Transcript CIST 1401 Chapter 2 - Albany Technical College eLearn

Chapter 2
Networking Standards
and the OSI Model
Collected and Compiled
By JD Willard
MCSE, MCSA, Network+,
Microsoft IT Academy Administrator
Computer Information Systems Instructor
Albany Technical College
Attention: Accessing Demos
• This course presents many demos.
• The Demos require that you be logged in to the Virtual Technical
College web site when you click on them to run.
• To access and log in to the Virtual Technical College web site:
– To access the site type www.vtc.com in the url window
– Log in using the username: CIS 1140 or ATCStudent1
– Enter the password: student (case sensitive)
• If you should click on the demo link and you get an Access Denied
it is because you have not logged in to vtc.com or you need to log
out and log back in.
• If you should click on the demo link and you are taken to the
VTC.com web site page you should do a search in the search box for
the CompTIA Network+ (2009 Objectives) Course and run the
video from within that page.
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
• 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
Networking Standards Organizations
• Standard
– Documented agreement
– Technical specifications/precise criteria
– Stipulates design or performance of
particular product or service
• Standards important in the networking world
– Wide variety of hardware and software
– Ensure network design compatibility
• Standards define minimum acceptable
performance
– Not ideal performance
Networking Standards Organizations
(cont’d.)
• Many different organizations oversee computer
industry standards
• Example: ANSI and IEEE set wireless standards
– ANSI standards apply to type of NIC
– IEEE standards involve communication
protocols
• Network professional’s responsibility
– Be familiar with groups setting networking
standards
– Understand critical aspects of standards
required by own networks
ANSI
• ANSI (American National Standards Institute)
– 1000+ representatives from industry and
government
– Determines standards for electronics industry
and other fields
• Requests voluntarily compliance with standards
• Obtaining ANSI approval requires rigorous testing
• ANSI standards documents available online
• ANSI is the official U.S. representative to the
International Organization for Standardization.
(ISO).
EIA and TIA
• EIA (Electronic Industries Alliance)
– Trade organization
• Representatives from United States electronics manufacturing
firms
– Sets standards for its members
– Helps write ANSI standards
– Lobbies for favorable computer and electronics industries legislation
• TIA (Telecommunications Industry Association)
– 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
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
• IEEE technical papers and standards
– Highly respected
ISO
• ISO (International Organization for
Standardization)
– Headquartered in Geneva, Switzerland
– Collection of standards organizations
• Represents 162 countries
• Goal of ISO
– Establish international technological
standards to facilitate global information
exchange and barrier free trade
• Widespread authority
ITU
• ITU (International Telecommunication Union)
– Specialized United Nations agency
– Regulates international telecommunications
– Provides developing countries with technical
expertise and equipment
– Founded in 1865; joined United Nations in 1947
– Members from 193 countries
• Focus of ITU
– Global telecommunications issues
– Worldwide Internet services implementation
ISOC
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•
•
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
ISOC oversees groups with specific missions
– IAB (Internet Architecture Board)
• Technical advisory group
• Oversees 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
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)
– 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)
The OSI Model
• Using the OSI model to discuss networking concepts has the
following advantages:
– Provides a common language or reference point between
network professionals
– Divides networking tasks into logical layers for easier
comprehension
– Allows specialization of features at different levels
– Aids in troubleshooting
– Promotes standards of interoperability between networks and
devices
– Provides modularity in networking features (developers can
change features without changing the entire approach)
The OSI Model
• However, you must remember the following limitations of the OSI
model.
– OSI layers are theoretical and do not actually perform real
functions.
– Industry implementations rarely have a layer-to-layer
correspondence with the OSI layers.
– Different protocols within the stack perform different functions
that help send or receive the overall message.
– A particular protocol implementation may not represent every
OSI layer (or may spread across multiple layers).
The OSI Model (7:43)
Development and Reason for Model Demo
The OSI Model
• Model for understanding and
developing network computer-tocomputer communications
• Developed by ISO in the 1980s
• Divides network communications into
seven layers
– Physical, Data Link, Network,
Transport, Session, Presentation,
Application
• Protocol interaction
– Layer directly above and below
• Application layer protocols
– Interact with software
• Physical layer protocols
– Act on cables and connectors
What is the OSI? Demo
The OSI Model (cont’d.)
• Theoretical representation
describing network
communication between two
nodes
• Hardware and software
independent
• 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 sometimes
imperfect
Flow of data through the OSI model
OSI Model Layer Mnemonics
Layer
Name
Mnemonic
(Bottom to
top)
Mnemonic
(Top to
bottom)
Layer 7
Application
Away
All
Layer 6
Presentation
Pizza
People
Layer 5
Session
Sausage
Seem
Layer 4
Transport
Throw
To
Layer 3
Network
Not
Need
Layer 2
Data Link
Do
Data
Layer 1
Physical
Please
Processing
The OSI Model
Overview of Layered Architecture Demo
The OSI Model
The layers of the model Demo
Upper Layers Demo
Lower Layers Demo
•The Application, Presentation
and Session layers are known
as the Upper Layers and are
implemented in software
•The Transport and Network
layer are mainly concerned
with protocols for delivery and
routing of packets and are
implemented in software as
well
•The Data Link is implemented
in hard- and software
•The Physical layer is
implemented in hardware only,
hence its name. These lower
two layers define LAN and
WAN specifications.
The OSI Model
•
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A more detailed description of each layer
follows later, but here's what basically
happens when data passes from Host A
to Host B:
The Application, Presentation and
Session layers take user input and
converts it into data
The Transport layer adds a segment
header converting the data into segments
The Network layer adds a network header
and converts the segments into packets /
datagrams
The Data Link layer adds a frame header
converting the packets/datagrams into
frames, the MAC sublayer converts the
frames into bits, which the Physical layer
can put on the wire.
These steps are known as data
encapsulation.
Packet Assembly and Disassembly
Process • Each successive layer adds
Source Computer
Destination Computer
formatting and peer control
information to the data in the
form of a header. At the
receiving end the headers are
stripped off by the
corresponding layers to
determine how to handle the
data. At the Data Link layer an
error checking mechanism
known as the Frame check
sequence is added as a trailer.
• When the bits stream arrives at
the destination, the process is
reversed and each layer will
remove their corresponding
header while the data flows up
the OSI model until it is
converted back to data and
presented to the user. This is
also known as decapsulation.
Application Layer
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•
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•
Top (seventh) OSI model layer
Window to network services
Does not include software applications
Protocol functions
– Facilitates communication between
software applications and lower-layer
network services
– Network interprets application request
– Application interprets data sent from
network
Application Layer
• Software applications
negotiate with application
layer protocols
• Application program
interface (API): set of
routines that make up part
of a software application
• Formatting, procedural,
security, synchronization,
and other requirements
• Examples of Application
layer protocol:
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•
•
•
HTTP, FTP and TFTP
SNMP and Telnet
DHCP and DNS
SMTP, POP and IMAP
Application layer functions while retrieving a Web page
The Application Layer Demo
Presentation Layer
• Presentation Layer (6)
• Network translator
• Protocol functions
– Accept Application layer data
– Format data
• Understandable to different applications
and hosts
• Examples of file types translated at the
presentation layer
– GIF, JPG, TIFF, MPEG, QuickTime, MIME
and ASCII
Presentation Layer
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•
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Presentation layer
services manage data
compression,
encryption and
decryption
o Example protocol:
Secure Sockets
Layer (SSL)
I/O redirectors work to
redirect resources to a
server
The Server and
Workstation Services
work at this layer
Presentation layer services while
retrieving a secure Web page
The Presentation Layer Demo
Session Layer
• Session Layer (5)
• Protocol functions
– Coordinate and maintain communications between two
network nodes
– Examples of protocols/API's that operate on this layer
are RPC and NETBIOS.
• Session
– Connection for ongoing data exchange between two
parties
• Connection between remote client and access server
• Connection between Web browser client and Web
server
Session Layer
• Functions
o Establishing and keeping
alive communications link
 For session duration
o Keeping communications
secure
o Synchronizing dialogue
between two nodes
o Determining if
communications ended
 Determining where to
restart transmission by
placing checkpoints in
the data stream
o Terminating communications
o Set terms of communication
 Decides which node will
communicate first
 Decides how long a node
can communicate
o Identify session participants
Session layer protocols managing voice
communications
The Session Layer Demo
Transport Layer
• Protocol functions
– Accept data from Session layer
– Manage end-to-end data delivery
• Ensure data transferred reliably and without errors through
sequencing and acknowledgements.
– Handle flow control
• Connection-oriented protocols
– TCP & SPX
– Establish connection before transmitting data
– Example: TCP three-way handshake
• SYN (synchronization) packet
– Client’s TCP protocol first sends synchronization (SYN) packet request to
server
• SYN-ACK (synchronization-acknowledgment)
– Server responds with synchronization-acknowledgment (SYN-ACK)
packet
• ACK
– Client responds with own acknowledgment (ACK)
Transport Layer (cont’d.)
• Checksum
– Unique character string
– Allows receiving node to determine if
arriving data matches sent data
• Connectionless protocols
– UDP
– Do not establish connection with another
node before transmitting data
– Do not check for data integrity
– Faster than connection-oriented protocols
Transport Layer (cont’d.)
• Segmentation
– Breaking large data units received from
Session layer into multiple smaller units
called segments
– Increases data transmission efficiency on
certain network types
• MTU (maximum transmission unit)
– Largest data unit network will carry
– Ethernet default: 1500 bytes
– Discovery routine used to determine MTU
Transport Layer (cont’d.)
• Reassembly
– Recombining the
segmented data units
• Sequencing
– Identifying segments
belonging to the
same group of
subdivided data
– Specifies order of
data issue
Segmentation and reassembly
The Transport Layer Demo
Network Layer
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Protocol functions
– Translate network addresses into physical counterparts
• ARP
– Decide how to route data from sender to receiver
• RIP, OSPF, IGMP, BGP
– Troubleshooting network connectivity
• ICMP (Internet Control Message Protocol)
– Ping and Tracert
Addressing
– System for assigning unique identification numbers to network devices
– Addresses the package using network address scheme (encapsulates into
packets)
Types of addresses
– Network addresses (logical or virtual addresses)
• IP, IPX
• Network address example: 10.34.99.12
– Physical addresses
• Physical address example: 0060973E97F3
Network Layer (cont’d.)
• Network layer handles routing
• Common Network layer protocol
– IP (Internet Protocol)
– Determines the best route on the network
• Factors used to determine path routing
– Delivery priority
– Network congestion
– Quality of service
– Cost of alternative routes
• Routers belong in the network layer
• Fragmentation
– Subdividing Transport layer segments
– Performed at the Network layer
• Segmentation preferred over fragmentation for greater network
efficiency
The Network Layer Demo
Data Link Layer
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•
Function of protocols
– Divide data received into
distinct frames for transmission
in Physical layer
(encapsulation)
– Appends Physical address and
Frame Check Sequence (FCS)
to the frame
Frame
– Structured package for moving
data
– Parts of data frame:
Destination ID, Sender ID,
Control Data
– Includes raw data (payload),
sender’s and receiver’s network
addresses, error checking and
control information
Data Link Layer (cont’d.)
• Possible communication mishap
– Not all information received
– Corrected by error checking
• Error checking accomplished by 4-byte Frame Check
Sequence (FCS) field
– Ensures data at destination exactly matches data
issued from source
– When source node transmits data, performs Cyclic
Redundancy Check (CRC) to get FCS
– Destination node’s Data Link layer services
unscramble FCS via same CRC algorithm
• Possible glut of communication requests
– Data Link layer controls flow of information
• Allows NIC to process data without error
Data Link Layer (cont’d.)
• Two Data Link layer sublayers
– LLC (Logical Link Control) sublayer
• Provides a common interface to the Network Layer,
reliability and flow control
• Defines SAPs (Service Access Points)
– MAC (Media Access Control) sublayer
• NDIS works at this level
• Manages access to the physical medium
• Defines IEEE LAN standards such as 802.3, 802.4,
802.5, and 802.11
• Converts the frames into bits and puts them on the wire
• Appends physical address of destination computer onto
data frame
• Physical (MAC) address
– Fixed number associated with each device’s network
interface
The Data Link layer and its sublayers
A NIC’s physical address
A NIC’s MAC address contains two parts: a block ID and a device
ID. The block ID is a six-character sequence unique to each
vendor. The remaining six characters known as the device ID are
added at the factory, based on the NIC’s model and manufacture
date.
The Data Link Layer Demo
Physical Layer
• Functions of protocols
– Accept frames from Data Link layer
– Generate signals as changes in voltage at the NIC
• Data sent as an unstructured raw bit stream over
physical medium
• Defines how the cable is attached to 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
Physical Layer (cont’d.)
• Physical layer protocols’ responsibilities 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
• Network administrators mostly concerned with
bottom four layers of OSI Model
The Physical Layer Demo
Applying the OSI Model
Functions of the OSI layers
The OSI Model in the Real World (6:00)
Communication Between Two Systems
• Data transformation
– Original software
application data differs
from application layer NIC
data
• Information added at
each layer
• PDUs
– Generated in Application
layer
• Segments
– Generated in Transport
layer
– Unit of data resulting from
subdividing larger PDU
Data transformation through the OSI Model
Communication Between Two Systems
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Packets
– Generated in Network layer
– Data with logical addressing
information added to
segments
Frames
– Generated in Data Link layer
– Composed of several smaller
components or fields
Encapsulation
– Occurs in Data Link layer
– Process of wrapping one
layer’s PDU with protocol
information
• Allows interpretation by
lower layer
Physical layer transmits frame
over the network
Data transformation through the OSI Model
Layers at Which Network Components Operate
Device
Layer
Hubs
Physical
Switches
Data Link
Bridges
Data Link
Routers
Network
Network Interface
Data Link and
Card
Physical
Wireless Access Point Data Link
Frame Specifications
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Frames
– Composed of several smaller components or fields
Frame characteristic dependencies
– Network type where frames run
– Standards frames must follow
Ethernet
– Developed by Xerox
– Four different types of Ethernet frames
– Most popular: IEEE 802.3 standard
Token ring
– Developed by IBM
– Relies upon direct links between nodes and ring topology
– Nearly obsolete
– Defined by IEEE 802.5 standard
Ethernet frames and token ring frames differ
– Will not interact with each other
– Devices cannot support more than one frame type per physical interface or NIC
IEEE Networking Specifications
• IEEE’s Project 802
– Effort to standardize physical and logical
network elements
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Frame types and addressing
Connectivity
Networking media
Error-checking algorithms
Encryption
Emerging technologies
• 802.3: Ethernet
• 802.5: Token Ring
• 802.11: Wireless
Network Standards Demo
IEEE Networking Specifications
IEEE 802 standards
Summary
• Standards are documented agreements
containing precise criteria that are used as
guidelines to ensure that materials, products,
processes, and services suit their purpose
• ISO’s OSI Model divides networking
architecture into seven layers
• Each OSI layer has its own set of functions
and interacts with the layers directly above
and below it
• Application layer protocols enable software to
negotiate their formatting, procedural,
security, and synchronization with the
network
Summary (continued)
• Presentation layer protocols serve as translators between the
application and the network
• Session layer protocols coordinate and maintain links between
two devices for the duration of their communication
• Transport layer protocols oversee end-to-end data delivery
• Network layer protocols manage logical addressing and
determine routes based on addressing, patterns of usage, and
availability
• Data Link layer protocols organize data they receive from the
Network layer into frames that contain error checking routines
and can then be transmitted by the Physical layer
• Physical layer protocols generate and detect voltage to transmit
and receive signals carrying data over a network medium
• Data frames are small blocks of data with control, addressing,
and handling information attached to them
The End