Department of Computer Science

To: Systems Design and Development

A company, INMATE Ltd, is preparing to tender a bid to design and build a system which restricts the freedom of prisoners convicted of minor offences through the use of electronic tagging. Basically, a qualifying prisoner may elect to be electronically tagged and released into the community instead of serving time inside a secure institution. Serving out a prison sentence in the community is very much regarded as a privilege offered only to minor offenders and more serious offenders approaching the end of a long sentence. As such, the privilege may withdrawn at any time and the prisoner sent immediately to a secure institution. INMATE has received a sufficiently detailed requirements specification to prepare the costs for the tender bid. As a member of one of INMATE’s development teams, you have been asked to set out a design for the system which will be later used as the basis for feasibility and costing studies. The government of the country inviting the tender bids has indicated that it intends to adopt a policy of supplying limited information over and above the initial specification given below. There are a number of reasons for this attitude - the most important being that it wants to be seen acting totally impartially to all parties bidding for the contract. However, the government reserves the right to incorporate ideas from unsuccessful bidding documents into the final specification for the successful bidder.

The initial requirement specification for the prisoner electronic tagging (PET) system is as follows. There are two categories of prisoner that may be invited to take part in the PET project. The first are known as Category X prisoners who are those who have committed minor offences (those carrying sentences which are less than one year). The second, known as Category Y prisoner are those approaching the end (in the final year) of longer sentences for more serious offences. If a Category Y prisoner fails to comply with any type 1 or type 2 rule (outlined below) he or she is immediately withdrawn from the PET project. On the other hand, it is recognised that Category X prisoners will be less used to the rigours of prison culture and discipline and therefore allowed up to two breaches of type 1 rules. Each time a Category X prisoner breaks a type 1 rule, a parole officer is dispatched to interview the prisoner and a field report is logged with the prisoner’s record at a control centre. If a Category X prisoner has already broken two type 1 rules, he or she automatically becomes a Category Y prisoner If a Category X prisoner breaks a type 2 rule, he or she is withdrawn from the PET project.

Having elected to join a PET project, the qualifying prisoner is asked to select a tagging device. There are currently two tagging mechanisms. One is a wrist band and the other is an ankle strap. Once a device has been selected, it is fitted and initialised by a supervisor. Initialisation involves associating the tagging device with a base station (the device and the base station both have unique serial numbers). The base station is then attached to an ISDN line (a permanently connected phone line between a home address and the control centre). In most cases, a prisoner has only one base station. However, under exceptional circumstances (perhaps a very sick relative) a prisoner may be granted permission to use more than one (but no more than three) different base stations. In these cases, a prisoner requesting permission for a base station change is first escorted to the new site by a parole officer. The parole officer then 'docks' the prisoners PET device to the new base station and alerts the control centre. (Docking involves connecting the PET device to the base station via a cable, and then disconnecting it). An operator at the control centre then reconfigures the prisoner's records.

Operation of the PET system is as follows: During non-curfew hours, a prisoner may move around within the community as long as he or she never strays further than a pre-defined distance from the base station which is known as the restriction zone. The base station enforces the restriction zone by regularly polling the PET device (using the prison service’s GPS system) Using the GPS system, a base station can accurately measure the distance between itself and the PET device to within approximately 10 metres. If the prisoner moves less than 50 metres outside the restriction zone, a type 1 rule is broken. More than 50 metres breaks a type 2 rule. The diameter of the restriction zone is determined by the parole officer - but is typically about 2 kilometres.

Inside curfew hours, a prisoner must be within 10 meters of the base station at all times. If a prisoner moves outside the 10 meter perimeter during curfew hours, this automatically breaks a type 2 rule. Between the curfew hours, the

the base station uses an internal sensing device to locate the position of the PET device and it can do this very accurately. The base station will automatically switch from GPS positioning to internal sensing when a PET device is docked. If internal sensing is in operation, the base station will only revert to GPS positioning if the PET device is docked and it is after the end of curfew time.

At the beginning and end of curfew time (normally 7pm to 9am but again defined by a parole officer) the prisoner must physically attach the PET device to the base station (there is a port on both devices). At the beginning and end of curfew time, the base station assesses the state of the PET device’s battery (as a percentage value) and logs this data with the prisoners record. The controller is alerted if the battery has less than a 50% charge. If a prisoner misses the curfew time docking by less than 5 minutes, a type 1 rule is broken. More than 5 minutes breaks a type 2 rule

The base station is solely responsible for day-by-day monitoring of the PET device. All events are logged with the prisoner’s record at the systems control centre. There are currently seven types of event which may be generated. The first indicates if a PET device is outside the restriction zone but within 50 meters of the perimeter. The second indicates if the PET device is more than 50 meters outside the restriction zone. The third and fourth events are generated if a PET device has missed a curfew time within 5 minutes, or later than 5 minutes. The fifth event is generated if the PET device is more than 10 meters from the base station during a curfew. The last two events are generated if a PET device is damaged or if the battery is low.

 The following table summarises the events and describes the actions which occur in response to each event

Where the action is Suspend from PET project a parole officer is immediately dispatched to the scene of the event generation and the local police are informed.

A controller is permanently employed to observe and act on the events at the control centre. On receipt of an event, a controller has the choice of dispatching a parole officer immediately, instigating a routine parole officer visit or simply logging the event with the prisoner records.

If an event indicates that a parole officer should be dispatched immediately and the assigned parole officer is unavailable, then the system automatically selects an on-duty parole officer closest to the region where the alarm is raised.