History of the Internet
1962
– concept of large network
1964
– concept of packet switching
1967
– work starts at DARPA
1968
– ARPANet original specs
1969
– four computers connected to ARPANet – UCLA, Stanford, UCSB, and Utah
1972
– ARPANet public demo and email used
1973 – TCP/IP defined for ARPANet
Other defining features:
–
Local networks can maintain own protocols
–
Error packets retransmitted from source
–
No global control of the network
–
32 bit address with 8 bits to designate target network
1983 – TCP/IP becomes official
protocol for ARPANet
1985 – Internet Protocol being
used by other networks, especially NSFNet
1990
--ARPANet decommissioned
1995
-- NSF stops funding the NSFNet
backbone. The Internet is now private.
Internet Architecture
·
Packet switching v circuit switching
·
Distributed resources v Star topology
·
Backbones
MCI Worldcom
GTE
Sprint
·
Internet Service Providers (ISP)
Internet Addresses
•
Domain Name System (DNS)
–
Legal aspects
–
Technical aspects
•
Top-level or zone
(.com, .mil, .edu)
•
Vaxa.oshkosh.edu (US
assumed)
•
Namibian.com.na
Message Movement
·
Message broken into packets
·
Packets sent independently
·
Packets reassembled and reordered at receiving machine
·
Each router forwards message using optimal path (determined
by hop count, proximity, queue length, and priority).
IP Headers
•
Encapsulated packet begins with these fields:
–
IP
Version ( 4 bits, currently v4)
–
Header
length (4 bits, normally 20 bytes)
–
Priority
level (7 bits)
–
Packet
length (16 bits – 65,535 byte max)
–
Packet
ID # (16 bits)
–
Flag
(3 bits – last or more fragments)
–
Fragment
offset (12 bits – used in packet reassembly)
–
Time to Live (8 bit – hop count)
–
Protocol of next layer (8 bits)
–
Parity check (16 bits)
–
Source address (32 bits)
–
Destination address (32 bits)
(32
bits can encode an address no larger than 4,294,967,296 or 2**32)
Internet Services
•
E-mail and listservs
•
Remote log-in – Telnet
•
Information Retrieval
–
FTP File transfer protocol
–
Gopher
–
World Wide Web
History of the Web
•
Tim Berners-Lee (CERN) – 1989
–
Hypertext linkage of technical documents
•
Marc Andreeson – U of Illinois –
–
Mosaic Browser
–
Later founded Netscape
Functions of a Browser
•
Display name of URLs
•
Translate name to Internet address
•
Request service of server holding document
•
Copy document to local computer
•
Display document