David Hedley's Tuesday Tech Talk OSI Model

David Hedley’s
Tuesday Tech Talks
OSI Model
Study Materials
© 2018 David M. Hedley All Rights Reserved.

David Hedley's Tuesday Tech Talks – OSI Model
• Specific brands and models are for illustration purposes only.
• They do not imply any endorsement by the vendor, in any way.
• This talk does not represent the business process of any employer or
client, past or present, this is based on my own work and study.
• I only include equipment that I have experience with.
• At the time of writing, I have not received any compensation, or
inducement from any vendor.

• Definition
• Open Systems Interconnection model (OSI model)
• “is a conceptual model that characterizes and standardizes the
communication functions of a telecommunication or computing system
without regard to its underlying internal structure and technology.”
• https://en.wikipedia.org/wiki/OSI_model

• Purpose: Understand the OSI Model.
• Question: Do I understand how this layer works?

• Triple Constraints
• Time
• Quality or Scope
• Budget

• History
• 1983 work from late 70’s by International Organization for Standardization
(ISO) and Comite Consultatif International Telephonique et Telegraphique
(CCITT) merged in to The Basic Reference Model for Open Systems
Interconnection
• Published as ISO 7498

• What is it?
• Divided in to 7 layers
• Each layer interacts with same layer on other host(s)
• Each layer interacts with layer above and below
• Abstraction

• The layers
• 7. Application
• 6. Presentation
• 5. Session
• 4. Transport
• 3. Network
• 2. Data Link
• 1. Physical Layer

• Mnemonic
•All People Seem To Need
Data Processors

• Why do I care?
• A lot of discussion and documentation in the networking field makes
reference to the OSI model.
• It does give a framework for troubleshooting, although TCP/IP traditionally
didn’t map 1 to 1, the concepts all apply.
• If you certify, you’ll get asked OSI model questions.

• Layer 7 Application
• 7.1.3.1 General
• 7.1.3.1.1 Application-processes exchange information by means of
application-entities which use application-protocols and presentation
services.
• 7.1.3.1.2 As the only layer in the Reference Model that directly provides
services to the application-processes, the Application Layer necessarily
provides all OSI services directly usable by application-processes.

• Layer 7 Application Layer
• 7.1.3.2 Connection-mode facilities
• In addition to information transfer, such facilities may include, but are not limited to the
following:
• a) identification of the intended communication partners (for example by name, by address,
by definite description, by generic description);
• b) determination of the acceptable quality of service (for example response time, tolerable
error rate, cost vis-a-vis the previous considerations);
• c) synchronization of cooperating applications;
• d) agreement on responsibility for error recovery;
• e) agreement on security aspects (e.g. authentication, access control, data integrity);
• f) selection of mode of dialogue; and
• g) identification of abstract syntaxes.

• Layer 6 Presentation (ASCII)
• The Presentation Layer provides for the representation of information that
application-entities either communicate or refer to in their communication.
• The Presentation Layer provides for common representation of the data
transferred between application entities. This relieves application-entities of
any concern with the problem of "common" representation of information,
• i.e. it provides them with syntax independence.
• The Presentation Layer ensures that the information content of the
Application Layer data is preserved during transfer. Cooperating application-
entities are responsible for determining the set of abstract syntaxes they
employ in their communication. The Presentation Layer is informed of the
abstract syntaxes that are to be employed. Knowing the set of abstract
syntaxes to be used by the application-entities, the Presentation Layer is
responsible for selecting mutually acceptable transfer syntaxes.
• NOTE - Presentation-entities have no role in determining the set of abstract syntaxes to be
used by the application-entities.

• Layer 5 Session
• The purpose of the Session Layer is to provide the means necessary for
cooperating presentation-entities to organize and to synchronize their
dialogue and to manage their data exchange. To do this, the Session Layer
provides services to establish a session-connection between two
presentation-entities, to support orderly data exchange interactions, and to
release the connection in an orderly manner.
• The only function of the Session Layer for connectionless-mode
communication is to provide a mapping of transport-addresses to session-
addresses.

• Layer 4 Transport (Segment)
• In connection-mode, the Transport Layer functions may include: (TCP)
• mapping transport-address onto a network-address;
• multiplexing (end-to-end) transport-connections onto network-connections;
• establishment and release of transport-connections;
• end-to-end sequence control on individual connections;
• end-to-end error detection and any necessary monitoring of the quality of service;
• end-to-end error recovery;
• end-to-end segmenting, blocking, and concatenation;
• end-to-end flow control on individual connections;
• supervisory functions;
• expedited transport-service-data-unit transfer; and
• suspend/resume.

• Layer 4 Transport (Segment)
• In connectionless-mode, the Transport Layer provides the following functions
to support connectionless-mode transmission: (UDP)
• mapping between transport-addresses and network-addresses;
• mapping end-to-end transport-connectionless-mode transmissions on to network-
connectionless-mode transmissions;
• NOIB - There may be specific situations where performing conversion from connection-mode
to connectionless-mode operation in the Transport Layer can be justified and may thus be
permitted provided that this requires only limited extensions to existing protocols. In such
cases it is accepted that communication using such conversions can only take place betweeen
OSI end systems supporting them (see 6.4).
• end-to-end error detection and monitoring of the quality of service;
• transport-service-data-unit delimiting; and
• supervisory functions.

• Layer 3 Network (Packet) (IP)
• The following are functions performed by the Network Layer:
• routing and relaying;
• network-connections;
• network-connection multiplexing;
• segmenting and blocking;
• error detection;
• error recovery;
• sequencing;
• flow control;
• expedited data transfer;
• reset;
• service selection;
• mapping between network-addresses and data-link addresses;
• mapping network-connectionless-mode transmissions to data-link-connectionless-mode transmissions;
• converting from data-link-connection-mode service to network-connectionless-mode service;
• enhancing a data-link-connectionless mode service to provide a network-connection-mode service; and
• network layer management.

• Layer 2 Data Link (Frame) (Ethernet)
• In connection-mode, the facilities provided by the Data Link Layer are:
• data-link-addresses; (MAC Addresses)
• data-link-connection;
• data-link-service-data-units;
• data-link-connection-endpoint-identifiers;
• error notification;
• quality of service parameters; and (TOS bits)
• reset.
• In connectionless-mode, the facilities provided by the Data Link Layer are:
• data-link-addresses;
• transmission of data-link-service-data-units of a defined maximum size; and
• quality of service parameters.

• Layer 1 Physical (1000BaseSX)
• The functions provided by the Physical Layer are:
• physical-connection activation and deactivation;
• physical-service-data-unit transmission;
• multiplexing; and
• Physical Layer management.

• Homework
• What test are you studying for?
• Do you have daily goals?
• Have you signed up for, or take a class?
• Are you doing practice labs?
• Have you taken any practice tests?
• Have you scheduled your test?
• Everything is a training opportunity, USE IT!
• (On your dry erase, you can take notes on the questions you don’t know, and use this to
walk out with mental notes on what you need to study up on.)

• Thanks for watching!
• You can subscribe to my YouTube Channel
https://www.youtube.com/channel/UCZ3pcIh5Zmbp3rdjhfR7BOg
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• Or connect with me on Linkedin https://www.linkedin.com/in/david-
hedley-541985/
• You can suggest topics in the comments!

David Hedley's Tuesday Tech Talk OSI Model

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