Re: Bearers in mixed CDMA+LTE modems

[Marcel Holtmann <marcel holtmann org>]

Hi Aleksander,

> >> I believe we need a MMBearerType enum in the 0.6 API, so that we can
> >> tell in CreateBearer() whether we want a 3GPP or CDMA (well, or POTS)
> >> bearer. This property would be redundant for 3GPP-only, CDMA-only or
> >> POTS-only modems, but would be mandatory if we have a mixed
> >> 3GPP(LTE)+CDMA bearer. This value would also be shown as a property in
> >> the Bearer interface, so that we can know the type of the bearer behind
> >> a given DBus path. Another possibility to avoid the new enum would be to
> >> assume that if "apn" is given when creating the bearer, we want a 3GPP
> >> bearer, while if no "apn" is given we really want a CDMA bearer. But not
> >> sure I like to rely just on this "apn"-based logic. What do others think?
> > 
> > The problem with that approach is handoffs.  If you create a 3GPP/LTE
> > bearer and then leave LTE coverage where the device hands off to EVDO,
> > now your 3GPP bearer is a CDMA bearer.  In this scenario there's no
> > interruption of packet data service and you don't even know anything
> > happened except that the access technology changed from LTE to EVDO.
> 
> Well, that is already some indication that we can use. If we had a 3GPP
> bearer connected, and suddenly the access technology changed to EV-DO,
> then we could internally mark the CDMA bearer as connected and mark the
> 3GPP one as disconnected. If done in that order, we wouldn't be issuing
> any state change notification. This, assuming that for mixed technology
> modems we have different technology-specific bearers. The only drawback
> of having technology-specific bearers is that for the user not using the
> Simple interface, it would mean needing to create two bearers with two
> CreateBearer() calls. But I don't think that that is a big deal; if the
> user of a mixed CDMA+LTE modem just creates a 3GPP bearer and gets it
> connected, and then we detect the connection handed off to CDMA, we can
> request the disconnection of the bearer and that's it. If the user
> didn't create a CDMA bearer, we would need to assume she didn't want a
> CDMA connection. If using the Simple interface, all that would be
> automatic, different bearers would be created automatically.

there is no guarantee that the IP connection details stay the same.

Before everybody goes crazy here you might wanna check if Verizon even
provides the same IP address when falling back to CDMA from LTE.

Regards

Marcel