New contention resolution techniques for optical burst switching

Optical burst switching (OBS) is a technology positioned between wavelength routing and optical packet switching that does not require optical buffering or packet-level parsing, and it is more efficient than circuit switching when the sustained traffic volume does not consume a full wavelength. However, several critical issues still need to be solved such as contention resolution without optical buffering which is a key determinant of packet-loss with a significant impact on network performance. Deflection routing is an approach for resolving contention by routing a contending packet to an output port other than the intended output port. In OBS networks, when contention between two bursts cannot be resolved through deflection routing, one of the bursts will be dropped. However, this scheme doesn’t take advantage of all the available resources in resolving contentions. Due to this, the performance of existing deflection routing scheme is not satisfactory. In this thesis, we propose and evaluate three new strategies which aim at resolving contention. We propose a new approach called Backtrack on Deflection Failure, which provides a second chance to blocked bursts when deflection failure occurs. The bursts in this scheme, when blocked, will get an opportunity to backtrack to the previous node and may get routed through any deflection route available at the previous node. Two variants are proposed for handling the backtracking delay involved in this scheme namely: (a) Increase in Initial Offset and (b) Open-Loop Reservation. Furthermore, we propose a third scheme called Bidirectional Reservation on Burst Drop in which bandwidth reservation is made in both the forward and the backward directions simultaneously. This scheme comes into effect only when control bursts get dropped due to bandwidth unavailability. The retransmitted control bursts will have larger offset value and because of this, they will have lower blocking probability than the original bursts. The performance of our schemes and of those proposed in the literature is studied through simulation. The parameters considered in evaluating these schemes are blocking probability, average throughput, and overall link utilization. The results obtained show that our schemes perform significantly better than their standard counterparts

Negative pressure wound therapy in orthopaedic post operative infections: Role in implant retention and dead space management

Introduction: Postoperative orthopedic infections in the presence of implants require timely and aggressive intervention for eradication of infection. Negative pressure wound therapy (NPWT) is beneficial in wound management and implant retention, ultimately leading to fracture union. Incidentally, the use of NPWT was of great help in reducing dead space, which is responsible for the chronicity of the infection. It results in collapse of the cavity without need for repeated debridement. Aims and Objectives: This study is done to evaluate the role of negative pressure wound therapy in orthopaedic post operative infections and it′s role in implant retention and dead space management. Materials and Methods: Thirty-four patients who developed postoperative infections are included in the study. After thorough wound lavage NPWT dressing was applied followed by wound closure either by secondary suturing, skin graft or flap cover. Results: Thirty-four patients were treated during 2012-2014 out of which 22 patients had implants, 2 were treated for dead space, and 10 for both. Conclusion: NPWT has a definite role in eradicating early postoperative infection in the presence of an implant. The greatest advantage is retention of the implant