Why udev USB port fixing rules are not working?

Question

I'm using Ubuntu 16.04.1 Server. There is a modem pool attached to one USB port of the server. When modem is turned off and back on again, the ttyUSB numbers are changing. I need to fix that ports. So, I put rules below to the file under /etc/udev/rules.d and restart the udev service with systemctl restart udev.service

# cat /etc/udev/rules.d/86-persistent-gsm-modem.rules 

KERNEL=="ttyUSB*", SUBSYSTEM=="tty", KERNELS=="1-1.5:1.0", DRIVERS=="ftdi_sio", ATTRS{product}=="Quad RS232-HS", ATTRS{manufacturer}=="FTDI", NAME="ttyUSB0"
KERNEL=="ttyUSB*", SUBSYSTEM=="tty", KERNELS=="1-1.5:1.1", DRIVERS=="ftdi_sio", ATTRS{product}=="Quad RS232-HS", ATTRS{manufacturer}=="FTDI", NAME="ttyUSB1"
KERNEL=="ttyUSB*", SUBSYSTEM=="tty", KERNELS=="1-1.5:1.2", DRIVERS=="ftdi_sio", ATTRS{product}=="Quad RS232-HS", ATTRS{manufacturer}=="FTDI", NAME="ttyUSB2"
KERNEL=="ttyUSB*", SUBSYSTEM=="tty", KERNELS=="1-1.5:1.3", DRIVERS=="ftdi_sio", ATTRS{product}=="Quad RS232-HS", ATTRS{manufacturer}=="FTDI", NAME="ttyUSB3"

When I turn off and back on again the modem still ttyUSB numbers are changing.

Is there a problem with rules, and how can I check if the rules are read by udev and executed?

Addition of udevadm output for /dev/ttyUSB0 for example.

udevadm info -a /dev/ttyUSB0

Udevadm info starts with the device specified by the devpath and then
walks up the chain of parent devices. It prints for every device
found, all possible attributes in the udev rules key format.
A rule to match, can be composed by the attributes of the device
and the attributes from one single parent device.

  looking at device '/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.5/1-1.5:1.0/ttyUSB0/tty/ttyUSB0':
    KERNEL=="ttyUSB0"
    SUBSYSTEM=="tty"
    DRIVER==""

  looking at parent device '/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.5/1-1.5:1.0/ttyUSB0':
    KERNELS=="ttyUSB0"
    SUBSYSTEMS=="usb-serial"
    DRIVERS=="ftdi_sio"
    ATTRS{latency_timer}=="1"
    ATTRS{port_number}=="0"

  looking at parent device '/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.5/1-1.5:1.0':
    KERNELS=="1-1.5:1.0"
    SUBSYSTEMS=="usb"
    DRIVERS=="ftdi_sio"
    ATTRS{authorized}=="1"
    ATTRS{bAlternateSetting}==" 0"
    ATTRS{bInterfaceClass}=="ff"
    ATTRS{bInterfaceNumber}=="00"
    ATTRS{bInterfaceProtocol}=="ff"
    ATTRS{bInterfaceSubClass}=="ff"
    ATTRS{bNumEndpoints}=="02"
    ATTRS{interface}=="Quad RS232-HS"
    ATTRS{supports_autosuspend}=="1"

  looking at parent device '/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.5':
    KERNELS=="1-1.5"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{authorized}=="1"
    ATTRS{avoid_reset_quirk}=="0"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bDeviceClass}=="00"
    ATTRS{bDeviceProtocol}=="00"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bMaxPacketSize0}=="64"
    ATTRS{bMaxPower}=="500mA"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bNumInterfaces}==" 4"
    ATTRS{bcdDevice}=="0800"
    ATTRS{bmAttributes}=="80"
    ATTRS{busnum}=="1"
    ATTRS{configuration}==""
    ATTRS{devnum}=="3"
    ATTRS{devpath}=="1.5"
    ATTRS{idProduct}=="6011"
    ATTRS{idVendor}=="0403"
    ATTRS{ltm_capable}=="no"
    ATTRS{manufacturer}=="FTDI"
    ATTRS{maxchild}=="0"
    ATTRS{product}=="Quad RS232-HS"
    ATTRS{quirks}=="0x0"
    ATTRS{removable}=="unknown"
    ATTRS{speed}=="480"
    ATTRS{urbnum}=="4960883"
    ATTRS{version}==" 2.00"

  looking at parent device '/devices/pci0000:00/0000:00:1a.0/usb1/1-1':
    KERNELS=="1-1"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{authorized}=="1"
    ATTRS{avoid_reset_quirk}=="0"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bDeviceClass}=="09"
    ATTRS{bDeviceProtocol}=="01"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bMaxPacketSize0}=="64"
    ATTRS{bMaxPower}=="0mA"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bNumInterfaces}==" 1"
    ATTRS{bcdDevice}=="0000"
    ATTRS{bmAttributes}=="e0"
    ATTRS{busnum}=="1"
    ATTRS{configuration}==""
    ATTRS{devnum}=="2"
    ATTRS{devpath}=="1"
    ATTRS{idProduct}=="0020"
    ATTRS{idVendor}=="8087"
    ATTRS{ltm_capable}=="no"
    ATTRS{maxchild}=="6"
    ATTRS{quirks}=="0x0"
    ATTRS{removable}=="fixed"
    ATTRS{speed}=="480"
    ATTRS{urbnum}=="31"
    ATTRS{version}==" 2.00"

  looking at parent device '/devices/pci0000:00/0000:00:1a.0/usb1':
    KERNELS=="usb1"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{authorized}=="1"
    ATTRS{authorized_default}=="1"
    ATTRS{avoid_reset_quirk}=="0"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bDeviceClass}=="09"
    ATTRS{bDeviceProtocol}=="00"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bMaxPacketSize0}=="64"
    ATTRS{bMaxPower}=="0mA"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bNumInterfaces}==" 1"
    ATTRS{bcdDevice}=="0404"
    ATTRS{bmAttributes}=="e0"
    ATTRS{busnum}=="1"
    ATTRS{configuration}==""
    ATTRS{devnum}=="1"
    ATTRS{devpath}=="0"
    ATTRS{idProduct}=="0002"
    ATTRS{idVendor}=="1d6b"
    ATTRS{interface_authorized_default}=="1"
    ATTRS{ltm_capable}=="no"
    ATTRS{manufacturer}=="Linux 4.4.0-34-generic ehci_hcd"
    ATTRS{maxchild}=="2"
    ATTRS{product}=="EHCI Host Controller"
    ATTRS{quirks}=="0x0"
    ATTRS{removable}=="unknown"
    ATTRS{serial}=="0000:00:1a.0"
    ATTRS{speed}=="480"
    ATTRS{urbnum}=="24"
    ATTRS{version}==" 2.00"

  looking at parent device '/devices/pci0000:00/0000:00:1a.0':
    KERNELS=="0000:00:1a.0"
    SUBSYSTEMS=="pci"
    DRIVERS=="ehci-pci"
    ATTRS{broken_parity_status}=="0"
    ATTRS{class}=="0x0c0320"
    ATTRS{companion}==""
    ATTRS{consistent_dma_mask_bits}=="32"
    ATTRS{d3cold_allowed}=="1"
    ATTRS{device}=="0x3b3c"
    ATTRS{dma_mask_bits}=="32"
    ATTRS{driver_override}=="(null)"
    ATTRS{enable}=="1"
    ATTRS{irq}=="16"
    ATTRS{local_cpulist}=="0-3"
    ATTRS{local_cpus}=="000f"
    ATTRS{msi_bus}=="1"
    ATTRS{numa_node}=="-1"
    ATTRS{subsystem_device}=="0x8383"
    ATTRS{subsystem_vendor}=="0x1043"
    ATTRS{uframe_periodic_max}=="100"
    ATTRS{vendor}=="0x8086"

  looking at parent device '/devices/pci0000:00':
    KERNELS=="pci0000:00"
    SUBSYSTEMS==""
    DRIVERS==""

Answer 1

First, udev will no longer rename the kernel-assigned device names. (Among other reasons, how should it cope with being asked to rename to something that's already taken by another device?)

Instead, use SYMLINK+="..." to create symlinks under /dev with your names of choice, for example SYMLINK+="ttyUSB-port0". (In fact the standard 60-serial.rules should already be creating symlinks under /dev/serial/by-path for you.)

Second, rules are processed not when udev starts, but only when the kernel sends out uevents indicating a new or changed device. To cause those manually, you need udevadm trigger -s tty (or just reconnect the device).