Editing GPRS (section)

=== Multiple access schemes ===
The [[multiple access method]]s used in GSM with GPRS are based on [[frequency-division duplex]] (FDD) and TDMA. During a session, a user is assigned to one pair of up-link and down-link frequency channels. This is combined with time domain [[statistical multiplexing]] which makes it possible for several users to share the same frequency channel. The '''packets''' have constant length, corresponding to a GSM time slot. The down-link uses [[first-come first-served]] packet scheduling, while the up-link uses a scheme very similar to [[reservation ALOHA]] (R-ALOHA). This means that [[slotted ALOHA]] (S-ALOHA) is used for reservation inquiries during a contention phase, and then the actual data is transferred using [[dynamic TDMA]] with first-come first-served.