December 1996
Published by:
The Office of Telecommunications
50 Ludgate Hill
London EC4M 7JJ
Tel: 0171 634 8700
Fax: 0171 634 8943
The provision of CLI display and other derived services requires that there is end to end availability and control of the CLI messages, and that these messages are generated in a consistent way. Unless this is achieved the CLI service can not be provided efficiently as the status of the message (eg the validity of the numbers displayed) can not be guaranteed by the provider selling the display service. Therefore, consistency is required between the network where the messages are generated (the originating network) and the network where the messages are displayed (the terminating network). Clearly where these are the same network there is less likelihood of any problem. But where interconnection between two or more networks occurs, some way of ensuring that all networks adhere to the same rules is required if customers of display and other services are to have confidence in such a service.
Against this background, the code was designed to achieve a number of objectives:
The code, has been the subject of a public consultation and has been drawn up by an industry group which included network operators, consumer representatives, the Data Protection Registrar and Oftel. Network operators have agreed to abide by the code and it forms part of their agreements for interconnection.
The code is not a technical standard in itself. Rather its purpose is to standardise a mutually agreed set of rules about how CLI is implemented in order to protect UK consumers by ensuring a necessary degree of consistency.
Oftel is acutely aware that changes in technology move so quickly that the code requires further work to clarify ongoing developments within the industry. The code already includes rules and processes to safeguard the implementation of simple Presentation CLI. However, we are conscious that further work is needed in respect of CLI wholly or partly provided by branch systems. This will be pursued soon.
1.1 The following constitutes a Code of Practice for operators of UK telecommunication networks interconnected with public telecommunication systems in the UK. This Code governs the responsibilities of such operators in relation to calling line identification (CLI) data in relation to the provision of a CLI display or related services. In particular it covers the responsibilities of networks in relation to the origination of CLI data; the transmission across networks of such data, and the delivery to a network terminating point of calling line identification data, including the information that governs the status of that data.
1.2 As UK telecommunication networks develop it may be necessary for the Rules in this Code to cover networks not currently included in Section 2 below. This will be achieved by the use of the mechanism to change the content of the Code, as set out in Section 3, in conjunction with, where necessary, other regulatory means.
1.3 For the avoidance of doubt the operation of this Code of Practice does not affect the ability of networks (both public and private) to use CLI data for network and/or account management purposes or, in cooperation with the relevant authorities, emergency calls and the tracing of malicious calls and similar activities.
2.1 Networks covered
2.1.1 This Code of Practice covers all public switched telephone networks in the UK.
2.2 Call types covered
2.2.1 All calls originating or terminating in the UK which are carried by one or more of the networks covered by this Code. (For the avoidance of doubt, transit calls that do not either originate or terminate in the UK are not covered.)
3.1 Status of the Code
3.1.1 This Code of Practice, and modifications to this Code, shall be published by the Director General of Telecommunications.
3.1.2 The Oftel library will keep up to date copies of the Code which will be available to the public either free or at a price that reflects the costs of copying the Code.
3.2 Modification Procedure
3.2.1 Modifications to this Code shall only be made by the Director General under the following circumstances:
1 with the unanimous agreement of all network operators to which the Code currently applies and all network operators to which the Code would apply if the modifications were made; or
2 to reflect a change in UK or EU legislation; or
3 to reflect a decision of the Data Protection Registrar or Data Protection Tribunal; or
4 to reflect one or more determinations, consents or directions of the Director General of Telecommunications which has the effect of applying to all Public Telecommunications Operators; or
5 after consultation with Public Telecommunications Operators and any other bodies or individuals that the Director General considers appropriate. All representations received by the Director General shall be reasonably considered.
4.1 This Code shall be incorporated in the interconnection agreements between public network operators. However, nothing in this Code absolves a network operator from operating according to the terms of its licence and/or any other legal instrument (including European regulations) which is applicable to that operator. In particular, where a licence condition conficts with this Code the licence condition shall take precedence.
5.1 In this Code there are some terms used that do not have precise meanings in everyday use. For the interpretation of this Code they have been given the following, more precise, meanings:
Calling Line Identification
subject to the exceptions listed below, either
(i) "Electric" CLI
the digits that comprise the national dialling sequence to establish a call in the reverse direction, whether or not such a call would succeed (eg the call would attempt to terminate on an outgoing calls only line). (Note: this dialling sequence does not necessarily have to create a call that would use the same path, but in the reverse direction.)
or
(ii) "Presentation" CLI
the digits (the "presentation number") that comprise a national dialling sequence and which meet the following conditions:
(a) dialling the presentation number must not establish a call for which the revenue is shared (other than by network operators) and;
(b) a line connection has to be able to be made as a result of dialling the presentation number (eg the call should not attempt to terminate on an outgoing calls only line) and
(c) the presentation number shall not be allocated to any party other than a Party or its affiliated companies who has been allocated, and remains allocated, the same national dialling sequence as an Electric CLI until such time as the Director General gives a network operator, or grouping of network operators, its agreement to this restriction being removed. For these purposes, an affiliated company shall mean in respect of the Party, any legal entity which directly or indirectly controls, is controlled by, or is under common control with, the Party, but only as such control exists, where the term "control" means the ownership, directly or indirectly, of more than 50% of the interest having the right to vote or manage the affairs of an entity.
In the case of presentation numbers it is further required:
(a) that the originating operator providing the presentation number service has the following responsibilities:
(aa) to have established and recorded the consent of the party to whom a connection would be made for their associated national dialling sequence to be used for that purpose;
(bb) to have established (with another operator, if applicable) that the same associated national dialling sequence has been and remains allocated to the presentation number applicant;
(cc) to have established the consent of the party to whom a connection would be made for their associated dialling sequence to be available for reverse searches made in the interests of good administration, and
(dd) to correctly datafill a presentation number,
and
(b) that an operator who has allocated a party a dialling sequence as Electric CLI shall, if requested by an originating operator for the purpose of facilitating a presentation number service, enter into an agreement with that operator to inform it if and when that allocation should cease.
Networks where customers making calls are contracted for those calls to a service provider shall have satisfied paragraphs (aa)(cc) where the network has notified the service provider under the relevant agreement no later than a period equal to one billing cycle in advance of the start of a Presentation CLI service on its network of the fact that the necessary consents referred to in (aa) and (cc) must be obtained and that the network must be notified should the associated national dialling sequence cease to be allocated to the presentation number applicant in accordance with paragraph (bb).
In the case of networks where customers making calls are contracted for those calls to a service provider any such arrangements under paragraph (b) last above shall be subject to receipt of notification from theservice provider that the associated dialling sequence has ceased to be allocated to the presentation number applicant.
Any meaningful digits (eg the country code) are permissible for all display CLI.
Exceptions
ISDN to ISDN: Conformity with international standards relating to CLI display and related services on ISDN where conveyance is restricted to ISDN to ISDN.
Classification of CLI data:
for display purposes CLI data can have one of three classifications:
a) Available: the CLI data is available for transmission to the network terminating point of the terminating network.
b) Unavailable: the CLI data is not for transmission to the network terminating point of the terminating network.
c) Withheld: the CLI data is not available for transmission to the network terminating point of the terminating network because the originating customer has taken specific action to indicate that the CLI should not be available at the NTP of the terminating network.
CLI display service and related services:
the delivery to the customer s NTP of data that allows that customer to gain access to the caller s CLI. This could be in the form of data that is displayed, recorded, interpreted by a data base or provided by means of an audio message, or by other means.
Indirect Access Network:
a network offering telecommunication services to the originator of a call, but where the Originating Network is not billing the originator of the call for that call.
Network Terminating Point:
has the same meaning as Annex A 2(I) of BT s Licence for fixed link terminating networks, and is the air interface for terminating mobile networks.
Originating Network:
the network to which the originating customer is first connected by means of an NTP or air interface. (Note: This means that the Code puts a responsibility on the Originating Network even if the customer is paying for the call via another network - eg indirect access - but the Code does not specify how the classification of CLI data is to be passed between networks. In this case it could be by means of the passing of the digit stream "141", or by some other means.)
Receiving Network:
the network in receipt of a call across any interconnect. The Receiving Network will also be a Transit Network or a Terminating Network.
Terminating Network:
the network to which the called customer is connected.
Transit Network:
any public switched telephone network involved in the conveyance of a call which is neither an Originating Network or Terminating Network.
A Responsibilities of the Originating Network:
It is the responsibility of the Originating Network to ensure that a call presented for hand over to another network is correctly classified at the network boundary. The following classification applies:
Rule 1 All calls emerging from networks which do not support the 141 per call blocking code or other acceptable means of blocking are set to "unavailable" classification.
Rule 2 All calls originating on any part of any network that does not support the 141 per call blocking code or other acceptable means of blocking are set to "unavailable".
Rule 3 All calls originating on parts of networks where customers have not been informed that CLI will be forwarded unless the blocking code or other acceptable means of blocking is operated are set to "unavailable" or, where blocking has been activated, to "withheld" or "unavailable".
Rule 4 All calls originating on parts of networks where the blocking code or other acceptable means of blocking are operational and customers have been informed shall be classified as:
a) "withheld" if blocking has been activated, or
b) "available" if blocking has not been activated.
Networks where customers making calls are contracted for those calls to a service provider shall have satisfied Rule 4 if the blocking code is operational and the network has informed the service providers no later than a period equal to two billing cycles in advance of the start of CLI display services, or the start of the sending of CLI for display or related services, (whichever is the earlier), on the network of the fact that CLI will be forwarded unless the blocking has been activated.
In the event that an Originating Network is unable to comply with Rules 1 to 4 above Rule 12 shall apply to the receiving network (see below).
Rule 5 Originating Networks shall offer one or more of the following options (at the customer s NTP):
a) dialling the prefix "141" inhibits the transmission of CLI data to the destination NTP.
b) dialling the prefix "141" results in a message (uncharged) which tells the customer what prefix to dial (or other action to take) in order to inhibit the transmission of CLI data to the destination NTP.
c) for those parts of networks where all calls are set to "unavailable", dialling "141" has no effect on the call (ie call progresses normally with the "unavailable" indicator) or causes the call to fail (eg number unobtainable tone).
d) dialling "141" causes the call to fail (eg number unobtainable tone). Note: network operators are reminded that b) is preferable to d).
B Responsibilities of Terminating Network
Except as allowed for in Rules 13 and 14, it is the responsibility of the Terminating Network to ensure that the classification of calls is respected in the delivery of thatcall to the final destination. In particular the following Rules will be applied:
Rule 6 A Terminating Network that supports a caller display and/or related services shall ensure that CLI data shall be available at the NTP for display purposes only for those calls classified as "available". In addition, any other service that allows the called party to call back or gain access to the calling line identification shall similarly be available only in relation to those calls with the "available" classification.
Rule 7 Where the Terminating Network supports a caller display service the indicator delivered to the destination customer must adhere to the following:
Indicator at interconnect Data at NTP (1) Withheld Withheld indicator, no CLI data Unavailable Unavailable indicator, no CLI data (2) Available CLI data
Notes:
1 This Code does not determine how the indicators should be displayed.
2 The indicator for "unavailable" might be an empty data set. The crucial factor is that it can be distinguished in some way from the "withheld" indicator.
Rule 8 Where the Terminating Network is not capable of supporting caller display services or related services no action is required on the basis of the call classification (but see Rules relating to transit networks).
Rule 9 Where a Terminating Network offers an anonymous call rejection service to its customers this service shall not operate in such a way as to have anticompetitive effects (eg by rejecting all calls classified as "unavailable"). This does not preclude the offering of anonymous call rejection services which reject calls classified as "unavailable" on a legitimate, differentiated services, basis (eg where the called customer is part of a closed user group).
C Responsibilities of Transit Networks
Except as allowed for by Rules 13 and 14, it is the responsibility of the Transit Network to ensure that the caller s CLI and the call classification does not alter from the point of entry to the point of exit. However, in exceptional circumstances, where the transit network is not capable of ensuring that the CLI and/or the classification remains constant a limited set of transformations is permitted.
Rule 10 Except as permitted by Rule 11 a Transit Network will not alter the classification or CLI of a call.
Rule 11 Where it is not technically possible to comply with Rule 10 the following transformations are allowable and/or mandatory as indicated. These transformations are hierarchical: where more than one transformation is possible, the transformation towards the top of the list shall take place:
a) A "withheld" classification will be maintained.
b) Subject to a), if the integrity of the CLI data can not be maintained the exit classification shall be "unavailable" (ie if the "withheld" indicator can be maintained, but the integrity of the actual CLI data can not, the exit classification shall still be "withheld", otherwise "unavailable").
c) Where the integrity of the classification can not be maintained, the exit classification for all calls shall be "unavailable".
D Responsibilities of Receiving Networks
The responsibility for maintaining the integrity of the CLI data and classification lies primarily with the network from which that data is being received. However, in the event that this network is unable to meet the Rules outlined above it is the responsibility of the Receiving Network to ensure that CLI data and classification defaults to a safe form.
Rule 12 In the event that the network from which CLI and/or classification data is being received can not, or does not, conform to the Rules set out above the receiving network shall operate Rule 11 at the point of entry.
E Responsibilities of networks providing customers with service by indirect access
Primary responsibility for ensuring that the caller s wishes in relation to the display of his or her CLI are observed lie with the Originating Network - see Rules 1 to 5 above. However, an indirectly connected network can also offer a blocking service if it wishes. As this method of blocking will be additional to dialling the prefix 141 the precise method of blocking is up to the indirect access operator. Networks offering such a service take on the responsibilities of Originating Networks if their customers activate this service.
Rule 13 Networks offering additional blocking services must ensure that calls where their customers have activated this service are correctly classified upon hand over to another operator.
The operation of Rule 13 opens up the possibility that different networks will have different instructions in relation to a single call. Where this is possible indirect access networks shall not override a "withheld" from the Originating Network.
Rule 14 Networks offering additional blocking services can only perform the following transformation of the classification: "Available" to "Withheld".
Code of Practice for Network Operators in Relation to CLI and Other Related Services