The main objectives of this dissertation work are to propose access protocols based on reservation for high-speed fiber optic networks and to investigate the performances of the proposed protocols.
As the speed of data transmission increases by using fiber optic technology, the ratio of the end-to-end signal propagation delay to the packet transmission time increases greatly. But, most existing network structures and access protocols have the limit of the ratio in which they can operate normally. Therefore, it is necessary to develop network structures and access protocols which operate without regard to the variation of the ratio. With this purpose, we propose access protocols based on reservation for multiwavelength optical networks and fiber optic unidirectional bus networks, respectively.
First, we propose access protocols using contention-based reservation schemes in a multiwavelength optical network with a passive star topology. A wavelength is used as a control channel and the others are used as data channels. To avoid multiple transmissions in the same wavelength or to the same destination simultaneously, a reservation method is introduced. According to the length of data packets and the structure of data channels, slotted and unslotted protocols are considered. And, according to the ratio of the end-to-end signal propagation delay to the transmission time of a data packet, basic and extended protocols are considered. Also, buffered and unbuffered protocols are considered according to the buffering of reservation at destination queues.
We analyze them by building a discrete-time Markov chain for the slotted protocol and a continuous-time Markov chain for the unslotted protocol. We obtain the system delay of data packets, the throughput per channel and the total system throughput. By numerical examples, we can observe that the delays for the proposed protocols remain small for a wide range of the system throughput. The basic reservation protocol has the smallest minimum delay among them. But, it can be applied only to the network where the ratio of the end-to-end signal propagation delay to the transmission time of a data packet, R, is smaller than 1. Other protocols have no constraint like the basic reservation protocol and exhibit good performances without regard to the range of R. But, due to the reservation overhead, the minimum delay increases linearly as R increases.
Second, we analyze the proposed contention-based reservation protocols for nonuniform bursty traffic. The queueing performance of each station is obtained in the limit as the number of station increases to infinity. We model the contention process by a transient Markov process and obtain the destination contention distribution of phase type considering the failure probability of reservation. We assume that the traffic is generated to each input station according to an independent Bernoulli process. We model each input queue by an independent Geom/PH/1 queueing system. Also, we analyze the protocols when the traffic is generated according to a Markov-modulated Poisson process (MMPP) in order to model the bursty nature of traffic. In this case, each input queue is modeled by an independent MMPP/PH/1 queueing system. We analyze these queueing systems using the matrix-geometric solution technique. Numerical examples show that the average performance of stations is improved if the packet arrival rates become nonuniform when packets are allocated uniformly to destination stations. But, if the traffic is allocated nonuniformly, the performance is degraded due to the increase of the destination contention. Also, we can observe that the increase of the burstiness affects the system performance negatively.
Finally, we propose a hybrid assignment protocol called the probabilistic reservation protocol in a fiber optic unidirectional bus system. In this protocol, a station with a packet to send transmits its packet with probability 1 if the currently passing slot is empty. If the slot is not available because an upstream station used it or a station reserved it to use in the last frame, the station attempts to reserve a slot of the next frame with the probability of $\tau_i$. If $\tau_i$'s are chosen suitably, the channel can be utilized to its full capacity and all stations can access the channel fairly. We obtain the performance of this protocol using an exact analytic model. Also, we introduce a computationally simpler approximate model and analyze the proposed protocol. By the exact model, the characteristics of the individual stations are obtained. And by the approximate model, the average characteristics of all stations are obtained. The variation of the performance to the change of the reservation probability is shown. We can observe that the differences of the performances between stations are kept small. And, we can observe that the variation of the packet arrival rate of a station does not affect the performance of the other stations significantly. It is shown that this protocol behaves as a random assignment protocol at low loads and as a demand assignment protocol at high loads. Since the transmission of packets is achieved within two frames, the maximum delay is bounded.
