IT Applications Theory Slideshows - VCE IT Lecture Notes

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Oct 23, 2013 (3 years and 9 months ago)

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VCE IT Theory Slideshows

By Mark Kelly

Vceit.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


P
hysical


D
ata


N
etwork


T
ransport


S
ession


P
resentation


A
pplication

Mnemonic


P
hysical


Programmers


D
ata


Do


N
etwork


Not


T
ransport

Throw


S
ession


Stale


P
resentation

Pizza


A
pplication

Away

Mnemonic


P
hysical


Programmers


D
ata


Do


N
etwork


Not


T
ransport

Throw


S
ession


Stale


P
resentation

Pizza


A
pplication

Away

Layer by layer

Highest 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 layer

Highest 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


Physical

Data

Internet


Network

Transport


Transport

Application


Session

Presentation

Application

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 Kelly

mark@vceit.com




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VCE IT THEORY SLIDESHOWS