Chapter Two

1
Chapter Two

• Networking Standards
• and the OSI Model

2
Objectives

• Identify organizations that set standards for
  networking
• Explain the layers of OSI Model
• Describe specific networking services within each
  layer of OSI Model

3
Objectives

• Explain how two systems communicate through OSI
  Model
• Discuss the structure and purpose of data frames
• Describe the two types of addressing contained in
  OSI Model

4
Standards

• Documented agreements containing technical
  specifications or other precise criteria that
  stipulate how a particular product or service
  should be designed or performed
• Many different industries use standards to ensure
  that products, processes, and services suit their
  purpose

5
Networking Standards Organizations

• American National Standards Institute (ANSI)
• Comprised of industry and government
  representatives
• Determine standards for electronics industry in
  addition to other fields
• Electronic Industries Alliance (EIA)
• Trade organization composed of representatives
  from electronics manufacturing firms across
  United States
• Sets standards for members, helps write ANSI
  standards, and lobbies for legislation favorable
  to the industry

6
Networking Standards Organizations

• Institute of Electrical and Electronic Engineers
  (IEEE)
• International society of engineering
  professionals
• Promotes development and education in electrical
  engineering and computer science fields
• International Organization for Standardization
  (ISO)
• Collection of standards organizations
• Goal is to establish international technological
  standards to facilitate global exchange of
  information and barrier-free trade

7
Networking Standards Organizations

• International Telecommunication Union (ITU)
• Formerly called Consultative Committee on
  International Telegraph and Telephony (CCITT)
• United Nations agency that regulates
  international telecommunications
• Assists developing countries

8
The OSI Model

• Open Systems Interconnection (OSI) Model
• Model for understanding and developing
  computer-to-computer communication
• Developed in the 1980s by ISO
• Divides network architecture into seven layers
• Network architect
• Professional involved in network design

9
The OSI Model
Figure 2-1 The OSI Model
10
Physical LayerData Link Layer

• Physical layer
• First layer of OSI Model
• Contains physical networking media
• Data Link layer
• Second layer of OSI Model
• Primary function is to divide data it receives
  from Network layer into distinct frames that can
  be transmitted by Physical layer

11
Frames

• 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
12
Network Layer

• Third layer of OSI Model
• Translates network addresses into their physical
  counterparts
• Decides how to route data from sender to receiver

13
Network Layer

• Because Network layer handles routing, routers
  belong in Network layer
• To route means to direct data based on
  addressing, usage patterns, and availability
• Network layer protocols also accomplish
• Segmentation
• Reassembly

14
Transport Layer

• Fourth layer of OSI Model
• Ensures that data are transferred between points
  reliably and without errors
• Handles flow control
• Method of gauging appropriate rate of data
  transmission

15
Transport Layer

• Sequencing
• Process of assigning a placeholder to each piece
  of a data block to allowing receiving nodes
  Transport layer to reassemble data in correct
  order
• Acknowledgement (ACK)
• Response generated in Transport layer
• Confirms to sender that its frame was received

16
Session Layer

• Fifth layer of OSI Model
• Establishes and maintains communication between
  two nodes on the network
• Session
• Refers to a connection for data exchange between
  two parties
• Term session is most often used in context of
  terminal and mainframe communications

17
Presentation Layer Application Layer

• Presentation layer
• Sixth layer of OSI Model
• Translates between application and network
• Application layer
• Seventh, or top, layer of OSI Model
• Provides interface to software enabling programs
  to use network devices

18
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

19
Applying the OSI Model
Table 2-1 Functions of the OSI layer
20
Communication Between Two Systems

• Token
• Special control frame indicating to rest of
  network that a particular node has right to
  transmit data
• Frame Check Sequence (FCS)
• Field in a frame responsible for ensuring that
  data carried by frame arrives intact

21
Communication Between Two Systems
Figure 2-3 Data transfer between two systems
22
Communication Between Two Systems
Figure 2-4 Data transformed through the OSI Model
23
Frame Specifications

• Ethernet
• Networking technology originally developed in
  1970s by Xerox
• Four types of Ethernet technology are used on
  LANs today
• Each type is governed by a set of IEEE standards

24
Frame Specifications

• Token Ring
• Networking technology developed by IBM in the
  1980s
• Relies upon direct links between nodes and a ring
  topology, using tokens to allow nodes to transmit
  data

25
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
26
Components of the Ethernet 802.3 Frame

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

27
Components of the Ethernet 802.3 Frame

• 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

28
Components of the Ethernet 802.3 Frame

• 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)

29
Typical Token Ring Frame

• 802.5 Standard
• IEEE standard for Token Ring networking devices
  and data handling

Figure 2-6 Typical Token Ring frame
30
Components of Token Ring Frame

• Start Delimiter (SD)
• Signifies beginning of packet
• Access Control (AC)
• Contains information about priority of the frame
• Frame Control (FC)
• Defines type of frame

31
Components of Token Ring Frame

• Destination Address
• Contains destination node address
• Source Address
• Contains address of originating node
• Data
• Contains data transmitted from originating node

32
Components of Token Ring Frame

• Frame Check Sequence (FCS)
• Used to check integrity of the frame
• End Delimiter (ED)
• Indicates end of the frame
• Frame Status (FS)
• Indicates whether destination node recognized and
  correctly copied the frame

33
Addressing Through the Layers

• Data Link layer address
• Also called MAC address, after Media Access
  Control (MAC) sublayer
• Number uniquely defining a network node
• Composed of Block ID and Device ID
• Manufacturer-hard codes the address on the NIC

34
Addressing Through the Layers

• Network layer address
• Resides at Network level of OSI Model
• Follows hierarchical addressing scheme
• Can be assigned through operating system software

35
IEEE Networking Specifications
Table 2-2 IEEE 802 standards
36
IEEE Networking Specifications

• To accommodate shared access for multiple network
  nodes, IEEE expanded OSI Model by separating Data
  Link layer into two sublayers
• Logical Link Control (LLC) sublayer
• Media Access Control (MAC) sublayer

37
Data Link Layer Sublayers

• LLC
• Upper sublayer
• Provides common interface
• Supplies reliability and flow control services
• MAC
• Lower sublayer
• Appends physical address of destination computer
  onto the frame

38
Subdivided Data Link Layer
Figure 2-7 LLC and MAC sublayers
39
Chapter Summary

• Standards are documented agreements containing
  technical specifications or other precise
  criteria used as guidelines to ensure materials,
  products, processes, and services suit their
  purpose
• Prominent standards organization include
• ANSI
• EIA
• IEEE
• ISO
• ITU

40
Chapter Summary

• OSI Model divides networking architecture into
  seven layers
• Physical layer
• Data Link layer
• Network layer
• Transport layer
• Session layer
• Presentation layer
• Application layer

41
Chapter Summary

• A data request from a software program is
  received by Application layer services and is
  transferred down through layers of OSI Model
  until it reaches the Physical layer
• Data frames are small blocks of data with
  control, addressing, and handling information
  attached to them
• Each node on a network can be identified by two
  types of addresses
• Network layer address
• Data Link layer address

42
Chapter Summary

• In addition to frame types, IEEE networking
  specifications apply to connectivity, networking
  media, error checking algorithms, encryption,
  emerging technologies, and more
• ISO expanded OSI Model by separating the Data
  Link layer into sublayers
• LLC layer
• MAC layer