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

Chapter 15 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 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

Chapter 15 The Internal Operating System – Part 2 – Networking Layers of the OSI Model

Chapter 15 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking OSI Transport Layer  Ultimate final address of destination is determined  All end-to-end communication including intermediate nodes

Chapter 15 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 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 systems

Chapter 15 The Internal Operating System – Part 2 – Networking OSI Application Layer Provides utilities and tools for application programs and users

Chapter 15 The Internal Operating System – Part 2 – Networking 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  Final delivery of packets  Application

Chapter 15 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking Comparison of OSI and TCP/IP

Chapter 15 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking Access for a Networked Operating System

Chapter 15 The Internal Operating System – Part 2 – Networking 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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