COMH is the communication handler and it handles all the communication between the UNIX workstation on which ONLINE is running and the various Antenna Base Computers (ABCs). COMH operates in a time division multiplexing (TDM) mode i.e. it sends the formatted user commands to the first antenna and then waits for an acknowledgment. If it receives an error free reply before the timeout period it selects the next antenna and the operation continues. In case COMH doesn't get a reply before the timeout period or if the reception is erroneous then it tries the same antenna again. After a total of three failures COMH passes on a Timeout or Checksum error (as appropriate) to ONLINE and then moves on to the next antenna.