CN1195453A

CN1195453A - Broadband digital subscriber loop systems

Info

Publication number: CN1195453A
Application number: CN97190672A
Authority: CN
Inventors: J·D·福蒂尔; H·威廉斯
Original assignee: GPT Ltd
Current assignee: GPT Ltd
Priority date: 1996-06-07
Filing date: 1997-06-09
Publication date: 1998-10-07
Also published as: RU98104084A; NO980503D0; WO1997047157A1; EP0843948A1; GB9611952D0; JPH11510985A; NO980503L; GB2313979A; GB9711785D0; AU3039797A

Abstract

A telecommunications system has broadband digital subscriber loop circuitry at each end of a link and is arranged to transmit telephony signals by digitising them and carrying them within the DSL signals whereby, in the event of failure of one of the DSL circuits or its associated power supply, the telephony signal is automatically switched to bypass to DSL circuits.

Description

Broadband digital subscriber loop systems

Nearly all hope is providing the telephone system operator of following broadband services all to need a kind of device that existing telephone service can be coexisted on same circuit with new broadband services for family and small business users on the existing telephone wire.

Past has been mentioned and has used filter to separate telephone signal and broadband signal.

If filtering all is audio frequency or the above bipolar signal of audio frequency, it will be a relative simple thing that these filters are provided.Though the Digital Subscriber Line signal has such feature,, the signal related with telephone set do not meet this simple model.Because historical reasons, phone now still uses 70 volts, 25 hertz ringing signal, and bidirectional operation and direct voltage of needs are operated on a pair of circuit.All these mean that the filter that is used for separating telephone signal and voltage must be extremely complicated or adopt the passive inductors part at its structure.

These two kinds of selections all cause final products bulky and expensive, and the both is unfavorable, because this product must be adapted at the limited space of DSL both link ends and medium burden for users must be risen.

As seeing, all need a low pass filter at main tie point (PCP) and user house at Fig. 1.Low pass filter separates telephone signal and broadband signal.

With regard to the signal path between PCP and the house, Fig. 1 has accurately represented the geometry of the reality of system.Can see that high pass filter is connected with circuit concurrently with low pass filter.This means that high pass filter should be enough durable with opposing ringing-current voltage, also want to block the DC on the circuit, these also will increase the expense of filter.

Telephone wire from PCP to the house is made up of the cable of all lengths.These cables are at cross-connecting box, and junction box and time tie point (SCP) connect.If these tie points are corroded, they will serve as a diode, cause the serious of broadband signal, unacceptable distortion.For addressing this problem, need a wet current " forward bias " diode, to eliminate the possibility of distortion.

This wet current must be enough big, can prevent WBD wideband distortion, but can not make switch or remote concentrator unit (RCU) that this electric current mistake is used as the electric current that the phone off-hook produces too greatly.The length of considering each telephone wire is different with loop circuit impedance, is difficult to grasp this balance.

A kind of alternative solution is to end analog telephone signal at PCP, passes with its digitlization and in the digital broadband circuit and carries result data.This has removed the requirement of filter and has allowed to optimize wet current, makes the distortion minimum of broadband signal.

A shortcoming of this method is, if this compound DSL circuit or in the power-fail of NTE or ONU just can not obtain telephone service.In these cases, require some telecommunication operator that promptly " life line " telephone service is provided.

According to the present invention, a telecommunication system is provided, every end at a link has the broadband digital subscriber loop circuit, and this system is designed to come by with the telephone signal digitlization and be loaded in the DSL signal and transmit telephone signal, when certain DSL circuit or its relevant power-fail, telephone signal is automaticallyed switch, and walks around this DSL circuit.

Fig. 2 has illustrated this thought.

When obtaining power supply and when all there is broadband DSL signal in the input of ONU and NTE, telephone circuit continues to deliver in broadband signal.If but power-fail or does not have input signal, indication takes place to lose efficacy or other fault at the other end power supply of link, then with the release relay group, thereby walk around ONU and NTE and return to switch and telephone plant between the telephone circuit of direct metal contact.

Shown circuit is related with PCP, and therefore the ringing-current detector is arranged.The circuit related with NTE is basic identical, but has " off-hook " detector, rather than the ringing-current detector.

Need a ringing-current detector at PCP, have ringing-current bit associated therewith circuit is set.Need a ringing-current generator at network termination equipment (NTE).Equally, need a line holding detector, have and take bit relevant circuit is set at NTE.Need a line holding relay at optical network unit (ONU).

Square 7, high impedance wide band detection circuit provide circuit can detect from the appearance of the broadband signal of circuit far-end or the device that does not occur.If shown in the position of relay, end from the signal of far-end, square 7 will detect and make relay to discharge.This means the appearance that square 7 can not detect from the broadband signal of the input port that is connected with " excitation " side of relay now.For this reason, square 7 has second high resistant input port detecting broadband signal from bypass link.In case the WBSR wideband signal recovery of far-end, square 7 will detect and field application relay once more by this input.

Discrete Multitone modulation (DMT) is a kind of efficient and simple method that transmits data on simulation medium.In DMT, the digital byte of a series of 2 to 16 bits is sent simultaneously, and each byte is modulated to a single-tone in the sound that a series of frequencies separate, these sound continuous adjacent and band limitings.

A DMT advantage of other modulator approach relatively is to modulate an independent sound or the one group of sound that separates with remainder.

In the realization of a DMT modulation, the needed 64Kbit/ of phone data second can be uploaded at a single-tone and carry, and have simplified the process of telephone signal and broadband signal multiple connection.

Claims

1. in a telecommunication system, having broadband digital subscriber loop circuit and this system at every end of link is designed by with the telephone signal digitlization and be stated from the DSL signal and transmit telephone signal, when being included in the inefficacy of a DSL circuit or line related, telephone signal is automaticallyed switch, get around the device of this DSL circuit.

2. claim 1 telecommunication system required for protection is characterized in that, wherein said DSL circuit adopts Discrete Multitone (DMT) modulation.

3. claim 1 and 2 telecommunication systems required for protection is characterized in that, modulate on the single carrier wave of telephone signal wherein in dmt signal.