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Interfaces  The RTU supports the following interfaces:
 Hypertext Transfer Protocol: HTTP
Simple Network Management Protocol: SNMP
Simple Mail Transfer Protocol: SMTP
Extensible Markup Language: XML
Point to Point Protocol: PPP
Short Message Service: SMS
Network Time Protocol: NTP
Pass Thru for Serial Devices
Hypertext Transfer Protocol: HTTP
The HTTP interface includes support for a built-in web server. This web server is used to serve documents that utilize the Hypertext Markup Language (HTML) and Extended Markup Language (XML) documents.
There are two main HTML documents. One of these is the Operations web page. This page shows the status of the RTU and each of its ports, and also allows operator commands to be entered.
The other main HTML document is the Logs web page. This page allows each of the audit, events, and timed logs to be retrieved and viewed, allowing operational staff to quickly and easily examine history surrounding an event.
Simple Network Management Protocol: SNMP
The RTU supports an SNMP agent that is compatible with Version 2c. Up to five IP addresses can be configured for SNMP managers. This means the RTU can send traps to as many as five different IP addresses, each of which would be running its own SNMP manager. The software running on each of these servers does not need to be the same application or even from the same vendor. Each trap is sent to each of the configured IP addresses.
The SNMP interface uses ports 161 and 162 by default, but the ports are configurable. The community strings are also configurable.
SNMP traps are sent as UDP datagrams. UDP does not guarantee delivery. The RTU implements a configurable mechanism that minimizes loss of traps. This mechanism is not part of the SNMP specification but is a simple extension to improve data reliability. If the mechanism is not enabled, then the SNMP interface behaves in the normal manner according to specification.
Each trap sent by the RTU has a number associated with it. If the acknowledgement mechanism is enabled, the RTU will re-send traps whose number has not been acknowledged (up to a configurable maximum number of re-sends). The acknowledgement specifies the number of the trap being acknowledged. The acknowledgement can be sent as an SNMP command or as a separate command over the HTTP interface.
Simple Mail Transfer Protocol: SMTP
SNMP is one way in which alarm (and other) notifications are sent out by the RTU. SMTP is another method. If the SMTP interface is enabled, notifications are sent as email messages. Each email message contains the same information as an SNMP trap, and the same acknowledgement mechanism is available to ensure the notifications have been received.
One or two email addresses can be configured as destinations for the email message notifications. Each notification message is sent to each of the configured email destinations.
It is possible to develop a software daemon to listen for email notifications from RTUs. Once each notification has been received, the daemon can open the message and take appropriate action. A large variety of actions can be taken, including: activating pagers; forwarding emails to relevant technicians; sending SNMP trap messages; feeding information into existing alarm systems; forwarding notifications using SMS messaging; etc.
Extensible Markup Language: XML
XML is widely used by the RTU and its utility application software.
All configuration settings for the RTU are available through two XML documents served by the RTU over its HTTP interface. One of these documents gives the rules script, while the other document gives all the other configuration settings.
A separate XML document gives the RTU status, including the status and values of each of the ports, at any point in time.
Each log file is served as an XML document. Also, each command entered over the HTTP interface receives a short XML document as a response.
View the online demonstration RTU to retrieve a live sample of these XML files.
Point to Point Protocol: PPP
All dialup connections are handled by PPP. PPP allows IP protocols to be used over a serial connection. This means that once the dialup connection has been established, communication with the RTU proceeds in exactly the same way it would have done if the RTU was connected using an Ethernet connection. RTUs that are connected via dialup work in exactly the same way as RTUs that are connected over an Ethernet network, only a little slower. RTUs are currently being successfully used over GSM (9,600 baud) and CDMA (14,400 baud) dialup connections.
The RTU can establish connection with a PPP server in 3 ways. The first two are defined by the PPP protocol and are known as PAP and PAP Callback.
The third method is an extension of PAP, although the protocol itself is not altered in any way. We call it PAP Dialback. PAP Dialback has two purposes:
maximum security as the RTU never actually dials into the host network
concentration of call costs into the Operations Center rather than billing for each RTU separately
For PAP Dialback to work, a utility program needs to be run on a server. This program monitors a modem. When an RTU has a notification to deliver, it dials this number. The utility program uses Caller ID to recognize the calling RTU and immediately hangs up. This method is very secure because the call is never answered, and consequently there is also no cost associated with it (this is true of mobile networks in Australia, please check with your service provider for local billing policies). Once the calling RTU has been identified from its Caller ID, the utility program arranges for the host server to call the RTU back. This means all call costs are incurred at the Operations Center rather than across a number of phone services. If the RTU is not called within a few minutes, it will start the cycle again.
Note that PAP Dialback is a feature of the RTU. The standard PAP and PAP Callback mechanisms are also available. All methods come standard in the RTU. Selecting which method to use is a matter of setting the configuration setting appropriately.
Short Message Service: SMS
If the RTU is connected to a GSM or CDMA modem, it can send SMS messages when it encounters a notifiable event. SMS messages can be sent to one or two destinations (numbers). A summary of the RTU’s status is sent, as far as practicable, within the 160 character limit for SMS messages with each message.
It is possible to develop a software daemon to listen for SMS messages from RTUs. Once each notification has been received, the daemon can open the message and take appropriate action. A large variety of actions can be taken, including: activating pagers; forwarding emails to relevant technicians; sending SNMP trap messages; feeding information into existing alarm systems; etc.
Please note that SMS services are provided by mobile phone service providers. The SMS service, whilst generally effective, does not guarantee delivery times or even delivery of messages. However SMS can provide a useful mechanism in addition to, or as a backup for, Ethernet or dialup connection. Please check with your service provider before deciding whether to use the SMS messaging facility.
SMS messages are sent whenever a notifiable event takes place. In order to prevent being flooded with SMS messages if fleeting alarms are experienced, it is possible to set a minimum time period to wait between sending of SMS messages. This time period is set to a default of 15 minutes but can be reconfigured as needed.
Network Time Protocol: NTP
The RTU can make use of an NTP time server to synchronize its real time clock. Where an RTU is connected via an Ethernet network, the RTU will synchronize its clock once a day. The time at which this synchronization will take place is configurable.
If the RTU is connected via dialup, and NTP is configured, the RTU will synchronize its clock whenever a dialup connection is established.
Pass Thru for Serial Devices
Devices that use serial communication can be connected to the Multi Function (serial) port of an RTU. The communications link to the RTU can then be used to communicate with the serial devices. This means that only one communications link needs to be established, to the RTU, and that link can then be used to also communicate with serial devices on the site.
Whether the RTU is connected via Ethernet or dialup (PPP), a socket (the port number is configurable) is established with the RTU. Any data received by the RTU over this socket is transmitted out of the serial port; similarly, any data received over the serial port is transmitted out over the socket.
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