Permutation-invariant codes encoding more than one qubit

A permutation-invariant code on m qubits is a subspace of the symmetric subspace of the m qubits. We derive permutation-invariant codes that can encode an increasing amount of quantum information while suppressing leading order spontaneous decay errors. To prove the result, we use elementary number theory with prior theory on permutation invariant codes and quantum error correction.Comment: 4 pages, minor change

Reliable multicast transport by satellite: a hybrid satellite/terrestrial solution with erasure codes

Geostationary satellites are an efficient way to provide a large scale multipoint communication service. In the context of reliable multicast communications, a new hybrid satellite/terrestrial approach is proposed. It aims at reducing the overall communication cost using satellite broadcasting only when enough receivers are present, and terrestrial transmissions otherwise. This approach has been statistically evaluated for a particular cost function and seems interesting. Then since the hybrid approach relies on Forward Error Correction, several practical aspects of MDS codes and LDPC codes are investigated in order to select a code

Application-Level QoS: Improving video conferencing quality through sending the best packet next

In a traditional network stack, data from an application is transmitted in the order that it is received. An algorithm is proposed where information about the priority of packets and expiry times is used by the transport layer to reorder or discard packets at the time of transmission to optimise the use of available bandwidth. This can be used for video conferencing to prioritise important data. This scheme is implemented and compared to unmodified datagram congestion control protocol (DCCP). This algorithm is implemented as an interface to DCCP and tested using traffic modelled on video conferencing software. The results show improvement can be made to video conferencing during periods of congestion - substantially more audio packets arrive on time with the algorithm, which leads to higher quality video conferencing. In many cases video packet arrival rate also increases and adopting the algorithm gives improvements to video conferencing that are better than using unmodified queuing for DCCP. The algorithm proposed is implemented on the server only, so benefits can be obtained on the client without changes being required to the client

Congestive Loss in Wireless Ad hoc Network: Network Performance Analysis

Communication in wireless network is quite susceptible to mobility, nodes capacity and power consumption level. These might contributes to the major problem of TCP performance degradation where there are highly potential of packet loss and packet reordering. In this research, we manage to observe the impact of packet behavior once the node’s capacity is limited when passing on-going data. This condition occurs when the node’s buffer starts to be overloaded. A simulation study by using OPNET Modeler 14.5 is conducted to achieve the purpose. A static ad hoc topology with the size of users (2n where n=0, 1, 2, 3 and 4) is used to observe several parameters such as throughput, number of packet dropped, retransmission count and end-to-end TCP delay. The results show that the size of buffer for ad hoc node influence the network performance whenever number of users is changed. In future, we plan to extend this study in a way of deeply understanding the effect of mobility in wireless network

Traffic monitoring for assuring quality of advanced services in future internet

The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-642-21560-5_16Services based on packet switched networks are becoming dominant in telecommunication business and both operators and service providers must evolve in order to guarantee the required quality. Increasing bandwidth is no longer a viable solution because of the business erosion for network operators which cannot expect revenues due to the large investments required to satisfy new applications demand of bandwidth. This paper presents devices and a specific architecture of services monitoring platform that allows network operators and service providers to analyze the perceived quality of service and check their service level agreements. Thus, a cost-effective service management, based on direct IP traffic measuring, can be supported on integrated monitoring systems to provide network-centric mechanisms for differentiated quality of service, security and other advanced services.This work has been partially developed in the framework of the Celtic and EUREKA initiative IPNQSIS (IP Network Monitoring for Quality of Service Intelligent Support)

Adopting Redundancy Techniques for Multicast Stream Authentication

Various schemes have been proposed to achieve strong authentication of streamed data in a lossy network by means of "light" digital signatures. Such techniques perform a strong authentication on only one packet, to which others are linked by means of hash functions, so that the authentication property propagates to them too. Most of these schemes make the basic assumption that the signature packet is not lost, even if no practical and precise solutions are proposed that guarantee such a property. In this paper we show how adoption of some redundancy techniques can be used in the context of multicast stream authentication in order to increase probability that the signature packets are received and correctly verified against their digital signature. Finally some experimental results are presented comparing computational overheads due to the authentication schemes both at the sender and at the receiver