Congestion control algorithms in challenging networks

The focus of this Master's thesis is to research the behaviour of different congestion control algorithms by different packet drop and latency values. Seven different transport layer protocol variants were researched. Five of them were TCP variants and two DCCP variants. Used research method was systematic simulation that was performed by Ns2-simulator. Congestion control algorithms try to avoid congestion and permit as efficient usage of the network as possible. Congestion control algorithms are also responsible about the fairness between different network users. Selfish and aggressive network protocol may seem efficient from its own perspective but for the overall efficiency such behaviour is questionable. Congestion control is based on noticing and reacting for congestion by tuning the transfer rate. There are many different methods to become aware of congestion but all of them are incapable to distinguish the reason for the interference at the transmission. The most common indication about congestion is a packet loss. Unfortunately there is no mechanism to know exactly the reason for the packet loss. Ali indications about congestion cause same congestion control behaviour and therefore algorithms may sometimes react incorrectly. A good example about this is an uncongested wireless network which has high packet drop rate. The simulations were divided into two parts. At the first part the good put of different TCP and DCCP variants through an uncongested bottleneck 1mk was researched by computer simulations. At the second part of the simulations the fairness of different TCP and DCCP variants at a bottleneck 1mk were researched

Upregulation of Coagulation Factor VIII and Fibrinogen After Pulmonary Endarterectomy in Patients with Chronic Thromboembolic Pulmonary Hypertension

ObjectivesChronic thromboembolic pulmonary hypertension (CTEPH) is associated with thrombotic states including elevated coagulation factor VIII (FVIII). Pulmonary endarterectomy (PEA) is the main treatment for CTEPH, and efficient anticoagulation is essential to prevent thromboembolism recurrence after surgery. We aimed to characterize longitudinal changes in FVIII and other coagulation biomarkers after PEA. MethodsCoagulation biomarker levels were measured at baseline and up to 12 months after operation in 17 consecutive patients with PEA. Temporal patterns of coagulation biomarkers, and correlation of FVIII with other coagulation biomarkers, were analyzed. ResultsBaseline FVIII levels were elevated in 71% of the patients (mean 216 +/- 67 IU/dl). FVIII doubled 7 days after PEA, peaking at 471 +/- 87 IU/dl, and gradually returned to respective baseline levels within 3 months. Postoperative fibrinogen levels were also elevated. Antithrombin decreased at 1 to 3 days, D-dimer increased at 1 to 4 weeks, and thrombocytosis was observed at 2 weeks. ConclusionsFVIII is elevated in most patients with CTEPH. After PEA, early but transient elevation of FVIII and fibrinogen, and delayed reactive thrombocytosis, occurs, and warrants careful postoperative anticoagulation to prevent thromboembolism recurrence.Peer reviewe