KR20010087609A - Interworking unit between atm and pstn trunk - Google Patents

Abstract

PURPOSE: An interworking unit(IWU) between ATM-PSTN trunks is provided to improve the transmission efficiency of ATM cell information in traffic load region except for a maximum load capacity region by mapping only valid channel among frames of a PSTN trunk to a payload. CONSTITUTION: An ATM line interface(10) transmits and receives an ATM cell with an ATM network. An IWU transmitter(11) generates an FP(Frame Pointer), an FSN(Frame Sequence Number), and an FS(Frame Status), maps an E1 frame to the ATM cell, and transmits the E1 frame to the ATM line interface(10). A controller(12) controls an entire operation of an IWU and controls each composition block. An IWU receiver(13) receives the ATM cell from the ATM line interface(10), divides the FP, the FSN, and the FS, and divides the ATM cell as the E1 frame. An E1 line interface(14) is connected with a PSTN for transmitting the E1 frame to the IWU transmitter(11) and receives the E1 frame from the IWU receiver(13) to transmit the received E1 frame to the PSTN.

Description

ATM-PYTIEN Trunk Interlock {INTERWORKING UNIT BETWEEN ATM AND PSTN TRUNK}

The present invention relates to an interworking device between an Asynchronous Transfer Mode (ATM) -Public Switched Telephone Network (PSTN) trunk, and in particular, by mapping only active channels actually used in a frame of a PSTN trunk to an ATM cell payload. The present invention relates to an ATM-PSTN inter- trunk interworking device that improves the effective information transmission efficiency and maintains the continuity of frames at the receiving side by displaying the usage status of each channel in the frame during the frame mapping.

Since the standardization of Broadband-Integrated Service Digital Network (B-ISDN) and ATM has been standardized, the ATM network is rapidly spreading, and it takes much time for the ATM network to be converted to a complete B-ISDN. Therefore, various network interworking situation appears, so it must be able to support existing networks flexibly.

In particular, depending on the network situation, the interworking between the ATM network and the PSTN network is various, that is, the interworking between ATM and PSTN is inter-channel interlocking and per trunk interlocking method including up to the interworking of the signal and between the two interlocking points without the intervention of the signal. There is an interworking method for setting a semi-permanent data path.

The former is a method that supports interworking between the B-ISDN signal and the PSTN signal in the interworking device of ATM and PSTN, and the latter is a POTS (Plain & Old Telephone Service) network in ATM network without interlocking control plane. This is a way to support transparent paths.

The inter-channel interworking is that each channel of the PSTN is mapped to one ATM Virtual Path Identifier (VPI) / Virtual Channel Identifier (VCI) so that channel data can be directly cellized, and each channel of the PSTN is emulated by the VC of the ATM network. In addition, there are various such per-channel interworking methods depending on the cellization method.

That is, in order to reduce the cell delay, there are a method of filling only a part of a cell and a method of filling several different channels in one cell.

The interworking per trunk (line, T1, E1) is that one trunk of the PSTN is emulated by the VC or VP of the ATM network, and various advantages are realized by implementing the lower digital paths of the STM (Synchronous Transfer Mode) transmission network as the ATM VP. It is necessary when you want to get.

And, during the evolution to ATM networks, local exchanges must support both POTS and ATM services, which is one solution for hybrid regional exchanges to accommodate these two services. It is accommodated by STM and ATM exchange respectively.

Therefore, interworking is required between the STM and the ATM switch, and this interworking is implemented by inter-channel interworking and inter-trunk interworking.

As described above, interworking between ATM and PSTN is implemented by inter-channel interworking and inter-trunk interworking during the evolution into ATM networks.Trunk interworking between ATM and PSTN according to the conventional interworking of signals when inter-trunk interworking between ATM and PSTN The implementation of the device is very complicated and there is a problem that the efficiency of transmitting ATM cell information in the area of traffic load is reduced by transmitting the entire frame of the PSTN trunk.

In addition, when an error occurs in the channel data due to unexpected cell misinsertion or cell loss because the receiver does not perform processing for cell misinsertion or cell loss when interworking between ATM and PSTN, the transmitter transmits the error. There was a problem that can not maintain the flow of the frame.

That is, even through the sequence count processing algorithm using the SCF (Sequence Count Field) in the SAR-PDU, it is difficult to restore the flow of the frame to the original when one or more cells are lost by the SCF alone.

The present invention has been made to solve the above problems, and the object of the present invention is to establish a call in the frame of the PSTN trunk and map only the effective channels that are actually in use to the payload of the ATM cell. ATM-PSTN improves the efficiency of ATM cell information transmission in the area and displays the usage status of each channel in the frame when mapping the frame so that the receiver can recover the frame and maintain the continuity of the frame even in the case of cell loss. It is to provide inter-trunk linkage.

1 is a block diagram of a subscriber switching system to which the inter-trunk interworking device of the present invention is applied;

2 shows a protocol stack for interworking ATM and PSTN;

3 is a view showing an effective channel mapping method for use in an inter- trunk interworking device ATM-PSTN of the present invention,

4 is a view showing an effective channel mapping method using the frame status made in the ATM-PSTN inter- trunk interworking apparatus of the present invention,

5 is a view showing the structure of an ATM cell according to the effective channel mapping method using the frame state in the ATM-PSTN inter- trunk interworking apparatus of the present invention,

Figure 6 is a block diagram of an ATM-PSTN inter- trunk interworking device of the present invention,

7 is a detailed configuration diagram of the IWU TX of FIG. 6;

8 is a detailed configuration diagram of the IWU RX of FIG. 6.

<Explanation of symbols for main parts of drawing>

10: ATM line interface 11: IWU TX

12 Controller 13 IWU RX

14: E1 line interface 16: FPGM

17: FSNGM 18: FB

19: FSGM 20: OCM

22: SB 23: FPHDLR

24: FHEXTR 25: FSNHDLR

26: FSHDLR 27: Main Controller

ATM-PSTN inter- trunk interworking device of the present invention for achieving the above object, after generating an ATM line interface for exchanging ATM network and ATM cell, FP, FSN, FS to map the E1 frame to ATM cell IWU TX to send to ATM line interface, controller to control the overall operation of IWU, control each component block, ATM cell from ATM line interface, receive FP, FSN, FS, separate it into E1 frame And an E1 line interface connected to an IWU RX and a PSTN, transmitting an E1 frame to the IWU TX, and receiving an E1 frame decomposed from the IWU RX and transmitting the E1 frame to the PSTN.

Hereinafter, with reference to the accompanying drawings will be described in detail the configuration and operation of the ATM-PSTN inter- trunk interworking apparatus according to the present invention.

First, FIG. 1 is a block diagram of a subscriber switching system to which an ATM-PSTN inter- trunk interworking apparatus of the present invention is applied, and includes an STM switch 1 for receiving POTS and N-ISDN traffic and transmitting the same to an STM transmission network. Per-channel interworking unit 2 for interlocking traffic per channel, Per-trunk interlocking unit 3 for interlocking per- trunk POT and N-ISDN traffic accommodated by the STM switch 1, ATM traffic and per-channel interlocking unit ( It consists of an ATM switch 4 for accepting both the POTS traffic interlocked in 2), and the POTS and N-ISDN traffic interlocked in the interlocking unit 3 per trunk and transmitting them to the ATM transmission network.

As in the above configuration, in order to accept POTS traffic, the ATM switch 4 that directly accepts the ATM traffic has to perform per-channel interworking through the per-channel interlocking unit 2 or interlock the traffic from the STM switch 1 per trunk. do.

That is, since the ATM switch 4 directly intercepts and accepts POTS traffic per channel, it is expensive. Therefore, traffic from the STM switch 1 should be transmitted to the ATM switch 4 in association with each trunk.

As described above, the ATM-PSTN trunk interworking device according to the present invention is applied in per-trunk interworking between ATM network and POTS network, that is, ATM network and PSTN network.

2 is a diagram illustrating a protocol stack for interworking ATM and PSTN. The interworking between two networks is performed by a mapping function of a protocol stack, and a circuit emulation service interoperability characteristic of an ATM forum is shown. In the Interoperability Specification, the mapping function is divided into two types of circuit emulation services (CES), structured and unstructured.

The structured service is an ATM network emulating N × 64, E1 / DS1, E3 / DS3, etc. using AAL1's Structured Data Transfer (SDT) method, and the unstructured service is N × 64, E1 / DS1. It is a service that transparently transmits E3 / DS3 data streams as it is.

The interworking mapping function of the present invention is similar to the mapping function of the CES standard of the ATM forum released in January 1997. However, the interworking per trunk between ATM-PSTN, only the channel being used dynamically according to the usage status of the channel in the frame. Mapping to cells improves the utilization of cell transmission.

The CES of the ATM Forum mainly transmits N × 64, E1 / DS1, E3 / DS3, etc. in the structured or unstructured state, assuming the CES of the subscriber network. In the case of using the structured service, only N channels among all the channels in the frame are mapped to ATM cells, and in this case, only N × 64 is fixedly subscribed to the subscriber network, and the channels mapped to the cells are fixed by the manager plane. Is assigned.

In addition, an interworking scheme suggested by the recently announced ATM Forum Specification of Dynamic Bandwidth (DBCES) Utilization-In 64kbps Time Slot Trunking over ATM has been proposed. In this scheme, mask bits similar to the frame status are used. Therefore, it is a function to add N or less channels configured by mutual agreement in advance to the interworking device having CES function variably according to the situation.

The interworking device according to the present invention is a case where a public ATM network and a PSTN network interwork with each other, and a PSTN trunk dynamically changes the number of channels in a frame from a minimum number to a maximum number of channels according to time and is randomly used. The effective telegram transmission efficiency of the cell payload can be improved.

On the other hand, frame mapping includes direct mapping, effective channel mapping, and effective channel mapping using the frame status. First, in the case of direct mapping, AAL1 is an isochronous structure in a cell using a synchronous redundancy time stamp (SRTS) and an SDT scheme. Provides a technique for transferring data.

In the case of PSTN frames, all frames in the trunk can be mapped directly to the SAR-PDU using SDT, where the frame boundaries are distinguished using the P format of the AAL1 header.

This is the simplest technique for transmitting trunk data without using any other mapping scheme, treating it as a raw stream of bits, but transmitting the entire frame as it is, regardless of whether the channels in the frame are in use or not. Therefore, when the load of the trunk is small, the transmission efficiency of the valid information for the total cell throughput is low.

FIG. 3 is a diagram illustrating an effective channel mapping method for use in an ATM-PSTN inter-trunk interworking device of the present invention. In this effective channel mapping method, only channels being used among channels in a frame to improve cell transmission efficiency of an ATM cell. Each channel mapped in the payload, and mapped into this cell, consists of channel data and a channel label to identify each channel, as shown in FIG.

In this way the frame boundary is indicated using the SDT defined in Recommendation I.363, and the pointer in P format points to the first frame boundary appearing in that cell and the next cell.

In this scheme, the cell delay depends on the number of channels used in the frame, and the smaller the number of channels used in the frame, the longer the cell delay, in the worst case, when the cell is filled with 46 or 47 octets all 13 bits per data sample. You must wait until.

The time out concept can be applied to limit the maximum cell delay, that is, if a time out occurs even before the cell is full, the cell that is not completely filled is transmitted as is.

The frame boundary is identified by the SDT scheme, each channel is identified by a channel label, and this channel label value is simply increased in the frame so that the boundary between the P frame and the P frame can be distinguished by finding the point where the simple increase ends. Can be.

The receiving side recovers by filling the unused data in the unused channel that has not been transmitted, and recovers the frame by filling the received data in the used channel.

FIG. 4 is a diagram illustrating an effective channel mapping method using frame statuses in an ATM-PSTN inter- trunk interworking apparatus of the present invention. When mapping a frame to a cell, channel mapping indicating the usage status of each channel in the frame before the frame data is shown. In this way, the channels being used are indicated by the frame status, and only the channels being used are mapped and transmitted.

As shown in FIG. 4, the frame state, which is the frame status area, is composed of 32 bits, and each of the bits indicates whether a corresponding channel is in use or not.

In the above scheme, the length of the mapped frame depends on the number of channels being used in the frame as in the effective channel mapping scheme, and the division between the frames also uses the SDT scheme. If there are few channels in use, several frames are mapped in one cell.

At this time, the frame pointer indicates the start of the first frame in the cell, and since the current channel is displayed in the frame status, the receiving side can detect this even if the number of used channels changes between frames.

In addition, the timeout concept may be applied to limit the maximum cell delay when the load is small.

5 is a diagram showing the structure of a cell according to the effective channel mapping method using the frame state in the ATM-PSTN inter- trunk interworking apparatus of the present invention, each cell has a pointer to the first frame in the cell, The use of pointers uses the P format only once when the sequence count is even for the boundary that first appears within one period of the sequence count, such as the SDT method of the ITU-T AAL1 Recommendation.

In addition, in order to compensate for strong frame recovery such as cell loss or misinsertion, the SDT scheme may be applied to every cell at a slight decrease in transmission efficiency.

Each frame mapped in a cell has a frame sequence number (FSN) field of 1 octet with a frame status (FS) area, and each frame is assigned a frame sequence number (FSN), which is a maximum of 256. Up to periods can be used and the period can be reduced by using only a few bits as needed.

Each cell has a pointer to the boundary of the first frame in the cell (FP: Frame Pointer), so even if a large number of cell losses occur in the middle, the frame boundary can be found. If within the period range of (e.g., up to 256), the flow can be recovered and maintained.

FIG. 6 is a block diagram of an ATM-PSTN inter- trunk interworking device, that is, an IWU (InterWorking Unit), which generates an ATM line interface 10 that exchanges an ATM network with an ATM cell, and generates FP, FSN, and FS. An IWU TX 11 for mapping an E1 frame to an ATM cell and transmitting it to the ATM line interface 10, a controller 12 for controlling the overall operation of the IWU, controlling each component block, and the ATM line interface ( 10) IWU RX 13 receiving ATM cells from the FP, FSN, and FS, separating the FP, FSN, and FS into an E1 frame, and transmitting an E1 frame to the IWU TX 11 in connection with a PSTN, wherein the IWU RX ( And an E1 line interface 14 which receives the resolved E1 frame from 13) and transmits it to the PSTN.

The IWU TX 11 and the IWU RX 13 operate independently of each other, and additional information such as control of the overall operation and channel status in the frame is connected to the outside through the controller 12.

FIG. 7 is a detailed configuration diagram of the IWU TX 11 of FIG. 6, which includes a check unit 15 for checking whether an E1 frame received from the E1 line interface 14 is active or inactive, and an ATM frame for the E1 frame. Frame Pointer Generate Module (FPGM) (16) for generating 8-bit FP required when mapping to cell, and FSNGM (Sequence Number) for generating frame number in lost cell when cell loss occurs Number Buffer Module (17), FB (Frame Buffer) (18) for storing the E1 frame passed through the check unit 15 to absorb the delay in mapping to the ATM cell, and FS consisting of 4 bytes The FSGM (Frame Status Generate Module) 19 for generating an FS as an active module and an inactive unit as a result of the E1 frame inspection by the check unit 15 and the FPGM 16. The output data of FSNGM (17), FB (18), FSGM (19) at FPGM (16) Is of a OCM (Output Control Module) (20) for outputting a control signal by using the 8-bit parallel data made of the ATM line interface 10.

FIG. 8 is a detailed configuration diagram of the IWU RX 13, and includes a Smooth Buffer 22 for absorbing a Cell Delay Variation (CDV) that may occur in an ATM network, and a frame boundary in an ATM cell. FPHDLR (Frame Pointer HanDLeR) (23) processing FP and FH (Frame Header) added to map E1 frame to ATM cell to separate FHEXTR (FSN, FS, E1, active channel data) Frame Header EXTRactor (24), and in the case of cell loss, calculates the number of E1 frames in the lost cell using the FSN and maintains the synchronization of the E1 trunk by creating null frames as many as the lost E1 frames. Frame Sequence Number HanDLeR (FSNHDLR) 25 and an FSHDLR (Frame Sequence HanDLeR) 26 for generating a complete E1 frame using the FS and the inputted active channel data and then transmitting it to the E1 line interface 14; It is the part that controls the overall operation of the IWU RX (13). The main controller 27 controls the operation of each module according to the states of normal, SN error, recovery, and the like.

Referring to the operation of the ATM-PSTN inter- trunk interworking device according to the present invention configured as described above are as follows.

The IWU inter-trunk interworking device according to the present invention can assemble and disassemble cells at high speed and recover lost frames due to cell loss.

First, when receiving the E1 frame from the E1 line interface 14, the IWU TX 11 generates FP, FSN, and FS, maps the E1 frame to an ATM cell, and then exchanges the ATM network with the ATM cell. 10) transmit the ATM cell.

When the ATM cell receives the ATM cell from the ATM line interface 10, the IWU RX 13 separates the FP, FSN, and FS, decomposes the ATM cell into an E1 frame, and then transmits a PSTN and an E1 frame. The E1 frame is transmitted to (14).

That is, in the case of the IWU TX 11, the FSGM 19 inspects all active channels in the E1 trunk to generate frame status (FS) or to perform FSF processing using an external input method, and performs FB processing. Only the active channel in (18) is attached to the generated FSF followed by the buffer in the ATM line interface 10.

In addition, the FPGM 16 and the FSNGM 17 generate and transmit the FP and the FSN, respectively.

That is, the FPGM 16 is a module for generating an 8-bit FP required when mapping an E1 frame to an ATM cell. The FPGM is used to distinguish the boundary of an E1 frame in an ATM cell. FP is generated by counting E1 frame data and generating an enable signal at the end of the E1 frame.

The FSNGM 17 is a module for generating an SN for finding the number of frames in a lost cell when cell loss occurs. The maximum number of counts is determined according to the number of FSN bits to be used, and increases by one in synchronization with the start of the frame.

The FSGM 19 is a module that constitutes a 4-byte FS. The FSGM 19 checks 8-bit input E1 frame data and generates an FS with 1 for active and 0 for inactive, and an FB (18). ) Absorbs the delay in mapping to the ATM cell.

Accordingly, the OCM 20 outputs the output data of the FPGM 16, the FSNGM 17, the FB 18, and the FSGM 19 as 8-bit parallel data using control signals generated from the FPGM 16. .

That is, the data inputted to the OCM 20 are finally arranged in a form stored in an ATM cell, and then transferred to the ATM line interface 10.

On the other hand, in the case of the IWU RX 13, the FPHDLR 23 processes the FP (Frame Pointer) of the cell currently being processed, and separates the frame headers (FSN, FS) from the FHEXTR 24, respectively, and the FSNHDLR (25). And FSHDLR (26).

At this time, if cell loss occurs during transmission in the ATM network, the number of frames in the lost cell is calculated using the FSN, and the same number of meaningless frames as the number of lost frames are inserted to maintain synchronization of the E1 frame.

The SB 22 is a buffer for absorbing CDV that may occur in an ATM network, and may be included in the IWU RX 13, and may be included or not according to a situation. The FPHDLR 23 may be an ATM cell. A module for processing FPs for classifying frame boundaries in a frame, wherein the processing of the FPs is not performed for every cell, but only for the first cell after the connection and the FP of the cell after cell loss occurs.

The FHEXTR 24 separates the FH added to map the E1 frame to the ATM cell, and outputs three pieces of FSN, FS, E1, and active channel data.

Then, in case of cell loss in the ATM cell, the FSNHDLR 25 needs to know the number of E1 frames in the lost cell for correct recovery, and when the FSN of the lost cell is used, the FSNHDLR 25 knows the number of E1 frames in the lost cell. It can create as many null frames as lost frames to maintain synchronization of the E1 trunks that may be missed by cell loss.

That is, in the case where cell loss occurs, the FSNHDLR 25 calculates the number of E1 frames in the lost cell using the FSN, makes null frames as many as the lost E1 frames, and maintains synchronization of the E1 trunk.

The FSHDLR 26 should use the information of the FS to recover the complete E1 frame, generate a complete E1 frame using the FS and the input active channel data, and transmit it to the E1 line interface 14.

The main controller 27 is a part for controlling the overall operation of the IWU RX 13 and controls the operation of each module according to states of initial, normal, SN error, recovery, and the like.

As described above, in order to improve the transmission efficiency of the ATM network, the present invention uses an effective channel mapping method using a frame state that transmits only a channel in which a call is set and is used instead of transmitting the entire PSTN frame as it is. There is an effect that can improve the ATM cell information transmission efficiency in the region of most traffic load except the region.

In addition, even in a cell loss situation, the continuity of frames can be maintained at the receiving side, and by providing a transparent path through the ATM virtual connection without including interworking of signals, that is, a transparent path from the ATM network to the POTS network without interlocking control planes. Compared with the signal interworking, the implementation is simple, and there is an effect that the ATM network can be utilized for interworking between networks supporting the PSTN network without significant complexity in the network evolution stage.

Claims (7)

An ATM line interface for exchanging ATM networks with ATM cells, An IWU TX that generates FP, FSN, FS, maps the E1 frame to an ATM cell and transmits it to the ATM line interface; A controller that controls the overall operation of the IWU and controls each building block; An IWU RX that receives an ATM cell from the ATM line interface, separates FP, FSN, and FS into an E1 frame; And an E1 line interface connected to a PSTN to transmit an E1 frame to the IWU TX, and to receive the disassembled E1 frame from the IWU RX to a PSTN. The method of claim 1, wherein the IWU TX, A check unit for checking whether an E1 frame received from the E1 line interface is active or inactive, a FPGM for generating an 8-bit FP required when mapping an E1 frame to an ATM cell, and a frame in a cell lost when a cell loss occurs FSNGM which generates SN to find the number, FB which stores the E1 frame passing through the check unit to absorb the delay in mapping to the ATM cell, and generates the FS according to the E1 frame check result by the check unit. FSGM and the OCM outputting the output data of the FPGM, FSNGM, FB, FSGM to 8-bit parallel data using the control signal generated from the FPGM to the ATM line interface Tien trunk interlock. 3. The interworking device of claim 2, wherein the FSGM generates the FS as 1 when the E1 frame is active and 0 when the FSGM is checked. . The method according to claim 1, wherein the IWU RX, SSN for absorbing CDV that can occur in ATM network, FPHDLR for processing FP for dividing frame boundary in ATM cell, and FH added for mapping E1 frame to ATM cell, are separated from FSN, FS, E1, FHEXTR, which outputs three pieces of active channel data, and in case of cell loss, calculates the number of E1 frames in the lost cell using the FSN, and maintains synchronization of the E1 trunk by creating null frames as many as the lost E1 frames. ATM-S, comprising FSNHDLR, FSHDLR which generates complete E1 frame using FS and input active channel data and transmits to E1 line interface, and main controller which controls overall operation of IWU RX. Inter-Trunk Interlock Device. The method of claim 1, wherein when the frame is mapped in the IWU TX, channels that are in use by the frame status are displayed by using an effective channel mapping method using the frame status, and only the channels that are in use are mapped and transmitted. Interlocking device between ATM and PST. 6. The interworking apparatus of claim 5, wherein the frame status area comprises 32 bits indicating whether each channel is in use. The method according to claim 1, wherein each cell has a pointer to the first frame in the cell in the structure of the cell according to the effective channel mapping method using the frame status during frame recovery in the IWU RX. The AMT-PTI trunk trunk interworking device, characterized in that the frame has a FSN area of 1 octet with the frame status (FS) area.