The WDM slotted Add/Drop Multiplexer (WSADM) technology relies on time slotted WDM rings, where a slot can carry a single WDM packet. All stations can insert and receive these WDM packets. This differs from previous architectures in which packets were carried over a single wavelength, while multiple packets could be carried in a single slot, thus taking advantage differently of the WDM dimension. The WSADM architecture is expected to reduce costs by exploiting low cost technologies. We propose mathematical models for evaluating the performance offered by WSADM optical packet rings, under two different packet insertion policies. In the slot reservation mode, a station can only use the slots that are periodically reserved for its exclusive usage. In the opportunistic insertion mode, a station can use any slot that is neither reserved, nor already occupied. These modes are bench-marked with a channel reservation mode in which each wavelength is dedicated to a single station.