Chapter 7
Telecommunications
Bonus Quiz!
1. ENIAC was the first modern computer
not to use vacuum tubes: T/F?
2. What is a “UPS” – United Parcel Service
NOT ACCEPTED.
3. Define Dual-booting.
Quiz!
1. F
2. Uninterruptible Power Supply.
3. Dual-booting is having two Operating
Systems (OSes) running on the same
machine.
Digital/Analog
Digital signals are composed of discrete
1s and 0s
Analog signals vary continuously
This discrepancy has led to technologies
like the modem, whose only purpose is to
convert from digital to analog and viceversa
Digital/Analog
Analog signals contain ALL the information
about something, which makes them
“perfect” copies
The downside is that they’re HUGE
Digital signals store the “important” parts
of the signal, drastically reducing its size
Like traditional animation, we’re fooled into
thinking these “slices” are the real thing
HDTV
The next generation of TVs use high-quality
digital signals to transmit amazingly clear
pictures
Currently, nice HDTV sets go for $2,000-$3,000
(in 2001, it was $7,000)
Originally, by May 2006 all TV broadcasting
would switch to the HDTV standard, but….
Now that date has been moved to February 17,
2009
The last-mile problem
There are 3 major types of cables used to
carry data into modern households
Twisted pair wire consists of two braided
copper wires twisted around each other
Twisted pair wire transmits data at 1-128
Mbps
Standard phone lines are twisted-pair, and
most households use this to connect to the
net
The last-mile problem
Coaxial cable (commonly called coax) is a
copper wire wrapped in an insulted metal
shield
It’s commonly used for cable TV, and can
transmit at up to 200 Mbps
Cable modems use this type of connection
The last-mile problem
Fiber-optic cable consists of hundreds of
hair-thin glass or plastic fibers bundled
together
Data is transmitted at 100 Mbps to 2
Gbps, using pulses of light
T1s and T3s use fiber-optics
The last-mile problem
The last-mile problems refers to the fact
that while the cost to put fast fiber-optic
connections from a provider to a town or
neighborhood is minimal, the cost to
replace the “last mile” of copper wire going
into all the houses is very, very high
That’s why we don’t all have T1
connections at home (off-campus, of
course)
Satellites
We’ll skip the discussion of satellite orbits
(GEO, MEO, LEO)
GPS relies on signals from satellites
3 signals are needed to establish position,
based on triangulation
Satellite A
GPS
You’re Here
Satellite C
Satellite B
Network Types
WAN – Wide Area Network – A communications net that
covers a wide geographical area (Phone Company’s lines)
LAN – Local Area Network – the type of net we’re on here
at IU
MAN – Supposedly a Metropolitan Area Network, but
nobody uses this
LAN types
Client/Server LAN – basically one very powerful
computer (the server) interacts with multiple less
powerful machines (the clients). Servers allow
communications between the clients and
regulate access to other resources, like printers
Peer-to-Peer (P2P) – All computers are equal in
power and directly connected to one another.
Also used to talk about file sharing systems.
When used this way, Gnutella is a P2P app, and
Napster was a C/S app.
Term
Network Interface Card, or NIC, is an
expansion card added to a computer’s
system unit that allows it to interact with
other computers
In common usage, this refers to an
ethernet card
Terms
Router – a special computer that directs
communicating messages when several
networks are connected together
Bridge – an interface used to connect the
same types of networks
Gateway – an interface used to connect
different types of networks
Network Topologies
C
Star (C/S)
C
C
S
C
C
C
Ring (P2P)
C
C
C
C
C
C
Bus (P2P)
C
C
C
C
C
C
C
C
C
C
C
C
C
C
Networks
Intranet – pages/resources intended for
internal (inside a company) use
Extranet – pages/resources intended for
external (non-company) use
Firewall – A system of hardware and/or
software designed to block unauthorized
access to the intranet and other resources
Censorware
Blocking software – generally either filter based
on keywords, a pre-generated list, or both
Problems – Middlesex and Essex in England
blocked accidentally
Political sites, sex and health information (breast
cancer), minority religious sites all blocked
“accidentally”
Site lists are usually secret
Thanks to new federal laws, public libraries and
schools often must use it or loose funding