hssi

from The Free On-line Dictionary of Computing (8 July 2008)

high speed serial interface
HSSI

   <hardware, communications> (HSSI) A {serial port} which
   supports serial transmit speeds of up to 52 megabits per
   second.  It is typically used for leased lines such as {DS3}
   (44.736 Mbps) and {E3} (34 Mbps) and for {Wide Area Network}
   devices such as {routers}.

   (1995-11-20)