A Case for Flow Adaptive Wireless links
Reiner Ludwig
University of California at Berkeley,
Technical Report UCB//CSD-99-1053, May 1999
[Full Text in PDF Format, 250KB]
Abstract
We study the performance problems that exist when loss responsive
flows traverse wireless links, where losses are often unrelated to
congestion. We present a novel concept - flow-adaptive wireless links -
which provides service differentiation by tailoring link layer error
control to the QoS requirements of each flow sharing the link.
Flow-adaptive links emphasize local error control as a necessary
complement to end-to-end error control, and are independent of transport
(or higher) layer protocol semantics. The key idea is that applications
use the IP layer as a level of indirection through which QoS requirements
are communicated to each link along the path, on a per flow basis. We then
demonstrate how this improves performance for the particular class of
reliable loss responsive flows. We prove in general that a well
engineered, fully reliable wireless link does not interfere with TCP's
end-to-end error recovery. Moreover, we propose a new error recovery
algorithm (TCP-Eifel) that can optionally be implemented in TCP to further
improve performance. By eliminating the retransmission ambiguity problem
the algorithm detects spurious timeouts, and uses these as an implicit
cross-layer signal to prevent unnecessary retransmissions in TCP.