[ILUG] Naive ADSL/WiFi questions (long (sorry!))?

[Ian O'Connell]

On 22/06/07, Proinnsias Breathnach <proinnsias at linux.ie> wrote:
> On Fri, Jun 22, 2007 at 11:47:11AM +0100, Ian O'Connell wrote:
> > >> desk to a network engineer i was informed that ping times and
> > >> latency are entirely unrelated....
> > >
> > >Guess what, they were right.
> > So ping isn't a tool for determining network latency then?
> >
>
> Actually - much as I *hate* to agree with Paul, he's right !
>
> ping is a tool for measuring the length of time it takes for an ICMP
> echo request to elicit an ICMP echo response and for that response to
> return to your machine.
>
> It can be used as a tool to test end-to-end connictivity of a link, to
> test that ICMP packets can make their way across the IP network. However
> ICMP is a very different protocol to TCP (and indeed UDP and other
> protocols which function over the IP layer).
>
> So, while ping _can_ tell you that there is a functioning network in
> place, and indeed that end-to-end connectivity exists for ICMP packets,
> and even how long the return path for ICMP packets is. It cannot be
> considered a useful measure of latency on the link, as ICMP may (or
> indeed may not) be subject to the same QoS restrictions as other
> traffic.

How are latency/ping related to any specific protocol though? below or
above the ip layer?
its possible to do udp pings with the right software on either end or
client side software to a standard service. latency is pretty much an
abstract concept in packet switched networks but the only established
way that i'm aware of to measure it would be a ping client of some
sort no?
(i'm not trying to be arguementative, i'm rather curious about this)


-- 


Ian.