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EnOcean Protocol Layers | Physical, Data Link, Network Layer

This page covers EnOcean Protocol Layers viz. Physical layer, Data Link layer and Network Layer. The functions of EnOcean Protocol Stack layers including data flow through layers are described.

Introduction: The EnOcean is energy harvesting wireless technology designed mainly for building automation. EnOcean can also be used across industries for M2M (Machine to Machine) communication, IoT (Internet of Things), smart homes etc. The frequency bands used in EnOcean technology are 868 MHz, 315 MHz, 902 MHz, 928 MHz and 2.4 GHz (for IoT). The EnOcean uses two modulation schemes ASK and FSK.

EnOcean technology uses ASK and FSK modulation schemes in different frequency bands as defined by the standard. Based on ASK and FSK, there are two physical layer variants in EnOcean technology. ASK is used by 315 MHz and 868 MHz frequencies where as FSK is used by 902 MHz and 928 MHz frequencies.

EnOcean protocol layers

The figure depicts EnOcean protocol stack. As shown it has all the OSI layers except session layer. The EnOcean specifications define radio protocol #1 and radio protocol #2 in two different versions for ASK and FSK respectively. Let us understand functions of EnOcean protocol layers.

Following points summarize data flow across lower three layers of EnOcean protocol stack viz. Physical,data link and network layer.

• The operations performed at the EnOcean transmitter are adressing of telegram, medium access control using CSMA/CA or LBT (Listen Before Talk), subtelegram structure formation including checksum/CRC-8 mechanism, encoding of subtelegram and radio transmission.

• The operations performed at the EnOcean receiver are radio reception, decoding of subtelegram, subtelegram structure decoding, checksum/CRC checking and telegram decoding for upper layers.

• Application layer manages equipment profiles and handles RPC and RMCC.
• Presentation layer takes care of radio telegram processing and encryption/decryption.
• Transport layer takes care of smart Ack and remote management.
Refer article on OSI and TCP-IP Layers >> which describes generic functions of OSI layer and data flow across TCP/IP layers.

EnOcean Physical Layer

Following are the services performed by Physical layer.
• Encoding at the transmitter and decoding at the receiver, handles inverse of bits operation at transmit end and consecutively handles the same at receiver to recover data bits appropriately to help in recovery of subtelegram at data link layer.
• Radio transmission and radio reception at transmitter at receiver respectively.

➨Frame formation at Physical Layer (As per FSK specification) = {Preamble, Synchronization word, Length, Data_PL }
Where, Preamble - 16 bit , Sync word - 16 bit, Length - Number of data bytes followed, Data_PL - Payload data bytes
➨Frame formation at Physical Layer (As per ASK specification) = {Preamble, SOF, DATA, SYNC/EOF}
Where, Preambke - 8 bits, SOF (Start Of Frame) - 4 bits, DATA - Payload, SYNC/EOF - indicates another byte will follow or not ("01" indicates byte follows, "10" indicates last byte)

Let us understand physical layer operations performed on the input data (i.e. one or more subtelegrams) received from data link layer. Following are the operations performed at the transmitter end.
➨This layer does frame formation as per format above after receiving data from data link layer based on ASK or FSK.
➨It converts bits to symbols as per modulation scheme i.e. ASK or FSK as per modulation parameters defined in the standard. ASK modulation uses either 315 MHz or 868 MHz RF carrier where as FSK modulation uses either 902 MHz or 928 MHz as per countrywise allocations. Refer ASK vs FSK vs PSK >> for difference between ASK and FSK modulation types.
➨In ASK, protocol is inverted before transmission on air interface and 8 to 12 coding scheme is used.
➨In FSK variant of physical layer, GFSK filter is used as per national regulations.

At the EnOcean receiver, reverse operations to above are being carried out to recover the data (i.e. subtelegrams) which are being forwarded to data link layer.

EnOcean Data Link Layer

Following are the services performed by Data link layer.
• Subtelegram structure formation
• Control Sum calculation
• Subtelegram timing related mechanism
• Medium access control (using CSMA/CA or LBT-Listen Before Talk)

➨Subtelegram structure = { RORG, DATA, TXID, STATUS, HASH/CHECKSUM }
Where, RORG - Subtelegram type, DATA - Payload, TXID - 4 byte unique identity, STATUS - identifies transmission is from repeater and also type of integrity mechanism used, HASH/CHECKSUM - Data integrity check value of previous all bytes in a subtelegram.

Let us understand data link layer operations performed on the input data (i.e. telegram ) received from network layer.
➨The data (i.e. telegram) received from the network layer is packed as per subtelegram structure. 8 bit checksum or 8 bit CRC is calculated and appended as shown in the structure above. The checksum is calculated by simple sum of all the bytes of subtelegram except "HASH" value field. The CRC-8 is calculated using generator polynomial X8+X2+X+1 and following algorithm as described in the specification. This "last byte" helps in data integrity check at the receiver.
➨To ensure reliability of transmission, three identical sub-telegrams are transmitted over a fixed period.
➨Like TDMA, all the transmitters transmit subtelegrams at different time intervals and within the defined Tx maturity limit (i.e. 40 ms). This helps in avoiding collision of subtelegrams in the air.
➨Moreover transmitters follow LBT (Listen Beforee Talk) algorithm to avoid collisions in the channel (i.e. air medium). The LBT technique consume more energy and hence it is avoided in energy harvesting wireless devices.

EnOcean Network Layer

Following are the services performed by Network layer.
• Addressing of telegrams i.e. Encapsulation at transmitter and Decapsulation at the receiver
• Switch telegram conversion i.e. choice/status processing
• Repeating i.e. status processing

Let us understand network layer operations performed on the input data (i.e. message or telegram or data) received from upper layers.
➨It handles number of repeater hops during telegram transmission. Maximum of two hops are allowed between transmitter and receiver. Status byte is used by network layer to indicate status of subtelegram during transmission i.e. repeatition status and its sender i.e. original transmitter or first/second repeater.
➨Network layer performs addressing of each telegram using encapsulation mechanism at transmitter and de-encapsulation at receiver. It inserts "DESTID" field with four bytes preceding to TXID in the original telegram before transmission.
➨Redundancy is used during transmission if no other secured mechanism is used such as acknowldege. Maximum of two repetitions are used.

NOTE : The article only describes generic functionalities implemented at various EnOcean protocol layers viz. EnOcean physical layer, EnOcean data link layer and EnOcean network layer. For complete details of all the protocol layers and their functions, fields, their sizes and their order, refer technical specification documents viz. EnOcean Radio Protocol V1.2 and V1.3 at EnOcean website >>.


EnOcean wireless technology Related Links

EnOcean device transmitter and receiver testing >>
➨Refer advantages and disadvantages of EnOcean Wireless technology >>
EnOcean technology basics >>

References

• EnOcean Certification Specification (part 1a), Air Interface (ASK) V1.4, Released on Feb.10, 2019
• Visit www.enocean.com for everything you would like to know about EnOcean technology from inventor and pioneer of this energy harvesting wireless technology.
• EnOcean Alliance



Other Standard Physical Layers

Wireless physical layer overview   11b physical layer   11a physical layer   fixed wimax physical layer-OFDM   mobile wimax physical layer-OFDMA   11n physical layer   GSM Physical layer   TD-SCDMA Physical layer   GPRS physical layer   LDACS1 Physical layer   10,40,100 Gigabit Ethernet Physical layer   Zigbee Physical layer   WCDMA Physical layer   Bluetooth Physical layer   WLAN 802.11ac Physical layer   WLAN 802.11ad Physical layer   LTE Physical layer


Other standard protocol stacks

Zigbee Protocol Stack   GSM Protocol Stack   WiMAX Protocol Stack   LTE Protocol Stack   Z-wave Protocol Stack

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IoT Wireless Technologies

THREAD    EnOcean    LoRa    SIGFOX    WHDI    NFC   Lonworks   CEBus   UPB  

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