Routers Part II

["Dr. Neal Krawetz" <hf () hackerfactor com>]

Hi folks,

So, I've been benchmarking a bunch of different routers and I've
noticed an oddity with Comcast "high speed internet" cable service.

The service is supposed to provide 4Mbps download (6Mbps in select areas)
and 384K uploads.

All of my benchmarks show uploads around 355K, so 384K is definitely
the correct upper threshold.  (Theoretical 384, actual 355.)

I am in one of the 6Mbps "select areas".
The interesting thing is, I can get over 6Mbps downloads, without
uncapping my cable modem.  Comcast appears to use a threshold trigger
at 9Mbps.  If you download, you can get up to 9Mbps.  But the second you
cross that 9Mbps mark, they cap you and drop back to 6Mbps.
(Benchmarks consistently show 5999Mbps - 6000Mbps after being capped.
That is real 6Mbps, not theoretical.)

Here's the catch: If you don't cross the 9Mbps threshold, then you
can happily live at 7-8Mbps indefinitely.

My configuration:
  Internet -> cable modem -> hub -> firewall -> DMZ -> firewall -> LAN

(When I say "hub", I really mean "hub" and not "switch".)
The hub allows my IDS to sit right outside the firewall.
I have a couple of hubs: 10Mbps and 100Mbps.
(BTW, true 100Mbps hubs are really rare.  I got mine at an auction.  If
you want one, check out your local university auctions.)

If I put in my 100Mbps hub, I can break 9Mbps and get quickly slapped
down to 6Mbps.
BUT: If I put in my 10Mbps hub, then the maximum becomes a fraction over
8Mbps.  (Theoretical 10, actual 8-9.)
Benchmarks consistently show 7-8Mbps sustained.


So my questions are...
(1) If they are supposed to cap at 6Mbps, why do they not enforce the cap
until 9Mbps?  (Not that I'm complaining!  Just curious...)

(2) Does the same cap trigger exist for people in Comcast 4Mbps areas?
Can you get higher than 4Mbps as long as you don't cross some threashold?
If so, what is the threshold?
Some routers permit upstream thresholds for QoS tuning.  The Linksys
WRT54G does this.

(3) Does the cap trigger exist for other cable modem providers?
What provider, and what threshold?

By the way:
- The Linksys RV0041 (router with built-in VPN) is reported to benchmark
  at under 1Mbps -- even over non-VPN connections.  Ouch.
- The Linksys WRT54G has a QoS threshold for WAN bandwidth.
  The factory setting is "auto".  "auto" is 3Mbps.
  If you manually crank it up to anything over 5Mbps (e.g., 10000), then
  you can get 4.5Mbps over 802.11g.  (Wow!  Almost 10%!  Ugh...)
  
                                        -Neal
--
Neal Krawetz, Ph.D.
Hacker Factor Solutions
http://www.hackerfactor.com/

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