Chapter 7

Telecommunications

Bonus Quiz!

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3.

ENIAC was the first modern computer not to use vacuum tubes: T/F?

What is a “UPS” – United Parcel Service NOT ACCEPTED.

Define Dual-booting.

Quiz!

1.

2.

3.

F Uninterruptible Power Supply.

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 vice versa

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 C C Ring (P2P) C C C Bus (P2P) C 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