Source : Free On-Line Dictionary of Computing

DS level
     
         (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.
     
        (1998-05-18)