The protocol spoken between two Steelhead appliances on the inner channel consists of nine different commands: DEF, ESC, REF, REQ, REP, ACK, EOF, INF, LOP.
Create a new DEFinition:
With the DEF command the sending Steelhead appliance will tell the receiving Steelhead appliance to learn a new reference. The two Steelhead appliances will store the label and the frame in their data store and both now can use the label to send references later.
ESCape this data:
With the ESC command the sending Steelhead appliance will tell the receiving Steelhead appliance to forward this data to the client or server but not to store it in the data store. This can happen with data which is too small (less than 16 characters) or when the data reduction policy for an in-path rule is set to compression only or to no data reduction at all.
Use this REFerence:
With the REF command the sending Steelhead appliance tells the receiving Steelhead appliance to use the frame from an earlier learned reference.
REQuest a reference:
When a REF command comes in and the receiving Steelhead appliance cannot find the label in its data store, it will request the frame from the sending Steelhead appliance with this command.
REPeat a reference:
When a request for a reference gets answered by the original sending Steelhead appliance it will happen via a REP command.
ACKnowledge an earlier command:
With the ACK command an earlier DEF, ESC or REP statement gets acknowledged so the original sending Steelhead appliance knows that it has been processed properly.
EOF: Outer channel was terminated:
With the EOF (End Of File) command, the sending Steelhead appliance tells that the outer channel has been properly terminated.
INF: INFormation packet:
With the INF packet the receiving Steelhead appliance tells the sender about possible failures (Duplicate references, duplicate requests) and changes in the SDR-A optimization policy.
LOP: Lower Overhead Protocol
Like the ESC command, but with a much smaller protocol overhead (three bytes instead of 15 bytes).