A GPSS SS may use Request IEs that are broadcast, directed at a multicast polling group it is a member of, or directed at its Basic CID. In all cases, the Request IE burst profile is used, even if the BS is capable of receiving the SS with a more efficient burst profile. To take advantage of a more efficient burst profile, the SS should transmit in an interval defined by a Data Grant IE directed at its Basic CID. Because of this, unicast polling of a GPSS SS would normally be done by allocating a Data Grant IE directed at its Basic CID. Also note that, in a Data Grant IE directed at its Basic CID, the SS may make bandwidth requests for any of its connections.

The procedure followed by SSs operating in GPSS mode is shown in Figure 33.

6.2.6.4 Polling

Polling is the process by which the BS allocates to the SSs bandwidth specifically for the purpose of making bandwidth requests. These allocations may be to individual SSs or to groups of SSs. Allocations to groups of connections and/or SSs actually define bandwidth request contention IEs. The allocations are not in the form of an explicit message, but are contained as a series of IEs within the uplink map.

Note that polling is done on either an SS or connection basis. Bandwidth is always requested on a CID basis and bandwidth is allocated on either a connection (GPC mode) or SS (GPSS mode) basis, based on the SS capability.

6.2.6.4.1 Unicast

When an SS is polled individually, no explicit message is transmitted to poll the SS. Rather, the SS is allocated, in the uplink map, bandwidth sufficient to respond with a bandwidth request. If the SS does not need bandwidth, it returns stuff bytes (0xFF). SSs operating in GPSS mode that have an active UGS connection of sufficient bandwidth shall not be polled individually unless they set the Poll Me (PM) bit in the header of a packet on the UGS connection. This saves bandwidth over polling all SSs individually. Note that unicast polling of a GPSS SS would normally be done on a per-SS basis by allocating a Data Grant IE directed at its Basic CID.

The information exchange sequence for individual polling is shown in Figure 34.

start

A

await SDU arrival

Incremental BW request for CIDx

process UL-MAP information elements

Send data (and requests)

A

NOTE—The SS local scheduler decides which connections get the granted bandwidth.

Figure 33—SS GPSS mode flow chart

Figure 34—Unicast polling

6.2.6.4.2 Multicast and broadcast

If insufficient bandwidth is available to individually poll many inactive SSs, some SSs may be polled in multicast groups or a broadcast poll may be issued. Certain CIDs are reserved for multicast groups and for broadcast messages, as described in Table 121. As with individual polling, the poll is not an explicit message but bandwidth allocated in the uplink map. The difference is that, rather than associating allocated bandwidth with an SS’s Basic CID, the allocation is to a multicast or broadcast CID. An example is provided in Table 59.

The information exchange sequence for multicast and broadcast polling is shown in Figure 35.

When the poll is directed at a multicast or broadcast CID, an SS belonging to the polled group may request bandwidth during any request interval allocated to that CID in the UL-MAP by a Request IE. In order to reduce the likelihood of collision with multicast and broadcast polling, only SS’s needing bandwidth reply; they shall apply the contention resolution algorithm as defined in 6.2.8 to select the slot in which to transmit the initial bandwidth request. Zero-length bandwidth requests shall not be used in multicast or broadcast Request Intervals.

The SS shall assume that the transmission has been unsuccessful if no grant has been received in the number of subsequent UL-MAP messages specified by the parameter Random Access Timeout (see 11.1.1.1). Note that, with a frame-based PHY with UL-MAPs occurring at predetermined instants, erroneous UL-MAPs may be counted towards this number. If the rerequest is made in a multicast or broadcast opportunity, the SS continues to run the contention resolution algorithm in 6.2.8. Note that the SS is not restricted to issuing the rerequest in a multicast or broadcast Request Interval.

Table 59—Sample uplink map with multicast and broadcast IE