The following enhancements have been made to VOS SDLC:

 o    The READS_LINK_STATUS_OPCODE has additional control_info
  fields.

 o    A s$control opcode has been added, which enables the SDLC
  meters to be reset by the application during run time.

 o    The circuit_type field of the sdlc_initialize_device_info
  structure is now used to indicate whether a leased or
  dial-up line is being used.

 o    The window size for sending and receiving SDLC frames has
  become user-settable.

 o    A slow-polling option enables a primary station to
  continuously poll secondary devices, even though they may be
  offline.

Documentation on each of these changes can be found in 
>system>doc>r7_sdlc.doc.