Most Commonly Used Networking Devices (Hubs, Repeaters And Bridges)

We generally use LANs to access the internet. But each LAN is connected to each other or directly to the internet through a series of networking devices. Connecting devices generally operate in different layers of the Internet model. In this post, we discuss only those that operate in the physical and data link layers. 

Types Of Network Connecting Devices Used As Connectors

Different types of network connecting devices are as follows:

• Repeaters and Hubs
• Bridges
• Routers
• Gateway
• Switches

The five categories contain devices which can be further defined as :

1. Those which operate below the physical layer (in OSI model) such as a passive hub.

2. Those which regenerate the original signal and operate in the physical layer (a repeater or an active hub).

3. Those which operate at the physical layer and data link layers. It utilizes the address protocol (a bridge or a two-layer switch).

4. Those which operate at the physical, data link, and network layers.It provides connections between two separate but compatible networks (a router or a three-layer switch).

5. Those which can operate at all five layers and provide translation services between incompatible networks (a gateway) .

Refer below the figure for clarity :

A LAN may be spread over a larger distance than its media can handle effectively. The number of stations also can be more than a number which can be handled and managed properly.

Such networks should be subdivided into smaller networks and these smaller subnetworks should be connected to each other through connecting devices.

A device called a repeater is inserted into the network to increase the coverable distance or a device called a bridge can be inserted for traffic management.

Let us now understand each of the networking devices in detail :

Repeaters Used as Networking Device

A repeater is a device that basically operates in the physical layer. Signals that carry information within a network can able to travel a fixed distance before attenuation endangers the integrity of the data.

Attenuation of signals basically limits the distance any medium can carry data. Devices that amplify signals to ensure data transmission are called repeaters. A repeater receives a signal and before it gets attenuated or corrupted, regenerates the original signal.

The repeater is not an amplifier because amplifiers simply amplify the entire incoming signal along with noise.A repeater does not actually connect two LANs , it connects two segments of the same LAN. The segments that are connected are still part of one single LAN. 

A repeater forwards each and every frame, it has no filtering capability. A repeater is a regenerator, not an amplifier. The location of any repeater on a link is important.

A repeater must be placed in such a way that a signal reaches it before any noise changes the order of any of its bits. A little noise can further alter the precision of a bit’s voltage without destroying it.

A repeater should be placed at a precise point on the link. Such that the signal reaches it before the noise has induced an error in any of the transmitted bits.

Thus with the use of repeaters, any network can be extended further without compromising the quality of data transmitted.

Hubs Used As Networking Device

 Hubs can be termed as multiway repeaters. It connects multiple LAN segments. A network uses a star topology with a central point called hub. 

Hub monitors all transmission from the stations . When there is only one transmission, the hub repeats the transmission on other lines. If there is collision, then the hub will send a jamming signal to all the stations. There are mainly two types of hubs :

1. Active Hubs 

They are like passive hubs but have electronic components for regeneration and amplification of signals. By using a active hub , the distance between devices can be increased. An active hub is equivalent to a multipoint repeater.

An active hub is actually a multipart repeater. It is commonly used to create connections between stations in a physical star topology

The main drawback of active hubs is that they amplify noise as well along with the signals. They are more expensive than passive hubs as well. 

2. Intelligent Hubs

In addition to signal regeneration, intelligent hubs perform some other intelligent functions such as network management and intelligent path selection.

A switching hub will choose only the port of the device where the signal needs to go, rather than sending the signal along all paths.

Bridges Used As Networking Device 

The Bridge is an internetworking device used to connect two LANs using simmilar LAN protocols. Bridge act as an address filter by picking up frames and transmit them to the correct destination. It operates in layer 2 of OSI model.  

A bridge can able to operate in the physical layer as well as in the data link layer of the OSI model .  It can regenerate the signal that it receives and it can check the physical (MAC) addresses of source and destination mentioned in the header of a frame.

It has access to MAC address of all the stations connected to it. A bridge must have a lookup table, that contains the physical address of every station connected to it. 

A bridge can operate in both the physical and the data link layer. As a physical layer device, it then regenerates the signal it receives. It divides the large network into segments and provides security by partitioning of data.

Types of Bridges:

• Simple Bridge
• Transparent Bridge
• Source Routing Bridge
• Mixed media bridge (translation  bridge)

A bridge consists of a conventional computer with a CPU , memory, and network interfaces. 

That’s all in this post. Stay tuned for other important networking devices explained in the next post.