The upload speed problem about the USB modem on Ubuntu.

Franko Fang huananhu at
Wed Dec 31 02:15:43 UTC 2008

Dear all develpers:

    I have a USB modem, it can reach the download speed up to 7.2Mbps and the upload speed up to 5.76Mpbs.

   On the Ubuntu 8.10, kernel version 2.6.27, the system will load the USB serial driver /lib/.../drivers/usb/serial/option.ko for my USB modem device.

   And after dialing up with baud rate 115200, I can get the download speed to be 7.2Mpbs, but however, I can only get the upload speed to be 1.5Mpbs. 

   I modified the option.c code, and changed the out queue length and size as follows:
   /* per port private data */
   #define N_IN_URB 4
   -#define N_OUT_URB 1
   +#define N_OUT_URB 4
   #define IN_BUFLEN 4096
   -#define OUT_BUFLEN 128
   +#define OUT_BUFLEN 4096

    Then reload the new option.ko driver for my USB modem, but however, the upload speed is still keeping 1.5Mpbs.
    I don't know why, and I also don't know where the upload speed is limited.

    Can who can tell me why it is? Is it the problems of the kernel driver? Or is it the problems of the system settings?
  Wait for the help urgently!

Best Regards,

Franko Fang
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