Suppliers who use channel partners as part of their distribution network can use a one- or two-tier distribution channel. In a single-tier distribution system, the provider develops relationships with channel companies such as VARs, system integrators (SIs), and managed service providers (MSPs) that sell to end customers. In a two-step system, the supplier sells products to an independent distributor who, in turn, supplies products to channel partners who then package solutions for end customers. The two-step model makes dealer agreements necessary to facilitate relationships between distributors and channel partners. Unlike a trader, a broker does not act for his portfolio, but facilitates transactions by bringing together buyers and sellers.