Download speed too slow (only a third of what is physically possible)

Please boot the MP in safe mode and test. Any difference?

After testing, reboot as usual (not in safe mode.)

Mac OS X: Starting up in Safe Mode

one ever said I had VDSL but I do get solid 18Mb and 2Mb upstream on my ADSL service.

I use aDSL and have been through 3-4 upgrades now to 20Mb service. I had to upgrade modem twice along the way, I maxed out 1Mb unit long ago, then next unit was only rated for basic ADSL of less than 8Mb, so went with new modem.

I also have had to replace ADSL filters about every 6-12 months all of a sudden found I was only getting 2Mb service. So simple but had me pulling my hair out.

How old is your Mac Pro? I ask because mine is original 1,1 and is fine though Intel no longer supports or issues drivers for Intel chipset used for networking. Have seen identical reports from others where they found Mac Pro to be slower than x-y-z (Mac notebook, PC notebook, etc).

It happened before Lion. Nor would it 'fix' networking.

it doesn't even sound like you are really getting VDSL a difference of .7Mb you should be talking to your provider and have them make sure that you are getting a proper signal and strength. If you are paying for VDSL I would assume you would want 12-20Mb service.

And using their modem or one cabable of and that supports VDSL.

So: have to ask:

age of router/switch/modem?

any firmware updates?

Had your ISP or provider and talk to them to sort this out?

They can point you in the right directon or come out. Test their DSLAM and other equipment to the drop point. Or come inside if that checks out. Maybe replace your rented modem or suggest one that they support.

What I read about VDSL:

VDSL (Very high bit-rate Digital Line Subscriber) is next generation DSL at super-accelerated rates of 52 Mbps (megabits per second) downstream and 12 mbps upstream. Downstream data rates refer to download speeds,

http://www.wisegeek.com/what-is-vdsl.htm

VDSL operates over the copper wires in your phone line in much the same way that ADSL does, but there are a couple of distinctions. VDSL can achieve incredible speeds, as high as 52 Mbps downstream (to your home) and 16 Mbps upstream (from your home). That is much faster than ADSL, which provides up to 8 Mbps downstream and 800 Kbps (kilobits per second) upstream. But VDSL's amazing performance comes at a price: It can only operate over the copper line for a short distance, about 4,000 feet (1,200 m).

The key to VDSL is that the telephone companies are replacing many of their main feeds with fiber-optic cable. In fact, many phone companies are planning Fiber to the Curb (FTTC),

http://computer.howstuffworks.com/vdsl2.htm

https://secure.wikimedia.org/wikipedia/en/wiki/Very_high_speed_digital_subscribe r_line_2

On both Macs, open the Network preference pane and compare all settings, including the advanced ones. Any differences?

Also, switch Ethernet cables and ports on the router or switch, and check that they're securely seated at both ends.

The MP probably has two Ethernet NIC's. Try the other one.

If none of the above makes a difference, reset the SMC by shutting down and unplugging the power cord for at least 15 seconds.

Preceding response was edited.

To proceed further, you'd have to do either of the following: measure the MP's bandwidth with a test instrument, or try a different router. If you can do either of those, let us know the results. Otherwise you'll have to take it to a service provider for testing. There may be something wrong with it, or it may just be incompatible with your router in some subtle way.

You could also connect the two Macs together directly and measure throughput with software.

Sorry.... I see people constantly use the wrong bite/byte and some state they have 8MB of RAM.

Boy do I feel like a fool and wasted a lot of effort!

Check the status of the Ethernet Interface using Network Utility. This gives you the actual connection speed to your Router/Switch, and provides several Error counters. Anything over a handful of errors at startup is very troubling over a local Ethernet connection cable.

If your Router/Switch supports Gigabit Ethernet, 8-conductor cables are required to achieve those speeds. Four-conductor cables will work without complaint, but will not achieve Gigabit speeds.