networking (1) dr. andy wu bcis 4630 fundamentals of it security
DESCRIPTION
OSI Layers 3TRANSCRIPT
NETWORKING (1)
Dr. Andy Wu
BCIS 4630 Fundamentals of IT Security
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OSI Model• Network communications protocols are developed using the
Open System Interconnection (OSI) model.• An ISO standard for worldwide communications. • The OSI model defines a framework for implementing
protocols in seven distinct layers.• Each layer makes use of the services of the layer below it to
provide a set of specific services to the layer above it. • Adjacent layers communicate with each other through a well-
defined interface, so that in principle, we could change one layer or even completely rewrite it without affecting the others.
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OSI LayersLayer Function Examples
Application User interfaceProgram level communication
HTTP, SMTP
Presentation Presentation format of dataData conversion if needed
ASCII, JPEG, MP3, Encryption
Session Establish and maintain communication channels OS, Application access scheduling
Transport Reliable or unreliable end-to-end communicationIdentifies upper layer processes that will receive data
TCP, UDP, SPX
Network Logical addressing and routingDelivering packets from source to destination
IP, IPX
Data Link Transforming physical layer into a reliable link and presenting it to upper layersIncludes MAC (802.3) and LLC (802.2) sublayers
Ethernet
Physical Transmission of bit stream over physical mediumSignaling
EIA/TIA 568B
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OSI Mnemonic
Away Application
Pizza Presentation
Sausage Session
Throw Transport
Not Network
Do Data Link
Please Physical
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Encapsulation• When data is passed down from higher
layers to lower ones, each layer creates its header and places the data given to it by the next-higher layer behind its own header, thereby encapsulating the higher layer’s data.
• The Data Link layer also creates a trailer.
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Encapsulation – Layer 4
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Encapsulation – Layer 3
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Encapsulation – Layer 2
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Network Communication
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Decomposition – Layer 2
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Decomposition – Layer 3
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Decomposition – Layer 4
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Protocol Data Unit• A term that describes a set of bytes that includes the layer’s header and
trailer (if any) and all data encapsulated.• From Layer X’s perspective, the higher-layer headers and the user data
form one large data field.
Layer(s) PDU
Application, Presentation, Session Data
TransportTCP SegmentUDP Datagram
Network IP Packet
Data Link Frame
Physical Bit