Transmission and Multiplexing (TM); High Bit-Rate Digital Suscriber Line (HDSL) Transmission System on Metallic Local Lines; HDSL Core Specification and Applications for Combined ISDN-BA and 2 048 kbit/s Transmission (V1.5.1)
The present document describes a transmission technique called High bit-rate Digital Subscriber Line (HDSL)@ as a means for the transportation of several types of applications. The present document defines the requirements for the individual HDSL transmission system@ the transmission performance@ the HDSL maintenance requirements and procedures and the mapping of information from the dedicated applications. An individual HDSL transceiver system is a two wire bi-directional transceiver for metallic wires using the echo cancellation method. Three systems may be utilized@ one transporting a bit rate of 784 kbit/s over each of three pairs used in parallel@ a second with an increased bit rate of 1 168 kbit/s and two pairs in parallel only and a third with a more increased bit rate of 2 320 kbit/s on one pair only. The line codes of systems specified in the present document are 2B1Q (2 Binary 1 Quaternary) and CAP (Carrierless Amplitude Phase modulation). Systems using a CAP line code are covered in annex B. Annex C summarizes the Committee T1 recommendation for the frame structure of 1 544 kbit/s applications. Only one of the line codes has to be realized in a transmission system. The present document defines the common circuitry for combining and controlling one@ two or three HDSL transceiver systems@ depending on the bit rate of the transceiver system used@ for the support of applications with a 2 048 kbit/s hierarchy. The common circuitry and the necessary number of HDSL transceiver systems form the HDSL core@ which is independent from the different applications defined in the present document. The applications of HDSL are determined by the functionality of the mapping and interface part@ some of which are defined as follows: - ISDN primary rate access digital section in accordance with ETS 300 233 [1]; - ONP leased line access D2048U based on ETS 300 246 [2] and ETS 300 247 [3]; - ONP leased line access D2048S based on ETS 300 418 [4] and ETS 300 419 [5]; - 2 Mbit/s access to the Synchronous Digital Hierarchy (SDH) via a TU-12. The HDSL core may be used for applications that are not restrictive to the access portion of the network but this is outside the scope of the present document. NOTE: If further applications are identified in future the present document may be enhanced to define the relevant interface and mapping requirements as far as these do not violate the specification of the HDSL core. Special applications of the HDSL core or part of the HDSL core can be: - fractional installation@ which provides reduced access capability only by a reduced number of HDSL transceivers@ to cater for an inexpensive system if the total capacity of 30 ? 64 kbit/s is not needed; - partial operation@ which is the persistent operation of the operable HDSL transceiver systems when others become inoperable; - fractional payload@ e.g. H0-channel. The bit-rate at the application interface will also be 2 048 kbit/s in these applications@ but not all the time slots in the G.704 frame may be used@ or there may be network specific interfaces used for these applications@ the definition of which is outside the scope of the present document. The present document does not specify all the requirements for the implementation of NTU@ LTU or REG. It serves only to describe the functionality needed.