Codes & Guidance Notes

ITC Rules of Operation for the use of ITU-R (CCIR)Teletext System B

Introduction

This technical note covers the operation and interaction of ITU-R (CCIR) Teletext system B services in the Vertical Blanking Interval^[1] (VBI) of a single television channel. It applies to services transmitted on Channel 3, Channel 4/S4C and Channel 5.

On Channel 3 and Channel 4/S4C, three categories of service are required to co-exist and on Channel 5 there are two categories, each of which may use the same teletext technical specification.

These rules of operation are intended to ensure that there are no technical conflicts between these services. In the case of the allocation of magazines to different licensees for the provision of page-based services, these Rules provide a mechanism for avoiding such conflicts. However these magazine allocations can be varied by the ITC in cases where all the licensees which are directly affected agree.

Technical Background

Each television line during the VBI can convey a single teletext data packet. The addressing structure allows identification of the packets according to the identity `Packet X/Y' where X can vary from 1 to 8 and Y varies from 0 - 31.

For mosaic graphics and text displayed on a public teletext receiver, X corresponds to the magazine number indicated by the first digit of the page number, and Y indicates the row number. Row numbers 0 to 24 are capable of direct display as part of the page, and rows 25 to 28 are page related rows carrying additional information. Row 29 is magazine related but is not associated with a specific page.

All packets with Y = 30 or 31 lie outside the page based transmissions and constitute independent data packets.

The page based teletext services will be provided in `parallel' mode, by control of the appropriate bit in row 0 of the page headers. This permits separate sourcing of pages of one magazine from those of another, and allows separate magazines to be allotted to different lines or sets of lines within the VBI.

The rules ordering the transmission of rows and pages within the magazine must be observed.

Within this document, further references to `magazine X' refer to all addressable pages in the range X00-XFF where X ranges from 1 to 8.

The Public Teletext Licensee using Capacity on Channel 3 and Channel 4/S4C

Page Based Services

The licensee may use magazines 1, 2, 3, 4 and 5 on Channel 3 and magazines 1, 2, 4, 5 and 6 on Channel 4/S4C. Within any page, packets with Y = 0 to 29 are available to the public teletext licensee. The main introductory page will be on page 100.

Channel 3, Channel 4/S4C and Channel 5

Page Based Services

Page-based ancillary services or provided by Channel 3 may use magazine 6, those provided by Channel 4 or S4C may use magazine 3 and those provided by Channel 5 may use magazine 5.

Any subtitling services will be provided on magazine 8 using page mode teletext.

Additionally, the television broadcast service provider may use magazine 8 for other page-based ancillary services provided that this does not interfere with or constrain the provision of subtitles.

Within any of these magazines, packets with Y = 0 to 29 will be available.

Data-Packet Based Services

Packet 8/30 (The Broadcast Service Data Packet) currently has two formats defined by the designation code following the packet address.

The Channel 3 licensee, Channel 4/S4C or Channel 5 must make provision for the transmission of Format 1 packets. Format 2 packets provide the Programme Delivery Control labels in accordance with EBU Document SPB459 and are available for use by Channel 3, Channel 4/S4C or Channel 5.

The "initial page for storage" field must be set to page 100 to reference the main introductory page provided by the public teletext licensee on Channels 3 and 4/S4C, and by the additional service licensee on Channel 5.

Commercial Additional Service Licensees on Channel 3 and Channel 4/S4C and the Additional Service Licensee on Channel 5

Page Based Services

The Commercial Additional Service licensees on Channel 3 and Channel 4/S4C may use magazine 7 to provide services to subscription (including pay per view) or closed user groups. The Additional Services Licensee on Channel 5 may use magazines 1, 2, 3, 4, 6 and 7 for any combination of services provided free-to-air or to subscription or closed user groups. The main introductory page will be on page 100.

Data-Packet Based Services

There is a re-definition of the packet X/Y identity in terms of data channels:

Sixteen channels are available, of these data channel 0 in Packet 8/30 is reserved for the Broadcast Service Data Packet.  In accordance with the current specification, Commercial Additional Services on Channels 3 and 4/S4C, and Additional Services on Channel 5 will be limited to data channels 8, 9, 10, 11 in Packet X/31.

VBI Line Allocations

The current allocation of VBI line numbers, within the UK PAL-I specification, to different service providers on Channel 3 and Channel 4/S4C is given in Table 1, and that for Channel 5 is given in Table 2.

Table 1: VBI Line Allocations for Channel 3 and Channel 4/S4C

Table 2: VBI Line Allocations for Channel 5

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