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1
Chapter 8 Networking
2
Introduction
A network is an interconnected system of cooperating computers
Common network terminology
How networks are built
How to talk to other people on the network
(communication)
How to use other computers on the network
(resource sharing)
3
Building a network
Ethernets most common implementation of LAN developed at Xerox
PARC.
How does it work ?
1. Each computer has an Ethernet card connected to the wire
2. A computer broadcasts a message onto the Ethernet together with
header and trailer information that contains destination address. Only
the Ethernet card whose address matches the destination address
accepts the message.
3. When a collision occurs, they try again.
4
Building a network
Routers
a device that links together
two or more networks
automatically routes
incoming message to the
correct network.
Router
LAN
LAN
5
Building a network
Gateways
high-capacity router to connect LAN to
wide area network
LAN Gateway Internet
6
Internet
Internet
the large collection of cooperating networks which uses
TCP/IP protocol.
Internet Protocol(IP)
a protocol about the addressing scheme
Transport Control Protocol(TCP)
a protocol about the way that large messages are sent as
several smaller messages and then reconstructed at the
destination
7
Internet
Internet address of our department
each computer on the Internet has its own IP address.
hardware independent address
cs.sookmyung.ac.kr : 203.252.206.1
pl.sookmyung.ac.kr : 203.252.195.218
cc.sookmyung.ac.kr : 203.252.201.4
cslinux2.sookmyung.ac.kr : 203.252.195.17
8
Users
Listing users users rusers -a {host}* display a list of users on your local host/ network
More user listings who [am i] rwho display a list of every user on local host.
Personal datafinger {userId}* display information about a list of users including
on a remote host
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Communicating with Users
Sending a line at a time write userId [tty]
copy its standard input, one line at a time, to the terminal associate with userId
Interactive conversationstalk userId [tty]
talk to a user on the Internet via a split-screen interface.
Messages to everyonewall [ fileName ]
copy its standard input to the terminals of every user on the local host
10
Communicating with Users
%write chang
message to chang
^D
% talk chang@cs
Messge from [email protected]: connection requested by u98…@cstalk: respond with: talk u98…@cs%talk u96…@cs
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Distributing data
Copying files
ftp -n [ hostName ]
manipulate files and directories on both your local host and a remote host
ftp ccConnected ..
Name ..
Password …
ftp>
12
Distributing data
Command Meaning
!command Executes command on local host
help
lcd change current local working directory
cd change current remote working directory
ls remoteDirectory list current remote working directory
pwd print current remote working directory
open hostName [ port ] a connection to the host with name hostName
close shuts down the current connection
get remoteFile [ localFile ] copy the remote file to the local file
put localFile [remoteFile] copy the local file to the remote file
quit
13
Distributed Processing
Remote login
rlogin -ec [-l userId] hostName login into the remost host hostName
Remote connection
telnet [host [port] ]
establishes a two-way connection with a remote port.
14
Distributed Processing
Executing remote commands
rsh [-l userId] hostname [command]
remote execution
create a remote shell on the host hostName to
execute command
access control
list hostnames in ~/.rhosts of the remote host
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Distributed Processing
% rlogin cs
% rlogin -l chang cs
% rsh cs
% rsh cs ls
% telnet cs
Command Meaning
open host Connect to host with optional port specifier
close close current connection
qut exit telnet
z suspend telnet
? print summary of telnet commands
16
World wide web
Mosaic started at UIUC the first web browser available on Intenet
Netscape can be used as in the PC need X-window to display
17
X-window
Client/Server 기반 윈도우 시스템
X server 와 X client
네트워크 기반 윈도우 시스템
X server 와 X client 가 같은 호스트 혹은
다른 호스트에 위치할 수 있다 .
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X-window 의 동작 과정
X server
X client
X client
X client
TerminalScreen
Mouse Keyboard
Display
X-window
X applications
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X-window 의 동작 과정
Display
consists of a terminal screen, a keyboard, and a mouse
X server
handles all the input and output of data at the display
one X server to each display
보통 X-window 는 X server 를 의미함 .
20
X-window 의 동작 과정
X client
디스플레이의 사용자와 대화하는 X 응용 프로그램
X client 의 예
- xterm, xclock, netscape, ….
출력을 X server 에 요청
X server 로부터 입력을 받음
- 마우스 클릭 , 윈도우 이동 , 키보드 누름 , …
21
X applications
What is an X application ?
Application program runnable on X-window
xterm, hanterm, xcalc, xfig, ghostview, xfm, …
Where are X applications ?
/usr/X11R6/bin on Linux
/usr/openwin/bin on Solaris
22
Display on X-window
Setting display
setenv DISPLAY hostname:0
setenv DISPLAY 203.252.196.78:0
Display on remote X-server
setting display and execute X-applications or
execute X-applications with -display option
xclock -display hostname:0
23
Access control on X-window
Access control
control access to X-server
xhost +hostname
added to the list allowed to connect to the X
server.