Why was the base_fee for the routing fee calculation of the Lightning Network included?

Question

Currently and as defined by BOLT 07 on the Lightning Network, the fees for forwarding an HTLC of amount amount_to_forward are computed as:

fee_base_msat +  amount_to_forward * fee_proportional_millionths / 1000000

I am wondering why the fee_base_msat was actually included and which concrete problem it solved that could not be solved if the fee_base_msat were dropped?

Answer 1

It was added as a compromise against more complicated ideas, actually. Base plus percentage is a pretty standard fee structure, so I went with it.

If I'd been more familiar with the finance world, it would have been expressed in basis points, though, not ppm.