Summary: The draft describes using the GTP-U bearer outer UDP header source port as the slice selector on F1-U/N3/N9 interfaces, since the S-NSSAI is invisible to the transport network. Although the document core idea is well described, it takes "a while" to get there making the draft a bit "heavy" to go through until section 3.3. IMHO, the draft can/should be shortened till section 3.3.

Nits: Section 4 says: 
"An example with different user plane slice types and transport paths is shown in the figure."  
AND
"The figure shows UDP port ranges, SST, transport path (in this example pseudowire/VPN) and transport path characteristics."

=> Would be useful to mention which figure you're referring to.

Thanks!