Method for estimating, in a broadband communication system comprising an access network and a plurality of broadband communication lines associated with the access network, a sustainable speed that can be sustained by a selected broadband communication line of said plurality of broadband communication lines, the method comprising: for each broadband communication line of said plurality of broadband communication lines, monitoring, at a plurality of monitoring time instants of a monitoring time period, an attainable speed that can be attained over the broadband communication line; grouping the broadband communication lines of said plurality of broadband communication lines into lines groups, each lines group comprising broadband communication lines associated with a same access network portion and sharing at least one line property; estimating the sustainable speed of the selected broadband communication line based on the respective attainable speeds monitored at said plurality of said monitoring time instants of said monitoring time period, characterized in that the method further comprises: for each broadband communication line of said plurality of broadband communication lines, determining (205,210) an attainable speed change that affects the broadband communication line over said monitoring time period comprising said plurality of said monitoring time instants, and determining, for each lines group, an expected maximum attainable speed change based on a statistic of the attainable speed changes that affect the broadband communication lines of the lines group over said monitoring time period, and in that said estimating the sustainable speed of the selected broadband communication line is further based on the expected maximum attainable speed change determined for the lines group which the selected broadband communication line belongs to. for each broadband communication line of said plurality of broadband communication lines, monitoring, at a plurality of monitoring time instants of a monitoring time period, an attainable speed that can be attained over the broadband communication line; grouping the broadband communication lines of said plurality of broadband communication lines into lines groups, each lines group comprising broadband communication lines associated with a same access network portion and sharing at least one line property; estimating the sustainable speed of the selected broadband communication line based on the respective attainable speeds monitored at said plurality of said monitoring time instants of said monitoring time period, characterized in that the method further comprises: for each broadband communication line of said plurality of broadband communication lines, determining (205,210) an attainable speed change that affects the broadband communication line over said monitoring time period comprising said plurality of said monitoring time instants, and determining, for each lines group, an expected maximum attainable speed change based on a statistic of the attainable speed changes that affect the broadband communication lines of the lines group over said monitoring time period, and in that said estimating the sustainable speed of the selected broadband communication line is further based on the expected maximum attainable speed change determined for the lines group which the selected broadband communication line belongs to. for each broadband communication line of said plurality of broadband communication lines, determining (205,210) an attainable speed change that affects the broadband communication line over said monitoring time period comprising said plurality of said monitoring time instants, and determining, for each lines group, an expected maximum attainable speed change based on a statistic of the attainable speed changes that affect the broadband communication lines of the lines group over said monitoring time period, and in that said estimating the sustainable speed of the selected broadband communication line is further based on the expected maximum attainable speed change determined for the lines group which the selected broadband communication line belongs to.