Bridges To Computing
General Information:
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This document was created for use in the "Bridges to Computing" project of Brooklyn College.
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You are invited and encouraged to use this presentation to promote computer science education in the U.S. and
around the world.
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Internet Hardware
• Dial-up
– POTS (Plain Old Telephone System)
– Modems.
– UART chips - universal asynchronous
receiver/transmitter.
– Point-to-Point Protocol (PPP)- streaming protocol
developed especially for dial-up Internet access.
– 28.8 Kbps (56 K modems, which were big
surprise, didn’t appear until 1995)
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Modem
• Stand for MOdulate DEModulate.
• Converts analogue signals to digital signals.
UART
• Universal Asynchronous Receiver Transmitter.
• Converts serial data to parallel data.
• Neccesary so that information can "get on the BUS".
Internet Hardware... cont
• ISDN (integrated services digital network)
– POTS
– ISDN Devices (look a lot like modems)
– Full digital communication over multiple
"channels".
• B channels carry data and voice information at 64 Kbps.
• D channels carry setup and configuration information
and carry data at 16 Kbps.
– BRI - one physical line, 2 B's 1 D, throughput total
to 128 Kbps.
– PRI (aka T1) - 23 64-Kbps B's, 1 64-Kbps D, total
throughput of 1.5 Mbps.
Internet Hardware... cont
• DSL (digital subscriber line)
– POTS
– DSL Devices (look a lot like modems)
– Replacing ISDN
– Requires special tested lines, and equipment.
– Typical upload speed is ~768 Kbps, download
~3+ Mbps.
– Requires short distance from a main phone
service switching, center (18,000 feet).
– Many, many channels on one line.
– Much much faster communication over each
channel.
Internet Hardware... cont
• Cable
– Uses regular insulated cable TV cables.
– Cable Devices (look a lot like modems)
– Offers faster service than most DSL connections:
1–10 Mbps upload and 6–50+ Mbps download.
• Variable bandwidth becoming more common.
– Cable Internet connections are theoretically
available anywhere you can get cable TV.
– Many, many channels on one line.
– Much much faster communication over each
channel.
Internet Hardware... cont
• Wireless
• (WiFi, 102.11B, Bluetooth, IR, Cellphones)
– Variety of device protocols.
– Variety of ranges.
– Unique problems (hidden sender, manets,
security)
– Emerging technology.
– Don't leave your wireless device unsecured
(anyone can listen).
– Long distance WiFi now available in bandwidth
that used to be used for TV signals.
DHCP & NAT
• DHCP (Dynamic Host Configuration Protocol)
– Protocol that allows IP address information to be
automatically handed out to machines.
– Eliminates need to hand enter lots of tedius network
information.
– Allow network addresses to be retrieved and reused.
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• NAT (Network Address Translation)
– Allows multiple machines to share one Internet IP
address connection (NAT).
– Router keeps track of all members of network and acts
as proxy on the web.