It has two ways to have multiple sessions at once:

• there are three physical input ports: a DB25 port running the RS-232 protocol, and two MMJ ports running the EIA-423 protocol
  • for the MMJ specs, see section 9.2.2, "DEC Corporate Modular Jacks"
• it can do multiple sessions over a single physical port, using TD/SMP (Terminal Device/Session Management Protocol)

Note that the specialized keyboard can be used, but if it's not available, a normal PC keyboard can be used too. (see table 8.11 "Local Function Key Defaults")