VCE IT Theory Slideshows

By Mark KellyMcKinnon Secondary

CollegeVceit.com

With help from howstuffworks.com

The OSI Model

Open System Interconnection Reference Model

VCE Software Development

• SD U3O1 KK03 - a brief overview of the concept of the OSI model for network protocols

• SD U3O1 KK04 - purposes and functions of the physical layer (Layer 1) of the OSI and the relationship of the physical layer to the Transmission Control Protocol/Internet Protocol model

What is it?

• A set of seven layers that define the different stages that data must go through to travel from one device to another over a network.

• It’s a guideline for programmers and hardware developers to use

• Lets their products work predictably with other software and hardware in networks.

Like an assembly line

• Data travels through the layers• At each layer, data is handled to prepare it for

the next layer

Higher levels are more abstract and sophisticated. Lower levels are increasingly specific and ‘primitive’.

Thanks to howstuffworks.com

7 layers, two sets

• Application Set – Layer 7: Application – Layer 6: Presentation – Layer 5: Session

• Transport Set – Layer 4: Transport – Layer 3: Network – Layer 2: Data– Layer 1: Physical

Mnemonic

• Physical• Data• Network• Transport• Session• Presentation• Application

Mnemonic

• Physical• Data• Network• Transport• Session• Presentation• Application

Mnemonic

• Physical Programmers• Data Do• Network Not• Transport Throw• Session Stale• Presentation Pizza• Application Away

Mnemonic

• Physical Programmers• Data Do• Network Not• Transport Throw• Session Stale• Presentation Pizza• Application Away

Layer by layerHighest to lowest

• Application Set • The layers where application software works

Layer 7: Application

– Layer 7: Application - This layer actually interacts with the operating system or application

– E.g. when users transfer files, read messages or perform other network-related activities.

– The interface between end-user applications and communications software.

– Protocols such as Telnet, HTTP, FTP, and SMTP communicate at this layer.

Layer 6: Presentation

• Layer 6: Presentation - Layer 6 takes the data provided by the Application layer and converts it into a standard format that the other layers can understand.

• Handles encryption, formatting, compression, and presentation of data formats (such as JPEG) to applications.

• SSL and TLS communicate at this layer

Layer 5: Session• Establishes, maintains and ends

communication with the receiving device• responsible for the startup, control, and

teardown of sessions for the presentation layer.• handles all transport and data delivery issues to

other systems (a focus on error recovery and controlling data flow).

• TCP and UDP protocols reside at this layer.

Layer by layerHighest to lowest

• Transport• The layers where “behind the scenes”

technical work happens

Layer 4: Transport

• This layer maintains flow control of data and provides for error checking and recovery of data between the devices.

• Flow control means that the Transport layer takes data coming from more than one application and integrates each application's data into a single stream for the physical network.

Layer 3: Network

• The network layer determines the way that the data will be sent to the recipient device.

• Logical protocols, routing and addressing are handled here.

• responsible for routing, addressing, and determining the best possible route.

• ICMP, IP, ARP, and IPSEC reside at this layer.• IP addresses are found at this layer.

Layer 2: Data Link• In the data layer, the appropriate physical

protocol is assigned to the data. • The type of network and the packet

sequencing is defined.• links the data from one host to another• MAC addresses are found at this layer.• Ethernet, FDDI, ATM, and Token Ring reside at

this layer.

Layer 1: Physical• This is the level where actual hardware is

considered.• It defines the physical characteristics of the

network such as connections, voltage levels and timing.

• Provides the physical transportation of data. • Focuses on connectors, currents, pins, light, and

other specifications that define cabling standards. • This layer focuses on binary transmission.

Fregsample…

Putting the OSI to real work

• OSI is only a model• It does not actually do any work• Protocol stacks are actual software tools• They often combine several OSI layers into

one of the stack’s layers.• Like TCP/IP…

Protocol Stack

• A protocol stack is a group of protocols that all work together to allow software or hardware to perform a function.

• (For protocol information, see the Protocol slideshow)

TCP/IP protocol stack

• TCP/IP is a protocol stack.• It uses four layers that map to the OSI model

TCP/IP + OSI layer summary

• TCP/IP Layer 1: Network Interface• TCP/IP Layer 2: Internet• TCP/IP Layer 3: Transport• TCP/IP Layer 4: Application

TCP/IP + OSI layer summary

TCP/IP LAYER OSI LAYERS

Network Interface PhysicalData

Internet Network

Transport Transport

Application SessionPresentationApplication

TCP/IP + OSI layers

• Layer 1: Network Interface - combines the OSI Physical and OSI Data layers

• Routes data between devices on the same network.

• Manages the exchange of data between the network and other devices.

•

Huh?

• SD U3O1 KK04 - purposes and functions of the physical layer (Layer 1) of the OSI and the relationship of the physical layer to the Transmission Control Protocol/Internet Protocol model

• The importance of the relationship of the OSI physical layer and the TCP/IP model baffles me.

TCP/IP + OSI layers

• Layer 2: Internet - corresponds to the OSI Network layer.

• The Internet Protocol (IP) uses the IP address, consisting of a Network Identifier and a Host Identifier, to determine the address of the device it is communicating with.

TCP/IP + OSI layers

• Layer 3: Transport - Corresponding to the OSI Transport layer, this is the part of the protocol stack where the Transport Control Protocol (TCP) can be found.

• TCP works by asking another device on the network if it is willing to accept information from the local device.

TCP/IP + OSI layers

• Layer 4: Application - Layer 4 combines the Session, Presentation and Application layers of the OSI model.

• Protocols for specific functions such as e-mail (Simple Mail Transfer Protocol, SMTP) and file transfer (File Transfer Protocol, FTP) reside at this level.

• So, the TCP/IP protocols don’t have corresponding layers for each function in the OSI Model.

• But developers use the OSI model to ensure that a certain level of network compatibility is maintained.

A simple analogy

• Layer 7: Application

• Mr A of A Corporation wants to send a message to Mr B of B corporation. He picks up the phone and calls for his personal assistant (his PA).

Layer 6: Presentation

• The PA writes down the message in German (which Mr A speaks) into his notebook.

Layer 5: Session

• The PA rips off the page with the message and sends it to the mail room with its destination address attached.

Layer 4: Transport

• The mail room takes the page (along with many other messages from employees), checks that the address is present and sorts messages into departments.

Layer 3: Network

• The mail room manager decides how best to send the message - does it needs to go airmail, by container ship, express post, bicycle courier?

Layer 2: Data

• The mail room manager puts the message into a standard waterproof envelope with its destination and delivery rules written on it (e.g. does the message need to be signed for? Does it need to be delivered to the recipient in person? How urgent is it?). Tim, the bicycle courier is summoned, and told to deliver the envelope.

Layer 1: Physical

• Tim jumps on his bike and pedals madly across town to Corporation B, making constant decisions about steering, changing gear, jumping gutters and swerving to miss oncoming traffic.

• He arrives at the front door of Corporation B and hands over the envelope to the receptionist.

And now, the process reverses.Layer 1: Physical

• The receptionist at Corporation B gives the envelope to corporation B's mail manager, who opens the envelope to see where it needs to go in their building.

Layer 2: Data

• The mail manager sees that it needs to go to Mr B. He puts the message into a standard Corporation B inter-office memo envelope.

Layer 3: Network

• Mr B's office number is written on the envelope, which is then given to the work experience kid. The kid is told where the office is, that he is to keep left in the corridors, and not interrupt Mr B if he is in a meeting.

Layer 4: Transport

• The kid trots down the corridors, checking office numbers and making sure the envelope is not being damaged by his sweaty hands.

Layer 5: Session

• The kid arrives at Mr B's office, checks the authenticity of the ID badge of Mr B's secretary, gets the secretary to sign a receipt for the message, and hands the envelope over.

Layer 6: Presentation

• The secretary opens the envelope, takes out the page, translates it into French (which Mr B speaks) and puts it in Mr B's in-tray.

Layer 7: Application

• Mr B removes the translated message from his in-tray, reads it and thinks about its contents.

And so it ends

• Note how each step of the process is logically separated from the others. Each layer interacts only with the layers directly above and below. It does not need to know how the other layers work: it just do its own job within its own limited walls.

The end

• The courier does not know or care what's in the envelope: the only thing concerning him is physically getting it from A to B. Once it's delivered, his job is done.

The end

• Mr A and Mr B neither know nor care what sort of bike Tim was riding or what route he took; they only care that the message arrived safely and quickly.

• Each step in the process had its role in the efficient transfer of the information in the message. Like a factory production line...

By Mark KellyMcKinnon Secondary Collegevceit.com

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VCE IT THEORY SLIDESHOWS