## 2 Related Work  
RFSA is an evolution of FSA to make it suitable when devices generate long messages divided into smaller packets or fragments. The concept of RFSA was originally proposed in [15] and later adapted to satellite communications [16; 17; 18; 19] and inter-vehicle communication [20; 21; 22]. The contention process is composed of a sequence of time frames divided into slots. When an end-device successfully transmits a packet in a slot of a given frame, that particular slot is reserved for the same end-device in subsequent frames. As a result, the end-device has the equivalent of an assigned time division multiple access (TDMA) channel for as long as it has packets to send. The slots that are either empty or where a collision occurs remain available in subsequent frames for the contention of other devices, just as in FSA. The work in [18] has studied the performance of RFSA in terms of average message delay and channel throughput in satellite communications. For the purpose of the analysis, the authors consider that each user (or end-device) generates messages according to a stationary Poisson process with a rate of \(\lambda\) messages per second, where each message consists of \(\upsilon\) packets of fixed length, and \(\upsilon\) is a random variable geometrically distributed with mean \(\overline{\upsilon}\). Results show that RFSA adapts to the nature of the traffic. The maximum channel throughput of RFSA ranges from that of slotted-ALOHA when \(\overline{\upsilon}=1\), to that of fixed assigned TDMA channels when \(\overline{\upsilon}\rightarrow\infty\). The work in [17; 19] has also analyzed the dynamic behavior of RFSA with long messages. The author assumes that each user generates messages according to a geometrically-distributed process, and each message consists of a group of packets, whose number is geometrically distributed. A Markovian model is formulated to analyze the throughput _versus_ average message delay trade-off characteristic. Results show that the performance of RFSA is very similar to slotted-ALOHA when the mean number of packets per message tends to one. However, RFSA outperforms slotted-ALOHA in terms of throughput and average message delay when the mean number of packets per message increases. The work in [22] studied the performance of the RFSA protocol with priority (PR-ALOHA) proposed for inter-vehicle communication. Priority is introduced in RFSA by reserving specific time slots in the frame of RFSA exclusively for high priority traffic. Traffic is divided into either low or high priority (e.g., safety-related messages or multimedia). When a user generates a normal priority message, it may contend for any empty slot that is not high priority. When the message is of high priority, the user may contend for any empty slot, including the slots not reserved for high priority traffic. As could be expected, the simulation results show that as the number of slots reserved for high priority increases, the delay of the high priority messages decreases. However, the throughput of the low priority messages decreases, and their delay increases. The work in [23] proposes the reservation-contention resolution diversity slotted ALOHA protocol (R-CRDSA) for satellite networks. R-CRDSA introduces the basic concept of CRDSA [24] in the RFSA protocol. In CRDSA, each user transmits several replicas of each packet in a frame using different randomly selected slots. The coordinator (e.g., satellite transponder) implements an interference cancellation (IC) algorithm that allows decoding data packets that were initially lost due to collision. When a packet is successfully decoded in a given slot, that slot is allocated to the successful user. This user will transmit the rest of the packets of its message in the allocated slot without any replicas in other slots. The authors assume long message arrivals at each user, where each message consists of a random number of packets with an arbitrary distribution.