Hey Mike, re read your posts and saw something about frame length. Was looking through the settings and saw under:

LAN >> Ports

Something about Maximum Frame Length and its set to 1522. Could this be to do with anything?

Maximum Frame
Enter the maximum frame size allowed for the switch port, including FCS. The allowed range is 1518 bytes to 9600 bytes.
Excessive Collision Mode
Configure port transmit collision behavior.
Discard: Discard frame after 16 collisions (default).
Restart: Restart backoff algorithm after 16 collisions.

Hello Mana.

The post on the BT forum is most probably the same one that I got my QoS settings from. They made quite a difference.

As for the Jumbo Packets, I did not have to make any changes to the 2750n for them. It seems to me that some routes that I pick up support jumbo packets, and some don't, though I haven't come across any that support them completely. I just disconnected and reconnected, every now and then, until I found one that supported them. You can see for definite if you capture and inspect the data, using Microsoft's Network Monitor software, but the speedtest.net results are a pretty good indication. I did try the maximum frame length change that you talked about, but I couldn't see any obvious differences that it made.

I said above that some connections support jumbo frames, and some don't. If you capture the data, and understand it, you can see what happens. For a connection that does not support it, you see the PC send a large frame, and get nothing back. It then sends a normal size frame, and continues in that way. In the IP header, the Do Not Fragment bit is set, which means that any node that does not support the large frames should just drop it, instead of breaking it up in to smaller frames. It should also send something back an ICMP frame to say that it has done so, but these are often discarded by firewalls. For connections that do support jumbo frames, though, you see the Ack(nowledgemant)s coming back. However, it looks to me that something on the way is ignoring the Do Not Fragment bit, because you get back multiple Acks. The Acks are usually for 2804 bytes, which is larger than the standard frame, but not as large as the frames that are actually sent. I think that the important thing, though, is that the large frames appear on the slowest part of the connection, where most can be gained, ie your VDSL connection.

I have noticed that all the frames for the download test are of the standard size, so I guess that there is fragmenting going on in this direction, too, but I am only seeing the results of it. If that was overcome, I guess that you would also see an improvement in the download speed results, too.

I am going to keep investigating, to see if I can understand more about what is happening.



Mike.