digital carrier

(hardware, communications)A medium which can carry digitalsignals; broadly equivalent to the physical layer of theOSI seven layer model of networks. Carriers can bedescribed as baseband or broadband. A baseband carriercan include direct current (DC), whereas broadband carriersare modulated by various methods into frequency bands which donot include DC.

Sometimes a modem (modulator/demodulator) or codec(coder/decoder) combines several channels on one transmissionpath. The combining of channels is called multiplexing, andtheir separation is called demultiplexing, independent ofwhether a modem or codec bank is used. Modems can beassociated with frequency division multiplexing (FDM) andcodecs with time division multiplexing (TDM) though thisgrouping of concepts is somewhat arbitrary.

If the medium of a carrier is copper telephone wire, thecircuit may be called T1, T3, etc. as these designationsoriginally described such.

T1 carriers used a restored polar line coding scheme whichallowed a baseband signal to be transported as broadband andrestored to baseband at the receiver. T1 is not used in thissense today, and indeed it is often confused with the DS1signal carried.

单词	digital carrier
释义	digital carrier digital carrier (hardware, communications)A medium which can carry digitalsignals; broadly equivalent to the physical layer of theOSI seven layer model of networks. Carriers can bedescribed as baseband or broadband. A baseband carriercan include direct current (DC), whereas broadband carriersare modulated by various methods into frequency bands which donot include DC. Sometimes a modem (modulator/demodulator) or codec(coder/decoder) combines several channels on one transmissionpath. The combining of channels is called multiplexing, andtheir separation is called demultiplexing, independent ofwhether a modem or codec bank is used. Modems can beassociated with frequency division multiplexing (FDM) andcodecs with time division multiplexing (TDM) though thisgrouping of concepts is somewhat arbitrary. If the medium of a carrier is copper telephone wire, thecircuit may be called T1, T3, etc. as these designationsoriginally described such. T1 carriers used a restored polar line coding scheme whichallowed a baseband signal to be transported as broadband andrestored to baseband at the receiver. T1 is not used in thissense today, and indeed it is often confused with the DS1signal carried.
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