The Rudin-Kisler ordering of P-points under $\mathfrak{b}=\mathfrak{c}$

M. E. Rudin proved under CH that for each P-point there exists another P-point strictly RK-greater (M. E. Rudin, Partial orders on the types of $\beta $\mathbb{N}$$,Trans\mathrm{.}Amer\mathrm{.}Math\mathrm{.}Soc\mathrm{.},155(1971),353-362)\mathrm{.}Assuming$\mathfrak{p}=\mathfrak{c}$ A. Blass showed the same, and proved that each RK-increasing $\omega$-sequence of P-points is upper bounded by a P-point, and that there is an order embedding of the real line into the class of P-points with respect to the RK-(pre)ordering (A. Blass, Rudin - Keisler ordering on P-points, Trans. Amer. Math. Soc., 179 (1973), 145-166). In the present paper the results cited above are proved under a (weaker) assumption $\mathfrak{b}=\mathfrak{c}$. A. Blass also asked in (A. Blass, Rudin - Keisler ordering on P-points, Trans. Amer. Math. Soc., 179 (1973), 145-166) what ordinals can be embedded in the set of P-points and pointed out, that such an ordinal may not be greater then ${\mathfrak{c}}^{+}$. In the present paper the question is answered showing (under $\mathfrak{b}=\mathfrak{c}$) that there is an order embedding of ${\mathfrak{c}}^{+}$ into P-points.