In general, backoff algorithms can be characterized by three key measures: the expansion/reset factor of the contention window, the probability distribution of contention slot selection, and the update mechanism of the contention window's bounds.
Schemes in  and  use non-uniform probability distribution for contention slot selection over the optimized contention window.
Let us further assume that x [greater than or equal to] 2 number of STAs from the group select the same contention slot [j.sub.x] within the window [0, [W.sub.i] -1], and the rest y STAs select their contention slots larger than [j.sub.x].
However, there is a slight difference in the contention slot selection process.
Hence, it would be safe (in terms of collision avoidance) not to select any of the contention slots in the overlapped region.
In this paper, we propose a reactive BEB which deterministically nullifies the selection chances of the overlapped contention slots in the adjacent contention stages.
Following this, any maintenance regions are scheduled first as indicated in , and then the minislots that are to be used during contention access (for bandwidth request transmissions) are scheduled, using a Contention Slot Allocator (CSA).
Performance Evaluation of Adaptive Contention Slot Allocators for CATV Networks based on the European Cable Comms.
Simulation Parameters Parameter Value UL data rate (QPSK, m=2) 9.6 Mbps UL Channel Bandwidth ([BW.sub.UL]) 6000 kHz Roll of factor ([gamma]) 0.25 DL data rate (16-QAM, m=4) 22.4 Mbps Minimum contention slots per UL-frame (c) 7 slots UL minislot size 16 bytes UL-frame Duration (F) ([approximately equal to] 2ms) 150 minislots Simulation time for each run 60s Distance from nearest/farthest SS to the BS 0.1-2.3 km Reed Solomon (short grants/long grants) 6/10 bytes Limit between short and long grants 245 bytes Maximum number of users in the network 200 Table 2.
In RT-Link, the time slots are assigned centrally at the base station similar to TRAMA and this protocol supports contention slots using Slotted ALOHA rather than CSMA.
Each cycle starts with scheduled slots followed by contention slots. The base station will take the responsibility of assigning time and frequency to each node by using a specific algorithm.