1. Introduction 2. Theory of Operation

1. Introduction 2. Theory of Operation
APN006 – SMS Gateway with Failover Detection
APN006 - 06 August, 2010
1. Introduction Ctek’s SMS Gateway application provides an out-of-band (SMS) communications path for intelligent
end-point controllers such as PLCs and custom industrial control solutions. The SMS Gateway
application works in tandem with the standard communications capabilities of the SkyRouter during
normal operation to determine the health of the bearer channel (network IP connection) and reacts to
bearer channel failures by routing controller messages over the SMS network to a far end server. As an
added benefit the SMS Gateway application makes controller information available to a conventional
wireless handset upon request. Figure 1 depicts the basic architecture of the application.
Figure 1
2. Theory of Operation Referring to Figure 1 we see that during normal operation the endpoint controller is messaging on the
wireless IP bearer channel shown in green. Simultaneously the controller is supplying a text message over
APN006 – SMS Gateway with Failover Detection
APN006 - 06 August, 2010
either a serial connection or over the TCP/IP connection. During normal operation (black) these messages
are available for SMS capable terminals such as handsets but are not passed on to the far end application
server.
When the SMS Gateway application detects a failure on the networks bearer channel it (optionally)
asserts a relay contact signal back to the controller and begins to pass the text message back to another
SkyRouter configured as an SMS receiver (red path). The receiver then repackages the incoming text
messages as TCP/IP messages and sends them to the configured server address and port. Text messages
originating from the controller continue to be available for SMS capable handsets. An SMS receiver can
serve many endpoints, the number being dependent on the amount of traffic being sent.
The text message sent from the controller can contain up to 120 valid ASCII characters and can be define
during setup to be bracketed by a Start and End character which do not count against the 120 character
limit. Start and End characters must be unique meaning that they cannot be used in the message payload.
3. SMS Gateway Application ‐ End Point Configuration Figure 2 below shows the configuration screen for the SMS Gateway End Point application. This
configuration must be consistent across a network of end points that will operate with one specific SMS
Receiver.
Figure 2
APN006 – SMS Gateway with Failover Detection
APN006 - 06 August, 2010
End Point Application Setup (screen fields and settings) Enable SMS Failover - Turn the failover detection logic on or off
MSISDN of SMS Destination - The 10-digit phone number of the SMS receiver. For shorter dialing plans
this number should be padded with zeros.
Primary and Secondary Failover Test - Up to two failover tests that can be performed to assess the health
of the network's bearer channel. Options are to ping (ICMP message) an IP address, to resolve a domain
name, or to disable the detection.
Test Rate - The repetition rate at which the failover test will be performed.
Retry Rate - The time interval before a failover test will be preformed again.
Retry Count - The number of time that a failover test will be performed before failover is determined to
be necessary.
Receive SMS Traffic From - Selects the physical connection to the end point controller for SMS
messages.
TCP Port Number - The TCP port that will be listened to if SMS traffic is coming in on Ethernet
Start Message Character - The numeric value of the character defined as the Start character. Value is in
decimal. This character must not be used in the message payload. Must be an ASCII character but need
not be a printable character. STX would be a candidate but any character can be used. If Null (00) no Start
character is defined.
End Message Character - The numeric value of the character defined as the End character. Value is in
decimal. This character must not be used in the message payload. Must be an ASCII character but need
not be a printable character. ETX would be a candidate but any character can be used. If Null (00) no End
character is defined.
APN006 – SMS Gateway with Failover Detection
APN006 - 06 August, 2010
4. SMS Gateway Application ‐ SMS Receiver Configuration Figure 3 below shows the configuration screen for the SMS Gateway - SMS Receiver application. This
configuration may be repeated in additional SMS Receivers to add capacity as required.
SMS Receiver Application Setup (screen fields and settings) Forward SMS Traffic To - Selects the physical connection to the far end application server or
communications device
Destination IP Address - The IP address of the far end application server or communications device if
LAN TCP connection is selected
Destination Port Number - The IP port of the far end application server or communications device if LAN
TCP connection is selected
Start Of Message Character - Must be the same as the corresponding character selected at the end point.
End of Message Character - Must be the same as the corresponding character selected at the end point.
Important Note - When settings are made or changed on any SkyRouter configuration screen the
screens update button must be pushed and then a Restart (top menu) must be performed.
APN006 – SMS Gateway with Failover Detection
APN006 - 06 August, 2010
5. Relay Output Management Screen Log in to the SkyRouter using Ethernet at 192.168.1.10, UID = ctek, password = ctek and select the Relay
Output screen. The screen is shown in figure 5 below.
Figure 3
APN006 – SMS Gateway with Failover Detection
APN006 - 06 August, 2010
Set Relay Output State - Used to turn the relay on or off. Select desired setting and then click on the
update button at bottom of screen.
Relay Initial Value - Sets the initial condition of the relay on power up. Setting choices are On, Off, or
Last where last will cause the relay to be restored to the state it was in when the unit powered down.
Relay Shut Off Timer - Provides a watch dog timer to turn relay off after a prescribed length of time.
Select Never to disable timer.
Allow SMS Control of Relay - Enable or disable the ability to change the state of the relay using SMS
(text messaging) commands.
Allow Web Browser Control of Relay - Enable or disable the ability to change the state of the relay using
the Relay Output web screen.
Web Browser Display Polarity - Using the web link text field below the user can create a relay control
link that appears on the initial login screen. This is called advertising the resource or simply advertising.
As an example figure 6 shows an advertising screen where the text entered into the Relay Output screen
was Power Control Relay. The IP Camera advertising link comes from a text field on the Routing screen
and the Admin Facilities link takes you to the standard SkyRouter administration menu.
For text advertised from the Relay Control screen the button on the advertised link displays either OFF or
ON depending on the state of the relay. However a closed relay is sometimes an ON and sometimes an
OFF. The polarity setting allows the user to address this issue when setting up the relay link.
Figure 4
APN006 – SMS Gateway with Failover Detection
APN006 - 06 August, 2010
Text For Web Link To Relay - Used to enter the text to be used for a relay advertising link. If blank relay
advertising will not occur.
Note - Changes to fields and selections other than Set Relay Output State require that the change be
followed by an update and then by a restart of the unit. Set Relay Output State is unique in that it only
requires an Update to toggle the relay.
6. SMS (text messaging) Commands SMS commands provide an economical method of communicating with the SkyRouter for simple status
and management activities. SMS has the added advantage of not requiring the bearer channel (IP data) to
be working. Therefore it can be thought of as an out of band management tool. Complete documentation
on all SkyRouter SMS commands can be found in TechNote TN0009 available on
www.ctekproducts.com. SMS commands sent to SkyRouters on GSM networks
(GPRS/EDGE/UMTS/HSPA) must be preceded by three equals signs as in ===STATUS. On CDMA
networks the equal signs are optional. The first letter of a SMS command must be upper case, all others
can be upper or lower case.
Action
Get SkyRouter Status
Reboot SkyRouter
Have SkyRouter update DDNS
Turn Relay On
Turn Relay Off
Get last text message sent to SMS Gateway
application by end point controller
SMS Command Text
===STATUS
===Boot
===WAKE
===R1
===R0
===GET
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