Incoming line identity and ALS

Incoming line identity and ALS

[Chris Pitchford]

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Hi all,

I've been looking through the 0.8 source code for some indication of ALS 
support.

ALS (or line-2) allow two different numbers to be attached to a mobile 
device. The device can accept calls from both numbers and make calls from 
either of the two numbers, effectively acting as if two lines were 
attached to the device.

http://en.wikipedia.org/wiki/Alternate_line_service

AT+CNUM reports all of the lines available on a mobile device that 
supports/is using ALS.

I guess there are two problems for supporting ALS in ofono.

First is selecting which line/number to use when making a call. I'm not 
certain how handsets make this distinction and I wonder if it might be 
vendor specific.. Changing out bound line seems to be set as a mode rather 
than on a
per-call basis. Switching out bound lines is sometimes locked with PIN1.

The other problem is identifying which line was called by a remote caller. 
I believe +CDIP includes this information (after each RING / +CRING)

From what I've seen of the API, it has the ability to report the caller 
identity for in bound calls and the dialed number for out bound calls, but 
I can't seem to find any reference to the number called for in bound calls 
which would be used to identify which line was ringing..

I was wondering if this service has been considered for ofono or if 
perhaps it is already there and I've missed it..

Cheers

Chris

Re: Incoming line identity and ALS

[Denis Kenzior]

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Hi Chris,

> Hi all,
>
> I've been looking through the 0.8 source code for some indication of ALS
> support.
>
> ALS (or line-2) allow two different numbers to be attached to a mobile
> device. The device can accept calls from both numbers and make calls from
> either of the two numbers, effectively acting as if two lines were
> attached to the device.

ALS was never part of the core GSM specification.  It was an extension 
supported by several network providers and phone manufacturers.  It was 
incorporated into recent GSM specifications as 'Multiple Subscriber Profile.'

> First is selecting which line/number to use when making a call. I'm not
> certain how handsets make this distinction and I wonder if it might be
> vendor specific.. Changing out bound line seems to be set as a mode rather
> than on a
> per-call basis. Switching out bound lines is sometimes locked with PIN1.

This is done as a supplementary service control sent to the network over USSD.  
The details are pretty sketchy but the basics are described in 22.030 Section 
6.5.6.1.

>
> The other problem is identifying which line was called by a remote caller.
> I believe +CDIP includes this information (after each RING / +CRING)
>
> From what I've seen of the API, it has the ability to report the caller
> identity for in bound calls and the dialed number for out bound calls, but
> I can't seem to find any reference to the number called for in bound calls
> which would be used to identify which line was ringing..

CDIP (like CLIP) is issued after every RING/CRING.  Whereas CLIP returns the 
calling line identity, CDIP returns the called line identity (e.g. the phone 
number the remote caller dialed.)  According to the specification it is not 
reported for outbound calls.

>
> I was wondering if this service has been considered for ofono or if
> perhaps it is already there and I've missed it..

oFono currently does not support ALS/MSP and we do not foresee enabling this 
feature in the near term.  If you would like to help out, code / research / 
documentation contributions are always welcome :)

Regards,
-Denis

Re: Incoming line identity and ALS

[Chris Pitchford]

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Quoting Denis Kenzior <denkenz@gmail.com>:

> Hi Chris,
>
>> Hi all,
>>
>> I've been looking through the 0.8 source code for some indication of ALS
>> support.
>>
>> ALS (or line-2) allow two different numbers to be attached to a mobile
>> device. The device can accept calls from both numbers and make calls from
>> either of the two numbers, effectively acting as if two lines were
>> attached to the device.
>
> ALS was never part of the core GSM specification.  It was an extension
> supported by several network providers and phone manufacturers.  It was
> incorporated into recent GSM specifications as 'Multiple Subscriber Profile.'
>

I'm glad it was made more official, I just wish it was more widely  
available. It's a fantastic feature.. one number for business, one for  
personally.. It's all good!


>> First is selecting which line/number to use when making a call. I'm not
>> certain how handsets make this distinction and I wonder if it might be
>> vendor specific.. Changing out bound line seems to be set as a mode rather
>> than on a
>> per-call basis. Switching out bound lines is sometimes locked with PIN1.
>
> This is done as a supplementary service control sent to the network  
> over USSD.
> The details are pretty sketchy but the basics are described in 22.030 Section
> 6.5.6.1.

Fantastic, there's somewhere for me to look.

>
>>
>> The other problem is identifying which line was called by a remote caller.
>> I believe +CDIP includes this information (after each RING / +CRING)
>>
>> From what I've seen of the API, it has the ability to report the caller
>> identity for in bound calls and the dialed number for out bound calls, but
>> I can't seem to find any reference to the number called for in bound calls
>> which would be used to identify which line was ringing..
>
> CDIP (like CLIP) is issued after every RING/CRING.  Whereas CLIP returns the
> calling line identity, CDIP returns the called line identity (e.g. the phone
> number the remote caller dialed.)  According to the specification it is not
> reported for outbound calls.

It seems that my phone doesn't support CDIP, although it does support  
line-2/ALS which is a bit odd. I'll investigate more on that..

One thing I'm not certain about is whether CDIP would report which  
line received the call, or which number the calller dialed as they  
could be different. I know other areas deal with routing information,  
but I wasn't sure which which number CDIP reported. It would be great  
for ALS support if it were the line that received the call, rather  
than the number dialed by the caller.. though that could be  
interesting in other situations.

>
>>
>> I was wondering if this service has been considered for ofono or if
>> perhaps it is already there and I've missed it..
>
> oFono currently does not support ALS/MSP and we do not foresee enabling this
> feature in the near term.  If you would like to help out, code / research /
> documentation contributions are always welcome :)

To be fair, you've already given me a lot of information, such as  
which standards describe the service. I'd be more than happy to try  
and help out. I personally use ALS and would love to see it  
incorporated and if I can help achieve that, all the better!

I guess the two tasks are discovering how to collect called line  
information from a device and updating/changing the API so called-line  
information is presented via ofono. I suppose they don't necessarily  
need to be done in that order.

I'll do more investigation and try and come back with something more  
constructive

Cheers

Chris

Re: Incoming line identity and ALS

[Denis Kenzior]

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Hi Chris,

> > CDIP (like CLIP) is issued after every RING/CRING.  Whereas CLIP returns
> > the calling line identity, CDIP returns the called line identity (e.g.
> > the phone number the remote caller dialed.)  According to the
> > specification it is not reported for outbound calls.
>
> It seems that my phone doesn't support CDIP, although it does support
> line-2/ALS which is a bit odd. I'll investigate more on that..

Many Phase 2+ devices only supported ALS and the rest of the CPHS standards.  
CPHS was largely merged into the 3G GSM standards.  If you're interested, 
google Common PCN Handset Specification.  This is where ALS comes from.

>
> One thing I'm not certain about is whether CDIP would report which
> line received the call, or which number the calller dialed as they
> could be different. I know other areas deal with routing information,
> but I wasn't sure which which number CDIP reported. It would be great
> for ALS support if it were the line that received the call, rather
> than the number dialed by the caller.. though that could be
> interesting in other situations.

This is entirely up to the network.  The likely scenario is that the network 
will normalize the number according to the network's rules.  While this sounds 
nice, it can still lead to some ambiguities.  E.g. in the US the following 
numbers (as presented in CLIP) are equivalent:
"15556677", 129
"15556677", 145
"5556677",129

> I'll do more investigation and try and come back with something more
> constructive

Sounds good.

Regards,
-Denis