SDSU CS 580 Client-Server Programming
Fall Semester, 2002
Networks
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San Diego State University -- This page last updated 23-Sep-02

Contents of Doc 8, Networks


References


Dr. Vinge's CS580 class notes, Spring 2000, http://www-rohan.sdsu.edu/faculty/vinge/courses/spring00/cs580/

Unix Network Programming by W. Richard Stevens, 1990, selected pages

Internetworking with TCP/IP Volume 1 Principles, Protocols, and Architecture, Third Edition, by Douglas E. Comer, selected pages

Computer Networks and Internets, Comer, 1997


Doc 8, Networks Slide # 2

Networks


Communication Network
A set of communication nodes that are interconnected to permit the exchange of information


Doc 8, Networks Slide # 3

How information is transmitted in a network


Information is transformed into electrical or optical signals

All signals are corrupted during transmission

Transmission adds noise to the signal

Digital data helps over come noise
Slightly corrupted 1's are distinguishable from slightly corrupted 0's
Digital data allows for error-control

Dynamic data like audio or video normally requires continuous transmission


Doc 8, Networks Slide # 4
Packets

Stream of bits is divided into separate packets

Kermit Packet Structure




Doc 8, Networks Slide # 5

Classes of Communication Services


End-to-end services as seen by the users:

Synchronous communications
Bit stream is delivered with a fixed delay and given error rate
Each bit reaches the destination with the same time delay after leaving the source

Asynchronous communications
Bit stream is divided into packets
Packets are received with varying delays, so packets can arrive out of order
Some packets are not received correctly
Connection-oriented
Packets are delivered in order
System confirms delivery and put packets in order
Error free
Connectionless
Packets are treated individually
Program has to worry about order, error and lost packets
Expedited Data
Faster delivery than normal


Doc 8, Networks Slide # 6

Our View of Network Communication with TCP/IP


TCP - Connection-oriented

UDP - Connectionless

TCP gives us a "pipe" between machines to allow us to send messages between machines

UDP

Fast

Client & Server must handle

Used by:



Doc 8, Networks Slide # 7
TCP

Handles

Receiver acknowledges each packet

Sender resends packet if it is lost

TCP has delays in


Doc 8, Networks Slide # 8
Addresses and Names

IP address is currently a 32-bit number

   130.191.3.100      (Four 8 bit numbers)

IPv6 uses 128 bit numbers for addresses

   105.220.136.100.0.0.0.0.0.0.18.128.140.10.255.255
   69DC:8864:0:0:0:1280:8C0A:FFFF
   69DC:8864::1280:8C0A:FFFF

Machines on a network need a unique IP address


Doc 8, Networks Slide # 9
127.0.0.1 (localhost)

Common loopback address

Refers to the current computer

Messages sent to 127.0.0.1 to not reach the network


Doc 8, Networks Slide # 10
Domain Name System (DNS)

Maps machine names to IP addresses
rohan.sdsu.edu <-> 130.191.143.100



Unix "host" command

Shows mapping between machine names and IP address
->host rohan.sdsu.edu
rohan.sdsu.edu has address 130.191.3.100
->host 130.191.3.100
100.3.191.130.IN-ADDR.ARPA domain name pointer rohan.sdsu.edu


Doc 8, Networks Slide # 11
Top Level DomainsCurrent TLD
Domain Names
Meaning
COM
Commercial organizations
EDU
Educational institutions
GOV
Government institutions
MIL
Military groups
NET
Major network support groups
ORG
Organizations not list above
ARPA
obsolete
INT
International organizations
CN,IN,MX,US
http://www.iana.org/domain-names.htm

More top level domains will be added later this year

Internet Corporation for Assigned Names and Numbers (ICANN http://www.icann.org/) oversees assigning TLDs

Doc 8, Networks Slide # 12

Ports


TCP/IP supports multiple logical communication channels called ports

Ports are numbered from 0 - 65536

A connection between two machines is uniquely defined by:

the protocol (TCP or UDP)
the IP address of local machine
the port number used on the local machine
the IP address of remote machine
the port number used on the remote machine

reserved port numbers1 - 1023
port numbers used by system1024 - 5000



Doc 8, Networks Slide # 13
Some Interesting Server Port Numbers
Service
Port Number
echo
7
discard
9
character generation
19
daytime
13
time
37
telnet
23
gopher
70
WWW
80

See file://rohan.sdsu.edu/etc/services for a local list of services

See http://www.isi.edu/in-notes/iana/assignments/port-numbers for more complete list

See IANA numbers page http://www.iana.org/numbers.html for more information about protocol numbers and assignment services

Doc 8, Networks Slide # 14
Telnet is Your Friend

Telnet & port 23

A server is running on port 23 on rohan
The server asks you log in

Telnet Client and other ports

Can send ASCII to a server



Doc 8, Networks Slide # 15
Examples to Try

Day Time

Type:

telnet   sdsu.edu    13


Course Web Site

Type

telnet www.eli.sdsu.edu 80
then type:

GET  /courses/fall02/cs580/index.html   HTTP/1.0 <CR>
<CR>
Note <Cr> indicates were you need to hit return




Copyright ©, All rights reserved.
2002 SDSU & Roger Whitney, 5500 Campanile Drive, San Diego, CA 92182-7700 USA.
OpenContent license defines the copyright on this document.

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