Transcript The OSI Model (continued)

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
Objectives (continued)
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
• Standards are documented agreements
containing technical specifications
• ANSI (American National Standards Institute) is
an organization composed of more than a
thousand representatives from industry and
government who together determine standards
for the electronics industry and other fields, such
as chemical and nuclear engineering, health and
safety, and construction
Networking Standards
Organizations (continued)
• ANSI also represents the United States in setting
international standards
• EIA (Electronic Industries Alliance) is a trade
organization composed of representatives from
electronics manufacturing firms across the United
States
Networking Standards
Organizations (continued)
• TIA (Telecommunications Industry Association)
Focuses on standards for information technology,
wireless, satellite, fiber optics, and telephone
equipment
• TIA/EIA alliance are its guidelines for how network
cable should be installed in commercial buildings,
known as the “TIA/EIA 568-B Series.”
Networking Standards
Organizations (continued)
• IEEE (Institute of Electrical and Electronics
Engineers), or “I-triple-E,” is an international
society composed of engineering professionals
• IEEE goals are to promote development and
education in the electrical engineering and
computer science fields
Networking Standards
Organizations (continued)
• ISO (International Organization for
Standardization), headquartered in Geneva,
Switzerland, is a collection of standards and
organizations representing 148 countries
• ISO’s goal is to establish international
technological standards to facilitate global
exchange of information and barrier-free trade
Networking Standards
Organizations (continued)
• The ITU (International Telecommunication Union)
is a specialized United Nations agency that
regulates international telecommunications,
including radio and TV frequencies, satellite and
telephony specifications, networking
infrastructure, and tariffs applied to global
communications
Networking Standards
Organizations (continued)
• ISOC (Internet Society), founded in 1992, is a
professional membership society that helps to
establish technical standards for the Internet
• ISOC oversees groups with specific missions, such
as the IAB and IETF
Networking Standards
Organizations (continued)
• IAB (Internet Architecture Board) is a technical
advisory group of researchers and technical
professionals interested in overseeing the
Internet’s design and management
• IETF (Internet Engineering Task Force), the
organization that sets standards for how systems
communicate over the Internet—in particular, how
protocols operate and interact
Networking Standards
Organizations (continued)
• IANA and ICANN
• Every computer / host on a network must have a
unique address
• Internet Assigned Numbers Authority (IANA) kept
records of available and reserved IP addresses and
determined how addresses were issued out
• Internet Corporation for Assigned Names and Numbers
(ICANN), a private, nonprofit corporation and is now
ultimately responsible for IP addressing and domain
name management
The OSI Model
• In the early 1980s, ISO began work on a
universal set of specifications that would
enable computer platforms across the world
to communicate openly
• This model, called the Open Systems
Interconnection (OSI) Model, divides network
communications into seven layers:
The OSI Model (continued)
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
computer’s Physical layer
• Transfer of information happens in milliseconds
The OSI Model (continued)
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
The OSI Model (continued)
• Application Layer
• World Wide Web (WWW)
• Email - SMTP (Simple Mail Transport Protocol or the
X.400)
The OSI Model (continued)
The OSI Model (continued)
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
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
The OSI Model (continued)
• Session Layer (continued)
• Session layer’s 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
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
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.
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)
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 network’s
maximum transmission unit (MTU)
The OSI Model (continued)
• Transport Layer (continued)
• Reassembly
• Sequencing
• Identifying segments that belong to the same group
The OSI Model (continued)
The OSI Model (continued)
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
The OSI Model (continued)
• Network Layer (continued)
• Routers belong in the Network layer
• Perform Fragmentation
The OSI Model (continued)
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)
The OSI Model (continued)
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
Applying The OSI Model
Applying The OSI Model
(continued)
• Communication Between Two Systems
• At each layer of the OSI Model, some information is
added to the original data
Applying The OSI Model
(continued)
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
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,
IEEE Networking Specifications
(continued)
• “Project 802” (continued)
• Emerging technologies,
• And more
• Can be applied to the layers of the OSI Model
IEEE Networking Specifications
(continued)
Chapter Summary
• Standards are documented agreements
containing precise criteria
• Significant standards organizations
• ANSI, EIA/TIA, IEEE, ISO, ITU, ISOC, IANA, and
ICANN
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
Chapter Summary (continued)
• Protocols in the Presentation layer, the sixth
OSI Model layer, serve as translators
between the application and the network
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
Chapter Summary (continued)
• Protocols in the Network layer, the third OSI
Model layer, manage logical addressing and
determine routes
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
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
Chapter Summary (continued)
• Protocols at the Physical layer generate and
detect voltage
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
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
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