IP layer / IPSec

[Olivier Bekoin]

"The term IPsec (IP Security Protocol) indicates a protocol of security,
defined to the IETF, which aims at making safe flows on the level IP."
(hhtp://www.hsc.fr)

I have a confusion and i ask this question about IP layer (network layer)
and IPSec.

is it the network layer of OSI model or the network layer of mapage TCP/IP
in 4 layers of the model with 7 layers OSI?

Thanks in advance

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