>>>>>>> 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. >>> >>> It's supposed to work that way according to the eHRPD docs. I tried to >>> drivetest this Friday but due to my own stupidity I forgot to take the >>> modem out of LTE+HRPD mode and into AUTO+eHRPD so I couldn't capture the >>> handoff and then I ran out of battery. My bad, I'll try again. >>> >> >> Needless to say that I would love to see the logs :-) >> >>> But at least the UE is supposed to make this transparent according to >>> 3GPP2 X.S0057-A. If the ME already has IP address information from the >>> network, in the VSNCP Configure-Request packet it sets the Attach-Type >>> configuration option to "handoff" and includes the existing IP >>> information (10.1.4.2). >>> >>> Section 13 (Handoff from E-UTRAN to eHRPD) states: >>> >>> "For optimized handoff, when the UE accesses eHRPD via the E-UTRAN radio >>> and the S101 tunnel, it shall send a VSNCP Configure-Request message >>> with Attach-Type set to handover to the HSGW for each of it's existing >>> PDN connections in the EPS system that it intends to maintain in eHRPD." >>> >>> Section 13.1.1 step 7 says: >>> >>> "The UI exchanges VSNCP messages with the HSGW for each PDN connection >>> that it currently has attachments to within E-UTRAN and that it wants to >>> maintain on eHRPD. The UI sets the Attach-Type to "handoff" in the >>> VSNCP Configure-Request message. Also, the UI includes the IP >>> address(es) it obtained via LTE in the VSNCP Configure-Request message." >>> >>> See also section 13.1.1 where it details what happens for optimized >>> handoff; non-optimized handoff is supposed to be the same, more or less. >>> >>> So let's assume that the IP address is supposed to stay the same. Next, >>> the standard talks in various places about separate bearers for EPS and >>> eHRPD, like 13.2.1: "When the UE returns to eHRPD to resume the existing >>> eHRPD session, the PDN connections are created per the context that the >>> UI had on E-UTRAN. Likewise, bearers are established to match those >>> that were available on E-UTRAN." >>> >>> Basically, it appears that bearers may change at various times, but the >>> IP addresses may stay the same across bearer changes in some cases too. >>> The problem is that we don't really want to expose that to clients much, >>> because it's not really that useful to know that bearers are dancing >>> around. You really just want to know if one of your existing bearers >>> *changed* attributes like IP addressing or QoS/TFT, since the modem and >>> network appear to do all they can to maintain characteristics between >>> E-UTRAN and eHRPD. I also still don't know how these changes are >>> presented via AT, WMC, or QMI, and how much of this the modem does >>> internally and hides from these interfaces but I'm still trying to >>> figure out. Unfortunately the end of my LTE coverage is about 30+ >>> minutes away in all directions... >>> >> >> Having read the document, it really seems that the whole eHRPD setup >> makes the handoff to/from LTE much much *much* more transparent than >> what I thought (keeping the IP addresses during the handoff is just one >> detail), and that we don't really need to take care of exposing them >> apart from just notifying about the change of technology being actively >> used (if possible to notify that). So for the generic case of "do LTE or >> CDMA, with LTE preferred" the setup is quite automatic. >> >> The other thing that comes to be a bit more clear is that for mixed >> LTE+CDMA modems, the need of requesting a CDMA-only connection may be a >> bit unclear: mixed LTE+CDMA modems don't really need >> to support CDMA-only connections (Optional Rm-interface protocol setup >> plus ATDT#777), as the CDMA network may really be handled just for >> handoff from LTE via eHRPD. Could you try to connect your LTE+CDMA modem >> using the standard CDMA connection sequence and see if it works? >> >> So, for the generic implementation of the mixed LTE+CDMA modem, I guess >> we should follow your suggestion of creating a generic Bearer that will >> do 3GPP-based connection sequence (PDP context setup and activation) >> when 4G is allowed, and otherwise try CDMA-based connection sequence >> (optional Rm-interface protocol setup plus ATDT#777). This single >> mutable object is probably the most dynamic/extensible implementation >> that we could give to plugin implementations. > > unless you have a really really smart modem firmware, the ATD#777 can > not work out to setup any kind of auto-handover connection. The PPP > connection is terminated at the network and not the modem level as in > 3GPP. There is a theory that can terminate PPP in the network for 2G/3G, > but even that I have never seen used in any network. And I doubt anybody > with a 4G network falling back to this. Way to expensive on the network > equipment to handle LTE loads via PPP. > > So once you fall back to any kind of ATD with PPP, I think you are stuck > in one technology. Especially if it termination endpoints of your PPP > connection are different. >
Yes, I think we're in the same page here. The ATDT#777-based connection to the CDMA network would only be used *if 4G is not an allowed mode* (i.e. we don't want LTE); we won't expect the modem to automagically handoff to LTE from a connection started with ATDT#777. Anyway, this would really be the generic implementation that specific plugins can reimplement with more detail. -- Aleksander _______________________________________________ networkmanager-list mailing list networkmanager-list@gnome.org http://mail.gnome.org/mailman/listinfo/networkmanager-list