SIMbae Call Control
Design Description for Implementation of GSMA
Network Access Control
Version 1.3
For more information:
info@abledevice.com
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Copyright © 2015 Able Device, Inc. All rights reserved.
Table of Contents
1.
Purpose ........................................................................................................................................................................... 3
2.
SIMbae Overview ............................................................................................................................................................ 3
3.
Network Friendly Operation ........................................................................................................................................... 4
4.
Logic Description of Call Control ..................................................................................................................................... 5
5.
Summary ......................................................................................................................................................................... 6
6.
Contact Information ....................................................................................................................................................... 7
List of References
1. IoT Device Connection Efficiency Guidelines, Version 1.0, 13th October 2014; GSM Association Doc-CLP-.03 –
M2M Device Guidelines
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1. Purpose
The purpose of this document is to detail the design of the network access control logic located within the Able Device
SIMbae operating system. The GSMA IoT Device Connection Efficiency Guidelines (Reference 1) was used as a basis for
the call control strategy. The guidelines explain the need for network access control and offer advice for achieving the
control. The following shows the implementation of a network control strategy integrated within the SIMbae system.
2. SIMbae Overview
SIMbae is a SIM operating code which provides the communications link between the SIM resident customer application
code and the cellular module. This link provides a natural location for the network control strategy since the SIMbae
system communicates with the module and can easily supervise the commands for call control of the module.
The basic structure of SIMbae is shown in Figure 1. SIMbae communicates the commands from the customer
application code to the cellular module. The ‘Call Control’ functional block (orange) is expanded to show the
implementation of the call control code.
Modem
Program
SIM
Program
Module Command Interpreter
SIM Bus
Customer
Application
SIMbae
Service Poll
SIM poll
Clock set
Request for poll
timing interval
SIMbae
Initialization
State Control for
Customer App
Change
required?
N
Program I/O Lines
Request for
Program of I/O
Lines
I/O Control
(input/Output
Set)
Application Logic- act on
input states rec''vd from
previous poll
-determine if I/O change or
read required
Set Inputs for Sensors
Set Output for Control
Change
required?
N
I/O Line Write
SMS – Data Msg Request
I/O Line Read Request
Call Success Report
Call Control
- Access Control Strategy
Device Application Requirement - DAR_XX
-DAR7
Network Friendly Mode – NFM_XX
-NFM back off timers
-NFM schedule
-On/off and reset to factory default
Set Outputs,
SMS, Data call
Request SMS
Request Data Call
Access Status report (IP:xxx.sss.ss)
Received I/O line
state, SMS, Data
I/O Input
Receive
Set I/O Status
Register
I/O Status Change
Indication
Error Control
End Execution
Figure 1.0: SIMbae Structure – Call Control Functional Block Contains the Network Friendly Control Process
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Since the SIMbae Call Control resides in the SIM, access to the function is also available from an external host processor
as indicated in Figure 1.1. For external processor control, the SIMbae system is accessed as in the SIMbae customer
application resident example (above), however the Customer application is only a minimal control function which
accesses the Call Control function when the external processor request authorization to place a call. SIMbae handles the
interface to and from the module as normal to communicate to the external processor.
SIMbae System with Only Network
Access Control Function
Customer application logic is contained in
external host processor
SIM
Program
Modem
Program
External
Control
Processor
Processor
Bus
Module Command Interpreter
SIM Bus
Supervisory Call Logic
(minimum system
implementation)
SIMbae
Service Poll
SIM poll
Call Authorization REQUEST
SIMbae
Initialization
Clock set
Request for poll
timing interval
State Control for
Customer App
Change
required?
N
I/O Control
(input/Output
Set)
X
Call Control
- Access Control Strategy
Call Request Authorization
Call Success Report
Call Request Authorization
Device Application Requirement - DAR_XX
-DAR_message timers
-DAR delay timer
-DAR message encryption keys
-DAR on/off control, escalation critera, reset
Call Success Report
Request SMS
Request Data Call
Network Friendly Mode – NFM_XX
-NFM back off timers
-NFM schedule
-On/off and reset to factory default
Access Status report (IP:xxx.sss.ss)
Received I/O line
state, SMS, Data
I/O Input
Receive
Set I/O Status
Register
Status Change
Indication
Error Control
End Execution
Figure 1.1: SIMbae Structure – Call Control Functional Block accessed by external processor application.
3. Network Friendly Operation
The Network Friendly Operation involves controlling the call attempts to a predetermined schedule in order to reduce
the nuisance retries due to failed calls and software errors. The control strategy shown in Table 1 is referenced to the
GSMA guidelines using the NFM notation to refer to ‘Network Friendly Mode” and DAR to refer to “Device Application
Requirement” as detailed in the GSMA requirements document. The control strategy shown in Table 1 is one example
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implementation where selection of the different functions is indicated by the “Enable” entry in the control logic. The
control table is securely held within the SIM and can only be accessed by a secure SIM program download which is
originated by the network. This allows for all remote devices using the SIMbae operating system to receive the pretested control strategy. Additionally, the network can tailor the control strategy as needed by sending the remote device
a SIM program download event using a secure OTA process with a modified “Enable” entry.
An example call control schedule is shown in Table 1.
GSMA req.
Enable
NFM_1
NFM_2
NFM_3
NFM_4
NFM_5
NFM_5.1
NFM_5.2
NFM_5.3
NFM_5.4
NFM_5.5
DAR_7
DAR_7.1
DAR_7.2
1
1
1
1
0
0
0
0
0
0
1
2
0
DAR_13
1
Control Description
On/Off
Report Control State to Requesting Application
Back-Off Timer Enable
Back-Off Timer Value - 60 seconds (default)
Back-Off Timer Value - 120 seconds
Back-Off Timer Value - 240 seconds
Back-Off Timer Value - 480 seconds
Back-Off Timer Value - 960 seconds
Back-Off Timer Value - 1920 seconds
Back-Off Timer Value - 3840 seconds
Keep Alive Data Connect
Keep Alive Timer 29 minutes (default)
Keep Alive Timer -xxx minutes (selectable)
Status Reporting to Network - xxx call events
IP: xxx.xx.xxx.xx
Table 1: Network Call Control Strategy
Logic is added to the SIMbae Call Control Code to implement the table functions; thereby the network control cannot be
modified by the customer application. Therefore, this operating structure offers immunity from the customer
application code being changed by fraudulent internet hacks and flawed customer application code.
4. Logic Description of Call Control
Simple logic is included in the SIMbae Call Control section to implement the call control strategy. Figure 2 shows
example logic to execute the provisions of the Network Control Strategy in the schedule example shown in Table 1. The
logic diagram shows that the call request is received from the customer application, and the call is allowed to proceed if
the Network Call Control is disabled or if the backoff timer has expired and the call is executed as expected. The status
of the call control as recommended by the GSMA guidelines is reported to the requesting application so the application
can track the status of the call success (see GSMA NFM_6 requirement in Referece 1).
For the DAR_7 requirement, the same logic is processed as the NFM back off timer, the DAR_7 requirement is able to
select a different time (backoff timer) corresponding to the 29 minutes for the keep alive message to be sent.
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For the DAR_13 requirement, the feature can be enabled/disabled by the network; this requires the cellular device to
make a data call containing a report to be sent to the network for the purpose of collecting call success/failure statistics.
The network's server IP address used to collect the statistics is stored in the SIMbae call control routine. The DAR_13
report’s enable/disable and IP address can be changed by an OTA program download changing the report times as
needed. The call report contains the number of success/failure events, call times, length of calls, and other data the
network needs to evaluate the device's utilization of the network. The statistics contained in the report can be used by
the network to modify the NFM functions of the Call Control Strategy as needed.
From Call Request
NFM enabled?
N
Y
From SIM poll
Replace call pending
with present call
request
N
Backoff Timer
Enabled?
Y
Backoff / DAR_7 Timer
Expired?
Y
Success/Fail
Process Call
Send Data Call to
Network Servier IP: xxx.xx.xxx.xx
Report Pending Status,
Time remaining, call
success/fail
(NFM_6)
To Call Requester
Network Management report time?
(DAR_13)
Y
N
END
Figure 2: SIMbae Call Control Logic
5. Summary
The design described here shows the simplicity of the control logic in SIMbae necessary for implementing a Network
Control Strategy as outlined in the GSMA document. The control strategy contained herein is a subset of the many
control functions offered by the GSMA document. The control functions shown in this document were selected for
minimum control and can be expanded as needed. The SIM resident code and function table can be updated by secure
OTA downloads in order to field update any changes and modifications. Also note that by having a common logic
program for all remote devices and the code being resident on the SIM instead of merged within the developer’s code,
the logic only needs to be pretested and verified once thus off-loading the developer of the customer application code
from re-certifying the developer’s network control code at each development cycle or code change.
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Having the network control code contained in the SIM makes the code secure and tamperproof. The SIM resident code
also allows for immunity from erroneous operation as a result of instability or software errors in the customer’s
application code.
6. Contact Information
For additional information:
Email: info@abledevice.com
www.abledevice.com
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