Sp09 MIS 460560 Chapter3 Part 1 OSI
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Transcript of Sp09 MIS 460560 Chapter3 Part 1 OSI
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Chapter 3
OSI 7 Layer Model
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OSI 7 Layer Model
OSI 7 Layer model is an example of
taxonomy
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Taxonomy
The science of classification
Scientific tool
Major categoriesof a phenomenon
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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 -
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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
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Taxonomy
Purposes:
Helping us understandcomplex phenomenon
Helping us explaincomplex phenomenon
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OSI 7 Layer Model is a taxonomythat is widely used in networking
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Networking is Complex
Complexprocess = involving a lot ofactivities
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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
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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
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This Picture Shows How OSI Model isUsed in Actual Data Communication
Packet
Frame
Packet
Frame
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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
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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
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OSI (Open Systems Interconnection) Seven-LayerModel
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)
OSI (O S t I t ti ) S L
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OSI (Open Systems Interconnection) Seven-LayerModel
Layer 6: Presentation Layer
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)
OSI (O S t I t ti ) S L
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OSI (Open Systems Interconnection) Seven-LayerModel
Layer 6: Presentation Layer
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)
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OSI (Open Systems Interconnection) Seven-LayerModel
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
OSI (O S t I t ti ) S L
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OSI (Open Systems Interconnection) Seven-LayerModel
Layer 4: Transport Layer
Breaking/disassemblinginformation into packets(segmentation) (at the SENDER)
Sequence numbering
Reassemblingpackets (at the RECEIVER)
OSI (O S t I t ti ) S L
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OSI (Open Systems Interconnection) Seven-LayerModel
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
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OSI (Open Systems Interconnection) Seven-LayerModel
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
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OSI (Open Systems Interconnection) Seven-LayerModel
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)
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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
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OSI Seven-Layer Model and Protocol Suite(Protocol Stack)
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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.
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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