First, the content of today
Second, the physical layer
1. The basic concept of the physical layer
2. Data Communication Basics
(1) A typical data communication model:
(2) Related Terms:
In fact, just beginning to understand the symbols quite difficult, I understand the following:
a symbol is a pulse, and a pulse can carry more bit of information, so you can carry a symbol n bit of information. "Membered" it is meant the smallest, so it should take minimal code. Such as when there are five discrete values, the minimum code is 8, requires a minimum of 3bit represented, taking a minimum, i.e. one symbol at this time = 3bit
(3) the basic modulation method:
(4) a communication procedure species commonly used code:
(5) Nessler's guidelines:
incense (6) Agricultural formula:
(7) Nessler's guidelines and Shannon formula applied in the data communication range:
3. The following physical layer transmission medium
(1) transmission media guide
(2) non-oriented transport medium
(3) Physical Layer Device - Hub
4. The channel multiplexing
(1) frequency division multiplexing (the FDM)
(2) time division multiplexing (the TDM):
(. 3) Statistical Time Division Multiplexing (STDM):
statistical time division multiplexing is time division multiplexed improved version
(4) Wavelength Division Multiplexing ( WDM):
wavelength division multiplexing frequency division multiplexing is the same thing, because once the frequency of a signal to know, then he can be calculated with the wavelength.
(5) code division multiplexing (CDMA):
So, when two people call, if we want to know what he and others say, we just need to get him a chip and vectors of the same chip on it.
The digital transmission technology
PCM Pulse Code Modulation two criteria:
- E1 rate is 2.048Mb / s
- T1 rate is 1.544Mb / s
How to 2.048Mb / s rate E1 is obtained:
6. The broadband access technology
There are a lot of broadband access technology, introduce common ADSL dial-up Internet access technology here:
