Session persistence (a.k.a. Session Affinity or Stickiness) is the ability of the LoadMaster to make sure a given Client always gets to the same Real Server, even across multiple connections. Persistence can make sure that all requests from a client are sent to the same server in a Server Load Balancer (SLB) array or server farm.

Source IP Address persistence is used for all Lync Services except the External Web Services which need to use Super HTTP Persistence.