Data Communication Important Questions-Osmania University

Data Communication Important Questions-Osmania University

Unit-1

1. Write short notes on :Protocol Architecture.
2. Discuss TCP / IP protocol layer architecture and functions in detail.(**)
3. Write short note on  (c) Line Configuration.-5
4. List and explain transmission impairments.
5. Write short notes on any two of the following:

(a)    Pulse code modulation and delta modulation.

6. Compare the three basic modulation techniques for transforming digital data into analog signals. (5)
7. What is pulse stuffing? Explain how it is helpful in design of TEDM. (5)
8. (b) Explain the concept of Delta Modulation.***
9. (a) Draw the wave forms and explain the following coding schemes:

(a)    Bipolar-AMI (ii) Differential Manchester

10. Explain Data Communications Interfacing with neat diagrams.
11. Explain about Amplitude modulation and Angle modulation. 10
12. Differentiate between Amplitude shift keying, frequency shift keying and phase shift keying. (4)

Unit:2

 

 

1. Write about on error detecting and one error correcting codes. Explain with examples.
2. Elaborate On data transmission techniques.
3. Explain the Transmission modes, transmission characteristics and categories of applications of optical fiber. . (5)
4. Explain the different phases of HDLC with suitable example. (5)
5. What are the topology options for Fiber channel?
6. Explain how the Go-Back-N Arq technique can handle different specific cases or contingencies.
7. Discuss the mechanisms of sliding-window flow control.
8. State the purpose of ARQ and explain stop and wait ARQ.
9. Explain HD LC protocol in detail.****
10. Explain HDLC frame structure.
11. Explain in-detail Cyclic Redundancy Check (CRC) error detection technique with suitable examples. 10
12. Write about Line-of-sight Transmission.
13. A channel has a data rate of 4 kbps and a propagation delay of

 20 ms. For what range of frame sizes does stop-and-wait give an efficiency of at least 50% ?

 

Unit:3 

1. Give architecture of ATM and explain its logical connections and cells.
2. Describe Frame relay.
3. Elaborate on various methods of multiplexing.
4. Contrast the architecture of a traditional telephone network circuit switch with soft switch architecture. Explain how flexibility has been achieved in soft switch architecture.
5. Draw the Event timing diagram to bring out differences between circuit switching and packet switching.
6. What is the need for ATM adaptation layer? What are some of the protocols and services provided by the AAL ? (10)
7. What are the characteristics of virtual channel convections?
8. Draw and explain the ATM cell format 5
9. Explain the concepts of packet switching and how routing is done in packet switching.
10. Write short notes on any two of the following:
1. ADSL
11. Explain in detail about statistical time division multiplexing.
12. Explain in detail about xDSL.
13. The difficult problem in the design of a synchronous time division multiplexer is that of synchronizing the various data sources.How can this problem be overcome? Explain with suitable example
14. What are the advantages and disadvantages of Frame Relay over X.25 ?
15. What are the different categories and types of services that can handled by ATM network
16. Give a comparison of the circuit switching, datagram packet switching and virtual circuit packet switching Techniques.

Unit:4

Discuss Ethernet and token ring by giving their frame formats. Explain the significance of each field.

 

Differentiate Ethernet and token ring.

(c) LANs. Transmission media.

(c) Layer 2 and Layer 3 switches

14. (a) Describe the operation of CSMAjCD.

(b) Write short notes on -virtual LANs.

(b) List various LAN topologies and explain the frame transmission in each LAN

topology. .. 6

ExplainLANprotocolarchitecture.

Explainfunctionsof aBridge. 10

a)      Layer 2 switches,

14. (a) Write about layer 2 and layer 3 switches.

(b) Explain briefly about Gigabit ethemet.

 

16. (a) Explain key elements such as topology, medium access control of LAN.

(I) Bridge protocol architecture (c) Fibre channel topologies

 

Unit:5

 

Discuss cellular wireless networks of third generation systems.

Describe IEEE 802.11.

How medium access control is done is wireless LANs?

discuss the  architecture and services defined by1 EEE 802.11.

Write short notes on any two of the following:

(a) Frequency hopping spread spectrum and direct sequence

spread spectrum.

(b) Typical call between two mobile users within an area controlled

by a single MTSO.

 

Explain Bluetooth architecture.

16. a) Give overview of operation of cellular systems.

15. Write about IEEE 802.11 architecture and services.

17. Write short notes on any two of the following:

(a) HDLC

(b) xDSL

(c) Overview of cellular systems.

Draw and explain the 1EEE 802.11 MAC Frame Format. (3)

What are the advantages and disadvantages of using CDMA for

TRANSMISSION MEDIA

TRANSMISSION MEDIA 
A transmission medium can be broadly defined as anything that can carry information from a source to a destination. For example, the transmission medium for two people having a dinner conversation is the air. The air can also be used to convey the message in a smoke signal or semaphore. For a written message, the transmission medium might be a mail carrier, a truck, or an airplane. In data communications the definition of the information and the transmission medium is more specific. The transmission medium is usually free space, metallic cable, or fiber-optic cable. The information is usually a signal that is the result of a conversion of data from another form.

Guided Media:
Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable. A signal traveling along any of these media is directed and contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic (copper) conductors that accept and transport signals in the form of electric current. Optical fiber is a cable that accepts and transports signals in the form of light.
1. Twisted-Pair Cable
A twisted pair consists of two conductors (normally copper), each with its own plastic insulation,
twisted together, as shown in Figure 7.3.

One of the wires is used to carry signals to the receiver, and the other is used only as a ground
reference. The receiver uses the difference between the two. In addition to the signal sent by the
sender on one of the wires, interference (noise) and crosstalk may affect both wires and create
unwanted signals. If the two wires are parallel, the effect of these unwanted signals is not the
same in both wires because they are at different locations relative to the noise or crosstalk
sources (e,g., one is closer and the other is farther). This results in a difference at the receiver. By
twisting the pairs, a balance is maintained. For example, suppose in one twist, one wire is closer
to the noise source and the other is farther; in the next twist, the reverse is true. Twisting makes it
probable that both wires are equally affected by external influences (noise or crosstalk). This
means that the receiver, which calculates the difference between the two, receives no unwanted
signals. The unwanted signals are mostly canceled out. From the above discussion, it is clear that
the number of twists per unit of length (e.g., inch) has some effect on the quality of the cable.
Applications
Twisted-pair cables are used in telephone lines to provide voice and data channels. The local
loop-the line that connects subscribers to the central telephone office-commonly consists of
unshielded twisted-pair cables. The DSL lines that are used by the telephone companies to
provide high-data-rate connections also use the high-bandwidth capability of unshielded twistedpair cables. Local-area networks, such as lOBase-T and lOOBase-T, also use twisted-pair cables.

Asynchronous Transfer Mode (ATM)

Asynchronous Transfer Mode (ATM) also called cell relay (transferring data in cells of a fixed size) that is operates at the data link layer (Layer 2) of OSI Model over fiber or twisted-pair cable, a high-speed switched network technology based on ITU-T Broadband Integrated Services Digital Network (B-ISDN) standard, developed by the telecommunications industry to implement the next generation network. ATM was designed for use in WANs such as the public telephone system and corporate data networks, though it has also been applied to create super-fast LANs.

ATM can carry all kinds of traffic: voice, video and data simultaneously at speeds up to 155 megabits per second. It Convert voice, video data to packets and passing large packet data through the same medium. ATM is differing from TCP/IP because it use fixed channel routing protocol routes between two end points. A real-time low-latency application such as VoIP and video takes precedence on an ATM network.

ATM is a dedicated connection-oriented switching technology, in which switches create a virtual connection or virtual circuit between the sender and receiver of a call that permanent or switched for the duration of the call. It is a small-packet switched system or similar to circuit-switched network, which breaks down messages into very small, fixed length packets called cells generally organizes digital data into 53 bytes in length (48 bytes of data plus a 5-byte header). 

ATM frame structure

An ATM header can have User-Network Interface (UNI) and Network-Node Interface (NNI) two formats.
• User-Network Interface (UNI) used for communication between end systems.
• Network-Node Interface (NNI) used for communication between switches.

Two type of connections are supported by ATM (Asynchronous Transfer Mode)
Point-to-point connections: It connects either unidirectional or bi-directional two end-systems.
Point-to-multipoint connections: It connects one unidirectional ATM to number of destination ATM.
It is different in packet sizes from Ethernet data or frames. ATM is a core protocol for SONET that is the backbone of ISDN. The advantage conferred by such small cells is that they can be switched entirely in hardware, using custom chips, which makes ATM switches very fast (and potentially very cheap).

The asynchronous part of the name refers to the fact that although ATM transmits a continuous stream of cells over a physical medium using digital signal technology, some cells may be left empty if no data is ready for them so that precise timings are not relevant. Every cell is encoding data with asynchronous time-division multiplexing (TDM) and it queued before being multiplexed over the transmission path.

Every cell are encodes data and processed within their time slot allocated to it. When cell time slot allocated is finished, the next cell starts same procedure. That’s why it's called asynchronous time-division multiplexing (TDM);

This is ATM's greatest strength, as it enables flexible management of the quality of service (QoS) so; an operator can offer different guaranteed service levels (at different prices) to different customers even over the same line. This ability will enable companies to rent virtual private networks based on ATM that behave like private leased lines but in reality share lines with other users.
Available ATM service: Generally four data bit rates are available for ATM services: constant bit rate (CBR), variable bit rate (VBR), available bit rate (ABR) and unspecified bit rate (UBR). 

Comparison of the OSI and TCP/IP Reference Models:

Comparison of the OSI and TCP/IP Reference Models:
The OSI and TCP/IP reference models have much in common. Both are based on the concept of
a stack of independent protocols. Also, the functionality of the layers is roughly similar. For
example, in both models the layers up through and including the transport layer are there to
provide an end-to-end, network-independent transport service to processes wishing to
communicate. These layers form the transport provider. Again in both models, the layers above
transport are application-oriented users of the transport service. Despite these fundamental
similarities, the two models also have many differences Three concepts are central to the OSI
model:
1. Services.
2. Interfaces.
3. Protocols.
Probably the biggest contribution of the OSI model is to make the distinction between these three
concepts explicit. Each layer performs some services for the layer above it. The service
definition tells what the layer does, not how entities above it access it or how the layer works. It
defines the layer's semantics.
A layer's interface tells the processes above it how to access it. It specifies what the parameters
are and what results to expect. It, too, says nothing about how the layer works inside.
Finally, the peer protocols used in a layer are the layer's own business. It can use any protocols it
wants to, as long as it gets the job done (i.e., provides the offered services). It can also change
them at will without affecting software in higher layers.

The TCP/IP model did not originally clearly distinguish between service, interface, and protocol,
although people have tried to retrofit it after the fact to make it more OSI-like. For example, the only real services offered by the internet layer are SEND IP PACKET and RECEIVE IP
PACKET.
As a consequence, the protocols in the OSI model are better hidden than in the TCP/IP model
and can be replaced relatively easily as the technology changes. Being able to make such
changes is one of the main purposes of having layered protocols in the first place. The OSI
reference model was devised before the corresponding protocols were invented. This ordering
means that the model was not biased toward one particular set of protocols, a fact that made it
quite general. The downside of this ordering is that the designers did not have much experience
with the subject and did not have a good idea of which functionality to put in which layer.
Another difference is in the area of connectionless versus connection-oriented communication.
The OSI model supports both connectionless and connection-oriented communication in the
network layer, but only connection-oriented communication in the transport layer, where it
counts (because the transport service is visible to the users). The TCP/IP model has only one
mode in the network layer (connectionless) but supports both modes in the transport layer, giving
the users a choice. This choice is especially important for simple request-response protocols

TCP/IP PROTOCOL SUITE NOTES

TCP/IP PROTOCOL SUITE 

The TCPIIP protocol suite was developed prior to the OSI model. Therefore, the layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the host-to-network layer is equivalent to the combination of the physical and data link layers. 

The internet layer is equivalent to the network layer, and the application layer is roughly doing the job of the session, presentation, and application layers with the transport layer in TCP/IP taking care of part of the duties of the session layer. TCP/IP is a hierarchical protocol made up of interactive modules, each of which provides a specific functionality; however, the modules are not necessarily interdependent. Whereas the OSI model specifies which functions belong to each of its layers, the layers of the TCP/IP protocol suite contain relatively independent protocols that can be mixed and matched depending on the needs of the system. 

The term hierarchical means that each upper-level protocol is supported by one or more lower-level protocols. At the transport layer, TCP/IP defines three protocols: Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and Stream Control Transmission Protocol (SCTP). At the network layer, the main protocol defined by TCP/IP is the Internetworking Protocol (IP); there are also some other protocols that support data movement in this layer.

1. Host-to-Network Layer: The TCP/IP reference model does not really say much about what happens here, except to point out that the host has to connect to the network using some protocol so it can send IP packets to it. This protocol is not defined and varies from host to host and network to network. 

2. Internet Layer: Its job is to permit hosts to inject packets into any network and have they travel independently to the destination (potentially on a different network). They may even arrive in a different order than they were sent, in which case it is the job of higher layers to rearrange them, if in-order delivery is desired. The internet layer defines an official packet format and protocol called IP (Internet Protocol). The job of the internet layer is to deliver IP packets where they are supposed to go. Packet routing is clearly the major issue here, as is avoiding congestion.

3. The Transport Layer: The layer above the internet layer in the TCP/IP model is now usually called the transport layer. It is designed to allow peer entities on the source and destination hosts to carry on a conversation, just as in the OSI transport layer. Two end-to-end transport protocols have been defined here. The first one, TCP (Transmission Control Protocol), is a reliable connectionoriented protocol that allows a byte stream originating on one machine to be delivered without error on any other machine in the internet. It fragments the incoming byte stream into discrete messages and passes each one on to the internet layer. At the destination, the receiving TCP process reassembles the received messages into the output stream. TCP also handles flow control to make sure a fast sender cannot swamp a slow receiver with more messages than it can handle. The second protocol in this layer, UDP (User Datagram Protocol), is an unreliable, connectionless protocol for applications that do not want TCP's sequencing or flow control and wish to provide their own. It is also widely used for one-shot, client-server-type request-reply queries and applications in which prompt delivery is more important than accurate delivery, such as transmitting speech or video. 

4. The Application Layer: The TCP/IP model does not have session or presentation layers. On top of the transport layer is the application layer. It contains all the higher-level protocols. The early ones included virtual terminal (TELNET), file transfer (FTP), and electronic mail (SMTP). The virtual terminal protocol allows a user on one machine to log onto a distant machine and work there. The file transfer protocol provides a way to move data efficiently from one machine to another. Electronic mail was originally just a kind of file transfer, but later a specialized protocol (SMTP) was developed for it. Many other protocols have been added to these over the years: the Domain Name System (DNS) for mapping host names onto their network addresses, NNTP, the protocol for moving USENET news articles around, and HTTP, the protocol for fetching pages on the World Wide Web, and many others.

III/IV---DATA COMMUNICATIONS SYLLABUS (Osmania University)

UNIT–I
Data Communication and Networking Overview, Protocol Architectures: OSI, TCP/IP and ATM. Data transmission, Guided and Wireless transmission.
Data Encoding: digital data-digital signals, digital data-analog signals, analog data-digital signals, analog data-analog signals

UNIT–II
Multiplexing, Circuit switching and Packet switching, Digital Data Communication Techniques, Asynchronous and Synchronous transmission, DSL and ADSL.

UNIT–III
Data Link Control: Error detection techniques, interfacing. Line configurations, Flow control, Error control, Data link control protocols, Protocol verification

UNIT–IV
Local Area Networks, LAN Technologies, MAC sub layer, CSMA/CD, Token Ring, Fibre channel, IEEE Standards, High Speed LAN: Switched, Fast, Gigabit Ethernets.

UNIT–V
Wireless LANs, 802.11 Broad band wireless, 802.16 Bluetooth, Bridge, Spanning Tree Bridge, Source Routing Bridge, Repeaters, Hubs, Switches, Routers and Gateways, Virtual LANs.


Suggested Readings:
1. William Stallings, Data and Computer Communications, 8thEdition, Prentice Hall of India, 2012

2. Andrew S. Tanenbaum, David J. Wetherall, Computer Networks, 5thEdition, Pearson, 2012

Open System Interconnection (OSI) model Notes

Open System Interconnection (OSI) model, OSI Model defines and is used to understand how data is transferred from one computer to another in a computer network . Two computers connected to each other with LAN Cable and  Connectors (RJ-45), sharing data with help of Network interface card(NIC) forms a computer network. But if one computer is based on MSWindows and other Is MAC OS. Then how are they going to communicate  with each other? In order to accomplish successful communication between the computers or network or different architecture- 7 layered Open System Interconnection (OSI) Model was introduced by ISO in1984. ISO is the organization dedicated to defining global communication and standards.

  This model is called Open System Interconnection (OSI) because this model allows any two different systems to communicate regardless of their underlying architecture. The model consists of seven functions, often referred to as layers. Every layer Added its own header to the packet from previous layer. The seven layers can be grouped into three groups - Network, Transport and Application. 

• Layer 1, 2 and 3 i.e. physical, data link, and network are network support layers.
• Layer 4, Transport layer provides end to end reliable data transmission.
• Layer 5, 6 and 7 i.e. Session, Presentation, and Application layer are user support layers. Each Layer is a package of protocols.

  

Layer 7 – Application Layer 

AL is used by Network Applications (Computer applications that used internet) i.e. chrome, firefox, outlook , skype, etc. Web browser ,  is a Network application running in your PC, does  not reside in Application Layer. But it uses application layer protocols like HTTP,HTTPS to do web surfing . All network applications depend on application layer protocols.  HTTP,HTTPS,FTP,SMTP, these protocols collectively called Application Layer. Application Layer provide services for network applications with help of protocols to perform user activities. Application Layer: Does not include firefox, chrome,etc.  It includes Application layer protocols that are needed to make these applications work correctly in a network called internet .

Layer 6 – Presentation Layer 

Presentation Layer receives data from Application layer. The data in the form of characters and numbers are converted to binary format:- Translation. Before  data is transmitted PL reduces the number of bits to represent original data:-Data Compression. To maintain integrity of data, the data is encrypted at sender side and decrypted in receiver side. SSL (secure socket layer)  protocol used in Presentation Layer for encryption and decryption.

Layer 5 – Session Layer 

Session Layer helps in setting up and managing   Connections and enabling sending data and receiving data followed by termination of connection. Session layer has Application programming interfaces.   (API’s ) eg: NETBIOS, which allows application of different    computers to communicate with each other. Before a session or connection is established with a server. Server performs function called Authentication.  Authorization: Determines if you have permission to access the files.

Session Management: Webpage contain text, images. These files are stored   separately on the web server. When you request for a website in a web browser.  Web browser opens a separate session to the web server to Download text and image files separately. These files received as data packets.  Session Layer  keeps a track of which data packet belong to which file ie  either text or image file and tracks where the received data  packet goes. This is called Session Management .

Layer 4 – Transport Layer 

Transport layer (also called end-to-end layer) manages end to end (source to destination) (process to process) message delivery in a network and also provides the error checking and hence guarantees that no duplication or errors are occurring in the data transfers across the network. It makes sure that all the packets of a message arrive intact and in order.

Three main Functions of Transport Layer:  Segmentation, Flow Control and Error Control

Segmentation:

Data is divided into small  data units called segments.

·         Each data unit contain source and destination port number and sequence number

·         Port number helps to direct each segment to the correct application

·         Sequence number  helps to reassemble the segments to form correct message

Flow Control: Transport layer makes sure that the sender and receiver communicate at a rate they both can handle. Therefore flow control prevents the source from sending data packets faster than the destination can handle. Here, flow control is performed end-to-end rather than across a link.

Error control: Transport layer also performs error control. Here error control is performed end-to-end rather than across a single link. The sending transport layer ensures that the entire message arrives at the receiving transport layer without error (damage, loss or duplication). Error correction is achieved through retransmission.

Protocols: These protocols work on the transport layer TCP, SPX, NETBIOS, ATP and NWLINK.

Transport layer provides two types of services:

 Connection Oriented Transmission(uses TCP Protocol)

(a) In this type of transmission the receiving device sends an acknowledgment, back to the source after a packet or group of packet is received.

(b) This type of transmission is also known as reliable transport method.

(c) Because connection oriented transmission requires more packets be sent across network, it is considered a slower transmission method.

(d) If the data that is sent has problems, the destination requests the source for retransmission by acknowledging only packets that have been received and are recognizable.

(e) Once the destination computer receives all of the data necessary to reassemble the packet, the transport layer assembles the data in the correct sequence and then passes it up, to the session layer.

Connectionless Transmission (uses UDP protocol)

(a) In this type of transmission the receiver does not acknowledge receipt of a packet.

(b) Sending device assumes that packet arrive just fine.

(c) This approach allows for much faster communication between devices.

(d) The trade-off is that connectionless transmission is less reliable than connection oriented.

Layer 3 – Network Layer 

Transport layer passes the data segments to network layer. Network layer works for the transmission of received data segment from one network to another network.Data units in Network layer are called packets .It is a layer where router resides. The function of Network Layer : Logical Addressing, Routing, Path Determination

Logical Addressing: IP addressing is done in Network Layer  called logical addressing

Every computer in a network has unique IP address.  Network Layer  assigns sender and receiver IP address to each segment to form a IP Packet

Routing: is method to route data packet from source to destination. It is based on logical address [IP + Mask].

Eg: Computer A is connected to network:1 and Computer B is connected to network:2 and from computer B there is a request to access facebook. Now face book server replies to computer B in a form of packet. This packet is to be delivered to computer B only. Since in a network each device has unique IP address. Network layer of Facebook server will add the source and destination IP address in the data packet. Suppose mask used is 255.255.255.0. This mask tells first three combinations represent the network and last one represent the host computer B.  Based on the IP address and Mask , routing decisions are made in computer network.

Path Determination: Computer can be connected to internet server or other computer in number of ways. Choosing the best possible path for data delivery from source to destination is called path determination

OSPF-Open shortest path first

BGP- Border Gateway protocol

ISIS- Intermediate system to Intermediate system

These protocols determine best possible  path for data packet delivery

Layer 2 - Data Link layer 

It is responsible for reliable node-to-node delivery of data. It receives the data from network layer and creates frames, add physical address to these frames and pass them to physical layer.

There are two types of addressing: 1.Logical Addressing (Done by Network Addressing) 2.Physical Addressing (Done by Data Link layer). MAC Address is a 12 digit alphanumeric number embedded in a  network interface card (NIC)of your computer. Data link layer is embedded as a software in NIC

Data link layer adds the header( i.e. Source and Destination physical address(MACAddress) and tail (Error control information) to the data packet to form a frame

Functions of Data Link Layer:             

Link Establishment and Termination: Establishes and terminates the logical link between two nodes.

Physical addressing: After creating frames, Data link layer adds physical addresses (MAC address) of sender and/or receiver in the header of each frame.

Frame Traffic Control: Tells the transmitting node to "back-off algorithm" when no frame buffers are available.

Frame Sequencing: Transmits/receives frames sequentially.

Frame Acknowledgment: Provides/expects frame acknowledgments. Detects and recovers from errors that occur in the physical layer by retransmitting non-acknowledged frames and handling duplicate frame receipt.

Frame Delimiting: Creates and recognizes frame boundaries.

Frame Error Checking: Checks received frames for integrity.

Media Access Management: determines when the node "has the right" to use the physical medium.

Flow control: It is the traffic regulatory mechanism implemented by Data Link layer that prevents the fast sender from drowning the slow receiver. If the rate at which data is absorbed by receiver is less that the rate produced in the sender, the data link layer imposes this flow control mechanism.

Error control: Data link layer provides the mechanism of error control in which it detects and retransmits damaged· or lost frames. It also deals with the problem of duplicate frame, thus providing reliability to physical layer.

Access control: When a single communication channel is shared by multiple devices, MAC sub-layer of data link layer helps to determine which device has control over the channel at a given time.

Feedback: After transmitting the frames, the system waits for the feedback. The receiving device then sends the acknowledgement frames back to the source providing the receipt of the frames.

Layer 1 – Physical Layer

The physical layer, the lowest layer of the OSI model, is concerned with the transmission and reception of the unstructured raw bit stream over a physical medium. It describes the electrical/optical, mechanical, and functional interfaces to the physical medium, and carries the signals for all of the higher layers. Physical layer defines the cables, network cards and physical aspects.

It is responsible for the actual physical connection between the devices. Such physical connection may be made by using twisted pair cable, fiber-optic, coaxial cable or wireless communication media. This layer gets the frames sent by the Data Link layer and converts them into signals compatible with the transmission media. If a metallic cable is used, then it will convert data into electrical signals; if a fiber optical cable is used, then it will convert data into luminous signals; if a wireless network is used, then it will convert data into electromagnetic signals; and so on.

OSI Model- Power Point Presentation