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Barcode scanner, MSSQL, retransmission...cause ?

HI, I'm experiencing intermittent slowdowns using barcode scanners in a warehouse. Here is the captured packets and the flow. One image is the flow without retransmission and the other is with. Barcode scanners are connected to WiFi and in the same subnet as SQL server. WiFi controller shows no dropped packets from client. It looks like SQL expects request from the client but when it doesn't receives it and then he sends retransmission TCP packet.

image description

Any suggestion about what could cause this behaviour, would be appreciated, thanks ;)

vmiro's avatar
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vmiro
asked 2018-09-24 09:55:57 +0000, updated 2018-09-24 10:02:25 +0000
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This is an interesting question, but we need more data I think. PCAPs would be more useful. You can anonymize them using TraceWrangler.

Is this pattern consistent? How often does this happen? Is it the same packet getting dropped (retransmitted) every time? Where capture point is? Directly on WiFi controller or before it?

Transation completion time difference between two samples is 0.5 sec, do you mean this slowdown? I suspect I wouldn't notice it :) But if you do thousands of scans.. maybe.

Packet_vlad's avatar Packet_vlad (2018-09-25 13:51:33 +0000) edit
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Seems you are tracing on or next to the server. So I think/guess (due to screenshot) the Response after the RPC call got lost. And a RTO is triggered. More can´t be said without having a trace. But it seems you have packet loss somewhere or some problems in your WIFI setup.

Christian_R's avatar
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Christian_R
answered 2018-09-26 10:22:38 +0000, updated 2018-09-26 10:27:19 +0000
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