Do online brokers offer access to Electronic Communication Network?

External question — Quantitative Finance Stack Exchange Author: user1700890 Original post: https://quant.stackexchange.com/questions/59906 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. I wonder which online broker offer access to Electronic Communication Network (ECN)? It does not look like individual can register with ECN.