Summarized here is the technical specification of the ADSL connection which was needed to setup the FreeBSD machine.
All or parts of information provided here may depend on the particular provider (Tokyo Metallic Communications) or its service (Single Plan.) If you are subscribing other provider or service, the information may not apply. Moreover, some parameter is by the authors own research and may be inaccurate.
The author is subscribing a Single Service Plan, that is explained by the provider as follows:
The service definition says that a user connects one PC to the network. However, provider's FAQ says that the one PC rule is not the limitation of use, but it is a limitation of the guarantee. Users are allowed to connect multiple PCs on their own risk.
So I'm doing. I believe it doesn't violate against the subscription agreement.
When I first applied for Tokyo Metallic Communications, there were nothing about dedicated software. Instead, the technical explanations said something like: "allocate an IP address via DHCP" or "client PC must be capable of DHCP." The simple DHCP based IP address management was one of the reason I chose Tokyo Metallic Communications as my ADSL provider.
However, the technical specifications of the Single Service Plan had changed. The new service is as follows:
It seemed that, technically, an ordinary PPPoE client will work fine. So I checked for the subscription agreement. It was unclear whether a subscriber may use an unauthorized PPPoE client. Later, the provide's FAQ about the use of Linux clients were published; it read as follows: "Tokyo Metallic Communications does not support the use of Linux machines, but users are allowed to try it on the users' own risk." I considered that the same thing as Linux should be allowed for FreeBSD.
The following is the technical specifications of PPPoE connection provided by Single Service Plan of Tokyo Metallic Communications. It can be seen as the specifications of TM Internet Mega Access, instead. Anyway, most of the parameters are not documented and are found by the author's own research. There will be some errors. You have been warned.
The most mysterious parameter in the above list will be MTU. Various literatures/documents says contradicting statements about MTU of PPPoE. They say: "MTU of PPPoE is 1492", "A value between 1900 and 1492; the correct value must be found by trial-and-error", "If your provider doesn't give you an accurate value, use smaller value than expected for safety." I see a web page that reads "PPPoE successfully negotiates MTU value, but it is always incorrect; unless you adjust the value with something smaller, it doesn't work."
I was uncomfortable about the idea of "something smaller for safety," so I installed the provider supplied TM Internet Mega Access on a Windows machine and monitored the PPPoE packets. The value 1454 was found in that way. Note that, for whatever reason, FLET'S ADSL services provided by NTT local companies use same MTU value.