KR20010048183A - Apparatus for converting ATM cell of AAL2 type to AAL2' type - Google Patents

Abstract

PURPOSE: An apparatus for transforming AAL2 type ATM cell into AAL2 ATM cell is provided to allow IMT-2000 base station controller to transmit audio data in the form of variable bit rate through AAL2 ATM cell by realizing an FPGA equipment capable of extracting the audio data from the AAL2 ATM cell to transform the same into AAL2 ATM cell. CONSTITUTION: A UTOPIA(Universal Test and Operations Physical Interface for ATM) interface(100) stores AAL2 ATM cell transmitted from a base station through E1-class line in a memory. A VCI(Virtual Channel Identifier) extracting unit(110) extracts a VCI of 2-bit among the ATM cells from the UTOPIA interface(100). A CPS(Common Part Sublayer) packet extracting unit(120) extracts a variable CPS packet from the ATM cells of the VCI extracting unit(10). A CAM(Content-Addressable Memory)(140) a CID in a CPS packet and a VCI in an ATM cell header. A CAM interface(130) transmits to the CAM(140) the VCI and CID extracted from the VCI extracting unit(110) and the CPS packet extracting unit(120), respectively. An SRAM(150) outputs a ATM cell header according to an address outputted from the CAM(140). An ATM cell header generating unit(160) generates AAL2 ATM cell header according to the ATM cell header from the SRAM(150). An AAL2 ATM cell generating unit(170) creates AAL2 ATM cell based on the cell header from the unit(160) and the CPS packet from the unit(120). A multiplexing interface(180) interfaces with a multiplexer on an ATM switch.

Description

Apparatus for converting ATM cell of AAL2 type to AAL2 'type}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base station controller of a next generation mobile communication system (International Mobile Telecommunications-2000; IMT-2000). In particular, voice data from the base station is AAL2 (ATM2). Mode) When the AAL2 ATM cell is loaded in the form of a cell, the AAL2 ATM cell extracts only the voice data of several users and converts it into an AAL2 'ATM cell. The present invention relates to an apparatus for converting an AAL2 ATM cell into a AAL2 'ATM cell, so that voice data having a Bit Rate (CBR) form can be transmitted from an IMT-2000 base station controller through an AAL2 ATM cell.

The AAL2 'type ATM cell is an ATM cell containing only one user's voice data in one ATM cell.

Currently, a technology for transmitting voice data in an ATM cell is widely known, and this is called VTOA (Voice Telephony Over ATM) in the ATM Forum. At this time, ATM cell type uses ATM Adaptation Layer (AAL) type 1 defined in ITU-T (International Telecommunication Union Telecommunication Standardization) Recommendation I.363.1 standard.

As such, voice data in a constant bit rate (CBR) format, that is, voice data, was transmitted through an ATM network in the form of an AAL 1 ATM cell. According to the VTOA, AAL1 is required to operate additional ATM networks such as Peak Cell Rate (PCR), Cell Loss Ratio (CLR), and Cell Delay Variation (CDV). There is data. As a result, additional bandwidth is required, and the operational data is continuously transmitted despite no traffic, thereby lowering the bandwidth usage efficiency.

And the AAL1 type should always transmit at the same bit rate, only one user data can be loaded in one ATM cell, and the voice signal should be determined as 64Kbps or multiple of 64Kbps (64Kbps * N). There was a problem in that it could not process compressed voice signals or silence.

Overcoming these shortcomings is the AAL2 ATM cell type shown in Figure 1, and the standard is defined in ITU-T Recommendation I.363.2.

As shown in Fig. 1, an AAL2 ATM cell is composed of a cell header of 5 bytes and a payload of 48 bytes. The payload consists of one byte of STF (STart Field) and 47 bytes of space to hold several Common Part Sublayer (CPS) packets. 1 shows an example of an AAL2 ATM cell, which contains four CPS packets. One byte of STF consists of a 6-bit Offset Field (OSF), a 1-bit Sequence Number (SN), and a 1-bit Parity (P). The OSF has an interval value from the STF to the first CPS packet. That is, if the length of the CPS packet is continuously added and the value exceeds 47 bytes, the remaining CPS packet length becomes the OSF value.

One CPS packet is variable and its length varies according to the characteristics of the voice data. The configuration is composed of a 3-byte CPS packet header and a maximum 45-byte CPS packet payload. Here, the first 8 bits of the three-byte CPS packet header are CID (Channel Identifier), the next 6 bits are LI (Length Indicator), the 5 bits are User to User Indication (UUI), and the remaining 5 bits are A cyclic redundancy check (CRC) value for 19 bits of. The CPS packet payload contains a variable voice signal of up to 45 bytes.

Attempts to carry voice in the form of AAL2 are increasing. The advantages of AAL2 are the ability to send variable voice data and the ability to put multiple users' data together in a single ATM cell. This allows for efficient use of bandwidth.

However, when adopting such AAL2, there is a problem that switching with a conventional commercial ATM switch is impossible. That is, a problem arises that the ATM switch cannot switch voice data of multiple users in the AAL2 ATM cell.

A solution proposed for this is the AAL2 'type ATM cell. As shown in Fig. 2, unlike the AAL2 ATM cell format, only one CPS packet is configured in the ATM cell payload. When the CPS packet is smaller than 48 bytes, "0" is inserted into the remaining payload. The configuration of the CPS packet is the same as that of AAL2.

Thus, this means that one ATM cell has only one CPS packet so that the ATM switch can be switched in an ATM switch.

However, a device for restoring such an AAL2 type ATM cell to an AAL2 'type ATM cell is not implemented.

Therefore, the present invention has been proposed to solve the conventional problems as described above, the object of the present invention is

When the voice data from the base station is loaded in the form of an AAL2 ATM cell, the AAL2 ATM cell can be ATM switched from the ATM switch by implementing a device that extracts only the voice data of several users from the AAL2 ATM cell and converts the voice data into an AAL2 'ATM cell. The present invention provides an apparatus for converting an AAL2 ATM cell into a AAL2 'ATM cell such that a variable bit rate (VBR) type voice data can be transmitted from an IMT-2000 base station controller through an AAL2 ATM cell.

In order to achieve the above object, an apparatus for converting an AAL2 ATM cell according to the present invention into an AAL2 'ATM cell,

A Universal Test and Operations Physical Interface for ATM (UTOPIA) matching unit for storing an AAL2 ATM cell transmitted from a base station through an E1 line in a memory;

A VCI extracting unit for extracting a VCI (Virtual Channel Identifier) of 2 bytes of ATM cells from the UTOPIA matching unit;

A CPS packet extracting unit for extracting a variable Common Part Sublayer (CPS) packet from an ATM cell from the VCI extracting unit;

A Content-Addressable Memory (CAM) for mapping user information (CID) in a Common Part Sublayer (CPS) packet and VCI information in an ATM cell header;

A CAM matching unit for transmitting the VCI extracted from the VCI extracting unit and the CID (Channel IDentifier) extracted from the CPS packet extracting unit to the CAM;

An SRAM for outputting a new ATM cell header according to the address output from the CAM;

An ATM cell header generation unit configured to receive an ATM cell header output from the SRAM and generate an AAL2 'ATM cell header;

An AAL2 'ATM cell generator for generating an AAL2' ATM cell from the cell header generated by the ATM cell header generator and the CPS packet extracted from the CPS packet extractor;

The technical configuration of the AAL2 'cell output from the AAL2' ATM cell generation unit is composed of a multiplexer matching unit for interfacing with a multiplexer on the ATM switch side at UTOPIA level 1.

1 is a diagram showing an AAL2 ATM cell type according to the ITU-T standard;

2 is a view showing an AAL2 'ATM cell form;

3 is a block diagram of an ATM cell multiplexing / demultiplexing apparatus of an IMT-2000 base station controller to which the present invention is applied;

4 is an apparatus block diagram for converting an AAL2 ATM cell into an AAL2 'ATM cell according to the present invention;

5 is a diagram illustrating an operation of extracting a CPS packet from an AAL2 ATM cell and converting the CPS packet into an AAL2 'ATM cell;

<Explanation of symbols for the main parts of the drawings>

100: UTOPIA matching part 110: VCI extraction part

120: CPS packet extraction unit 130: CAM matching unit

140: CAM 150: SRAM

160: ATM cell header generation unit 170: AAL2 'ATM cell generation unit

180: multiplexer matching unit

Hereinafter, an apparatus for converting an AAL2 ATM cell of the present invention as described above into an AAL2 'ATM cell will be described in detail with reference to the accompanying drawings.

3 is a block diagram of an ATM cell multiplexing / demultiplexing apparatus of an IMT-2000 base station controller to which the present invention is applied.

A plurality of E1 line interface units (LIUs) 10-13 that perform ATM physical layer functions and interface with E1 lines to the base station; A UTOPIA function performing unit 20-23 corresponding to the E1 line matching unit 10-13 one to one to perform a universal test and operations physical interface for ATM (Utopia) layer 1 (level 1) interface; A plurality of type conversion receivers 30-33 performing a type conversion interface function so that ATM cells between the UTOPIA function performing unit 20-23 and an ATM switch can be ATM switched; A multiplexer (40) for multiplexing the ATM cells from the type conversion receiver (30-33); ATM cell routing unit (cubit) 50 for matching the ATM cell transmitted from the multiplexer 40 to the ATM cell bus.

Although not shown in FIG. 3, a processor is configured to control the overall operation of the ATM cell multiplexing / demultiplexing apparatus of the IMT-2000 base station controller.

The ATM cell multiplexing / demultiplexing apparatus of the IMT-2000 base station controller can handle all 16 channels. The AAL2 ATM cell transmitted from the base station through the E1 line passes through the E1 line matching unit 10-13 and the UTOPIA function performing unit 20-23, and then is transmitted to the type conversion receiver 30-33. Therefore, the ATM switch is converted into an AAL2 'cell capable of ATM switching, and then multiplexed into one line in the multiplexer 40 and then transmitted to the ATM switch through the ATM cell routing unit (COBIT) 50.

Each type conversion receiver 30-33 is equipped with an apparatus for converting an AAL2 ATM cell according to the present invention into an AAL2 'ATM cell.

An apparatus for converting an AAL2 ATM cell according to the present invention into an AAL2 'ATM cell includes a UTOPIA matching unit 100 for storing an ATM cell transmitted from the corresponding UTOPIA function performing unit in a memory, as shown in FIG. A VCI extraction unit (110) for extracting two bytes of VCIs (Virtual Channel Identifiers) among ATM cells from the UTOPIA matching unit 100; A CPS packet extracting unit (120) for extracting a variable Common Part Sublayer (CPS) packet from an ATM cell from the VCI extracting unit (110); A Content-Addressable Memory (CAM) 140 for mapping user information (CID) in a Common Part Sublayer (CPS) packet and VCI information in an ATM cell header; A CAM matching unit (130) for transmitting the VCI extracted by the VCI extractor (110) and the CID (Channel IDentifier) extracted by the CPS packet extractor (120) to the CAM (140); An SRAM 150 for outputting a new ATM cell header according to the address output from the CAM 140; An ATM cell header generation unit (160) for receiving an ATM cell header output from the SRAM (150) and generating an AAL2 'ATM cell header; An AAL2 'ATM cell generator 170 for generating an AAL2' ATM cell from the cell header generated by the ATM cell header generator 160 and the CPS packet extracted from the CPS packet extractor 120; A multiplexer matching unit 180 is configured to interface the AAL2 'cell output from the AAL2' ATM cell generation unit 170 with the multiplexer 40 at UTOPIA level1.

Referring to the operation of the apparatus for converting the AAL2 ATM cell according to the present invention as described above AAL2 'ATM cell as follows.

The AAL2 ATM cell transmitted from the base station through the E1 line passes through the E1 line matching unit 10-13 and the UTOPIA function performing unit 20-23, and then is transmitted to the type conversion receiver 30-33.

The UTOPIA matching unit 100 having an AAL2 ATM cell is provided with a memory capable of storing two ATM cells and a control unit for controlling the memory (not shown in FIG. 4). The controller generates an address and a control signal for storing the input ATM cell in the memory. Thus, when the input ATM cell is stored in the memory of the UTOPIA matching unit 100, the VCI extractor 110 extracts the VCI value of 2 bytes from the header of the stored ATM cell and transmits it to the CAM matching unit 130.

The CPS packet extractor 120 extracts a CPS packet from an AAL2 ATM cell from which the VCI is extracted by the VCI extractor 110. That is, a CPS packet is extracted by reading and decoding a 6-bit length indicator (LI) value (which has an octet value less than the CPS packet payload) of the 3-byte header of the CPS packet. Then, the CID (8 bits) of the extracted CPS packet is transmitted to the CAM matching unit 130. 5 shows a configuration in which three CPS packets are carried in one AAL2 ATM cell.

The CAM matching unit 130 transmits the VCI and the CID to the CAM 140 in accordance with the operation clock of the CAM 140.

The CAM 140 maps the user information CID in the CPS packet and the VCI information in the ATM cell header so that the 5-byte value of the ATM cell header can be freely changed. The desired header value is saved in advance and used. This is because when the AAL2 'ATM cell generation unit 170 includes a mapping table for AAL2' cell conversion of the AAL2 cell, the AAL2 'ATM cell generation unit 170 needs to be changed and modified whenever the information is changed. This is because the CAM 140 only needs to be changed.

When the VCI value and the CID value are input from the CAM matching unit 130, the CAM 140 generates an address of the external SRAM 150 in which the VCI value and the VCI value matched with the CID value are stored. Then, the data corresponding to the address is output from the SRAM 150 to the ATM cell header generation unit 160.

The CAM 140 is a MU9C4320L ATMCAM from MUSIC Semiconductors, which has a size of 4096 * 32 bits, and controls operation directly through an address bus and a control bus for fast operation.

When data is output from the SRAM 150, the ATM cell header generation unit 160 generates a 5-byte header of a new ATM cell using this data.

The AAL2 'ATM cell generation unit 170 receives the CPS packet extracted by the CPS packet extraction unit 120 and receives a 5-byte cell header from the ATM cell header generation unit 160 to display the AAL2 as shown in FIG. Create an ATM cell. When an AAL2 cell carries three CPS packets, three AAL'2 ATM cells are generated. At this time, the AAL2 'ATM cell carries a CPS packet in a CPS-PDU (Protocol Data Unit) payload of 47 bytes (except STF, which is 1 byte of 48 bytes), and pads the remaining space with "0" to fill 47 bytes.

The ATM switch is converted into an AAL2 'ATM cell capable of ATM switching, and then output through the multiplexer matching unit 180, multiplexed into one line in the multiplexer 40, and then the ATM cell routing unit (COBIT) 50. Is sent to the ATM switch.

As described above, in the apparatus for converting an AAL2 ATM cell according to the present invention into an AAL2 'ATM cell, voice data is transmitted from an ALA2 (AAL2; ATM Adaptation Layer 2) Asynchrous Transfer Mode (ATM) cell. In the form of FPGA, the AAL2 ATM cell extracts only the voice data of several users from the AAL2 ATM cell and converts it into an AAL2 'ATM cell, thereby enabling the AAL2 ATM cell to be ATM switched from the ATM switch. Rate (VBR) type voice data can be transmitted from an IMT-2000 base station controller through an AAL2 ATM cell.

The present invention also has a multiplexing function that can process four lines simultaneously.

Claims (1)

In the base station controller of the IMT-2000 mobile communication system, A Universal Test and Operations Physical Interface for ATM (UTOPIA) matching unit for storing an AAL2 ATM cell transmitted from a base station through an E1 line in a memory; A VCI extracting unit for extracting a VCI (Virtual Channel Identifier) of 2 bytes of ATM cells from the UTOPIA matching unit; A CPS packet extracting unit for extracting a variable Common Part Sublayer (CPS) packet from an ATM cell from the VCI extracting unit; A Content-Addressable Memory (CAM) for mapping user information (CID) in a Common Part Sublayer (CPS) packet and VCI information in an ATM cell header; A CAM matching unit for transmitting the VCI extracted from the VCI extracting unit and the CID (Channel IDentifier) extracted from the CPS packet extracting unit to the CAM; An SRAM for outputting a new ATM cell header according to the address output from the CAM; An ATM cell header generation unit configured to receive an ATM cell header output from the SRAM and generate an AAL2 'ATM cell header; An AAL2 'ATM cell generator for generating an AAL2' ATM cell from the cell header generated by the ATM cell header generator and the CPS packet extracted from the CPS packet extractor; And a multiplexer matching unit for interfacing the AAL2 'cell outputted from the AAL2' ATM cell generation unit with a multiplexer on the ATM switch side to UTOPIA level 1, wherein the AAL2 ATM cell is converted into an AAL2 'ATM cell.