A Scheduler for a Television Transmission System

Prepared by Elena Volynskaya (ElenaV@iconsolutions.com)

Overview

The television broadcasting companies or "networks" own and lease equipment for composing, transmitting and receiving shows and non-show material. Such equipment includes studios and tape devices for composing shows and playing them back; transmitters, antennae and transponders for distributing the programs; receivers for receiving at the affiliate stations and monitoring the transmissions at the Master Earth stations where the programs are composed and where they are distributed from. Sometimes, because of the weather conditions the programs cannot be distributed over the satellites and then the network leases or uses its own phone or fiber lines that can be used to transmit the signal terrestrially.

The network has to use this equipment efficiently, as well as make sure that there are no conflicts between different programs in using it and therefore there are no outages on the air, which is not only embarrassing, but may also cost a lot of money. Therefore, there is a need to schedule and manage the use of various network and non-network composition and distribution facilities as well as affiliate station facilities, required to play back and distribute program feeds to the destination affiliate stations.

Fundamentally, scheduling refers to the decision making process of assigning resources to activities over time. In this design we will be concerned with resource allocation, i.e. identifying and allocating the resource(s) required to handle an activity and manage the on-going availability of the resource(s) over time.

We would like you to design an object-oriented scheduling module that provides a basic scheduling algorithm that can be extended to support the specific resource allocation requirements outlined in this document. These requirements are simplified for the purposes of this design problem.

Facilities

There are two major groups of facilities in a network inventory: the ones needed for the composition of shows and the ones needed for show distribution.

• All facilities can be divided into types based on the function they perform. For instance, some of those types are studios, channels, transmitters and transponders. Some of the facility types can be classified further, but for the purposes of this design we will not go beyond simple classification.
• Facilities can be public, i.e. available to be used by anybody, and private, available to be used only by some user group(s).
• A sequence of facilities that create a video transmission is called a path. Depending on what a transmission is used for, it has to consist of a certain combination of facilities.
• Normally each facility can be used in only one transmission at a time, i.e. it cannot be shared. However, some types of composition and distribution facilities can be shared between the transmissions. Some of such types are studios, the same live show can be transmitted to different audiences; antennae, multiple video signals can be beamed to transponders by an antenna, provided all of those transponders are on the same satellite.
• Most of facilities can be used on any two transmissions that are scheduled back to back, i.e. first transmission from 8am to 8:15am and the next from 8:15am to 8:30am. However, some facility types cannot be used on two transmissions scheduled back to back, because they need a tune-up time before they can be switched. For example, if a transmitter is used with one transponder from 8am to 8:15am, it cannot be used with a different transponder starting from 8:15, but it can be used with the same transponder. The same goes for antenna and satellite: an antenna needs time to be turned and tuned to a different satellite. This time needed for an antenna or transmitter to be adjusted is called guardband and is specific for a facility type.

Ordering Facilities

In order to create a transmission that will be executed in production, a facility order has to be composed which will provide information on how and in what combination those facilities will be used, at what time, etc. However, to design a facility order module would constitute its own problem, so for our purposes you can consider a facility order to be a separate module that will have an interface to the Scheduler application.

The important types of facility orders you will need to know about are (1) reservation orders and (2) air date orders. Reservation orders are created to tentatively schedule a group of transmissions to happen at a certain time on certain days of the week for a range of dates, for example, schedule a transmission to happen from April 1 to June 15 from 9am till 9:30am on Mondays. Air date orders are either created from reservation orders or independently for a certain date.

Scheduling Facilities

A scheduled usage of a facility is also called a "booking".

• A facility is available all the time, 24 hours a day 7 days a week, unless there is a reason for it to be taken out of service. Such periods of non-availability are called constraints.
• Both constraints and bookings can be made One-Time-Only or Recurring, which means booking for contiguous time-intervals that occur on one or more days of the week for a specified date range.
• In order to schedule a facility to be used in a transmission the following data has to be provided: the start and the end date of the booking, the start and the end time of the booking, the type (One-Time-Only or Recurring) of the booking and, in case of a Recurring booking, the days of the week when the booking is valid.

Constraints

Constraints can be existing scheduled activities, or they can denote general unavailability of a facility such as when a facility is scheduled for maintenance or a particular user group has no rights to use it. However, the right to use a facility can be granted to the group of users for a period of time. Recurring constraint means that a facility will be unavailable for the specified period of time on the specified days of the week for a range of dates.

Bookings

A recurring booking means that a facility has been reserved to be used in a transmission for the specified period of time, although it does not mean that it will actually be used in production. These bookings are requested by reservation orders and are converted into production bookings at the time an air date order is created.

OTO booking means that a facility is going to be used in production for the specified time period. It can also be referred to as a "production booking".

Conflicts

A conflict will occur if a booking or a constraint for a facility is requested that overlaps in time with an existing booking or constraint. A conflict also occurs if two bookings are scheduled so that no ample time is available for the guardband adjustments.

However, if a booking for an air date order is requested that overlaps with a recurring booking created for the corresponding reservation order, this situation is not considered a conflict and has to be resolved by translating existing reservation into a production booking.

Scheduler Application

The Scheduler application should implement resource allocation for the transmission scheduling. It should have an interface to the Facilities Inventory and the Facility Order modules. The major requirements to the application are:

• The application has to provide conflict free facility bookings. As mentioned earlier, certain classes of composition and distribution facilities can be used in multiple transmissions simultaneously, which normally would be considered a conflict. Assuming there are business rules that would resolve a conflict of this type, you are requested to include this consideration in your design.
• When a booking is rejected because of the conflict(s) the system’s response should include full description of the conflict(s).
• The interface to the Scheduler should assume that bookings may be requested either for an individual facility or for the whole transmission. In case of a request for the whole transmission the Scheduler should book as many facilities used in the transmission as it can.
• The Scheduler should also be able to determine whether a requested transmission is complete. You can assume that there is a number of business rules known to the Scheduler that will enable it to make that decision.
• The design should take into account concurrency issues, such as simultaneous requests for a facility bookings by more than one user.

Use Cases

Case 1: Constraint request for aFacility

Case 2: Constraint request for aFacility

Case 3: Reservation booking request for aFacility

Case 4: Reservation booking request for aFacility

Case 5: Production booking request for aTransmitter

Case 6: Production booking request for aFacility from an air date aOrder created from a booked reservation order rOrder

Case 7: Production booking request for aTransmission

Case 8: Production booking request for aTransmission

Case 9: Production booking request for a composition facility of class Studio aCmpFac

Case 10: Production booking request for a composition facility of class Studio aCmpFac

Case 11: Production booking request for aFacility by a user from aUserGroup1

Case 12: Production booking request for aFacility by a user from aUserGroup1

Glossary