An Investigation into Transport Protocols and Data Transport ...

8.1. Methodology 148
Implementation of New-TCP Algorithms A single sysctl [Rub97] is
used to switch between New-TCP algorithms without the requirement
of rebooting the machine.
Appropriate Byte Sizing (RFC3465) [All03] The counting of ack’s by
the number of bytes acknowledged rather than the number of ack’s
received to counter the problems of reduced cwnd growth under delayed
ack’s.
SACK Processing Improvements The current implementation of SACK
processing in the Linux kernels requires a processing time which is
O(cwnd) [Lei04]. This has serious performance implications when dealing
with a large number of packets in flight which is common with large
BDP’s. A more robust algorithm was implemented with complexity of
O(lost packets) (which is equivalent to number of un-sacked packets).
Cap Sets cwnd to minimum of packets in packets in-flight and ssthresh,
and therefore reduces the influence of miscalculations in the network
stack which helps prevent packets bursts.
Throttle Patch A build-up of ack packets at the sender can cause an overflow
in the Linux network ring buffers which causes all packets to be
dropped. A modification to prevent this behaviour was implemented.
Undo Patch The Linux implementation of undo’s [SK02] was modified to
suit the appropriate New-TCP network stack.
Web100 Instrumentation of the TCP stack were recorded and logged via
Web100 Linux kernel patch [MHR03] in order to validate and check all
results gathered.