Tymnet circuits carries 8 bit characters thru the net on a path fixed for a login session. There were several additional signals that travelled thru over the path mostly in their turn without queue jumping. They were mostly called ‘balls’ and identified by color.

Tymnet was originally designed to drive ‘start-stop’ dumb ASCII terminals which had no logic in themselves. The 110 b/sec model 33 Teletype was the first target. ‘TD’ (terminal driver), referred to below, is the Tymnet component that stood between the Tymnet circuit and the dial-up phone line over which the ASCII terminals accessed Tymnet.

Originated by a network node when data has been lost. This was rare.
The reflection of a black ball from a TD. Delivered to application.
Initiated by application in order to wait until previous printing at terminal had ceased.
Reflection by TD of orange ball, delivered to application that was likely waiting for it.
Zapper (not a ball)
Tear down circuit. Issued at either end; delivered to kernel at application end.
Clear all buffered data ahead of signal. Sometimes issued by application.
Queue jumping signal from TD, initiated by terminal, to interrupt application that might, perchance, be looping.
Red & Green
These balls concern full duplex dumb terminals and are described here; they are not relevant to DSR.

A paper by Laroy with real content!
Here is some PDP-10 assembler code dealing with Tymnet logic. It seems to be the “TYMBASE interface handler” that Sumex, an early Tymnet customer, used to adapt their host to Tymnet. I do not recall that they asked for or received any code from Tymshare.
Here we learn of “Black Ball, Glass Ball, Gray Ball, Green Ball, Orange Ball, Red Ball” in some unidentified glossary.