Why when running an application layer program written by myself, if there is no delay before sending messages between nodes, the messages will not be received normally?

[黄轩]

[Gabriel Ferreira]

Network is not up yet? Socket connection failed/lost/stuck somewhere? Needs to be debugged to be certain.

On Friday, July 25, 2025 at 11:26:42 AM UTC+2 黄轩 wrote:

[黄轩]

The attachment contains two programs I wrote. I want to test the impact of the 80211 channel access protocol. However, I must delay the node before sending a message, otherwise the node will not be able to successfully receive the signal due to collision. I would like to know if the 80211 protocol can handle it by itself without me having to delay it.

[Tommaso Pecorella]

Usually you need to add a random delay when you install applications in the nodes, as in reality you never have two or more nodes starting at the very same time.

The L2 mechanisms to resolve collisions are great, but they can do little or nothing in case of nodes synchronization - which leads to unnatural synchronized bursts.

[Tom Henderson]

In this case, I do not think that the applications on the nodes need to have their start times randomized, because the Wi-Fi channel access mechanism (DCF) will randomize the access.

If there are at least two nodes trying to access the channel at the same time because they have a backlog of packets queued, there will eventually be a collision in the channel access when nodes happen to pick the same random backoff value, but Wi-Fi will detect this via a missing acknowledgment and resend the packets with different random backoffs, and they will (usually) be successfully retransmitted at some point in the future.

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