Introduction - KNX

Review M-Bus documentation as included in the Open Metering Systems 

Specification documents. 

Introduction....................................................................................................................1 

Data Encryption .............................................................................................................2 

Authentication / Device Signatures ...........................................................................2 

Encryption..................................................................................................................2 

Encryption Algorithm ................................................................................................2 

Encryption key exchange...........................................................................................2 

M-Bus signature field. ...............................................................................................3 

Infrastructure..................................................................................................................3 

System Installation And Initialisation............................................................................3 

Operational Data Transfer..............................................................................................3 

Tariffing .....................................................................................................................3 

Valve commands........................................................................................................3 

Meter fault / alarm handling ......................................................................................4 

Time Synchronisation ................................................................................................4 

Indexes Log................................................................................................................4 

Gas Volume, transfer and calculation........................................................................4 

Other Data Transfers..................................................................................................4 

Other issues....................................................................................................................5 

Frame Format.............................................................................................................5 

Wireless modes ..........................................................................................................5 

Differences between OMS/MUC and Dutch approach .................................................5 

Introduction 

This document contains a review by KEMA Consulting of the Open Metering 

Systems Specification documents. 

The following documents were reviewed: 

• OMS-Spec-Vol1_General_v100.pdf 

• OMS-Spec_Vol2_Primary_v102.pdf 

• MUC_080128_inkl_Anlagen.pdf 

The review focuses on the communication / M-Bus specifics in the documents above, 

and on the differences between these specifications and the Dutch Smart Meter 

documentation. 

The following topics are specifically reviewed: 

• Data Encryption 

• Infrastructure 

• System Installation And Initialisation 

• Operational Data Transfer 

Review M-bus.doc 1 04/12/2008

Data Encryption 

Authentication / Device Signatures 

Signatures, or authentication in any way, are not included in the Dutch smart meter 

specifications. This is referred to in the OMS documents (OMS-Spec- 

Vol1_General_v100.pdf section 3.6.2) as work in progress. 

Encryption 

The Dutch smart meter specifications require two-way data encryption. The MUC to 

Meter data may contain control data (time synch, valve control, etc) so should be 

encrypted. The Meter to MUC data should be encrypted for privacy reasons (to mask 

zero or low consumption of temporarily uninhabited quarters). 

The MUC documents require only encryption for MUC to Meter data 

(MUC_080128_inkl_Anlagen.pdf SRR section 5.3.9). 

Note that the EN13757 only specifies encryption for Meter to MUC data. 

Encryption Algorithm 

The encryption algorithm is in both the Dutch smart meter specification and the OMS 

documents AES-128. 

The block chaining mode is in both specification documents CBC (Cipher Block 

Chaining). 

In the Dutch specification, the initialisation vector is binary zero, in the OMS 

specification the initialisation vector (IV) is built from data that is sent (in the same 

transaction as are the encrypted data) as unencrypted byte stream. 

Encryption key exchange 

In the Dutch smart meter specifications, a new encryption key is encrypted with a 

meter-specific default encryption key to prevent exchange of an unencrypted plaintext 

encryption key. This allows a relatively secure modification of encryption keys. 

In the OMS documents there is no exchange of encryption keys; hence changing 

encryption keys in an operational meter is not possible. The encryption keys in the 

OMS specification are configured in the production facility. The encryption key is 

then sent unencrypted from the meter to the MUC, and from there to the Head End, 

during installation. (MUC_080128_inkl_Anlagen.pdf SRR section 5.3.9). 

Comments: 


• Does this mean that a “rogue” MUC can inquire with a meter and receive its 

encryption key? 

• How is the installation process initiated? 

M-Bus signature field. 

The M-Bus signature field (EN 13757-3 section 5.10) is modified to support the AES 

128 encryption algorithm. The OMS documents (OMS-Spec_Vol2_Primary_v102.pdf 

section 4.2.2.2) however include the Hop Counter in the LSB of the signature field, to 

support repeater functionality in wireless networks. We are not sure if this 

implementation is according to the (preliminary) EN-13757-5 standard (ref also 

OMS-Spec_Vol2_Primary_v102.pdf section 2.2.1). The Dutch Smart meter 

documents do not support repeater or relaying functionality in wireless networks, and 

strictly follow the signature definitions in EN 13757-3 section 5.10. 

Infrastructure 

In the Dutch Smart Meter documents, the Electricity meter is built into the MUC 

gateway. This means the option to exchange electricity data over the M-Bus 

connection is not specified. 

In the MUC specification, the MUC and the Electricity meter are separate objects, and 

the exchange of E-data is described. This allows for a more flexible approach. 

System Installation And Initialisation 

The Dutch smart meter documents include detailed specifications of initialising 

connections. Specifically the binding of newly installed wireless meters to a MUC is 

described in detail. 

This is not included in the OMS specifications. 

Operational Data Transfer 

Tariffing 

The Dutch smart meter specification does not include exchange of tariff data. The 

OMS documents do (OMS-Spec-Vol1_General_v100.pdf section 3.7 and 

MUC_080128_inkl_Anlagen.pdf section 3). 

This means the Dutch meters can not display tariff or cost indications, just 

consumption data consisting of measured or calculated data. 

Valve commands 

Valve commands and Valve status reporting are handled differently in the Dutch and 

MUC documents (MUC_080128_inkl_Anlagen.pdf section 5.2.3) : 

Dutch definition 

German definition 

DIF 01H 89H 

VIF FDH FDH 

VIFE 1FH 1AH 


Contents 

00 – closed 

01 – opened 

02 – released (ready to 

open) 

00 – closed 

01 – opened 

02 – released (ready to 

open) 

03 – moving 

04 - ready 

The Dutch approach is to refer to the valve as remotely controlled device; the MUC 

approach is to refer to the valve as Digital Output. 

Note that in the German approach I personally would have selected “Digital Input” 

(VIFE=1BH) for valve status (MUC_080128_inkl_Anlagen.pdf SRR section 5.3.4). 

Meter fault / alarm handling 

(MUC_080128_inkl_Anlagen.pdf section 5.2.4) 

The extended error flag (German definition DIF=n4H, VIF=FDH, VIFE=17H) is not 

used in the Dutch version. The error flag in the Data Header is used in the Dutch 

version. This limits the number of errors in the Dutch definition to eight bits, five of 

which are predefined. 

Time Synchronisation 

The Dutch smart meter specifications include time synchronisation. Whether or not 

Daylight Savings Time is used is up to the grid company managing the meter. 

The MUC documents include Summer/Wintertime (DST) updates 


Indexes Log 


In the Dutch smart meter specifications, the M-Bus devices (meters) do not maintain 

logging. The MUC maintains all historic logs, meters transfer current measured data. 

The indexes log functions are therefore not used in the Dutch version. 

Gas Volume, transfer and calculation 

OMS chooses to Define a new gas metering device to enable transfer of corrected 

volumes (OMS-Spec_Vol2_Primary_v102.pdf section 4.3.1). In our opinion, the 

device is still a regular gas meter; however the data item is different. We choose to 

define a new DIF/VIF combination to signify corrected gas volumes. This would, in 

theory and in future systems, also allow the transfer of both corrected and uncorrected 

volumes by one single M-Bus device (MUC_080128_inkl_Anlagen.pdf SRR section 

5.3.2). 

Other Data Transfers 

The Dutch Smart meter specifications do not define large storage indexes for metered 

data, however the meter reading of the previous full hour is stored as storage index 

#1. The is never more than one measured value stored in the Dutch meters. In the 

MUC documents, measurement and reading logs are defined 

(MUC_080128_inkl_Anlagen.pdf SRR section 5.4). 


Other issues 

Frame Format 

The MUC_080128_inkl_Anlagen.pdf SRR section 5, ANNEX A: WIRELESS M- 

BUS MESSAGES, refers to the FT1.2 message format. For all wireless transmissions 

the FT3 message format should be used. This is corrected in the OMS-Spec- 

Vol1_General_v100.pdf and OMS-Spec_Vol2_Primary_v102.pdf. 

Wireless modes 

I strongly suggest to choose between S2 and T2 modes for wireless transmissions. 

Leaving the choice open will probably not help much in designing interoperable 

systems. (MUC_080128_inkl_Anlagen.pdf SRR section 3.1). 

Differences between OMS/MUC and Dutch approach 1 

Topic RWE spec Dutch spec 

Identification 

Serial Number R/W R - Header 

Meter Type R R - Header 

Manufacturer text R - 

Manufactured date R - 

Volume / Tariff 

Volume Index Corrected W - 

Volume Index with Active Tariff R - 

New Tariff – Effective date/time W - 

Valve 

Valve State R/W R/W 

Valve Number of Closes R - 

Battery 

Remaining Battery Days R - 2 

System State 

Date and Time R/W R/W 

Time Synchronisation Offset W - 

Extended Error Flag R/W - 

Daylight Saving R/W - 

Information Transfer 

Meter Information Request R - 

Transparent Information R/W - 

Configuration 

Time between RF polls R/W - 3 

1 Note that the Dutch specification explicitly specifies that all DIF/VIF codes in the EN13757-3 can be 

exchanged. It is likely that some data objects do not contain useful information, but technically they 

can be exchanged. In this table we only refer to data objects that will contain “defined and useful data”. 

2 Calculated in MUC 


Topic RWE spec Dutch spec 

Number of days of non-communication R/W - 

Encryption Key Exchange R/W 4 W 

Data 

Metered value, actual R R 

Metered value, previous hour R R 

3 Fixed value. 

4 One-Time in production facility. No key changes allowed in online systems.

Introduction - KNX

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