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(Digital Signal or Data Service level) Originally an AT&T classification of transmitting one or more voice conversations in one digital data stream. The best known DS levels are DS0 (a single conversation), DS1 (24 conversations multiplexed), DS1C, DS2, and DS3.
By extension, the DS level can refer to the raw data rate necessary for transmission:
DS0 64 Kb/s DS1 1.544 Mb/s DS1C 3.15 Mb/s DS2 6.31 Mb/s DS3 44.736 Mb/s DS4 274.1 Mb/s
(where K and M signify multiplication by 1000 and 1000000, rather than powers of two). In this sense it can be used to measure of data service rates classifying the user access rates for various point-to-point WAN technologies or standards (e.g. X.25, SMDS, ISDN, ATM, PDH).
Japan uses the US standards for DS0 through DS2 but Japanese DS5 has roughly the circuit capacity of US DS4, while the European standards are rather different (see E1). In the US all of the transmission rates are integral multiples of 8000 bits per second but rates above DS1 are not necessarily integral multiples of 1,544 kb/s.