Calculating overheads

Calculating overheads

[Alan Goodman]

Hi,

I am looking to figure out the most fool proof way to calculate stab 
overheads for ADSL/VDSL connections.

ppp0      Link encap:Point-to-Point Protocol
           inet addr:81.149.38.69  P-t-P:81.139.160.1 Mask:255.255.255.255
           UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1492  Metric:1
           RX packets:17368223 errors:0 dropped:0 overruns:0 frame:0
           TX packets:12040295 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:100
           RX bytes:17420109286 (16.2 GiB)  TX bytes:3611007028 (3.3 GiB)

I am setting a longer txqueuelen as I am not currently using any fair 
queuing (buffer bloat issues with sfq)

The connection is a BT Infinity FTTC VDSL connection synced at 
80mbit/20mbit.  The modem is connected directly to the ethernet port on 
a server running a slightly tweaked HFSC setup that you folks helped me 
set up in July - back when I was on ADSL.  I am still running pppoe I 
believe from my server.

The largest ping packet that I can fit out onto the wire is 1464 bytes:

# ping -c 2 -s 1464 -M do google.com
PING google.com (31.55.166.216) 1464(1492) bytes of data.
1472 bytes from 31.55.166.216: icmp_seq=1 ttlX time\x11.7 ms
1472 bytes from 31.55.166.216: icmp_seq=2 ttlX time\x11.9 ms

# ping -c 2 -s 1465 -M do google.com
PING google.com (31.55.166.212) 1465(1493) bytes of data.
 From host81-149-38-69.in-addr.btopenworld.com (81.149.38.69) icmp_seq=1 
Frag needed and DF set (mtu = 1492)
 From host81-149-38-69.in-addr.btopenworld.com (81.149.38.69) icmp_seq=1 
Frag needed and DF set (mtu = 1492)

Based on this I believe overhead should be set to 28, however with 28 
set as my overhead and hfsc ls m2 20000kbit ul m2 20000kbit I seem to be 
loosing about 1.5mbit of upload...

No traffic manager enabled: 
http://www.thinkbroadband.com/speedtest/results.html?id\x141116089424883990118
HFSC traffic manager: 
http://www.thinkbroadband.com/speedtest/results.html?id\x141116216621093133034

Am I calculating overhead incorrectly?

Alan