Major Internet services & protocols
Application layer
File transfer
Ping
Info
retrieval
FTP
Traceroute
Remote
login
Web
Search
in DBs
E-mail
WAIS
SMPT
gopher
HTTP
TELNET
News
NNTP
TCP
ICMP
IP
Data link protocol
Network media
DNS
UDP
ARP, RARP,
IGMP
IEEE
IEEE
IEEE
IEEE
802.3
802.4
802.5
802.11 etc.
1
DNS
Domain Name System (a distributed DB used by TCP/IP
applications to map between hostnames and IP addresses).
DNS name space
Unnamed root
arpa
com
edu
gov
int
mil
net
org
tr . . . uk
edu
emu
emu.edu.tr
domain
metu
cmpe
ander
……..
ander.cmpe.emu.edu.tr
host name
domain name
2
An example:
Using the local DNS server of EMU
IP = 193.140.41.94
Local
DNS
server
IP = 193.140.41.163
hilarion
4
IP=193.140.41.163
hilarion
5
3
resolv.
conf.
6
LAN
daytime: . . .
1
2
mesarya
helium% telnet hilarion daytime
Trying 193.140.41.163
Connected . . . .
.....
helium% more /etc/resolv.conf
nameserver 193.140.41.94
3
An example of resolution of a name in DNS
Given: a fully qualified name ftp.dd.edu
Required: IP address for this name.
Your host
Start appl. with ftp.dd.edu
Application
Resolver
Now use
IP=192.3.4.5
IP of ftp.dd.edu?
ftp.dd.edu?
See edu name
root
name
server
Unnamed
root
server at 138.4.7.2
edu
name
See dd.edu name server
ftp.dd.edu?
DB
IP
addresses
of root
name
servers
There are 13
root name
servers in the
Internet…
edu
server at 155.1.20.2
ftp.dd.edu?
ftp.dd.edu
is 192.3.4.5
Local name server
(193.140.41.94 in
EMU)
dd
name
server
dd
ftp
(192.3.4.5)
4
Protocols in a Web client-server system
Appl. program
Select link
Web browser

page

GET
Disconnect
(from server)

OK

connect IP
of
host
TCP
Looking
up host
UDP
IP
Data link & Physical
Network
Web
server
DNS
server
5
HTTP protocol
It uses 2 types of messages:
request (client  server)
response (server  client)
A request
request
Web
client
response
Web
server
A response
Request line
Response line
General header
General header
Request header
Response header
Entity header
Entity header
Entity body
Entity body
Request line = Method URL HTTPversion
GET|PUT|HEAD|POST|DELETE|. . .
Response line = HTTPversion Status code Reason
Examples:
A request:
GET http://www.w3.org/project.html HTTP/1.0  Request
line only...
A response:
HTTP/1.0 200 Document follows
MIME-Version: 1.0
Server: CERN/3.0
Content-type: text/html
Content-length: 8 000





Resp. line
General header
Response header
Entity header
Entity header
6
A very simple Web server
#define WEBPORT 7777 /* non-standard port */
main (void)
{
struct sockaddr_in abc;
…
s = socket(…);
abc.sin_family = AF_INET;
abc.sin_addr.s_addr = htonl (INADDR_ANY);
abc.sin_port = htons (WEBPORT);
bind(s, (struct sockaddr *)&abc, …);
listen(s,5);
loop: ns = accept(s, …);
recv(ns, buf, …);
/* Analysis of received request in buf is done here */
…
/* Prepare the standard HTTP header for the reply */
strcpy(buf, “HTTP/1.0 200 OK\r\n”);
send(ns, buf, …);
strcpy(buf, “SIMPLE SERVER 1.0 \r\n”);
send(ns, buf, …);
/* other lines of reply header are sent here */
…
fd = open (“index.html”, …);/* open a file for the reply*/
while(read(fd, buf, …) > 0) send (ns, buf, …);
close(fd);
strcpy(buf, “\r\n”);
/* the last(blank) line */
send(ns, buf,…);
close(ns);
goto loop;
}
7
A web client-server system
Host www.abc.com
HTML text: . .
..........
www.abc.com
..........
..........
Link to
www.abc.com
Web client (browser)
Page A
.........
www.x.com
.........
Web server
Network(internet)
Web server
Host
www.x.com
Page B
.........
. . . . . .
.........
Link to
www.x.com
8
Timing diagram for a web client-server system
What you see:
User:
Select link www.abc.com
Connect: looking up host
www.abc.com
IP addr
.
Connect: contacting host
www.abc.com
Web DNS
Host
Host
client server(s) www.abc.com www.x.com
UDP
TCP:connect IP=. .
OK.
Connect: host
www.abc.com contacted.
Waiting for reply.
GET pageA.html
Response
Page A.html
.........
www.x.com
.........
User:
Select link www.abc.com
Connect: looking up host
www.abc.com
IP addr
.
Connect: contacting host
www.abc.com
Disconnect
UDP
TCP:connect IP=. .
Time
9
Uniform Resource Locator (URLs) of Web as pointers to
resources in Internet
Type
General form
Example
http
http://host:port/path
http://www.abc.com/pagea.html
ftp
ftp://host /dir/file
ftp://ftp.mit.edu/pub/readme
telnet
telnet://host:port
telnet://kantara
gopher
gopher://host:port/path
gopher://gopher.mit.edu/
11/labraries
news
news: newsgroup
news: comp.os.unix
or news:newsarticle
news:abcd@comp.os.unix
mailto
mailto:address
mailto: murata@cs.ui.edu
local file
path name
/usr/prog.c
wais
wais://host:port/dbase
wais://abc.mit.edu/computers
nntp
nntp://host:port/
nntp://kantara/comp.os.unix/127
(network
newsgroup/articlenumb
news
transfer
protocol)
10