ARPANET Host-to-Host Protocol

In addition to the 14 message opcodes defined in McKenzie, ITS and WAITS knows about these five additional opcodes:

RAS←←17         ; Reset Allocation by Sender.  Tells the receiver to
                ; clear allocations.

RAP←←20         ; Reset Allocation Please.  Sent from receiver to sender
                ; to ask it to send an RAS.

NXR←←20         ; Non-existent Receive link.  Tells sender the link it
                ; used is non-existant (eg, data message).

NXS←←22         ; Non-existent Send link.  Tells receiver the link it
                ; used is non-existant (eg, ALL).