CIS 1140 Networking Fundamentals

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Chapter Lesson Notes: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16

Chapter 2 Networking Standards and the OSI Model

Objectives 

• Identify organizations that set standards for networking 

• Explain the layers of OSI Model 

• Describe specific networking services within each layer of OSI Model

• 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

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

• Networking Standards Organizations
  

American National Standards Institute (ANSI)

n    Comprised of industry and government representatives

n    Determine standards for electronics industry in addition to other fields

Electronic Industries Alliance (EIA)

n    Trade organization composed of representatives from electronics manufacturing firms across United States

n    Sets standards for members, helps write ANSI standards, and lobbies for legislation favorable to the industry

Institute of Electrical and Electronic Engineers (IEEE)

n     International society of engineering professionals

n     Promotes development and education in electrical engineering and computer science fields

International Organization for Standardization (ISO)

n     Collection of standards organizations

n     Goal is to establish international technological standards to facilitate global exchange of information and barrier-free trade

International Telecommunication Union (ITU)

n    Formerly called Consultative Committee on International Telegraph and Telephony (CCITT)

n    United Nations agency that regulates international telecommunications

n    Assists developing countries

The OSI Model

Open Systems Interconnection (OSI) Model

n    Model for understanding and developing computer-to-computer communication

n    Developed in the 1980s by ISO

n    Divides network architecture into seven layers

Network architect

n    Professional involved in network design

Physical layer

n    First layer of OSI Model

n    Contains physical networking media

Data Link layer

n    Second layer of OSI Model

n    Primary function is to divide data it receives from Network layer into distinct frames that can be transmitted by Physical layer

Frames

Structured package for moving data

Includes raw data (or payload) along with sender’s and receiver’s:

n     Network addresses

n     Error-checking and control information

Network Layer

Third layer of OSI Model 

Translates network addresses into their physical counterparts 

Decides how to route data from sender to receiver

Because Network layer handles routing, routers belong in Network layer

n    To route means to direct data based on addressing, usage patterns, and availability

Network layer protocols also accomplish:

n    Segmentation

n    Reassembly

Transport Layer

Fourth layer of OSI Model

Ensures that data are transferred between points reliably and without errors

Handles flow control

n    Method of gauging appropriate rate of data transmission

Sequencing

n    Process of assigning a placeholder to each piece of a data block to allowing receiving node’s Transport layer to reassemble data in correct order

Acknowledgement (ACK)

n    Response generated in Transport layer

n    Confirms to sender that its frame was received

Session Layer

Fifth layer of OSI Model

Establishes and maintains communication between two nodes on the network

Session

n    Refers to a connection for data exchange between two parties

n    Term session is most often used in context of terminal and mainframe communications

Presentation layer

n    Sixth layer of OSI Model

n    Translates between application and network

Application layer

n    Seventh, or top, layer of OSI Model

n    Provides interface to software enabling programs to use network devices

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)

n    API used in network environment

n    Stores messages sent between nodes in queues

n    Forwards these messages to their destination

Applying the OSI Model

Communication Between Two Systems

Token

n    Special control frame indicating to rest of network that a particular node has right to transmit data

Frame Check Sequence (FCS)

n    Field in a frame responsible for ensuring that data carried by frame arrives intact

Frame Specifications

lEthernet

n    Networking technology originally developed in 1970s by Xerox

n    Four types of Ethernet technology are used on LANs today

Each type is governed by a set of IEEE standards

Frame Specifications

Token Ring

n    Networking technology developed by IBM in the 1980s

n    Relies upon direct links between nodes and a ring topology, using tokens to allow nodes to transmit data

A Typical Ethernet Frame

l802.3 standard

n     IEEE standard for Ethernet networking devices and data handling

Components of the Ethernet 802.3 Frame

Preamble

n    Marks beginning of entire frame

Start of Frame Delimiter (SFD)

n    Indicates beginning of addressing frame

Destination Address

n    Contains destination node address

Source Address

n    Contains address of originating node

Length (LEN)

n    Indicates length of packet

Data

n    Contains data, or segmented part of data, transmitted from originating node

Pad

n    Used to increase size of the frame to its minimum size requirement of 46 bytes

Frame Check Sequence (FCS)

n    Provides an algorithm to determine whether data were correctly received

Most commonly used algorithm is Cyclic Redundancy Check (CRC)

Typical Token Ring Frame

802.5 Standard

n     IEEE standard for Token Ring networking devices and data handling

Components of Token Ring Frame

Start Delimiter (SD)

n    Signifies beginning of packet

Access Control (AC)

n    Contains information about priority of the frame

Frame Control (FC)

n    Defines type of frame

Destination Address

n    Contains destination node address

Source Address

n    Contains address of originating node

Data

n    Contains data transmitted from originating node

Frame Check Sequence (FCS)

n    Used to check integrity of the frame

End Delimiter (ED)

n    Indicates end of the frame

Frame Status (FS)

n    Indicates whether destination node recognized and correctly copied the frame

Addressing Through the Layers

Data Link layer address

n    Also called MAC address, after Media Access Control (MAC) sublayer

n    Number uniquely defining a network node

n    Composed of Block ID and Device ID

n    Manufacturer-hard codes the address on the NIC

Network layer address

n    Resides at Network level of OSI Model

n    Follows hierarchical addressing scheme

n    Can be assigned through operating system software

IEEE Networking Specifications

To accommodate shared access for multiple network nodes, IEEE expanded OSI Model by separating Data Link layer into two sublayers:

n    Logical Link Control (LLC) sublayer

n    Media Access Control (MAC) sublayer

Data Link Layer Sublayers

LLC

n    Upper sublayer

n    Provides common interface

n    Supplies reliability and flow control services

MAC

n    Lower sublayer

n    Appends physical address of destination computer onto the frame