This read-write value sets the initial contention-resolution back-off window, expressed as a power of 2, that a subscriber unit uses when first attempting to transmit data packets in contention mode, with 16 at the headend indicating a proprietary adaptive retransmission algorithm. Admins tune this separately from the ranging back-off values because data contention behavior can need different tuning than initial ranging. For example, on an upstream channel with heavy contention-based data traffic, an admin might increase cwdIfUpChannelTxBackoffStart to reduce data collisions distinct from any ranging contention tuning.