In the below diagrams and the next articles, every ISP is referenced by its Autonomous System (AS) Number.
"Within the Internet, an Autonomous System (AS) is a collection of connected Internet Protocol (IP) routing prefixes under the control of one or more network operators that presents a common, clearly defined routing policy to the Internet."Source: Wikipedia
Basically, every ISP can be clearly identified by its AS Number. Some ISPs may have multiple AS Number (such as CAT Telecom below).
Planet's AS Number is 23900.
NAPT's AS Number is 55508.
100% of Planet Internet traffic is going through the NAPT
In the above picture, AS23900 represents Planet. AS55508 is the NAPT AS. Just mouse over the AS number to see which ISP it belongs to. Source: Hurricane Electric Internet Services
That is certainly the root cause for the raising complains heard from this ISP.
One Internet upstream connection means no redundancy. If the upstream provider is down, the whole network cannot reach the outside world.
From this diagram, we can also see that the NAPT sources its Internet from CAT Telecom in Thailand.
CAT Telecom is a good ISP in Thailand delivering quality bandwidth. Although, as it is a state-owned company, Internet censorship is enforced in its network and some websites may not be reachable (e.g. anonymous proxy websites, lèse majesté content, pornographic content, information about abortion). For more details, please refer to the wikipedia webpage about Internet censorship in Thailand.