PlusNet LLU not the same as BT Wholesale

Hi there

Now that I have a working LLU with PlusNet been doing some checking.

MTU on Tiscali LLU is fragmenting packets at 1440 rather than allowing upto 1500. Isn't this a similar mistake that BT made before changing it? Both www.dslreports.com and the TCP analyzer at www.speedguide.net show 1440, despite my settings all at 1500 and prior to LLU these sites reported my packets as arriving unfragmented at 1500, now they are being resized by Tiscali LLU to 1440, the speedguide analyser states:

In reply to:

---

MTU = 1440
MTU is not fully optimized for broadband. Consider increasing your MTU to 1500 for better throughput. If you are using a router, it could be limiting your MTU regardless of Registry setting

---

Also interleaving is on by default, rather than OFF by default with BT Wholesale.

I guess I need to reduce my MTU down to 1440 to save the overheads ofTiscal LLU splitting them up? Isn't this a potential problem with the LLU network if the routers have the overhead of splitting packets greater than 1440 up?

Nice observation.

"I guess I need to reduce my MTU down to 1440 to save the overheads ofTiscal LLU splitting them up?"

Worth a try.

It comes as a bit of a surprise (to put it politely) to see this showing up again.

Had the circumstances been different I might have said you were perhaps worrying unnecessarily and that there might be a good reason for it.

Fwiw I don't recollect seeing this "feature" on any of Be, Bulldog or F2S/Easynet's LLU services. Afaik they all work just fine with MTU 1500.

I wonder if any other Tiscali'd punters are seeing this?

Hi

Just done some speed tests to see how this hurts performance:

Using MTU at 1500 and RWIN at 128480: Download speeds really consistant at around 3700.
Using MTU at 1440 and RWIN at 128800: Download speeds shot up to around 4250.

So sticking with the norm BT optimised settings (whatever MTU you use above 1440 in my case 1500) would cost me around 500Kbits/sec on download speed.

I would guess if users do not change their MTU (and few would) then this causes extra work for the routers on the network having to fragment larger packets and results in more of them flying around? Seems incredible Tiscali Wholesale has made this error that BT fixed easily a couple of years ago.

"cost me around 500Kbits/sec on download speed."

Worthwhile but not huge.


"Seems incredible Tiscali Wholesale has made this error that BT fixed, easily a couple of years ago. "

A comma in the right place there would have helped

The problem was discovered in Autumn 2002 when the network ground to a halt on a daily basis for many people, regardless of ISP. BTw finally finished rolling out their fixes in mid 2003, which is easily a couple of years ago .

The MTU fix was merely a temporary workaround till BTw took the 10/100 Ethernet bits out of their infrastructure to be replaced with GigE or whatever (bigger packets allowed) and allowed MTU 1500 packets to pass unhindered - as you say, surely Tiscali can't be repeating the same mistake?

Bear in mind that BTw's problems arose in part because they initially *hid* the need to have smaller packets than MTU 1500 would create (I can't remember why they did this, but they did). Tiscali are not hiding it, thus they will not experience quite the same problems, or to the same degree.

Hi

In reply to:

---

Seems incredible Tiscali Wholesale has made this error that BT fixed, easily a couple of years ago

---

I noticed that and did a quick edit, not quick enough.

Thanks for the info and links.

Yes seems incredible that Tiscali LLU seems to have made a similar mistake.

Hi

Could you confirm if the upload speed is 800kps?

I'm able to be switched to LLU. The Faster upload would be very handy. But this MTU issue may be a bummer.

Phil

Hi

Upload speed seems to vary and must depend on the line noise, and I haven't seen it sync above 700 on the upload, but it is still more than normal MaxDSL.

I do not think MTU will impact too much and you can always optimise it anyway on your computer.

Hope that helps.

Hi

Many thanks for that report. I don't expect the full 800kps here too.

How was the switch over - not too many problems?


Phil

Hi

There is another post around here with my "problems".

It worked for a few hours then I lost sync with the exchange, it took 11 days to get the connection working again!

Have you changed your mind yet

I can confirm both Be and Bulldog work fine with 1500