The keyboard handling within the terminal behind both telnet and SSH support in Guacamole sends the proper control characters for Ctrl-A through Ctrl-Z (0x01 through 0x1A), but does not implement the rest of the C0 control character keyboard shortcuts, such as Ctrl-^ (commonly Ctrl-Shift-6).
Overall, we are missing:
From Russ Brown:
I am using Guacamole to support telnet sessions to terminal servers, that end on the consoles of network devices, like Cisco routers and switches. These devices sometimes require break sequences and Ctrl-Shift-6 (Ascii 30). Break sequences interrupt the booting of devices; Ctrl-Shift-6 followed by x interrupts ping sequences or telnet sessions from those devices to other systems.
Are such things possible with Guacamole Telnet? I do see some evidence of being able to put in Right-Alt-number-keypad sequences but that doesn't seem to produce the exact key sequence needed ... it just puts out a tilde followed by the cartoony graphics associated with ASCII characters 1-31.