Hi Denis,
> > Disabling IPv6 stateless address would be a bold move
> indeed, since it is declared mandatory in both IETF and 3GPP
> standards. Please see [RFC4294] and [3GPP 23.060]. The
> section "Dynamic IPv6 Address Allocation" in 23.060 is very
> clear on how IPv6 address allocation in 3GPPP networks is
> done. See also the section about IPv6 prefix delegation
> (relevant to IPv6 tethering) and applicable parts of 24.008.
> >
>
> This still needs to be figured out. We are aware that
> autoconfiguration
> is mandatory in 3GPP. However, this seems to be going against 27.007.
There is no contradiction. Let me explain what I mean. The 3GPP standards
mostly talk about MS (mobile station) which comprises of both TE and MT
(terminal equipment and modem terminal). As such, 3GPP specifications place
requirements on both TE and MT. The 27.007 defines a TA (terminal adapter),
which is one possible interface between TE and MT. However, 27.007 is not
mandatory, vendor specific interfaces are also allowed. As a consequence other
interfaces, such as ISI and CAIF, also exist.
While stateless address autoconfiguration is mandatory for MS, a funky AT modem
could potentially have an internal IPv6 stack as part of the TA function and
perform address configuration against the network and then proxy any IPv6
traffic between the TE and the network. This would meet the requirements of
3GPP. The *intent* in the 3GPP standards is that TEs can behave as standard
IPv6 hosts (so PCs can use a standard IPv6 stack), which means that the TE is
expected to run the autoconfiguration protocols against the network in the
normal case. Nothing in 27.007 specifically prevents that. The static address
configuration parameters in the AT commands are optional and will simply be
missing, if the modem just acts as a bitpipe between TE and the network,
allowing the TE to run its IPv6 stack in the normal way.
However, a funky AT modem that implements an IPv6 stack internally and exposes
static address configuration parameters towards TE is certainly possible. Such
a modem would presumably also block the router advertisements coming from the
network, which would effectively disable stateless address autoconfiguration
for the TE. This is not something you need or should do in connman. Standard
IPv6 stack is sufficient.
> So in the end both might be required.
On this I agree. Stateless address autoconfiguration is needed because it is
mandatory in both IETF and 3GPP standards (sorry for the repetition). Static
configuration (optional in IETF standards) may also be needed but that remains
to be seen. It depends on what kind of funky AT modems are and will be out
there.
> In the end oFono's philosophy is to always err on the side of 27.007.
> So far this strategy has never been (completely) wrong.
27.007 provides a nice checklist for the functionality of the modem, so in that
sense you're right. In another way it also serves as a lowest common
denominator for the same functionality. However, what 27.007 does not do is
specify system behaviour. It's easy to jump to conclusions just by looking at
what AT commands are available. Most of the commands are optional, because a
lot of freedom has intentionally been left for the implementors. It is also
why, IMO, the specification is so bad and we have to fight with all these
quirky AT modem implementations.
Remember that 3GPP standards specify the behavour between MS and the nework.
I.e., they place requirements on both TE and MT. The AT interface (TA function)
stands in between and the combination of TE+TA+MT must function in accordance
to 3GPP standards. My point is, you *really* need to read other 3GPP
specification, like 23.060 and 24.008, in order to understand what requirements
3GPP places on oFono. Reading 27.007 will not tell you that.
Regards,
MikaL
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