Networking Devices

Now that you are familiar with the various types of media and connections, you should learn about some devices commonly found on today's network.

NIC: 

NIC

The network interface card, as its name suggests, is the expansion card you install in your computer to connect, or interface, your computer to the network. This device provides the physical, electrical, and electronic connections to the network media. Generally all NICs have one ot two light emitting diodes (LEDs) that help in diagnosing problems with their functionality.

HUB:

A hub is a devices that connects all segments of the network together.Every device in the network connects to the hub through the single cable. Any transmission received on one port will be sent out all the other portsin the hub, including the receiving pair for the transmitting device. A broadcast sent out by any device on the hub will be propagated to all devices connected to hub. Any two or more devices connected to hub have capability of causing collision with each other. The LED will turn orange from green on collision, and we will have to turn off the hub, and wait for a while, then restart the hub, now the hub will be work properly. This was the major drawback of hubs.

SWITCH:

Like a hub, a switch connects multiple segments of the network together, with one important difference. Whereas a hub broadcast anything it receives, a switch recognizes frame boundaries and pays attention to the MAC address of the incoming frame as well as the port on which it was received. A switch, when it is installed in the network, first time it broadcasts to store MAC address of the devices in the network in its table, whenever it receives a data packet then it matches MAC address from its MAC table and forward it to specific port. In this way, probability of collision is being reduced. There are two types of switches:

• Manageable: operates on Data Link Layer and Network Layer, it may be used to implement routing protocols in a small network.
• Non-manageable: operates on Data Link layer. It has MAC table, it does not support routing protocols.

switching methods:

• Cut-through Method: cut-through switching is a method for packet switching systems, wherein the switch starts forwarding a frame (or packet) before the whole frame has been received, normally as soon as the destination address is processed. This technique reduces latency through the switch, but decreases reliability.
• Store & Forward Method: information is sent to an intermediate station where it is kept and sent at a later time to the final destination or to another intermediate station. The intermediate station, or node in a networking context, verifies the integrity of the message before forwarding it.

BRIDGE:
A bridge, specifically a transparent bridge,is a network device that connects two similar network segments together. The primary function of a bridge is to keep traffic separated on both sides of the bridge. Bridge is used in bus topology. for example :

MSMQCLIENT1 wants to send data to MSMQCLIENT5, bus will broadcast the data in upper segment and try to broadcast in lower segment also, since MSMQCLIENT5 is in upper segment so it will be wastage of resource utilization by broadcasting data in lower segment. hence we use bridge, it will match MAC address of the data packet header with its MAC table, since MSMQCLIENT5 is not in lower segment so it will not allow data flow in lower segment.


ROUTER

Representation of a router

A router is a network device that connects multiple, often dissimilar, network segments into an internetwork. The router, once connected, can make intelligent decisions about how best to get network data to its destination based on network performance data that it gathers from the network itself. Router operates at Network layer. It decide the best route with the help of network layer address. We will study about router and routing protocols in detail later on. Router Vendors:
Cisco, Juniper, ZDNet etc


GATEWAY
A gateway is any hardware and software combination that connects dissimilar network environments. Gateways are the most complex of network devices because they perform translations at multiple layers of the OSI model. For example, a gateway is the device that connects a LAN environment to a mainframe environment. E-mail gateway translates LAN based mail messages into the SMTP format that Internet mail uses.

MODEM

A modem is a device that modulates digital data onto an analog carrier for transmission over an analog medium and then demodulates from the analog carrier to a digital signal again at the receiving end.


FIREWALLS

Its job is to protect LAN resources from attackers on the Internet. Similarly, it can prevent computers on the network from accessing various services on the Internet. It can be used to filter packets based on rules that the network administrator sets. Firewalls can be stand-alone "black boxes", or can be set up in software on a server or router.