Networking Fundamentals: OSI Model Layers and Protocols

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. 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

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 Chapter 15 The Internal Operating System – Part 2 – Networking

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 Chapter 15 The Internal Operating System – Part 2 – Networking

5. Open Systems InterconnectionModel 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 OSI Reference Model Chapter 15 The Internal Operating System – Part 2 – Networking

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

7. 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

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 Chapter 15 The Internal Operating System – Part 2 – Networking

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 Chapter 15 The Internal Operating System – Part 2 – Networking

10. 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

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 Chapter 15 The Internal Operating System – Part 2 – Networking

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 Chapter 15 The Internal Operating System – Part 2 – Networking

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

14. 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 TCP/IP Chapter 15 The Internal Operating System – Part 2 – Networking

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 Chapter 15 The Internal Operating System – Part 2 – Networking

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

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 Chapter 15 The Internal Operating System – Part 2 – Networking

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 Chapter 15 The Internal Operating System – Part 2 – Networking

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

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 Chapter 15 The Internal Operating System – Part 2 – Networking