In a near-ground outdoor (NGOD) environment, a wireless optical communication system usually uses pulse position modulation (PPM) since it provides better power efficiency than on-off keying modulation. In the literature, schemes based on non-return-to-zero PPM have been investigated. We extend this work to a return-to-zero (RZ) PPM scheme with a NGOD application. As a case study, we develop an optimization model to maximize the transmission distance based on a RZ-4PPM system. We show that, with the reduced pulse duration, the transmission distance can be further improved. The model involves three different Gaussian terms, and details of the solution procedure are included.
An effective QoS-constrained IP network must incorporate the time-priority scheduling paradigm. Policies based on priorities can be exerted to different layers of a packet switching network. For example, at the admission control layer, real-time applications should have the priority higher than non-real-time ones to get the required connection. Preemption is associated with priority. A scheduling discipline is non-preemptive if, once a stream has been given the service like a transmitter, the service cannot be taken away until the job is complete. It has been well known that, at the layers other than the connection layer, the traffic usually presents a self-similar (SSM) behavior. One primary attribute of the SSM traffic is the heavy tailed (HT) distributions. In this paper, we propose several capacity allocation models taking the following features into account: (1) The packet inter-arrival time follows the exponential distribution; (2) The packet length follows the Pareto distribution; (3) There are multiple priority classes; and (4) The low priority class can be preempted by a high priority class. The new models are mainly used at the connection level due to feature (1). However, the new models distinguish themselves from those conventional ones due to features (2), (3), and (4).
The latest evolution of packet switching networks
is represented by the DiffServ and MPLS
architectures, where much attention has been
paid to the issue on traffic stream priorities.
This article addresses some
subsequent issues. First, it seems reasonable for
routers to include the preemption policy into packet
scheduling. Secondly, the parallel forwarding may find
its indispensable place. Thirdly, the path-node incidence
is perhaps more appropriate for network modeling than
the link-node incidence. Finally, it appears that
nonlinear models incorporating load-dependent
parameters would play a role in future IP networks.
In summary, the 3P or 4P features -- Priority, Preemption, and
Parallelism plus Path-node incidence may bring significant
changes into the nowadays packet switching networks.
The traffic control is a critical issue in ATM networks. In ATM, the traffic control is implemented at different levels: cell level, call level and network flow level. The virtual path (VP) distribution involves both call level and flow level controls. The VP distribution is a logic network design problem based on the physical network. Several VP optimization schemes have been proposed, and a large number of these schemes are based on the flow assignment (FA) model. In this paper, an improved flow model is proposed with a non-linear objective function. The proposed model incorporates two concepts: VP capacity and VP flow, to perform the optimization. The proposed model distributes traffic on all available VPs evenly, and has redundant capacities. Hence, the resulting VP system is resilient to input traffic changes and physical link failures. In addition to the proposed FA model, we introduce a stochastic programming (SP) methodology to allocate virtual paths when the incoming traffic changes stochastically. Experimental results show that the proposed flow model and the stochastic methodology improve the performance of ATM networks.
The growth of the Internet and the World Wide Web has created an enormous demand for wideband data distribution around the globe. Satellite networks provide global reach and wide area coverage, especially to remote, rural and inaccessible regions. With a limited bandwidth, congestion is likely to occur when the demand for the bandwidth is high. In this paper, we present a capacity and flow assignment (CFA) model for the satellite ATM networks. We then present a stochastic programming approach to optimize the CFA in the satellite networks. The proposed model has been evaluated with a prototype network with 4 nodes, and the simulation results are promising.