Performance Enhancement Proxy for Heterogeneous Networks

Abstract

Transmission Control Protocol (TCP) is widely used in data communications for various types of applications. Application layer protocols like Hyper Text Transfer Protocol (HTTP), File Transfer Protocol (FTP), use TCP as transport layer protocol over heterogeneous networks. Links like wired, wireless (e.g., Wi-Fi, WLAN, WiMAX, 3G), and satellite constitute the heterogeneous networks which have varied Round Trip Time (RTT) and a mixture of congestive losses and link losses due to Bit Error Rate (BER). A variety of TCP variants exist that address the issues pertaining to specific link characteristics or application environments. On a wireless link, BER is normally in the range of 106 to 1011 which is very high as compared to that of wired link (i.e., 1012 to 1014 ). RTT also varies from 1 ms to 1500 ms for different link types. However, a protocol addressing the requirements of TCP for links with variable RTT and BER is equally desirable. In the present research work, this issue is addressed by designing a new TCP variant named as Tarang and a dynamic TCP layer architecture named as ADYTIA. ADYTIA addresses the issue of single variant usage for all networking scenarios and application environments. Tarang is a new TCP protocol designed for the link with variable RTT and BER. It improvises the start-up performance on high RTT link by using the concept of normalized round trip time and a modified approach to increase the congestion window (cwnd) in slow-start phase. When congestion occurs, instead of halving cwnd as per the traditional Additive Increase Multiplicative Decrease (AIMD) approach, Tarang uses the utilized link bandwidth to set the value of cwnd and slow-start threshold (ssthresh). This way, Tarang can provide better throughput as compared to the default TCP variant (Cubic in Linux and NewReno in Windows family operating systems) and can replace the default TCP variant in various operating systems. Tarang outperforms other existing TCP variants in most of the cases and also maintains fairness. However, always there is a scope for developing new protocols giving better performance for specific cases. Furthermore, usually, fairness becomes a bottleneck in utilizing a specific costly link more effectively and also when a high priority application demands higher throughput. Existing TCP/IP implementations force operating systems to fix and use single TCP variant for all applications and links. This kind of rigid binding of TCP variant with host operating system results in poor performance for various emerging applications and upcoming networking technologies. Hence, Adaptive and Dynamic TCP layer Interface Architecture (ADYTIA) is proposed in this research work. It selects the best possible variant depending on the application and its link characteristics. Depending on the changes in the link characteristics (and link usage), ADYTIA dynamically changes the variant during the lifetime of communication . ADYTIA allows easy plugging of newly designed TCP variant and accordingly Tarang is plugged in ADYTIA. ADYTIA addresses fairness within a homogeneous network by using single optimized variant based on the information base that is created inherently. However, fairness is affected in complex heterogeneous networks. To address this issue, ADYTIA is integrated with Performance Enhancement Proxy (PEP) at gateways of complex heterogeneous networks. The proposed work has been thoroughly tested on both simulation environment and testbed setup. ADYTIA along with PEP has also been tested on live Internet. Tarang was able to outperform other existing variants for variable RTT and BER. In a worst-case scenario with BER of 106 and RTT of 1500 ms (i.e., multi-hop satellite link), Tarang improved performance by 20-30 times compared to other existing variants. Based on the various experiments conducted with different combinations of link parameters (i.e., RTT, BER, Bandwidth), application types (e.g., FTP) and TCP variants, ADYTIA's ability to select best suitable variant results in improved performance compared to other single variant usages. With FTP as an application type and link with high bandwidth ( > 10 Mbps) and RTT (e.g. 600 ms ), ADYTIA selects Hybla for a link without losses (e.g. BER 1011) and Tarang for a link with losses (e.g. BER 106). In this case, the selection of the specially crafted variant results in 20% to 80% improvement in performance. Brie y, this research work develops a new protocol Tarang (a TCP variant) for a link with variable BER and RTT that addresses most of the issues of heterogeneous networks. Further, ADYTIA has been developed for the dynamic selection of TCP variant based on the application and link types. It also allows the change of variant based on the variation in link characteristics and the plugging of newly designed TCP variants. Furthermore, ADYTIA has been integrated with PEP to address the fairness and deployment issues. Hence, this research work allows an individual to design a protocol or a TCP variant that is focused on futuristic applications and links or a specific scenario. TCP variants' selection based on applications and links would motivate the research community to develop and deploy each newly designed variant on operating systems.