This standard defines the information content, structure and possible printed representations of the UPU ID-tag. This is an identifier for individual mail items which: is globally unique; can be applied to any item which is not already ID-tagged by any postal administration (or other issuer) which previously processed the item; NOTE 1 The UPU ID-tag provides a standard means of ID-tagging which can be applied on a world-wide basis, allowing inter-administration mail items to be encoded without risk of disruption of the automated system of the delivery post. It may be applied to any size of item. can be read, with a high degree of reliability, by any postal handling organisation possessing appropriate equipment. NOTE 2 ID-tags are encoded on items using a bar code symbology. As with any other form of bar code, poor quality printing, ink smudging, damage to the item, etc., can result in read errors. The UPU ID-tag encoding specifications incorporate an error protection mechanism to allow detection and correction of a large proportion of such errors. The UPU ID-tag defined in this standard may be placed on items so that, in subsequent processing, individual items can be recognised and associated with computer-based information relating to the item concerned. NOTE 3 Items need not be ID-tagged if this is not required for processing purposes, though it is anticipated that the use made of ID-tagging will increase. Examples of ID-tag applications are given in Clause 7. Whilst being generally applicable to domestic mail, the standard has been designed to allow the encoding of cross-border mail and to support its application in the automated processing of such mail. NOTE 4 UPU regulations prevent the encoding of information on the bottom 15 mm strip on the front of international letter mail. This standard has been designed to avoid the possibility of incompatibilities between ID-tag implementations and explicitly allows and encourages the application of UPU ID-tags, in area R1, on the reverse side of items. This will enable exchange of data about the items and use of these data for automated processing. For example, the origin post might send an encoded or video image electronic copy of item delivery address blocks to the delivery post, enabling the latter to more efficiently process received items. Similarly, the delivery post might return time-of-processing data to the origin post, enabling it to monitor delivery service quality more closely. A key purpose of the standard is to allow information about items to be exchanged between postal handling organisations. Such exchange will take place through the electronic communication of messages (e. g. EDI messages), or through the exchange of computer files. NOTE 5 The detailed requirements, content and usage procedures for these messages or files are/will be defined in other standards, which use the UPU ID-tag as the means of associating information with the item concerned. A standard for the Electronic communication of mailpiece images and related item attributes is in course of development. Further information on the status of this can be obtained from the secretariat of the UPU Standards Board. NOTE 6 The information content of UPU ID-tags may include specification of the time at and facility or domain in which the UPU ID-tag was applied. A receiving facility can therefore calculate the elapsed delay to which the item has been subjected, and can relate this to expected delays between the two facilities. This allows easy measurement of transit times, even in the absence of electronic data transmission. Knowledge of delays on an item-by-item and statistical level will improve the diagnosis of problems and is expected to lead to an improvement in delivery service quality. 4) References to "this standard" should be interpreted as references to S18 as a whole, not only to part A. 5) Where reference is made to a form of ID-tagging which is not in accordance with this specification, the term domestic ID-tag is used consistently throughout the text. ID-tag on its own therefore refers to the forms of ID-tagging specified in this standard. The term standard ID-tag or UPU ID-tag is used in the text where it is desired to emphasise the fact that reference is being made to the ID-tag specified in this standard, and not to a domestic ID-tag. Effective 1 April 2003, the standard shall be applied in all cases in which ID-tags are placed in area R1 on the reverse side of letter mail items of size up to and including C5. NOTE 7 ID-tags encoded in area R1 are required to be compliant with S18 (see UPU standard S19 and article RE 204 of the Letter Post Manual [2]). Where ID-tags are used, and are applied in area R1 on the reverse side of letter mail items of size up to and including C5, the application of the standard is mandatory. As a result, with effect from 1 April 2003, only BNB-78 and BNB-62 ID-tags, as defined in parts 2 and 3 of this standard, may be encoded in area R1 (see UPU standard S19 and article RE 204 of the Letter Post Manual [2]). NOTE 8 The above does not limit application of the standard to items of size greater than C5. Nether does it prevent its application in cases in which the ID-tag is printed in an area other than R1. However, whilst the application of the standard in such cases is recommended, it is not mandatory. Other forms of identification may be used in locations other than R1. Issuers using automated sorting systems are, however, strongly encouraged to identify items using this standard even when the items carry some means of identification which has been applied by another agency, outside of issuer control. NOTE 9 Application of the standard is presently not mandatory for ID-tagging systems which use other locations, including on the front-side of letter mail items, or which apply to other types of item, such as flats. However, future extensions of the standard might cover these cases. NOTE 10 It is admissible to allow customer-allocated item identifiers in the delivery address block and/or to place identifiers in digital postage marks. Such identifiers need not (and probably should not) follow this standard, but might be covered by separate standards. NOTE 11 ID-tags have a potential value even where other forms of item identification are used. For example, the IDtagging of items which carry an indicium-based identification can be used to improve security by aiding in the detection of duplicate indicia. The use of the UPU ID-tag should also provide an improved probability of correct processing of the item, especially in the case of cross-border mail.