Transcript Inside and Outside the OS

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
access control hardware protocol
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Packet Header
 Also known as the preamble
 Contains
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Description of the packet
Destination address of receiver
Source address of sender
Information about the data being sent
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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
 Simplifies synchronization of the sending and
receiving systems by providing clear start and stop
points
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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
Chapter 15
The Internal Operating System – Part 2 – Networking
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Application
Presentation
Session
Transport
Network
Data Link
Physical
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Layers of the OSI Model
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OSI Physical Layer
 Responsible for transmission of bits
 Implemented primarily through
hardware
 Encompasses signaling method,
electrical and mechanical interfaces
 Example: RS-232, 10Base5
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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
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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
message
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OSI Transport Layer
 Ultimate final address of destination is determined
 All end-to-end communication including intermediate
nodes
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OSI Session Layer
 Establishes a dialogue between two
applications or processes between
systems
 Terminates connection at end of
session
 Manages logins, password
exchange, logoffs
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OSI Presentation Layer
 Provides format and code conversion
services
 Examples
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File conversion from ASCII to Unicode
Encryption, decryption
Data reformatting
Conversion between data formats used by
different email systems
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OSI Application Layer
• Provides utilities and tools for
application programs and users
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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 reassembled at the other end
 Uses IP for addressing and routing between networks
 Transport
 Reliable end-to-end connectivity
 Final delivery of packets
 Application
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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
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Comparison of OSI and TCP/IP
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Network Services
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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
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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
 Unix / Linux
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Access for a Networked
Operating System
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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
 Any two computers can communicate with one
another within security constraints
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The Internal Operating System – Part 2 – Networking
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Copyright 2003 John Wiley & Sons
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