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

Chapter 15 – Part 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 ... 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... 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... 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