reuse CID=3 problem for 2G/3G?

[Norbert van Bolhuis]

Hi,

We're using a Cinterion ELS61-E R2 modem and ModemManager-1.14.0.
It looks like we're facing a PDN activation problem which maybe caused 
by ModemManager.

Our modem is happily connected, using 4G and PDP Context ID (CID) 1.
The CID refers to type=ipv4 and APN=blablabla.com.bla.bla.gprs.

The APN to use is actually blablabla.com but MM reports:

<debug> [1613584864.390514] [modem0/bearer0] found 3 PDP contexts
<debug> [1613584864.391031] [modem0/bearer0]   PDP context [cid=1] 
[type='ipv4'] [apn='blablabla.com.bla.bla.gprs']
<debug> [1613584864.391381] [modem0/bearer0]   PDP context [cid=2] 
[type='ipv4'] [apn='']
<debug> [1613584864.391730] [modem0/bearer0]   PDP context [cid=3] 
[type='ipv4'] [apn='blablabla.com']
<debug> [1613584864.409742] [modem0/bearer0] looking for best CID 
matching APN 'blablabla.com' and PDP type 'ipv4'...
<debug> [1613584864.410388] [modem0/bearer0] found exact context at CID 1

I guess APN blablabla.com.bla.bla.gprs and blablabla.com are equivalent.
So far so good.

Problems start to happen when the modem is 'moved' to 3G.

A "NW DETACH" is received and the modem reconnects/reregisters, using 3G.
Subsequently the PDP Context is activated, the following happens:

<debug> [1613521691.482972] [modem0/bearer0] found 3 PDP contexts
<debug> [1613521691.483181] [modem0/bearer0]   PDP context [cid=1] 
[type='ipv4v6'] [apn='']
<debug> [1613521691.483333] [modem0/bearer0]   PDP context [cid=2] 
[type='ipv4'] [apn='']
<debug> [1613521691.483478] [modem0/bearer0]   PDP context [cid=3] 
[type='ipv4'] [apn='blablabla.com']
<debug> [1613521691.484516] [modem0/bearer0] looking for best CID 
matching APN 'blablabla.com' and PDP type 'ipv4'...
<debug> [1613521691.484884] [modem0/bearer0] found exact context at CID 3
<debug> [1613521691.496086] [modem0/ttyACM1/at] --> 'AT^SWWAN=1,3,2<CR>'

This fails constantly, see:

<debug> [1613521693.000910] [modem0/ttyACM0/at] <-- '<CR><LF>+CGEV: ME 
PDN DEACT 3<CR><LF><CR><LF>+CGEV: ME PDN DEACT 3<CR><LF>'
<debug> [1613521693.063200] [modem0/ttyACM1/at] <-- '<CR><LF>ERROR<CR><LF>'
<debug> [1613521693.073351] [modem0/ttyACM1/at] operation failure: 100 
(Unknown error)
<debug> [1613521693.084974] [modem0] couldn't connect bearer: Unknown error

This goes on for like 40 minutes.

Afaik, for 2G/3G it is not allowed to use an APN for a CID other than 1
or maybe only by our/some operators.

Can you confirm?
Why is MM not (re)using CID 1 (for 2G/3G)?
Is this a MM problem or am I missing something?

NOTE: since we're using ModemManager-1.14.0 we do not
have the "cinterion: load initial EPS bearer cid only once"
fix (commit 35ecd45b66ff46e24ee99c199cbfc37702796cdd)

Thanks!

Regards,
Norbert van Bolhuis