Networking Standards and the OSI Model

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Networking Standards and the OSI Model

• Ref Dean (3rd), Chapter 2

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Overview

• Standards organizations
• OSI Model and its layers
• Functions of each OSI Model layer
• How two network nodes communicate through OSI
  Model
• Data packets and frames
• Addressing covered by OSI Model

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Networking Standards Organizations

• Standards agreements containing technical
  specifications
• ANSI (American National Standards Institute)
• EIA (Electronic Industries Alliance)
• TIA (Telecommunications Industry Association)
• TIA/EIA alliance
• IEEE (Institute of Electrical and Electronics
  Engineers)
• ISO (International Organization for
  Standardization)
• ITU (International Telecommunication Union)
• ISOC (Internet Society)
• IAB (Internet Architecture Board)
• IETF (Internet Engineering Task Force)
• IANA and ICANN

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Open Systems Interconnection (OSI) Model

• OSI Model consists of seven layer that describe
  communication between two nodes
• OSI Model specifications enable computers across
  world to communicate
• Began in early 1980s by ISO

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The OSI Model Layers
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OSI Models Seven Layers

• 7 Provides network services to OS through
  network client software
• 6 Data compression, decompression encryption,
  and decryption
• 5 Connection between client and server or peer
• 4 Packet control, sequencing and error
  correction
• 3 Packet construction, transmission and
  reception
• 2 Bit stream connection protocol
• 1 Network wiring and specifications
• Ref Sheet 8 of blueprints

Ref Cisco Academy
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The OSI Model (continued)

• Application Layer
• Separates data into protocol data units (PDUs)
• Application layer PDUs progress down through OSI
  Model layers 6, 5, 4, 3, 2, and 1
• Data traverses the network until it reaches the
  second computers Physical layer
• Transfer of information happens in milliseconds

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The OSI Model (continued)
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The OSI Model (continued)

• Application Layer
• Does not include software applications, such as
  Microsoft Word or Netscape
• Services communicate between software programs
  and lower-layer network services
• File, print, message, database, and application
  services

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The OSI Model (continued)

• Application Layer
• World Wide Web (WWW)
• Email - SMTP (Simple Mail Transport Protocol or
  the X.400)

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The OSI Model (continued)

• Presentation Layer
• Protocols at the Presentation layer accept
  Application layer data and format it
• Serves as a translator and are the standards
  which are involved in multimedia
• Presentation layer protocols perform the coding,
  compression and also manage data encryption and
  decryption

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The OSI Model (continued)

• Session Layer
• Protocols in the Session layer coordinate and
  maintain communications between two nodes
• Session refers to a connection for ongoing data
  exchange between two parties

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The OSI Model (continued)

• Session Layer (continued)
• Session layers functions are establishing and
  keeping alive the communications link for the
  duration of the session
• Keep the communication secure
• Synchronizing the dialog between the two nodes
• Determining whether communications have been cut
  off, and, if so, figuring out where to restart
  transmission and terminating communications

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The OSI Model (continued)

• Transport Layer
• Protocols in the Transport layer accept data from
  the Session layer and manage end to-end delivery
• Ensures that the data is transferred from point A
  to point B reliably, in the correct sequence, and
  without errors

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The OSI Model (continued)

• Transport Layer (continued)
• Without Transport layer services, data could not
  be verified or interpreted by its recipient
• Handles flow control
• Some Transport layer protocols take steps to
  ensure that data arrives exactly as it was sent.

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The OSI Model (continued)

• Transport Layer (continued)
• Such protocols are known as connection-oriented,
• TCP is one example of a connection-oriented
  protocol
• Three Step Process
• Request (Client sends)
• Acknowledgment (ACK)
• Client Acknowledgement (ACK)

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The OSI Model (continued)

• Transport Layer (continued)
• Checksum method of error checking
• Connectionless protocols
• Process is known as segmentation
• Necessary for data units to match a networks
  maximum transmission unit (MTU)

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The OSI Model (continued)

• Transport Layer (continued)
• Reassembly
• Sequencing
• Identifying segments that belong to the same
  group

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The OSI Model (continued)

• Network Layer
• Primary function of protocols at the Network
  layer
• Translate network addresses
• Decide how to route data
• Network layer addresses
• Also called logical addresses or virtual
  addresses

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The OSI Model (continued)

• Network Layer (continued)
• Routers belong in the Network layer
• Perform Fragmentation

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The OSI Model (continued)

• Physical Layer
• Lowest, or first, layer of the OSI Model
• Protocols at the Physical layer
• Accept frames from the Data Link layer
• Generate voltage so as to transmit signals
• Receiving data detect voltage and accept signals
• Pass on to the Data Link layer

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The OSI Model (continued)

• Data Link Layer
• Primary function of protocols is to divide data
  into distinct frames that can then be transmitted
  by the Physical layer
• IEEE has divided the Data Link layer into two
  sublayers
• Logical Link Control (LLC)
• Media Access Control (MAC)

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Applying OSI Model

• Communication Between Two Systems
• At each layer of the OSI Model, some information
  is added to the original data

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Communication between Two Systems
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Data Encapsulation
Presentation
Transport
Network
Data Link
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Application Program Interface (API)

• Routine that allows a program to interact with
  the operating system
• Belongs to Application layer of OSI Model
• Microsoft Message Queueing (MSMQ)
• API used in network environment
• Stores messages sent between nodes in queues
• Forwards these messages to their destination

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Application (HTTP) Request
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Application (HTTP) Response
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Data Preparation by Presentation Layer
Figure 2-4 Data transformed through the OSI Model
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Session Layer Traffic Cop
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TCP Segment in Transport Layer
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Transport Layer Segmentation
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IP Packet in Network Layer
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Data Link Sublayers
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Generic Data Link Layer Frame

• Structured package for moving data
• Includes raw data (or payload) along with
  senders and receivers
• Network addresses
• Error-checking and control information

Figure 2-2 A simplified data frame
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A Typical Ethernet Frame

• 802.3 standard
• IEEE standard for Ethernet networking devices and
  data handling

Figure 2-5 Ethernet frame as specified by the
IEEE 802.3 standard
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Ethernet 802.3 Frame Components

• Preamble
• Marks beginning of entire frame
• Start of Frame Delimiter (SFD)
• Indicates beginning of addressing frame
• Destination Address
• Contains destination node address

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Ethernet 802.3 Frame Components

• Source Address
• Contains address of originating node
• Length (LEN)
• Indicates length of packet
• Data
• Contains data, or segmented part of data,
  transmitted from originating node

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Ethernet 802.3 Frame Components

• Pad
• Used to increase size of the frame to its minimum
  size requirement of 46 bytes
• Frame Check Sequence (FCS)
• Provides an algorithm to determine whether data
  were correctly received
• Most commonly used algorithm is Cyclic Redundancy
  Check (CRC)

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Recap of OSI Layers Functions
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Summary of Applying OSI Model
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Applying The OSI Model (continued)

• Frame Specifications
• Two major categories of frame types
• Ethernet
• developed at Xerox in the early 1970s
• Token Ring
• developed by IBM in the 1980s

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IEEE Networking Specifications

• Project 802
• Effort to standardize physical and logical
  elements of a network
• Frame types and addressing
• Connectivity,
• Networking media,
• Error checking algorithms,
• Encryption,

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IEEE Networking Specifications (continued)

• Project 802 (continued)
• Emerging technologies,
• And more
• Can be applied to the layers of the OSI Model

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IEEE Networking Specifications
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Summary

• Standards are documented agreements
• Standards organizations ANSI, EIA/TIA, IEEE,
  ISO, ITU, ISOC, IANA, and ICANN
• OSI Model
• Seven layers Physical, Data Link, Network,
  Transport, Session, Presentation, Application
• Describes communication between two nodes
• Provides framework for interoperability
• IEEE specifications provide technical details for
  networking, such as Data Link 802.2, Ethernet
  802.3, and wireless 802.11

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Chapter Summary

• Standards are documented agreements containing
  precise criteria
• Significant standards organizations
• ANSI, EIA/TIA, IEEE, ISO, ITU, ISOC, IANA, and
  ICANN

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Chapter Summary (continued)

• Excellent model for understanding communications
• Protocols in the Application layer, the seventh
  layer of the OSI Model, enable software programs
  to negotiate

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Chapter Summary (continued)

• Protocols in the Presentation layer, the sixth
  OSI Model layer, serve as translators between the
  application and the network

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Chapter Summary (continued)

• Protocols in the Session layer, the fifth OSI
  Model layer,
• coordinate and maintain links between two devices
  
• synchronize dialog
• Primary function of protocols in the Transport
  layer, the fourth OSI Model layer, is to oversee
  end-to-end data delivery

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Chapter Summary (continued)

• Protocols in the Network layer, the third OSI
  Model layer, manage logical addressing and
  determine routes

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Chapter Summary (continued)

• Network layer addresses, also called logical or
  virtual addresses, are assigned to devices
  through operating system software
• Primary function of protocols at the Data Link
  layer, the second layer of the OSI Model, is to
  organize data they receive from the Network layer
  into frames

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Chapter Summary (continued)

• Data Link layer is subdivided into the Logical
  Link Control and MAC sublayers
• LLC sublayer ensures a common interface
• MAC sublayer is responsible for adding physical
  address data to frames
• Protocols at the Physical layer generate and
  detect voltage

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Chapter Summary (continued)

• Protocols at the Physical layer generate and
  detect voltage

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Chapter Summary (continued)

• Data request from a software program is received
  by the Application layer protocols and is
  transferred down through the layers of the OSI
  Model until it reaches the Physical layer
• Data frames are small blocks of data with
  control, addressing, and handling information
  attached to them

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Chapter Summary (continued)

• Data request from a software program is received
  by the Application layer protocols and is
  transferred down through the layers of the OSI
  Model until it reaches the Physical layer
• Data frames are small blocks of data with
  control, addressing, and handling information
  attached to them

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Chapter Summary (continued)

• In addition to frame types and addressing
  schemes, the IEEE Networking Specifications apply
  to connectivity, networking media, error checking
  algorithms, encryption, emerging technologies,
  and more
• Significant 802 standards are 802.3, which
  describes Ethernet 802.5, which describes Token
  Ring and 802.11, which describes wireless
  networking

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Questions