Hi All, just wondering if there isany discernible difference in
latency between sending say a 100 byte UDP packet and sending a 1500
byte UDP packet across the Internet. Any ideas? or pointers?

thanks in advance.

John <john.casey@gmail.com> wrote:
> Hi All, just wondering if there isany discernible difference in
> latency between sending say a 100 byte UDP packet and sending a 1500
> byte UDP packet across the Internet. Any ideas? or pointers?

Yes, just as there is a discernible difference in length between two
arbitrary peices of string

Discernible is one of those "it depends" sorts of things, along with
what is "across the Internet."

rick jones
--
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where do you want to be today?
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

In article <1177507187.702782.325670@r35g2000prh.googlegroups .com>,
John <john.casey@gmail.com> wrote:

> Hi All, just wondering if there isany discernible difference in
> latency between sending say a 100 byte UDP packet and sending a 1500
> byte UDP packet across the Internet. Any ideas? or pointers?

Many routers, especially the ones that tend to be used on low-speed
links, won't do anything with a packet until it has received the entire
thing. Since it takes more time to transmit 1500 bytes than 100 bytes,
every hop that goes through one of these routers will add latency
proportional to the link speed and packet size. If you go through lots
of these hops, the latencies will accumulate.

--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***

On Apr 25, 6:06 pm, Barry Margolin <bar...@alum.mit.edu> wrote:

> Many routers, especially the ones that tend to be used on low-speed
> links, won't do anything with a packet until it has received the entire
> thing. Since it takes more time to transmit 1500 bytes than 100 bytes,
> every hop that goes through one of these routers will add latency
> proportional to the link speed and packet size. If you go through lots
> of these hops, the latencies will accumulate.

This may even be true of all routers. I don't think there's such a
thing as 'cut-through' routing. Most low-end switches don't cut
through and most high-end switches don't either. (Or is my information
out of date?)

In any event, it will definitely be the case every time a packet
transits a link that has a different speed from the previous link.
Cutting through is only possible if both links are the same speed.
(Well, it's technically possible from a faster link to a slower link,
but AFAIK, never done.)

A 56Kbps connection will typically add about 200 milliseconds to a
1,500 byte packet but only 15 milliseconds to a 100 byte packet.
(Total of header+data.) A 10Mbps or faster connection won't add more
than a millisecond or two to either. (100Mbps or faster will add way
less than 1mS.) Typically, latency over the Internet is dominated by
the speed-of-light-in-fiber effect, plus any latency due to slow links
at the very end.

Now, if you're sending a lot of packets, you may see latency due to
your previous packets building up in the queues on loaded links.
(Generally a packet won't be sent until all previous packets between
the same two endpoints have been sent.)

DS