HTTP Cisco IOS upgrade

I am to work on some Cisco switches and routers upgrades.

I was going to do it TFTP as I have done in the past.

My boss said is better with "HTTP".

I m not sure what he means and it sucks if I have to ask him.

Does anyone here know what he means by upgrade IOS with HTTP? I am trying to find this with Google yet I could use some extra help.

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Thank you