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Means of Communication

"Never underestimate the bandwidth
of a station wagon full of tapes."
- Dr. Warren Jackson, Director, UTCS

The stationary workstations in the office are usually connected to the servers through the LAN. The network is wire-based offering continuous, high bandwidth communication. Mobile computers open other connections through the telephone lines (wire-based dial-up using a modem) or using portable phones (cellular dial-up using GSM). Examples of the latency and bandwidth of the different networks are given in Table 2.2.

The telephone lines have lower bandwidth than the wire-based and you normally have to pay some non-negligible fee [34] for the connection and/or the communication time, but connections can be made from almost anywhere (as long as there is a telephone wire to the house).

Wire-less communications, such as GSM, have even lower bandwidth than telephone lines; they are usually more expensive to use, and are less reliable, but in theory they can be used from anywhere (you do not even have to go to the nearest phone (outlet)).

Table 2.2: Networks

Latency	Bandwidth	Network
0.5 msec.	600 Mbps	ATM + FDDI (LAN)
	150 Mbps	ATM (LAN + country)
	100 Mbps	Fast Ethernet (LAN)
1 msec.	10 Mbps	Ethernet (LAN)
	2 Mbps	Wireless Ethernet (LAN)
100 msec.		Internet (interstate)
	100 Kbps	Serial line and V34 modem (country)
500 msec.	10 Kbps	Radio based (GSM)

(adapted from [2])

In the following subsections I will clarify my use of the terms (fully) connected, weakly connected, and disconnected.

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