# The SetAcceptableLatency command¶

In the introduction we showed how spike events are delivered as quickly as possible, then queued at the receiving node until it is time for them to be applied. MUSIC does its very best to make the transmission time look like zero time, so the total in-simulation delay from the source to the target is the delay from the input proxies to the targets. The spike events have to be delivered through the MUSIC connection to the recipient nodes no later than that time.

In practice, MUSIC can — and, when you have recurrent connections, has to — use a bit of in-simulation time to deliver events. It’s often more effective to send several steps worth of events in one packet than to send one packet of data per time step. In order to do this, MUSIC needs to know how much time is available for such delays.

The SetAcceptableLatency command specifies this time for each input port. A simulation model may add, delete or alter connections at any point during a simulation, and this may happen locally in a large, distributed network, so it is in practice not possible for MUSIC to figure out the minimum time by itself. We (hopefully) know what our code will be doing, so we set this manually.

If the acceptable latency is longer than the minimum delay across the connections from an input proxy, spikes may be delivered to those targets later than they were supposed to be, thereby breaking the simulation in subtle or obvious ways. In simple feed-forward cases like in our example, MUSIC does not need to use any of that extra delay so things may work fine, but in complex simulations with recurrent connections this may no longer be the case.