imates the ONU queue status, typically based on the actual transmission in the previous cycle. For example, if an ONU has no traffic to send, it transmits idle frames during its alloca- tion period. The OLT would then observe the idle frames and decrease the bandwidth allocation to that ONT in the following cycle. In the opposite case, the OLT constantly increases the allocation size until idles are detected, slowly adjusting to growing traffic. Under a performance point of view, SR algorithms are superior in achieving high effi- ciency, as can be easily understood. However they are more complex to implement, also for the need of managing the return signals from all the ONUs. 11.2.2.3 GPON Capacity per User The evaluation of the GPON capacity per user is not simple in that it depends critically on the bundle of services provided to the users. As a first step, let us assume that all the users have the same service profile composed by a Mbit/s broadcast signal and a set of unicast services. Let us start with an evaluation of the downstream capacity per user. Due to the intrinsic broadcast capability of the GPON fiber infrastructure, the broadcast signal can be delivered in a dedicated part of the downstream TDM frame that will be received by all the end users. The remaining part of the downstream frame (2Gbit/s in our example) has to be divided among the users. Assuming a splitting ratio of 32, a bare physical bandwidth of 62.5Mbit/s is assigned to each user. However, in order to evaluate the effective bandwidth per user, we have to take into account the statistical multiplexing at the end of the OLT that acts on the low activity of the sources and the statistical multiplexing at the ONU switch that grooms signals. In the case of a realistic bundle of services (see Chapter 2) statistical multiplexing at the OLT allows a gain factor of the order of 4-5 over the bare physical bandwidth assigned to the user. The statistical multiplexing at the ONU guarantees, for sure, that the ONU port can manage, with its queuing ca