Explanatory Document

• Introduction
• Backround
• Description of NTS
• OCCN Process
• NCCN Process
• History of the Dispute
• The Retail Uplift
• Alternative methodologies considered by Oftel
• The Director General’s decision and reasons
• Starting Charges and Updating
• Wide Area Tandems
• Retrospection
• Interest Charges
• Next Steps
• Disputes
• INCA

Annex 1 Explanation of graphs

• Graph 1 Relationship between Network Charge Differential and numbers of points of connection
• Graph 2 Method for setting and updating operator-specific conveyance charges
• Table Calculating Network Charge Differentials

Whereas the Secretary of the State granted to British Telecommunications on 22 June 1984 a licence (the "BT Licence") under section 7 of the Telecommunications Act 1984 (the "Act") for the running of the telecommunication systems specified in Annex A to that licence;

Whereas by virtue of section 109 of and paragraph 20 of Schedule 5 to the Act the BT Licence has effect as if granted to British Telecommunications plc ("BT");

Whereas the Secretary of State has granted to each of the operators listed in the schedule, a licence under Section 7 of the Act for the running of a telecommunications system as specified in the licence

Whereas the operators listed in Schedule 1 have entered into a Standard Interconnect Agreement with BT on the dates shown in the schedule

Whereas the Standard Interconnect Agreement covers charges BT pays other operators for interconnect services and provides for BT to propose a revised charge and the date on which the variation is to become effective by way of issuing an Operator Charge Change Notice

Whereas BT proposed to each of the operators listed in Schedule 1, revised charges for access to Number Translation Services on 18 December 1998 by varying the value of the conveyance charge used in calculating the charges

Whereas each of the operators listed in Schedule 1 rejected the proposed charges

Whereas Regulation 6(6) of the Telecommunications (Interconnection) Regulations 1997 provides that where there is a dispute between operators, the Director General shall, at the request of either party, take steps to resolve the dispute

Whereas, on 27 January 1999 in accordance with the provisions of Regulation 6(6) of the Telecommunications (Interconnection) Regulations 1997, BT has referred to the Director General for determination of the charges for conveyance for Number Translation Services.

Whereas a draft of this Direction and the explanatory document were issued to the industry on 27 August 1999 and comments invited. Responses to specific comments made are contained in the explanatory document to this Direction

Therefore pursuant to Regulation 6(6) of the Telecommunication (Interconnection) Regulations 1997 the Director General makes the following Direction:-

1. The Director General has issued a direction in accordance with the provisions of Regulation 6(6) of the Telecommunications (Interconnection) Regulations 1997 for the resolution of the dispute between BT and each of the operators listed in the associated Schedule under the terms of their Interconnect Agreement. The direction sets out the route factor that should be applied to BT’s single tandem conveyance charge to calculate each operators interconnection charges for Number Translation Services (NTS). The revised charges shall take effect from 1 November 1999.

2. The term Number Translation Services describes a range of specially tariffed services, primarily used for telemarketing, which include 080X/0500 Freephone, 0345/0645/0845 local call fee access, 0870/0990 national call fee access and 08xx/09xx Premium Rate Services. It does not include services operating on 07xx numbers such as personal numbering, which although technically similar in many cases, offer different services than those for which NTS was established. NTS services are offered at specific price points in order that customers calling from any fixed network will be able to associate the number range with a particular pricing arrangement. For example, 0800/0500 calls are free to the caller.

3. In January 1996, following a detailed consultation, Oftel determined a formula for the financial arrangements, which should apply to Number Translation Services where the call originated on one operator’s network and terminated on another. This formula is:

Originating operator (ONO) retains: P - D + C

Terminating operator (TNO) receives: D - C

where:

P is the actual retail price charged by the originating operator to the customer;

C is the pence per minute charge for conveyance over a single tandem segment of BT's network determined in this determination (multiplied by the number of minutes of the call) plus an uplift to allow for retail costs incurred by the originating operator in handling these calls;

D is the Deemed Retail Price for the call and is:

• in the case of Freefone services, zero;

• in the case of national call fee services, the net retail price after discounts charged by the originating operator for national calls

• in the case of local call fee access services, the net retail price after discounts charged by the originating operator for local calls, disaggregated into two rates (for short and long duration calls) to allow for the effects of the originating operator’s minimum call charge.
• in the case of Premium Rate Services, BT's retail price minus 3.5% to allow for average discounts and a further 4.4% to compensate for bad debts.

4. The principle underpinning the NTS formula was that originating operators should be able to cover their costs if they set prices at the deemed level. Terminating operators receive what is left from the retail price after the originating operator’s cost have been deducted (excepting Freefone calls) and can also seek payment from their own customers (ie the service providers to whom calls are passed) for terminating calls.

5. Paragraph 13 of BT’s Network Charge Control (NCC) Standard Interconnect Agreement, or Standard Contract, describes the process used by operators including BT for offering and amending charges in payment for access to another operator’s services, including NTS. Where BT as an originating operator proposes to change its retail price or its interconnection charge for call origination which results in a change to the price paid to the terminating operator for terminating calls, BT issues an Operator Charge Change Notice (OCCN) offering the new charge to the terminating operator.

6. Similarly where a terminating operator proposes a change to its terminating payment it issues an OCCN to BT seeking the new payment.

7. The operator receiving the OCCN has 14 days to decide whether to accept or reject the new charge and to notify the originator of the OCCN. Failure to notify within 14 days signals a rejection of the proposal. Where the charge is rejected both operators have a further 14 days to settle the resultant dispute. If after this second period the dispute remains unsettled either operator may refer the dispute to Oftel. The Director General will carry out a full investigation into the dispute and determine the outcome within six months of referral.

8. Where BT proposes to change the interconnection charges for access to its own services it notifies changes by publication of a Network Charge Change Notice (NCCN). These are not open to rejection by operators but Oftel can review NCCN’s if it or an operator regards the new charge proposal to be unfair or inaccurate in any way. If found to be so the Director General can make an order requiring BT to amend or withdraw the NCCN.

9. On 30 January 1996 Oftel published the determination of Interim Charges for BT’s Initial Standard Services for the year ending 31 March 1996. This determination described the original NTS formula at Annex 6.

10. Although the determination applied for access to BT’s services, Annex 6 stated how the Director General proposed that the rules set out should apply to other operators for their charges to BT for access to their NTS services.

11. Annex 6 also stated that:

……"BT’s single tandem charge is the basis for calculating the average charge of conveyance for an Operator when it accesses BT’s NTS services. BT has suggested that the number of switching stages within its network required to access the services of an Operator may be greater than the number of switching stages required for an Operator to access BT’s services. Oftel also recognises that costs may vary for other reasons among Operators. Nevertheless, on the information available, the Director General considers that the use of the BT single tandem charge is the only practical starting point. Oftel will review this charge prior to future determinations if more precise information about Operators’ costs becomes available."

12. In preparing subsequent Standard Services determinations it became clear that it would be impracticable for Oftel to analyse costs and produce charges for each originating operator. In April 1998, therefore, when Oftel published the determination of Final Charges for BT’s Standard Services for 1996/97, Annex 3 contained the additional statement that:

….."If Oftel were, however, asked to determine route factors for access to another operator’s NTS the Director General would look favourably at applying route factors which correspond to the average number of switching stages and components for the operator concerned."

13. This new statement was designed to encourage BT to produce route factors and supporting data for each operator with whom it interconnected for NTS calls and thereby enable it to, more accurately, recover its conveyance costs.

14. On 30 June 1998, as a consequence of the above, BT issued a Review Notice to 30 operators, under the terms of its Standard Interconnect Agreement, seeking to retrospectively revise interconnection conveyance charges for the financial year 1996/97. It gave each operator a revised charge based on route factors calculated from its historic calls samples taken during that year. BT was seeking to incorporate these new charges into the final settlements for that year based on the final determination

15. These review notices were rejected by a number of operators primarily on two grounds. Firstly BT had provided no visibility on how each route factor had been calculated. Secondly operators felt it was unreasonable for BT to seek to recover additional charges for a period which had ended some 15 months earlier and for which a final determination had been made by Oftel. Furthermore the determination contained illustrative figures based upon single tandem charges which many had used in calculating the payments they made to or received from the service providers. Owing to the competitive nature of service provider business operators could not expect to recover BT’s additional charges from their own customers retrospectively.

16. This dispute is the subject of a separate determination request to Oftel for which a draft Direction rejecting BT’s proposal was issued for consultation on 16 August 1999. The final Direction will be made shortly.

17. On 18 December 1998 BT issued an OCCN proposing a change in payments to terminating operator’s for all NTS calls resulting from a re-calculation of their conveyance charges based upon route factors calculated from BT’s latest call sample. The new charges were proposed to take effect from 13 February 1999.

18. Once again the majority of operators rejected BT’s proposal on three key grounds. Here again BT’s new charge had no supporting evidence. One or two operators had calculated their own route factors, having analysed their traffic origination patterns, and arrived at different (lower) figures than BT’s but were unable to verify how BT’s offer was calculated.

19. The second reason was that operators maintained they needed time to change their network configuration in order to minimise their conveyance costs. They claimed to be unable to do this until they knew what their current route factors were and then needed time to plan and implement the necessary changes.

20. Finally operators felt that route factors reflect how calls are actually routed across BT’s network, which may not always be by the most efficient path. Calls can be re-routed for network management reasons eg faults or congestion and may therefore incur additional costs through no fault of the terminating operator. The resultant charges may be higher than if optimum routing of calls was measured.

21. Oftel was also concerned about the relevance of route factors to current conveyance charges since they were based on historic call samples which were taken in April 1998 and may not reflect any investment undertaken by operators since that date.

22. BT rejected operators’ arguments on the grounds that they should already know where their traffic originates and should therefore have been able to estimate their own route factors which should also align fairly closely with BT’s calculations. In fact a small number of operators had done this and two pointed out differences with BT’s figures. BT did acknowledge one or two minor errors in their calculations which have since been corrected.

23. BT also argued that if all operators had taken the trouble to anticipate their route factors, having known for some time that BT intended to de-average conveyance charges, they could have planned and set in motion any necessary network changes well in advance of BT’s proposal.

24. This dispute was referred to Oftel for determination by BT on 27 January 1999.

25. Allied to this dispute is the question of BT’s retail cost recovery currently achieved by the application of the ‘retail uplift’ as mentioned in the description of NTS in paragraph 3 above.

26. In making the original NTS determination Oftel acknowledged the requirement of originating operators to recover, not only their network costs from calls but also their associated retail costs. BT insists these should include billing, bad debt liability and generic marketing costs aimed at recruiting new customers and encouraging all customers to make more calls including NTS calls.

27. A number of operators have maintained that BT’s marketing costs are irrelevant and should be removed from the calculation. This is because it is the service providers’ marketing which causes consumers to make the calls and not BT’s. BT, on the other hand argues that without its considerable marketing efforts designed to grow its system size, there would be fewer customers to make any calls. This document will not discuss the merits of either view.

28. The uplift is a constant charge applied to all NTS calls and is obtained by expressing BT’s retail costs as a percentage of its network costs, for its Retail Systems Business, using figures contained in BT’s latest audited Financial Statements. This percentage (currently 61.5%) is multiplied by BT’s LRIC single tandem conveyance charge to give a single (per second) charge for its retail activities which is independent of any de-averaged conveyance charge. The uplift charge is reviewed annually following publication of BT’s latest Financial Statements.

29. This methodology was never intended to provide a definitive calculation of BT’s retail costs for NTS calls but it was the best available at the time. Oftel acknowledges the concerns that have been frequently expressed by both BT and other operators that this allowance may either under or over compensate BT for these costs.

30. To this end Oftel has undertaken to review the methodology with the aim of devising a transparent and more soundly based means of allowing for BT’s retail cost recovery. We aim to complete the review by Christmas 1999, in the meantime the existing uplift charge will continue to be used.

31. In reaching the decisions, detailed in paragraphs 43 to 49, Oftel has worked closely with BT and the industry, through a working group (the NTS Focus Group) sponsored by the Operator Policy Forum (OPF). There have also been a number of individual meetings with operators, wishing to express their views in detail and confidentially, and with BT to explore and agree the processes to be adopted.

32. BT’s original proposals were based on route factors which represent an average of the number of switching stages of BT’s PSTN used by NTS traffic originated by BT and terminated on an operators system or network. These are calculated from a (one in 300) sample of an operators NTS traffic taken every six months by BT.

33. Whilst providing a reasonably accurate measure of the average routing of each operators traffic concern was expressed that calls which were routed over more switching stages than necessary for network management reasons were included in the calculations. These would have the effect of artificially inflating the average route factor. BT maintain that this is not the case and that the factors represent optimum routing but their inability to demonstrate this caused other operators to remain sceptical over the accuracy of their charges.

34. As a result of this, on 4 May 1999 Oftel issued a briefing note to the OPF outlining an alternative methodology for calculating each operators starting conveyance factor. Attention was drawn to the use of the EBC (element based charging) matrix of interconnection switching components which if applied correctly should provide an optimum routing factor for all calls. The proposal was that whilst this still did not produce actual charges for all calls it probably gave a more transparent means of calculation than the route factors previously produced without any supporting evidence.

35. Having established a basis for calculating starting charges, concern remained that the data used was based on a BT call sample taken several months earlier and did not allow for any subsequent additions to operators’ network configuration. The May briefing paper described how an additional process was therefore required to take account of:

1. any changes to an operators interconnection arrangements between the last call sample date and the effective date of this direction and…
2. further additional points of interconnection as they are made

36. In an attempt to meet this requirement BT developed a Rule of Thumb (Rule of Thumb) methodology which fulfilled two functions. It could provide another theoretical set of starting charges based upon the number and location of each operator’s point of interconnection with BT at the time. It could then easily amend the starting charges as additional points of interconnection were ordered and installed.

NB: A point of interconnection is where an operators network interconnects with BT at a Digital Main Switching Unit (DMSU) or Wide Area Tandem (WAT). The number of points of interconnection corresponds to the number of BT’s switches to which the operator is directly connected.

37. The Rule of Thumb split the UK into 10 geographic regions and assumed that 10% of any operators’ traffic originated in each region. Key points of interconnection in each region were identified and BT set an optimum number across all 10 regions in order for any operator to obtain a single tandem conveyance charge. Any less than the optimum would result in a charge consisting of a mixture of single and double tandem medium charges.

38. Upon closer examination regionally based operators with fewer points of interconnection and which were concentrated in specific geographic areas could be penalised under the assumption that all traffic originated evenly across the 10 Rule of Thumb regions. Some of these operators target their services at localised markets and generate calls from specific regions. Their calls are likely to originate locally and should be charged at single tandem yet under the Rule of Thumb they would incur a high proportion of double tandem charges.

39. An operator whose traffic originates predominantly in London and the South East, for instance, would be assumed to have only 20% of their traffic as single tandem and 80% at double tandem whereas in reality most if not all of their traffic may be single tandem. In order to achieve lower charges under the Rule of Thumb that operator might seek to build out their network to conform to the Rule of Thumb requirements by adding routes to points of interconnection which carry little or no real traffic. This could then potentially leave them with stranded investments when BT’s INCA system takes over charging on a ‘per call’ basis next year.

40. Other smaller operators, not willing to extend their networks, would be allocated very high factors by the Rule of Thumb regardless of where their traffic originated. In reality their charges would be much higher than single tandem but they would be based on actual traffic measurement. Oftel believes that to determine high Rule of Thumb factors and consequential charges based on a totally theoretical model would be unacceptable.

41. Whilst the Rule of Thumb did provide a ready means of allowing for the effects of adding new points of interconnection it would not necessarily give credit for network build based on operators’ knowledge of their traffic patterns if these did not align with the Rule of Thumb regions. The potential for conflict with the eventual INCA charges if operators built out their networks to meet Rule of Thumb objectives is a key concern for Oftel.

42. Having consulted the NTS focus group on various methodologies Oftel considered that the options available still lacked sufficient validity and transparency. We asked BT to look at any other methods of calculating and updating charges that may prove more acceptable. In particular we wanted starting charges to relate to actual network usage. As a consequence the simple and highly transparent methodology described below has been adopted for this Direction.

43. The original route factors offered by BT were based on call samples taken in April 1998 when only 14 operators had traffic levels sufficient to provide meaningful samples. All other operators’ charges were an average of the 14 measured operators. By August 1999, however, BT was able to provide new route factors using September 1998 call samples which included 34 operators measured NTS traffic.

44. Using the latest factors BT has calculated a Network Charge Differential (NCD) for each operator which indicates by what percentage their conveyance charge increases above single tandem. The September 1998 route factors split each operators traffic into the proportion conveyed over single tandem and double tandem short, medium and long services. An EBC allowance has been applied to reflect optimum and therefore least cost routing. No account is taken, however, of the effects of operators nominating where their traffic should terminate. In these circumstances call routing may exceed the optimum and charges will reflect this.

45. The resultant percentages are then applied to the charges for each standard service as shown in the following illustrative example:

This operators NCD        = (.4685 x 20% + .6506 x 30% + .7452 x 35% + .9018 x 15%)

= 0.6850ppm

= 146% of the single tandem charge

46. Graph 1 at Annex 1 shows each measured NCD at September 1998 plotted against the number of points of interconnection with BT each operator had at 1 September 1998. Broadly it can be seen that operators with few points of interconnection have relatively high NCDs as they will tend to have higher proportions of double tandem traffic.

47. Graph 2 at Annex 1 shows how a curve has been drawn through the lowest NCDs for any given number of points of interconnection. The curve has been extended down to just above the x axis to give virtual single tandem at around 68 points of interconnection. The Table at Annex 1 lists the NCD corresponding to each number of points of interconnection.

48. The starting charges will be based on each operator’s NCD at the effective date of this Direction (see paragraph 60). As new points of interconnection are added (see paragraph 62) the effect on an operator’s terminating payments can easily be assessed from the Table.

49. It must be emphasised that this is an interim charging solution which contains a number of compromises designed to soften the impact of charge de-averaging and to give operators the opportunity to prepare for INCA based charging by the middle of next year. Oftel strongly advises operators against planning network investments solely to achieve the greatest benefits from this charging model without regard to the longer term effects of INCA. It is likely that some operators will see an increase in their charges when INCA takes effect next year. Oftel recommends that operators work with their BT account managers to optimise their INCA charges in advance.

Wide Area Tandems (WATs)

50. Oftel was asked to include an additional allowance for interconnection at WATs. Some operators felt this was equivalent to more than one point of interconnection at a DMSU. Although WATs generally have a greater geographic reach than DMSUs, the costs to operators of connecting to a WAT are little different than for a DMSU. Furthermore the area covered by each WAT is different and the average benefits gained across all WATs has not been measured. As the charges are already generous to most operators Oftel has not made a further WAT allowance. Here again operators should plan their future investments with INCA based charging in mind where WATs will almost certainly offer benefits.

51. In making the determination request BT has sought an effective date of 13 February 1999 as proposed in its OCCN issued on 13 December 1998. BT considered that operators had known since the original NTS determination that it would eventually seek to recover its actual conveyance costs. Oftel has always supported the principle of cost recovery but only on the basis that the resultant charges are as accurate and transparent as possible.

52. BT maintained that operators should know where their traffic originates from the CLI (calling line indicator) data and should therefore have been able to configure their networks in advance in order to minimise their costs. They should not, therefore, have been surprised at the level of the new charges.

53. Operators, on the other hand maintain that CLI data alone does not allow them to accurately optimise their networks and they were therefore reluctant to try and anticipate their likely revenues until they had seen BT’s route factors. In any case there is no incentive to invest in expensive network build when everyone was charged at the same single tandem rate.

54. Some operators had attempted to estimate their ‘real’ termination payments but found that those offered in BT’s December 1998 OCCN were often lower than anticipated. As they were unable to check BT’s confidential data sources to understand how its conveyance charge was calculated, many rejected BT’s offer.

55. BT suspended its offer to all operators who rejected the OCCN and these have continued to receive payments based on single tandem charges. Operators who accepted BT’s proposal have been receiving lower payments since February 1999. Similarly new operators and those opening services since February 1999 have been offered payments based on BT’s average route factor. Many of these have complained to Oftel as a result.

56. If this direction were to take effect from 13 February 1999, operators currently receiving single tandem based payments would be required to refund the difference (plus interest at the Oftel rate) to BT from February to the date of this Direction.

57. Oftel considers this a highly sensitive matter and one which could have potentially serious consequences for some operators’ businesses.

58. We have also taken into account many terminating operators’ contractual requirement to make prompt and competitive payments to their service providers. In order not to risk losing service provider business they are likely to be unwilling or unable to seek similar refunds and would have to absorb the additional costs.

59. Finally, the protracted time taken to agree the methodology used in this direction has created further delay for which operators should not be penalised.

60. The Director General has therefore decided that BT’s de-averaged conveyance charges should take effect from 1 November 1999 but operators will have the opportunity to minimise their starting charges. Orders for additional points of interconnection received and agreed by BT, under existing normal processes, within 14 days of the date of the Direction will be included in NCD calculations in addition to any other orders already being delivered and points of interconnection already in place.

61. BT estimates agreement of orders will take around 25 working days from receipt of Advance Capacity Orders (ACOs). The resultant charges should take a further 5 days to calculate and will have effect from 1 November. Once charges have been calculated BT will issue a proposed contract amendment in the form of a pricing letter in order to implement this Direction.

62. BT will review each operator’s interconnection charge at quarterly intervals from 1 November. Any additional points of interconnection or agreed orders received at the date of the review will be included in future charges.

63. BT’s single tandem charge will apply until 1 November 1999.

64. In accordance with Condition 13.13 of BT’s Standard Interconnect Agreement, where the determined charge differs from the charge already paid, interest on over or underpayments will be charged at the Oftel rate. This is the London Inter Bank Offered Rate (LIBOR) plus 3/8 per cent as defined in Annex D to BT’s Standard Interconnect Agreement.

65. This direction applies to BT and the operators listed in Schedule 1. Other operators may seek to receive payments based on the determined charges from the effective date by issuing an OCCN to BT within one month of the date of this Direction. Thereafter the determined charges shall apply from the effective date of the OCCN in accordance with Condition 13 of BT’s Standard Interconnect Agreement.

66. Any operator who has received payments lower than those received by operators listed in Schedule 1, during the period from 13 February 1999 to 1 November 1999, may seek a refund of the difference, plus interest, from BT.

67. This Direction has established the methodology BT will apply in setting operators’ NTS charges and as a result its payments for access to their services. BT will calculate the individual charges as quickly as possible after the starting point number of NCD’s has been established (see paragraph 62).

68. Oftel believes the relative transparency of the methodology should enable operators to understand how their charge has been arrived at. Should any operator seek to reject their revised charge they will be required to provide full evidence of why they believe the charge is incorrect on the basis of the methodology determined by Oftel. Disputes without such supporting evidence or arising from a failure to respond to BT’s charge notification may be dismissed and the operator advised to reach a negotiated agreement with BT.

69. This determination will cease to have effect when the Director General is satisfied that BT’s INCA system is able to accurately measure actual calls and charge accordingly.

70. BT’s INCA system for billing calls to operators’ NTS services is scheduled to be introduced from April 2000. Its originating retention will then be charged on a call by call basis, no longer using a theoretical figure calculated from the lowest possible charge which relates to the number of points of interconnection. As mentioned in paragraph 48, operators with few points of interconnection may therefore notice an increase in BT’s charges and a consequential reduction in their terminating payments.

Oftel
November 1999

Graph 1 shows the relationship between the Network Charge Differential and the number of Points of Interconnection (POIs) as at September 1998. It is based on the 7 responses to the request, outlined in the draft determination, for the numbers of NTS POIs held by operators in September 1998. The Network Charge Differential (NCD) is calculated using actual network usage and NCC charges and represents the percentage uplift on single tandem charges payable by operators. Broadly, the higher the number of POIs, the lower the NCD. This reflects relatively high proportions of Double Tandem traffic experienced when operators have relatively few POIs.

The straight line in Graph 2 represents the methodology that will be used for setting and updating charges. It was found by drawing a straight line through the lowest NCD data points and so envelops all the revised NCD/POI data points provided by OLOs. The Table to this Annex gives the NCD which corresponds to each number of POI

The equation of the new straight line (y = 138.2 – 0.6x) provides a mechanism for setting de-averaged charges and for updating those charges to reflect investment on additional POIs undertaken by operators. Operators can use the table attached to calculate their charge (in terms of the percentage uplift on single tandem charges).

Freefone - No fee calls to BT’s non-geographic NTS services which are free to calling customers

INCA - BT’s automated billing system for interconnection charges

IP - Internet Protocol; refers to the special network arrangements required for transmitting data over the Internet.

Local Call Fee Access - Calls to non-geographic NTS services for which calling customers are charged at the local call rate

National Call Fee Access- Calls to non-geographic NTS services for which calling customers are charged at the national call rate

NTS - Number Translation Services - calls to certain non-geographic numbers including freefone, local call fee access, national call fee access and Premium Rate services

Point of Interconnection - also known as a Switch Connection ie where an operator’s network interconnects with BT at a Digital Main Switching Unit (DMSU) or Wide Area Tandem (WAT)

PRS - Premium Rate Services: Calls to certain non-geographic numbers for entertainment or information services

Tandem – A main exchange in BT’s network which acts as a single switching point for calls.