Computer Science 1033A/B Lecture Notes - Lecture 5: Domain Name System, Top-Level Domain, Internet Protocol Suite

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Warm up questions
GIF uses a lossy compression
8-bit indexed colour uses 256 colours?
Vector images look good even if you re-size them to make them bigger
Computer network
a group of interconnected computers (could be connected with wires, wirelessly, satellites)
let's look at some ways to configure a network and think about the pros and cons of each
assume we have a map of the United States.....good/bad about certain network layouts??
The Internet
the internet is a global system of interconnected computer networks that use the standardized
Internet Protocol Suite (TCP/IP) to serve billions of users worldwide
a network of networks
the internet is hardware, not software!
The WWW is software that runs on the internet
How does the Internet work?
a standard protocol (way of communicating)
the ideas behind this protocol were funded by the Advanced Research Projects Agency (ARPA)
of the US Department of Defence (DoD)--around 1969
thus the Internet was originally called the ARPANET
opposite of your home telephone where you get a direct line that only you and the person you
are talking to can use
no direct line at the outset of the message! If a communication line is broken, another line is
imagine that I had written a manuscript, printed it but I had NOT stapled it together. I have to
get it from our classroom to my publisher in Toronto at Bloor and Yonge. I could:
Idea 1: Give the whole manuscript to one of you and tell you at the beginning to take the
whole manuscript, and drive down to Bloor and Yonge in Toronto—and stop all traffic on
these roads while you do this This is how a phone line works!
Called Circuit Switching
Idea 2: ????
each page in the manuscript is similar to a packet
packet: a small group of bytes consisting of a header (tells where it is going: destination, and
where it came from: source) and the body. (often 64 bytes for header and 512 bytes for body)
protocol: rules for a format and transmission of data
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does a few things
at the sending end:
takes a large chunk of data (such as a web page, email message, etc) and breaks it into
small packets
sends the packets out on to the internet
at the receiving end:
detects lost packets, packets with errors because of network congestion, traffic load
balancing, or other unpredictable network behaviour, and requests the packet to be
resent from the source
rearranges and reassembles the packets back into the web page, email message, etc on
the receiving machine
like a GPS
picks a route for a packet, stopping at routers which pick the next best machine/network to send
the package to
if a communication line is down or broken, sends the package back to TCP and TCP sends it
again to try a different route
needs to be able to identify all the machines on the internet, thus each machine has it's own
unique address
uses IP adresses
IP address
just like your home address
each machine has its own address, called an IP address
consists of 4 numbers with dots between them
each number ranges from 0 to 255
EXCEPT: IP addresses are NOT geographical
ways to represent it
is always 32 bits
How to send the message
TCP breaks web pages into packets of bytes
TCP figures out IP address of where it wants to send the packets (destination)
TCP figures out IP address of where the packet is coming from (source)
sends off each packet to first machine (IP address) on the route (does not pre-plan route)
packet stops at first machine, likely a router; then the router sends it to the next machine on the
journey (IP address) and so on until it gets to the final IP address (destination)
called Packet Switching
Domain names
in 1973, IP address became the standardized way to identify machines on the internet
in 1984, University of Wisconsin came up with a name server, that maps a name to an IP
in 1985, Domain Name System is established and the initial top level domain names are
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