Hardware for

  N e t w o r k i n g  

CPT 105 · Franklin College · Erich Prisner · 2002-2007

Why Networking?

Data Transmission: digital/analog

We distinguish between digital and analog data transmission.

DT can be synchronous or asynchronous

DT: simplex, half-duplex, duplex

simplex transmission: only one-way.
half-duplex: only one-way at a time.
(full) duplex: two-way transmission.

What: Communication media

The bandwidth measures the capacity of the link.

What ++ -- shape
wire pair (twisted pair) already in use (telephone lines) low bandwidth, suspectible to noise two conductors, twisted around
coaxial cable higher bandwidth, more noise-resistant center conductor, isolation, other conductor, isolation
fiber optics no metal, high bandwidth, no noise, very secure. glass or plastic fibers, transmission by light,
radio waves (like WiFi, Bluetooth, ...)    
microwave transmission (special radio waves) high speed line-of-sight  
infrared line-of-sight, small distance  
satellite transmission expensive microwave transmission to and from satellite

In principle, all these media can be used for digital or analog transmission. fiber optic cables are more suited for digital transmission, the others have originally been used for analog transmission.

How phone lines are used:


Integrated Services Digital Networks. Digital transmission. Bandwidth of about 128 Kbit/sec. Uses twistes pairs.


Digital subscriber line. Uses ordinary copper telephone lines, by exploiting (high) frequencies that are unused for phoning. High bandwidth ,  you are always online, and have a dedicated line. But the service is not available everywhere (in rural areas) and works fastest if you are close to the provider.

See an ad on DSL, it contains even more information about DSL


uses the coaxial cable (cable TV). very high bandwidth, about 10 megabit/sec. Is always on (dedicated line). However you share the bandwidth with your neighbors. Not all cable lines are suitable, they must be duplex.

See an ad on Cable Internet, another one with FAQs


Modulation is the conversion from digital to analog signals. The converse is called demodulation For both you need a Modulatordemodulator.


Software installed on all computers of the network to allow communication. Nodes are linked by some medium and sent short messages. Each message has an address (and also the source address). Nodes open messages only if they are addressed to them. Examples:

Network Topologies


Wide area network. links are temporarily (switched or dial-up service) or permanently (dedicated service) connected. The mainframe computer controlling the net is called host computer. Between this and the WAN is the front-end processor.


Local area network.

Essentially ethernet or token ring protocols used.

Another distinction for networks

Some more network devices

A bridge connects different similar LANs.
A router connects several computers and routers (like a hub), but also transmits data to the correct destination. Most contain built-in firewalls.
An IP switch directs traffic if several networks are connected.
A gateway lets a node communicate to a dissimilar network, and translates protocols.