Advantages we gain by using the OSI layered model
� The OSI model divides network communication processes into smaller and simpler components, thus aiding component development, design, and troubleshooting.
� It allows multiple-vendor development through the standardization of network components.
� It en
The OSI Reference Model
One of the greatest functions of the OSI specifications is to assist in data transfer between disparate hosts regardless if they're Unix-Windows-or Mac-based.
But keep in mind that the OSI model isn't a physical model; it's a conceptual and comprehensive
The OSI model has seven layers:
Application (Layer 7)
Presentation (Layer 6)
Session (Layer 5)
Transport (Layer 4)
Network (Layer 3)
Data Link (Layer 2)
Physical (Layer 1)
(Please Do Not Throw Sausage Pizza Away)
(All People Seem to Need Data Processing )
The OSI's seven layers are divided into two groups
The top three layers define the rules of how the applications working within host machines communicate with each other as well as with end users.
The bottom four layers define how the actual data is transmitted from end to end.
The Application Layer
The Application layer of the OSI model marks the spot where users actually communicate or interact with the computer. Technically, users communicate with the network stack through application processes, interfaces, or APIs that connect the application in
The Presentation Layer
It presents data to the Application layer and is responsible for data translation and code formatting.
A successful data-transfer technique is to adapt the data into a standard format before transmission. Computers are configured to receive this generical
The Session Layer
The Session layer is responsible for setting up, managing, and then tearing down sessions between Presentation layer entities. This layer also provides dialog control between devices, or nodes. It coordinates communication between systems and serves to or
The Transport Layer
The Transport layer segments and reassembles data into a data stream. Services located in the Transport layer handle data from upper-layer applications and unite it onto the same data stream. They provide end-to-end data transport services and can establi
Connection-Oriented Communication protocol of the Transport Layer
Before a transmitting host starts to send segments down the model, the sender's TCP process contacts the destination's TCP process to establish a connection. The resulting creation is known as a virtual circuit. This type of communication is called connec
Steps in the Connection-Oriented session or "The Three-Way Handshake" of the Transport Layer
1. The first "connection agreement" segment is a request for synchronization. (SYN)
2. The next segments acknowledge the request and establishes connection parameters�the rules�between hosts. These segments request that the receiver's sequencing is synchr
The Network Layer
The Network layer manages logical device addressing, tracks the location of devices on the network, and determines the best way to move data. This means that the Network layer must transport traffic between devices that aren't locally attached. Routers ar
Two types of packets are used at the Network layer:
Data Packets: These are used to transport user data through the internetwork. Protocols used to support data traffic are called routed protocols. Two examples of routed protocols are Internet Protocol (IP) and Internet Protocol version 6 (IPv6).
Route-Upd
Here are some key points about routers that you really should commit to memory:
� Routers, by default, won't forward any broadcast or multicast packets.
� Routers use the logical address in a Network layer header to determine the next-hop router to forward the packet to.
� Routers can use access lists, created by an administrator, to
The Data Link Layer
The Data Link layer provides the physical transmission of the data and handles error notification, network topology, and flow control. This means the Data Link layer ensures that messages are delivered to the proper device on a LAN using hardware (MAC) ad
The IEEE (Institute of Electrical and Electronics Engineers) Ethernet Data Link layer has two sublayers:
Media Access Control (MAC): Defines how packets are placed on the media. Contention media access is "first come, first served" access, where everyone shares the same bandwidth�hence the name. Physical addressing is defined here, as are logical topologies.
One of the major components of the Data Link layer is the result of the IEEE's 802 subcommittees and their work on standards for local area and metropolitan area networks (LANs/MANs). The committee met in February 1980, so they used the 80 from 1980 and t
802.1 LAN/MAN Management (and Media Access Control Bridges)
802.2 Logical Link Control
802.3 CSMA/CD (Ethernet)
802.4 Token Passing Bus
802.5 Token Passing Ring
802.6 Distributed Queue Dual Bus (DQDB) Metropolitan Area Network (MAN)
802.7 Broadband Local
The Physical Layer
The Physical layer does two important things: it sends bits and receives bits. Bits come only in values of 1 or 0. The Physical layer communicates directly with the various types of actual communication media.
This layer is also where you identify the int
What Network devices operate at all seven layers of the OSI model?
Network management stations (NMSs)
Web and application servers
Gateways (not default gateways)
Network hosts
The following four devices are the most popular at the Physical layer of the OSI model
Network Interface Cards (NICs)
Transceivers
Repeaters
Hubs
Seven layers of the OSI model and their functions:
Application: File, Print, Message, database and application services
Presentation: Data encryption, compression, and translation services
Session: Dialog control
Transport: End-to-end connection
Network: Routing
Data Link: Framing
Physical: Physical Topol
The OSI's seven layers are divided into two groups.
The top three layers define the rules of how the applications working within host machines communicate with each other as well as with end users: Application, Presentation, Session
The bottom four layers define how the actual data is transmitted from end
Function of the three top layers of the OSI
Application: Provides a user interface
Presentation: Presents data - Handles processing such as encryption
Session: Keeps different applications' data separate
Function of the four bottom layers of the OSI
Transport: Provides reliable or unreliable delivery - Performs error correction before re-transmit
Network: Provides logical addressing, which routers use for path determination
Data Link: Combines packets into bytes and bytes into frames - Provides acces
The OSI reference model has seven distinct layers. Each layer performs functions that help applications to run on a network. Identify the layer responsible for end-to-end connection by clicking it.
Transport
Drag the IEEE 802 standards to match them with their areas.
802.2 Logical Link Control
802.4 Token Passing Bus
802.5 Token Passing Ring
802.11 Wireless LAN
802.3 CSMA/CD
Your company's network is facing a continuous problem of busy network during peak working hours. To resolve this issue, you decide to break the company's busy network into segments. Drag the interconnectivity device that you will use from the bottom onto
In this scenario, you will use a bridge to resolve the problem of busy network during peak working hours.
A bridge is a device used to divide a busy network into segments and reduce network traffic. It is an interconnectivity device that is used to connec
Data Link layer
The second layer of the OSI model. It describes the logical topology of a network, which is the way that packets move throughout a network. It also describes the method of media access. See also Open Systems Interconnect (OSI).
Data packet
A unit of data sent over a network. A packet includes a header, addressing information, and the data itself. A packet is treated as a single unit as it is sent from device to device. Also known as a datagram.
Data frame
A frame is the Protocol Data Unit encapsulation at the Data Link layer of the OSI reference model. A data frame encapsulates packets from the Network layer and prepares the data for transmission on a network medium.
What is Encapsulation?
The technique used by layered protocols in which a layer adds header information to the Protocol Data Unit (PDU) from the layer above. As an example, in Internet terminology, a packet contains a header from the Data Link layer, followed by a header from t
Introduction to Encapsulation
When a host transmits data across a network to another device, the data goes through encapsulation: It's wrapped with protocol information at each layer of the OSI model. Each layer communicates only with its peer layer on the receiving device.
Protocol Data Units (PDUs)
To communicate and exchange information, each layer uses Protocol Data Units (PDUs). These hold the control information attached to the data at each layer of the model. They're usually attached to the header in front of the data field but can also be in t
At a transmitting device, the data-encapsulation method works like this:
1. User information is converted to data for transmission on the network.
2. Data is converted to segments, and a reliable connection is set up between the transmitting and receiving hosts.
3. Segments are converted to packets or datagrams, and a logical
Modulation Techniques
Modulation is the process of varying one or more properties of a waveform, called the carrier signal, with a signal that typically contains information to be transmitted.
Modulation of a waveform transforms a baseband (Ethernet or wireless) message signal
What is a modem?
A modulator is a device that performs modulation of a signal and a demodulator is a device that performs demodulation, the inverse of modulation. We typically just call these modems (from modulator-demodulator), which can perform both operations.
What's the purpose of digital modulation?
The purpose of digital modulation is to transfer a digital bit stream over an analog bandpass channel. (A good example would be data transmitting over the public switched telephone network, where a bandpass filter limits the frequency range to 300-3400 Hz
What is frequency-division multiplexing (FDM)?
Analog and digital modulation use something called frequency-division multiplexing (FDM), where several low-pass information signals are transferred simultaneously over the same shared physical network, using separate passband channels (several different
What is Time-division multiplexing (TDM)?
Time-division multiplexing (TDM) is a method of transmitting and receiving many independent signals over a common signal path by means of synchronized network devices at each end of the transmission line so that each signal appears on the line only a frac
What is full duplex and half duplex?
Full duplex: The capacity to transmit information between a sending station and a receiving unit at the same time.
Half duplex: The capacity to transfer data in only one direction at a time between a sending unit and receiving unit.
Hardware address
A Data Link layer address assigned to every NIC at the MAC sublayer. The address is in the format xx:xx:xx:xx:xx:xx. Each xx is a two-digit hexadecimal number.
Institute of Electrical and Electronics Engineers (IEEE)
An international organization that sets standards for various electrical and electronics issues.
International Organization for Standardization (ISO)
The standards organization that developed the OSI model. This model provides a guideline for how communications occur between computers.
Internet Architecture Board (IAB)
The committee that oversees management of the Internet. It is made up of two subcommittees: the Internet Engineering Task Force (IETF) and the Internet Research Task Force (IRTF).
Internet Research Task Force (IRTF)
An international organization that works under the Internet Architecture Board to research new Internet technologies.
Local Area Network (LAN)
A network that is restricted to a single building, a group of buildings, or even a single room. A LAN can have one or more servers. LANs are defined by the Data Link protocols they run. For example, Ethernet networks are LANs, but PPP networks are not. Th
Logical address
A Network layer address that defines how data is sent from one network to another. Examples of logical addresses are IP and IPv6.
Logical Link Control (LLC)
A sublayer of the Data Link layer that provides an interface between the MAC sublayer and the Network layer.
Media Access Control (MAC)
A sublayer of the Data Link layer that controls the way multiple devices use the same media channel. It controls which devices can transmit and when they can transmit.
Open Systems Interconnect (OSI)
A model defined by the ISO ( International Organization for Standardization) to categorize the process of communication between computers in terms of seven layers. The seven layers are Application, Presentation, Session, Transport, Network, Data Link, and
Packet
The basic division of data sent over a network.
Routed protocol
A protocol (such as IP or IPv6) used to transmit user data through an internetwork. By contrast, routing protocols (such as RIP, IGRP, and OSPF) are used to update routing tables between routers.
Session layer
The fifth layer of the OSI model, which determines how two computers establish, use, and end a session. Security authentication and network-naming functions required for applications occur here. The Session layer establishes, maintains, and breaks dialogs
Remember the OSI layers
The Application, Presentation, and Session layers are upper layers and are responsible for communicating from a user interface to an application.
The Transport layer provides segmentation, sequencing, and virtual circuits.
The Network layer provides logic
Know the sublayers of the Data Link layer.
The Data Link layer has two sublayers: LLC and MAC.
The LLC sublayer is responsible primarily for the multiplexing of Network layer protocols.
The MAC sublayer is responsible for physical addressing and determining the appropriate time to place data on th
Know the devices that operate at each layer of the OSI model
Hubs and repeaters see only bits, making them Layer 1 devices. Because all networking devices have physical connectivity to the network, they all operate at Layer 1, but hubs and repeaters operate only at this layer, whereas other devices work in higher l
Which layer chooses and determines the availability of communicating partners along with the resources necessary to make the connection, coordinates partnering applications, and forms a consensus on procedures for controlling data integrity and error reco
Application layer is responsible for finding the network resources broadcast from a server and adding flow control and error control (if the application developer chooses).
Which layer is responsible for converting frames from the Data Link layer into electrical signals?
The Physical layer takes frames from the Data Link layer and encodes the 1s and 0s into a digital signal for transmission on the network medium.
At which layer is routing implemented, enabling connections and path selection between two end systems?
The Network layer provides routing through an internetwork and logical addressing.
Which layer defines how data is formatted, presented, encoded, and converted?
The Presentation layer makes sure that data is in a readable format for the Application layer.
Which layer is responsible for creating, managing, and terminating sessions between applications?
The Session layer sets up, maintains, and terminates sessions between applications.
Which layer manages the transmission of data across a physical link and is primarily concerned with physical addressing and the ordered delivery of frames?
Protocol Data Units (PDUs) at the Data Link layer are called frames. As soon as you see the word frame in a question, you know the answer.
Which layer is used for reliable communication between end nodes over the network and provides mechanisms for establishing, maintaining, and terminating virtual circuits as well as controlling the flow of information?
The Transport layer uses virtual circuits to create a reliable connection between two hosts.
Which layer provides logical addressing that routers use for path determination?
The Network layer provides logical addressing, typically IP addressing, and routing.
Which layer specifies voltage, wire speed, and connector pin-outs and moves bits between devices?
The Physical layer is responsible for the electrical and mechanical connections between devices.
Which layer combines bits into bytes and bytes into frames and uses MAC addressing?
The Data Link layer is responsible for the framing of data packets.
Which of the following OSI model layers identifies the topology used in a network?
Physical
At which of the following OSI layers does the hub operate?
Physical
Which of the following layers synchronizes data exchange between applications on separate devices?
Session
Which of the following layers provides mechanisms to transport data between network devices through error checking, service addressing, and segmentation?
Transport
Which of the following devices operates at the network layer of the OSI model?
Router
At which of the following layers does a bridge handle frames?
Data link
Which of the following organizations is responsible for developing network standards?
IEEE
Host 1 sent a SYN packet to Host 2. What will Host 2 send in response?
SYN/ACK
A connection-oriented session is set up using what is called a three-way handshake. The transmitting host sends a SYN packet, the receiving host sends a SYN/ACK, and the transmitting host replies with the last ACK packet. The session is now set up
TCP and UDP reside at which layer of the OSI model?
4
TCP and UDP are Transport layer protocols. The Transport layer is Layer 4 of the OSI model.
Which layer of the OSI model provides a user interface in the form of an entry point for programs to access the network infrastructure?
Application
The top layer of the OSI model gives applications access to the services that allow network access.
You are connected to a server on the Internet and you click a link on the server and receive a time-out message. What layer could be the source of this message?
Application
If the remote server is busy or does not respond to your web browser request, this is an Application layer problem.
Which layer of the OSI model is responsible for code and character-set conversion as well as recognizing data formats?
Presentation
The Presentation layer makes data "presentable" for the Application layer.
At which layers of the OSI model do bridges, hubs, and routers primarily operate, respectively?
Data Link, Physical, Network
Bridges, like switches, are Data Link layer devices. Hubs, like repeaters, are Physical layer devices. Routers are Network layer devices.
Which layer of the OSI model is responsible for converting data into signals appropriate for the transmission medium?
Physical
The Physical layer's job is to convert data into impulses that are designed for the wired or wireless medium being used on the attached segment.
A receiving host has failed to receive all the segments that it should acknowledge. What can the host do to improve the reliability of this communication session?
Decrease the window size.
A receiving host can control the transmitter by using flow control (TCP uses windowing by default). By decreasing the window size, the receiving host can slow down the transmitting host so the receiving host does not overflow its
Which Layer 1 devices can be used to enlarge the area covered by a single LAN segment? (Choose two.)
Hub
Repeater
Segmentation of a data stream happens at which layer of the OSI model?
Transport
When data is encapsulated, which is the correct order?
Data, segment, packet, frame, bits
What are two purposes for segmentation with a bridge? (Choose two.)
To create more collision domains
To add more bandwidth for users
Acknowledgments, sequencing, and flow control are characteristic of which OSI layer?
Layer 4
A reliable Transport layer connection uses acknowledgments to make sure all data is received reliably. A reliable connection is defined by the use of acknowledgments, sequencing, and flow control, which is characteristic of the Transport layer (La
Which of the following is true regarding sequencing and acknowledgments? (Choose all that apply.)
The segments delivered are acknowledged back to the sender upon their reception.
Any segments not acknowledged are retransmitted.
Segments are sequenced back into their proper order upon arrival at their destination.
What is the purpose of flow control?
To provide a means for the receiver to govern the amount of data sent by the sender
At which layer of the OSI model would you find IP?
Network
IP is a Network layer protocol. TCP is an example of a Transport layer protocol, Ethernet is an example of a Data Link layer protocol, and T1 can be considered a Physical layer protocol.
Of the following, which is the highest layer in the OSI model?
Presentation
Routers perform routing at which OSI layer?
Network
Which of the following mnemonic devices can you use to remember the first letter of the name of each layer of the OSI model in the proper order?
Please Do Not Throw Sausage Pizza Away.
Which IEEE standard specifies the protocol for CSMA/CD?
802.3
The 802.3 standard, commonly associated with Ethernet, specifies the media-access method used by Ethernet, which is known as Carrier Sense Multiple Access with Collision Detection (CSMA/CD).
Here are the features of the OSI model layers:
Physical Layer:
Synchronizing bits
How bits are represented on the medium
Wiring standards for connectors and jacks
Physical topology
Bandwidth usage
Multiplexing strategy
Data Link Layer:
Synchronizing transmissions
Physical addressing
Logical topology
M
The OSI layers are described below:
� Physical: Transmits bits from one computer to another and regulates the transmission stream over a medium
� Datalink: Packages bits of data from the physical layer into frames, transfers them from one computer to another, and receives acknowledgement fr
Drag the OSI model layers to match them with their features.
1. Data Link ==> Synchronizing transmissions
2. Network ==> Logical addressing
3. Session ==> Tearing down a session
4. Application ==> Service advertisement
5. Physical ==> Synchronizing bits
6. Presentation ==> Encryption
7. Transport ==> Windowing
In the figure, drag the functions of the OSI layer model from the right onto their respective layers.
Application Layer: Talks to application software
Presentation Layer: Reformats, encrypts/decodes, compresses/decompresses
Session Layer: Makes connection at both ends
Transport Layer: Disassembles and reassembles segments
Network Layer: Finds best possibl
In the figure, mark the layer of the OSI model which is responsible for connectionless communication, addressing and routing data, and message forwarding by clicking on it.
The Network layer is responsible for connectionless communication, addressing and routing data, and message forwarding
Drag the OSI layers to match them with their descriptions.
1. Datalink ==> Packages bits of data from the physical layer into frames, transfers them from one computer to another, and receives acknowledgement from the addressed computer
2. Application ==> Allows programs on a network node (computer) to access netw
At which of the following layers of the OSI model does a bridge operate?
Data link
On which OSI layer does the UDP protocol work?
Transport
Which of the following specifications of IEEE (Institute of Electrical and Electronic Engineers) defines the standard for fiber-optic cables?
802.8 Fiber-Optic LANs and MANs
Which of the following layers of the OSI model is responsible for establishing a communication session between the processes running on different communication entities in a network?
Layer 5 (session layer)
Which of the following devices work at the data link layer of the OSI reference model?
Switches
Bridges
What is the function of TDM (time-division multiplexing)?
Transmits and receives independent signals over a common signal path by means of synchronized network devices
Which of the following are functions of the presentation layer of the OSI model?
Data encryption
Character-code translation
Data compression
Which OSI layer is responsible for packet forwarding?
Network layer
At which layer of OSI is the Frame Check Sequence for error detection performed?
Layer 2
Layer 2 of the OSI model is the ____.
Data Link layer
Which of the following units of data does the data-link layer send from the network layer to the physical layer of the OSI model?
Data frames
Which of the following provides protection against network eavesdropping and signal interference and works at the physical layer?
Shielded twisted pair (STP)
HTTP, FTP, and Telnet work at which layer of the OSI model?
Application
HTTP, FTP and Telnet use TCP at the Transport layer; however, they are all Application?layer protocols, so the Application layer is the best answer for this question.