Color correction techniques in digital photography often rely on the use of color correction charts, which require including this relatively large object in the field of view. We propose here to use QR Codes to pack these color charts in a compact form factor, in a fully compatible manner with conventional black and white QR Codes; this is, without losing any of their easy location, sampling and digital data storage features. First, we present an algorithm to build these new colored QR Codes that preserves the original QR Code functionality - much more than other coloring proposals based on the random substitution of black and white pixels by colors - that relies on the ability of the native CRC code to correct and counteract these alterations. Second, we demonstrate that, as a result, these QR Codes can allocate far many more colors than the conventional color correction charts, enabling much more accurate color correction schemes in a more convenient and usable format.

In this paper, we evaluate a low latency handoff protocol for MIPv4, the post-registration handoff method. This mechanism proposed by the IETF tries to improve the performance of hierarchical mobile IP by decreasing the handoff latency. We give a detailed description of the protocol behavior by means of an ns simulation and propose a simple queuing model to study the influence of various parameters on the protocol performance.

Mobile IP allows node mobility involving changes of point-of-attachment to the Internet. In order to reduce the impact on the performance and the signaling overhead, hierarchical mobility management schemes have been introduced. These schemes define protocols that allow movements within a domain to be handled locally, without involvement of the mobile node's home network. In order to reduce more the packet losses during handoff, new schemes have been defined, such as smooth handoff. By storing packets temporarily in the access point after the mobile host has left and forwarding them to the new access point as soon as the mobile has connected to it, it is possible to reduce significantly the packet loss. In this paper we develop an analytical model and a simulation program using OPNET Modeler to evaluate the packet loss and packet delay for UDP streams and the throughput for TCP streams that are involved in a handoff. We show that, in spite of the buffering capabilities of the previous access point, packets may still get lost. The reason for this loss is identified and solutions to this problem are proposed.

We study tree networks of discrete-time queues loaded with periodic traffic sources. By using the so-called Benes method, exact closed-form expressions are obtained for the queue length distributions. The models developed can be used to study the superposition of periodic sources emitting bursts of cells in ATM networks. The results obtained show the significant effect that this kind of traffic can have on the performance of these systems.

This paper determines packet level performance measures of a MAC protocol for a wireless ATM local area network. A key characteristic of the MAC protocol is the identifier splitting algorithm with polling, a contention resolution scheme used to inform the base station about the bandwidth needs of a mobile station when no piggybacking can be used. We consider higher layer packets that are generated at the mobile station and investigate the influence of the traffic characteristics of the packet arrival process on the efficiency of the protocol and on the delay that packets experience to access the shared medium.

The authors propose a versatile point process as a model for a large class of variable bit rate sources and their superpositions. The process belongs to the class of discrete-time batch Markovian arrival processes. Its use leads to computationally tractable and accurate solutions for the following performance measures of the related statistical multiplexer: buffer occupancy distribution, cell loss probability, and conditional cell loss probability. It is shown that the output process of the multiplexer belongs to the same class of processes.>