Dispatch systems in the energy and railway sectors
IP-telephony has long been used in corporate telephone systems and PSTN. But technological dispatch telephone systems in departments such as the management of rail transportation and power transmission networks still use classic TDM telephony, or analog equipment. A feature of these dispatch systems is that the work of the managing dispatcher and the controlled on-duty controlled facility (electrical substation or railway station) are strictly regulated by industry standards and rules. Often these rules come from the technical limitations of the original analogue dispatch systems.
Dispatch systems in the energy and railway sectors require additional special functions that are not able to implement standard telecommunication protocols (such as, for example, analog frequency alarms such as R1.5, R2, DTMF, which send control frequencies / tones to the tonal frequency channel in voice transmission band), therefore, ADACE departmental telephone systems for energy and OTC for railway transport were developed.
In the ADASE network, there are 2 types of subscribers: a remote subscriber (this can be a telephone, or a PBX), and a dispatcher. ADASE equipment used analogue tone frequency channels (TCH), which were transmitted using high-frequency communication equipment via overhead power lines (HF over VL) from the control center to the controlled substation where the duty officer is located.
Such a telephone communication system provides for the establishment of subscriber - subscriber connections, the dispatcher - subscriber. Due to the limited resource of the trunk connection between the substation and the dispatch center (one or more analogue PM channels) and the need to ensure the priority of the channel occupation by the dispatcher, an in-channel frequency alarm ADASE was developed.
Typical ADASE construction scheme:
In addition to the standard functions of occupying, releasing the channel, dialing, sending busy / free signals, the ADACE alarm provides the dispatcher priority when occupying the PM channel. That is, the dispatcher has the right to break the conversation of a lower priority (for example, subscriber - subscriber), which occupied the PM channel, followed by automatic occupation (dispatcher - subscriber), or intervene in the conversation (thus creating a three-way conference), followed by manual a gap (by sending the corresponding control frequencies to the channel).
In operational-technological communication on the railway, there are 2 types of stations: managerial, which is installed in the dispatch center, and to which dispatch telephones are connected, and executive, to which telephone sets, for example, a station duty officer, are connected.
Such a system allows you to create the so-called "group channel" or distributed conference, to which the dispatcher and attendants are connected. The attendant console is equipped with a pedal. In the normal position, the dispatcher can listen to the conference, but when you press the pedal, all the attendants will turn off the microphones, and then only the dispatcher speaks to the conference. The duty devices are equipped with a tangent (such as push-to-talk). Attendants speak to the conference only when the tangent is pressed.
The OTC alarm system (two or several consecutive sounds in the channel out of 7 possible in the tonal range) allows the dispatcher to make group calls (only a group of executive station subscribers), circular (all executive station subscribers), or individual. Using the control frequencies of the reverse and direct control, the logic of the controller’s pedals and the duty switch are organized. In addition, the analog alarm allows you to display on the remote control of the dispatcher the subscribers connected to the conference and those who are being dialed.
OTC includes various types of communication: distillation, road distribution, etc. They use various analog trunks (2 or 4 wires), but the logic of operation remains the same.
Manufacturers of digital PBXs have implemented support for these analog alarms. In addition, digital devices with the ISDN BRI interface began to be supported as dispatcher devices (which, for example, made it possible to increase the length of the connecting line to 1000m).
In the case of ADACE, the standard E1 with ISDN signaling is used as trunk connections between stations, therefore, ensuring the priority of the dispatcher’s occupation is not so important here - it can always (with incomplete trunk loading) take an additional time slot. The ADACE alarm system itself is supported in areas of the last mile where there is no possibility of organizing E1, as well as on subscriber PBX interfaces to support analogue dispatcher consoles.
Typical application of digital PBX with ADASE
In the case of OTC, the analog alarm provided complex functions (monitoring the status of subscribers connecting to the conference, the priority of the dispatcher's voice in the conference), which led to the completion of ISDN Q.931 signaling for their implementation. Such ISDN-like signaling is described in the industry standard digital OTC 35 145-2000. Digital exchanges retained support for analog signaling on subscriber interfaces to provide the ability to connect analog remotes. In this case, the PBX acts as a signaling converter between the analog intra-channel and digital.
Typical Digital PBX Application Scheme for OTC
As in the electric power industry, and in the dispatch control of railway transport, the main reasons for replacing digital exchanges established 20 years ago are:
1) obsolete PBXs, lack of technical support and spare parts
2) Limited functionality of ISDN controllers' devices: insufficient number of speed dial buttons, lack of head and DECT headset
3) the need to integrate video surveillance and
4) Reserved observability and controllability of the equipment
5) Limited scalability for growing number podkon objects' roll.
From the point of view of modern IP-telephony systems, ADACE lines or group channels are conferences with an expanded set of functions: intervention and forced disconnection of subscribers, presence, invitation of subscribers to the conference by sending a call.
Problems encountered when using IP-telephony for dispatch systems:
1) Presence (monitoring the status of connecting subscribers to the conference)
In the case of ADACE on the dispatcher’s end device, it is necessary to display the state of the end device of the on-duty controlled object (whether it is a telephone connected via an analog line or VoIP endpoint) - whether the call is on (ringback using color light), whether the subscriber is currently talking or the subscriber is free to making a call. Also, in the case of working with analog lines, the dispatcher needs to see the line occupancy and the identifier of the neighboring dispatcher (or low-priority subscriber) who occupied it.
In the case of OTC on the terminal device of the dispatcher, it is necessary to display graphically the subscribers already connected to the conference. In addition, the dispatcher can participate in several conferences and see which of the subordinates is connected to each of the conferences.
2) Intervention
The intervention procedure (Barge-in) applies only to ADACE. Regardless of the type of terminal device of the slave, the dispatcher must determine who the person on call is talking to and, if necessary, break the existing connection (low-priority subscriber - on-duty) and automatically connect to this on-call (create a dispatcher-on-call connection).
3) Distributed conference in UTS
In current OTC systems, disconnection between the dispatch center and station A does not make it impossible to make a call between stations A and B. Using the only VoIP conference server in the dispatch center makes such connections impossible (if the connection is disconnected). Therefore, in OTC VoIP systems, it is recommended to use distributed conference with the installation of conference servers at most stations. However, this architecture increases the complexity of managing conferences, and also greatly increases the delay in voice transmission.
4) Joint with analog lines
A large number of already installed analog lines and ADASE and OTS subscribers do not allow to switch to VoIP completely. Therefore, the conference server must support in-channel analog frequency alarms. Modern CPUs allow you to process such alarms at the software level without the use of expensive DSPs. Therefore, a joint with analog lines can be organized as follows: the line is connected to the E1 multiplexer to the corresponding interfaces that are physically matched with the line. The analog signal from the line is digitized and at the output of the multiplexer represents one of the 64kbps time slots of the E1 stream (E1 signaling is not important in this case, since the signal is transmitted in the analog band in the analog line).
5) The priority of the dispatcher’s voice in the conference
In analogue dispatcher communication systems (in particular, OTC), the dispatcher’s conversation with the subscriber took place in simplex mode, and the dispatcher could interrupt the subscriber with his voice: when the dispatcher speaks, the equipment mutes the subscriber’s speech. In modern systems, all conversations occur in duplex mode, but sometimes the internal regulations of the dispatchers require the priority of the dispatcher's voice.
6) Application of PTT tangent and pedals
In OTC systems, telephone sets (digital ISDN or analog) with a push-to-talk button (tangent) on the handset are used as terminal subscriber devices. In some cases, a push-to-talk foot pedal is also used. Modern VoIP phones are rarely equipped with such tangents and pedals. An example of such an apparatus is a telephone: Cisco 79xx with a Plantronics WS-2620 handset.
7) End devices dispatchers.
Modern concepts for the development of dispatch systems involve the use of monoblocks with touch screens, which run a soft phone with the necessary set of functions, as dispatcher devices. The main requirements for such devices: reliability (for example, no fans), low power consumption (maybe even PoE power), a set of peripherals (DECT / Bluetooth headsets, PTT, remote microphones).
VoIP is currently being approved for use in both the energy and railway sectors. The main task in the implementation of such systems is to make them as similar as possible in terms of the logic of work from users to already used ones, and also to ensure a junction with those already installed.
About me: I work as a leading engineer in a company engaged in the development of such systems for energy and railway companies in Eastern Europe and Russia
Departmental analogue dispatch systems
Dispatch systems in the energy and railway sectors require additional special functions that are not able to implement standard telecommunication protocols (such as, for example, analog frequency alarms such as R1.5, R2, DTMF, which send control frequencies / tones to the tonal frequency channel in voice transmission band), therefore, ADACE departmental telephone systems for energy and OTC for railway transport were developed.
Equipment for Long-Range Automatic Communication of Power Systems - ADASE 1200/1600
In the ADASE network, there are 2 types of subscribers: a remote subscriber (this can be a telephone, or a PBX), and a dispatcher. ADASE equipment used analogue tone frequency channels (TCH), which were transmitted using high-frequency communication equipment via overhead power lines (HF over VL) from the control center to the controlled substation where the duty officer is located.
Such a telephone communication system provides for the establishment of subscriber - subscriber connections, the dispatcher - subscriber. Due to the limited resource of the trunk connection between the substation and the dispatch center (one or more analogue PM channels) and the need to ensure the priority of the channel occupation by the dispatcher, an in-channel frequency alarm ADASE was developed.
Typical ADASE construction scheme:
In addition to the standard functions of occupying, releasing the channel, dialing, sending busy / free signals, the ADACE alarm provides the dispatcher priority when occupying the PM channel. That is, the dispatcher has the right to break the conversation of a lower priority (for example, subscriber - subscriber), which occupied the PM channel, followed by automatic occupation (dispatcher - subscriber), or intervene in the conversation (thus creating a three-way conference), followed by manual a gap (by sending the corresponding control frequencies to the channel).
Operational and Technological Communication - OTC.
In operational-technological communication on the railway, there are 2 types of stations: managerial, which is installed in the dispatch center, and to which dispatch telephones are connected, and executive, to which telephone sets, for example, a station duty officer, are connected.
Such a system allows you to create the so-called "group channel" or distributed conference, to which the dispatcher and attendants are connected. The attendant console is equipped with a pedal. In the normal position, the dispatcher can listen to the conference, but when you press the pedal, all the attendants will turn off the microphones, and then only the dispatcher speaks to the conference. The duty devices are equipped with a tangent (such as push-to-talk). Attendants speak to the conference only when the tangent is pressed.
The OTC alarm system (two or several consecutive sounds in the channel out of 7 possible in the tonal range) allows the dispatcher to make group calls (only a group of executive station subscribers), circular (all executive station subscribers), or individual. Using the control frequencies of the reverse and direct control, the logic of the controller’s pedals and the duty switch are organized. In addition, the analog alarm allows you to display on the remote control of the dispatcher the subscribers connected to the conference and those who are being dialed.
OTC includes various types of communication: distillation, road distribution, etc. They use various analog trunks (2 or 4 wires), but the logic of operation remains the same.
Transition to digital systems (90s)
Manufacturers of digital PBXs have implemented support for these analog alarms. In addition, digital devices with the ISDN BRI interface began to be supported as dispatcher devices (which, for example, made it possible to increase the length of the connecting line to 1000m).
In the case of ADACE, the standard E1 with ISDN signaling is used as trunk connections between stations, therefore, ensuring the priority of the dispatcher’s occupation is not so important here - it can always (with incomplete trunk loading) take an additional time slot. The ADACE alarm system itself is supported in areas of the last mile where there is no possibility of organizing E1, as well as on subscriber PBX interfaces to support analogue dispatcher consoles.
Typical application of digital PBX with ADASE
In the case of OTC, the analog alarm provided complex functions (monitoring the status of subscribers connecting to the conference, the priority of the dispatcher's voice in the conference), which led to the completion of ISDN Q.931 signaling for their implementation. Such ISDN-like signaling is described in the industry standard digital OTC 35 145-2000. Digital exchanges retained support for analog signaling on subscriber interfaces to provide the ability to connect analog remotes. In this case, the PBX acts as a signaling converter between the analog intra-channel and digital.
Typical Digital PBX Application Scheme for OTC
Switch to VoIP
As in the electric power industry, and in the dispatch control of railway transport, the main reasons for replacing digital exchanges established 20 years ago are:
1) obsolete PBXs, lack of technical support and spare parts
2) Limited functionality of ISDN controllers' devices: insufficient number of speed dial buttons, lack of head and DECT headset
3) the need to integrate video surveillance and
4) Reserved observability and controllability of the equipment
5) Limited scalability for growing number podkon objects' roll.
VoIP in industry control systems
From the point of view of modern IP-telephony systems, ADACE lines or group channels are conferences with an expanded set of functions: intervention and forced disconnection of subscribers, presence, invitation of subscribers to the conference by sending a call.
Problems encountered when using IP-telephony for dispatch systems:
1) Presence (monitoring the status of connecting subscribers to the conference)
In the case of ADACE on the dispatcher’s end device, it is necessary to display the state of the end device of the on-duty controlled object (whether it is a telephone connected via an analog line or VoIP endpoint) - whether the call is on (ringback using color light), whether the subscriber is currently talking or the subscriber is free to making a call. Also, in the case of working with analog lines, the dispatcher needs to see the line occupancy and the identifier of the neighboring dispatcher (or low-priority subscriber) who occupied it.
In the case of OTC on the terminal device of the dispatcher, it is necessary to display graphically the subscribers already connected to the conference. In addition, the dispatcher can participate in several conferences and see which of the subordinates is connected to each of the conferences.
2) Intervention
The intervention procedure (Barge-in) applies only to ADACE. Regardless of the type of terminal device of the slave, the dispatcher must determine who the person on call is talking to and, if necessary, break the existing connection (low-priority subscriber - on-duty) and automatically connect to this on-call (create a dispatcher-on-call connection).
3) Distributed conference in UTS
In current OTC systems, disconnection between the dispatch center and station A does not make it impossible to make a call between stations A and B. Using the only VoIP conference server in the dispatch center makes such connections impossible (if the connection is disconnected). Therefore, in OTC VoIP systems, it is recommended to use distributed conference with the installation of conference servers at most stations. However, this architecture increases the complexity of managing conferences, and also greatly increases the delay in voice transmission.
4) Joint with analog lines
A large number of already installed analog lines and ADASE and OTS subscribers do not allow to switch to VoIP completely. Therefore, the conference server must support in-channel analog frequency alarms. Modern CPUs allow you to process such alarms at the software level without the use of expensive DSPs. Therefore, a joint with analog lines can be organized as follows: the line is connected to the E1 multiplexer to the corresponding interfaces that are physically matched with the line. The analog signal from the line is digitized and at the output of the multiplexer represents one of the 64kbps time slots of the E1 stream (E1 signaling is not important in this case, since the signal is transmitted in the analog band in the analog line).
5) The priority of the dispatcher’s voice in the conference
In analogue dispatcher communication systems (in particular, OTC), the dispatcher’s conversation with the subscriber took place in simplex mode, and the dispatcher could interrupt the subscriber with his voice: when the dispatcher speaks, the equipment mutes the subscriber’s speech. In modern systems, all conversations occur in duplex mode, but sometimes the internal regulations of the dispatchers require the priority of the dispatcher's voice.
6) Application of PTT tangent and pedals
In OTC systems, telephone sets (digital ISDN or analog) with a push-to-talk button (tangent) on the handset are used as terminal subscriber devices. In some cases, a push-to-talk foot pedal is also used. Modern VoIP phones are rarely equipped with such tangents and pedals. An example of such an apparatus is a telephone: Cisco 79xx with a Plantronics WS-2620 handset.
7) End devices dispatchers.
Modern concepts for the development of dispatch systems involve the use of monoblocks with touch screens, which run a soft phone with the necessary set of functions, as dispatcher devices. The main requirements for such devices: reliability (for example, no fans), low power consumption (maybe even PoE power), a set of peripherals (DECT / Bluetooth headsets, PTT, remote microphones).
VoIP is currently being approved for use in both the energy and railway sectors. The main task in the implementation of such systems is to make them as similar as possible in terms of the logic of work from users to already used ones, and also to ensure a junction with those already installed.
About me: I work as a leading engineer in a company engaged in the development of such systems for energy and railway companies in Eastern Europe and Russia