Patent Application
20060188259
The invention relates to transmission of HDSL signals. The invention also relates to processing and transmission of electronic HDSL signals converting the signals to optical signals and then reconverting the signals to electronic signals. The invention also relates to telecommunication isolation links that use optical fibers and transmit HDSL 1, HDSL 2 or HDSL 4 signals.
Isolation links are known for protection from GPR. Such links have a CO circuit at the service provider's side and a SUB circuit at the subscriber's side. These circuits are often referred to as a CO Card and a SUB Card respectively because the circuit is constructed on a printed circuit card. Between the CO Card and the SUB Card optical fibers extend, passing the signals in each direction. The purpose of the optical fiber is to prevent passage of any high voltage that could damage circuitry or related equipment. Each of the CO Card and the SUB Card are also equipped at their entry locations with protection circuitry to prevent any voltage spike from passing into the Card. But, if a large or extended voltage rise occurs that overwhelms the protection elements, it cannot pass through the optical portion of the system. Therefore any damage is prevented or limited. These potentially damaging events are called ground potential rise or GPR. In a typical isolation link installation the SUB Card is installed near to a subscriber or near to a place where a GPR risk is present. The CO Card is installed a sufficient distance away that a GPR event will not affect the CO Card. An isolator link made by RLH Industries of Orange Calif. is one such device; it is specified for use up to twelve miles of single mode optical fiber.
Fiber optic link systems are compatible with most telecommunication services in common use today. Each fiber optic link card transmits a single copper line over 2-strands of fiber optic cable. The CO side of the link is typically installed outside the high voltage area—typically outside the “300 volt point”. Most CO side cards have the ability to operate from telephone line power (sealing current). From the CO side location a copper derived signal is transmitted over an all-dielectric fiber optic cable (single-mode or multimode). The SUB side of the link is placed at the high voltage site to regenerate the copper signal.
Telecommunications makes use of HDSL signals for rapid high bandwidth transmission of information in digital form. There are several formats for such transmission one of which is HDSL. Typically a system is adapted to transmit one of the three types of HDSL protocols, HDSL 1, HDSL 2 and HDSL 4. The use of each of HDSL1, 2 and 4 is variously adopted by service providers according to their particular needs. HDSL 1 and HDSL 4 use two channels while HDSL 2 uses one channel.
There is presented a need to convert HDSL signals for transmission across optical fiber lines. There is further presented a need for a fiber optic link for HDSL signals and also for a universal link that can be used adaptively for whichever of the HDSL 1,2 or 4 signal protocols is presented.
In one aspect the invention is a system and method for transmitting HDSL signals over an optical fiber transmission line by converting the signal from an electrical form to an optical form and then back to electrical form.
In another aspect the invention is an optical isolator link having a CO Card at the service provider's end and a SUB Card at the subscriber's end and optical fiber transmission lines connected between them in which HDSL signals can be converted from electrical to optical form and back to electrical form.
In another aspect the invention is a universal optical isolator link and method that can function with whichever of HDSL1, 2, or 4 signals are to be used.
In another aspect the invention is a universal optical isolator link that converts HDSL1 and 4 and HDSL 2 signal to a 320 MHz signal into an optical transmitter for conversion to an optical signal.
In another aspect the invention is a universal optical isolator link that has identical circuits at each end of optical fiber transmission lines which circuits convert incoming HDSL 1 or 4 or HDSL 2 electrical signals into 320 MHz signals for transmission over an optical transmission line and which also receive optical HDSL 1 or 4 or HDSL 2 320 MHz signals and convert those signals into standard HDSL 1 or 4 or HDSL 2 signals as the case may be.
The invention in one aspect resides in a method and system for bidirectional sending HDSL signals over optical fiber. This method and system requires that the original electric analog HDSL signal be converted to a form and with the same content that can be sent over optical fiber and then at a receiving location be reconverted to the original electrical analog signal.
In another aspect the invention is a method and system for sending HDSL signals through a fiber optic isolator link. In this aspect, an incoming signal from a signal provider through a telecommunications central office is received by the isolator at a Central Office circuit and sent through a transhybrid device that has an analog to digital converter. The digital signal at 32 MHz is then serialized and sped up by a factor of 10 to 320 MHz. That digital signal form is then converted to an optical signal and sent to a subscriber location. At the subscriber location the incoming digital optical signal is converted back to a digital electrical signal, deserialized and demultiplexed and converted back to analog regenerating the original 32 MHz analog electrical signal. Similarly, for a signal sent from a subscriber the same procedure is implemented by the same circuit components as are in the Central Office circuit at the opposite end of the isolator link. Specifically, the signal from the subscriber is received at a Subscriber circuit and sent through a transhybrid device that has an analog to digital converter. The digital signal at 32 MHz is then serialized and sped up to 320 MHz. That digital signal form is then converted to an optical signal and sent to the Central Office circuit. At the central office circuit the digital optical signal is converted back to a digital electrical signal, deserialized and demultiplexed and converted back to an analog signal regenerating the original analog electrical signal that was sent from the subscriber location.
The invention in one aspect resides in such a universal HDSL fiber optic link capable of handling HDSL 1 or 4 or HDSL 2 signals. This aspect is the present preferred embodiment which will be described herein and which description also is sufficient description of each aspect of the invention. In a more particular aspect the universal capability is carried out in circuitry that is the same on both sides of the optical fiber link so that when implemented such as on a circuit card they are interchangeable.
The universal HDSL link that is capable of handling HDSL 1 or 4 or HDSL 2 has two circuits. The first circuit is referred to as the Central Office or CO circuit (also referred to as a CO Card), and the second circuit is referred to as the Subscriber or SUB circuit (also referred to as the SUB Card). “Central Office” is the telephone service provider's equipment office, referred to generally as “Telco”. As will be seen, when the invention is implemented as a bi-directional optical isolator link, the CO circuit and the SUB circuit are identical insofar as processing the HDSL signal. They each can operate universally and bidirectionally with any of HDSL 1 or 4 or HDSL 2.
Insofar as practical herein the signal entering the CO Card from a signal provider will be designated the CO source signal or CO source data stream and the signal entering the SUB Card from its origin (usually the subscriber) will be designated the SUB source signal or SUB source data stream.
In an alternative convention, when the context permits, an HDSL signal received by the respective circuit card from its local HDSL signal source will be referred to as a received signal and an HDSL signal, having been sent by one of the circuit cards over the optical fiber line, that is received and processed by the other card will be referred to as a transmitted signal. Accordingly, it can be appreciated that a received signal at one end of the link is processed by the circuit at that location and is transmitted over the optical fiber as a transmitted signal to the other processing circuit at the other end of the optical fiber link.
It is presumed that those skilled in the art can follow the references in context of describing the flow of signals.
Referring to
FIGS. 4 shows how the lines from the Central Office 30 are connected to the lines 14 and 16 at the CO Card 12. The HDSL 1 or 4 or HDSL 2 signal is provided by the provider from the CO 30 and is sent to the CO Card 12 by the two lines 14 and 16. In particular, HDSL 1 requires two pair connection and is provided through connections 14a, 14b, 16a and 16b. HDSL 4, which also requires two pair connection, is also connected at connectors 14a, 14b, 16a 15 and 16b. HDSL 2 requires only one pair connection and can be connected through connections 14a and 14b or 16a and 16b. Those skilled in the art will be able to fashion these connections through conventional connectors. At the subscriber side the same connectivity applies where the SUB source signal is transmitted from the subscriber facility which is near a potential GRI source such as a high voltage power line as shown, using lines 20 and 22 for HDSL 1 and 4 or 20 or 22 for HDSL 2.
Similarly an HDSL 2 line carrying the SUB source single channel HDSL 2 signal or one channel of either HDSL 1 or 4 signal enters the SUB card 18 at connection line 20. An additional input connection line 22 is used when HDSL 1 or 4 is used, for the other channel.
Each of the CO Card 12 and the SUB Card 18 can be defined as having a duplex input/output section A, a recieved signal processing section B, a transmitting signal processing section C, and a control logic section D. Also there is an optional DSP section E and an optional switch section F. Other optional circuitry can be associated with the cards, not necessarily the same on each of them. For example, on SUB Card 18, there can be provision for local power that may not be (but could be) used on CO Card 12. However, it is a feature of this invention that the cards are interchangeable, so that for example, provision for local power may be on both even if it is not used on the CO Card when span power is used; and of course, local power may be used on the CO Card in some installations. Alternatively, a SUB Card configured for local power can be used at the CO location when local power instead of span power is to be used there.
The CO Card 12 in section A has various electronic components and devices on it to protect the card itself. These are designated line conditioning circuitry (LCC) 30a and 30b. Two types of protection devices are shown; circuit 32a and 32b protects against spikes and transformer 34a and 34b is an isolation device. These protection devices prevent superfluous voltage spikes and anomalies from damaging the Card. This would include noise and signals exceeding normal operations.
After the LCC 30a, the CO source HDSL 2 signal and one channel of the CO source HDSL 1 or 4 signals goes through an electronic transhybrid 36a. An additional transhybrid 36b is used when HDSL 1 or HDSL 4 is used. The transhybrid circuit 36a and 36b separates the CO source signal (the received signal from the service provider) from the SUB source signal (the transmitted signal from the subscriber). The transhybrid 36a and 36b also specially filter and screen out any signal other than the HDSL signal. Inside the transhybrid 36a and 36b, the CO source signal is transformed from an analog signal into a serial stream of digital data, representing the original received analog signal, through an A to D (analog to digital) converter 38a and 38b and filter 40a and 40b and digital interface register circuit 42a and 42b. This conversion and filtering is controlled by an on-card control logic device 44 (implemented in a FPGA-Field Programmable Gate Array) designated as section D.
Sampled serial digital data of the original received HDSL signal is occurring at 32 MHz (32 Megahertz or 32 million bits of data per second).
Each of the transhybrids 36a and 36b is also configured to operate bidirectionally to also handle the transmitted SUB source signal coming in, so that in the transhybrid 36a and 36b there is a reverse direction D to A converter 46a and 46b and associated filter 48a and 48b.
In the transmitting and signal processing section B there is a serializer 50 and a fiber optic transmitter 46.
Therefore, in the case of HDSL 2, the two 32 MHz data streams and in the case of HDSL 1 or 4, all four 32 MHz data streams (2 for transhybrid 36a and 2 for transhybrid 36b); along with timing and control signals from the control logic circuitry 44 are fed into the serializer 50 on the card. The serializer 50 time multiplexes each 32 MHz channel into a time multiplexed serialized digital data stream of all the 32 MHz channels into one channel. To do so, the serializer increases the speed of the data to ten times the original speed, or 320 MHz (320 million bits of data per second).
The data is then translated from a time multiplexed I serial digita data stream to an optical signal by means of a fiber optic transmitter 52. Data exits the CO Card 12 through this transmitter 52, is transmitted over the optical fiber 54 and is received by the fiber optic receiver 56 on the SUB Card 18. The fiber optic receiver 56 translates the optical signals back into electrical time multiplexed serial digital streamed data at 320 MHz and sends it into the de-serializer 58 on the SUB card 18.
The 320 MHz serialized signal is then separated into its individual 32 MHz channels by the de-serializer 58. The de-serializer 58 and SUB Card control logic device 60 (also an FPGA) control the timing and synchronization of these signals. Each 32 MHz channel is then fed into its corresponding transhybrid by the control logic circuit 60. The control logic circuit 60 also controls the timing of this function.
The transmitted serialized data stream of the original analog signal is then fed into the reverse direction side of the transhybrid 62a if the signal is HDSL 2, and into both transhybrids 62a and 62b if HDSL1 or HDSL4 was used. This (these) transhybrid(s) circuit(s) transform(s) the digital data stream(s) into electrical analog data again by utilizing their internal D to A (Digital to Analog) converters. The details of the transhybrid 56a, 56b are shown in
The two circuits, the CO Card 12 and the SUB Card 18 are duplicates. Therefore, the Sub source signal that is transmitted to and through the SUB Card for transmission over the fiber optic link to the CO Card is processed in the same way as is the CO source signal through the CO Card over the fiber optic link to the SUB Card and the received SUB source signal into the CO Card from the SUB Card is processed in CO Card in the same way as the received COI source signal from the CO Card is processed in the SUB Card. This duplicate circuitry operates in each card in the exact same way utilizing the same control logic and transhybrids, serializer and deserializer, as well as a separate fiber optic transmitter, and fiber optic.
Power for the entire cards' circuit can come from two sources. Circuitry is provided in the CO Card that will take span power from the central office and translate it into three separate supplies for the HDSLU card 12. Span power is voltage provided by the central office to power external cards at the customer's location. These voltages which are created by the on board power circuitry are 3.3 volts, 5 volts and 12 volts. The HDSLU cards 12 and 18 can also be powered by external local power. The external power input can be from 24 to 54 Volts Direct Current (VDC). Currently, circuitry is oriented that span power is generally used on the CO Card 12 and external power is generally used on the SUB Card 18. However sometimes it is desirable or necessary to use local power at the CO location. In such case a SUB Card can be used as a CO Card because the SUB Card is equipped to use local power and is identical in all its operating functions.
A blue Light Emitting Diode (LED) indicator is provided on each card to show that power is active on the card. Another orange LED indicates that the regenerating card is successfully receiving the serial data from the originating card. Two other green LEDs indicate that each HDSL channel on the card is active.
One of the unique features of the circuitry is that normally the transhybrids are used in conjunction with a DSP and software to modify and change or improve the signal received through the hybrid. The present invention uses a hardware only version in which data is not changed, but only passed between the transhybrids on each card, therefore eliminating the need for any software handling. In particular the portion of the signal that contains control bits is deleted by rendering the control bits to a default non-operating condition. However, in some cases, there can be the possibility of certain long distance lines or “noisy lines” that may require more intricate, intelligent and complicated processing of HDSL signals to recreate them from the CO to the SUB card. In such cases an optional DSP capability can be implemented as shown in
As shown in
Switch 1 is for turning off and on the HDSLU line 1. If turned on, power is received and HDSLU signal is transmitted and received over line 1. If turned off, power is still received if a line is connected, but no transmission of signal occurs.
Switch 2 is the same as switch 1, for line 2.
Switch 3 is a loop back function. If turned off, normal operation occurs for both lines. If turned on, line 1 and line 2 are connected to each other through all circuitry and fiber optics. Meaning that signals coming in on line 1 go through all normal processes, but if a fiber optic cable is connected between the fiber optic transmitter and fiber optic receiver, then the signal from line 1 will return and be output to line 2. And signal from line 2 will also go to line 1. The purpose of this option is to be able to test an individual card to see if it is functioning without having to connect to its companion card. They help in allowing service personnel to debug a system and tell if only one card has a problem.
Switch 4 currently has no function but may be used for extra gain/volume in the future or it may be used to set which card is the primary and secondary card. In most cases, the CO card is the primary card providing timing to the secondary SUB card for communications. In normal operation, it is set to “CO” for a CO card, and “SUB” for a SUB card. However, it also has a second purpose. CO cards can't be powered from local power. But there can be cases where customers want to use local power on a CO card. A customer can in that case use a SUB card and set switch 2 to “CO” and use local power on it. This SUB card now becomes a primary controlling CO card that already has circuitry to use local power inputs.
The HDSLU card currently doesn't use DSP processing for the control and use of HDSL signals. However, there can be the possibility of certain long distance lines or “noisy” lines that may require more intricate, intelligent and complicated processing of HDSL signals to recreate them from CO to SUB card. Unused connections for a DSP processor and its accompanying circuitry exists on the HDSLU card for this purpose.
When populated, the DSP circuitry can perform complicated mathematical algorithms on the HDSL data from the transhybrids that will screen out and reconstitute an HDSL signal into its most pure form. This reduces interferences such as noise and echoes that can occur on difficult lines.
The data is then sent back to the hybrids for normal operation.
A preferred transhybrid is the AFE1230 made by Burr-Brown, a subsidiary of Texas Instruments.
The following lists the flow of steps for each of the CO Card and the SUB Card:
Connection:
1. Connect HDSL lines to inputs of HDSLU CO card.
2. Connect customer HDSL equipment to corresponding outputs of HDSLU SUB card.
3. Apply local power to HDSLU SUB card.
Operation:
1. Received HDSL signal goes into HDSL line 1 and/or 2 input.
2. Corresponding transmitted HDSL signal comes out of same inputs.
3. Received HDSL signal is processed and turned into digital values by A to D hybrid.
4. Digital values from both input 1 and 2 are combined into one stream of data.
5. Digital information is serialized via serializer.
6. Serial data is transmitted via optical transmitter.
7. Received serial data is received by optical receiver.
8. Received data is then deserialized by deserializer.
9. Digital data is sorted into channel 1 or 2 for transmission by receiving card.
10. Digital values are restored to HDSL signal by D to A hybrid.
11. Corresponding HDSL signal is transmitter to corresponding output.
Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently it is intended that the claims be interpreted to cover such modifications and equivalents.
