NSP – Network Service Provider
Network Service Provider is a company that offers internet backbone services to an Internet service provider (ISP). NSPs does this by allowing ISPs access their network infrastructure or a network access points (NAP).
Internet service providers (ISPs) are those companies that sells Internet services like Internet access and network bandwidth to different consumer organization and individuals.
There are many Network Service Providers that offers Internet services directly to an end user ( an individual or an organization). Such NSPs could be considered as ISPs. In this way, a telecommunication company, cable TV operator offering Internet services and a wireless data provider could be considered very similar to an NSP.