Also supported by the VT420, VT510, VT520, VT525
Actually as far as I can tell the VT510 does not support TD/SMP
(Terminal Device/Session Management Protocol). No mention of multiple
sessions in this VT510 manual as there are in this VT520 manual.
http://www.bitsavers.org/pdf/dec/terminal/vt5xx/
http://www.bitsavers.org/pdf/dec/terminal/vt5xx/598-0013866_VT510_Installat…
http://www.bitsavers.org/pdf/dec/terminal/vt5xx/EK-VT520-IN_VT520_Installat…