6.3 HBES RF Data Link Layer specific to HBES RF Multi systems
6.3.5 Data Link Layer protocol
6.3.5.1 RF Repetition counter for end devices
The RF Repetition counter shall be set to 2 for end devices.
6.3.5.2 The Layer-2 of an RF Retransmitter 6.3.5.2.1 General requirements
Any RF Retransmitter shall be either one of the following two types: a fast Repeater or a slow Repeater.
A Repeater shall repeat once any Telegrams received coming from the device it is configured with.
For HBES RF Multi, filtering is the rule.
Fast Repeaters shall be mains powered but slow Repeaters may be battery driven.
Operating on fast HBES RF Multi Telegrams, it shall receive and repeat any fast Frame. It shall use the frequencies F1, F2 and F3. Operating on slow HBES RF Multi Telegrams, it shall receive and repeat any slow Frame. It shall use the frequencies S1 and S2.
The HBES RF Repeater can be generic device. The selection of fast or slow Repeater function is done by HMI.
A Repeater shall repeat frames whatever the LFN value is but shall not repeat a frame that is already in the history list. There is only one entry per HBES Serial Number; the LFN is overwritten.
On fast RF channels, the Repeater shall adapt the preamble length according to the product it is linked with. This is, the preamble length shall be 15 ms or 4,8 ms. This implies a scanning sequence according to Figure 6 for a fast Repeater or Key
S for scan, Hop for Hopping, Rx for receiving mode 1 ms for hopping, 1 ms for listening or scanning or less.
Figure 7 for fast and slow Repeater or Figure 10 for a slow Repeater.
A fast and slow Repeater may lose or delay the repetition of fast Frames in case a simultaneous slow Frame occurs, therefore this implementation is not recommended. The interFrame time of 5 ms between a reception and the following transmission apply to Repeaters.
Receive frame
Idle Wait for time slot
Send Ack
6.3.5.2.2 Working principle
Figure 19 — General Repeater algorithm By default, the system is scanning the RF channels.
At regular intervals (depending on the kind of Repeater), the Repeater shall scan its RF channels to see if a HBES Frame is being transmitted. If not, it shall inspect the Frame queue. In case of a non-empty queue, the first Frame in the queue shall be transmitted. Else it shall get back to its scanning idle state.
If a Frame is detected, the Repeater shall receive the Frame. It shall then check the Frame to determine if the Frame is a correct HBES Frame. It can also check if it has recently sent the same Frame to avoid any distortion or echo effect. If the Frame is considered as bad, the Repeater shall get back to its scanning idle state.
If the Frame is correct then the Repeater shall queue that Frame. The Repeater shall then get back to its scanning idle state, waiting for the next Frame.
6.3.5.2.3 Fast Repeaters
Fast Repeaters shall have two working modes, HBES RF Ready or HBES RF Multi. For the HBES RF Ready, refer to the relevant clauses. In this mode, all the Telegrams to be repeated shall be located on the same frequency. As the preamble received may be only 1 ms-long, the Repeater shall listen to the RF channel continuously and the queued Telegrams can be immediately transmitted.
Figure 20 — HBES RF Ready algorithm
In the HBES RF Multi mode, the Telegrams to be repeated can be located on different frequencies (F1, F2, F3). The preamble of each Frame shall be 15 ms long; this allows the Repeater to be in complete low power mode most of the time.
Listen
Waiting for a F1sh frame Acquire noise level
Frame detected Repeat queued
frame
Queue frame
Frame repeated
Receive frame Frame
received Check frame
Goodframe
Badframe
No Frame detected and queue not empty
Figure 21 — Fast HBES RF Multi Repeater algorithm
The scan described above is a real scan amongst the RF channels not used (e.g. F2 and F3 if the Frame is received on F1). It is mandatory to do a scan on each RF channel prior to transmitting because of the hidden node problem, as it may result in HBES Frames at the same moment on different RF channels.
6.3.5.2.4 Slow Repeaters
With this Repeater, the Telegrams to be repeated can be located on different frequencies (S1, S2). The preamble of each Frame shall be 500 ms long; this allows the Repeater to be in complete low power mode most of the time.
Figure 22 — Slow Repeaters algorithm
The scan described above is a real scan amongst the RF channels not used (e.g. S2 if the Frame is received on S1). It is mandatory to do a scan on each RF channel prior to transmitting because of the hidden node problem as it may result in HBES Frames at the same moment on different RF channels.
Transmit frame Listen before talk
Try to use the same channel, change if it is too noisy
Frame repeated
Frame received Channel
OK
Good frame
Badframe
Scan
F1, F2 and F3
Timer interrupt
No frame detected
Frame detected Wait
for the end of the preamble
Receive frame End of preamble Check frame
CRC, recent history
IdleIdle
Queue frame
Frame queued
Frame queue inspection Frame queue
not empty Frame queue empty
Frame detected
Transmit frame Listen before talk
Try to use the same channel, change if it is too noisy
Frame repeated
Frame received Channel
OK
Good frame
Badframe
Timer interrupt Scan
No frame detected
Frame detected Wait
for the end of the preamble
Receive frame End of preamble Check frame
CRC, recent history
IdleIdle
Queue frame
Frame queued
Frame queue inspection Frame queue
not empty Frame queue empty
Frame detected
S1 and S2