In RPL for selecting the best parent with the trust model In order to select a trusted parent, direct and indirect trust must be calculated. For direct trust computation, the number of packets sent to node A by node B and the number of packets forwarded by node A on behalf of node B must be counted and I have trouble in determining the number of forwarded packets. Any help will be useful for solving this problem.
You can look at the values of uip_stat.ip.sent and uip_stat.ip.forwarded. Make sure to enable uIP statistics (#define UIP_CONF_STATISTICS 1).
Related
I am trying to send a P2P packet from a source to a destination node using classic RPL protocol of Contiki-ng. Unfortunately, the packet can traverse only 8 hops. If the destination is placed somewhere with distance greater than 8 hops, the packet cannot reach to the destination. I tried both the storing (hop-by-hop) and non-storing (source routing). Does anyone know how I can increase this limitation? Thank you in advance!
I have two master nodes connected to the same CAN bus, both send data to my PC.
first master ID = 0xFFA1
second master ID = 0xFFA2
Since the first master ID is lower than the second it takes control of the bus more than the second master. And this causes some delay in the data.
Is there a way to make load balancing between two nodes so that each node send an almost equal amount of messages.
I tried making the first node send data while switching between two IDs 0xFFA1 and 0xFFB2,
and the second node sends data with ID 0xFFB1. And it didn't help.
There is no such thing as "masters" in CAN, nor in higher layer protocols like CANopen for that matter (a "master" in CANopen is just a supervisor node). Who gets to send what is defined by the CAN identifiers - CAN is primarily focusing on data, not nodes. What matters is what is sent, rather than who is sending/receiving, since every message is broadcasted.
It sounds as if you have 2 nodes that wildly spam the bus with identifier 0xFFA1 and 0xFFA2 messages, as fast as they are able, leading to 100% bus load. Then the node sending 0xFFA2 will "starve". Sending data "as fast as you are able" is never the correct way to use CAN.
Instead you need to define a higher layer protocol that dictates real-time characteristics. In control systems, this is most commonly done by having nodes send data at fixed intervals, such as once per 10ms or 100ms. This alone should fix your starvation problem.
If you want to prevent nodes from sending at the same time, then you could provide a means for them to synchronize. A trick used in CANopen and other protocols, is to have one node send out a "sync" message at given fixed time intervals.
After reading this sync message, all nodes should act within x ms from receiving it.
Steps
I have created a private node and use --maxpeer of 1 (network id =1223123341)
Add user's X node by admin.addPeer(enode of user X) successfully. (same network id and genesis)
Base on my understanding that maxpeer will limit the node that can conect from the network to 1 node only(user's X node)
Question - if user's X node update his --maxpeer to 5 and give the network id and genesis file to other nodes, does it means there can now 5 who can conect to this network? Who control the maxpeer in a private network (e.g. network id =1223123341)
If you want to avoid 51% attacks, you should consider running permissioned chains. You can either do this by keeping your genesis block of the Proof-of-Work or -Stake network private, but you would have to share it with any participant in the network and you will not know if this can be leaked at some point. And if it does, there is no way to stop other users from participating.
Another option is to use Proof-of-Authority networks. Both Geth and Parity support that. This allows only strictly defined nodes to seal blocks and everyone else can just use the network, but not change the set of rules defined by the authorities.
Note: I work for Parity.
The --maxpeers option controls the number of peers for that particular instance. So, yes, if node 1 has --maxpeers=1 and node 2 has --maxpeers=5, you will not be limited to just 2 nodes in the network. Nodes don't all need to know about every other node either, so node 2 may be peers with nodes 3-7 and not know anything about node 1 (in other words, with the example you provided, the total number of nodes could be even more than 5).
AFAIK, there is no configuration to limit the total number of nodes in a network, and I don't see what you would want one. You are given enough control at the node level.
I have a strange finding about the heartbeat-protocol in CANopen. Maybe somebody else has seen something like this and maybe it is supposed to work like this... Anyway, here's what it's about:
In CANopen there are two timeout-based life-guarding mechanisms: the first is node guarding, which I will not mention further, since it's considered old news.
The other one is called heartbeat. It is pretty simple: Any participant on the network sends a regular message stating its node ID and its state. The frequency is defined by object 0x1017sub0 and is called heartbeat-producer-time. If it is set to zero, no heartbeat is being sent.
Any other participant can then define a number of nodes it wants to find on the network plus the maximum time there may be between two consecutive heartbeat-messages. This information is stored in object 0x1016sub1..n as 32-bit entries for as many nodes as this particular node wants to listen to.
The entries consist of the node ID (bits 22 to 16) and the mentioned maximum time that may elaps between heartbeats, called the heartbeat-consumer-time (in bits 15..0). Again if the entry is zero, it is being ignored.
As you may have gathered, there is no distinction between network-master (node ID 1) and slaves (node IDs 2 to 127).
So far the theory, now for my problem:
I configure one of the slave-nodes in my network as a heartbeat-consumer for the master, so there's an entry in object 0x1016sub1 that looks like this: 0x000107D0. Meaning that a heartbeat-message from the master is expected after at least two seconds.
I have observed that this works in two examples. If I send a master-heartbeat for a time and then stop, the node either returns to pre-operational mode or sends an appropriate emergency-message.
If I don't send any master-heartbeat-messages, I would expect that after I start the node (send it into operational mode) it takes at most two seconds for the node to either return to pre-operational mode or send an appropriate emergency-message or perhaps even both. But in the two examples I tried, nothing happened. If I never send any heartbeat, the node never expects one and just keeps on running.
The two examples are very different from each other. I am not sure whether they use the same CANopen-stack library perhaps.
Is there an explanation?
If you read CANopen User Manual, section 1.3.1.6, page 39, you will notice that the heartbeat consumer is first activated upon receiving a heartbeat from the producer. I would assume then that, since in your example the first heartbeat is never sent, the consumer is not activated.
While reading the ERTS user's guide, I found this section:
The only signal ordering guarantee given is the following. If an entity sends multiple signals to the same destination
entity, the order will be preserved. That is, if A sends a signal S1 to B, and later sends the signal S2 to B, S1 is
guaranteed not to arrive after S2.
I've also happened across this while doing further research googling:
Erlang Reference Manual, 13.5:
Message sending is asynchronous and safe, the message is guaranteed to eventually reach the recipient, provided that the recipient exists.
That seems very vague and I'd like to know what guarantees I can rely on in the following scenario:
A,B are processes on two different nodes.
Assume A does not crash and B was a valid node at some point.
A and B monitor each other.
A sends messages M1,M2,M3 to B
In the above scenario, is it possible that B receives M1,M3 (M2 is dropped),
without any sort of 'DOWN'/'EXIT'/heartbeat timeout being received at A?
There are no other guarantees other than the ordering guarantee. Note that by default you don't even know who the sender is, unless the sender encodes this in the message.
Your example could happen:
A sends M1 and M2
B receives M1
The node on which B resides gets disconnected
The node on which B resides comes up again
A sends M3 to B
B receives M3
M2 can be lost on the network link in this scenario. It is highly unlikely this happens, but it can happen. The usual trick is to have some kind of notion of such errors. Either by having a timeout trigger, or by monitoring the node or Pid which is the recipient of the message.
Updated scenario:
In the updated scenario, provided I read it correctly, then A would get a 'DOWN' style message at some point, and likewise, it would get a message telling you that the node is up again, if you monitor the node.
Though often, such things are better modeled using an idempotent protocol if at all possible.
Reading through the erlang mailing-list and the academic faq, it seems like there are a few guarantees provided by the ERTS implementation, however I was not able to determine whether or not they are guaranteed at a language/specification level, too.
If you assume TCP is "reliable", then the current implementation guarantees that
given A,B are processes on different nodes (&hosts) and A monitors B, A sends to B, assuming A doesn't crash, any message delivery failures* between the two nodes or host/node/process failures on B will lead to A getting a 'DOWN' message (or 'EXIT' in the case of links). [ See 1 and 2 ]
*From what I have read on the mailing-list thread , this property is almost entirely based on the fact that TCP is used, so "message delivery failure" means any situation where TCP decides that a failure has occurred/the connection needs to be closed.
The academic faq talks about this like it's also a language/specification level guarantee, however I couldn't yet find anything to back that up.