1. 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

2. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-2 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

3. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-3 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

4. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-4 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

5. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-5 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

6. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-6 Layers of the OSI Model

7. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-7 OSI Physical Layer  Responsible for transmission of bits  Implemented primarily through hardware  Encompasses signaling method, electrical and mechanical interfaces  Example: RS-232, 10Base5

8. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-8 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

9. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-9 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

10. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-10 OSI Transport Layer  Ultimate final address of destination is determined  All end-to-end communication including intermediate nodes

11. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-11 OSI Session Layer  Establishes a dialogue between two applications or processes between systems  Terminates connection at end of session  Manages logins, password exchange, logoffs

12. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-12 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

13. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-13 OSI Application Layer Provides utilities and tools for application programs and users

14. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-14 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

15. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-15 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

16. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-16 Comparison of OSI and TCP/IP

17. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-17 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

18. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-18 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

19. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-19 Access for a Networked Operating System

20. Chapter 15 The Internal Operating System – Part 2 – Networking 15.2-20 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