Riassunto
Packet switching has emerged as a telecommunications technique with unlimited potential. Because it permits communications resources to be used at utmost efficiency, packet switching can adapt to a wide range of user services and user demands. Public packet switching networks have been built or are planned in more than 20 countries around the world, and numerous private and experimental networks are currently using packet switching. Presently packet switching is used primarily in connection with computer and data communication. However, its effectiveness for voice, video, and other wideband telecommunications services has been demonstrated, and as advanced data processing techniques improve the computer processors that form the heart of the packet switches, this application of the technique will undoubtedly become widespread. This book explains how packet networks operate, how they compare to alternative techniques, and how the many options in the design and use of packet networks are interrelated. The needs of both suppliers and users of packet net- works are addressed throughout the book, particularly because one's viewpoint can have a significant impact on design choices.
Contenuti
One What is a Packet?.- 1. To Switch or Not to Switch.- What Is Packet Switching?.- Why Use a Switched Network?.- Summary.- Suggested Readings.- 2. Packet Switching in a Telephone World.- Switching through the Telephone.- Transparent and Transactional Switching.- Approaches to Switching Compared.- Data Communications versus Voice Communications.- Data Call Statistics.- The Why and Where of Packet Switching.- Summary.- Suggested Readings.- 3. Circuit Switching/Message Switching/Packet Switching—A Quick Comparison.- Circuit Switching.- Message Switching.- Packet Switching.- Circuit Switching of Data—Advantages and Disadvantages.- Message Switching of Data—Advantages and Disadvantages.- Packet Switching of Data—Advantages and Disadvantages.- Summary 38 Suggested Readings.- 4. Getting Started with Network Basics.- The Network Environment.- The Example of the Public Telephone Network.- The Network User and the Network Supplier—Two Sides of the Coin.- Design Considerations.- Summary.- Suggested Readings.- 5. What Is an Erlang? An Introduction to Telecommunications Traffic Engineering.- Statistical Behavior of Network Users.- Traffic and User Satisfaction.- Blocking, Lines, and Erlangs.- Networks with Storage and Delay Instead of Blocking.- Capacity of Networks—Some Examples.- Summary.- Suggested Readings.- 6. Quantitative Tradeoffs—Packet, Circuit, and Message Switching.- Packet Switching—Operational Detail and Possible Faults.- Packet Switching—Overhead Structure Fundamentals.- Delay Comparison—Ideal Case.- Data Traffic Impact on Processor Loading.- Overhead in Circuit Switching and Packet Switching.- A Nationwide Data Network.- Summary.- Suggested Readings.- Two Operational Protocols—Packet Switching In Networks.- 7. Protocol Structures in Packet Switched Networks.- Types of Network Protocols.- The International Standards Organization (ISO) Protocol Hierarchy.- The ARPANET Approach to Protocols.- Virtual Circuit.- Datagrams.- Two Classes of Terminals.- Summary.- Suggested Readings.- 8. The User-Network Interface—The X.25 Standard.- The Packet-Switched Network User’s Perspective.- The X.25 Protocol—Level 3 Features and Facilities.- User Actions under the X.25 Protocol.- Summary.- Suggested Readings.- 9. Control and Monitoring in a Network—Some Considerations.- The Role of Control.- Network Control Centers for Packet Networks.- Summary.- Suggested Readings.- Three Packet Networks in the Real World-Topology, Routing, Robustness, and Some Lucky Guesses.- 10. Topological Principles—Some Tricks to Make Packet Switching Work Better.- Alternative Topological Structures.- The General Topological Design Problem.- Desirable Topological Features for Packet Switching.- Summary.- Suggested Readings.- 11. Network Design Case Example—Even a Bad Guess Is Better Than None.- The Network Design Requirements.- The Impact of Topology and Data Rate on Network Resources.- Detailed Requirements and Bad Guesses.- Summary.- Suggested Readings.- 12. Routing in Packet Networks.- Alternative Routing Methods.- Advantages and Disadvantages of Routing Methods.- Approaches to Adaptive Directory Routing.- Summary.- Suggested Readings.- Four Packet Switching Without Packet Switches.- 13. Resource Sharing and Multiple Access Techniques.- The General Problem of Communications Resource Sharing.- The Satellite-Based ALOHA Technique.- The Network Aspect of the Packet Broadcast Channel.- Capacity and Delay of the ALOHA Channel.- ALOHA Channel Delay Characteristics.- Summary.- Suggested Readings.- 14. Improvements on the Basic ALOHA Channel—Slots and Reservations.- Increasing the Capacity of the Packet Broadcast Channel.- The Slotted ALOHA Channel.- Slotted ALOHA Channel with Capture.- Packet Broadcast Channels with Capacity Reservation.- Highlight Comparison of Multiple Access Techniques.- Summary.- Suggested Readings.- 15. Terrestrial Packet Radio Systems.- Terrestrial Repeaters and Local Networks.- Carrier Sense Multiple Access—Listen Before You Send.- Summary.- Suggested Readings.- 16. Combination of Satellite and Terrestrial Connectivity—The General Optimization Problem.- Serving Users without Dedicated Earth Stations—The General Problem.- Deriving the Optimum Value of the Number of Earth Stations.- Applications and Examples of the Random Network Analysis.- Summary.- Suggested Readings.- Five Data Networks, Packet Switching, and the Common Carriers.- 17. The Carrier Marketplace.- Common Carrier Services and Facilities.- Common Carriers in the United States.- Summary.- Suggested Readings.- 18. Value-Added Networks (VANs) and Packet Switching.- Public Networks and the Role of VANs.- The Telenet Packet Switched Network.- The Tymnet Nationwide Data Network.- Worldwide Packet Switching Services.- Summary.- Suggested Readings.- 19. A Tariff for Every Occasion.- A Sample of Common Carrier Communications Tariffs.- A Current and Future Tariff Cost Model.- Summary.- Suggested Readings.- 20. Some New Common Carrier Prospects.- Some Proposed New Telecommunications Services.- AT&T’s Advanced Communications Service (ACS).- The Nationwide Network of Satellite Business Systems (SBS).- The Xerox Telecommunications Network (XTEN).- ACS, SBS, and STEN Compared.- Summary.- Suggested Readings.- Six Integrated Networks and the Future of Packet Switching.- 21. Hybrid Techniques: Combining Circuit and Packet Switching.- Classification of Information and Switching Techniques.- Approaches to Integrating Circuit and Packet Switching.- The Master Frame Approach to Integrated Switching.- Summary.- Suggested Readings.- 22. Integrated Services Networks.- Voice Digitization.- General Structure of Integrated Services Packet Switched Networks.- Cost/Performance Analysis.- Summary.- Suggested Readings.- 23. The Outlook for Packet Switching—And What to Do about It.
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