DE4437417A1 - Method for monitoring digital signal connections - Google Patents

Abstract

In a method for monitoring bidirectional digital signal connections between a starting point and an end point in each direction of transmission, the transmission quality is determined with the aid of additional information also transmitted in in each case one direction of transmission and the result is transmitted as message in the other direction of transmission. To monitor the state of quality, errors are detected in each case at the endpoint by comparing additional information items relating to the quality at the starting point with quality information items obtained at the endpoint, which errors are accumulated over a predetermined time interval to form an error sum which is assessed. The result of this assessment is transmitted to the starting point as message. To monitor for correct switching-through, a starting point identification is added to the message which is compared at the endpoint with a starting point identification to be expected which has previously been reported to the endpoint. A mismatch is signalled back and the outgoing signal is replaced by an alarm indication signal (AIS). <IMAGE>

Description

The invention relates to a method for monitoring bidirectional digital signal connections between one Starting point and one end point per transmission direction, the transmission quality in each case one Transmission direction with the help of co-transmitted Additional information is determined and the result in the other transmission direction is transmitted as a telegram.

For monitoring subsections of Digital signal connections were made for the synchronous digital Hierarchy (SDH) the procedure of tandem connection Monitoring proposed (CCITT Recommendation G.803). For this becomes a byte of existing overhead as a tandem Connection overhead (TCOH) that defines itself that distinguishes it, unlike the rest Overhead bytes at the beginning of the digital signal connection formed and evaluated at the end of the marriage Intermediate points may be changed. For the real one Monitoring method has been proposed so far TCOH byte in two halves of 4 bits to share. At the beginning of the section to be monitored, the state of Determined connection and via a corresponding code in one half of the TCOH byte towards the end  transfer. The remaining 4 bits of TCOH are intended as Data channel can be used.

To date, two methods have been used for the use of the data channel proposed. A proposal includes usage based on an HDLC transmission protocol. This is it a very comfortable and flexible procedure. The However, protocol handling requires HDLC controllers, a Circumstance, the use of this method for Lower bitrate connections considered inappropriate appears because of the multitude of Digital signal connections z. B. on one hochbitratigen interface card accumulate, too unacceptably high cost. To avoid this Problems became as second procedure a use of the Data channels with the simplest messages by setting individual Bits, but in its scope of information and its flexibility is extremely limited and therefore neither the present nor future requirements for a Monitoring procedure is sufficient.

The purpose of the invention is to provide a method of monitoring the quality state of digital signal connections to propose, in which the data channel described above better than the known proposals, one good assessment of the quality status is possible and that still be realized with little technical effort. This is achieved by monitoring the Quality status at each endpoint by comparing Additional information showing the quality at the starting point with quality information obtained at the end point Errors are detected that the detected errors on a summed up period to a total error be that the error sum is evaluated and that the Result of this evaluation as a telegram to the starting point is transmitted.  

The procedure is designed so that only a few data (the 4 Bit status information about the initial state (IEC) as well the determination of the connection status at the end of the section) in Frame clock of the transmission system (eg 8 kHz at SDH), d. H. must be realized by hardware implementation. Subsequent processing can then be performed in the time frame T (eg 1s), so much slower for many channels, with a common processor.

Furthermore, the length of the telegram to one Maximum value (Lmax) limited. For received telegrams must therefore only the telegram start recognition and the Storage in a telegram receive memory of the length Lmax done individually for each channel. The same applies to the transmit memory with the length Lmax and the read out the transmission memory. For the processing itself stands the common processor acting on the receive and Transmitter memory accesses the period T available.

Future extensions are possible as it is a protocol-oriented procedure and additional Information content can be defined.

By the measures listed in the dependent claims are advantageous developments and improvements in the Main claim specified invention possible.

Monitoring for correct switching is according to a Development of the invention thereby possible that the Telegram an initial point identification is attached, those in the endpoint with a previously communicated to the endpoint expected starting point identification and that a mismatch is reported back and that outgoing signal replaced by an alarm indication signal (AIS) becomes.  

However, it may also be independent of the main claim measures to transfer the assessed Quality information to be provided at the starting point, that for monitoring for correct switching of the telegram an initial point identification is attached, that the Starting point identification in the end point with a previously the Endpoint communicated expected Starting point identification is compared and that a Noncompliance is returned and the outgoing Signal is replaced by an alarm indication signal (AIS).

An embodiment of the invention is in the drawing illustrated by several figures and in the following Description explained in more detail. It shows

Fig. 1 is a greatly simplified representation of the start and end points of a bidirectional digital signal connection (tandem connection) with a control device (Tandem Connection Controller),

Fig. 2 is a detailed illustration of the start and end points,

Fig. 3 is a schematic representation of the method steps at the initial point,

Fig. 4 is a schematic representation of the method steps at the end point,

Fig. 5 is a table of various signals and functions at different points of the digital signal connection,

Fig. 6 to Fig. 8 structures of various telegrams,

Fig. 9 shows a digital signal connection during writing of start point addresses (source addresses) by the tandem connection controller and

Fig. 10 shows a digital signal connection during the checking of the connection through the Tandem Connection Controller.

In the following description will be various International standard abbreviations used in the following are listed:

A Adaption Function AIS Alarm Indication Signal AU Administrative Unit GDP Bit Interleaved Parity DEC Differential error count DL (Tandem Connection) Data Link DSI Differential signal information EF Error Free Second IT Errored Second HO Higher order HOC Higher Order Connection IEC Incoming Error Count LO Lower Order LOC Lower Order Connection LOP Loss of pointers OEC Outgoing Error Count OSI Outgoing signal information SES Severely Errored Second sk Sink So source TCC Tandem Connection Controller TCM Tandem Connection Monitoring (function block)   TCOH Tandem Connection Overhead TCSC Tandem connection set up controller TT Trail Termination Function TU Tributary Unit VC Virtual Container Z5 Network Operator Byte Z5 Z6 Network Operator Byte Z6

The method according to the invention shows a possibility of tandem connection monitoring (TCM) by forming a sublayer according to CCITT recommendation G.803 both for higher order connections (VC3 / VC4) and for lower order connections (VC12). The necessary functional blocks TCM source, TCM sink, TC controller and their arrangement in the network architecture are shown in FIGS. 1 and 2

Fig. 1 illustrates a tandem connection TC to be monitored. This can be of any length. At the beginning and at the end point of the TC, a monitoring circuit TCM source 1 , 2 and a monitoring circuit TCM sink 3 , 4 are respectively provided. TCM Source 1 inserts 4 bits DL and IEC into the Z5 and Z6 bytes, respectively, in the data stream to be transmitted from left to right. IEC refers to the number of parity violations already arriving at the TCM source 1, while DL is supplied to the TCM source 1 from the TCM sink 3 and among other things - as explained later - characterizes the quality of the right-to-left signal transmission.

The TCM sink 3 determines this transmission quality and sets the byte Z5 or the byte Z6 to 0, before the outgoing signal leaves the TC. The same functions are fulfilled by the TCM source 2 and the TCM sink 4 . A TC monitoring circuit (Tandem Connection Controller = TCC) 5 is used to set up and monitor the digital signal connection.

This contains a TCSC = tandem connection set up controller 6 and a TC monitor 7 . When setting up a digital signal connection, the source addresses are forwarded to the TCM-Sinks 3, 4 from the TCSC 6, wherein the switch shown schematically 8, 9 are placed in the lower position. As will be explained in more detail later in connection with FIGS. 7 to 10, an advantageous monitoring of the digital signal connection TC is thereby possible.

The monitoring of the quality state is explained in more detail below with reference to FIG. 2, which shows the TCM source 1 , 2 and TCM sink 3 , 4 in more detail than FIG . The digital signal to be transmitted is supplied to the TCM source 1 at 11 . By an evaluation of the bit parity known per se, a sum of the parity violations (error sum) IEC of the incoming signals is formed at 12 and inserted into bits 1 to 4 of the byte Z5 or Z6 of the signal to be transmitted. In the TCM sink 4 , the error sum, which is called OEC, is then formed at 14 in the same way, since it relates to the end or the output of the TC. In addition, at 14, the difference DEC between the two error sums OEC and IEC is formed, which indicates the number of errors arising within the TC. Both sums DEC and OEC are analyzed at 15 .

A counter is used to record the number of erroneous frames occurring within one second. By means of evaluation logic, a statement is then made about the quality of the signal at the TC end and the transmission quality within the TC. The result of this evaluation is stored in a second register 16 and transmitted within a query routine via a special data channel (DL) assigned to the TC every second as a status report to the TCC 5 . At the same time, this data channel is used for the transmission of the TC path trace, which was stored as an address during the installation of the TCM sink at 17. Furthermore, the DL is still used for setting the source addresses at the TC end by means of the function to be explained TCSC (TC device).

The TCM source 2 and the TCM sink 3 are similar to the TCM source 1 and the TCM sink 4 . Their parts are therefore provided with the same reference numerals.

For monitoring the TC, a byte in the POH is newly defined as Tandem Connection Overhead (TCOH) defined.

The proposed solution refers to the CCITT Study Group XVIII. Rep. R106. This is the Z5 byte (HOC), the Z6 byte (LOC) acc. G.709 and the NR byte according to ETSI / TM 3007 used as TCOH.

The TCOH has the following tasks, which are described in more detail below to be discribed:

• - Transport of the counting result already at the starting point the digital signal connection incoming error IEC from Start point to the end point of the digital signal connection - im following also called Tandem Connection = TC,
• - Formation of the "Data Link" (DL) for the transmission of the Status report and TC path trace.

In Fig. 3, the formation of the IEC is exemplified at a VC3 / VC4 as the source signal 21 . The present signal quality at the beginning of a TC is determined by the number of code violations. This number is obtained by a parity bit evaluation 22 (BIP8 check or BIP2 check) over a given frame and a subsequent comparison of the thus obtained BIP code BIP8 (VC3 / VC4) with the content of the corresponding POH byte B3 (POHVC3 / VC4) of the next frame at 23 . The result of this operation represents the IEC, is inserted at 24 into bits 1 to 4 of the TCOH (Z5 byte) and transmitted at 25 as the new VC3 / VC4 to the end point. The byte B3 is linked with the new byte Z5 to a byte B3 *. For a VC12 source signal, the B3 byte (BIP8) from the POH of the VC3 / VC4 is replaced by the V5 byte (bits 1 and 2 , BIP2) from the POH of the VC12.

At the end of the TC ( Figure 4), a parity bit check 26 of the incoming signal 27 is again performed and at 28 the determined code word is compared with the corresponding parity byte of the POH. The result of this comparison is called OEC.

As part of an error analysis 29 , the OEC determines whether bit errors have occurred during transmission or whether a defect (AIS, LOP) has occurred. If a defect is detected, this is supplied to the evaluation logic 30 and recorded in a second register 31 . If bit errors are detected (OEC ≠ 0), a counter 32 is incremented. The meter reading is polled every second. Subsequently, the counter 32 is reset. The count (= number of erroneous frames) is the evaluation logic 30 supplied, which determines the quality of the examined second interval as follows:

Count / defect specified quality 0 EF = Error Free Second <30% of examined frame or detected defect ES = Error Second 30% of examined frame or detected defect Second SES = Severely Errored

The result of this determination is recorded in the OSI second register 31 . This is dimensioned so that the quality statement for the last three seconds intervals is recorded. The content of the second register is returned as Outgoing Signal Information (OSI) via the Data Link in the TCOH of the opposite direction. The OSI describes the state of the signal leaving the TC.

The OEC will also be available at 33 with the one included in the TCOH IEC compared. The result of this operation is called DEC indicates and indicates the number of code violations that within the TC.

The further processing of DEC takes place analogously to the further processing of OEC described above by means of an error analysis 34 and a counter 35 . The storage of the result takes place in the DSI second register 36 , which is executed analogously to the OSI second register 31 . The DSI describes the transmission quality within the TC and is also reported back to the starting point.

The necessary in describing the TCOH Parity bit matching (B3-B3 *) is done according to known Method. Since the BIP check each about the content of a entire VC (including the overhead), this leads Registered IEC or DL in the TCOH (Z byte) a change in the GDP code. That at the beginning of a path formed B3 byte (or V5, bit 1 and 2) must therefore be adapted to make a subsequent BIP check a correct one Result leads. This adjustment is done via a "Exclude-OR" the following overhead byte contents: original Z5 (Z6) of the present frame new Z5 (Z6) for the current framework (TCOH) original B3 (V5) of the following frame.  

The result of this join is the matched byte B3 * for the following frame.

If, at 37 ( Figure 4), the TCOH is reset at the end of the TC (all bits to zero), then the B3 or V5 byte must be changed or compensated again.

The data OSI, DSI are combined in a telegram ( FIG. 6) and transmitted to the associated TCM source ( FIG. 3). There they are inserted at 24 into bits 5 to 8 of the Z5 byte.

Basically, the following states can be monitored a TC occur:

• - undisturbed transmission (possibly with bit errors)
• - faulty transmission with defect before TC
• - Disturbed transmission with defect in the TC The occurring cases with the assigned values for OSI and DSI are compiled in FIG .

The data link (TCOH bits 5 to 8 ) handles three different data transfers:

• Transmission of the TC status report between the TC ends, as described in connection with FIGS. 2 to 4 (telegram structure in FIG. 6).
• - Transmission of the path trace setpoints (source addresses) from the TCC function to the TC ends (TCM function) when setting up a TC (telegram structure in Fig. 7).
• - Feedback on the stored "Expected Start Address" (telegram structure in Fig. 8).

The TC status report ( Figure 6) consists of the TC path trace and the contents of the second registers for OSI and DSI, which contain the values of the last three seconds. A query routine reads the contents of the registers, summarizes the path trace information in a standard telegram and sends them once per second via the Data Link. Using the function TC monitor 7 ( FIG. 1), the values for OSI and DSI can then be read out of the DL at any desired location and sent for further processing. Since the OSI and DSI values are transmitted three times for one second interval, it is possible to correct erroneous transfers by a majority vote.

Since only one telegram per second is transmitted may allow processing of data transmitted in the data channel Data in a comparatively slow cycle and thus for many TCs done by a common processor.

Each time the TC standard telegram is transmitted, a comparison of the transmitted trace identifier with preset source addresses takes place in the TCM function at the TC end. If no match is detected, the error message "TC Path Trace Mismatch" is generated. The received signal is not forwarded but sent to AIS ( Figure 5).

FIG. 5 shows signals occurring in the form of a table in the method according to the invention at different or at different points of a TC occurring defects. In column a, various possible signals are indicated at the input of the TC, namely a valid AU or TU, an alarm indication signal AIS or an error signal LOP. According to column b, in the case of the arrival of AIS or LOP at the starting point TC, an AU or TU is generated. If there is already a valid AU or TU, the compensation of the GDP takes place according to column c.

The IEC code sent by the TCM source for the cases listed is shown in column d. It is 0 to 8 depending on the number of incoming errors, 15 in the case of an AIS and 14 in the case of an LOP in the starting point. At the end point of the TC (TC sink), a valid AU or TU can be present in all three cases or one of the signals AIS or LOP can occur. In the case of a valid AU or TU, there is still the alternative shown in column f that there is a false connection (trace mismatch) or not.

Column g then shows the values possible for OEC at the end point of the TC between 0 and 8. Column h shows the various possibilities of the OSI byte. The columns i and k show the corresponding values or bytes for DEC or DSI. Stars mean that there are different possibilities depending on the result of the error analysis. If the sixth bit of the OSI byte is 1, the transmission is defective, so AIS is used in column 1. However, if the sixth bit is 0, then there is a valid AU or TU with the quality characteristics indicated by bits 7 and 8 . In this case, compensation is made according to column m BIP. Column n then shows the signal leaving the TC.

When a TC is established, the endpoints of the connection must be told from which sources they should receive a signal so that the correct routing of a path can be checked during transmission. The setting of these source addresses in the TC ends is done with the TCSC function 6 ( Figure 1) via the DL. The telegram according to FIG. 7 is sent out by the TCSC function in the configuration according to FIG . This causes the corresponding TCM function 41 , 42 ( Figure 9) to store the transmitted 16-byte string as the "expected source address". The correct storage is confirmed by returning the telegram as shown in FIG. 8. After switching through the TC according to FIG. 10, the end points start to send the telegram according to FIG. 6. The start signal for this is the non-receipt of a telegram according to FIG. 7 for more than three seconds.

The TC monitor function 7 monitors the Z5 / Z6 byte and makes the information contained in the Data Link DL available to the responsible network management. The TC monitor function 7 together with the TCSC function 6 forms the Tandem Connection Controller (TCC) 5 .

The TCM function will be in two different Split sub-functions that either editing a digital signal accepted at a network boundary (TCM source) or one to be transferred to a network boundary Accept digital signal (TCM sink).

These subfunctions are subdivided into one Adaptation and a termination function, each for a transmission direction is the processing of a Take over digital signal.

The TCM source adaptation has the following tasks:

• - Transparent transmission of the digital signal to the TCM source termination function when a virtual Container of higher or lower order with valid Frame start has been received.
• - Detecting an error signal (AIS, LOP) and generate a substitute signal with valid pointer (Pointer) and valid B3 byte for a virtual container higher Order or V5 byte in a virtual container low order. The remaining POH and the useful content are set to "1".

The formation of the TCOH takes place in the TCM source termination function and includes the following Tasks:

• - For VC4 level digital signals, the BIP-8 value, for Digital signals of the VC12 level of the BIP-2 value are calculated.
• - The calculated BIP value is compared with the contents of the B3 byte or V5 byte (bits 1 and 2 ) of the following frame and the result of the comparison is inserted in bits 1 to 4 of the Z5 / Z6 byte.
• - Bits 5 to 8 of the Z5 / Z6 byte use the "TCM Data Link" coming from the TCM sink function.
• - The B3 byte (V5 byte) for the previous frame becomes decoupled, adapted and reinserted.

Subsequently, the digital signal is forwarded.

The TCM sink termination terminates the TCOH and comprises doing the following tasks:

• - For VC4 level digital signals, the BIP-8 result, for level VC12 digital signals, the GDP-2 result calculated and recorded in a register (OEC).
• - The calculated GDP result is measured with the IEC in the Z5 / Z6 byte compared and the result in another register arrested (DEC).
• - The content of the two registers (OEC and DEC) becomes one Evaluation supplied and leads to the formation of the Status report.
• - The TC path trace transmitted in the Z5 / Z6 byte is detected and combined into a 16-byte block. By comparison A target value is used to detect a TC path trace mismatch become.
• - One transmitted in the data link of the Z5 / Z6 byte "TC Path Trace Set up Command" is detected and the subsequently transmitted address as setpoint for the TC path trace saved in a register.
• - The Z5 / Z6 byte is output at the TC Termination sink function set to "0" and the corresponding B3 byte (or V5 byte) also reset (i.e., re-adjusted).
• - Will the evaluation of IEC and OEC a defect (AIS / LOP) or a TC path trace mismatch is detected the digital signal in the TCM sink termination function terminates and to the TCM sink adaptation an information Hand over "AIS".

The TCM sink adaptation has the following tasks:

• Transparent passage of one of the TCM sink termination coming digital signal when the Signal not terminated in TCM sink termination is.
• - Sending AIS when the digital signal in the TCM sink termination terminated and information "AIS" was detected.

Claims (9)

1. A method for monitoring bidirectional digital signal connections between a starting point and an end point per transmission direction, wherein the transmission quality is determined in each case a transmission direction with the help of co-transmitted additional information and the result is transmitted in the other transmission direction as a telegram, characterized in that for monitoring the Quality status in each case at the end point by comparing additional information concerning the quality at the starting point are detected with the quality information obtained at the end point error that the detected errors over a given period are added up to a total error, that the error sum is evaluated and that the result of this evaluation is transmitted as a telegram to the starting point. 2. The method according to claim 1, characterized in that the predetermined period is at least one second. 3. The method according to any one of the preceding claims, characterized in that the evaluation in, preferably three, stages are done. 4. The method according to any one of the preceding claims, characterized in that the division of the steps to ITUT TSS Recommendation G.826. 5. The method according to any one of the preceding claims, characterized in that the additional information  Bit parity information is that as another Additional information transmit the error sum at the starting point is that at the end point, the difference between the Error sum at the end point and the transmitted error sum is formed and evaluated and that the weighted difference within the telegram is transmitted to the starting point. 6. The method according to any one of the preceding claims, characterized in that the telegram a Starting point identification is attached. 7. The method according to claim 6, characterized in that the starting point identification in the endpoint with a before the endpoint communicated to be expected Starting point identification is compared. 8. The method according to claim 7, characterized in that a mismatch is returned and that outgoing signal replaced by an alarm indication signal (AIS) becomes. 9. Method for monitoring bidirectional Digital signal connections between a starting point and one endpoint per transmission direction, the Transmission quality in each direction of transmission determined with the help of co-transmitted additional information and the result in the other direction of transmission is transmitted as a telegram, characterized in that for monitoring for correct switching of the telegram an initial point identification is attached, that the Starting point identification in the end point with a previously the Endpoint communicated expected Starting point identification is compared and that a Noncompliance is returned and the outgoing Signal is replaced by an alarm indication signal (AIS).