Chapter 15 – Part 2 Networks

Chapter 15 – Part 2 Networks

The Internal Operating System

The Architecture of Computer Hardware and Systems Software:

An Information Technology Approach 3rd Edition, Irv Englander

John Wiley and Sons 2003

Wilson Wong, Bentley College Linda Senne, Bentley College

Network Basics

 Communication paths

 Protocol standards

 Data transmission

 By character or byte at a time

 By sending the entire message at a time

 By subdividing the messages into packets and sending each packet at a time

 Frames are packets that have been further

subdivided to meet requirements of the media

Packet Header

 Also known as the preamble

 Contains

 Description of the packet

 Destination address of receiver

 Source address of sender

 Information about the data being sent

Advantages of Packets

 Reduces communication overhead

 Reasonable unit for routing of data

 Alternative to dedicating a channel for the entire length of the message

 Packets from several sources can share a single channel

 Each sender/receiver pair appears to have a channel to itself

 Receiving computer can process an entire block of

data instead of a character or byte at a time

OSI Reference Model

 Open Systems Interconnection Model

 Developed by International Standards Organization (ISO)

 Contains seven layers

 All People Seem To Need Data Processing

 People Do Not Through Sausage Pizza Away

 Application

 Presentation

 Session

 Transport

 Network

 Data Link

 Physical

Layers of the OSI Model

OSI Physical Layer

 Responsible for transmission of bits

 Implemented primarily through hardware

 Encompasses signaling method,

electrical and mechanical interfaces

 Example: RS-232, 10Base5

OSI Data Link Layer

 Responsible for error-free, reliable transmission of data

 Frames sized for compatibility with the MAC protocol

 Flow control, error detection and correction, retransmission

 Uses MAC addresses

OSI Network Layer

 Responsible for addressing and routing of messages to final destination

 Breaks up messages into frames that meet the requirements of intervening networks

 Local network – no routing

 Physical address is appended to each packet

 Symbolic addresses are converted to physical address through a lookup table

 External network – routing required

 External tables are used to assist in routing

OSI Transport Layer

 Ultimate final address of destination is determined

 All end-to-end communication including intermediate nodes

OSI Session Layer

 Establishes a dialogue between two applications or processes between systems

 Terminates connection at end of session

 Manages logins, password

exchange, logoffs

OSI Presentation Layer

 Provides format and code conversion services

 Examples

 File conversion from ASCII to Unicode

 Encryption, decryption

 Data reformatting

 Conversion between data formats used by

OSI Application Layer

• Provides utilities and tools for

application programs and users

TCP/IP

 Transmission Control Protocol/Internet Protocol

 Physical and Data Link layers are not specified by the TCP/IP protocol

 Internet Protocol

 Implemented in workstations and routers

 Messages are segmented into packets and are re- assembled at the other end

 Uses IP for addressing and routing between networks

 Transport

 Reliable end-to-end connectivity

TCP & UDP

 Most TCP/IP applications use TCP for transport layer

 TCP provides a connection (logical

association) between two entities to regulate flow check errors

 UDP (User Datagram Protocol) does not

maintain a connection, and therefore does not

guarantee delivery, preserve sequences, or

protect against duplication

Comparison of OSI and TCP/IP

Network Services

 Protocol Stacks

 Sockets

 Network file transfers

 Print services

 Web services

 Messaging services

 Application program access to network services

 RPC – remote procedure calls

 Security and network management services

 Remote processing and login services

Network File Transfers

 FTP

 Internet file transfer protocol

 Logical names for machine or drive

 Windows

 Network files can be accessed

transparently by being mounted directly

into the current file system

Access for a Networked

Operating System

Network Systems

 Distributed system

 Collection of independent computers that appear to the users of the systems as a single computer

 Client-Server system

 Control is centralized in the server computer

 Client computers have network access limited to services provided by the servers

 Peer-to-Peer system

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