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Network layer. Discovery and polling quick start

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BartSchipperijn edited this page Jun 14, 2017 · 13 revisions

The Network layer. Compile and run example page describes how to compile and run EviNS on you local machine. There you can find the EviNS configuration for polling and the discovery procedure with some simple examples. Please go to this page for more details.

The current page describes in more detail how to start polling and send data. To start polling you have to take some simple steps:

  1. Start discovery
  2. Set protocol to send data
  3. Start polling
  4. Send data
  5. Get position

Table of Contents

1. Discovery

The discovery procedure is used to find the neighbours in the network. Using the neighbour information the routing table for the static (polling) routing protocol will be updated and can be used for data transmission.

To update the routing table, start the discovery procedure once more.

Start discovery

The NL format to start discovery (see also Polling commands / Star topology): 

NL,start,discovery,<Discovery period>,<Discovery total time>

During the discovery total time, the modem will try to discover neighbours / times.

In the example below we run the discovery procedure for 30 seconds. After 30 s of discovery time (30/10 – 3 times sending a broadcast), you will get an NL,routing asynchronous message which means the discovery procedure is completed. During the discovery time, the channel is busy and you cannot transmit messages. 

NL,start,discovery,10,30
NL,discovery,ok
NL,routing,3->3,2->2,4->4

2. Set protocol to send data

If you got the routing asynchronous message after the discovery procedure, the routing table will be updated for polling.

Since the discovery procedure uses flooding routing protocols, to start polling you have to set the polling protocol first. 

NL,get,protocols
NL,protocols,polling,sncfloodr

NL,set,protocol,polling
NL,protocol,polling

After that, you can check if the routing table was updated. 

NL,get,routing
NL,routing,3->3,2->2,4->4

3. Polling

Due to the underwater conditions and channel busyness it is sometimes not possible to deliver a big amount of data. In order to control such amount, we decided to integrate a message queue, which can be transmitted due to a polling request.

Set polling sequence (optional)

The discovery procedure automatically sets the polling sequence (a list of addresses known by the routing table) using the updated routing table. During the polling loop these addresses will be requested to send data.

If necessary, you can manually change the polling sequence (for instance to make sure certain modems are addressed first).

Set polling sequence: 

 # Check routing table
NL,get,routing
NL,routing,3->3,2->2,4->4
 # Set polling sequence 2,3,4
NL,set,polling,seq,2,3,4
NL,polling,2,3,4

Start polling loop 

NL,start,polling,[n|nb]

As you see, the start polling command has the optional flags b and nb. These flags decide if we need to get data buffered on the remote address.

b to get burst data from the remote address
nb to ignore burst data, to send only pbm to update the position

4. Send data

Message types

There are 4 types of messages: sensitive, tolerant, broadcast and alarm (see the description below).

Tolerant Tolerant messages are queued and are never dropped. A tolerant message will be sent if its remote address is requested during the polling loop. The message will be removed from the queue if it was successfully delivered.
Sensitive Sensitive messages are queued in limited numbers. If there are more than 3 of them, the oldest one will be dropped. A sensitive message will be sent if its remote address is requested during the polling loop. The message will be removed from the queue if it was successfully delivered.
Broadcast Broadcast messages are not queued. This message type has priority over tolerant/sensitive messages and will be sent first, other data will sent later. The message will be removed if it was successfully delivered.
Alarm An alarm message will be broadcasted through the whole network immediately while everything else will be ignored. The polling loop will be stopped.

Send different message types

Format: 

NL,send,[alarm|broadcast|tolerant|sensitive],Len,Dst,Data

In the example below it is assumed that you have 4 EvoLogics modems:

  1. Modem 1 is on the surface, starts the polling loop and polls through the modems with addresses 2,3,4.
  2. Modem 2,3,4 are on the bottom, collecting data to send to the surface.
Example:

Step 1: Preparations to start polling loop and send data

Modem 1: 

 # start discovery and wait till the async message NL,routing..
NL,start,discovery,5,10
NL,discovery,ok
NL,routing,2->2,3->3,4->4
 # set protocol polling
NL,set,protocol,polling
NL,protocol,polling
 # start polling loop with a burst data request
NL,start,polling,b
NL,polling,ok

Modem 2, 3, 4: 

 # set protocol polling
NL,set,protocol,polling
NL,protocol,polling

Step 2 : Sending /Receiving tolerant, sensitive, broadcast data from the bottom

Sending tolerant / sensitive / broadcast messages from Modem 2, 3, 4

Modem 2: 

 #send tolerant messages to modem 1
NL,send,tolerant,24,1,I am modem 2. Tolerant 1
NL,send,0
NL,send,tolerant,24,1,I am modem 2. Tolerant 2
NL,send,0
NL,send,tolerant,24,1,I am modem 2. Tolerant 3
NL,send,0

Modem 3: 

 # send 4 sensitive messages to modem 1. The max amount of
 # sensitive messages is 3. The first one (oldest) will be dropped
NL,send,sensitive,25,1,I am modem 3. Sensitive 1
NL,send,0
NL,send,sensitive,25,1,I am modem 3. Sensitive 2
NL,send,0
NL,send,sensitive,25,1,I am modem 3. Sensitive 3
NL,send,0
NL,send,sensitive,25,1,I am modem 3. Sensitive 4
NL,send,0

Modem 4: 

 #send broadcast messages to modem 1. Only the newest one will be transmitted.
NL,send,broadcast,25,1,I am modem 4. Broadcast 1
NL,send,0
NL,send,broadcast,25,1,I am modem 4. Broadcast 2
NL,send,0

=====> Modem 1 receives messages from the modems 2,3 and 4 successively due to the polling sequence

Modem 1: 

 # receiving all tolerant messages form modem 2
NL,recv,24,1,2,I am modem 2. Tolerant 1
NL,recv,24,1,2,I am modem 2. Tolerant 2
NL,recv,24,1,2,I am modem 2. Tolerant 3
 # receiving 3 newest sensitive messages form modem 3
NL,recv,25,1,3,I am modem 3. Sensitive 2
NL,recv,25,1,3,I am modem 3. Sensitive 3
NL,recv,25,1,3,I am modem 3. Sensitive 4
 # receiving the last broadcast message form modem 4
NL,recv,25,1,4,I am modem 4. Broadcast 2

Step 3 : Sending /Receiving tolerant, sensitive, broadcast data from the surface

Modem 1: 

 # send tolerant messages to modem 2
NL,send,tolerant,27,2,I am modem 1. Tolerant to 2
NL,send,0
 # send sensitive messages to modem 3
NL,send,tolerant,28,3,I am modem 1. Sensitive to 3
NL,send,0
 #send broadcast messages to modem 4
NL,send,broadcast,30,4,I am modem 1. Broadcast 3 to 4
NL,send,0

Modem 2: 

NL,recv,27,1,2,I am modem 1. Tolerant to 2

Modem 3: 

NL,recv,28,1,3,I am modem 1. Sensitive to 3

Modem 4: 

NL,recv,30,1,4,I am modem 1. Broadcast 3 to 4

Sometimes you will receive the same message multiple times because the message could not be successfully delivered and modem 1 will try to send it again on the next loop.

Step 4 : Sending alarm message

An alarm message will be broadcasted through the whole network.The polling loop will be stopped if an alarm message was received.

Modem 4: 

NL,send,alarm,,1,SOS

Modem 1, 2, 3: 

NL,recv,3,4,255,SOS

5. Get position

Using the Evins configuration file described in Network layer. Compile and run example, there is an extra socket where you can get position information (the nmea interface).

The EviNS positioning module runs in the background. During the polling loop and data exchange we are getting positions of each modem in the network.

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