Thanks Matthew, this is precisely what I was attempting to ask. So it sounds like packet size affects the total rate of sending packets more or less depending on the medium. And as for mediums, it sounds like:
- Ethernet has such a high per-packet overhead that the maximum rate of packet sending is more or less the same irrespective of packet size - PPP has low overhead (? Or is generally so slow?) that packet size does affect total number of packets sent. Any idea how this'd play into a typical cablemodem or DSL connection? -david > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:p2p-hackers- > [EMAIL PROTECTED] On Behalf Of Matthew Kaufman > Sent: Wednesday, January 31, 2007 11:35 AM > To: theory and practice of decentralized computer networks > Subject: Re: [p2p-hackers] Silly question about UDP > > Alen Peacock wrote: > > On 1/27/07, David Barrett <[EMAIL PROTECTED]> wrote: > >> > >> Is it actually any cheaper to send a 0-byte UDP packet than to send > >> one that > >> is sized at the MTU? > > > > In terms of CPU and bus burnage, small UDP packets are going to be > > WAAAAAY more expensive than sending/receiving large UDP packets. It > > isn't too hard to confirm this through simple experiments. > > Agreed, but this is the answer to a different question. I think that > David (who may correct me if I'm wrong), wants to know "if I'm sending > packets regularly, is there any advantage to making sure it is as small > as possible, or is there no real difference if I just fill it all the > way up?" vs. the other equally good question that you've answered which > is "if I need to move X megabytes of data over the net, is there an > advantage to using the entire MTU for each in order to minimize the > number of packets sent?". > > The answer to the first is "yes, there's some advantage to trying to > keep the size of your packets down by sending data efficiently, but this > advangtage depends on the link technology your packets run over... for > some, like ethernet LANs, there's a lot of per-packet overhead that > dominates, for others like a PPP modem connection, every byte counts" > > The answer to the second is "absolutely, given that some links have > large per-packet overhead and most routers and hosts have large fixed > overheads of CPU time for each packet that arrives, you should use as > much of the MTU as you can for each packet you send... while making sure > that A) you don't fragment and B) you know what head-of-line blocking > is, and how it matters to your application (if at all)" > > Matthew Kaufman > [EMAIL PROTECTED] > _______________________________________________ > p2p-hackers mailing list > [email protected] > http://lists.zooko.com/mailman/listinfo/p2p-hackers _______________________________________________ p2p-hackers mailing list [email protected] http://lists.zooko.com/mailman/listinfo/p2p-hackers
