OSI ModelOSI Model

Uses of Computer Networks

B i A li ti• Business Applications• Home Applications• Mobile Users• Social IssuesSocial Issues

Business Applications of Networks

A network with two clients and one server.

Business Applications of Networks (2)

The client-server model involves requests and replies.

Home Network Applications

A i f i• Access to remote information• Person-to-person communication• Interactive entertainment• Electronic commerceElectronic commerce

Home Network Applications (2)

In peer-to-peer system there are no fixed clients and servers.

Home Network Applications (3)

Some forms of e-commerce.

Mobile Network Users

Combinations of wireless networks and mobile computing.

Network Hardware

• Local Area Networks• Local Area Networks• Metropolitan Area Networks• Wide Area Networks• Wireless Networks• Home Networks• Internetworks• Internetworks

Broadcast Networks

Types of transmission technologyB d t li k• Broadcast links

• Point-to-point linksp

Broadcast Networks (2)

Classification of interconnected processors by scale.

Local Area Networks

Two broadcast networks(a) Bus(a) Bus(b) Ring

Metropolitan Area Networks

A metropolitan area network based on cable TV.

Wide Area Networks

Relation between hosts on LANs and the subnet.

Wide Area Networks (2)

A stream of packets from sender to receiver.

Wireless Networks

i f i l kCategories of wireless networks:• System interconnectiony• Wireless LANs• Wireless WANs

Wireless Networks (2)

(a) Bluetooth configuration(b) Wireless LAN

Wireless Networks (3)

(a) Individual mobile computers(b) A flying LAN

Home Network Categories

• Computers (desktop PC, PDA, shared peripherals• Entertainment (TV, DVD, VCR, camera, stereo, MP3)• Telecomm (telephone, cell phone, intercom, fax)• Appliances (microwave, fridge, clock, furnace, airco)• Telemetry (utility meter, burglar alarm, babycam).y ( y g y )

Network Software

• Protocol Hierarchies• Design Issues for the Layers• Connection-Oriented and Connectionless Services• Service Primitives• The Relationship of Services to Protocolsp

Network SoftwareProtocol HierarchiesProtocol Hierarchies

Layers, protocols, and interfaces.

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The philosopher-translator-secretary architecture.

Protocol Hierarchies (3)

Example information flow supporting virtual communication in layer 5.

Design Issues for the Layers

• Addressing• Error Control• Flow Control• Multiplexing• Routing

Connection-Oriented and Connectionless S iServices

Six different types of service.

Service Primitives

Five service primitives for implementing a simple connection-oriented service.

Service Primitives (2)

Packets sent in a simple client-server interaction on a connection-oriented network.

Services to Protocols Relationship

The relationship between a service and a protocol.

Reference Models

• The OSI Reference Model• The OSI Reference Model• The TCP/IP Reference Model• A Comparison of OSI and TCP/IP • A Critique of the OSI Model and Protocols• A Critique of the TCP/IP Reference Model

Reference Models

The OSIThe OSI reference model.

Reference Models (2)

The TCP/IP reference model.

Open Systems Interconnection (OSI) is a set of internationally recognized, non-proprietary standards for networking and for

operating system involved in networking functionsoperating system involved in networking functions.

7 Layers

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LAYER 7 – The APPLICATION Layer

• The top layer of the OSI modelThe top layer of the OSI model

• Provides a set of interfaces for sending and i i li ti t i t dreceiving applications to gain access to and

use network services, such as: networked file transfer message handling and databasefile transfer, message handling and database query processing

• The application layer is responsible for providing services to the user.

LAYER 6 – The PRESENTATION Layer

• Manages data-format information for networked communications (th t k’ t l t )(the network’s translator)

• For outgoing messages, it converts data into a generic format for network transmission; for incoming messages, it converts data from ; g g ,the generic network format to a format that the receiving application can understand

• This layer is also responsible for certain protocol conversions dataThis layer is also responsible for certain protocol conversions, data encryption/decryption, or data compression/decompression

• A special software facility called a “redirector” operates at this layer to determine if a request is network related on not and forwardto determine if a request is network related on not and forward network-related requests to an appropriate network resource

• The presentation layer is responsible for translation, compression, d iand encryption.

LAYER 5 – The SESSION Layer

• Enables two networked resources to hold ongoing communications g g(called a session) across a network

• Applications on either end of the session are able to ex hange data f th d ti f th ifor the duration of the session

• This layer is:

R ibl f i i i i i i i d i i i• Responsible for initiating, maintaining and terminating sessions

• Responsible for security and access control to session information (via session participant identification)information (via session participant identification)

• Responsible for synchronization services, and for checkpoint services

LAYER 4 – The TRANSPORT Layer

• Manages the transmission of data across a networkg

• Manages the flow of data between parties by segmenting long data streams into smaller data chunks (based on allowed “packet” size for a given transmission medium)

• Reassembles chunks into their original sequence at the receiving end

• Provides acknowledgements of successful transmissions and t d f k t hi h i ithrequests resends for packets which arrive with errors

• The transport layer is responsible for the delivery of a message from one process to anotherof a message from one process to another

LAYER 3 – The NETWORK Layer

• Handles addressing messages for delivery, as well as translating g g y, glogical network addresses and names into their physical counterparts

R ibl f d idi h t t t i i b t• Responsible for deciding how to route transmissions between computers

• This layer also handles the decisions needed to get data from oneThis layer also handles the decisions needed to get data from one point to the next point along a network path

• This layer also handles packet switching and network congestion control

• The network layer is responsible for the delivery of individual packets from the source host to the destination hostpackets from the source host to the destination host.

LAYER 2 – The DATA LINK Layer

• Handles special data frames (packets) between the Network p (p )layer and the Physical layer

• At the receiving end, this layer packages raw data from the physical layer into data frames for delivery to the Network layer

• At the sending end this layer handles conversion of data into raw formats that can be handled by the Physical Layer

The data link layer is responsible for moving• The data link layer is responsible for moving frames from one hop (node) to the next

LAYER 1 – The PHYSICAL Layer

• Converts bits into electronic signals for outgoing messagesg g g g

• Converts electronic signals into bits for incoming messages

• This layer manages the interface between the the computer y g pand the network medium (coax, twisted pair, etc.)

• This layer tells the driver software for the MAU (media h i k i f d (NIC dattachment unit, ex. network interface cards (NICs, modems,

etc.)) what needs to be sent across the medium

• The bottom layer of the OSI modelThe bottom layer of the OSI model

• The physical layer is responsible for movements of individual bits from one hop (node) to the next.

Remember

A convenient aid for remembering the OSI layer names is to use the firstA convenient aid for remembering the OSI layer names is to use the first letter of each word in the phrase:

All People Seem To Need Data ProcessingAll People Seem To Need Data Processing