The majority of the overhead is in the ATM cell encapsulation. An Ethernet frame (1500 bytes) must be broken down and transmitted in ATM cells within the Telco's ATM cloud. ATM cells are a fixed 53 bytes, 48bytes of which are useful payload. That's 9.5% overhead right there. Most people blame PPPoE itself, but that's a mere 0.5% overhead--basically inconsequential.
Your friend's 1mbit DSL is performing just as expected. Some providers (I think Verizon does, or used to) will sync higher than the advertised speed to make up for the overhead, but that's relatively rare anymore. Greg > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:hardware- > [EMAIL PROTECTED] On Behalf Of Naushad Zulfiqar > Sent: Monday, September 22, 2008 3:02 PM > To: [email protected] > Subject: [H] DSL overheads, theoretical speeds vs actual > > I have a friend of mine who seems to be complaining that his DSL is on > the > slow side. > > I went over to his house and checked it out and it seems relatively > decent > to me. > > He has a 1 Mbps DSL connection which equals to a theoretical 128 KBps. > > I installed utorrent and downloaded ubuntu as a test. > > With all the speed tweaks, I manage to get around 110-118 KBps steady. > > That's around a loss of 10-18 KBps. > > Is that about normal with the PPPoE, TCP/IP and DSLAM overheads? I > would > say it's aboooooooooout normal. Maybe a bit wee on the high side, but > nothing to cry about. > > > > -- > Best Regards, > > > Zulfiqar Naushad
