scope:

This European Telecommunication Standard (ETS) defines the stage 1 of the Connectionless Broadband Data Service (CBDS) which can be provided by Metropolitan Area Networks (MANs) (see ETS 300 211 [6]) and an Asynchronous Transfer Mode (ATM) based network. Whilst this bearer service category is aiming primarily at Local Area Network (LAN) interconnections (see ISO/IEC DIS 8802-1 [16]), other uses are also envisaged.

This 4 part ETS defines a CBDS which is independent of the layers above. The bearer service category could be provided by any network but it is particularly suited for MANs and an ATM based network. Each Protocol Data Unit (PDU) is transferred transparently and separately without the establishment of an endto- end connection, with no guarantee of delivery and no acknowledgement of delivery. However, the underlying network provides a highly reliable service which is reflected by the defined Quality of Service (QOS) parameters.

If certain applications require a better QOS, higher layer protocols, e.g. connection-oriented transport protocols, will perform additional functions. Since the network provides a transparent transfer of data, at least in principle, any higher layer protocol may be employed.

This 4 part ETS contains a stage 1 description of the CBDS, according to CCITT Recommendation I.130, which contains a general description and a list of communication attributes. However, this document goes beyond a stage 1 description where additional information seems to be required for an early implementation of the CBDS.

This part, Part 1, contains an overview of the CBDS. The description of the basic bearer service category is given in Part 2 of this ETS, ETS 300 217-2 [12]. Part 3, ETS 300 217-3 [13] defines the supplementary services. Part 4, ETS 300 217-4 [14] describes the address screening supplementary service.