The architecture of computer hardware and systems software an information technology approach ch15p2

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


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
Chapter 15

15.2-2


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

Chapter 15

15.2-3


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

Chapter 15

15.2-4


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









Application
Presentation
Session
Transport

Network
Data Link
Physical

15.2-5


Layers of the OSI Model

Chapter 15

15.2-6


OSI Physical Layer
 Responsible for transmission of bits
 Implemented primarily through
hardware
 Encompasses signaling method,
electrical and mechanical interfaces
 Example: RS-232, 10Base5

Chapter 15

15.2-7


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

Chapter 15

15.2-8


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

Chapter 15

15.2-9

OSI Transport Layer
 Ultimate final address of destination is determined
 All end-to-end communication including intermediate
nodes

Chapter 15

15.2-10


OSI Session Layer
 Establishes a dialogue between two
applications or processes between
systems
 Terminates connection at end of
session
 Manages logins, password
exchange, logoffs

Chapter 15

15.2-11


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
different email systems

Chapter 15

15.2-12


OSI Application Layer
• Provides utilities and tools for
application programs and users

Chapter 15

15.2-13


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
Chapter 15

15.2-14


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
Chapter 15

15.2-15


Comparison of OSI and TCP/IP

Chapter 15

15.2-16


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
Chapter 15

15.2-17


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
Chapter 15

15.2-18


Access for a Networked
Operating System

Chapter 15

15.2-19


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
Chapter 15

15.2-20