Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a...
-
Upload
earl-skinner -
Category
Documents
-
view
221 -
download
0
Transcript of Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a...
![Page 1: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/1.jpg)
Network Services
![Page 2: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/2.jpg)
2
1960's
1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies
ARPANET originally connected 4 universities & enabled scientists to share info & resources across long distances
![Page 3: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/3.jpg)
3
1980's
1983 - The TCP/IP protocols becomes the only set of protocols used on the ARPANET
This sets a standard for all networks, and generates the use of the term Internet as the net of nets
![Page 4: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/4.jpg)
4
1990's
1993 - CERN releases WWW, developed by Tim Berners-Lee
It uses HTTP and hypertext, revolutionizing the way info is presented & accessed on Internet
![Page 5: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/5.jpg)
5
1990's
1993-1994 - Web browsers Mosaic & Netscape Navigator are introduced
Their GUI makes WWW & Internet more appealing to the general public
![Page 6: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/6.jpg)
6
Today’s Goal: Internet Services
• To look at several services provided by the Internet– FTP– Telnet– Web– eMail– Instant messaging– VoIP
But first, we need to find out about the addressing scheme used on the Internet
![Page 7: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/7.jpg)
7
Internet Addressing
• Regular post cannot be delivered unless we write a destination address on the envelope
• Same is true for the Internet
• Regular post can be delivered at the intended address even if the given address is not precise. That is not the case for Internet addressing
![Page 8: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/8.jpg)
8
203.215.177.33
www.vu.edu.pk
IP addressDNS address
![Page 9: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/9.jpg)
9
IP Address (1)
• A unique identifier for a computer on a TCP/IP network
• Format: four 8-bit numbers separated by periods. Each 8-bit number can be 0 to 255
• Example:– 203.215.177.33 (IP address of the VU Web server)
![Page 10: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/10.jpg)
10
IP Address (2)
• Networks using TCP/IP route messages based on the IP address of the destination
• Any IP addresses (as long as they are unique) can be assigned within a PN
• However, connecting a PN to the Internet requires using unique, registered IP addresses
![Page 11: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/11.jpg)
11
Domain Names
• IP addresses are fine for computers, but difficult to recognize and remember for humans
• A domain name is a meaningful, easy-to-remember ‘label’ for an IP address
• Examples:
203.215.177.33 www.vu.edu.pk
216.239.33.101 www.google.com
![Page 12: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/12.jpg)
12
DNS: Domain Name System (1)
• DNS is the way that Internet domain names are located & translated into IP addresses
• Maintaining a single, central table of domain name/IP address relationships is impractical– Billions of DNS-IP translations take place every day– The DNS-IP tables get updated continuously
![Page 13: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/13.jpg)
13
DNS: Domain Name System (2)
• Tables of DNs & IP addresses are distributed throughout the Internet on numerous servers
• There is a DNS server at most ISPs. It converts the domain names in our Internet requests to actual IP addresses
• In case it does not have a particular domain name in its table, it makes a request to another DNS server on the Internet
![Page 14: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/14.jpg)
14
Internet Services
There are many, but we will look at only the following:
• FTP
• Telnet
• Web
• Instant messaging
• VoIP
![Page 15: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/15.jpg)
15
FTP: File Transfer Protocol
• Used to transfer files between computers on a TCP/IP network (e.g Internet)
• Simple commands allow the user to:– List, change, create folders on a remote computer– Upload and download files
• Typical use: Transferring Web content from the developer’s PC to the Web server
![Page 16: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/16.jpg)
16
Telnet Protocol
• Using Telnet, a user can remotely log on to a computer (connected to the user’s through a TCP/IP network, e.g. Internet) & have control over it like a local user, including control over running various programs
• In contrast, FTP allows file operations only
• Typical use: Configuring and testing of a remote Web server
![Page 17: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/17.jpg)
17
The Web • The greatest, shared resource of information
created by humankind
• A user may access any item on the Web through a URL, e.g.
http://www.vu.edu.pk/cs/index.html
• Before, going any further, let us dissect this URL
![Page 18: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/18.jpg)
18
http://www.vu.edu.pk/cs/index.html
ProtocolIdentifier
ServerAddress
Directory & File Name
![Page 19: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/19.jpg)
19
How does the Web work?
![Page 20: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/20.jpg)
20
User’sComputer
User launches the browser on his/her computer
Browser
![Page 21: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/21.jpg)
21
User’sComputer
User types in the URL into the browser
![Page 22: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/22.jpg)
22
User’sComputer
The browser breaks down the URL
http://www.vu.edu.pk/cs/index.html
httpProtocolIdentifier
www.vu.edu.pkServer’s Name
cs/index.htmlDirectory &File Name
![Page 23: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/23.jpg)
23
User’sComputer
DNSServer
Browser sends server’s name to the DNS server
Domain Name
IP Address
![Page 24: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/24.jpg)
24
User’sComputer
WebServer
Internet
Browser establishes a connection with the server
![Page 25: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/25.jpg)
25
User’sComputer
WebServer
Browser sends a ‘GET’ request for cs/index.html
![Page 26: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/26.jpg)
26
User’sComputer
WebServer
Server sends the requested file to the browser
![Page 27: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/27.jpg)
27
User’sComputer
Browser displays index.html
X
![Page 28: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/28.jpg)
28
• Computer-to-computer messaging
• Inexpensive, and quite quick, but not instant!
• The most popular service on the Internet, even more than surfing, but soon to be overtaken by instant messaging
• Billions are sent every day
![Page 29: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/29.jpg)
29
How does an eMail system work?
![Page 30: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/30.jpg)
30
But first, the components:
• eMail client
• SMTP server
• POP3 server
![Page 31: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/31.jpg)
31
eMail Clients
• Programs used for writing, sending, receiving, and displaying eMail messages
• Examples: Outlook, Communicator, Hotmail, YahooMail
![Page 32: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/32.jpg)
32
SMTP: Simple Mail Transfer Protocol
A protocol used to send and receive eMail messages over a TCP/IP network
![Page 33: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/33.jpg)
33
POP3: Post Office Protocol
• A protocol used for receiving eMail messages
• A POP3 server maintains text files (one file per user account) containing all messages received by a user
• eMail client interacts with the POP3 server for discovering and downloading new eMail messages
![Page 34: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/34.jpg)
34
Sender’sComputer
The message is prepared using the eMail client
eMail Client
![Page 35: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/35.jpg)
35
Sender’sComputer
SMTPServer
The eMail client sends it to the SMTP server
![Page 36: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/36.jpg)
36
Sender’sComputer
SMTPServer
POP3Server
If the receiver is local, it goes to the POP3 server
![Page 37: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/37.jpg)
37
Sender’sComputer
POP3Server
The receiver picks it at his/her convenience
Receiver'sComputer
SMTPServer
![Page 38: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/38.jpg)
38
Sender’sComputer
SMTPServer
SMTPServer
Internet
Otherwise, it is sent to receiver's SMTP server
![Page 39: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/39.jpg)
39
Sender’sComputer
SMTPServer
POP3Server
SMTPServer
Which forwards it to the local POP3 server
![Page 40: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/40.jpg)
40
Sender’sComputer
SMTPServer
POP3Server
SMTPServer
The receiver picks it at his/her convenience
Receiver'sComputer
![Page 41: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/41.jpg)
41
The Trouble with eMail
• Slow response times
• No way of knowing if the person we are sending eMail to is there to read it
• The process of having a conversation through eMail by exchanging several short messages is too cumbersome
Instant messaging (IM) solves these problems
![Page 42: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/42.jpg)
42
Instant Messaging
• The IM services available on the Internet (e.g. ICQ, AIM, MSN Messenger, Yahoo! Messenger) allow us to maintain a list of people (contacts) that we interact with regularly
• We can send an instant messages to any of the contacts in our list as long as that contact is online
![Page 43: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/43.jpg)
43
Using Instant Messaging (1)
• Whenever a contact in our list comes online, the IM client informs us through an alert message and by playing a sound
• To send an instant message to a contact, just click on the contact in the IM client, and start typing the message
![Page 44: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/44.jpg)
44
Using Instant Messaging (2)
• The selected contact will receive that message almost immediately after you press ‘Enter’
• When the contact’s IM client receives the message, it alerts the contact with a blinking message and by playing a sound
![Page 45: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/45.jpg)
45
Using Instant Messaging (3)
• That contact then can type a response to the received message, and send it instantly
• Several such conversations can be carried out simultaneously, each occupying a separate IM windows
![Page 46: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/46.jpg)
46
How instant messaging works?
![Page 47: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/47.jpg)
47
User launches the IM client
My Computer
IM Client
Internet
![Page 48: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/48.jpg)
48
IM client finds the IM server & logs in
My Computer IM Server
![Page 49: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/49.jpg)
49
It sends communication info (IP address, etc) to the IM server
My Computer IM Server
Temporary File
![Page 50: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/50.jpg)
50
IM server finds user’s contacts & sends him/her the communication info for the ones online
My Computer IM Server
![Page 51: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/51.jpg)
51
IM server also tells the contacts that the user is online; sends his/her communication info to them
My Computer IM Server
Contact’sComputer
![Page 52: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/52.jpg)
52
My Computer IM Server
Contact’sComputer
Now the user’s & the contact’s IM clients are ready to communicate directly (P2P)
The IM server doesn’t play any part in this P2P communication
![Page 53: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/53.jpg)
53
My Computer IM Server
ContactA’s Computer
As new contact’s come online, IM server informs them about the user being online & vice versa
ContactB’s Computer
![Page 54: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/54.jpg)
54
My Computer IM Server
ContactA’s Computer
Multiple, simultaneous conversations are possible
ContactB’s Computer
![Page 55: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/55.jpg)
55
My Computer IM Server
ContactA’s Computer
When the user logs-off, his/her IM client informs the IM server
ContactB’s Computer
![Page 56: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/56.jpg)
56
My Computer IM Server
ContactA’s Computer
IM server erases the temporary file and informs the user’s contact’s about his/her ‘offline’ status
ContactB’s Computer
![Page 57: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/57.jpg)
57
Key Point
• Once the IM server provides the communication info to the user and his/her contact’s IM client, the two are able to communicate with each other without the IM server’s assistance
• This server-less connection is termed as a P2P connection
![Page 58: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/58.jpg)
58
Question
• Why do we require the server in the first place?
• Why doesn’t my IM client look for the user’s contact’s IM client without the IM server’s help?
![Page 59: Network Services. 2 1960's 1969 - DoD-ARPA creates an experimental network – ARPANET – as a test-bed for emerging networking technologies ARPANET originally.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649e2a5503460f94b18c8d/html5/thumbnails/59.jpg)
59
Answer
• Many users (including almost all home users) do not have permanent IP addresses. They are assigned temporary IP addresses by their ISP each time they connect to the Internet
• The server-based IM scheme removes the need of having permanent IP numbers
• It also gives IM users true mobility, allowing them the use of IM from any Internet-connected computer