ESP8266: SEND FAIL - causes, how to avoid, and how to recover?

[AndrewNode]

We have an ESP8266 that works well usually (AT 0.5 with firmware 1.4 - latest release as of today).

The problem is, when we sent larger amounts of data (like 200KB), we occassionally get a SEND FAIL message from the ESP8266.
We are waiting for "SEND OK" after each AT+CIPSEND.
We have tried sending in 2040 byte chunks and smaller chunks (no difference)
We have tried varying delays between each successful AT+CIPSEND, from 100ms to 2seconds (no difference)
We have tried adjusting the AT+RFPOWER - and this helped a little, but didn't completely solve the problem.

I'm using the ESP8266 as an AP and transmitting data to an iPhone that is right next to it.
What would cause the SEND FAIL response from the ESP8266? We have a similar IC that we're testing alongside the ESP8266 that sends without the failures.
How can you recover from the send fail / re-start the sending?

[ESP_Faye]

Hi,

You can capture the WiFi packets to analyze.

Can you send data successfully if you try to send again after SEND FAIL?

[AndrewNode]

After the send fail, if I try to resend, I don't get any response from the 8266's UART

I have been using a packet sniffer and what I noticed is that the 8266 does a number of retransmissions - perhaps as expected, then sends a TCP connection close packet, and then a few more retransmissions before stopping communications.

(I had posted twice about this same topic as I didn't realize my intiial post was simply awaiting approval - but I had briefly mentioned about using a packet sniffer there).

[ESP_Faye]

Hi,

Retransmissions mean that your network environment is not good. So the TCP transmission fail.

If you could provide the AT logs and WiFi packets, we will help analyze them.

Thanks for your interest in ESP8266 !