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

[Arun Ravindran <ext-arun.1.ravindran@nokia.com>]

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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.

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).

>>> 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.

> If so, then the
> powered property does not map to LTE at all.  Your proprietary CFUN/COPS
> map to the TechnologyPreference setting in RadioSettings.
>
Regards,
Arun