bearer mobile (mobile communications) (Bm)
To distinguish the transmission channels of GSM networks or DCS networks from those in ISDN, the channels were marked with an additional small "m", which stands for "mobile".
Bm thus corresponds in its characteristics to a B channel for mobile networks.
The D channel of ISDN also has an adequate counterpart in GSM networks: Dm. For services that cannot use the Dm channel, an additional traffic channel with a low data rate was created, the "low-rate traffic channel", or Lm for short, which stands for low mobile.