Real-time media or multimedia services in 3GPP GSM/EDGE-compliant mobile
radio networks call for reducing the actual latency of transmissions.
Resources are assigned by the network to set up or reconfigure a TBF
associated to the uplink/downlink transmission of radio blocks from/to an
MS. A 5-bit "Coding" field is configured in the header of the involved
RLC/MAC messages to select the transmitting/receiving window size. An
additional signaling bit, also called scaling bit, is asserted/negated
according to two opportunities offered by the new MAC protocol to
properly select the window size. Thanks to the introduction of the
scaling bit a subdivision of the time windows for type of services is
made possible. Non real-time services, e.g. file transfer, all of
standard window sizes for MSs with multistat capability, as reported in
3GPP TS 44.060, V7.3.0 (2006 February), Release 7, subclause 9.1.9, for
EGPRS TBFs. Delay-sensitive services, e.g. media or multimedia real-time
transmissions, avail of new window sizes with scaled down values remapped
to start from 1 to (maximum) 64 RLC/MAC blocks. The scaling bit is
asserted or negated by BSC accordingly. Both peer entities comprised in a
TBF are receiving the RLC/MAC messages with the proper setting of the
scaling bit and the 5-bit coding IF; these entities decode the scaling
bit and behave accordingly. The behavior includes either assuming the
standard window size or scaled window size addressed by the same
predetermined 5-bit "coding" information element.