NetCamera NVW
Answer If a firewall exists on the network, port 80 is open for ordinary data communication.
Question | What is Spread Spectrum? |
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Answer | Spread Spectrum technology is a wideband radio frequency |
| technique developed by the military for use in reliable, secure, |
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| trade off bandwidth efficiency for reliability, integrity, and |
| security. In other words, more bandwidth is consumed than in |
| the case of narrowband transmission, but the |
| produces a signal that is, in effect, louder and thus easier to |
| detect, provided that the receiver knows the parameters of the |
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| tuned to the right frequency, a |
| like background noise. There are two main alternatives, Direct |
| Sequence Spread Spectrum (DSSS) and Frequency Hopping |
| Spread Spectrum (FHSS). |
Question | What is DSSS? What is FHSS? And what | are their |
| differences? |
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Answer | uses a | |
| narrowband carrier that changes frequency in a pattern that is | |
| known to both transmitter and receiver. Properly synchronized, | |
| the net effect is to maintain a single logical channel. To an | |
| unintended receiver, FHSS appears to be | |
| impulse noise. | |
| generates a redundant bit pattern for each bit to be | |
| transmitted. This bit pattern is called a chip (or chipping code). | |
| The longer the chip, the greater the probability that the original | |
| data can be recovered. Even if one or more bits in the chip are | |
| damaged during transmission, statistical techniques | |
| embedded in the radio can recover the original data without | |
| the need for retransmission. To an unintended receiver, DSSS | |
| appears as low power wideband noise and is rejected | |
| (ignored) by most narrowband receivers. |
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