An End-to-End Transport Protocol for Extreme Wireless Network Environments
Kalyanaraman,Shivkumar
Rensselaer Polytechnic Institute
Subramanian,Vijaynarayanan
Rensselaer Polytechnic Institute
Ramakrishnan,K.K.
AT&T Labs Research
As the Joint forces move towards the vision of network-centric warfare
(NCW), it is extremely important that the network services be reliable
and dependable, even under degraded network conditions. Tactical
wireless and satellite based networks are prone to disruptions over
multiple time-scales: bursty bit errors and packet loss (small
time-scale), interference, jamming and capture effects (medium
time-scale) and long-term path disruptions due to persistent channel
impairments and mobility (large time-scale). TCP does not work well
over such channels because it misinterprets erasure for congestion,
and its reliability mechanisms become untargeted when there are
disruptions. Large round-trip-times (RTT) as in satellite networks,
and uncoordinated optimizations at multiple layers (PHY, MAC and
transport) lead to poor performance.
In this paper we describe LT-TCP, a robust transport protocol
(improving TCP) that is applicable for extreme wireless environments
including a mix of multi-hop ad-hoc meshed networks (MANETs), airborne
networks and satellite networks. LT-TCP uses an adaptive, end-to-end
hybrid ARQ/FEC reliability strategy and ECN for incipient congestion
detection.
The novelty lies in our adaptive methods that respond to learning
about the underlying random packet loss and disruption process. The
overhead of FEC or smaller segments is imposed just-in-time and
targeted to maximize the performance benefit (measured as improved goodput
and timeout reduction) even when the path characteristics are
uncertain. We show that LT-TCP substantially improves performance over
regular TCP even for packet loss rates of up to 40% - 50%, thus
substantially
extending the dynamic performance range of TCP over lossy wireless
networks.
Shivkumar Kalyanaraman is an Associate Professor at the Department of
Electrical, Computer and Systems Engineering at Rensselaer Polytechnic
Institute in Troy, NY. He received a B.Tech degree from the Indian
Institute of Technology, Madras, India in July 1993, followed by M.S. and
Ph.D. degrees in Computer and Information Sciences at the Ohio State
University in 1994 and 1997 respectively. He also holds an Executive
M.B.A. (EMBA) degree from Rensselaer Polytechnic Institute (2005). His
research is in topics such as congestion control architectures, quality of
service (QoS), last-mile community wireless and free-space optical
networks, network management, multimedia networking, and performance
analysis. His special interest lies in developing the inter-disciplinary
areas overlapping with networking, including control theory, economics,
databases, scalable simulation technologies, video compression and
optoelectronics. He was selected by MIT's Technology Review Magazine in
1999 as one of the top 100 young innovators for the new millenium. He is
an associate member of the IEEE and a member of ACM. He is on the
editorial board of ACM/Springer Wireless Network Journal and was till
recently an area editor of ACM Computer Communication Review (CCR).