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Network+ Guide to Networks
5th Edition
Chapter 2
Networking Standards and the OSI
Model
Objectives
• Identify organizations that set standards for
networking
• Describe the purpose of the OSI model and each of
its layers
• Explain specific functions belonging to each OSI
model layer
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Objectives (cont’d.)
• Understand how two network nodes communicate
through the OSI model
• Discuss the structure and purpose of data packets
and frames
• Describe the two types of addressing covered by the
OSI model
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Networking Standards Organizations
• Standard
– Documented agreement containing technical
specifications/precise criteria
– Stipulates design or performance of particular product
or service
– Used by industries to ensure that products, processes
and services suit their purposes.
• Standards are essential in the networking world
– Wide variety of hardware and software
• Ensures network design compatibility (ex. cable plug &
wall plate)
• Standards define minimum acceptable performance
– Not ideal performance
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
List of Standards Organizations
ANSI:
• ANSI (American National Standards Institute)
– 1000+ representatives from industry and government
– Determines standards for electronics industry and
other fields(chemical& nuclear engineering, health&
safety, etc.)
– Represents US in setting international standards
Notes on Network+ Guide to Networks, 5th Edition modified by Dr.
Feda AlShahwan
List of Standards Organizations
EIA and TIA
• EIA (Electronic Industries Alliance)
– Trade organization
• Representatives from United States electronics
manufacturing firms
– Sets standards for its members + write ANSI
standards
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
EIA and TIA (cont’d.)
• TIA (Telecommunications Industry Association)
– Formed in 1988
• EIA subgroup merged with former United States
Telecommunications Suppliers Association (USTSA)
– Focus of TIA
• Standards for information technology, wireless,
satellite, fiber optics, and telephone equipment
• TIA/EIA 568-B Series
– Guidelines for installing network cable in commercial
buildings
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
List of Standards Organizations
IEEE
• IEEE (Institute of Electrical and Electronics
Engineers)
– International engineering professionals society
• Goal of IEEE
– Promote development and education in electrical
engineering and computer science fields
– Hosts symposia, conferences, and chapter meetings
– Maintains a standards board (establishes its own
electronic and computer standard industries &
contributes to other standards bodies)
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
IEEE Student Chapter at CCSF
• Last semester, the chapter arranged a tour of a data
center
• I'll let you know what's coming up this semester
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
List of Standards Organizations
ISO
• ISO (International Organization for Standardization)
– ISO in Greek means equal
– Headquartered in Geneva, Switzerland
– Collection of standards organizations
• Representing 157 countries
• Goal of ISO
– Establish international technological standards to
facilitate global exchange of information and barrier
free trade
• Widespread authority : textiles, packaging, banking,
etc.
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
List of Standards Organizations
ITU
• ITU (International Telecommunication Union)
– Specialized United Nations agency that regulates
international telecommunications including radio & TV
frequencies, satellite & telephony specifications and
networking infrastructure.
– Provides developing countries with technical
expertise and equipment
– Founded in 1865 (Paris)
• Joined United Nations in 1947
– Members from 191 countries
• Focus of ITU
– Global telecommunications issues
– Worldwide Internet services implementation
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
List of Standards Organizations
ISOC
• ISOC (Internet Society)
– Founded in 1992
– Professional membership society
– Establishes technical Internet standards
• Current ISOC concerns
–
–
–
–
–
Rapid Internet growth
Keeping Internet accessible
Information security
Stable Internet addressing services
Open standards
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
ISOC (cont’d.)
• ISOC oversees groups with specific missions
– IAB (Internet Architecture Board)
• Technical advisory group
• Overseeing Internet’s design and management
– IETF (Internet Engineering Task Force)
•
•
•
•
Sets Internet system communication standards
Particularly protocol operation and interaction
Anyone may submit standard proposal
Elaborate review, testing, and approval processes
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
List of Standards Organizations
IANA and ICANN
• IP (Internet Protocol) address
– Address identifying computers in TCP/IP based
(Internet) networks
– Reliance on centralized management authorities
• IP address management history
– Initially: IANA (Internet Assigned Numbers Authority)
– 1997: Three RIRs (Regional Internet Registries)
• ARIN (American Registry for Internet Numbers)
• APNIC (Asia Pacific Network Information Centre)
• RIPE (Réseaux IP Européens)
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
IANA and ICANN (cont’d.)
• IP address management history (cont’d.)
– Late 1990s: ICANN (Internet Corporation for
Assigned Names and Numbers)
• Private nonprofit corporation
• Remains responsible for IP addressing and domain
name management
• IANA performs system administration
• Users and business obtain IP addresses from ISP
(Internet service provider)
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
ICANN's Stormy History
• 2002: ICANN was sued by one of their own board
members to force them to disclose financial
documents
• 2003: ICANN sued Verisign to make them shut
down their "Site Finder" service, which captured all
mistyped URLs and showed them Verisign ads
• 2004 Verisign sued ICANN saying they had
overstepped their authority
• 2008 Ten worst spam offenders notified by ICANN
– Links Ch 2a, 2b, 2c
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
The OSI Model
• Open System Interconnection model
• Model for representing theoretically the
communication between two nodes on a network
regardless of their underlying software or hardware
• Developed by ISO (1980s)
• Divides network communications into seven layers
– Physical, Data Link, Network, Transport, Session,
Presentation, Application
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
The OSI Model (cont’d.)
• Protocols:
– Rules by which computers communicate
– A set of instructions written by a programmer to
perform a function or a set of functions
– Some are included with a computer’s OS and others
are files installed with SW programs.
– Performs services unique to the layer
– Interact with protocols in the above/below layers
directly
• Application layer protocols
– Interact with software
– Email, spreadsheet, etc.
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
The OSI Model (cont’d.)
• Physical layer protocols
– Act on cables and connectors
– To issue and receive signals
• Logically each layer communicates with its peer
corresponding layer in the second node
• The communication process starts at layer 7
(application) and initiated by a user or device to start
data exchange, the application layer separates data
into PDU. Then, PDU progress down through OSI
model layers (6,5,4,3,2,1) and header is added to
the data unit except layer 7. After that data traverses
network until it reaches second node’s physical layer
and data progress up the OSI(ms)
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
The OSI Model (cont’d.)
• Every network communication process represented
• PDUs (protocol data units)
– Discrete amount of data
– Application layer function
– Flow through layers 6, 5, 4, 3, 2, and 1
• Generalized model and sometime imperfect
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Figure 2.1 Flow of data through the OSI model
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Mnemonics for the OSI Model
• Bottom Up
– Please (Programmers)
– Do
– Not
– Throw
– Sausage (Salty)
– Pizza
(Pretzels)
– Away
• Top Down
– All
– People
– Seem
– To
– Need
– Data
– Processing
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Application Layer
•
•
•
•
Top (seventh) OSI model layer
No software applications (MS word, Firefox, etc.)
Separate data into PDU
Protocol functions (services)
– Facilitates communication
• Between software applications and lower-layer network
services
– Network can interpret application request
– Application can interpret data sent from network
– Format, security, synchronization and other network
requirements negotiation between SW programs &
networks (ex: Library Web page & HTTP)
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Presentation Layer
• Allows hosts and applications to use a common
language
• Protocol functions
– Serves as translator
– Accept Application layer data
– Formats data to make it understandable to different
applications and hosts
• Examples
– Text encoding methods ASCII and EBCDIC
– Compression methods like GIF, JPEG and TIFF for
images and MPEG and Quicktime for audio & video.
– Data encryption and decryption (ex. Bank account)
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Session Layer
• Protocol functions
– Establishes, coordinates, maintains and terminates
communications between two nodes
• Session
– Connection for ongoing data exchange between two parties
• Historically used for terminals & mainframes
• Now: Web browser & server; remote client & access server
• Functions
–
–
–
–
Establishing and keeping alive communications link
Securing the communication & ensuring authorization
Synchronize dialogue between nodes
Determining if communications ended
• Determining where to restart transmission, which node
communicate first, duration of communication
– Terminating communications
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Transport Layer
• Protocol functions
– Accept data from Session layer
– Manage end-to-end data delivery (reliably, no errors,
correct sequence)
– Handles flow control
• Process of gauging the appropriate rate of transmission
based on the recipient (how fast it can accept data)
– Provides reassembly
• Process of reconstructing segmented data units
– Provides sequencing
• Method of identifying segments belonging to the same
group of subdivided data, it indicates start of unit data,
order of groups of data
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Transport Layer (cont’d.)
– Provides segmentation, and error control
• Process of breaking large data units received from the
session layer into multiple smaller units called
segments
» Increase transmission efficiency
» Match a network MTU

Maximum Transmission Unit

Largest data unit carried by the network

Ethernet default: 1500 bytes

Discovery routine used to determine MTU
• Run discovery routine upon establishing a connection
with the network to learn the MTU size
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Transport Layer
Types of Transport Layer Protocols: TCP and UDP
• TCP
• Connection-oriented
– Establishes a connection before transmitting data
– Three-way handshake
SYN
SYN/ACK
ACK
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Transport Layer
• TCP
– Require acknowledgements from receiver to ensure
data was received correctly (reliable transmission)
– Checksum
• Process that uses a unique character string allowing
receiving node to determine if arriving data unit exactly
matches data unit sent by source
• Ensures data integrity
Send data, wait for ACK
ACK
Send more data, wait for ACK
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Transport Layer
• UDP
• Connectionless protocol
– Do not establish connection with another node before
transmitting data—no handshake
– Make no effort to ensure data is reliable ( no errors)
– Faster than connection-oriented protocol
– Useful when data must be transferred quickly, such
as streaming music or video
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Transport Layer (cont’d.)
Figure 2-2 Segmentation and reassembly
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Network Layer
• Establishes network connections, translates network
address to physical address and determines routing
• Addressing
– System for assigning unique identification numbers to
devices on a network
– Two types of addressing:
• Network/logical/virtual address
– Hierarchal scheme (subset of data that incrementally
narrow down the location of a node)
– Depends on network protocol
– 139.141.161.3
• Physical/MAC/datalink/hardware address
– Unique
– 0060973E97F3 (12 hex digits)
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Network Layer
• Protocol Functions
– Address translation (network & Physical)
– Packet formation
• Process of adding logical addressing information—IP
address to transport layer segment to produce network
layer packet
– Routing
• Process of determining the best path from point A on
one network to point B on another network
• Intelligently direct data based on addressing, patterns
of usage and availability
• Routing considerations
-Delivery priorities
-Quality of service
-Network congestion
-Cost of alternative routes
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Network Layer
– Fragmentation
• Network layer protocol (IP) subdivides Transport layer
segments received into smaller packets ensures that
packets are not larger than the network’s maximum
transmission unit size
• This is usually avoided by adjusting the Maximum
Segment Size in the Transport layer, because it makes
data transfer inefficient
• Router : device that connects network segments and
directs data
• Common Network layer protocol
– IP (Internet Protocol)
– Protocol that instructs the network where the HTTP
request is coming from & where it is going to (src
&dst)
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Data Link Layer
• Function of protocols
– Divide data received into distinct frames for
transmission in Physical layer
– Add Physical address to the frame: MAC addresses
like 00-30-48-82-11-BD
• Frame
– Structured package for moving data
• Includes raw data (payload), sender’s and receiver’s
physical addresses, error checking and control
information
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Data Link Layer (cont’d.)
• Frames may be damaged as they pass through the
Physical layer, so the Data Link layer has errorchecking
– Error checking
• Frame check sequence
• CRC (cyclic redundancy check)
• Possible glut of communication requests
– Data Link layer controls flow of information
• Allows NIC to process data without error
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Data Link Layer (cont’d.)
• Two Data Link layer sublayers
– LLC (Logical Link Control) sublayer
– MAC (Media Access Control) sublayer
• MAC address components
– Block ID
• Six-character sequence unique to each vendor
– Device ID
• Six-character number added at vendor’s factory
• MAC addresses frequently depicted in hexadecimal
format
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Example of MAC Address
• Whole MAC address: 00-30-48-82-11-BD
– Block ID
• 00-30-48
• Identifies the vendor
– Device ID
• 82-11-BD
• Different for each NIC from the same vendor
• If two NICs have the same MAC address, they have
problems networking
– This can happen with cheaply made refurbished
NICs, or with copied virtual machines
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Data Link Layer (cont’d.)
Figure 2-5 The Data Link layer and its sublayers
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Data Link Layer (cont’d.)
Figure 2-6 A NIC’s Mac address
Notes on Network+ Guide to Networks, 5th Edition modified by Dr.
Feda AlShahwan
Finding Your MAC Address
• Start, CMD, Enter
• IPCONFIG /ALL
• Scroll up to see the first entry
MAC Address (also
called "Physical
Address")
IP Address
Notes on Network+ Guide to Networks, 5th Edition modified by Dr.
Feda AlShahwan
Physical Layer
• Functions of protocols
– Accept frames from Data Link layer
– Generate signals as changes in voltage at the NIC
• Copper transmission medium
– Signals issued as voltage
• Fiber-optic cable transmission medium
– Signals issued as light pulses
• Wireless transmission medium
– Signals issued as electromagnetic waves
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Physical Layer (cont’d.)
• Physical layer protocols responsibility when
receiving data
–
–
–
–
–
Detect and accept signals
Pass on to Data Link layer
Set data transmission rate
Monitor data error rates
No error checking
• Devices operating at Physical layer
– Hubs and repeaters
• NICs operate at both Physical layer and Data Link
layers
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Applying the OSI Model
Table 2-1 Functions of the OSI layers
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Communication Between Two Systems
• Data transformation
– Original software application data differs from the bits
sent onto the cable by the NIC
• Header data added at each layer (ex. Format
specification, network address,…) except layer 7and
trailer is added at data link layer
• Each layer has a different data structure, called a
Protocol Data Unit (PDU)
• Segments
– Generated in Transport layer
– Unit of data resulting from subdividing larger PDU
from the Session layer
– Addressed with TCP Ports (when using TCP)
Notes on Network+ Guide to Networks, 5th Edition modified by Dr.
Feda AlShahwan
Communication Between Two Systems
(cont’d.)
• Packets
– Generated in Network layer
– Data with logical addressing information added to
segments
– Addressed with IP addresses
• Frames
– Generated in Data Link layer
– Composed of several smaller components or fields
– Addressed with MAC addresses
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Communication Between Two Systems
(cont’d.)
• Encapsulation
– Occurs in each layer
– Process of wrapping one layer’s PDU with protocol
information
• Allows interpretation by lower layer
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Communication Between Two Systems
(cont’d.)
Figure 2-7 Data transformation through the OSI model
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Communication Between Two Systems
(cont’d.)
• Example: get mail message from remote mail server
• Communication Steps for Server/Client exchange:
– Application Layer: accepts data, formulates request
and adds an application header transfer PDU to
presentation layer.
– Presentation Layer: determines whether & how it
format and encrypt the data request received and
adds presentation header  transfer PDU to session
layer
– Session Layer: adds session header ( transmission
rate, how to communicate with network)  transfer
PDU to transport layer.
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Communication Between Two Systems
(cont’d.)
– Transport Layer: segments the PDU (max. size of
segment is dictated by the type of network
transmission method for example Ethernet) and adds
transport header ( sequence identifier, checksum,
flow control and acknowledgment)  transfer PDU
(segments) to network layer.
– Network Layer: adds network header that contains
the logical address of the destination  transfer PDU
(packet) to data link layer.
– Data Link Layer: adds data link header for checking
errors and trailer for indicating end of packet 
transfer PDU (frame) to physical layer.
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan
Communication Between Two Systems
(cont’d.)
– Physical Layer: Does not interpret or add any
information to the frame but transmits them over the
broadband connection across the network after
converting binary digits into pulses.
– The frames arrive at the mail server and accepted by
its physical layer and reverse the process
Notes on Network+ Guide to Networks, 5th Edition modified by Dr. Feda AlShahwan