Internet and Intranet Fundamentals

Class 1Sessions A & B

Topics

• Background Material– Open Systems Interconnection (OSI)

Networking Model

Open Systems Interconnection Model

• Develop in early 80s – ISO - International Organization for

Standardization• ISO 7498

– ITU-T - International Telecommunications Union, Telecommunications Standards Sector

• CCITT Recommendation X.200• http://www.itu.int/

• Layered Model

Open Systems Interconnection Model

• Seven Layers– Application (S/W)– Presentation (S/W)– Session (S/W)– Transport (S/W)– Network (S/W and H/W)– Data Link (F/W and H/W)– Physical (H/W)

Open Systems Interconnection Model

• Each layer should– represent a different level of abstraction– perform a well-defined function– be developed with internationalization in mind– minimize information flow across its boundaries to

other layers– optimal number: enough layers to partition

functions well but small enough to remain tractable

OSI Application Layer

• Application and User Interfaces• File Transfer• E-Mail• Database Access• Program to Program Communication• http, ftp, gopher, smtp, telnet

OSI Presentation Layer• Data Transformations• Data Syntax• Syntax Conversion• Data Structure• Text Compression• SSL

– secure sockets layer– straddles this and next lower layer

OSI Session Layer

• Application Interface to Network• Establishing Connections• Session Control• Sometimes Merged with Transport Layer

OSI Transport Layer

• Host-to-Host Layer• Error Free End-to-End Connections

– virtual connections– doesn’t know about intervening routers

• TCP in TCP/IP• Often Implemented in Operating System

OSI Network Layer

• Communications Subnet Layer• Network Routing• Packets• Congestion and Flow Control• Accounting• IP in TCP/IP• Typically Implemented as I/O Driver

OSI Data Link Layer

• Breaks Up Input Data from Network Layer and Transmits as Data Frames

• Typically an Interface Card with Firmware– Ethernet card

• Acknowledgement• Error Handling

– Retransmission• Flow Control

OSI Physical Layer

• Transmits Raw Bits• Includes Communication Channel

– copper wire– fiber– microwave

• Signaling Levels– voltages, timing

• Pin Configurations

OSI Reference ModelApplication

Presentation

Session

Network

Transport

Data Link

Physical

Application

Presentation

Session

Network

Transport

Data Link

Physical

Network

Data Link

Physical

OSI vs. TCP/IP Models

Application

Presentation

Session

Network

Transport

Data Link

Physical

Application

Network

Transport

NetworkInterface

OSI TCP/IP