RE: Sierra Wireless (MC8780) HSDPA speed issue

[Rory Filer]

Hi Ralf, 

Actually the Windows and Linux models are the same from the modem's point of view, but the PPP client is inside the NDIS driver. 

I've pasted in the response from our UMTS engineer below, but I'm not sure how much help it will be; here it is:

-----Begin Included...
There is no specific AT command that would limit the data rate on the device - except for AT!HSDCAT but I do not think that he would be using this. Other commands such as AT+CGEQREQ probably would not help, so they should clear them. 

>From the email below it seems that he used the same device on Windows so the device configuration should be OK. The location could be an issue but I would assume that he tried using the device with Windows at the same location. 

One problem that I have seen with USB is that the USB modem throughput will be low if there are other devices on the same USB hub of the laptop
----End Included

There it is. If you could get your hands on another machine and put Linux on it - or maybe temporarily make your windows machine into Dual Boot with Ubuntu (using wubi) and see how that compares that might help, but I am out of useful ideas at this point. 

Regards

Rory



-----Original Message-----
From: Ralf Nyren [mailto:ralf@xxxxxxxxx] 
Sent: Monday, March 16, 2009 5:48 AM
To: Greg KH
Cc: Rory Filer; Stephen Clark; linux-kernel@xxxxxxxxxxxxxxx; Kevin Lloyd
Subject: Re: Sierra Wireless (MC8780) HSDPA speed issue

Thanks Rory,

I have tried changing OBUFSIZE in ppp_async.c (still kernel 2.6.28.7), first
512 and then 4096. However the speed "limit" of about 100KB/s remains the same.
So perhaps there's some setup/firmware issue with the hardware. If I understand
things correctly the Windows driver uses a proprietary protocol to init the card
while in Linux you use the AT command interface. Could be something there which
makes a difference I guess.

Best regards, Ralf

On Sun, 15 Mar 2009, Greg KH wrote:

> On Sun, Mar 15, 2009 at 03:30:54PM -0700, Rory Filer wrote:
>> Hi Ralf
>>
>> Using the driver we sent you on a call-box (i.e. with a "perfect"
>> simulated network connection) on Ubuntu 8.04 we were seeing ~4 Mbps on
>> the downlink. So I would rule out any problem with the driver and
>> conclude it must be something in either PPP/Linux or in the modem. In
>> order to rule out the modem, I've got a question into one of our UMTS
>> engineers and will send you a reply when we get the answer.
>>
>> We did play around a little with 2.4 kernels of Linux and discovered
>> there is a buffer in PPP_ASYNC.C which, when its size is increased,
>> doubled the throughput. If you are savvy enough with Linux, you might
>> want to try playing with that. We stopped short of any thorough
>> testing of changing this array size, but were pleased with the result.
>> If I recall properly, the size of this array is (was, in 2.4) 256
>> bytes. Doubling it gave an immediate improvement. We were guessing
>> that the small size of this buffer was fine in the "old days" when
>> modems peaked at ~56 kbps. Even 8 years ago that was the fastest you
>> could go with a GPRS product, now our new HSPA+ products yields 21
>> Mbps on Telstra's network! Quite a difference.
>
> Ah, the OBUFSIZE #define in drivers/net/ppp_async.c?
>
> Anyone care to bump this size up and see if that helps out?
>
> thanks,
>
> greg k-h
>

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