Telcomm basics
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2W/4W circuits can transmit signals over the same physical link (2W) or separate links (4W). Bandwidth measures a circuit's capacity and is calculated by subtracting the minimum and maximum supported frequencies. Baud rate counts the number of signal changes per second, while bit rate measures the number of bits transmitted per second. Two-wire circuits have low bandwidth and support analog voice and low-speed data transmission, while four-wire circuits have greater bandwidth and support digital transmission with improved quality over longer distances. Telecommunication systems include key telephone systems, PBXs, ACDs, voice messaging, and IVR to connect terminal devices.
Telcomm basics
- 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.
Editor's Notes
- #7: Within such a two - wire circuit, two wires are required to complete the electrical circuit, with the current in one wire opposite to the current in the other, and both wires carry the information signal. Less than 18000 ft supports only a single conversation).
- #8: (traditionally defi ned as equal to or greater than 50 miles, or 80 km)