Many of the protocols of Internet admonish one thing and reward the opposite. The “slow start” scheme admonishes the sender to refrain from sending many packets too soon yet rewards him, on the average, for sending more. This is not a necessary property of network protocols. X25 does not have this property. Both protocols are opportunistic and exploit available bandwidth. TCP takes several seconds to detect increased bandwidth, by which time it may no longer be available.

The style of protocol definition may be at fault here. X.25 defines a protocol at an interface. It describes a contract between the two parties, the network subscriber and the network. Software tests for compliance with the protocol.

The protocol also has efficiency problems.

Here is an admonition for crackers not to use said site to learn how to break systems. I doubt that it serves any ends.

A New York Times article noted that streaming protocols pointedly ignore slow start conventions and may thus dominate conforming traffic. They did mention that incentives might be necessary.