Cable Modem Clog?

[RedPenguin]

Can a cable modem due to P2P activity or just high connections,
espeically if it's like 5 years old become clogged with connections,
just like a router is known to be? I am wondering becuase once I start
up a P2P application, my web browsing is slow, access to the modem's
setup page gets slower, everything does until I close the P2P app. It
didn't do it when I have a slower cable Internet from the cable
company. Could it be the modem?

 

[RedPenguin]

To extend my previous message, the modem is a Motorola Surfboard
SB4101. My ISP said that they will swap me with a new modem, no
problem. This modem is 4-5 years old. I know that possibly getting a
new modem may not help things but can I really lose anything by getting
a new one? The old one only supports DOCSIS 1.1. I know there is a
DOCSIS 2.0, how can I tell which my ISP uses? Also, on one part of
Motorola's website, it says my modem only supports up to 100 times
faster than 28.8k, which when I did 28.8k x 100 (for the kilobits 100
times faster) than divided by 8 to get kilobytes, I only get 360, but
my Internet is cable of 384. The strange part though is when I go to
product specifcations, it can support like 30mb downstream and 10mb
upstream, which when calculate is pletny.

Also, is there any real way to locate a network bottleneck? I have one
ClarkConnect (linux) router/gatewa with two NICs (excelty the same)
which has one crossover cable going to the modem and another going to a
router which is now just a switch's uplink, then a crossover to another
router turned switch, than an 8 port switch. I do not use the hardware
routers as routers anymore becuase P2P just kills them usually no
matter what I do, but it doesn't kill ClarkConnect.

 

[Paul]

Can a cable modem due to P2P activity or just high connections,
espeically if it's like 5 years old become clogged with connections,
just like a router is known to be? I am wondering becuase once I start
up a P2P application, my web browsing is slow, access to the modem's
setup page gets slower, everything does until I close the P2P app. It
didn't do it when I have a slower cable Internet from the cable
company. Could it be the modem?

A look at a couple articles, suggests to me that the cable modem
doesn't know about connections. It is not a router. (Of course,
you could have a router connected to the cable modem. Or the
cable modem product might include a router, if it has multiple
Ethernet connectors on the modem itself.)

http://www.cs.ndsu.nodak.edu/~mrehman/mp/assignment2/cableanddsl.html
http://www.comsoc.org/ci/private/2001/mar/pdf/fellows.pdf

One thing you have to keep in mind. TCP/IP is a reliable protocol.
Sure, you download packets from a web server when you surf.
But when the packets are sent to you, the agent at the other end
of the network (the server) is looking for acknowledgement that
the packets were received. So while there may be a lot of bandwidth
at play in the "forward direction", there is a little bit of
bandwidth needed in the "reverse direction", to carry
acknowledgements.

Things get complicated, if you do P2P and web surf at the same time.
P2P has most of its bandwidth leaving your house. Your cable modem
may have an asymmetric characteristic - you are allowed a large
download bandwidth, and a small upload bandwidth. Your P2P activity
is pushing data through the tiny upload bandwidth. Now, while this
is happening, let's open a web page. You download the web page, and
your computer wants to send an acknowledgement packet back out
to the web server on the net. But there is already a flood of traffic
from the P2P that is also leaving your house. The acknowledgement
packet has to wait its turn, so there is a delay before the
acknowledgement packet leaves the house. It means your attempts to
download a web page, are being head-of-line blocked by the P2P going
in the other direction.

Do I know for sure that is what is happening ? Of course not. It
is a theory. Now, you can do an experiment, to prove whether this
is the right theory or not.

Open up the documentation for your P2P software. What you are
looking for, is the option to establish a "Cap" or upper limit
on the bandwidth the P2P uses. Normally people would just let it rip,
but what you want to do, is set a bandwidth number for the P2P packets
leaving your house.

Say your cable provider, provides a max of 10Mbit/sec download and
2Mbit/sec upload. The 2Mbit/sec number is what is being used by
your P2P. You go into the P2P software, and tell it "don't use more
than 1Mbit/sec". That allocates half the available bandwidth for
P2P, and leaves a few opportunities for your acknowledgement packets
to "leave home".

If you are still having problems, in your next posting, include a
diagram showing the hardware you are using. Something like this,
only with a little more detail (brand names and model numbers).
Some people have very complicated distribution in their homes,
but don't tell people about it when they post.

--- Cable_modem -------- Wired_Router V V
| | | | | |
#1 #2 #3 Wireless_Router--+ +--- Laptop
etc.

Also, it would be good to know what kind of service you got from
the cable company (10Mbit/sec download, 2Mbit/sec upload), and
what traffic level your P2P can sustain (like the entire 2Mbit/sec).
I'm sure the P2P is pretty good at doing its thing

HTH,
Paul

 

[RedPenguin]

Yeah I knew that stuff already, I already limit my upload so that it
doesn't eat it all up. It's limited to 40kb/s total, so I make it
20kb/s or something less. I have a 3mb down with 320kbit up. Could this
connection alone be what is killing things?

 

[Paul]

Yeah I knew that stuff already, I already limit my upload so that it
doesn't eat it all up. It's limited to 40kb/s total, so I make it
20kb/s or something less. I have a 3mb down with 320kbit up. Could this
connection alone be what is killing things?

Probably not, if you have limited it. Is there any way to verify
that the limit is really in effect ? Do you know for sure, when
you set a limit, the software actually uses that limit ?

Does your P2P use encrypted headers ? I'm not really up on the
P2P software, but I read an interesting thread one night, about
how some ISPs have networking equipment that does packet payload
inspection, and unencrypted P2P can actually be recognized by
the equipment. (And this is for real, because by using a version
of software that encrypted headers, their P2P thruput increased
from the "normal" 2KB/sec they were getting to about 200KB/sec.)
So at the very least, if doing P2P, I'd want to be using software
that makes payload inspection impossible.

I was hoping to find some simple network characterization software,
but I suppose that is too much to hope for.

About all I can suggest at this point, is to type the name of your
P2P software into a search engine, and see what the latest
twist is in the ISP versus P2P war is. The fact that they bothered
to buy network equipment that does payload inspection, tells you
the ISPs have a financial incentive to stop people from using P2P.

Does this behavior change if you connect one and only one computer,
directly to the cable modem ? I.e. Remove any router boxes. Just
in case it is a number of connections issue, and the problem is
with whatever you use for routing.

Paul

 

[Bill Hopkins]

To extend my previous message, the modem is a Motorola Surfboard
SB4101. My ISP said that they will swap me with a new modem, no
problem. This modem is 4-5 years old. I know that possibly getting a
new modem may not help things but can I really lose anything by
getting a new one? The old one only supports DOCSIS 1.1. I know there
is a DOCSIS 2.0, how can I tell which my ISP uses? Also, on one part

192.168.100.1 will give the the modem's status.

Also, is there any real way to locate a network bottleneck?

Yes. Bypass the ClarkConnect router/gateway.

IOW, connect a single PC directly to the SB4101. Try your BT app now. Also
try FTP downloads and uploads. Better ? Worse ? Same ?

 

[kony]

To extend my previous message, the modem is a Motorola Surfboard
SB4101. My ISP said that they will swap me with a new modem, no
problem. This modem is 4-5 years old. I know that possibly getting a
new modem may not help things but can I really lose anything by getting
a new one?

No, but I doubt it'll help. Unless you modem is dropping
the connections (check it's logs, presuming it generates
one) or it's signal levels are low (roughly it should be
-15dB RX, 30dB TX, SNR 30dB, or higher (for each)), it's
probably fine.

The old one only supports DOCSIS 1.1. I know there is a
DOCSIS 2.0, how can I tell which my ISP uses?

Ask them

Also, on one part of
Motorola's website, it says my modem only supports up to 100 times
faster than 28.8k, which when I did 28.8k x 100 (for the kilobits 100
times faster) than divided by 8 to get kilobytes, I only get 360, but
my Internet is cable of 384. The strange part though is when I go to
product specifcations, it can support like 30mb downstream and 10mb
upstream, which when calculate is pletny.

Likely that "100X" was just a popular marketing notion at
the time rather than an accurate spec, your modem's
attainable throughput is significantly higher than your line
cap, it is not a problem.

Also, is there any real way to locate a network bottleneck? I have one
ClarkConnect (linux) router/gatewa with two NICs (excelty the same)
which has one crossover cable going to the modem and another going to a
router which is now just a switch's uplink, then a crossover to another
router turned switch, than an 8 port switch. I do not use the hardware
routers as routers anymore becuase P2P just kills them usually no
matter what I do, but it doesn't kill ClarkConnect.
RedPenguin wrote:

You should not be able to "kill" your routers with a capped
20KBps upload limit, unless you are trying to do an
excessive number of simultaneous connections. What does
kill mean though, that you have to reset or reboot it?

I would tend to suspect you don't need the Clarkconnect box
at all (unless it performs some other advanced routing or
firewall controls you *need*), just a better router. Some
otherwise reasonable routers tend to run a bit hot, as I
mention below about modems... I usually put a heatsink on
mine, just any old thing that barely fits under the case top
then arctic alumina epoxy it on.

Does the problem occur when you are more modest in your P2P
usage? I would expect the Clarkconnect router is the
problem, you might open a command line and tracert to the
router, then modem, then your cable company's equipment or
some point beyond it... like yahoo.com or wherever, though
better if an IP adress so you don't have the domain name
lookup too.

You might also try pathping (to cable co., or shortly beyond
but not too far beyond as it'll take a long time, several
minutes to complete it).

In other words, I doubt your cable modem is the problem
unless it's just worn out (passively cooled cheap consumer
gear may only last a single-digit # of years, sometimes as
low as 1 or 2 if there are cheap capacitors in it) or
overheating (does the case feel significantly warmer than
when network is totally idle?).