Due to certain shortcomings in TCP and UDP, the Stream Control Transmission Protocol (SCTP) was defined for transporting telephony signaling traffic. The partially reliable extension of SCTP, PR-SCTP, has been considered as a candidate for prioritizing content sensitive traffic and trading reliability against timeliness for applications with soft real time requirements. 

In this thesis, we investigate the applicability of PR-SCTP for event logging applications. Event logs are inherently prioritized. This makes PR-SCTP a promising candidate for transporting event logs. However, the performance gain of PR-SCTP can be very limited when application message sizes are small and messages have mixed reliability requirements. Several factors influence PR-SCTP’s performance. One key factor is the inefficiency in the forward_tsn mechanism of PR-SCTP. We examine the inefficiency in detail and propose several solutions. Moreover, we implement and evaluate one solution that utilizes the Non-Renegable Selective Acknowledgements (NR-SACKs) mechanism currently being standardized in the IETF, which is available in the FreeBSD operating system. Our results show a significant performance gain for PR-SCTP with NR-SACKs. In some scenarios, the average message transfer delay is reduced by more than 75%. Moreover, we evaluate NR-SACK based PR-SCTP using real traces from an event logging application called syslog. It significantly improves the syslog application performance as compared to SCTP, TCP and UDP.

Networking research and development have historically focused on increasing network throughput and path resource utilization, which particularly helped bulk applications such as file transfer and video streaming. Recent over-provisioning in the core of the Internet has facilitated the use of interactive applications like interactive web browsing, audio/video conferencing, multi- player online gaming and financial trading applications. Although the bulk applications rely on transferring data as fast as the network permits, interactive applications consume rather little bandwidth, depending instead on low latency. Recently, there has been an increasing concern in reducing latency in networking research, as the responsiveness of interactive applications directly influences the quality of experience.

To appreciate the significance of latency-sensitive applications for today's Internet, we need to understand their traffic pattern and quantify their prevalence. In this thesis, we quantify the proportion of potentially latency-sensitive traffic and its development over time. Next, we show that the flow start-up mechanism in the Internet is a major source of latency for a growing proportion of traffic, as network links get faster.

The loss recovery mechanism in the transport protocol is another major source of latency. To improve the performance of latency-sensitive applications, we propose and evaluate several modifications in TCP. We also investigate the possibility of prioritization at the transport layer to improve the loss recovery. The idea is to trade reliability for timeliness. We particularly examine the applicability of PR-SCTP with a focus on event logging. In our evaluation, the performance of PR-SCTP is largely influenced by small messages. We analyze the inefficiency in detail and propose several solutions. We particularly implement and evaluate one solution that utilizes the Non-Renegable Selective Acknowledgments (NR-SACKs) mechanism, which has been proposed for standardization in the IETF. According to the results, PR-SCTP with NR-SCAKs significantly improves the application performance in terms of low latency as compared to SCTP and TCP.

Interactive applications such as web browsing, audio/video conferencing, multi-player online gaming and financial trading applications do not benefit (much) from more bandwidth. Instead, they depend on low latency. Latency is a key determinant of user experience. An increasing concern for reducing latency is therefore currently being observed among the networking research community and industry.

In this thesis, we quantify the proportion of potentially latency-sensitive traffic and its development over time. Next, we show that the flow start-up mechanism in the Internet is a major source of latency for a growing proportion of traffic, as network links get faster.

The loss recovery mechanism in the transport protocol is another major source of latency. To improve the performance of latency-sensitive applications, we propose and evaluate several modifications in TCP. We also investigate the possibility of prioritization at the transport layer to improve the loss recovery. The idea is to trade reliability for timeliness. We particularly examine the applicability of PR-SCTP with a focus on event logging. In our evaluation, the performance of PR-SCTP is largely influenced by small messages. We analyze the inefficiency in detail and propose several solutions. We particularly implement and evaluate one solution that utilizes the Non-Renegable Selective Acknowledgments (NR-SACKs) mechanism, which has been proposed for standardization in the IETF. According to the results, PR-SCTP with NR-SCAKs significantly improves the application performance in terms of low latency as compared to SCTP and TCP.