how reliable is ping?

how reliable is ping?

[Luca Ferrari]

Hi,
in my company we installed a new DSL line, supposed to be faster than the 
previous one. And in fact it seems to be, in interactive use, but if I use 
ping to test connectivity against the old line I can see higher times. So my 
questions is: why does ping show high times and then the line goes faster? Is 
ping reliable enough to test network speed, or should I use another tool? (at 
last, a chrono and a file transfer!)

Thanks,
Luca
-- 
Luca Ferrari,
fluca1978@infinito.it

Re: how reliable is ping?

[Helge Pettersen]

Ping is supposed to show the network speed, but I wouldn't rely on it.
Use some http-based service (a java applet that measures the times it
takes to download a specific image, and shows the bandwith).
It's the best to find someone with a huge line, however I don't know
of any in italia. If you dare, try looking around at itavisen.no (a
norwegian crappy it newspaper with a huge bandwith to test that), and
manuovre to "speedometeret" and "trykk her for A ta testen".

On Mon, 6 Dec 2004 10:19:19 +0100, Luca Ferrari <fluca1978@infinito.it> wrote:
> Hi,
> in my company we installed a new DSL line, supposed to be faster than the
> previous one. And in fact it seems to be, in interactive use, but if I use
> ping to test connectivity against the old line I can see higher times. So my
> questions is: why does ping show high times and then the line goes faster? Is
> ping reliable enough to test network speed, or should I use another tool? (at
> last, a chrono and a file transfer!)
> 
> Thanks,
> Luca
> --
> Luca Ferrari,
> fluca1978@infinito.it
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-admin" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>

Re: how reliable is ping?

[Adrian C.]

You can also try www.bandwidthplace.com, www.speedtest.ch, and
basically many oogle results on "bandwidth test site". I wouldn't rely
on ping to test bandwidth.

--Adrian.


On Mon, 6 Dec 2004 10:29:21 +0100, Helge Pettersen <tubamann@gmail.com> wrote:
> Ping is supposed to show the network speed, but I wouldn't rely on it.
> Use some http-based service (a java applet that measures the times it
> takes to download a specific image, and shows the bandwith).
> It's the best to find someone with a huge line, however I don't know
> of any in italia. If you dare, try looking around at itavisen.no (a
> norwegian crappy it newspaper with a huge bandwith to test that), and
> manuovre to "speedometeret" and "trykk her for A ta testen".
> 
> 
> 
> On Mon, 6 Dec 2004 10:19:19 +0100, Luca Ferrari <fluca1978@infinito.it> wrote:
> > Hi,
> > in my company we installed a new DSL line, supposed to be faster than the
> > previous one. And in fact it seems to be, in interactive use, but if I use
> > ping to test connectivity against the old line I can see higher times. So my
> > questions is: why does ping show high times and then the line goes faster? Is
> > ping reliable enough to test network speed, or should I use another tool? (at
> > last, a chrono and a file transfer!)
> >
> > Thanks,
> > Luca
> > --
> > Luca Ferrari,
> > fluca1978@infinito.it
> >
> > -
> > To unsubscribe from this list: send the line "unsubscribe linux-admin" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >
> -
> To unsubscribe from this list: send the line "unsubscribe linux-admin" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>

Re: how reliable is ping?

[Marcel Gschwandl]

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IMHO ping isn't even meant to be used for bandwidth testing as it only shows 
roundtrip times which have nothing to do with bandwidth but with latency.
So if you want to test your bandwidth you will have to use the already 
mentioned websites.

hth
Marcel

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Re: how reliable is ping?

[urgrue]

Indeed, ping tests latency, not bandwidth. "bing" is an equivalent program
for testing bandwidth. but the best way to test it is to find some fast
sites and simply download something. typically university ftp sites have
quite good bandwidth, like ftp.funet.fi, ftp.sunet.se, etc. those two are up
here in scandinavia, it might be best to find one near you.

On Mon, Dec 06, 2004 at 11:06:14AM +0100, Marcel Gschwandl wrote:
> IMHO ping isn't even meant to be used for bandwidth testing as it only shows 
> roundtrip times which have nothing to do with bandwidth but with latency.
> So if you want to test your bandwidth you will have to use the already 
> mentioned websites.
> 
> hth
> Marcel

Re: how reliable is ping?

[Alexander Economou]

My question would be if the dsl you purchased is from the same ISP.If not
then probably your packets are routed through another network that may
need more hops to reach the destination network(hypotheticaly
speaking).There are many possible reasons for your problem.I would suggest
you to try mtr (available on freshmeat)

> Indeed, ping tests latency, not bandwidth. "bing" is an equivalent program
> for testing bandwidth. but the best way to test it is to find some fast
> sites and simply download something. typically university ftp sites have
> quite good bandwidth, like ftp.funet.fi, ftp.sunet.se, etc. those two are
> up
> here in scandinavia, it might be best to find one near you.
>
> On Mon, Dec 06, 2004 at 11:06:14AM +0100, Marcel Gschwandl wrote:
>> IMHO ping isn't even meant to be used for bandwidth testing as it only
>> shows
>> roundtrip times which have nothing to do with bandwidth but with
>> latency.
>> So if you want to test your bandwidth you will have to use the already
>> mentioned websites.
>>
>> hth
>> Marcel
>
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-admin" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>


------------------/
Alexander Economou
--==GNET NOC==--
------------------\

Re: how reliable is ping?

[Matías López Bergero]

If you have a box en the other side I would recommend your this:
http://dast.nlanr.net/Projects/Iperf/

I use this program to measure the bw of my hdlc links.

BR,
Matías.


Alexander Economou wrote:
> My question would be if the dsl you purchased is from the same ISP.If not
> then probably your packets are routed through another network that may
> need more hops to reach the destination network(hypotheticaly
> speaking).There are many possible reasons for your problem.I would suggest
> you to try mtr (available on freshmeat)
> 
> 
>>Indeed, ping tests latency, not bandwidth. "bing" is an equivalent program
>>for testing bandwidth. but the best way to test it is to find some fast
>>sites and simply download something. typically university ftp sites have
>>quite good bandwidth, like ftp.funet.fi, ftp.sunet.se, etc. those two are
>>up
>>here in scandinavia, it might be best to find one near you.
>>
>>On Mon, Dec 06, 2004 at 11:06:14AM +0100, Marcel Gschwandl wrote:
>>
>>>IMHO ping isn't even meant to be used for bandwidth testing as it only
>>>shows
>>>roundtrip times which have nothing to do with bandwidth but with
>>>latency.
>>>So if you want to test your bandwidth you will have to use the already
>>>mentioned websites.
>>>
>>>hth
>>>Marcel
>>
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Re: how reliable is ping?

[Jeff Woods]

At 12/6/2004 11:06 AM +0100, Marcel Gschwandl wrote:
>IMHO ping isn't even meant to be used for bandwidth testing as it only 
>shows roundtrip times which have nothing to do with bandwidth but with latency.

Indeed.  Most people seem to completely confuse bandwidth (speed) with 
latency (lag).  Ping measures *only* latency.

I like to use these two datacomm scenarios to highlight the difference 
between latency and bandwidth:

1.  Telegraph (as popular in the 19th century):  The time to send a 
keypress from one town to another is almost instantaneous (limited 
primarily by the speed of light as the voltage pulse travels the wire and 
by the speed with which the solenoid can respond to the pulse).  But each 
letter takes more than one keypress (packet) providing only slightly faster 
than 1 baud even with a skilled operator.  This is a very low bandwidth 
(slow speed: bad) with very low latency (less lag: good).  Using this for 
an Internet connection would result in good ping times (unless the operator 
was behind in sending or receiving) but horrid speed.

2.  Truck load of tape:  Fill a truck (packet) with tapes full of data and 
drive it from one site to another.  The packet size is huge.  The latency 
may be minutes, hours or days depending on how far the truck has to 
go.  But when the packet arrives the number of bytes transferred per second 
can be phenomenal.  For example, moving 600 SDLT600 tapes holding 600GB 
each across town in an hour would be 360,000GB/hour or 100GB/second, but 
the latency would be an hour.

Back in reality, a compromise giving reasonably low latency and reasonably 
high bandwidth is what everyone wants.  Personally, I'm trying to get my 
latency below 100ms so that my reflex response time in CounterStrike is 
fast enough to see the guy that killed me.  My IDSL bandwidth of only 
144Kbps is irrelevant (except when I'm downloading service packs or 
"multimedia" ;).

--
Jeff Woods <kazrak+kernel@cesmail.net>
"Never underestimate the bandwidth of a C5A full of tape libraries!" 

Re: how reliable is ping?

[Stephen Samuel]

Luca Ferrari wrote:
> Hi,
> in my company we installed a new DSL line, supposed to be faster than the 
> previous one. And in fact it seems to be, in interactive use, but if I use 
> ping to test connectivity against the old line I can see higher times. So my 
> questions is: why does ping show high times and then the line goes faster? Is 
> ping reliable enough to test network speed, or should I use another tool? (at 
> last, a chrono and a file transfer!)

There are many things that test network reactivity, and ping
only checks one or two of them.

Ping times only indicate how long it takes a packet to make it
from my box to yours, and back. The command is mostly intended
to just check to make sure that the machine is up.

  Note that some routers give ping packets lower priority, aince
they're (almost) never sending any real data.

Cable connections often have a beter intrinsic bandwidth
availability but they're more sporadic because they're shared
among some number of users in your neighborhood -- in other
words, you might get really good bandwith at 4AM and
sorse-than-modem bandwidth at 7PM.

In truth, ping times don't predict bandwidth. If you have two
machines at the same colo site, one which is bandwidth limited
to 18Kb/s and the other with an unlimited 10Mbit connection,
they may both give you the same ping times, but vastly different
download speeds.

Similarly, a modem user in your city may give a slightly better
ping time than a well-connect box across the country (or even
across the ocean), but still give far worse downloads.

Snother difference between cable and DSL is that, because
DSL is shared, the ping times are less *predictable*.  If
you're playing counterstrike, very low average latency with
short bursts of high-latency can be far more bothersome than
a slightly higher average latency that is more stable.


-- 
Stephen Samuel +1(604)876-0426                samuel@bcgreen.com
		   http://www.bcgreen.com/~samuel/
    Powerful committed communication. Transformation touching
      the jewel within each person and bringing it to light.