Serial Multisession

Glen Slick glen.slick at
Thu Jun 24 16:10:04 CDT 2021

On Thu, Jun 24, 2021 at 1:41 PM Grant Taylor via cctalk
<cctalk at> wrote:
> Does anyone know anything about the "Serial Multisession" that the VT
> LAN 40, and presumably other terminals, supports?
> I've not heard about it before and intend to do some research.  But I
> figured that it was an interesting enough topic, that is multiplexing
> terminal sessions over a single serial link, to warrant further discussion.
TD/SMP, short for Terminal Device/Session Management Protocol, was a
terminal multiplexer system introduced by DEC on their VT330/340
terminals in 1987. The terminal-side was referred to as SSU. TD/SMP
allowed data from two separate host sessions to be sent to a
compatible computer terminal over a single serial port. The format was
patented and never described in depth, limiting it to DEC's own
terminal servers and terminals.

Also supported by the VT420, VT510, VT520, VT525

Terminal device session management protocol

SSU software was available on OpenVMS

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