[mobile-broadband-provider-info: 1/3] Expand DTD to include information for Visual Voicemail

[Thomas Haller <thaller src gnome org>]

commit de5d67ff47cf2e6734b09425d092bdde2a77dd54
Author: Chris T <chris talbothome com>
Date:   Mon Jun 21 11:56:58 2021 -0400

    Expand DTD to include information for Visual Voicemail
    
    This commit expands the DTD include settings for visual voicemail (VVM) activation. The two document 
references are:
    
    [1] https://www.gsma.com/newsroom/wp-content/uploads/2012/07/OMTP_VVM_Specification_1_3.pdf
    This is the primary VVM specification
    
    [2] https://source.android.com/devices/tech/config/voicemail
    This includes some information that is not obvious from the VVM Specification.
    
    VVM's control signals are over Short Message Service (SMS), and there are (at least) three required 
settings:
    - The VVM Specification ("otmp" is the primary one [1], but [2] notes that there is a second one, "cvvm", 
and T-Mobile USA is at least one carrier that uses "cvvm"
    - The destination visual voicemail number that communicates with the client, and
    - The Carrier Prefix, which is the prefix to every VVM control SMS.
    
    With these settings, a VVM client can activate and set up visual voicemail, as all other required 
settings will be received from the carrier (and thus are not needed in mobile-broadband-provider-info). One 
such client in development that will use these settings is vvmd:
    https://gitlab.com/kop316/vvmd/
    
    To my knowledge, all carriers that have VVM adhere to the VVM OMTP/CVVM standard (as these are the only 
standards that Android has), and will use settings.

 serviceproviders.2.dtd | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)
---
diff --git a/serviceproviders.2.dtd b/serviceproviders.2.dtd
index 37573a6..347378a 100644
--- a/serviceproviders.2.dtd
+++ b/serviceproviders.2.dtd
@@ -11,7 +11,7 @@
 <!-- that piggy-back on the primary provider. -->
 <!ATTLIST provider primary (true|false) #IMPLIED>
 
-<!ELEMENT gsm (network-id*, msisdn-query*, voicemail*, balance-check*, balance-top-up*, apn*)>
+<!ELEMENT gsm (network-id*, msisdn-query*, voicemail*, visual-voicemail*, balance-check*, balance-top-up*, 
apn*)>
 <!ELEMENT apn (plan*,
                usage?,
                name*,
@@ -32,6 +32,23 @@
 <!-- for historical/legacy reasons network providers may support various alternative -->
 <!-- dial strings that can be used to access voicemail services -->
 
+<!ELEMENT visual-voicemail (standard*,
+                            destination-number*,
+                            carrier-prefix)>
+
+<!ELEMENT standard EMPTY>
+<!ATTLIST standard type (cvvm|otmp) #REQUIRED>
+<!-- Whether the carrier supports OTMP or CVVM for Visual Voicemail -->
+
+<!ELEMENT destination-number (#PCDATA)>
+<!-- This is the destination number to activate/deactivate Visual
+     voicemail over SMS.
+-->
+
+<!ELEMENT carrier-prefix (#PCDATA)>
+<!-- At the beginning of an SMS "Status" or "Sync" message, this will appear.
+-->
+
 <!ELEMENT balance-check (ussd*,
                          dtmf*,
                          sms*,