r per subscriber station (GPSS). Grants, given as durations, are carried in the UL-MAP messages. The subscriber station (SS) needs to convert the time to amount of data using the UIUC (Uplink Interval Usage Code). Bandwidth grant (bit rate capacity) is per subscriber station (GPSS). A base station grants bandwidth to a subscriber station. A subscriber station (SS) may redistribute band- width among its connections, maintaining QoS and service level agreements. Such an arrangement is suitable for many connections per terminal, off-loading the base station's work. This allows more sophisticated reaction to QoS needs. There is low overhead involved, but an intelligent subscriber station is required. There is also bandwidth grant per connection (GPC) where a base station grants bandwidth to a connection. This is mostly suitable when there are few users per subscriber station. This situation involves a higher overhead but allows for a simpler subscriber station. Bandwidth requests (bit rate capacity) requests come from the connection. There are several kinds of requests: Implicit requests (UGS-unsolicited grant service). In this case there are no actual messages, and they are negotiated at connection setup. METROPOLITAN AREA NETWORKS BW (bandwidth) request messages. Here the BW special request header is used. These requests can be up to 32 kb long with a single message. They may be incre- mental or aggregate, as indicated by the MAC header. For non-UGS services only, the request may be piggybacked. They are placed in the GM (grant management) and are always incremental and may be up to 32 kb long per request in the CID (channel identifier). Poll-me bit is for UGS services only and is used by the subscriber station (SS) to request a bandwidth poll for non-UGS services. Figure 13.18 is a typical BW (bandwidth) request message. To maintain QoS in the Grant per Subscriber Station operation, the following measures are taken: Use of a semidistributed approach. A base station sees the requests for each connection. Based on t