Every weapon has a base speed (one can check for base speeds in items sections of diablo2 sites). With suffixes or shael rune or IAS jewels, one can increase this to needed levels.
There is a concept called WIAS (Weapon Increased Attack Speed), to determine weapon speeds. It is basically taking the negative of the weapon base speed (listed in arreat summit), and adding the IAS on the weapon. The WIAS information along with the weapon type is used to determine the attack speeds.
For example feral axe has -15 base speed, having 1 shael (%20 IAS) annd 1 IAS jewel (%15 IAS) makes it