Understanding the Internet’s
Underlying Architecture
Transmission Control Protocol (TCP)
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The language that computers use to
communicate over the internet
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Breaks information into packets
Packets are then sent throughout the network to
their destination
At the destination, packets are assembled back to
their original form
Internet Protocol (IP)
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Ensures that packets are sent to the right
destination
Each packet is put in a separate IP envelope
that has the destination address on it
All packets go to the same destination
Routers determine most efficient path (they
could be different for different packets)
Networking Hardware
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Hubs: Link groups of computers together
Bridges: Link Local Area Networks (LAN)
Gateways: Similar to bridges but translate
data from one type to another
Repeaters: Amplify data signals for long
distance transmission
Routers: Transmit data packets between two
different networks
Caching
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To make browsing faster, different computers
will save web pages — called caching
Cache can be:
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On your computer
On your ISP’s computer
On the web server
DNS Server Types
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Domain Name Service
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special Host servers dotted around the Internet
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They help translate computer identifiers that humans
can use into the IP addresses computers need to route
information
three different types of these (DNS) servers
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Root name servers
Primary name servers
Local name servers
Root Name Servers
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Only thirteen of them throughout the world
Control a database that contains the location of DNS primary
name servers for every top-level domain (TLD)
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.com, .edu, .gov, .us, …
There over one hundred of top-level domains, counting country
codes
Local name servers send them the top-level portion of a domain
name
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they look-up and return the IP Address of the primary name server
for that particular top-level domain
Primary & Local Name Servers
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A primary name server controls the DNS
database for a given top-level domain
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The edu primary name server knows where to
find the local server for uwm.edu
A local name server keep track of the subdomains and computers for that organization
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The uwm.edu local name server knows which
computers match alphar.csd.uwm.edu or
miller.cs.uwm.edu
Local Name Servers
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The name servers transform the domain
name that humans can remember into an IP
address the computers can work with
But what is an IP address?
IP Addresses
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Needed a way to identify individual
computers on the internet
Each computer has a unique address
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For one computer to send a message to another,
it must know the IP address of the destination
IP stands for Internet Protocol
IP Addresses
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Format:
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Do the math:
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x.x.x.x
Where each x is a number from 0 to 255
256*256*256*256 = 4,294,967,296 addresses
Despite this, we are running out of IP
addresses
Static vs Dynamic
Packet Switching
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A telephone line connection is fixed from
start point to end point
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This is called a circuit-switched network
In internet, the connection line is not fixed
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There can be more than one path between source
and destination
This is called a packet-switched network
TCP/IP
Source file
packet
Destination file
Application data
TCP layer
IP layer
Other layers
Internet
packet
TCP/IP — Benefits
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Each packet individually addressed
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Allows for packets to travel any route to
destination
Net is decentralized, so not all packets will follow
same route
Allows for overall faster transfer
Better error correction
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If a packet is damaged, only need to get that one
back rather than whole file
To Learn More…
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Check out the animated explanation at
http://www.learnthenet.com/english/animate/webworks.html
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Here are several pages on web components
http://www.learnthenet.com/english/section/www.html
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Here is a more detailed treatment of the web
http://www.cio.com/WebMaster/sem2_home.html