I have a TP-Link WDR 3600 router and have installed OpenWrt Chaos Calmer 15.05.1

I have been able to configure basic LAN and WiFi - wifi bridges to a second router to give an internet link.

I can log in to the shell using PUTTY and can edit files using Notepad++ with the NppFTP extension.

I am trying and failing to add a 3G USB dongle. ZTE MF730M which has a MBIM interface.

I set up a new Interface:

3g-wan     RX: 0.00 B (0 Pkts.) TX: 0.00 B (0 Pkts.)
Protocol UMTS/GPRS/EC-DVO
Modem device /dev/tty/USB0
Service Type UMTS/GPRS
APN giffgaff.com
PIN
PAP/CHAP username giffgaff
PAP/CHAP password password
Dial number AT*99#

Trying to connect via Luci or ifup does not create a connection.

I have the following USB modules installed:
kmod-ledtrig-usbdev     3.18.23-1
kmod-usb-core     3.18.23-1
kmod-usb-serial     3.18.23-1
kmod-usb-serial-option     3.18.23-1
kmod-usb-serial-wwan     3.18.23-1
kmod-usb2     3.18.23-1
libusb-1.0     1.0.19-1
usb-modeswitch     2014-08-26-993a9a5427..37a

Following insertion of the modem logread shows:

[51982.010000] usb 1-1.1: new high-speed USB device number 11 using ehci-platform
[51982.120000] usb 1-1.1: unable to read config index 2 descriptor/start: -32
[51982.130000] usb 1-1.1: chopping to 2 config(s)
[51982.140000] usb 1-1.1: string descriptor 0 read error: -71
[51982.150000] usb 1-1.1: can't set config #1, error -71
[51982.280000] usb 1-1.1: USB disconnect, device number 11
[51982.560000] usb 1-1.1: new high-speed USB device number 12 using ehci-platform

Which suggests that the USB modem is not recognised in some way.

BUT the output from cat /sys/kernel/debug/usb/devices is:

T:  Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=480  MxCh= 1
B:  Alloc=  0/800 us ( 0%), #Int=  1, #Iso=  0
D:  Ver= 2.00 Cls=09(hub  ) Sub=00 Prot=01 MxPS=64 #Cfgs=  1
P:  Vendor=1d6b ProdID=0002 Rev= 3.18
S:  Manufacturer=Linux 3.18.23 ehci_hcd
S:  Product=EHCI Host Controller
S:  SerialNumber=ehci-platform
C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=  0mA
I:* If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
E:  Ad=81(I) Atr=03(Int.) MxPS=   4 Ivl=256ms

T:  Bus=01 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=480  MxCh= 4
D:  Ver= 2.00 Cls=09(hub  ) Sub=00 Prot=01 MxPS=64 #Cfgs=  1
P:  Vendor=05e3 ProdID=0608 Rev=85.36
S:  Product=USB2.0 Hub
C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=100mA
I:* If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
E:  Ad=81(I) Atr=03(Int.) MxPS=   1 Ivl=256ms

T:  Bus=01 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#= 14 Spd=480  MxCh= 0
D:  Ver= 2.00 Cls=02(comm.) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
P:  Vendor=19d2 ProdID=1405 Rev=f0.f7
S:  Manufacturer=ZTE,Incorporated
S:  Product=ZTE Mobile Broadband Station
S:  SerialNumber=1234567890ABCDEF
C:* #Ifs= 3 Cfg#= 1 Atr=c0 MxPwr=500mA
A:  FirstIf#= 0 IfCount= 2 Cls=02(comm.) Sub=06 Prot=00
I:* If#= 0 Alt= 0 #EPs= 1 Cls=02(comm.) Sub=06 Prot=00 Driver=(none)
E:  Ad=82(I) Atr=03(Int.) MxPS=  16 Ivl=32ms
I:* If#= 1 Alt= 0 #EPs= 0 Cls=0a(data ) Sub=00 Prot=00 Driver=(none)
I:  If#= 1 Alt= 1 #EPs= 2 Cls=0a(data ) Sub=00 Prot=00 Driver=(none)
E:  Ad=81(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E:  Ad=01(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
I:* If#= 2 Alt= 0 #EPs= 2 Cls=08(stor.) Sub=06 Prot=50 Driver=(none)
E:  Ad=83(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E:  Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=125us

This shows the ZTE modem listed.

I am a bit confused and would welcome advise to solve this.

Thanks

Ted