Today’s Objectives

Understand the OSI Model

Know the names of the 7 layers of the OSI model

Know about encapsulation

How do you describe networking?

• You use the OSI Reference Model

• What’s OSI?

Open System Interconnection

• OSI presents an abstract reference model to describe the computer communications.

More OSI Info

• Who made up the OSI?

• It was created by the International Organization for Standardization (ISO)

What is the OSI Reference Model?

• It is a conceptual framework specifying the network functions that occur at each layer

• It is a way of picturing how information travels through networks.

OSI Reference Model (standard)

• Any application process should be able to communicate freely with any any application process in any other computer that supports the same standards…

• The OSI Reference Model shows how this takes place.

OSI Reference Model

• The OSI reference model describes how data makes its way from application programs through a network medium to another application located on another computer on a network

• To accomplish this task data must travel from the application layer to the physical layer on one computer across the network media and from the physical layer to the application layer of another computer

Computer A Computer B

OSI Reference Model Layers

• The Application Layer provides services to application processes (such as electronic mail, file transfer, and terminal emulation) that are outside of the OSI model.

• The application layer identifies and establishes the availability of intended communication partners (and the resources required to connect with them), synchronizes cooperating applications, and establishes agreement on procedures for error recovery and control of data integrity.

OSI Reference Model

• The Presentation Layer ensures that information sent by the application layer will be readable by the application layer of the receiving system.

• The presentation layer is also concerned with the data structures used by programs and therefore negotiates data transfer syntax for the application layer.

OSI Reference Model

• The Session Layer establishes, manages, and terminates sessions between applications and manages data exchange between presentation layer entities

(Ensures Interhost communication)

OSI Reference Model

• The Transport Layer is responsible for reliable network communication between end nodes.

• The transport layer provides mechanisms for the establishment, maintenance, and termination of virtual circuits, transport fault detection and recover, and information flow control.

OSI Reference Model

• The Network Layer provides connectivity and path selection between two end systems.

• The network layer is the layer at which routing occurs.

OSI Reference Model• The Data Link Layer provides

reliable transit of data across a physical link.

• The data link layer is concerned with – physical addressing, – network topology, – line discipline, – error notification,– ordered delivery of frames, – flow control.

OSI Reference Model

• The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems

OSI Reference Model

Host Layers:}Media Layers:} Control physical delivery of

messages over a network

Provide accurate data delivery between computers

• As data moves down through the layers of the OSI model, headers are added.

Computer A

Computer B

• As data moves up through the layers of the OSI model, headers are removed.

OSI Reference Model

• There are other models by different vendors

• Most vendors use the OSI Model

• OSI is conceptual other than tangible

• Used to educate how networks function at each layer

What does the OSI Model do?

• It reduces complexity (from one big problem to 7 small ones)

• It standardizes interfaces

• It facilitates modular engineering

• It assures interoperable technology

• Accelerates evolution

• Simplifies teaching & learning

Review Time!

• Divide into two groups

• Play Jeopardy

• Bonus answer is the layer number

Jeopardy Review

• This layer of the OSI model provides services to application processes and identifies and establishes the availability of intended communication partners, synchronizes cooperating applications and establishes agreement on procedures for error recovery and control of data integrity.

15 pts

What is the APPLICATION LAYER of the OSI?

Layer 1 (add 3 pts)

Jeopardy Review

• This layer of the OSI model is responsible for reliable network communications between end nodes. It also provides mechanisms for the establishment, maintenance, and termination of virtual circuits and information flow control.

10 pts

What is the TRANSPORT LAYER of the OSI?

Layer 4 (add 5 pts)

Jeopardy Review

• This layer of the OSI model establishes, manages, and terminates sessions between applications and manages data exchange between layer entities.

15 pts

What is the SESSION LAYER of the OSI?

Layer 5 (add 3 pts)

Jeopardy Review

• This layer of the OSI model defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between systems.

10 pts

What is the PHYSICAL LAYER of the OSI?

Layer 1 (add 5 pts)

Jeopardy Review

• This layer of the OSI model provides connectivity and path selection between two end systems. It is also the layer at which routing occurs.

15 pts

What is the NETWORK LAYER of the OSI?

Layer 3 (add 3 pts)

Jeopardy Review

• This layer of the OSI model is concerned with physical addressing, network topology, line discipline, error notification, ordered delivery of frames, and flow control.

10 pts

What is the DATA LINK layer of the OSI?

Layer 2 (add 5 pts)

Jeopardy Review

• This layer of the OSI model ensures that information sent by the application layer will be readable by the application layer of another system.

15 pts

What is the PRESENTATION LAYER of the OSI?

Layer 6 (add 3 points)

Jeopardy Review

• Headers and trailers are added to data as it moves from a source to a destination.

15 pts

What is ENCAPSULATION?