He was referring to the updated RFC 4821.
" In the absence of ICMP messages, the proper MTU is determined by starting with small packets and probing with successively larger packets. The bulk of the algorithm is implemented above IP, in the transport layer (e.g., TCP) or other "Packetization Protocol" that is responsible for determining packet boundaries."
It is designed to support working without ICMP. It's draw back is the ramp time, which makes it useless for small transactions, but it can
be
argued that small transactions don't need larger MTUs.
Jack
That is also somewhat mitigated in that it operates in two modes. The first mode is what I would call "passive" mode and only comes into play once a black hole is detected. It does not change the operation of TCP until a packet disappears. The second method is the "active" mode where it actively probes with increasing packet sizes until it hits a black hole or gets an ICMP response.