Transcript
For discussion only
CCS-WG Paper No. 8/2002
TELECOMMUNICATIONS STANDARDS ADVISROY COMMITTEE WORKING GROUP ON COMMON CONNECTION STANDARDS (CCS)
Standardisation of ADSL Splitter 非對稱數碼用戶線路 (ADSL) 分離器的標準化事宜 Introduction This paper proposes the standardisation of POTS splitter for "partialbandwidth" deployment of ADSL in Hong Kong, in accordance with the relevant ITU-T recommendation. Technical Background 2. Splitter for ADSL is used along with ADSL terminal equipment in "partialbandwidth" service deployment, i.e. when the same copper transmission line is shared between the ADSL service and another service operating at the low frequency band, which may be POTS or ISDN basic rate access (BRA) service. As the bandwidth requirements of POTS and ISDN BRA services differ, there are two types of splitter for ADSL: POTS splitter and ISDN splitter. 3. The purpose of a POTS splitter is twofold, as is ISDN splitter. For ADSL signals, protection from the high-frequency transients and impedance effects that occur during POTS operation, such as ringing transients, ring trip transients, and off-hook transients and impedance changes, is provided. For POTS voiceband service, the low-pass filters provide protection from ADSL signals which may impact, through non-linear or other effects, remote devices (handset, fax, voiceband, modem, etc.) and central office operation. This filtering should be performed while maintaining the quality of the end-to-end voiceband connection. Two POTS splitter functions are defined: one for the remote end and one for the central office end. The function can be implemented either internally to the modem or externally. 4. Technical details of splitter for ADSL are covered in ITU-T Recommendation G.992.11. In the Recommendation, there are several options for POTS splitter but no specification of ISDN splitter. On the other hand, the ETSI had recently published a specification2 of ISDN splitter, which was subsequently adopted by the ITU in the new ITU-T Recommendation G.992.33 as 1
ITU-T Rec. G.992.1 (07/99), Asymmetric digital subscriber line (ADSL) transceivers ETSI TS 101 952-1-3 v1.1.1 (2002-05), Access network xDSL transmission filters; Part 1: ADSL splitters for European deployment; Sub-part 3: Specification of ADSL/ISDN splitters 3 ITU-T Rec. G.992.3 (07/02), Asymmetric digital subscriber line (ADSL) transceivers - 2 (ADSL2) 2
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approved in July 2002. There is however no corresponding U.S. version of ISDN splitter in Rec. G.992.3. Industry Consultation 5. The issue of splitter for ADSL service co-existing with telephony service on the same copper pair was initially raised by PCCW-HKT at the LAL CoP Forum4, and subsequently carried forward to this WG for discussion regarding its standardisation to facilitate broadband Type-II Interconnection. According to PCCW-HKT, inappropriate splitter would cause problems in both the telephony and the ADSL services, including incorrect calling number display, degraded fax and modem services, broadband services being affected by telephone ringing, etc. Upon discussion at the 53rd CCS-WG meeting, members generally considered that international standard should be followed as far as possible. 6. Following the 53rd CCS-WG meeting, OFTA convened a separate ad hoc meeting with the four wireline-based FTNS operators to further discuss the issue. At the meeting, it was agreed that the local splitter standard should be based on the PCCW-HKT splitter specification published earlier at the LAL CoP Forum, with reference to ITU-T Recommendation G.992.1 where applicable. The draft splitter standard compiled as such is enclosed at Annex 1 to this paper. The draft POTS splitter standard largely matches the North American splitter specification as defined in Annex E.2 of Rec. G.992.1. 7. Shortly after the ad hoc meeting, PCCW-HKT raised its concern that the ADSL splitter should conform to a 144 kbps limit for cut-off between narrowband and broadband services, given the TA statement on broadband interconnection5 made in November 2000. A data rate of 144 kbps corresponds to ISDN BRA as defined in ITU-T Recommendation G.961, and so the corresponding splitter is an ISDN splitter for ADSL. The choice between POTS splitter and ISDN splitter was further discussed in the LAL CoP Forum. Wharf New T&T, Hutchison Global Communications and New World Telephone were of the preliminary view that POTS splitter with 4 kHz cut-off frequency should be adopted first, while PCCW-HKT would not give its view until OFTA conduct a consultation with the industry on this approach.
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The LAL CoP Forum, with the participation of all four wireline FTNS operators, was established under the auspices of OFTA to develop with an Industry Code of Practice (CoP) for interconnection of Local Access Link (LAL). 5 TA Statement on Broadband Interconnection issued on 14 November 2000.
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Considerations 8. It should be clarified that the limit of 144 kbps stated in the concerned TA Statement of November 2000 regarding demarcation between narrowband and broadband services is only specified for the applicability of principles related to interconnection. In deciding the boundary between the lower bandwidth and the upper bandwidth in a spectrum sharing arrangement, the availability of equipment and the requirements of services conveyed over the local loops must be taken into consideration. 9. The specification for POTS splitter was standardised by the ANSI, the ETSI and the ITU several years ago, while that for ISDN splitter was only available lately from ETSI. The POTS splitter on the market is therefore expected to be more stable and interoperable when compared to ISDN splitter. There is also wider availability of standardised POTS splitter on the market than ISDN splitter. Furthermore, ADSL service deployed in coexistence with telephony service has been practised in Hong Kong for quite some time. The specification of POTS splitter for ADSL currently in use locally is therefore considered a stable and practical one ready for adoption as the local standard, with product conforming to such standard readily available on the local market. 10. The penetration of ISDN BRA service in Hong Kong is fairly limited, as the number of such lines has been consistently around 10,000 only over these few years. In case there is a need to deploy ADSL in a partial-bandwidth mode, the chance of ADSL service riding on an existing telephone line is much higher than that for an ISDN BRA line. There is therefore a more urgent need for a standard of POTS splitter. 11. The ADSL splitters currently being deployed in Hong Kong are mostly, if not all, having a cut-off frequency of 4 kHz separating voice and broadband services, thus constituting a de-facto POTS splitter standard. In the TA Statement6 on Type II Interconnection issued in April 2002, the practice of using existing in-situ splitter under a Type II Interconnection arrangement was endorsed. Accordingly, formalisation of such POTS splitter standard for general use in Hong Kong is expected to minimise market interruption in bringing about competition through Type II Interconnection.
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TA Statement on Type II Interconnection for the Conveyance of Narrowband Services Using the Lower Portion of the Bandwidth Available over Copper-based Local Loops issued on 4 April 2002
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Proposal 12. It is proposed that the specification of POTS splitter for ADSL in Annex 1 to this paper be adopted as a standard for broadband Type II interconnection in Hong Kong. Upon adoption by the TA, the splitter standard will be incorporated into HKTA 2201 and HKTA 2032 Specifications (corresponding to splitter at the central office side and the remote side respectively) in their next revisions. 13. Given that the specification in Annex 1 is largely in line with Annex E.2 of Rec. G.992.1, internal splitter conforming to this option of the ITU Recommendation will also be acceptable as conforming to HKTA 2032 Specification. 14. The standards development of ISDN splitter for ADSL shall be kept in view and the relevant international standard may be considered for adoption by the TA as and when required, subject to market need and industry consensus. Advice Sought 15.
Members are invited to consider the proposal in paragraphs 12 - 14.
Office of the Telecommunications Authority December 2002
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Annex 1 to CCS-WG Paper No. 8/2002 Proposed specification of ADSL/POTS Splitter for broadband Type-II Interconnection Parameter Insertion Loss Insertion Loss Distortion Return Loss
Reference clause in ITU-T Rec. G.992.1 Annex E E.1.3 E.1.4 E.1.2
Delay Distortion
E.2.3.1.4
Longitudinal Balance
E.2.3.2.1
ADSL Band Attenuation
E.2.4.1
Loading of ADSL Signal Path Capacitance in Idle State DC Resistance with U-interface open DC Resistance with U-interface shorted
E.2.4.2 E.2.3.3.1 E.2.2 E.2.2
Performance requirement (Frequency Limit) 1004 Hz < 1 dB 250 - 4000 Hz < +/- 1 dB 300 Hz > 14 dB 1000 Hz > 18 dB 2000 Hz > 18 dB 3400 Hz > 14 dB 200 - 600 Hz < 250 µs 600 - 3200 Hz < 200 µs 3200 - 4000 Hz < 250 µs 200 - 1000 Hz > 58 dB 3000 Hz > 53 dB 32 - 300 Hz > 65 dB 300 - 1104 Hz > 55 dB 30 - 1104 kHz < 0.25 dB 20 - 30 Hz < 0.3 µF > 5 M ohms < 25 ohms
NOTE: 1. For measurement of loss or loss distortion, a matching impedance of 600 ohm shall be used for termination. 2. The method of measurement shall follow that specified in the corresponding reference clause in the ITU-T recommendation. 3. For Capacitance in Idle State, some legacy equipment may have a value of up to 0.5 µF for the CO splitter.
Annex 1 to CCS-WG Paper No. 8/2002 December 2002
