Performance Enhancement Proxy for Heterogeneous Networks ---amit by Rakesh D. Vanzara

Guided by: Dr. HAresh S. Bhatt and Dr. Priyanka Sharma With Synopsis and CD 09EXTPHDE28

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
ow. 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.