JP3295834B2 - Time division multiplex data receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time division multiplexed data receiving apparatus, and more particularly to an ISDN (Integrated State).
Services Digital Network)
The present invention relates to a time-division multiplexed data receiving apparatus that establishes multi-frame synchronization in layer 1 of a protocol and detects frame errors in layer 2 of the protocol.

[0002]

2. Description of the Related Art Generally, a communication control device has a function of multiplexing data transferred from an information processing device and transmitting the multiplexed data to a communication line, and a function of restoring multiplexed data received from the communication line and transferring the multiplexed data to the information processing device. have. When receiving data from a communication line, even if there is an error in the restored data, the data is transferred to the information processing device as valid data as long as the data is synchronized with the line.

As a prior art, ITU-T (Intern)
national Telecommunication
Union-Telecommunication
Standardization Sector) Recommendation I. The frame synchronization specified in layer 1 (the first layer) of the ISDN primary rate user network interface conforming to H.431 will be described.

FIG. 5 shows the frame structure of the layer 1 of the ISDN primary rate user network interface, and FIG.
Each of the layer 1 multi-frame configurations of the primary rate user network interface is shown.

[0005] The layer 1 defines the electrical and physical conditions, and the primary rate user network interface defines a frame configuration for bit transmission and a method for establishing frame synchronization. Also, a layer 2 described later
(Layer 2) specifies a procedure for realizing efficient and high-quality data transfer. In the primary rate user network interface, a high-level data link control procedure: HDLC (High level Data)
Link control procedure) is defined.

In FIG. 5, a frame of a layer 1 is 1
It is composed of F bits having a 93-bit length, followed by 24-bit time slots 2a to 2x. Each of the time slots 2a to 2x is composed of consecutive 8 bits. These time slots 2a to 2x all indicate multiplexing units called channels. One channel is assigned to an integer number of time slots, and occupies the same time slot position for each frame.

In FIG. 6, a multi-frame is composed of 24 frames, and each frame has F bits corresponding to the multi-frame number. A multi-frame synchronization signal FAS (Frame Alignnm) of a binary pattern “001011” formed by F bits every four frames
ent Signal) to achieve frame synchronization. In the figure, bit m is maintenance information, and bits e1 to e1.
e6 is a CRC (Cyclic Redundancy)
(Check) operation is error control information for error detection.

In the data multiplexed in the ISDN primary rate user network interface, 24 frames defined by a multi-frame repeatedly appear on a line. In order to achieve frame synchronization with the multiplexed data, it is necessary to detect a multi-frame synchronization signal formed of F bits every four frames. As long as the multi-frame synchronization signal can be correctly detected, the data in the time slot is valid because the frame is synchronized.

[0009] Here, if an error occurs in the multi-frame synchronization signal, the synchronization is lost. However, it is necessary to make it appear that the synchronization is continuously established for a temporary error of the multi-frame synchronization signal due to a bit error or the like. Therefore, the multi-frame synchronization signal is monitored a specified number of times, and the loss of synchronization is detected based on the result of the monitoring. That is, when the multi-frame synchronization signal is continuously incorrect beyond the specified number of times, it is determined that the synchronization has been lost, and the data in the time slot is invalidated. For example, if the multiframe synchronization signal is incorrect three consecutive times, it is treated as out of synchronization, and the data in the time slot is invalidated.

[0010]

As described above, in the conventional apparatus, the multiframe synchronization signal is monitored a specified number of times, and it is determined whether or not the synchronization has been established based on the monitoring result. Therefore, it is not possible to determine that the synchronization has been lost unless the multi-frame synchronization signal is monitored a specified number of times. Therefore, when the synchronization is actually lost, the data received during the monitoring cannot be invalidated. . Therefore, the layer 2 may receive a large amount of invalid HDLC frames generated due to the loss of synchronization.

Unless a loss of synchronization is detected in the layer 1, this invalid HDLC frame is treated as valid data. Therefore, there is a disadvantage that invalid data is transferred to the information processing apparatus.

Incidentally, the bit synchronization circuit described in Japanese Patent Application Laid-Open No. 4-10725 discloses a FIFO (First)
In First Out) This relates to non-multiplexed data in which the received data stored in the memory and the pseudo frame synchronization signal can be directly compared. Therefore, the above-mentioned loss of synchronization of the time division multiplexed data cannot be detected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the prior art, and has as its object to receive time-division multiplexed data capable of discarding invalid data generated due to loss of synchronization of the time-division multiplexed data. It is to provide a device.

A time division multiplexed data receiving apparatus according to the present invention provides an ISDN (Integrated Service).
In a time division multiplexed data receiving apparatus that establishes multi-frame synchronization in layer 1 of the Digital Network (Digital Network) protocol,
Error detecting means for detecting error of error control information included in the frame and calculating the error by detecting the error control information in the frame; and N times (N: An integer of 2 or more, the same applies hereinafter) frame out-of-synchronization detecting means for detecting multi-frame out-of-synchronization when continuously detected, and detecting the multi-frame out-of-synchronization by the frame out-of-synchronization detecting means, and then returning to the multi-frame synchronization established state It is characterized by including a frame discarding means for discarding a frame received until then. In this case, the layer 1 and the layer 2 are preferably layers 1 and 2 of an ISDN temporary group rate user network interface, and the frame in the layer 2 is HDLC (High).
level Data Link Control p
(frame).

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation of the present invention is as follows.

When the synchronization is lost, an erroneous HDLC frame may be continuously received at Layer 2. For this reason, the erroneously received HD
A threshold value is set for the number of LC frames, and when the threshold value is reached, it is determined that the synchronization has been lost, and the data is discarded.

Next, an embodiment of the present invention will be described with reference to the drawings. In this example, the case of the H11 channel of the ISDN primary rate user network interface will be described. The H11 channel is assigned to slots 1 to 24 in the frame.

FIG. 1 is a block diagram showing the configuration of an embodiment of a time division multiplexed data receiving apparatus according to the present invention. In the figure, a communication control device 6 converts data transferred from an information processing device 5 into an HDLC frame by a layer 2 HDLC frame transmitting / receiving circuit 8, multiplexes the data in a layer 1 data multiplexing / restoring circuit 9, and transmits the data to a communication line 7. .
The data received from the communication line 7 is restored as data in the layer 1 data multiplexing / restoring circuit 9.
Then, the HDLC frame is recognized by the layer 2 HDLC frame transmitting / receiving circuit 8, and the data in the frame is transferred to the information processing device 5.

FIG. 2 is a diagram showing a relationship between a layer 1 frame and data allocated to a channel. In the figure, data 12 on the line of the ISDN primary rate user network interface is represented by repetition of frame 1 composed of F bits 4 defined in layer 1 and 24 time slots 2a to 2x. Since the H11 channel is assigned time slots 2a to 2x of frames 1 to 24, all the time slots 2a to 2 except F bit 4 are kept while frame 1 is synchronized.
The bit string of x is received as valid data 13.

FIG. 3 is a view showing how the restored data looks when the channel data is transmitted as multiplexed data to the line and the synchronization is lost due to the occurrence of noise. In the figure, when data is transmitted from a communication partner, the communication partner transmits data 14a.
Before and after the binary pattern “0111” called a flag 15
An HDLC frame 16a into which “1110” is inserted is created. Until the HDLC frame 16b including the next data 14b appears, the flag 15 is inserted between the HDLC frames 16a and 16b.

The bit string 20 thus created
Is multiplexed into all the time slots 2a to 2x, and is transmitted as multiplexed data 21 to which F bits 4 are added.

The multiplexed data 21 contains noise 17
Occurs, misreading of data occurs. In general, since the noise 17 appears over a plurality of frames, a misread occurs in the F bit 4 forming the multi-frame synchronization signal, which causes a loss of synchronization.

In order to detect an out-of-synchronization in the layer 1, the multi-frame synchronization signal must be consecutively incorrect for a specified number of times.
Need to be monitored.

Even during this monitoring, many misreads of data occur in the time slots 2a to 2x. The time slots 2a to 2x of the H11 channel are also extracted from the multiplexed data 21 and the bit string 22 is read. At the time of restoration, misreading occurs in the data 18a and 18b of the HDLC frame.

Here, the data 18a and 18b include an error detection bit string for HDLC frame inspection. Since an error is detected by this error detection bit sequence or the error detection bit sequence itself is misread, H including the data 14c recognized by the layer 2 is used.
It can be seen that there is an error in the DLC frame 16c and the HDLC frame 16e including the data 14e.

When data is misread in the flag 19a, the layer 2 recognizes the HDLC frame 16d by the normal flags 15 before and after the misreading. In this case, the portion of the data 14d is a portion of the data 14d formed by misreading the flag 19a, and thus no error detection bit string is added. Therefore, this H
It can be seen that there is also an error in the DLC frame 16d.

As described above, when a loss of synchronization occurs,
An erroneous HDLC frame may be received continuously. Focusing on this point, the present invention sets a threshold value for the number of consecutive erroneous HDLC frames, and when the threshold value is reached, it is determined that the synchronization has been lost, and the data received thereafter is invalidated. .

FIG. 4 is a flowchart showing the operation of the out-of-synchronization detecting section 11 in FIG. That is, each time the out-of-synchronization detecting unit 11 receives the HDLC frame,
The data transfer to the information processing device 5 is controlled by performing the operation shown in FIG. FIG. 4 shows an operation when the above-described threshold value is set to “2”. Hereinafter, when an error-free HDLC frame is received when no out-of-synchronization has occurred, when an out-of-synchronization has not occurred, an HD having an error due to a bit error is received.
When only one LC frame is received, and when layer 1
In the case where two out-of-sync HDLC frames are received continuously due to out-of-synchronization which have not detected out-of-sync, the respective operations will be described.

Operation When Receiving an HDLC Frame Without Error When Synchronization Has Not Occurred When an HDLC frame is received, the synchronization is not detected and the HDLC frame has no error.
The count value of the LC frame counter 10 is cleared to “0” (steps 23 → 24 → 26). Then, the received data of the HDLC frame is transferred to the information processing device 5 (step 31).

Operation when only one HDLC frame having an error due to a bit error is received when no out-of-synchronization occurs. When an HDLC frame is received, no out-of-synchronism is detected, but an error is detected in the HDLC frame. HDL
The count value of the C frame counter 10 is incremented by "1" (steps 23 → 24 → 25). At this time, HDLC
Since the count value of the frame counter 10 has not reached the threshold value “2”, the data of the received HDLC frame is transferred to the information processing device 5 (step 25).
→ 27 → 31).

Although the out-of-synchronization is not detected in the layer 1, H which has an error due to the out-of-synchronization that has already occurred.
Operation when Two DLC Frames are Received Consecutively First, when the first HDLC frame is received, no out-of-synchronization is detected. However, since the HDLC frame has an error, the count value of the HDLC frame counter 10 is reduced. “1” is added (steps 23 → 24 → 25). Here, since the count value of the HDLC frame counter 10 has not yet reached the threshold value “2”, the data of the received HDLC frame is transferred to the information processing device 5 (steps 25 → 27 → 31).

Subsequently, when the second HDLC frame is received, no out-of-synchronization is detected, but the HDLC frame contains an error.
"1" is added to the count value of 0 (step 23 → 2
4 → 25). At this time, the HDLC frame counter 10
Has reached the threshold value "2", the count value of the HDLC frame counter 10 is first cleared to "0" (steps 25 → 27 → 28).
As a result, the synchronization loss can be detected (Step 29), and the received HDLC frame is discarded (Step 30). The discard of the HDLC frame is continued until the next multi-frame synchronization is established.

When the out-of-synchronization of the multiframe is detected in the layer 1, the received HDLC frame is discarded (steps 23 to 30).

Here, the smaller the threshold value of the number of HDLC frames is, the faster the loss of synchronization in layer 1 can be detected, and more invalid frames can be discarded. If the threshold value is set to “2” as described above, the fastest detection is possible.

As described above, in the conventional apparatus, the out-of-synchronization occurring in the layer 1 cannot be immediately detected, and thus invalid data cannot be discarded until the out-of-synchronization is detected. Can be detected quickly and more invalid data can be discarded.

In the above description, the case of layer 1 and layer 2 of the ISDN primary rate user network interface has been described. However, the present invention is applied to the case of layer 1 and layer 2 of the ISDN secondary rate user network interface. Clearly what you can do.

The present invention can take the following aspects in connection with the description of the claims.

(1) The time-division multiplexed data receiving apparatus according to any one of claims 1 to 4, wherein N is 2.

[0039]

As described above, the present invention provides an ISDN
In a time division multiplexed data receiving apparatus that establishes multi-frame synchronization in layer 1 of a protocol and detects errors in a frame in layer 2 of the protocol, after detecting an error of a frame received in layer 2 N times consecutively, Discarding the received frame has the effect that the loss of synchronization can be quickly detected and more invalid data can be discarded.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a time division multiplexed data receiving device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a layer 1 frame and data allocated to a channel.

FIG. 3 is a diagram showing how to view restored data when channel data is transmitted to a line as multiplexed data and synchronization is lost due to noise;

FIG. 4 is a flowchart showing an operation of an out-of-synchronization detecting unit in FIG. 1;

FIG. 5 is a diagram showing a layer 1 frame structure of an ISDN primary rate user network interface.

FIG. 6 is a diagram illustrating a layer 1 multi-frame configuration of an ISDN primary rate user network interface.

[Explanation of symbols]

 Reference Signs List 5 information processing device 6 communication control device 7 communication line 8 layer 2 HDLC frame transmitting / receiving circuit 9 layer 1 data multiplexing / restoring circuit 10 HDLC frame counter 11 out-of-synchronization detecting section

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04Q 11/04 304

Claims (3)

(57) [Claims] 1. An ISDN (Integrated Se)
In a time-division multiplexed data receiving apparatus that establishes multi-frame synchronization at layer 1 of a RMS (Digital Networks) protocol, error control information for error detection included in the frame is detected and calculated at layer 2 of the protocol, and a frame error is detected. An error detecting means for performing detection, and a frame synchronization for detecting a loss of multi-frame synchronization when N-times (N is an integer of 2 or more, the same applies hereinafter) consecutively detecting errors of a frame received in Layer 2 in a multi-frame synchronization established state Time-division multiplexing, comprising: an out-of-frame detection unit; and a frame discarding unit that discards a received frame until the multi-frame synchronization is established again after the out-of-frame detection is detected by the out-of-frame detection unit. Data receiver. 2. The method according to claim 1, wherein the first and second layers are ISDN.
2. The time-division multiplexed data receiving apparatus according to claim 1, wherein the apparatus is a layer 1 and a layer 2 of a temporary group rate user network interface. 3. The frame in the layer 2 is HD
LC (Highlevel Data Link Co)
3. The time-division multiplex receiving apparatus according to claim 1, wherein the time-division multiplex receiving apparatus is a frame (control procedure) frame.