Re: [PATCH] atmodem: CEREG support for LTE network status reporting in AT modem

[Denis Kenzior <denkenz@gmail.com>]

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Hi Arun,

On 02/24/2011 04:34 AM, Arun Ravindran wrote:
> Hi Denis,
>>>> -----Original Message-----
>>>> From: ofono-bounces(a)ofono.org [mailto:ofono-bounces(a)ofono.org] On
>>>> Behalf Of Denis Kenzior
>>>> Sent: Wednesday, February 23, 2011 5:50 PM
>>>> To: ofono(a)ofono.org
>>>> Cc: tomasz.gregorek(a)gmail.com
>>>> Subject: Re: [PATCH] atmodem: CEREG support for LTE network status
>>>> reporting in AT modem
>>>>> After discussing internally with Fred Joly I would like to come back
>>>> on the 4 properties :
>>>>> - Suspended is applicable in LTE in case of CS Voice Call using CSFB
>>>> My understanding was that CS Fallback physically switches technologies.
>>>>   It is not 'suspending' LTE like it does with GPRS.  Am I wrong on
>>>> this
>>>> one?
>>> I would say yes. :)
>>> In case you are obliged to fallback from 4G to 2G without support of
>>> DTM, exaclty like in GPRS.
>>  From what I understood you physically lose the EPS network registration
>> and fall back to 3G / 2G.  How is this the same as the suspended
>> property where your attached status does not change?
>>>
> For CSFB there are two settings. First one is that the UE should be
> voice centric.
> A voice centric UE will always try to make voice service available
> either using IMS or by CSFB.
> And if it cannot avail voice service using the above mechanisms, then it
> should leave E-UTRA and re connect to GERAN/UTRA. A data centric UE in
> turn will not leave E-UTRA if it cannot make a voice service available.
> (23.221, section 7.2a)
> 
> The second is that the voice call mode (domain), this can be set to CS,
> CS preferred, PS or PS preferred. A UE with CS or CS preferred will
> always try to make voice service through CS (CSFB or by re connecting to
> GERAN/UTRA). 24.167 and also 23.221 describes these setting. I think the
> AT commands for these in 27.007 are AT+CEMODE and +VCMOD
> 
> A UE indicates its CSFB capability in attach and location/routing area
> updates. The network in turn also indicates whether these are supported
> in network.
> 23.272 section 6.2 details a CSFB for MO call, where PS handover is
> supported. 6.3 where PS handover is not supported and 6.5 where how to
> return to E-UTRA when PS is suspended.
> 

So everyone keeps talking of suspensions.  However, I still see no CGEV
that supports this event.  It still looks like a 2G holdover that is
being implemented by vendor specific extensions.  Or is this just an
oversight on 3GPP's part and suspensions can happen in LTE as well?

> My understanding is that the context behaves the same way as in GPRS,
> where it can be suspended, deactivated or handed over while doing CSFB
> and the attach status will not change because when you are doing CSFB
> you have done a combined attach (EPS/IMSI).
> 

Attach status fair enough.  However, does the reported technology change
as well?  There are important implications here, e.g. being able to
deactivate the last context, etc.

Overall I think we need detailed traces for all such scenarios and
consider all possibilities.  Currently I'm not convinced sharing LTE and
GPRS logic is the right way to go.

>>>> Perhaps, but again we have no control of the attach procedure with LTE.
>>>>   So the implementation has to rely on vendor specific radio settings.
>>>> Same arguments about shoehorning logic apply here.
>>> I'm a bit puzzled by this statement. It is not specific to LTE, but
>>> related to +CFUN proprietary implementation against  +COPS or +CGATT 
>>> usage, isn't it?
>>>
>> The current GPRS logic is controlled with the equivalent of CGATT.  This
>> is a well-defined command by 3GPP, but it is not applicable to EPS
>> domain.  It is applicable only to PS domain, correct?
> 27.007 release 10, section 10, lists all commands applicable to EPS and
> CGATT is one of them.
> 

My fault, I mis-interpreted that section.  You're of course correct that
CGATT is indeed applicable.

Regards,
-Denis