day 1.3 OSI-Reference

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OSI Reference Model:

OSI Reference Model

How to Remember:

All - Application People - Presentation Seems - Session To - Transport Need of - Network Data - Data Link Processing - Physical How to Remember

Why a Layered Network Model?:

Why a Layered Network Model? 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical Reduces complexity (one big problem to seven smaller ones) Standardizes interfaces Simplifies teaching and learning

Devices Function at Layers:

Devices Function at Layers 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical NIC Card

Host Layers:

Host Layers 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical Host layers: Provide accurate data delivery between computers }

Media Layers:

Media Layers 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical Host layers: Provide accurate data delivery between computers Media layers: Control physical delivery of messages over the network } }

Application Layer:

Application Layer Provides network services to application processes (such as electronic mail, file transfer, and terminal emulation) 7 Application

Presentation Layer :

Presentation Layer Network services to applications Ensures data is readable by receiving system Format of data Negotiates data transfer syntax for application layer 7 Application 6 Presentation Data representation

Session Layer :

Session Layer Inter-host communication Establishes, manages, and terminates sessions between applications 7 Application 6 Presentation 5 Session Network services to applications Data representation

Transport Layer:

Transport Layer 7 Application 6 Presentation 5 Session Transport 4 Inter-host communication Network services to applications Data representation End-to-end connection reliability Concerned with data transport issues between hosts Data transport reliability Establishes, maintains, and terminates virtual circuits Fault detection and recovery Information flow control

Network Layer:

Network Layer 7 Application 6 Presentation 5 Session Transport 4 Network 3 Inter-host communication Network services to applications Data representation End-to-end connection reliability Addresses and best path Provides connectivity and path selection between two end systems Domain of routing

Data Link Layer :

Data Link Layer 7 Application 6 Presentation 5 Session Transport 4 Network 3 Data Link 2 Inter-host communication Network services to applications Data representation End-to-end connection reliability Addresses and best path Access to media Provides reliable transfer of data across media Physical addressing, network topology, error notification, flow control

Physical Layer:

Physical Layer 7 Application 6 Presentation 5 Session Transport 4 Network 3 Data Link 2 Physical 1 Inter-host communication Network services to applications Data representation End-to-end connection reliability Addresses and best path Access to media Binary transmission Wires, connectors, data rates

Communications:

7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical Host A Communications Application Presentation Session Transport Network Data Link Physical Bits Frames Packets Segments Host B

Data Encapsulation:

Data Encapsulation Application Presentation Session Transport Network Physical Data Link Application Presentation Session Transport Network Physical Data Link Host A Host B Data } {

Data Encapsulation:

Data Encapsulation Application Presentation Session Transport Network Physical Data Link Application Presentation Session Transport Network Physical Data Link Data } { Data Network Header Host A Host B

Data Encapsulation:

Data Encapsulation Application Presentation Session Transport Network Physical Data Link Application Presentation Session Transport Network Physical Data Link Data } { Data Network Header Frame Header Frame Trailer Data Network Header Host A Host B

Data Encapsulation:

Data Encapsulation Application Presentation Session Transport Network Physical Data Link Application Presentation Session Transport Network Physical Data Link Data } { Data Network Header Frame Header Frame Trailer Data Network Header 0101101010110001 Host A Host B

Layers 1 & 2: Physical & Data Link Layers:

Layers 1 & 2: Physical & Data Link Layers

MAC Address:

MAC Address 24 bits ROM RAM 24 bits 0000.0c12. 3456 Serial Number Vendor Code MAC address is burned into ROM on a network interface card

Layer 3: Network Layer:

Layer 3: Network Layer © 1999, Cisco Systems, Inc. www.cisco.com

Network Layer: Path Determination:

Network Layer: Path Determination Which Path? Which Path? Layer 3 functions to find the best path through the internetwork

Layers 4–7: Transport, Session, Presentation, and Application Layers:

Layers 4–7: Transport, Session, Presentation, and Application Layers

Transport Layer:

Segments upper-layer applications Establishes an end-to-end connection Sends segments from one end host to another Optionally, ensures data reliability Transport Layer

Transport Layer— Establishes Connection:

Transport Layer— Establishes Connection Synchronize Synchronize Acknowledge Negotiate Connection Receiver Data Transfer Connection Established (Send Segments) Sender

Transport Layer— Sends Segments with Flow Control:

Transport Layer— Sends Segments with Flow Control Transmit Buffer Full Not Ready Stop Process Segments Buffer OK Ready Go Resume Transmission Receiver Sender

Transport Layer— Reliability with Windowing:

Transport Layer— Reliability with Windowing • Window Size = 1 Sender Send 1 Receive 1 Receiver Ack 2 Send 2 Receive 2 Ack 3 Sender Send 1 Send 2 Receive 1 Receive 2 Receiver • Window Size = 3 Send 3 Receive 3 Ack 4 Send 4

Transport Layer— An Acknowledgement Technique:

Transport Layer— An Acknowledgement Technique Sender Receiver Send 2 Send 1 Send 3 Ack 4 Send 5 Send 4 Send 6 Ack 5 Send 5 Ack 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7

Transport to Network Layer:

Transport to Network Layer End-to-End Segments Routed Packets

Session Layer:

Coordinates applications as they interact on different hosts Session Layer Network File System (NFS) Structured Query Language (SQL) Remote-Procedure Call (RPC) AppleTalk Session Protocol (ASP) DEC Session Control Protocol (SCP) Service Request Service Reply

Presentation Layer:

Provides code formatting and conversion for applications Presentation Layer ASCII EBCDIC Encrypted • Text • Data login: PICT TIFF JPEG GIF • Graphics • Visual images • Sound • Video MPEG QuickTime MIDI

Application Layer:

User Interaction Application Layer Word Processor Presentation Graphics Spreadsheet Database Design/Manufacturing Project Planning Others COMPUTER APPLICATIONS Electronic Mail File Transfer Remote Access Client-Server Process Information Location Network Management Others NETWORK APPLICATIONS INTERNETWORK APPLICATIONS Electronic Data Interchange World Wide Web E-Mail Gateways Special-Interest Bulletin Boards Financial Transaction Services Internet Navigation Utilities Conferencing (Voice, Video, Data) Others

Summary:

OSI reference model describes building blocks of functions for program-to-program communications between similar or dissimilar hosts Layers 4–7 (host layers) provide accurate data delivery between computers Layers 1–3 (media layers) control physical delivery of data over the network Summary