, which almost all personal computers have.

 

 

o   There are also modems that come as an expansion board that you can insert into a vacant expansion slot. These are sometimes called onboard or internal modems.

 

 

Types of Modem:

a)    Dial-Up Modems:

Modems used on dial-up networks convert data between the analog form used on telephone lines and the digital form used on computers. An external dial-up modem plugs into a computer at one end and a telephone line on the other end.


Dial-up modem


b)    Broadband Modems:

A broadband modem like those used for DSL or cable internet access uses advanced signaling techniques to achieve dramatically higher network speeds than earlier-generation dial-up modems. Broadband modems are often referred to as high-speed modems. Cellular modems are a type of digital modem that establishes Internet connectivity between a mobile device and a cell phone network.

External broadband modems plug into a home broadband router or other home gateway device on one end and the external Internet interface such as a cable line on the other.

The router or gateway directs the signal to all the devices in the business or home as needed. Some broadband routers include an integrated modem as a single hardware unit.


Broadband modem



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