25 June 2003
Discussions concerning telecommunications industry regulation and the privacy protection of telephone callers (including dial-up Internet users) may be made unduly difficult and confusing in the absence of a common understanding of the term "Calling Line Identification" ("CLI") and knowledge of how CLI based services work.
This document describes what CLI is and how CLI based services work, including how telephone call carriers in Australia intentionally and unnecessarily disclose blocked calling party numbers to Internet Access/Service Providers.
Calling Line Identification ("CLI") is a telephone network signalling capacity that generates data, at the time a telephone call is established, that identifies the calling party telephone number/s (i.e. the billing telephone number and in some instances also other numbers, such as an extension number in an office).
CLI based services are a set of products, developed using that telephone network signalling capacity, that package the calling party number information (and sometimes also other information) in different ways in order to sell, or freely provide, it to consumers of telecommunications services. Calling Number Display ("CND") is a CLI based service.
CLI is transmitted within the telephone network, but CLI based services are taken past the network into the customer access network or 'local loop', using software installed in the telephone exchanges .
In the Calling Number Display Industry Code (C522) , developed by Australian Communication Industry Forum ("ACIF Code") , a broad and internationally unusual  description of "CLI - Calling Line Identification" is used. The description includes both personal information (e.g. calling party number) and also other information that is not, of itself, necessarily personal information (e.g. the date and time of a call). It states:
As CLI is generated at the time a call is established, obviously it cannot include the call's duration, which is not known at call establishment. Further, the term "Calling Line Identification" clearly refers to the calling line, CLI does not include the called party's number.
The phrasing in the ACIF Code is, apparently, an inaccurately summarised version of information that originated in the 1992 AUSTEL Telecommunications Privacy Report which stated:
"Calling Line Identification is data that is generated at the time a call is established. In general, when a telephone call is made through parts of the network with the technical capacity information is passed within the network about -
- the called party's phone number
- the calling party's phone number
- the time of day
- the duration of the call
- the routing of the call" 
CLI is the information containing the calling party's phone number. CLI, and the other information, is passed through the telephone network.
While there is merit, in terms of protecting privacy, in placing restrictions on the use and disclosure of a range of information passed through the telephone network, an inaccurate description of "CLI" that includes a range of data, in addition to calling party number, can be used to claim that "CLI" is necessary for the operation of all telecommunications services. However, in fact, some service providers do not need to know the calling party number, although they may need to know the time and duration of a call and Australian telephone network service providers are technically and readily capable of preventing unnecessary disclosures of personal information.
It should also be noted that some people use the term "CLID" instead of "CLI" when they mean 'Calling Line IDentification'. However, other people use "CLID" when they mean 'Calling Line Identification Display'. Hence, use of the term "CLID" should be avoided in order to minimise potential misunderstandings.
In the remainder of this document "CLI" means data that is generated at the time a telephone call is established that identifies the calling party telephone number/s.
This section provides an overview of how Calling Line Identification services operate. It has been derived from:
CLI has been passed between telephone call carriers for many years. It is only in relatively recent years that telephone network technologies developed to the stage that supplementary CLI based services could be provided to end users, such as Calling Number Display ("CND") and CND Blocking services.
The Australian Telecommunications Authority ("AUSTEL"), in its 1992 Telecommunications Privacy Report, explained why carriers need to share CLI:
"The sharing of CLI between carriers is mandatory under the General Carrier Licences held by AOTC [Australian and Overseas Telecommunications Corporation, later renamed Telstra] and Optus because it is essential to the introduction of long distance service competition. In a competitive long distance environment a particular call may be carried on networks operated by different carriers and service providers. For example, where a company in Adelaide chooses Optus as its long distance carrier and makes a call to Sydney, AOTC carries the call to the nearest point of interconnection with Optus, Optus carries the call from that point to the point of interconnection in Sydney nearest to the called party and then hands the call back to AOTC for delivery through the AOTC's Sydney local loop to the called party. Without the passage of CLI, Optus would be unable to identify and bill the Adelaide company." 
It is clearly often essential for telephone call carriers to pass CLI through their networks during passage of a call between the originating and terminating telephone exchange.
CLI is passed to carriers irrespective of whether the supplementary services, that enable delivery of a calling party number to the called party, are activated within the telephone network. In the international and ACIF telephone network signalling system specifications, the supplementary services are named:
The "Calling Number Display (CND)" service, as referred to in Australia, is a CLIP service.
The CND Blocking service, as referred to in Australia, is a CLIR service.
For each telephone line service, the default status of the CLIR/CND Blocking service is configured in the relevant telephone exchange (i.e. in the exchange to which a line is connected).
In Australia, in the case of an unlisted (silent) number, telephone service providers are required (by an enforceable Industry Code of Practice) to set the default status of the line to blocking (a "permanent block"), unless the telephone service subscriber has specifically requested otherwise. They are also required to place a permanent block on any other number on request by the subscriber.
Apart from those rules, telephone service providers choose the default status of the lines they provide, for example, Telstra's default is CND not blocked, while Optus's default is CND blocked (as at early June 2003).
When a call is made, it is (should) be transmitted by the originating network with a line blocking status in accord with the default setting, unless the caller has dialled a code to instruct the exchange to send that call with a different setting.
However, any carrier involved in transmission of the call can over-ride the caller's express line blocking instructions and disclose blocked numbers, including unlisted/silent numbers, to the called party. This is occurring in Australia (as at June 2003) on calls made, at the least, to Internet Access/Service Providers.
The following sections describe how blocking instructions are transmitted through the telephone network and the steps carriers can take to over-ride the caller's, and the originating carrier's, line blocking instructions without their consent or even knowledge.
During the initial phase of an outgoing telephone call, an Initial Address Message ("IAM") is sent to initiate seizure of an outgoing circuit and to transmit number and other information relating to the routing and handling of the call. The initial signalling message sent by the originating exchange includes, among other things:
It is the "Address Presentation Restricted Indicator" that, at least in technical theory, controls whether or not the calling party number is made available to the called party by way of the Calling Line Identification Presentation/Calling Number Display service.
If the default line status is blocking, (for example, most silent numbers and possibly many Optus numbers), all calls made from the line are transmitted by the originating exchange with an Address (number) Presentation Restricted Indicator ("APRI") set to "presentation restricted", unless the caller dials an unblocking code which instructs the exchange to transmit that call with the APRI set to "presentation allowed".
Although this technological process is capable of working effectively to prevent disclosure of 'blocked' calling party numbers, it is only effective if all carriers involved in transmission of a call respect the blocking instructions sent to them by the originating carrier.
As discussed earlier herein, the Calling Party Number is normally transmitted across interconnecting telephone networks because the information is often essential for billing callers for the calls they make. The Calling Party Number (and any additional calling party numbers) are transmitted regardless of the setting of the Address Presentation Restricted Indicator ("APRI").
Whether or not a "presentation restricted", i.e. blocked, calling party number is delivered to the called party depends on, for example:
The originating and/or transit network providers do, however, have the technical capability to prevent transmission of blocked calling party numbers to other network providers, for example, if they are not satisfied that a transmitting or terminating network provider will respect Calling Line Identification Restriction settings. In this regard, for example, the ACIF specifications state:
"2.1 General description
When Calling Line Identification Restriction (CLIR) is applicable and activated, the originating node provides the destination node with a notification that the calling party's ISDN number and any sub-address information are not allowed to be presented to the called party. In this case no calling party number is included in the call offering to the called party's installation.
Note - When CLIR is subscribed to, some network providers may not wish to send the originating identity of the calling customer to other network providers." (ACIF G500:2002, Part F.2)
This technical capability is used, for example, by network providers in Europe to strip calling party numbers from call signalling messages sent to network providers that do not, or may not, comply with EU privacy protection laws. For example, the U.K. Office of Telecommunications Code of Practice for CLI services states:
"Rule CLI-19 If the network to which a call is being forwarded cannot, or does not, conform to the Rules set out above, and if any of the received CLI information is classified as 'withheld' or 'unavailable' the forwarding network shall not send any CLI information to that network and the CLI classification shall be set to 'unavailable'." [2a]
When a call reaches the terminating telephone exchange, that is, the exchange to which the called party's line is connected, the exchange normally checks the Address Presentation Restriction Indicator.
If the APRI is set to "presentation restricted" the exchange does not (should not) send the calling party's number down the line to the called party.
If the APRI is set to "presentation allowed", the exchange transmits the calling party number during the ringing stage of delivery of the call to the called party (if the called party is subscribed to the CLI Presentation service).
The called party's telephone answering equipment may receive the calling party's number in various ways including: in the form of information that is displayed on a telephone or computer screen, or automatically recorded in a database, or as an audio message, etc.
Some Internet Access/Service Providers who sell a dial-up Internet access service receive blocked Calling Party Numbers from telephone network providers by a means entirely different from the receipt of CLI, a calling party number, in an incoming or transitting telephone call.
In many instances, the ISP does not receive the telephone call at all. Instead the telephone call carriers use their privileged access to blocked Calling Party Numbers to collect the number from an incoming telephone call that terminates on their own equipment, and then disclose the Calling Party Number to an ISP in a message that has nothing to do with telephone call signalling system messages. Moreover, the Calling Party Number is not necessary, nor is it used, to identify/authenticate the ISP's customer for the purposes of providing Internet access or billing.
An example of the above is Telstra's MegaPOP service . Although Telstra claims that line blocking is "not available" for calls to its MegaPOP service , blocking is technologically available, but Telstra chooses to ignore callers' line blocking requests. Other call carriers, including at least Comindico and Optus, provide dial-in services to ISPs (similar to Telstra's MegaPOP service) and disclose blocked calling party numbers in the same manner. The process operates as follows.
As can be seen from the above, it is not necessary for the ISP to know the calling party number in order to provide the Internet access service. The ISP knows which of its customers to bill from the user name/password received in the RADIUS server message.
In addition, Telstra is readily capable of not disclosing the calling party number to the ISP. It has at least two means of preventing disclosure of blocked calling party numbers:
In this regard, RADIUS server messages include a field titled "Calling Station Id" which will contain the calling party number if it was received by the RADIUS server. (Insertion of data in this field is optional, it is not essential to operation of a RADIUS server ). Telstra's RADIUS Information Document dated 7 February 2003 , made available on Telstra's web site to assist service provider's to correctly configure their RADIUS server to work with Telstra's, states:
"6.1.5 Called & Calling Station Id
The calling number consists of an area code and the first part of the telephone number from which the call was made. For privacy reasons the last three digits of the number have been replaced [i.e. by Telstra] with the letter x."
and provides an example in Section 6.1.2 as follows:
Attribute Attribute Number Example Value Explanation ... Calling-Station-Id 31 "0396403xxx" Telephone number the user dialled from. Complete numbers can be provided for authorised Service Providers.
Also on their website, Telstra states  :
"During the call authentication with the HSP [Host Service Provider, e.g. ISP], Telstra provides information that will allow the HSP to determine the charge of the call in progress [to be billed to the HSP by Telstra ]. Sufficient Calling Line Identification (CLI) information will be included in the RADIUS authentication request. Full CLI will not be passed to the HSP and, where this is available from the network, the four least significant digits of the CLI will be masked out before transmission to the HSP". [emphasis added]
Nevertheless, Telstra sends the full calling party number when the Host Service Provider is an ISP. It is not known what Telstra's current practice is when the HSP is a non-ISP company providing dial-in access to its staff.
Furthermore, although Telstra's MegaPOP system was launched in November 2000 , it was not until 18 months later, in March 2002, that Telstra activated calling line identification on its MegaPOP network. As reported in the Australian IT on 25 June 2002 :
"[Telstra] is citing technical, commercial and privacy concerns as obstacles to clear before it can allow ISPs to override blocks on caller line identification.
Telstra spokesman John Court said the number-one telco activated caller line identification on its MegaPOP network in March - meaning Telstra Wholesale, Telstra Retail and Telstra resellers had access to the service but the rest of the ISP world did not.
The number-one telco also had to overcome technical issues because the product would work differently depending on whether the customer ISP was using MegaPOP, ISDN, PSTN or another platform.
Mr Court said ISPs were unlikely to be given caller line identification en masse. Telstra might charge a fee for the service and this would be determined by negotiation with ISPs on an individual basis."
The article did not make clear whether, at that time, the CLI based product that Telstra was providing to ISPs involved only provision of calling party numbers for calls made without a CLI block, or whether Telstra had commenced over-riding CLI blocking in order to include blocked numbers in the product.
Subsequently, in October 2002, The Australian IT reported that "IIA chairman [sic] Peter Coroneos confirmed that Telstra, an IIA member, had begun to prevent CLI-blocking on all calls terminating at customers of its wholesale ISP service, MegaPop" .
Several months later, Telstra issued a newsletter with telephone bills which contained a footnote stating in tiny print that Telstra's Line Blocking Service is "Not available for calls to 000 or MegaPoP National access service" .
Line (CLI) blocking has only become "not available" because Telstra has specifically chosen to configure its telephone network/equipment to over-ride the CLI blocking instructions it receives with telephone calls, in order to include silent and other blocked numbers in a CLI based product that Telstra has chosen, apparently for commercial reasons, to package with the MegaPOP product that it sells to ISPs.