The statement that all ISP's over-sell is oversimplified.
All ISPs statistically multiplex the bandwidth requirements for off-net connectivity. Over-selling a peering relationship is impossible, as the ISP is selling only a speed-rated connection to it's own network. The assumption (or contractual service level) is generally that the ISP will augment either transit or peering as the resource becomes saturated.
The issue on hand is not the local or last mile bandwidth between the (retail) ISP and the customer, but the interconnection between the retail and the wholesale bandwidth providers. Two of the wholesale providers in question have publicly stated that their interconnections with specific retail providers are congested, and are not being augmented per their private contracts with the retail networks.
The above explanation is also a simplification, because for example Verizon is also a premium wholesale network in North America and several MSOs have also been building national transport networks.
All ISPs statistically multiplex the bandwidth requirements for off-net connectivity. Over-selling a peering relationship is impossible, as the ISP is selling only a speed-rated connection to it's own network. The assumption (or contractual service level) is generally that the ISP will augment either transit or peering as the resource becomes saturated.
The issue on hand is not the local or last mile bandwidth between the (retail) ISP and the customer, but the interconnection between the retail and the wholesale bandwidth providers. Two of the wholesale providers in question have publicly stated that their interconnections with specific retail providers are congested, and are not being augmented per their private contracts with the retail networks.
The above explanation is also a simplification, because for example Verizon is also a premium wholesale network in North America and several MSOs have also been building national transport networks.