计算机网络概论 英文版

• Internet provides a general purpose mechanism on which
– all services are built – and individual services are supplied by application programs that run on computers attached to the Internet
– Lost (i.e., never delivered) – Duplicated (more than one copy arrives) – Delivered out-of-order
• A programmer who uses the message paradigm must insure that the application operates correctly
– Multicast
• a message can be multicast to some of the computers on a network, 1-tomany
– Broadcast
• a message can be broadcast to all computers on a given network, 1-to-all
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3.2.2 Message Transport in the Internet
• Message service does not make any guarantees • So messages may be
Chapter 3
Internet Applications and Network Programming
© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.
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Topics Covered
• • • • • • • • • • • • • 3.1 Introduction 3.2 Two Basic Internet Communication Paradigms 3.3 Connection-Oriented Communication 3.4 The Client-Server Model of Interaction 3.5 Characteristics of Clients and Servers 3.6 Server Programs and Server-Class Computers 3.7 Requests, Responses, and Direction of Data Flow 3.8 Multiple Clients and Multiple Servers 3.9 Server Identification and Demultiplexing 3.10 Concurrent Servers 3.11 Circular Dependencies Among Servers 3.12 Peer-to-Peer Interactions 3.13 Network Programming and the Socket API
Computer Networks and Internets, 5e
By Douglas E. Comer
Lecture PowerPoints By Lami Kaya, LKaya@ieee.org
© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved. 1
• The message paradigm allows delivery in different forms:
– Unicast
• a message can be sent from an application on one computer directly to an application on another, 1-to-1
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Topics Cowk.baidu.comered
• • • • • • • • • 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 3.22 Sockets, Descriptors, and Network I/O Parameters and the Socket API Socket Calls in a Client and Server Socket Functions Used by Both Client and Server The Connection Function Used Only by a Client Socket Functions Used Only by a Server Socket Functions Used with the Message Paradigm Other Socket Functions Sockets, Threads, and Inheritance
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3.2 Two Basic Internet Communication Paradigms
• The Internet supports two basic communication paradigms:
– 3.2.1 Stream Transport in the Internet – 3.2.2 Message Transport in the Internet
• Later parts of the text provide the necessary information by explaining data communications and protocols used to form the Internet
© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.
• It is possible to devise new services without changing the Internet • Chapter covers two key concepts of Internet applications:
– describes the conceptual paradigm that applications follow when they communicate over the Internet – presents the details of the socket Application Programming Interface (socket API) that Internet applications use
• Figure 3.1 summarizes the differences
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3.2.1 Stream Transport in the Internet
– the network never delivers part of a message, nor does it join multiple messages together – if a sender places exactly n bytes in an outgoing message, the receiver will find exactly n bytes in the incoming message
– the network can choose to combine smaller blocks into one large block or can divide a large block into smaller blocks
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• • • • • • Stream denotes a paradigm in which a sequence of bytes flows from one application program to another Internet's mechanism arranges two streams between a pair of communicating applications, one in each direction The network accepts input from either application, and delivers the data to the other application The stream mechanism transfers a sequence of bytes without attaching meaning to the bytes and without inserting boundaries A sending application can choose to generate one byte at a time, or can generate blocks of bytes The network chooses the number of bytes to deliver at any time
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3.1 Introduction
• The Internet offers users a rich diversity of services
– none of the services is part of the underlying communication infrastructure
3.2.2 Message Transport in the Internet
• In a message paradigm, the network accepts and delivers messages • Each message delivered to a receiver corresponds to a message that was transmitted by a sender
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3.1 Introduction
• Internet application programmers can get started easily • It is possible to create Internet applications without knowing how networks operate
– However, understanding network protocols and technologies allows them to write efficient and reliable code that enables applications to scale across many sites