Dihydroxyhexanoic acid derivatives of the general formula . The hub defines a manipulation axis for the device and is flexibly connected to the support portions to allow displacing the manipulation axis for the device between the support portions. New devices with a transport network for transporting the communications data can thus be integrated in a private branch exchange by using TDM-based devices. A powered vacuum pump is also provided for producing and maintaining a partial vacuum in the sealed chamber for keeping the socket and sleeve joined. The yoke assembly preferably comprises an upwardly angled yoke tube slidably coupled and pivoted to the frame front at the tube’s lower end.