24 hours
Command not retrieved
If the GSME has not retrieved the buffered command within 24 hours of the Tunnel Message Pending flag being set, the command may be discarded and the GPF reports0x819D GSME Command Not Retrieved.
Key Concept
Tapping Off Mechanism
The Tapping Off Mechanism (TOM) gives the Gas Proxy Function a copy of selected commands sent to a Gas Smart Metering Equipment device and their outcomes, so that related Gas Energy Service Interface (ESI) data can stay synchronised.
Purpose
A controlled copy path through the Communications Hub
Most GBCS messages pass through the Communications Hub without alteration. TOM is a defined exception for a fixed set of GSME-bound commands. It allows the Gas Proxy Function (GPF) to keep copies of GSME data that are not provided through native ZigBee Smart Energy mirroring.
The tap-off is additional to the normal route: the Communications Hub continues to relay the GSME's Remote Party Response to the WAN. It does not divert or replace that response.
Message flow
How TOM works
CHF = Communications Hub Function
Buffer and retrieve
The Communications Hub buffers the command for the GSME and the GPF sets its Tunnel Message Pending flag. The GSME retrieves the command using TransferData.
Retain the TOM command
Once retrieval is confirmed, the Communications Hub retains the command contents and starts the six-hour TOM response timer.
Process and respond
The GSME processes the command and returns either a response or an Invalid Command alert. The response records the outcome of each instruction.
Copy to the GPF
If at least one elemental instruction succeeded, the Communications Hub sends the retained command and its TOM response to the GPF.
Synchronise Gas ESI data
For an immediate command, the GPF applies the successful instructions and exposes the updated data over the WAN and HAN. It stores a future-dated command until activation. The original Remote Party Response is still relayed to the WAN.
Defined scope
TOM commands
9 commands
Schedule 8 defines TOM for the following commands. A response to one of these commands is a TOM Response.
| Message code | Use case | Command |
|---|---|---|
0x006B | GCS01a | Set Tariff and Price on GSME |
0x006F | GCS05 | Update Prepayment Configurations on GSMEThe GPF processes only the Calendar cluster ZSE commands. |
0x0071 | GCS07 | Send Message to GSME |
0x0015 | CS11 | Clear ZigBee Device Event LogA TOM command only when addressed to the GSME. |
0x007C | GCS23 | Set CV and Conversion Factor Value(s) on GSME |
0x007E | GCS25 | Set Billing Calendar on GSME |
0x00D8 | GCS25a | Set Billing Calendar on GSME - all periodicities |
0x0088 | GCS44 | Write Contact Details on GSME |
0x00A3 | GCS01b | Set Price on GSME |
Failure handling
Two timers, two distinct alerts
6 hours
TOM outcome not received
After confirmed retrieval, a separate six-hour timer waits for the TOM Response. If it expires, the GPF reports0x819E Tap Off Message Response or Alert Failure.
Future-dated activation
For future-dated tariff and price commands with message codes 0x006B or0x00A3, the GPF stores the command rather than immediately publishing its data. When it later receives alert 0x8F66, it matches the Message Code and Originator Counter to the stored command before applying the update. A missing match results in 0x819E.
Interpretation
Important boundaries
- TOM applies to the fixed command list above, not to every message sent to a GSME.
- The tap-off copy supports GPF data synchronisation; the WAN response route remains intact.
- GCS25 and GCS25a both appear in the TOM command list, but that does not change their separate GBCS-version applicability. SeeSRV 6.8 for the active mapping.