session stalled when transfer files between two sites with unstable internet connection

net.core.rmem_default = 524288


net.core.rmem_max = 524288

net.core.wmem_default = 524288

net.core.wmem_max = 524288

net.ipv4.tcp_wmem = 4096 87380 524288

net.ipv4.tcp_rmem = 4096 87380 524288

net.ipv4.tcp_mem = 524288 524288 524288

net.ipv4.tcp_rfc1337 = 1

net.ipv4.ip_no_pmtu_disc = 0

net.ipv4.tcp_sack = 1

net.ipv4.tcp_fack = 1

net.ipv4.tcp_window_scaling = 1

net.ipv4.tcp_timestamps = 1

net.ipv4.tcp_ecn = 0

net.ipv4.route.flush = 1

ref: http://ubuntuforums.org/showthread.php?t=891695