请教SCTP协议问题

westfox

请问大虾对RFC2960 Chunk Type定义的理解
Chunk Types are encoded such that the highest-order two bits specify
   the action that must be taken if the processing endpoint does not
   recognize the Chunk Type.
因为Chunk Type 只有8bits,上面这段话应该说明Chunk Type高2bits已被占用，那样只有0-63 Type值可用了，对吗？
可是在rfc3758中又定义了Foward-TSN Chunk Type = 192，这样就会产生二义性了？？？
困惑中....