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

5 Building a network  Gateways  high-capacity router to connect LAN to wide area network LAN Gateway Internet

6  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 : pl.sookmyung.ac.kr : cc.sookmyung.ac.kr : cslinux2.sookmyung.ac.kr :

8 Users  Listing users usersrusers -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 data finger {userId}*  display information about a list of users including on a remote host

9 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 conversations talk userId [tty] talk to a user on the Internet via a split-screen interface.  Messages to everyone wall [ 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 Messge from talk: connection requested by talk: respond with: talk %talk

11 Distributing data  Copying files ftp -n [ hostName ] manipulate files and directories on both your local host and a remote host  ftp cc Connected.. Name.. Password … ftp>

12 Distributing data

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

15 Distributed Processing % rlogin cs % rlogin -l chang cs % rsh cs % rsh cs ls % telnet cs

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.

18 X-window 의 동작 과정 X server X client Terminal Screen MouseKeyboard Display X-window X applications

19 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 :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.