S allocates bandwidth to a SS by also specifying the burst profile to be used by the SS. The downlink profile is also controlled by the BS, although changes are at the request of the SS, which alone can monitor the strength of the received signal. Bandwidth Allocation Flexible allocation of available bandwidth among subscribers and connections is a third key element of the 802.16 MAC. The variety of services and scalability to potentially hundreds of subscribers per BS will clearly put heavy demands on the efficient use of bandwidth. The bandwidth requirements of individual subscribers are established when a connection is made and a number of messaging options in the standard allow SSs to request additional uplink bandwidth, to inform the BS of total bandwidth needs or allow the BS to poll individual SSs or multicast groups to establish these requirements. These mechanisms ensure efficient use of available bandwidth and flexibility to Chapter Twelve Table 12-7: 802.16 GPC and GPSS Classes of Subscriber Station SS class Capabilities GPC subscriber station Bandwidth granted to the SS can only be used for the connection that requested it. GPSS subscriber station Bandwidth granted by the BS need not be used only for the connection requesting it. The SS can use granted bandwidth for any of its connections. accommodate a wide variety of services or to respond to changing requirements of individual services. The MAC defines two classes of SSs (Table 12-7) - Grant per connection (GPC) and grant per subscriber station (GPSS), which differ in terms of the flexibility available to the SS in using its allocated bandwidth. At the cost of some additional complexity, GPSS provides greater efficiency and scalability than GPC, for example allowing a SS to respond more quickly to changing environmental conditions. GPSS requires additional intelligence in the SS in order to manage the QoS of its connections, but is clearly one aspect of the autonomy that has to be delegated to subscriber stations in a mesh network. Mobile WiMAX The