1. Network Devices
Itishree Mishra
XII A

2. What are network devices???
Computer networking devices are units that mediate data in a computer network. Computer networking devices are also called network equipment, Intermediate Systems (IS)or Interworking Unit (IWU). Units which are the last receiver or generate data are called hosts or data terminal equipment.

3. Functions of network devices
Separating (connecting) networks or expanding network
e.g. repeaters, hubs, bridges, routers, switches, gateways
Remote access
e.g. 56K Modems and ADSL modems

4. Expanding Network
Networks cannot be made larger by simply adding new computers and more cables
Less efficient !!
Can install components to
segment (divide) large LAN to form smaller LANs
connect LANs
Required components
Repeaters, bridges, routers, switches or gateways

5. Types of network devices
Modem
RJ-45
Ethernet card
Hub
Switch
Repeater
Bridge
Router
Gateway

6. MODEM :
A MODEM is a computer peripheral that allows you to connect and communicate eith other computers via telephone lines.

7. MODEM stands for modulation and demodulation.
Allow computers to communicate over a telephone line
Enable communication between networks or connecting to the world beyond the LAN

8. Cannot send digital signal directly to telephone line
Sending end: MODulate the computer’s digital signal into analog signal and transmits
Receiving end: DEModulate the analog signal back into digital form

9. Types of modems 1.Internal modems: 2. EXTERNAL MODEMS:
The modems that are fixed within the computer.
2. EXTERNAL MODEMS:
The modems that are connected externally to the computer.

10. Working of a modem
MODEM converts digital signals to A/F (Audio Frequency) tones which are in the frequency range that the telephone lines can transmit and also it can convert transmitted tones back to digital information.

11. RJ-45
RJ 45 is the short for Registered jack 45. RJ 45 is an eight wire connector, which is commonly used to connect computers on the local area networks i.e., LAN’s especially Ethernets. (Ethernet is a LAN architechture developed by Xerox Corp along with DEC and Intel. It uses either bus or star topologyand suports data transfer rates upto 10 Mbps.)

12. RJ-45 jack.
Inserting an RJ-45 connector into its jack.

13. Ethernet card
Ethernet is a LAN architecture developed by Xerox corp. in association with DEC and Intel. Ethernet uses either bus or star topology and supports data transfer rates up to 10 mbps.
The computers that are part of Ethernet, have to install a special card called Ethernet card .

14. An Ethernet card contains connections for either coaxial or twisted pair cables or both.
Inserting Ethernet card in its slot on motherboard

15. HUB Hub can be defined as one common point for connecting
all the network devices.
Various LAN segments are
connected to hub in order to
organize the working of the
network. A network hub connects the various
ports of the optic fiber cable and helps
establish a single network connection or
segment.

16. How a hub works
The most common operation it performs is that it repeats all the information it receives and forward it to all PC terminals attached to it.
This repetition of data
results in unnecessary
data traffic being sent to
the network. Therefore the data is sent in bulk without the identification of its destination.

17. Limitations and Features
Cannot link unlike segments
Cannot join segments with different access methods (e.g. CSMA/CD and token passing)
Do not isolate and filter packets
Can connect different types of media
The most economic way of expanding networks

18. SWITCH
 A network switch is a small hardware device that joins multiple computers together within one local area network (LAN). Technically, network switches operate at layer two (Data Link Layer) of the OSI model.

19. Network switches appear nearly identical to network hubs, but a switch generally contains more intelligence (and a slightly higher price tag) than a hub.
Unlike hubs, network switches are capable of inspecting data packets as they are received, determining the source and destination device of each packet, and forwarding them appropriately.
By delivering messages only to the connected device intended, a network switch conserves network bandwidth and offers generally better performance than a hub.

20. Functioning
A switch is a telecommunication device which receives a message from any device connected to it and then transmits the message only to the device for which the message was meant. This makes the switch a more intelligent device than a hub (which receives a message and then transmits it to all the other devices on its network). The network switch plays an integral part in most modern Ethernet LANs. 

21. Advantages of Switches
Switches divide a network into several isolated channels (or collision domains)
Reduce the possibility of collision
Collision only occurs when two devices try to get access to one channel
Can be solved by buffering one of them for later access
Each channel has its own network capacity
Suitable for real-time applications, e.g. video conferencing
Since isolated, hence secure
Data will only go to the destination, but not others

22. Limitations of Switches
Although contains buffers to accommodate bursts of traffic, can become overwhelmed by heavy traffic
Device cannot detect collision when buffer full
CSMA/CD scheme will not work since the data channels are isolated, not the case as in Ethernet
Some higher level protocols do not detect error
E.g. UDP
Those data packets are continuously pumped to the switch and introduce more problems

23. REPEATER
A repeater is an electronic device that receives a signal and retransmits it at a higher level or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.

24. In digital communication systems, a repeater is a device that receives a digital signal on an electromagnetic or optical transmission medium and regenerates the signal along the next leg of the medium. In electromagnetic media, repeaters overcome the attenuation caused by free-space electromagnetic-field divergence or cable loss. A series of repeaters make possible the extension of a signal over a distance.
Repeaters remove the unwanted noise in an incoming signal. Unlike an analog signal, the original digital signal, even if weak or distorted, can be clearly perceived and restored. With analog transmission, signals are restrengthened with amplifiers which unfortunately also amplify noise as well as information.

25. BRIDGE Has one input and one output
Used to isolate network traffic and computers
Has the intelligent to examine incoming packet source and destination addresses.
But cannot interpret higher-level information
Hence cannot filter packet according to its protocol

26. How bridges work
Bridges work at the Media Access Control Sub- layer of the OSI model.
Routing table is built to record the segment no. of address.
If destination address is in the same segment as the source address, stop transmit.
Otherwise, forward to the other segment.

27. Differences Between Bridges and Repeaters

28. ROUTER
In a common configuration, routers are used to create larger networks by joining two network segments.
A router can be a dedicated hardware device or a computer system with more than one network interface and the appropriate routing software. All modern network operating systems include the functionality to act as a router.
Routers will normally create, add, or divide on the Network Layer as they are normally IP-based devices.

29. How a router functions
As packets are passed from routers to routers, Data Link layer source and destination addresses are stripped off and then recreated
Enables a router to route a packet from a TCP/IP Ethernet network to a TCP/IP token ring network
Only packets with known network addresses will be passed - hence reduce traffic
Routers can listen to a network and identify its busiest part
Will select the most cost effective path for transmitting packets

30. Distinguishing Between Bridges and Routers
Bridges forward everything they don’t recognize
Routers select the best path
Routers are layer 3 devices which recognize network address
Bridges are layer 2 devices which look at the MAC sublayer node address

31. GATEWAYS
Any device that translates one data format to another is called a gateway.
A gateway is a network device that connects dissimilar networks. It establishes an intelligent connection between a local network and external networks with completely. different structures.

32. Some examples of gateways include a router that translates data from one network protocol to another, a bridge that converts between two networking systems, and a software application that converts between two dissimilar formats.
The key point about a gateway is that only the data format is translated, not the data itself. In many cases, the gateway functionality is incorporated into another device.
The gateway often acts as a proxy server and a firewall.