SCADA & TETRA

2009

• TRANSMISSION MODE OVER AIR INTERFACE• LINK MODE• ALOHA• SCADA PROCEDURE• IMPLEMENTATION

3 Transmission modes are possible over air interface

• Circuit mode• SDS mode• IP packet mode

2009

MODES

Circuit mode

2009

How it Works

Resource allocation request

Time slot allocation‘transparent’ exchanges

Protocol dedicated for the application

Consequences

Fixed establishment timeNo allocation if network is overloaded7,2 Kb/s or 4,8 Kb/s protectedProtocol managed by application and, in most case, it’s a low efficient half-duplex one.

NOT SUITABLE FOR SHORT EXCHANGES and LOW EFFICIENCY

IP Packet mode

2009

How it works

Resource allocation request

Time slot allocation‘advanced link’ protocol

Mobile full busy on the allocated time slot

Transmission de packet IP

Consequences

Fixed establishment timeNo allocation in case when the network is overloadedVery efficient protocol(managed by infrastructure)Mobile can’t be use for audio communication (incoming or outgoing) during IP packet exchange (but to cancel the ongoing data transfer)Address mapping (IP address and ITSI address)

NOT SUITABLE FOR SHORT BUT VERY EFFICIENT FOR LONG DATA

Mode SDS

2009

How it Works

Direct transmission over common signalling channel(s) {MCCH &

SCCH}

Quantified amount of data

‘basic link’ Protocol + granting delay

Consequences

No resource allocationIn case when the network is overloaded, transmissions are not refused but they need more time.4 types with different size,up to 2 KbitEfficient protocol which nay be optimized according to terminal equipments

WELL SUITABLE FOR SHORT EXCHANGES

TRANSMISSION TIME

2009

DATA EXCHANGE SIZE

Transmissiontime

CIRCUIT MODE

IP PACKET MODE

SDS MODE Establishmenttime

2 Kbit

LINK MODE

Two possibilities for link modes

• radio/radio mode which uses two radio links serially connected

• direct mode which uses only one radio link

2009

LINK MODES

2009

Équipement PEI

TETRA network

Mobile TETRA

ÉquipementPEIMobile TETRA

IP

Different or identical radio sites

Équipement

TETRA network

ÉquipementPEIMobile TETRA

Only one radio site used

RADIO/RADIO MODE

DIRECT MODE

ALOHA

2009

Induced traffic and event traffic

BS air interface MS terminal equipment

Waiting oportunity

opportunityCollision possibility

opportunity

ack

Repeat if collision

Density of opportunities is automatically managed by infrasructure according to received traffic

Ack or response

EVENT

Data or request

EVENT TRAFFIC

Induced traffic

ALOHA

As for any radio system, only one mobile may transmit atthe same time on the same channel.

In order to avoid collisions, any radio site allocates time slots to mobiles for transmission – what formed the ‘protected’ uplink traffic. As example, if the infrastructure waits for an acknowledge or a response from a mobile, a time slot is allocated to this mobile for this transmission; in this way the response is protected against collisions with others mobile transmissions.Unfortunately, the uplink traffic is made from responses, acknowledges and also by exchanges initiated by mobiles. This last traffic can’t be protected, it is transmitted during not protected time intervals managed by the infrastructure.During these time slots (sometimes named ‘opportunities’), there could be some collision and a special mechanism allows the mobiles to repeat transmission during following opportunities with the lowest probability to collide again.

Transmission capacity of a channel used always ‘open’ (that is permanent opportunities is about one third of the capacity of the same channel used with protected mode (polling)

2009

ALOHA

2009

ALOHA PROCEDURE

BS air interface MS terminal equipment

Waiting for an opportunity

opportunityPossibility of collision

opportunity

ack

Repeat if collision

Density is automatically regulated by infrastructure according to measured traffic.

SCADA PROCEDURE

2009

POLLING PROCEDURE

Server BS air interface MS RTU

poll

Allocated time slot

poll

IP response

response

PEI

DIRECT MODE

SCADA PROCEDURE

2009

POLLING PROCEDURE

MS air interface BS BS air interface MS RTU

poll

Aloha Interval

poll

response

response

PEI

RADIO / RADIO MODE

opportunity

PEI

SCADA TRAFIC EVALUATION

2009

Traffic (Time Slot)

downlink uplink uplink ALOHA*

poll 0,5response 8

TOTAL 0,5 8

UNIT TRAFIC WITH RADIO / RADIO PROCEDURE

*load transmitted with ALOHA is weighted three time more than with protected mode

Trafic (Time Slot)

downlink uplink uplink ALOHA*

poll 0,5 1response 8 8

TOTAL 8,5 11

UNIT TRAFFIC WITH DIRECT PROCEDURE

SCADA CAPACITY

2009

MCCH or SCCH CHANNEL CAPACITY

DIRECT MODE CAPACITYWith this procedure, the uplink is the most limiting path.Typical capacity is 1.25 SCADA polling per second and per channel

RADIO / RADIO MODE CAPACITYGenerally, the scada server is in the same area than the RTU it manages (same radio site coverage) the uplink way is the limiting pathTypical capacity 0.91 SCADA polling per second and per channel.

MCCH and SCCH channels carry following traffic :• Broadcast traffic for system informations• mobiles registration traffic• roaming/hand-over traffic• audio communication signalling trafficUseful capacity (payload) is lower than the overall capacity. overall capacity : 17 TS / Second

payload : 10 TS / seconds (typical)

TRANSMISSION TIME

2009

DIRECT PROCEDURE

Le temps de transit global est détaillé dans le tableau

suivant.

TRANSMISSION TIME

2009

RADIO / RADIO MODE

Le temps de transit global est détaillé dans le tableau

suivant.Le temps de transit global est détaillé dans le tableau suivant.

SCADA sur TETRA

2009

IMPLEMENTATION

SCADA server

Standard PC

Mode bus

serial

IP

Ethernet

TETRA network mobile RTUPEI

serial

TETRA network mobile RTUPEI

serial

SCADA server mobile

I PEI

serial

I

IMODE RADIO/RADIO

MODE DIRECT

FALL BACK MODE (from RTU view)

TETRA network

mobile RTUPEI

sérial

Radio site1 (BS)

Radio site2 (BS)

- In most cases the mobiles (RTUs) are under coverage of several radio sites- In normal conditions, these mobiles communicate through the preferential site- If this site is out of service, a mobile may automatically revert to another radio site

2009

FALL BACK MODE (from SCADA seveur view)

TETRA network

mobileSCADA server

PEI

sérial

Radio site1 (BS)

Site radio2 (BS)- In this mode, the server changes its radio

site to that of the RTU

2009

TETRA network

SCADA server

Radio site1 (BS)

Radio site2 (BS)

Automatic switching

DIRECT MODE

RADIO/RADIO MODE

-In this mode, traffic is automatically routed to another radio site covering the RTU

IP

AUDIO CALL FROM SCADA RTU

TETRA network

mobile RTUPEI

sérial

Radio site2 (BS)

It is useful to have an audio communication between the dispatch operator and a technician on-site through the mobile connected to the RTU while data go on transmission between this RTU and the SCADA serverSuch function is automatically achieved in the following way:- the audio communication is established with signalling exchanges over the common signaling channel (MCCH or SCCH) also used for data exchanges (SDS)- infrastructure allocates another channel for the audio communication- the mobile connected to the RTU moves to the assigned channel; data communications and audio communication are provided smultaneously by the STCH (stealing channel) on frame 18.- THIS FUNCTION CAN’T BE ACHIEVED WITH PACKET DATA

2009

Dispatchoperator

LS Micro LS Micro

PHONIE et SCADA

Réseau TETRA

mobile AutomateSCADA

PEI

série

Site radio(BS)

2009

Micro HP

Poste opérateur

Micro HP

-La capacité d’acheminement des données simultanément avec une communication est limitée. Elle est suffisante pour écouler le trafic d’un seul RTU, pas pour le trafic de plusieurs RTU

-CONCLUSION: en mode radio/radio, le mobile attaché au serveur scada ne peut pas être utilisé pour les communications phonie.

MODE DIRECT ou RADIO/RADIO

MAINTENANCE in DIRECT MODE

TETRANetwork

mobile RTUPEI

serial

SCADAServer

Diagnostic from the site

2009

Verify Availability

Polling interface

Polling RTU

Status radio

Status radio

PC Diagnostics

SCADA sur TETRA

2009

QUESTIONS ???

THANK YOU FOR YOUR ATTENTION.