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Protocol Interaction (ISO’s Open Systems Interconnection (OSI model)) the 7 layers

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The OSI (Open System Interconnection) Reference Model

Not UPS, but APS transport network data physically.

The OSI Reference Model

Created by the International Organization for standardization in the 70’s

Accepted world wide as standard for data network communications

An example of layered approach This allow changes at one layer not

affecting functions at other layers – encapsulation of implementation details

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3 + 4 division

The top three layers know nothing about the network

The bottom four layers handles about network communications.

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The Top Three

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The Bottom Four

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Data Encapsulation

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The Application Layer

Includes the following protocols: File Transfer Protocol (FTP) Hypertext Transfer Protocol (HTTP) Simple Mail Transfer Protocol (SMTP) Post Office Protocol, Version 3 (POP3) Internet Mail Access Protocol (IMAP) Simple Network Management Protocol

(SNMP) Domain Name System (DNS) Dynamic Host Configuration Protocol (DHCP)

The Application Layer

IE, an application, interacts with this layer to carry out FTP related operations

I can write an app using C#, IIS and Visual Studio 2012 that sends emials using SMTP library. If the SMTP service is available, the app can actually send the emails.

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The Presentation Layer

The presentation layer uses the following translation process:

1. The sender translates its abstract syntax to transfer syntax, such as encrypted data.

2. The sender transmits data to the receiver.

3. The receiver translates transfer syntax to it in abstract syntax.

Example, PC and Apple data formats conversion Other examples are Unicode, compression,

encryption/decryption, and multimedia data

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The Session Layer The two most important functions at

this layer are Dialog control

Two way alternate TWA Two way simultaneous TWS

Dialog separation For example, you have two browser

sessions connected to your bank account, this layer makes sure messages in this two sessions are not mixed up

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The Transport Layer Includes the following protocols:

Transmission Control Protocol (TCP) User Datagram Protocol (UDP) IPX NetWare Core Protocol (NCP) Sequenced Packet Exchange (SPX) 

Performs the following functions: Packet acknowledgment Data segmentation – different from Fragmenting Flow control (Figure 2.5 and 2.6) Error detection

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Connection-Oriented and Connectionless Protocols

Connection-Oriented (CO) Protocols

Connectionless (CL) Protocols

Require a handshake Do not require a handshake

Have larger headers and more overhead

Have smaller headers and less overhead

Provide packet acknowledgments, data segmentation, flow control, and error detection and correction

Do not provide additional services

Acknowledge transmitted packets, so they are considered reliable

Do not acknowledge transmitted packets, so they are considered unreliable

Example: TCP Example: UDP

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The Network Layer (level 3) Includes the following protocols:

Internet Protocol (IP and IP v6) Internetwork Packet Exchange (IPX) NetBIOS Extended User Interface (NetBEUI)

Performs the following functions: IP level Addressing Fragmenting (message size) Routing Protocol identification

Routing

Two types of packets: data and route-update It uses the routing table to determine where

to send One protocol per routing table (IP and IP v6

use different tables) It drops the packet if it cannot determine

where to send It does not forward broadcast messages ,

which can be used to build up the routing table

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Routing Example (figure 2.8)

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The Data-Link Layer

Includes the following protocols: Ethernet (10Base2, 10Base5, 10BaseT,

100BaseT, etc) Token Ring Fiber Distributed Data Interface (FDDI) Serial Line Internet Protocol (SLIP) Point-to-Point Protocol (PPP)

The selection of data-link layer protocols defines NIC and driver, cable, and hubs/switch

Mostly LAN level communications or between routers

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The Data-Link Layer (Cont.)

Includes the following protocol components: Frame format Media Access Control (MAC) mechanism Physical layer specifications (Coaxial cable

or UTP) Performs the following functions:

Hardware addressing (MAC address, 48 bits) Error detection Protocol identification

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The Physical Layer Defines the hardware elements of the

network, including The network medium How the network is installed The type of signaling 

Includes the following elements: Cables (UTP – EIA/TIA 568A

(Electronics/Telecommunications Industry Association))

Network interface adapters (also called network interface cards, or NICs)

Hubs

Encapsulation

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Encapsulation – steps

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Summary: The OSI Reference Model

OSI Model Layer

Function

Physical Defines the hardware elements and structure of the network installation

Data-link Provides addressing, data encapsulation, and media access control

Network Provides end-to-end routing and addressing

Transport Provides packet acknowledgment, flow control, and error detection

Session Provides dialog control and dialog separation

Presentation

Translates syntaxes between different systems

Application Provides an interface to applications running on the computer