Purpose and function of network device

Here are the list of the  network devices :

* Hubs
* Switches
* Routers
* Access Points
* Hardware firewall devices

These are the devices that make up the network itself.

Client Devices:

* Desktop and laptop computers
* Tablets
* Smart Phones

These are the devices that the network exists for, the devices that access the network and utilise it.

 service devices:

* Printers
* Servers
* Storage units

These are the focus of the network, the devices the users are trying to access.

Hub:

• First we have the hub. Don’t see many of these, and I’ve never seen one in production use! A good place to start then. A hub is basically a repeater, like a parrot, everything it hears, it repeats. Any data in to any port is immediately sent out of all other ports. This means that each port on a hub is within the same segment, and collisions are more and more likely with more ports.
•  1 segment, 1 collision domain.
• using hub for connectivity creates the traffic congestion

Switch:

• Next the switch. A switch starts off like a hub, but for every request it receives, it remembers the MAC address of the requester, and the port the request came in on. That way, once a request destined for that MAC is seen, it only needs to be sent out of one port, not many. This effectively makes each port into it’s own collision domain. We are still at layer two though, still on the same IP subnet, so still at one segment.
• 1 segment, many collision domains.

Router:

• Routers work at the level above switches, effectively moving packets based on IP address, rather than MAC address. This makes each port on a router a separate segment, and by virtue of that a separate collision domain.
•  many segments, many collision domains.
• routers are used to connect networks together and route packets of data from one network to another
• Breaking up a broadcast domain is important because when a host or server sends a network broadcast, every device on the network must read and process that broadcast—unless you’ve got a router. When the router’s interface receives this broadcast, it can respond by basically saying, “Thanks, but no thanks,” and discard the broadcast without forwarding it on to other networks. Even though routers are known for breaking up broadcast domains by default, it’s important to remember that they break up collision domains as well. There are two advantages of using routers in your network:
• They don’t forward broadcasts by default.
• They can filter the network based on layer 3 (Network layer) information (e.g., IP address).

Four router functions in your network can be listed as follows:

• Packet switching

• Packet filtering

• Internetwork communication

• Path selection

AP:

• Access points are effectively hubs for wireless devices. Using the shared medium of the same “channel” of the spectrum each client device shares the bandwidth of the access point.
• 1 segment, 1 collision domain.

Firewall:

•   firewall is a software or hardware-based network security system that controls the incoming and outgoing network traffic by analyzing the data packets and determining whether they should be allowed through or not, based on applied rule set. 
• Firewalls can be defined in many ways according to your level of understanding. 
• A firewall establishes a barrier between a trusted, secure internal network and another network (e.g., the Internet) that is not assumed to be secure and trusted.
• Many personal computer operating systems include software-based firewalls to protect against threats from the public Internet. 
• Many routers that pass data between networks contain firewall components and, conversely, many firewalls can perform basic routing functions.