Snort Struggles: How to detect the FTP service name?

I am muddling through learning Snort and feeling a bit daft. I'm trying to write a rule that allows me to detect the FTP service name used in a .pcap. I analyzed the .pcap with sudo snort -c local.rules -A full -l . -r ftp-png-gif.pcap I looked up some ways to find the ftp service name and I found a few like sudo snort -r snort.log.1671731339 -X -n 10 which would probably do the trick, but I'm not sure why. I get that -X has something do the preprocessor, but I'm not sure why this outputs anything with FTP, or how to find where the FTP service name is in the output.
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Cyber Forum250d ago
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Fox'Say!250d ago
UPDATE: I used the sudo snort -r snort.log.1671731339 -X -n 10 command and got results for the 10 packets that look like this. As you can see, I found a packet that said 220 Microsoft FTP Service, but I still don't know why this worked or how they knew the answer would be within 10 packets of the log.
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