Hub, repeater, switch, router, gateway, bridge

HUB

Hub is a controller that controls the traffic on the network.

 The following important properties of hub are: 

1) It amplify signals.

2) It propagates signals through the network.

3) It does not require filtering.

4) It does not require path determination for switching.

5) It is used as network concentration points.

Hubs are basically two types:
1) Active hub
2) Passive hub

Active hub: Active hub works as repeater which is a hardware device that regenerates the received bit pattern before sending them out .
Passive hub : A passive hub is a simple hardware device which provide a simple physical connection between the attached devices.

Advantages of hub: It cannot filter the traffic full stop feeling generally refers to a process or device that screens network traffic for certain characteristics such as source address and destination address and protocol.

Disadvantages of hub: On a hub, more than one user may try to send data on the network at same time. If more than one node attempt to transmit at the same time, a collision occurs. When collision occurs data from each device hits each other and is damaged.

Repeater:

Repeater is and hardware device which is operated on the physical layer. Repeater installed on a link receives the signal before it becomes to week or corrupted, regenerates the original bits patterns and put the refresh copy back on the link. The repeater does not change the functionality of the network.

Switch: A switch forwards each incoming packet only to that that provides access to the destination system.

Router: router is an inter-networking device. It operates at network layer. Router routes packets between potentially different networks. Data comes in one of the line, the router reads the address information in the packet to determine its ultimate destination. Then using information in its routing table or routing policy it directs the packet to the next network on its journey. Router perform the traffic directing functions on the internet. Router is a sophisticated device because it contains a software and can take a decision to choose best path for data transmission it is basically used for inter networking.

The most familiar type of routers are home and small offices that simply pass data , such as web pages and email, between the home computers and the owners cable on DSL modem, which connects to the internet (ISP).

Routing algorithms:

1) Non Adaptive: non adaptive algorithm do not base their routing decisions on measurements and estimates of the current traffic and topology. Instead the choice of the route to use to get from i to j is computed in advance, offline, and download it to the IMPs when the network is booted. This procedure is sometimes called static routing.

2) Adaptive: adapting algorithm attempt to change the routing decisions to reflect changes into topologies and the current traffic. Three different families of adaptive algorithms exist differing in the information they use.

Gateway: Gateway is used for connecting two dissimilar network means a gateway can accept and transfer data packets between different networks, it is a protocol converter. Gateway is a dedicated device that run on dedicated computer. Gateways are essential device that direct network traffic in some fashion and translate that information. Gateway is generally software installed within a router . It operates in all seven layers of the open system interconnection (OSI) model. It must adjust the data size and format as well.
 Gateways can be of two types:
1) Connection oriented gateways
2) Connection-less gateways.

Bridge: Bridge is operated on the data link layer and are not required to check upper layer information. A bridge eliminates unnecessary traffic and minimize the chances of collisions occurring on a network by dividing the segments and filtering traffic based on MAC address. 
Bridge filter network traffic by only looking at MAC address. Therefore they can rapidly forward traffic representing any network layer protocol. Because Bridges only took a MAC address and not concerned with protocol. So, bridges are only concerned with passing packets, or not passing packets on the destination MAC address.
The following properties of bridge are:

• They are more intelligent than hub that it analyse incoming packets and forward them based on addressing information.
• They collect and pass packets between the network segments.
• The control broadcast to network.
• They maintain address table tasks .