只要是Internet,本質上就是shared resource based on best effort,除非拉point to point的leased line才沒有shared resource的問題(純就上Internet而言,拉leased line透過ISP接Internet一樣是shared resource ),頂多是提高貢獻度較高的客戶的優先權而已(一般用QoS來描述,但鵝認為應該用Class Of Service來描述比較精確 )....BTW,有個古老的tag line是這麼寫的----With QoS,ISPs with congested backbone could say "I'll drop someone else's packet for U if U pay more $$ to me"....