TCP over Wireless Links: Mechanisms and Implications

In wireless networks, the implicit assumption which TCP makes that losses indicate network congestion is no longer valid. Losses in wireless networks can result from bit errors, fading and handoffs. There are two different approaches to improve TCP performance in case of wireless losses: (1) hide non-congestion-related losses from the TCP sender, using either TCP-aware or TCP-unaware reliable link layer protocols, or using split connections with separate wireline and wireless TCP connections, or (2) adapt the TCP sender to realize that some losses are not due to congestion, e.g., using selective acknowledgments or explicit loss notification. In this paper, we classify popular mechanisms that have been recently proposed to solve the wireless transport problem, and contrast them according to their complexity, ease of deployment, and performance in different scenarios. We conclude that some TCP sender adaptations work well for certain environments only, while others are generally useful. Local recovery works best when the wireless link delay is small, and split connection schemes allow application /transport level optimizations, but exhibit overhead and lack robustness

SARS-CoV-2 vaccination modelling for safe surgery to save lives: data from an international prospective cohort study

Background: Preoperative SARS-CoV-2 vaccination could support safer elective surgery. Vaccine numbers are limited so this study aimed to inform their prioritization by modelling. Methods: The primary outcome was the number needed to vaccinate (NNV) to prevent one COVID-19-related death in 1 year. NNVs were based on postoperative SARS-CoV-2 rates and mortality in an international cohort study (surgical patients), and community SARS-CoV-2 incidence and case fatality data (general population). NNV estimates were stratified by age (18-49, 50-69, 70 or more years) and type of surgery. Best- and worst-case scenarios were used to describe uncertainty. Results: NNVs were more favourable in surgical patients than the general population. The most favourable NNVs were in patients aged 70 years or more needing cancer surgery (351; best case 196, worst case 816) or non-cancer surgery (733; best case 407, worst case 1664). Both exceeded the NNV in the general population (1840; best case 1196, worst case 3066). NNVs for surgical patients remained favourable at a range of SARS-CoV-2 incidence rates in sensitivity analysis modelling. Globally, prioritizing preoperative vaccination of patients needing elective surgery ahead of the general population could prevent an additional 58 687 (best case 115 007, worst case 20 177) COVID-19-related deaths in 1 year. Conclusion: As global roll out of SARS-CoV-2 vaccination proceeds, patients needing elective surgery should be prioritized ahead of the general population