Firmware Download in NATed Clients
Currently Docsis based RDK STBs support the following CDL methods

SNMP and bootfile triggered downloads
TFTP based downloads
However, IP client devices do not have a public IP address, and can only be reached through their Gateway STBs
IP Client STBs hence rely on TR-069 and ACS directive for Code Download
It can be triggered from CDL server just as in the case of gateways,
The IP client device is connected to Gateway device and it is behind the XG1.
Download RPC is used to trigger download to the IP Clients
- The CDL server triggers the request to ACS based on the Serial and MOUI of IP Client device.
The ACS selects the device based on the request from CDL server.
Then ACS uses the download RPC to trigger the firmware download.

Code Download Terminologies

Term	Definition
ACS	Auto-Configuration Server
Bootloader	Refers to the first stage bootloader responsible for lunching the firmware image.
B-DRI	Used in the event the disaster recovery image is corrupt. The capabilities are limited to ensuring that a secure download of the firmware image can take place.
P-DRI	Disaster Recovery Image. Refers to a disaster recovery image that is launched if the firmware image is invalid due to corruption of other reasons. When the device is running an DRI image, then it is DRI mode. If a normal firmware image is running, then it is in normal mode.
OTP	One time programmable memory.

Code Download - Example Decision Flow

When firmware updates are required, the device needs to know where to go to get the firmware update file. ACS calls "Download" method to download Firmware image to Device with the following arguments

Command Key
FileType
URL
Username
Password
FileSize
TargetFileName
DelaySeconds
SuccessURL
FailureURL CPE uses the above information to trigger for firmware download.