I have three Windows machines, listed below.  I am measuring my
Internet upload and download speeds using http://test.lvcm.com (other
bandwidth speed test sites report approximately the same results). 
I've tried this under both FireFox and Internet Explorer 6.

Problem:  Two of the PCs measure no better than 2.2 Mbps download
speed on a 4 Mbps Comcast broadband cable modem, no matter what tweaks
I try.  I tried using the TCP Optimizer utility from
http://www.speedguide.net on "Machine A" to adjust Windows registry
settings, but saw only a little improvement (from 2.05 Mbps to 2.2
Mbps).

A third PC, connected to the same cable modem, consistently measures
about 4 Mbps!  Upload speed on all three is the same, about 380 kbps,
in line with the Comcast upload speed limit of 384 kbps.

My question:  What do I have to do to achieve the 4 Mbps download
speed I'm supposed to be getting on the two problem PCs?

Machine A (downloads at 2 Mbps max)
-----------------------------------
HW:   Dell Optiplex GX110 MiniTower
OS:   Windows 2000 Service Pack 4 (latest patches)
CPU:  600 MHz x86 Family 6 Model 8 Stepping 1
RAM:  384 MB
AntiVirus:  Norton AntiVirus 8.07.17C with AutoProtect enabled
Firewall:   ZoneAlarm Pro 6.0.667.000

Machine B (downloads at 2 Mbps max)
-----------------------------------
HW:   IBM ThinkPad X40 Laptop
OS:   Windows XP Pro Service Pack 2 (latest patches)
CPU:  1.0 GHz Pentium M (on AC power)
RAM:  768 MB
AntiVirus:  Norton AntiVirus 2004 10.0.1.13 with AutoProtect enabled
Firewall:   ZoneAlarm 6.0.667.000

Machine C (downloads at 4 Mbps)!
--------------------------------
HW:   IBM ThinkPad T40 Laptop
OS:   Windows 2000 Service Pack 4 (latest patches)
CPU:  1.6 GHz Pentium M (on AC power)
RAM:  1 GB
AntiVirus:  Symantec AntiVirus 9.0.3.1000 AutoProtect enabled
Firewall:   ZoneLabs Integrity Desktop 3.5.175.057

I tried disabling AntiVirus AutoProtect, but this made no significant
difference.  I do not wish to disable ZoneAlarm even for a second
while connecting to a broadband connection, but I don't see how
ZoneAlarm could cause such a huge degradation in download speeds (or
maybe you can point me to a web site that proves that it does).

I've watched the Windows Task Manager CPU meter while doing the speed
test, and it doesn't move much, certainly no where near 100% CPU
Utilization, so I don't think this problem is related to CPU speed or
the Firewall or AntiVirus software, despite the fact that the fastest
machine does indeed get the desired 4 Mbps download speed.

Is it possible to achieve approximately 4 Mbps downloads on a 1.0 GHz
Windows XP machine (Machine B)?  I tried this machine on a friend's
802.11g wireless LAN with a solid connection and a Comcast cable
modem, and once again http://test.lvcm.com reported 2 Mbps top
download speed.  Other than that, all tests are using hard wired
Ethernet either directly to the cable modem or through a Netgear
switch (100 Mbps Ethernet).

In one test I used Windows Internet Connections Sharing (ICS), as follows:

Machine C --> Machine A (Windows ICS, two Ethernet cards) --> Comcast Cable Modem

Machine C measured 4 Mbps, but Machine A (in the middle) measured only
2 Mbps!  None of this makes sense to me.  I am only running the test
on one machine at a time.

If someone comes up with a networking tweak or Windows registry
setting allowing me to get anywhere above 3 Mbps on Machine A and B,
I'll be very happy!  Or if you can point me to a reliable web site
that explains why there's no way I'll see anything better than 2 Mbps
on Machine A or B no matter what I try, I won't be that happy, but at
least I'll have answer.

---

Clarification of Question by tvbob-ga on 03 Oct 2005 22:42 PDT

I ran the "Tweak Tester II" program at http://www.dslreports.com/tweaks

Results:  http://ttester.broadbandreports.com/tweak/block:2d84a9?service=cable&speed=4000&os=win2k&via=normal

---

Request for Question Clarification by sublime1-ga on 04 Oct 2005 01:20 PDT

tvbob...

Your RWIN seems very large. Try these settings:

RWIN = 49640
Window Scaling = Off
TTL = 128
Max Duplicate Acks = 2

Set those values with Dr TCP, from this page on DSLreports:
http://www.dslreports.com/drtcp

Let me know where this takes you...

sublime1-ga

---

Clarification of Question by tvbob-ga on 04 Oct 2005 11:00 PDT

I can try that DrTCP tweak when I get home, but I think solzaire has
zeroed in on the true download performance killer:  newer versions of
ZoneAlarm.  See http://forum.zonelabs.org/zonelabs/board/message?board.id=gen&message.id=27745#M27745
for example.  A LOT of people are reporting that forum that ZoneAlarm
is reducing download speed by 1.5 Mbps or more (a problem only with
newer versions).  I'm also seeing a ton of page faults in the Windows
Task Manager, next to vsmon.exe (ZoneAlarm Vector Services I presume).

Hi tvbob -

Although this may seem odd, the speed reduction may have to do with
how ZoneAlarm was installed. During my research, I found that a "clean
install vs. an upgrade from a previous version" caused differences in
performance with ZoneAlarm.

Here are some links to what I found:
http://www.dslreports.com/forum/remark,14369470~reverse=0;days=10;root=security;mode=nest
http://www.nwc.securitypipeline.com/showArticle.jhtml?articleId=169500001&pgno=2
http://forum.zonelabs.org/zonelabs/board/message?board.id=inst&message.id=40073#M40073

If you indeed have upgraded ZA from an older version, it might make
sense to try & uninstall ZA & run a clean install. Of course, I would
recommend you disconnect your PC from the network before you do this,
so that nothing bad sneaks in.

If you cannot un-install & clean install ZA, then this might be of
help to you. However, I dont know if it will work with your version of
ZA or not.

http://forum.zonelabs.org/zonelabs/board/message?board.id=inst&message.id=34990#M34990

If you do wish use the method above, you may need to boot into SAFE
mode in Windows as the files mentioned in the link may be locked.

Hope that helps.

====================

keyword search:

zonealarm slows down speed (on google.com)
zonealarm degrade speed (on google.com)
upgrade problems (searched on zonelabs.com)

====================

Best regards,
-solzaire

Thanks for the suggestion, but I've been having these download
performance problems for many months, so I don't think it is related
to the problems people are seeing with ZoneAlarm 6, which was
installed (via upgrade) just recently.  I had the usual problems with
ZoneAlarm 6 (lots of new pop-ups), but once I got passed all that,
it's been OK.

But it IS true that my "good" PC (from work) has a much older version
of ZoneAlarm, so you may be on to something.  During the speed test, I
see the vsmon.exe task (part of ZoneAlarm), using 5-11% of the CPU (on
the 600 MHz Dell).  And vsmon.exe is using 26,616 K of memory, and the
Task Manager's Page Fault counter for vsmon.exe went up by 307 during
a single bandwidth speed test.  That doesn't seem right!  Hmmm.