Disadvantages of Wireless Networking

Mobility and flexibility aren't everything in a network. Wireless networks have some inherent disadvantages, although some are more perceived than actual. Generally speaking, the following hold true:

- Wireless networks arc cither slower or shorter-range than wired networks

- Wireless networks tend to be more expensive than wired networks

- The limited number of frequencies available for wireless communications means that fewer transmission paths are available, unless some method of conserving frequencies is used

- Environmental conditions have more of an effect on wireless networks than on wired networks

- Many people are concerned that wireless transmissions are less secure than wired transmissions

Even if some of these considerations (such as the security concerns) are more perceived than actual, perceived detriments often do as much damage to a product's acceptance as real ones, so they're worth considering.

Wireless communications are inherently limited by their lack of cabling. If the wireless medium is a radio-frequency signal, then it can travel for a long way, but it's slow (and often uncertain) compared to a wired connection. Slow, in this context, means that a high-speed wireless link is about 1.6 Mbps for a LAN and 64 Kbps for a WAN. Considering that most wired LANs run upward of 10 Mbps and many WAN technologies start at more than 1 Mbps, wireless speeds don't compare very well.

If the medium is an infrared signal, then it's faster (as fast as a wired network), but it's limited in the distance that it can extend without regenerating the signal and is also dependent on line-of-sight between the device sending the signal and the one receiving it. Even trees can disrupt an infrared signal.

Text 6

I. Memorize the following words and word combinations:

1. vulnerable - уязвимый

2. precipitation - стремительность

3. sensitive - чувствительный

4. jumble of cables - путаница в проводах

5. to interfere with - вмешиваться, повлиять на

6. under normal circumstances - в обычных условиях

7. spectrum sharing technology - технология распределения спектра

8. to encounter with - сталкиваться, встречаться

9. trade off - компромисные решения,

согласование

10. stamina - выносливость, стойкость

II. Read Text 6 attentively. Check up yourself how much you have memorized

from it:

a) Say what the cost of wireless connections depends on;

b) Recall why wireless networks are vulnerable to environmental factors;

c) Say when two transmissions will interfere with each other.

III. Write down your answers into your exercise-book. Translate them into Russian.

Higher Cost.

Wireless technology is relatively new and complex, so like other new computing technology it tends to be expensive. Wireless LAN network cards, for example, run about $400 for an Ethernet connection, while wired ones are available for $50 to around $100. Connection time for dialup wireless connections costs, too (but then so do some wired dialup connections). (This applies to wireless solutions that let you dial into your company's network.) Of course, wireless networks don't carry the cost of pulling cable, which is not inconsiderable (the exact amounts depend on your installation, requirements, and the part of the country you're in), and gets quite expensive for complex installations.

Because of their physical structure, wireless networks are vulnerable to environmental factors that under normal circumstances don't affect wired networks, such as

- Physical obstructions (like walls)

- Other wireless transmissions on the same local frequency

- Rain or other precipitation

Of course, not all these circumstances affect all wireless communications the same way, and newer technology has improved the situation. Environmental factors, however, are still a consideration.

For example, properly shielded wired connections aren't sensitive to other wired connections in the same area. You can have a jumble of cables in the same space, and as long as you're using properly shielded cables the signals won't interfere with each other under normal circumstances. (If your cable installation uses UTP, don't worry the twists in the wires contained in the cable help protect against interference.)

Wireless networks are different. Because the medium of transmission is a naked electronic signal using a certain frequency, two transmissions on the same frequencies in the same area will interfere with each other unless some sort of spectrum-sharing technology is used. This is really no different from the interference problem that you encounter with poorly shielded cables, such as the ribbon cables used to connect printers to PCs.

One of the challenges facing wireless networking is that the higher the frequency used (and thus the bandwidth), the more vulnerable the signal is to interference. There's a direct tradeoff between carrying capacity and stamina.

Text 7

I. Memorize the following words and word combinations:

1. bandwidth - полоса частот

2. throughput - производительность

3. fragility - недолговечность

4. suffer from attenuation - страдать от ослабления

5. tapping - перехват сообщений

6. to intercept the signal - перехватить сигнал

7. vulnerable - уязвимый

8. fiber-optic cable - оптоволоконный кабель

9. illicit access - незаконный доступ

10. to scramble the information - перепутать информацию

11. direct sequencing - прямая последовательность

12. hopping - переключение

13. frequency-hopped transmission - передача со скачкообразной

частотой

14. unshielded microwave transmission - незащищенная

ультракоротковолновая

передача

II. Look through the text. Say what the main ideas of the text are. Write them down into your exercise-book.

III. Read Text 7 attentively. Answer the questions to the text in writing:

1. What techniques permit greater throughput on the same bandwidth?

2. Why does it cost you far more to get the wireless speed?

3. How secure are wireless transmissions?

III. Translate the 2^nd and the 3^rd paragraphs in written form/

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