basics of telecomm. starts with definition of bandwidth, two wire and four wire circuits

1. 2W / 4W
 Signal in both directions over the same
physical link or path
 Signal in both directions over separate
physical links or paths and in support of
simultaneous, two - way transmission

2. Bandwidth
 Measure of the capacity of a circuit or channel
 Total frequency on the available carrier for the
transmission of data.
 Difference between the minimum and
maximum frequencies supported
 Capacity of the circuit = information signal +
signaling and control (overhead )
 Total signaling rate of the circuit typically
greater than the effective transmission rate .

3. Bandwidth
 measurement of analog bandwidth, measured
as the difference between the highest and
lowest frequencies
 over a circuit or within a channel. Hertz refers
to the number of electromagnetic waveforms
transmitted per second (i.e., signals per
second or cycles per second).

4. Baud Rate
 number of signal events (i.e., signal changes
or signal transitions) occurring per second
over an analog circuit
 The baud rate can never be higher than the
raw bandwidth of the channel, as measured in
Hz
 The relationship between baud rate and bit
rate depends on the sophistication of the
modulation scheme used to manipulate the
carrier

5. Bits per second (bps)
 bit rate, or the number of bits transmitted over
a circuit per second
 It is the measurement of bandwidth over digital
circuits and should not be confused with the
speed of the electromagnetic signal, that is,
the velocity of propagation
 In other words, bps refers to the number of bits
that pass a given point in a circuit, not the
speed at which they travel over a distance.

6. Two Wire Circuit
 Typically, use a single twisted - pair, copper wire
 Generally cover short distance
 offers relatively little bandwidth, or capacity, and
is single channel in nature
 Generally analog, therefore, error performance
(quality) is relatively poor
 Characterized as voice grade
 Also support low - speed data transmission
through a modem

7. Four Wire Circuit
 Typically, use of two copper pairs
 one for transmission ( forward path , or upstream path )
 one for reception ( reverse path , or downstream path )
 Also possible over a single physical link or path and over
a variety of transmission media, including twisted - pair,
coaxial cable, or fiber - optic cable
 accommodate multiple, simultaneous communications in
a full - duplex mode (multi-channel)
 Support out of band signalling
 typically offers much greater bandwidth, or capacity
 Generally digital , therefore, improved error performance
(quality)
 Long - haul circuits usually are four – wire

8. Telecomm Systems
 Key Telephone System (KTS)
 Private Branch Exchange (PBX)
 Automatic Call Distributor (ACD)
 Voice Messaging System (VMS)
 Interactive Voice Response (IVR)

9. PCM

10. ELEMENTS OF TELECOMMUNICATION
SYSTEM
 Purpose of a telecommunication system is to
provide the means to pass information from
any terminal device to any other terminal
device selected by the originator.
 Telecommunication system can be divided into
four main parts. They are
 End system or Instruments
 Transmission system
 Switching system
 Signaling.