How to log USB modem data for a specific device?

[Jeffrey Walton]

Hi Everyone,

I'm having trouble with a C application that opens a USB modem. The
application is not receiving some data from a USR modem. Conexant
modems are OK.

I'm working through
https://www.kernel.org/doc/Documentation/usb/usbmon.txt . I found the
modem at Bus=01 Dev=24:

T:  Bus=01 Lev=03 Prnt=07 Port=00 Cnt=01 Dev#= 24 Spd=480  MxCh= 0
D:  Ver= 2.00 Cls=02(comm.) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
P:  Vendor=0baf ProdID=0303 Rev= 2.00
S:  Manufacturer=U.S.Robotics
S:  Product=USB Modem

This is where my confusion lies. It is not clear to me how to
determine which socket to use for step #3 in usbmon.txt. Step #3 says:

   # cat /sys/kernel/debug/usb/usbmon/3u > /tmp/1.mon.out

How do I determine which socket to use for Bus=01 Dev=24?

Thanks in advance.