This may happen with other non-Dell models as well.
"network device not available" or "PXE-E07 - Device not ready"
This is failing due to when the BStrap.efi is running, the NIC UNDI driver is not loaded for the USB NIC.
This behavior was fixed in DS 7.6 HF7 (also in 8.0 codebase) by changing the PXE server to write out *.pxe files under SBS\Images of all data that would be communicated out on UDP 4011 to client machines.
However, this change is not enabled by default. If you're having this issue do the following on the PXE/SBS servers:
Browse to 'HKLM\Software\Altiris\Deployment'
Create a new DWORD named "WritePxeFiles" (\WritePxeFiles) and set it to a value of 1.
Unable to boot Dell XPS 13 with Dell Supported StarTech USB NIC
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