It's probably CenturyLink, which is the 3rd largest LEC behind AT&T and Verizon. (Comcast isn't classified as a Local Exchange Carrier, it a cable operator.)

It definitely is CenturyLink. Their Level 3 interconnects have been saturated for awhile, longer than March.

AT&T and Netflix signed an interconnection agreement, so LEC three must be CenturyLink (who also announced a 1Gb broadband trial in Portland)

http://mashable.com/2014/07/29/netflix-att-peering-deal/