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PC 106 PPT-06

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MLG College of Learning, Inc

The document discusses the OSI model, which defines 7 layers for network communication: Physical, Data Link, Network, Transport, Session, Presentation, and Application. It was developed by ISO to standardize network architectures and allow components from different vendors to communicate. Each layer has a set of well-defined functions and builds upon the layers below it, with standards developed independently for easier introduction and less effect of changes on other layers. This model divides network communication into simpler components and encourages standardization.

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OSI Model
Need for standards ï‚— Over the past couple of decades many of the networks that were built used different hardware and software implementations, as a result they were incompatible and it became difficult for networks using different specifications to communicate with each other. ï‚— To address the problem of networks being incompatible and unable to communicate with each other, the International Organization for Standardization (ISO) researched various network schemes.
International Organization for Standardization ï‚— The International Organization for Standardization (ISO) is an International standards organization responsible for a wide range of standards, including many that are relevant to networking. ï‚— In 1984 in order to aid network interconnection without necessarily requiring complete redesign, the Open Systems Interconnection (OSI) reference model was approved as an international standard for communications architecture.
Standardization within the OSI framework  The model defines in general terms the functions to be performed at that layer and facilitates the standards-making process in two ways: Because the functions of each layer are well defined, standards can be developed independently and simultaneously for each layer. This speeds up the standards-making process. Because the boundaries between layers are well defined, changes in standards in one layer need not affect already existing software in another layer. This makes it easier to introduce new standards.
Advantages of Layered model ï‚— It divides the network communication process into smaller and simpler components, thus aiding component development, design and troubleshooting. ï‚— It allows multiple-vendor development through standardization of network components. ï‚— It encourages Industry standardization by defining what functions occur at each layer of the model. ï‚— It allows various types of network hardware and software to communicate. ï‚— It prevents changes in one layer from affecting other layers, so it does not hamper development.
OSI model Layers
LAYER 7 – The APPLICATION Layer • The top layer of the OSI model • Provides a set of interfaces for sending and receiving applications to gain access to and use network services, such as: networked file transfer, message handling and database query processing • Provides a variety of functions: Identifies communication partners Determines resource availability Synchronizes communication • Protocols include:- FTP, HTTP, POP3, Telnet etc
LAYER 6 – The PRESENTATION Layer • The presentation layer is concerned with the syntax and semantics of the information exchanged between two systems. • Functions include:  Translation: - The processes (running programs) in two systems are usually exchanging information in the form of character strings, numbers, and so on. The information must be changed to bit streams before being transmitted.  Encryption: - To carry sensitive information, a system must be able to ensure privacy. Encryption means that the sender transforms the original information to another form and sends the resulting message out over the network.  Compression: - Data compression reduces the number of bits contained in the information. Data compression becomes particularly important in the transmission of multimedia such as text, audio, and video.  Examples of Presentation layer protocols: SSL, MIME  Example of presentation layer formats are:  Text - RTF, ASCII, EBCDIC  Images - GIF, JPG, TIF  Audio - MIDI, MP3, WAV  Movies - MPEG, AVI, MOV
LAYER 5 – The SESSION Layer • The session layer establishes, maintains, and synchronizes the interaction among communicating systems. • Functions include: Dialog control: - The session layer allows two systems to enter into a dialog. It allows the communication between two processes to take place in either half-duplex (one way at a time) or full-duplex (two ways at a time) mode.  Synchronization: - The session layer allows a process to add checkpoints, or synchronization points, to a stream of data. • Example protocols: - NetBIOS, SOCKS
LAYER 4 – The TRANSPORT Layer • The transport layer is responsible for process-to-process delivery of the entire message. • Functions include:  The transport layer is responsible for the delivery of a message from one process to another.  Service-point addressing: - Computers often run several programs at the same time. For this reason, source-to-destination delivery means delivery not only from one computer to the next but also from a specific process (running program) on one computer to a specific process (running program) on the other.  Segmentation and reassembly: - A message is divided into transmittable segments, with each segment containing a sequence number.  Connection control: - The transport layer can be either connectionless or connection-oriented.  Flow control: - Like the data link layer, the transport layer is responsible for flow control. However, flow control at this layer is performed end to end rather than across a single link.  Error control: - Like the data link layer, the transport layer is responsible for error control. However, error control at this layer is performed process-to- process rather than across a single link.  Layer 4 protocols include:
LAYER 3 – The NETWORK Layer  The network layer is responsible for the source-to-destination delivery of a packet, possibly across multiple networks (links). • Functions include:  The network layer is responsible for the delivery of individual packets from the source host to the destination host.  Logical addressing: - The physical addressing implemented by the data link layer handles the addressing problem locally. If a packet passes the network boundary, we need another addressing system to help distinguish the source and destination systems.  Routing: - When independent networks or links are connected to create intemetworks (network of networks) or a large network, the connecting devices (called routers or switches) route or switch the packets to their final destination.  The most common Network layer protocols are:  Internet Protocol (IP)  Internetwork Packet Exchange (IPX)  AppleTalk
LAYER 2 – The DATA LINK Layer • The data link layer transforms the physical layer, a raw transmission facility, to a reliable link. • Functions include:  The data link layer is responsible for moving frames from one hop (node) to the next.  Framing: - The data link layer divides the stream of bits received from the network layer into manageable data units called frames.  Physical addressing: - If frames are to be distributed to different systems on the network, the data link layer adds a header to the frame to define the sender and/or receiver of the frame.  Flow control: - If the rate at which the data are absorbed by the receiver is less than the rate at which data are produced in the sender, the data link layer imposes a flow control mechanism to avoid overwhelming the receiver.  Error control: - The data link layer adds reliability to the physical layer by adding mechanisms to detect and retransmit damaged or lost frames.  Access control: - When two or more devices are connected to the same link, data link layer protocols are necessary to determine which device has control over the link at any given time. • Datalink protocols:- ATM, Frame Relay, X.25, IEEE 802.3
LAYER 1 – The PHYSICAL Layer • The physical layer coordinates the functions required to carry a bit stream over a physical medium. • Functions include:  The physical layer is responsible for movements of individual bits from one hop (node) to the next.  Physical characteristics of interfaces and medium: - The physical layer defines the characteristics of the interface between the devices and the transmission medium.  Representation of bits: - The physical layer data consists of a stream of bits (sequence of Os or 1s) with no interpretation. To be transmitted, bits must be encoded into signals--electrical or optical.  Data rate: - The transmission rate-the number of bits sent each second-is also defined by the physical layer.  Synchronization of bits: - The sender and receiver not only must use the same bit rate but also must be synchronized at the bit level.  Line configuration: - The physical layer is concerned with the connection of devices to the media.  Physical topology: - The physical topology defines how devices are connected to make a network.  Transmission mode: - The physical layer also defines the direction of transmission between two devices: simplex, half-duplex, or full-duplex. • Example protocols: - EIA/TIA-232, IEEE 802.3, RS-232, USB, Bluetooth.
Remember ï‚— A convenient aid for remembering the OSI layer names is to use the first letter of each word in the phrase: ï‚— All People Seem To Need Data Processing ï‚— Please Do Not Throw Sausage Pizza Away
PC 106 PPT-06

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PC 106 PPT-06

  • 2. Need for standards ï‚— Over the past couple of decades many of the networks that were built used different hardware and software implementations, as a result they were incompatible and it became difficult for networks using different specifications to communicate with each other. ï‚— To address the problem of networks being incompatible and unable to communicate with each other, the International Organization for Standardization (ISO) researched various network schemes.
  • 3. International Organization for Standardization ï‚— The International Organization for Standardization (ISO) is an International standards organization responsible for a wide range of standards, including many that are relevant to networking. ï‚— In 1984 in order to aid network interconnection without necessarily requiring complete redesign, the Open Systems Interconnection (OSI) reference model was approved as an international standard for communications architecture.
  • 4. Standardization within the OSI framework ï‚— The model defines in general terms the functions to be performed at that layer and facilitates the standards-making process in two ways: Because the functions of each layer are well defined, standards can be developed independently and simultaneously for each layer. This speeds up the standards-making process. Because the boundaries between layers are well defined, changes in standards in one layer need not affect already existing software in another layer. This makes it easier to introduce new standards.
  • 5. Advantages of Layered model ï‚— It divides the network communication process into smaller and simpler components, thus aiding component development, design and troubleshooting. ï‚— It allows multiple-vendor development through standardization of network components. ï‚— It encourages Industry standardization by defining what functions occur at each layer of the model. ï‚— It allows various types of network hardware and software to communicate. ï‚— It prevents changes in one layer from affecting other layers, so it does not hamper development.
  • 7. LAYER 7 – The APPLICATION Layer • The top layer of the OSI model • Provides a set of interfaces for sending and receiving applications to gain access to and use network services, such as: networked file transfer, message handling and database query processing • Provides a variety of functions: Identifies communication partners Determines resource availability Synchronizes communication • Protocols include:- FTP, HTTP, POP3, Telnet etc
  • 8. LAYER 6 – The PRESENTATION Layer • The presentation layer is concerned with the syntax and semantics of the information exchanged between two systems. • Functions include:  Translation: - The processes (running programs) in two systems are usually exchanging information in the form of character strings, numbers, and so on. The information must be changed to bit streams before being transmitted.  Encryption: - To carry sensitive information, a system must be able to ensure privacy. Encryption means that the sender transforms the original information to another form and sends the resulting message out over the network.  Compression: - Data compression reduces the number of bits contained in the information. Data compression becomes particularly important in the transmission of multimedia such as text, audio, and video. ï‚— Examples of Presentation layer protocols: SSL, MIME ï‚— Example of presentation layer formats are:  Text - RTF, ASCII, EBCDIC  Images - GIF, JPG, TIF  Audio - MIDI, MP3, WAV  Movies - MPEG, AVI, MOV
  • 9. LAYER 5 – The SESSION Layer • The session layer establishes, maintains, and synchronizes the interaction among communicating systems. • Functions include: Dialog control: - The session layer allows two systems to enter into a dialog. It allows the communication between two processes to take place in either half-duplex (one way at a time) or full-duplex (two ways at a time) mode.  Synchronization: - The session layer allows a process to add checkpoints, or synchronization points, to a stream of data. • Example protocols: - NetBIOS, SOCKS
  • 10. LAYER 4 – The TRANSPORT Layer • The transport layer is responsible for process-to-process delivery of the entire message. • Functions include: ï‚— The transport layer is responsible for the delivery of a message from one process to another.  Service-point addressing: - Computers often run several programs at the same time. For this reason, source-to-destination delivery means delivery not only from one computer to the next but also from a specific process (running program) on one computer to a specific process (running program) on the other.  Segmentation and reassembly: - A message is divided into transmittable segments, with each segment containing a sequence number.  Connection control: - The transport layer can be either connectionless or connection-oriented.  Flow control: - Like the data link layer, the transport layer is responsible for flow control. However, flow control at this layer is performed end to end rather than across a single link.  Error control: - Like the data link layer, the transport layer is responsible for error control. However, error control at this layer is performed process-to- process rather than across a single link. ï‚— Layer 4 protocols include:
  • 11. LAYER 3 – The NETWORK Layer ï‚— The network layer is responsible for the source-to-destination delivery of a packet, possibly across multiple networks (links). • Functions include:  The network layer is responsible for the delivery of individual packets from the source host to the destination host.  Logical addressing: - The physical addressing implemented by the data link layer handles the addressing problem locally. If a packet passes the network boundary, we need another addressing system to help distinguish the source and destination systems.  Routing: - When independent networks or links are connected to create intemetworks (network of networks) or a large network, the connecting devices (called routers or switches) route or switch the packets to their final destination. ï‚— The most common Network layer protocols are:  Internet Protocol (IP)  Internetwork Packet Exchange (IPX)  AppleTalk
  • 12. LAYER 2 – The DATA LINK Layer • The data link layer transforms the physical layer, a raw transmission facility, to a reliable link. • Functions include:  The data link layer is responsible for moving frames from one hop (node) to the next.  Framing: - The data link layer divides the stream of bits received from the network layer into manageable data units called frames.  Physical addressing: - If frames are to be distributed to different systems on the network, the data link layer adds a header to the frame to define the sender and/or receiver of the frame.  Flow control: - If the rate at which the data are absorbed by the receiver is less than the rate at which data are produced in the sender, the data link layer imposes a flow control mechanism to avoid overwhelming the receiver.  Error control: - The data link layer adds reliability to the physical layer by adding mechanisms to detect and retransmit damaged or lost frames.  Access control: - When two or more devices are connected to the same link, data link layer protocols are necessary to determine which device has control over the link at any given time. • Datalink protocols:- ATM, Frame Relay, X.25, IEEE 802.3
  • 13. LAYER 1 – The PHYSICAL Layer • The physical layer coordinates the functions required to carry a bit stream over a physical medium. • Functions include:  The physical layer is responsible for movements of individual bits from one hop (node) to the next.  Physical characteristics of interfaces and medium: - The physical layer defines the characteristics of the interface between the devices and the transmission medium.  Representation of bits: - The physical layer data consists of a stream of bits (sequence of Os or 1s) with no interpretation. To be transmitted, bits must be encoded into signals--electrical or optical.  Data rate: - The transmission rate-the number of bits sent each second-is also defined by the physical layer.  Synchronization of bits: - The sender and receiver not only must use the same bit rate but also must be synchronized at the bit level.  Line configuration: - The physical layer is concerned with the connection of devices to the media.  Physical topology: - The physical topology defines how devices are connected to make a network.  Transmission mode: - The physical layer also defines the direction of transmission between two devices: simplex, half-duplex, or full-duplex. • Example protocols: - EIA/TIA-232, IEEE 802.3, RS-232, USB, Bluetooth.
  • 14. Remember ï‚— A convenient aid for remembering the OSI layer names is to use the first letter of each word in the phrase: ï‚— All People Seem To Need Data Processing ï‚— Please Do Not Throw Sausage Pizza Away