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Computer Networks and Internets
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Internet Growth
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What a Network Include
• Transmission hardware
• Special-purpose hardware device
– Interconnect transmission media
– Control transmission
– Run protocol software
• Protocol software
– Encodes and format data
– Detects and corrects problems
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What a Network Does
• Provide communication that is
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Reliable
Fair
Efficient
Secure
From one application to another
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What a Network Does – Con’t
• Automatically detect and corrects
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Data corruption
Data loss
Duplication
Out-of-order delivery
• Automatically finds optimal path from source
to destination
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Ping program
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Ping Program – Con’t
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Traceroute Program
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Network Programming
• Network allows arbitrary applications to
communicate
• Programmer does not need to understand
network technologies
• Network facilities accessed through an
Application Program Interface
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Basic Paradigm for Internet
Communication
• Establish contact
• Exchange data (bi-directional)
• Terminate contact
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Establishing Contact
• Performed by pair of applications
• One application starts and wait for contact
(called server)
• Other applications initiate contact (called
client)
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Representations and Translations
• Humans use names such as:
– www.netbook.cs.purdue.edu (computer)
– ftp (applications)
• Network protocols require binary values
• Library routines exist to translate from names
to numbers
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Example API
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Illustration of API Calls
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Definition of the API
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connection await_contact (appnum a)
connection make_contact (computer c, appnum a)
appnum appname_toappnum(char* a)
computer cname_to_comp(char* a)
int send(connection con, char* buffer, int length, int
flags)
• int recv(connection con, char* buffer, int length, int
flags)
• int recvln(connection con, char* buffer, int length)
• int send_eof(connection con)
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Summary of Example API
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Illustration of Echo Application
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Examples
• echoserver.c and echoclient.c
• chatserver.c and chatclient.c
• webclient.c and webserver.c
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Summary
• Studying networks is important because
– The world is interconnected
– Applications now operate in a distributed
environment
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