Cover traffic

There are two types of cover traffic: drop and loop. They differ in two ways:

• Destination selection for a drop cover packet is the same as for a request: a random mixnode, excluding the source node and, if there is exactly one, its connected gateway mixnode. Loop cover packets are always sent from a node to itself.
• Drop cover packets are replaced by packets from the request/reply queue for the session. Loop cover packets are never replaced.

Nodes should dispatch drop and loop cover packets in each active session according to Poisson processes. The average drop/loop rates should be the same for all mixnodes in a session, and for all non-mixnodes in a session; see the parameters chapter. Note that the rates should be halved in some phases; see the sessions chapter.