6 osi vimp

1

6. 6. Network ModelNetwork Model

ENG224

INFORMATION TECHNOLOGY – Part I6. Network Model

2

Why Network Protocol Models?

• Network communication is an extremely complex task

• Need cooperative efforts from all nodes involved

• A standard model helps to describe the task of a networking product or service

• Also help in troubleshooting by providing a frame of reference

ENG224


3

Who define Network Model?

• Need non-profit making organizations• ISO - International Standards Organization

e.g. OSI, MPEG-1, 2, 4, etc. (http://www.iso.ch/)

• IEEE - Institute of Electrical & Electronic

Engineers

e.g IEEE 802, IEEE 754, etc. (http://www.ieee.org)

• ITU - International Telecommunication Union

e.g. V.34, H.323, H.324, etc. (http://www.itu.int)

ENG224


4

The OSI 7-layer Model

All

People

Seem

To

Need

Data

Processing

Away

Pizza

Sausage

Throw

Not

Do

Please

• OSI - Open Systems Interconnection

• Defined in 1984 and become an international standard

ENG224


5

Layered Architecture

• Layering specifies different level of functions and services

• Each layer works with the layer below and above it

• Each layer provides services to next layer

• Shield the upper layer from the details of actual implementation

ENG224


6

Relationship of OSI layers

VirtualCommunication

PhysicalCommunication

ENG224


7

Protocols in a layered architecture

• Network communication is possible only if machines speaking the same languages (protocols)

• Since each layer work independently, each layer speaks different languages (protocols)

• Lead to the concept of a Protocol Stack

• Network communication is possible only if the Protocol Stacks on two machines are the same

ENG224


8

• To identify the language (protocol) of each layer, identifier (header and trailer) are added to data

ENG224


9

1. Physical Layer

• Define how cable is attached to the Network Adapter Card• How many pins in the connector?

• The impedance?

• Max/min electrical voltage?

• Responsible for transmitting bits from one computer to another

Example protocols: Ethernet, Token Ring (Physical part)

Appl.

Pres.

Sess.

Tran.

Netw.

Data.

Phys.

Appl.

Pres.

Sess.

Tran.

Netw.

Data.

Phys.

ENG224


10

2. Data Link Layer

• Make data frames

• Provide error-free frame transfer by acknowledgment and retransmission

Example protocols: Ethernet, Token Ring

Frame

Appl.

Pres.

Sess.

Tran.

Netw.

Data.

Phys.

Appl.

Pres.

Sess.

Tran.

Netw.

Data.

Phys.

ENG224


11

ENG224


12

3. Network Layer

• Logical address to physical address translation

For TCP/IP running on Ethernet

Logical address: IP address

158.132.148.99

Physical address: Ethernet address

00 00 E2 15 1A CA

• Determine the route from source to destination computer

Example protocols: IP, IPX

Appl.

Pres.

Sess.

Tran.

Netw.

Data.

Phys.

Appl.

Pres.

Sess.

Tran.

Netw.

Data.

Phys.

ENG224


13

ENG224


14

4. Transport Layer

• Ensure packets are delivered error free, in sequence

• Translate between packets and message

1 3 2

Receiving

1 2 3

Sending

Example protocols: TCP, SPX, NWLink

Appl.

Pres.

Sess.

Tran.

Netw.

Data.

Phys.

Appl.

Pres.

Sess.

Tran.

Netw.

Data.

Phys.

ENG224


15

5. Session Layer Example application program: Winsock, UNIX Socket

Appl.

Pres.

Sess.

Tran.

Netw.

Data.

Phys.

Appl.

Pres.

Sess.

Tran.

Netw.

Data.

Phys.

• Establishment, maintaining and release of session

• Provide dialog management

• Regulate which side transmit, when, for how long (Sync.)

• Provide synchronization between user tasks

ENG224


16

A. Consecutive sessions on a transport layer connection

1 2 3

B. Consecutive sessions on a multiple transport layer connections

1 2 3

What is a Session?

C. Both

1 2 3

ENG224


17

6. Presentation Layer Example application program: redirector (NT), SSL

Appl.

Pres.

Sess.

Tran.

Netw.

Data.

Phys.

Appl.

Pres.

Sess.

Tran.

Netw.

Data.

Phys.

• Translate data from Application Layer to the format suitable for session layer (the network)

• Provide data encryption, compression

• Changing or converting character set, graphic, and file format

ENG224


18

7. Application Layer Example protocols: FTP, Telnet, HTTP

• Entry point for application to access network

• Directly support user applications

• E.g. File transfer, email

• General capabilities:

Network access, flow control, Error recovery

Appl.

Pres.

Sess.

Tran.

Netw.

Data.

Phys.

Appl.

Pres.

Sess.

Tran.

Netw.

Data.

Phys.

ENG224


19

Example: File Transfer

PictureTel

Pic tur eTel

FTP ServerFTP Client

Network

• The most traditional network task

• Implemented by a simple Application Layer protocol called FTP

ENG224


20

Utility: WS_FTP

ENG224


21

FTP

TCP

IP

Ethernet

FTP

TCP

IP

Ethernet

PictureTelPictureTe l

FTP ServerFTP Client

WS_FTP

Layers 1,2

Layer 3

Layer 4

Layers 5-7

Layers 1,2

Layer 3

Layer 4

Layers 5-7

ENG224


22

The 802 Project Model

• IEEE launched the Project 802 in 1980 February

• Predate the ISO standard, but the development was performed in roughly the same time

• Objective: To clearly define the network standards for different kind of physical components of a network - the interface card and the cabling

• Enhance the Data Link and Physical layers of the OSI model

ENG224


23

IEEE 802 Categories 802.1 Internetworking 802.2 Logical Link Control (LLC)

802.3 Carrier-Sense Multiple Access with Collision Detection (CSMA/CD) LAN (Ethernet)

802.4 Token Bus LAN 802.5 Token Ring LAN

802.6 Metropolitan Area Network (MAN)

802.7 Broadband Technical Advisory Group 802.8 Fiber-Optic Technical Advisory Group

802.9 Integrated Voice/Data Networks

802.10 Network Security 802.11 Wireless Networks

802.12 Demand Priority Access LAN, 100 BaseVG-AnyLAN

ENG224


24

Enhancements to the OSI Model

• Divide the Data Link layer into 2 sub-layers

• Logical Link Control Sub-layer

• Define the use of service access points (SAPs) as an interface for higher layer to Data Link layer

• Media Access Control Sub-layer

• Directly interface with the network card

• For delivering error-free data communications

ENG224


25

Media AccessControl (MAC)

Logical Link Control (LLC)

802.3802.3 802.4802.4

802.5802.5 802.12802.12

802.2802.2

802.1802.1

ENG224


Documents

6 osi vimp