Chapter 15 Part 2 Networks The Internal

Chapter 15 – Part 2 Networks The Internal Operating System The Architecture of Computer Hardware and Systems Software: An Information Technology Approach 3 rd 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 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking § § § § Application Presentation Session Transport Network Data Link Physical 5

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

OSI Physical Layer § Responsible for transmission of bits § Implemented primarily through hardware § Encompasses signaling method, electrical and mechanical interfaces § Example: RS-232, 10 Base 5 Chapter 15 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 9

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 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 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 12

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

Comparison of OSI and TCP/IP Chapter 15 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 18

Access for a Networked Operating System Chapter 15 The Internal Operating System – Part 2 – Networking 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 The Internal Operating System – Part 2 – Networking 20