/*
Milan, Italy
Originally published: 17/10/2016
latest revision: 15/10/2017
PJON™ protocol acknowledge specification v1.0
Invented by Giovanni Blu Mitolo,
released into the public domain

Related implementation: https://github.com/gioblu/PJON/
Compliant versions: PJON v9.0 and following
*/

PJON™ protocol acknowledge specification v1.0

The PJON Standard supports both synchronous and asynchronous acknowledgement. This two mechanisms are defined to ensure that a packet transmission ended positively with no errors and can be used individually or together.

Synchronous acknowledge

Channel analysis       Transmission                 Response
 _____  ____________________________________________  _____
| C-A || ID |  HEADER  | LENGTH |CRC8| CONTENT |CRC8|| ACK |
|-----||----|----------|--------|----|---------|----||-----|
|  0  || 12 | 00000100 |   6    |    |    64   |    ||  6  |
|_____||____|__________|________|____|_________|____||_____|

The graph above contains a standard packet transmission with synchronous acknowledge request where the character @ or 64 is sent to device id 12 with 00000100 header. As defined by the PJON protocol layer specification v3.0 the third bit from right up in the header requests to transmitter a synchronous acknowledge response. How the synchronous acknowledgement procedure works depends on the medium and the strategy used, see PJDL v2.0, PJDLR v2.0, PJDLS v2.0 and TSDL v2.0 specification.

Asynchronous acknowledge

Channel analysis               Transmission                Response
 ____________________________________________________________  ___
|ID| HEADER |LENGTH|CRC|BUS ID|BUS ID|ID|PACKET ID|DATA|CRC32||ACK|
|--|--------|------|---|------|------|--|---------|----|-----||---|
|12|10001111|  20  |   | 0002 | 0001 |11|   99    | 64 |     || 6 |
|__|________|______|___|______|______|__|_________|____|_____||___|
                       |RXINFO| TX INFO |       

The graph above contains a standard packet transmission with asynchronous acknowledge request where the character @ or 64 is sent to device id 12 with 0001111 header containing its packet id 99. As defined by the PJON protocol specification v3.0 the fourth bit from right up in the header requests to transmitter an asynchronous acknowledgment response and the presence of the packet id. The second bit from right up signals the inclusion of the sender's info necessary to send back an asynchronous acknowledgment packet when received.

PJON™ recursive acknowledgement pattern

In a scenario where there is no direct communication between two devices, a synchronous acknowledgement can't be obtained successfully, so an asynchronous acknowledgement packet has to be sent back from receiver to the packet's transmitter to inform of the correct packet reception.

 BUS 0.0.0.1                      BUS 0.0.0.2
 ______             ______             ______
|      |           |      |           |      |
| ID 0 |___________|ROUTER|___________| ID 0 |
|______|           |______|           |______|

A router in the center is connected with two different buses, bus 0.0.0.1 and 0.0.0.2, communication between device 0 of bus 0.0.0.1 with device 0 of bus 0.0.0.2 can be obtain only through the router.

Transmission                                             Response
 __________________________________________________________  ___
|ID| HEADER |LENGTH|CRC|BUS ID|BUS ID|ID|PACKET ID|DATA|CRC||ACK|
|--|--------|------|---|------|------|--|---------|----|---||---|
|0 |10001111|  20  |   | 0002 | 0001 |0 |   99    | 64 |   || 6 |
|__|________|______|___|______|______|__|_________|____|___||___|
                       |RXINFO| TX INFO |         

In the packet shown above device 0 of bus 0.0.0.1 sends @ (64) to device 0 of bus 0.0.0.2. Being the header 00001000 bit up (asynchronous acknowledgement request) the packet is formatted containing the 2 bytes integer packet id 99 (used by receiver to send back an asynchronous acknowledgement packet) immediately after the sender information. Being header's 00000100 bit up (synchronous acknowledgement request) receiver will acknowledge synchronously with an PJON_ACK (6) in case of correct reception or PJON_NAK (21) in case of mistake. This precise case is used as an example to show both features used at the same time to obtain an efficient and secure way to transmit packets with correct transmission certainty.

BUS 0.0.0.1                                          BUS 0.0.0.2

1 Packet send - 2 sync ack, forward - 3 sync ack, async ack send
 ______                      ______                      ______
|      |                    |      |                    |      |
| ID 0 |____________________|ROUTER|____________________| ID 0 |
|______|                    |______|                    |______|
   5 sync ack                   4 ack, async ack forward

/* If packet length - its overhead is 2, it is an asynchronous
   acknowledgement packet containing only its packet id */

1) Device 0 sends the packet, the router has a route to device 0 of bus 0.0.0.2 so responds with a synchronous acknowledgement

 __ ________ ______ ___ _______ _______ __ _________ ____ ___  ___
|ID| HEADER |LENGTH|CRC|BUS ID |BUS ID |ID|PACKET ID|DATA|CRC||ACK|
|0 |10001111|  20  |   |0.0.0.2|0.0.0.1|0 |   99    | 64 |   || 6 |
|__|________|______|___|_______|_______|__|_________|____|___||___|
                       |RX INFO| TX INFO  |

2) Device 0 of bus 0.0.0.1 wait for an asynchronous acknowledgement of the packet sent. Router sends to device id 0 of bus 0.0.0.2 and receives a synchronous acknowledgement

 __ ________ ______ ___ _______ _______ __ _________ ____ ___  ___
|ID| HEADER |LENGTH|CRC|BUS ID |BUS ID |ID|PACKET ID|DATA|CRC||ACK|
|0 |10001111|  20  |   |0.0.0.2|0.0.0.1|0 |   99    | 64 |   || 6 |
|__|________|______|___|_______|_______|__|_________|____|___||___|
                       |RX INFO| TX INFO  |

3) Device 0 of bus 0.0.0.2 sends an asynchronous acknowledgement packet to device 0 of bus 0.0.0.1. Router has a route to device 0 of bus 0.0.0.1 so responds with a synchronous acknowledgement and device 0 of bus 0.0.0.2 ends the transaction after receiving a synchronous acknowledgement by the router

 __ ________ ______ ___ _______ _______ __ _________ ___  ___
|ID| HEADER |LENGTH|CRC|BUS ID |BUS ID |ID|PACKET ID|CRC||ACK|
|0 |10001111|  19  |   |0.0.0.1|0.0.0.2|0 |   99    |   || 6 |
|__|________|______|___|_______|_______|__|_________|___||___|
                       |RX INFO| TX INFO  |

4) Device 0 of bus 0.0.0.1 receives the asynchronous acknowledgement packet forwarded by the router and responds with a synchronous acknowledgement.

 __ ________ ______ ___ _______ _______ __ _________ ___  ___
|ID| HEADER |LENGTH|CRC|BUS ID |BUS ID |ID|PACKET ID|CRC||ACK|
|0 |10001111|  19  |   |0.0.0.1|0.0.0.2|0 |   99    |   || 6 |
|__|________|______|___|_______|_______|__|_________|___||___|
                       |RX INFO| TX INFO  |

This documents doesn't want to specify in any way the routing mechanism (still not officially specified), but uses routing as a necessary example to showcase clearly the power of the recursive acknowledgement pattern.

This document is automatically generated from the github repository. If you have noticed an error or an inconsistency, please report it opening an issue here