Date Added: Sep 2010
Next Generation Network (NGN) is envisage to integrate heterogeneous wireless systems. NGN is expected to have Quality as the major challenging issue. More specifically, NGN aims at providing guaranteed Quality of Service (QoS) and Quality of Experience (QoE) i.e. what quality a network provider can offer (or claims) & what quality user experiences. NGN user may be interested in changing its network operator or is forced to change the serving access point (AP) or base station (BS) in order to achieve a given level of QoE. Seamless transfer of user's service from existing operator to a new operator bearing dissimilar radio access technology is called Vertical Handover (VHO).