Sp09 MIS 460560 Chapter3 Part 1 OSI

8/10/2019 Sp09 MIS 460560 Chapter3 Part 1 OSI

1/25

Chapter 3

OSI 7 Layer Model


2/25

OSI 7 Layer Model

OSI 7 Layer model is an example of

taxonomy


3/25

Taxonomy

The science of classification

Scientific tool

Major categoriesof a phenomenon


4/25

Taxonomy

Examples

In biology animal science:

See

http://www.factmonster.com/ipka/A0776195

.html http://www.indianchild.com/animal_kingdom

.htm
http://www.factmonster.com/ipka/A0776195.htmlhttp://www.factmonster.com/ipka/A0776195.htmlhttp://www.indianchild.com/animal_kingdom.htmhttp://www.indianchild.com/animal_kingdom.htmhttp://www.indianchild.com/animal_kingdom.htmhttp://www.indianchild.com/animal_kingdom.htmhttp://www.factmonster.com/ipka/A0776195.htmlhttp://www.factmonster.com/ipka/A0776195.html


5/25

Taxonomy

In biology animal science:

There are billions of different kinds of living things (or organisms) on earth.To help study them, biologists have devised ways of naming andclassifying them according to their similarities and differences.

The system most scientists use puts each living thing into seven groups(or

taxons), organized from most general to most specific. Therefore, eachspecies belongs to a genus, each genus belongs to a family, each familybelongs to an order, etc.

From largest to smallest, these groups are:

Kingdom

Phylum

Class

Order

Family

Genus

Species


6/25

Taxonomy

Purposes:

Helping us understandcomplex phenomenon

Helping us explaincomplex phenomenon


7/25

OSI 7 Layer Model is a taxonomythat is widely used in networking


8/25

Networking is Complex

Complexprocess = involving a lot ofactivities


9/25

OSI (Open Systems Interconnection) Seven-LayerModel (OSI Model)

Taxonomy

Grouping networking activities into 7 majorgroups

Outlining of what it takes to send data fromone computer to another


10/25

OSI (Open Systems Interconnection)Seven-Layer Model

Mnemonic phrase: Please Do Not ThrowSausage PizzaAway

Layer 7 =Application Layer

Layer 6 = Presentation LayerLayer 5 = Session Layer

Layer 4 = Transport Layer

Layer 3 = Network LayerLayer 2 = Data Link Layer

Layer 1 = Physical Layer


11/25

This Picture Shows How OSI Model isUsed in Actual Data Communication

Packet

Frame

Packet

Frame


12/25

OSI (Open Systems Interconnection)Seven-Layer Model

Understand the sequenceof the activities

Networking activities performed in thesenders computer will also be performed inthe receivers computer in reverse

Understand the encapsulationand thedecapsulationof the message

OS (O S i ) S


13/25

OSI (Open Systems Interconnection) Seven-LayerModel

Layer 7: Application Layer(The first layer at the sender,the last layer at the receiver)

Taking command from the user (at the SENDER)

Executing the command (at the RECEIVER)

OSI (O S t I t ti ) S L


14/25


Layer 6: Presentation Layer

Converting the command from the format that is

used by the Application layer into the format thatcan be processed further by the lower layers ofthe OSI model (at the SENDER)

Converting the code that is received from thelower layers of the OSI model into the formatthat is used by the Application layer (at theRECEIVER)



15/25



Encryptinginformation that is received from the

Application layer (at the SENDER)

Decryptingencrypted information that is receivedfrom the lower layers of the OSI model (at the

RECEIVER)



16/25



Compressinginformation that is received from the

Application layer (at the SENDER)

Decompressingthe compressed information that isreceived from the lower layers of the OSI model (at the

RECEIVER)


17/25


Layer 5: Session Layer

Establishing connection, determining the type ofconnection, managing multiple connections, andterminating the connection

The types of connection

Full duplex: Two way, simultaneous

Half duplex: Two way, NOT simultaneous

Simplex: One way



18/25


Layer 4: Transport Layer

Breaking/disassemblinginformation into packets(segmentation) (at the SENDER)

Sequence numbering

Reassemblingpackets (at the RECEIVER)



19/25


Layer 3: Network Layer

Addingsource and destination logical addresses

(e.g., IP addresses) to each of the packets(at theSENDER)

Destination address: to allow the packet to be sent to the rightparty

Source address: to allow the receiver to contact the sender if

there is a problem with the packet received

Decapsulating the packets (at the RECEIVER)

OSI (Open S stems Inte connection) Se en La e


20/25


Layer 2: Data-Link Layer

Creatinga frame= packet + source and destinationphysical addresses(e.g., MAC address) + error

checking/detection information (e.g., Cyclic RedundancyCheck (CRC)) (at the SENDER)

Determiningwhich computer has access over thecommunication medium (at the SENDER)

Decapsulatingthe frames (at the RECEIVER)

OSI (Open Systems Interconnection) Seven Layer


21/25


Layer 1: Physical Layer

Converting the binary codeof the frame intoactual electrical signal/light/radio wave(at theSENDER

)

Converting the electrical signal/light/radio waveback into the binary codeof the frame (at theRECEIVER)

Physically sending the electricalsignal/light/radio wavefrom one computer toanother over communication medium

N t ki P t l (P t l)


22/25

Networking Protocol (Protocol)

Every activity(ies) in each layer must be performed based on certainrules (Protocol)

For two (or more) computers to exchange resources successfully, allcomputers must use the same (compatible) protocol

A set ofprotocols is called Protocol Suite/Protocol Stack

Example: TCP/IPis a protocol suite that governs networkingactivities in Network layer to Application layer. Ethernetis a protocol

suite that governs networking activities in Data Link layer to Physicallayer

For two (or more) computers to exchange resources, more than oneprotocol (even more than one protocol suite)must be used.

Why? No protocol controls all networking activities


23/25

OSI Seven-Layer Model and Protocol Suite(Protocol Stack)


24/25

Networking Protocol (Protocol)

OSI 7 layer model is also used to group:

Networking protocols (Protocols)

Application layer protocol:

Protocols that specify howApplication layer activitiesmust beperformed. Examples: Telnet, SMTP, POP3, FTP, NNTP, HTTP

Presentation layer protocol:

Protocols that specify how Presentation layer activitiesmust beperformed. Examples: Telnet, SMTP, POP3, FTP, NNTP, HTTP

And so on.


25/25

Benefits of OSI Seven-Layer Model

OSI Seven-Layer Model is a taxonomy to organize: Networking activities(processes) Networking protocols Network devices (technology)(hardware and software)

Example: Web browsertakes the command from the user (e.g.,www.uah.edu), uses a set of rules (i.e., HTTP) to compose arequest message, and then passes the request message to thelower layers of the OSI model. Because this activity/process, i.e.,taking the command from the user and passing it to the lowerlayers of the OSI model, is included in the Application layer, Webbrowseris considered to be Application layer software

Example: UTP cablecarries electrical signal carrying data fromone computer to another. Because this activity/process, i.e.,carrying electrical signal from one computer to another, is includedin the Physical layer, UTP cableis considered to be Physicallayer device

Documents

Sp09 MIS 460560 Chapter3 Part 1 OSI