Aalo cell format of an atm protocol for communicating voice traffic in a cdma system

Abstract

The present invention relates to an Asynchronous Transfer Mode (ATM) protocol, and more particularly to an ATM Adaptation Layer 0 (AAL0) cell format for increasing trunk path efficiency when communicating voice traffic data by using the ATM protocol in a CDMA system. In a conventional CDMA system, the ATM is used to communicate multimedia traffic, including voice traffic data, through a backbone network, and AAL5 cell is most widely used in the ATM since it provides a simple and efficient process for data traffic. However, when processing full-rate voice traffic (i.e., 24 bytes of voice data per 20 ms-frame), two AAL5 cells are needed to communicate the full-rate voice data because one AAL5 includes only 16 bytes of data. This may result in few problems (e.g., traffic overload, cell loss and so forth). In order to eliminate the above problems, the present invention employs an AAL0 cell, in which 8 bytes of trailer are sacrificed and assigned to the voice traffic data, to enhance trunk path efficiency.

Description

TECHNICAL FIELD

The present invention relates to an Adaptation Layer 0 (AAL0) cell format for communicating voice traffic data in a CDMA system using an Asynchronous Transfer Mode (ATM) protocol, and more particularly to an AAL0 cell format of the ATM which is configured to allow one frame of full-rate voice traffic data to be processed with only a single AAL0 cell.

BACKGROUND ART

Generally, the cell, such as an AAL2 or AAL5, of the ATM protocol used in a CDMA system consists of a 5-byte header field and a 48-byte data field (as shown in FIG. 1). It is used to communicate multimedia traffic, including voice and data traffic, through a backbone network.

An AAL5 cell of the ATM protocol contains an 8-byte trailer appended to the traffic data when converting voice traffic or data traffic signal into the cell. In a prior CDMA system, the 8-byte trailer has been widely used to communicate the traffic data because it provides an efficient process for converting the data traffic signal. However, appending the 8-byte trailer may become burdensome for the AAL5 cell when a voice signal is processed with the AAL5 cell. While each frame of half, quarter and one-eighth rate voice traffic data may be processed with one AAL5 cell, two AAL5 cells are needed to communicate the full-rate voice traffic data (i.e. a 24-byte data frame). This is because 56 bytes are required for the full-rate data (i.e., a sum of 5 (header), 24 (voice data), 19 (control data), and 8 (trailer) bytes). This may result in traffic overload. Because a base station transmission system (BTS) and a base station controller (BSC) are synchronized by means of 20 ms sync signal, the second cell of the two AAL5 cells having the fall-rate voice data may be lost (i.e., the cell may be discarded) during a communication between the BTS and BCS if the first cell comes in and then the second cell comes in after the sync signal for the first cell arrives.

Also, when a transformation between an AA5 cell and an AAL2 cell is to be made in order to communicate between the BTS and the BSC using the ATM cell, an AAL5 cell consists of 5 bytes of a header field, 24 bytes of a voice or data traffic field, a Control-Data field, 1 byte of a HEC field for error detection, and a PAD field used to pad meaningless data (as shown in FIG. 2). An AAL2 cell consists of 5 bytes of a header field, 1 byte of a START field (composed of a 6-bit Offset field, a 1-bit Sequence-Number field and 1-bit parity bit field), 48 bytes of a voice or data traffic field, and a PAD field (as shown in FIG. 3).

Therefore, when communication is performed from the BTS to the BSC through the AAL5/AAL2 cells, converting a full-rate voice traffic data into an AAL5 cell at the BSC may cause not only traffic overload, but also cell loss due to the discard by the sync signal at the BSC that attempts to decode the cell data. In addition, communication between BTS and BSC through AAL5/AAL2 produces another problem, that is, a separator is necessary to separate each voice traffic data in the process of decoding AAL2 cell data converted from many of AAL5 cells.

DISCLOSURE OF THE INVENTION

Thus, the present invention is provided in order to solve the prior problems described above. The purpose of the invention is to provide an AAL0 cell format that enables efficient voice communication in a CDMA system using ATM by allowing one frame of full-rate voice traffic data to be processed with one cell using the AAL0 protocol.

In accordance with the present invention, there is provided an ATM protocol for communicating voice data through a vocoder in a CDMA backbone network. The vocoder includes a cell-processing part, a payload-extracting part and an AAL0 cell-generating part, and an AAL0 cell format for the voice data which consists of: 5 bytes of a Header field; 1 byte of a Length field indicating the size of the voice data; 24 bytes of a Voice-Data field containing the voice data; 19 bytes of a Control-Data field containing information for controlling the voice data; 1 byte of an Error-Detection field containing information for detecting an error of the voice data; and 3 bytes of a PAD field for padding data used to exactly fit into the ATM cell.

BRIEF DESCRIPTION OF DRAWINGS

The above object and features of the present invention will become more apparent from the following description of the preferred embodiments provided in conjunction with the accompanying drawings.

FIG. 1 shows an ATM cell format.

FIG. 2 shows an AAL5 cell format of the ATM cell.

FIG. 3 shows an AAL2 cell format of the ATM cell.

FIG. 4 shows an AAL0 cell format used to communicate voice data in a CDMA system using the ATM protocol according to one embodiment of the present invention.

FIG. 5 schematically represents a process for communicating voice data between a BTS and a BSC using the AAL0/AAL2 cells, which are shown respectively in FIG. 4 and FIG. 3, in a CDMA system using the ATM protocol.

BEST MODE FOR CARRYING OUT THE INVENTION

In accordance with an embodiment of the present invention, an AAL0 cell format for communicating fall-rate voice traffic data in a CDMA system using an ATM protocol is described in detail in the following description with reference to the appended figures.

FIG. 5 is a block diagram of a device for implementing an AAL0 cell format for communicating full-rate voice traffic data in a CDMA system using an ATM protocol, wherein the device comprises a vocoder 100.

The vocoder 100 generates 5 bytes of a Cell Header field 10, 1 byte of a Length field 20 indicating the size of the voice data, 24 bytes of a Voice-Data field 30 containing the full-rate voice data, 19 bytes of a Control-Data field 40 containing an information for controlling the full-rate voice data, 1 byte of an Error-Detection field 50 containing an information for detecting an error of the voice data, and 3 bytes of a PAD field 60 for padding data used to exactly fit into the ATM cell. The vocoder 100 consists of a cell-processing part, a payload-extracting part and an AAL0 cell-generating part.

According to an embodiment of the present invention, an AAL0 cell format for communicating the full-rate voice traffic data in a CDMA system using an ATM protocol is described with reference to FIG. 4 and FIG. 5.

After receiving the fall-rate voice data, the vocoder 100 generates 5 bytes of a Cell Header field 10 and 1 byte of a Length field 20 indicating the size of the voice data based on the size of the full-rate voice data. Also, the vocoder 100 generates 24 bytes of a Voice-Data field 30 containing the full-rate voice data corresponding to the length field and 19 bytes of a Control-Data field 40 in the next region. Further, the vocoder 100 generates 1 byte of an Error-Detection field 50 for determining the error of the AAL0 cell, 3 bytes of a PAD field 60 to exactly fit into the ATM cell, and finally sends the above data to the BTS.

Thereafter, the full-rate voice data is converted to an AAL0 cell, which is generated by the vocoder 100 in the BTS. Then, in the BTS, the AAL0 cell is converted to AAL2 and sent to the BSC. Finally, the vocoder 100 of the BSC performs communication by converting to AAL0 cell the AAL2 cell, which is transmitted from the BTC.

INDUSTRIAL APPLICABILITY

As the above describes, by using the AAL0 cell format for communicating fall-rate voice traffic data in a CDMA system using an ATM protocol, it becomes possible to increase the efficiency of a trunk by reducing the size of the full-rate voice signal to one cell.

Reducing the load of a processor, correcting the error of synchronization time (errors can occur when using two cells for transmitting data), resolving cell loss and increasing the efficiency of the trunk produces the advantage of being able to transmit signals of several subscribers through one AAL0/2 cell.

In a situation where two AAL5 cells of the first user and another two AAL5 cells of the second user are converted to one AAL2 cell in order to process large data, a separator is conventionally required for separating the first user's cells and the second user's cells from the data in the conversion of the AAL5/AAL2 cells. However, another benefit of the present invention is that the conversion of AAL0/AAL2 cells doesn't require such a separator because the cell frame of the data is divided according to the user.

Claims

1. In an Asynchronous Transfer Mode (At) protocol for communicating voice data through a vocoder in a CDMA backbone network, wherein the vocoder includes a cell-processing part, a payload-extracting part and an ATM Adaptation Layer 0 (AAL0) cell-generating part, said AAL0 cell format for the voice data consisting of: 5 bytes of a Header field; 1 byte of a Length field indicating a size of the voice data; 24 bytes of a Voice-Data field containing the voice data; 19 bytes of a Control-Data field containing information for controlling the voice data; 1 byte of an Error-Detection field containing information for detecting an error of the voice data; and 3 bytes of a PAD field for padding data used to exactly fit into the ATM cell.