Windows Tutorials - Herong's Tutorial Examples - Version 5.62, by Dr. Herong Yang
Winsock 2 SPI and LSP Layers
This section describes the Winsock 2 SPI (Service Provider Interface) architecture and LSP (Layered Service Provider) layers.
A Winsock 2 SPI (Service Provider Interface) is an interface between the Winsock 2 API, WS2_32.DLL, and a TCP/IP transport service provider or a TCP/IP-based namespace service provider.
The Winsock 2 SPI is well designed so that it can be implemented as multiple layers:
Multiple LSPs can be installed on a single system. Each of them can perform
a specific communication function like filtering URL to prevent accessing certain websites.
The diagram below shows the relation of Winsock SPI and LSP layers:
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