Check out the packets retransmitted and ACKS and SACKS numbers - and this was one of the better tests - sigh.

WEB100 Enabled Statistics:
Checking for Middleboxes . . . . . . . . . . . . . . . . . . Done
checking for firewalls . . . . . . . . . . . . . . . . . . . Done
running 10s outbound test (client-to-server [C2S]) . . . . . 950.0kb/s
running 10s inbound test (server-to-client [S2C]) . . . . . . 6.11Mb/s

------ Client System Details ------
OS data: Name = Windows XP, Architecture = x86, Version = 5.1
Java data: Vendor = Sun Microsystems Inc., Version = 1.6.0_03

------ Web100 Detailed Analysis ------
10 Mbps Ethernet link found.
Link set to Full Duplex mode
No network congestion discovered.
Good network cable(s) found
Normal duplex operation found.

Web100 reports the Round trip time = 30.78 msec; the Packet size = 1380 Bytes; and
There were 125 packets retransmitted, 528 duplicate acks received, and 555 SACK blocks received
The connection stalled 12 times due to packet loss
The connection was idle 2.78 seconds (27.79%) of the time
C2S throughput test: Packet queuing detected: 0.40%
S2C throughput test: Packet queuing detected: 12.06%
This connection is receiver limited 10.79% of the time.
This connection is sender limited 1.66% of the time.
This connection is network limited 87.55% of the time.

Web100 reports TCP negotiated the optional Performance Settings to:
RFC 2018 Selective Acknowledgment: ON
RFC 896 Nagle Algorithm: ON
RFC 3168 Explicit Congestion Notification: OFF
RFC 1323 Time Stamping: OFF
RFC 1323 Window Scaling: ON

Server 'miranda.ctd.anl.gov' is probably behind a firewall. [Connection to the ephemeral port failed]
Client is probably behind a firewall. [Connection to the ephemeral port failed]
Information: Network Middlebox is modifying MSS variable
Server IP addresses are preserved End-to-End
Client IP addresses are preserved End-to-End