[wplug] DSL speed

[Patrick Wagstrom]

Patrick Wagstrom wrote:
> Zach wrote:
>> The speed test at dslreports.com is showing my download speed as 625
>> Kb/s. This seems a lot less than the 768 Kb/s I'm supposed to have. My
>> latency to their test server in NY was 50ms. Is there anything I can
>> do to to increase my download speed? I'm using Ubuntu 7.04 Live CD
>> until I can buy a new computer. Running 2.6.18 kernel and
>> Debian/Ubuntu.
> 
> That actually sounds pretty good.  You've got two layers of overhead 
> going on in your connection: encapsulation to PPPoE and then TCP/IP.  
> For most packets, these numbers are both small (8 octets for PPPoE, 20 
> octets for IP, 20 octets for TCP).  In that case you're losing about 4% 
> right off the bat to overhead.  However, depending on the way data is 
> transmitted it could be far worse.  Telnet usually transmits single 
> octets, which means that on a DSL you're sending 49 octets of which 1 
> octet is data.  Yay for 98% overhead.
> 
> Another issue is that there is inherent noise in the DSL line.  This 
> causes some data to retransmit, lowering your throughput even more.  
> Noise is present on most lines (cable too), but the nature of the phone 
> network means its slightly more susceptible.
> 
> This is normal.  Getting 625Kb/s on a 768Kb/s is great.  If you were 
> around 400Kb/s that would be an issue.

I also realized that I forgot any addition splicing their network may do. 
If they're running ATM lines, then you've got killer overhead.  ATM 
typically transfers 53 octets cells, of which 5 are overhead.  Depending on 
the configuration of the network, this may, or may not, get passed down to you.