CA2270100A1 - Method for connecting communication systems via a packet-oriented data transmission link - Google Patents
Method for connecting communication systems via a packet-oriented data transmission link Download PDFInfo
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- CA2270100A1 CA2270100A1 CA 2270100 CA2270100A CA2270100A1 CA 2270100 A1 CA2270100 A1 CA 2270100A1 CA 2270100 CA2270100 CA 2270100 CA 2270100 A CA2270100 A CA 2270100A CA 2270100 A1 CA2270100 A1 CA 2270100A1
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- sub
- atm
- communication systems
- connecting communication
- structure element
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/04—Selecting arrangements for multiplex systems for time-division multiplexing
- H04Q11/0428—Integrated services digital network, i.e. systems for transmission of different types of digitised signals, e.g. speech, data, telecentral, television signals
- H04Q11/0478—Provisions for broadband connections
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/54—Store-and-forward switching systems
- H04L12/56—Packet switching systems
- H04L12/5601—Transfer mode dependent, e.g. ATM
- H04L2012/5638—Services, e.g. multimedia, GOS, QOS
- H04L2012/5646—Cell characteristics, e.g. loss, delay, jitter, sequence integrity
- H04L2012/5652—Cell construction, e.g. including header, packetisation, depacketisation, assembly, reassembly
- H04L2012/5653—Cell construction, e.g. including header, packetisation, depacketisation, assembly, reassembly using the ATM adaptation layer [AAL]
- H04L2012/5656—Cell construction, e.g. including header, packetisation, depacketisation, assembly, reassembly using the ATM adaptation layer [AAL] using the AAL2
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Data Exchanges In Wide-Area Networks (AREA)
Abstract
A method for connecting communication systems via a packet-oriented data transmission link wherein, for a connection of communication systems, data packets serving for data transmission are sub-divided into sub-structure elements, such that an allocation of the sub-structure elements to channels of multiplex connections provided in the communication systems occurs.
Description
, CA 02270100 1999-04-23 SPECIFICATION
TITLE
METHOD FOR CONNECTING COMMUNICATION SYSTEMS
VIA A PACKET-ORIENTED DATA TRANSMISSION LINK
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to a method for connecting communication systems via a packet-oriented data transmission link, wherein the communication systems provide multiplex connections respectively formed of a periodic sequence of channel-individual information segments such that data packets serving for data transmission are sub-divided into sub-structure elements which are, in turn, allocated to channels of the multiplex connections.
Descriation of the Prior Art Sonderausgabe telcom report and Siemens-Magazin COM: ISDN im Buro -HICOM", Siemens AG, Berlin and Munich, 1985, particularly pages 50 through 57, discloses a communication system which includes a primary multiplex terminal, often referred to as an S2m interface, for a connection to either a communication network or a further communication system. In general, an SZM interfaces includes, first, payload data channels that are designed as ISDN-oriented B-channels (Integrated Services Digital Network) with a transmission rate of 64 kBitls and, second, a signaling channel that is designed as an ISDN-oriented D-channel with a transmission rate of 64 kBit/s.
The data transmission rate of 2 Mbitls is thus available for a data transmission between two communication systems. The data transmission rate of 2 Mbitls is thereby permanently off; i.e., independent of the transmission capacity actually utilized.
Unused, free transmission capacities cannot be utilized in some other way.
As a result of the increasing need for the transmission of video information in modern communication technology such as, for example, still and motion pictures in picture telephony applications, the significance of transmission and switching technologies for high and variable data transmission rates (above 100 Mbit/s) is increasing. A known data transmission method for high data rates is what is referred to as the asynchronous transfer mode (ATM). A data transmission on the basis of the asynchronous mode currently enables a variable transmission bit rate of up to Mbitls.
The present invention is directed to a method with which such a packet-oriented data transmission can be realized between a plurality of communication systems.
SUMMARY OF THE INVENTION
For a better understanding of the functioning of a packet-oriented data transmission between communication systems, known principles will be discussed in greater detail.
In the data transmission method known as the asynchronous transfer mode (ATM), data packets of a fixed length, what are referred to as ATM cells, are used for the data transport. An ATM cell is composed of a cell header, what is referred to as the "header", that is five bytes long and contains switching data relevant for the transport of an ATM cell and of a payload data field, or "payload", that is 48 bytes long.
A data transmission that is internal within the communication system, for example between a switching network module and a network terminal unit, usually occurs via what is referred to as a "PCM highway" according to the TDM method (Time Division Multiplex). Given a data transmission via an ATM network connected to the network terminal unit, a conversion of the continuous data stream internal within the communication system into data packets according to the ATM format is necessary -also often referred to as "ATM layer" in the literature.
A conversion of the continuous data stream based on the TDM method onto the ATM format occurs according to the ATM adaptation layer AAL type 1 (ATM
Adaption Layer). An adaptation of the "ATM layer" to the switching layer (layer 3) occurs according to the OSI reference model (Open Systems Interconnection) with the ATM
adaption layer AAL.
All 32 channels succeeding one another in time in a TDM frame communicated via a PCM highway are converted by the ATM adaption layer AAL (type 1 whereas each having respectively one byte of payload data information) onto the ATM
cell format in the way described below.
TITLE
METHOD FOR CONNECTING COMMUNICATION SYSTEMS
VIA A PACKET-ORIENTED DATA TRANSMISSION LINK
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to a method for connecting communication systems via a packet-oriented data transmission link, wherein the communication systems provide multiplex connections respectively formed of a periodic sequence of channel-individual information segments such that data packets serving for data transmission are sub-divided into sub-structure elements which are, in turn, allocated to channels of the multiplex connections.
Descriation of the Prior Art Sonderausgabe telcom report and Siemens-Magazin COM: ISDN im Buro -HICOM", Siemens AG, Berlin and Munich, 1985, particularly pages 50 through 57, discloses a communication system which includes a primary multiplex terminal, often referred to as an S2m interface, for a connection to either a communication network or a further communication system. In general, an SZM interfaces includes, first, payload data channels that are designed as ISDN-oriented B-channels (Integrated Services Digital Network) with a transmission rate of 64 kBitls and, second, a signaling channel that is designed as an ISDN-oriented D-channel with a transmission rate of 64 kBit/s.
The data transmission rate of 2 Mbitls is thus available for a data transmission between two communication systems. The data transmission rate of 2 Mbitls is thereby permanently off; i.e., independent of the transmission capacity actually utilized.
Unused, free transmission capacities cannot be utilized in some other way.
As a result of the increasing need for the transmission of video information in modern communication technology such as, for example, still and motion pictures in picture telephony applications, the significance of transmission and switching technologies for high and variable data transmission rates (above 100 Mbit/s) is increasing. A known data transmission method for high data rates is what is referred to as the asynchronous transfer mode (ATM). A data transmission on the basis of the asynchronous mode currently enables a variable transmission bit rate of up to Mbitls.
The present invention is directed to a method with which such a packet-oriented data transmission can be realized between a plurality of communication systems.
SUMMARY OF THE INVENTION
For a better understanding of the functioning of a packet-oriented data transmission between communication systems, known principles will be discussed in greater detail.
In the data transmission method known as the asynchronous transfer mode (ATM), data packets of a fixed length, what are referred to as ATM cells, are used for the data transport. An ATM cell is composed of a cell header, what is referred to as the "header", that is five bytes long and contains switching data relevant for the transport of an ATM cell and of a payload data field, or "payload", that is 48 bytes long.
A data transmission that is internal within the communication system, for example between a switching network module and a network terminal unit, usually occurs via what is referred to as a "PCM highway" according to the TDM method (Time Division Multiplex). Given a data transmission via an ATM network connected to the network terminal unit, a conversion of the continuous data stream internal within the communication system into data packets according to the ATM format is necessary -also often referred to as "ATM layer" in the literature.
A conversion of the continuous data stream based on the TDM method onto the ATM format occurs according to the ATM adaptation layer AAL type 1 (ATM
Adaption Layer). An adaptation of the "ATM layer" to the switching layer (layer 3) occurs according to the OSI reference model (Open Systems Interconnection) with the ATM
adaption layer AAL.
All 32 channels succeeding one another in time in a TDM frame communicated via a PCM highway are converted by the ATM adaption layer AAL (type 1 whereas each having respectively one byte of payload data information) onto the ATM
cell format in the way described below.
In addition to the "header", the first byte within the "payload" area of an ATM cell is employed as a pointer. This pointer serves the purpose of restoring the synchronization between transmitter and receiver in case one or more ATM cells has been lost due, for example, to a transmission error. The communication of the payload data information begins with the second byte of the payload area. The payload data bytes allocated to the individual channels of the TDM frame are thereby communicated successively. A transmission of the first byte (the byte allocated to the channel number 0) of the TDM successor frame occurs immediately after a communication of the last byte (the byte allocated to the channel number 31 ) of a TDM frame. The pointer thereby points to the first byte of a TDM frame beginning within the payload area of an ATM cell. Fig. 1 shows an illustration of this structure.
An allocation of the bytes stored in the payload area of an ATM cell to a channel of a TDM frame thus occurs via the position of the byte in the payload area of the ATM
cell. A transmission of the data occurs independently of the occupancy of a channel, as a result whereof the existing network resources are definitely unnecessarily occupied.
Added thereto is the fact that the filling time for an ATM cell amounts to 6 msec (125Ns per byte). As a result, echo problems can occur in the network due to the transmission delay - also often referred to as "delay" in the literature. This effect is intensified by the employment of compression algorithms as employed, for example, within the framework of mobile radio telephony. Given a compression of 1:10, the filling time for an ATM cell thus amounts to 60 msec, the echo problems being yet further intensified as a result thereof.
Given the employment of compression algorithms that leave the information to be communicated unmodified due to the removal of redundant information sequences, a variable data stream arises from the continuous data stream dependent on the existing redundancy. Given a data transmission with a constant transmission rate such as, for example, given a packet-oriented data transmission according to ATM
adaption layer AAL Type 1, this leads to problems. For this reason, compression algorithms are preferably employed that generate a continuous stream; for example, on the basis of statistical predictions. Currently, however, non-compression algorithms can lead to a falsification of the information to be communicated in certain situations, so that these compression algorithms can, in fact, be employed for a transmission of speech but are unsuitable for a transmission of facsimile or data.
A critical advantage of the present invention, therefore, is that only sub-structure elements are transmitted via the ATM network whose allocated channels are currently occupied. This leads to an improved utilization of the existing network resources.
A further advantage of the present invention is that, due to the transmission of an individually adjustable plurality of payload data bytes allocated to a terminal equipment connection in a sub-structure element of a data packet, a data transmission with a variable transmission rate can be realized. This enables the employment of compression algorithms that, dependent on the redundancy present in the data to be transmitted, generate a variable data stream without falsification of the information from a continuous data stream.
Due to the definition of the first payload data segment of an ATM cell as a pointer that references the starting address of a first sub-structure element located in the payload area of the ATM cell, a synchronization of the communication system given a loss of one or more ATM cells can be realized in a simple way.
Additional features and advantages of the present invention are described in, and will be apparent from, the Detailed Description of the Preferred Embodiments and the Drawings.
DESCRIPTION OF THE DRAWINGS
Fig. 1 shows a schematic illustration of the data format according to the TDM
method and of the corresponding ATM data format according to the ATM adaption layer AAL Type 1;
Fig. 2 shows a schematic illustration of the corresponding ATM data format and of the data format of a sub-structure element according to the ATM adaption layer AAL
Type 2; and Fig. 3 shows a schematic illustration of the corresponding ATM data format, according to the ATM adaption layer AAL Type 5.
An allocation of the bytes stored in the payload area of an ATM cell to a channel of a TDM frame thus occurs via the position of the byte in the payload area of the ATM
cell. A transmission of the data occurs independently of the occupancy of a channel, as a result whereof the existing network resources are definitely unnecessarily occupied.
Added thereto is the fact that the filling time for an ATM cell amounts to 6 msec (125Ns per byte). As a result, echo problems can occur in the network due to the transmission delay - also often referred to as "delay" in the literature. This effect is intensified by the employment of compression algorithms as employed, for example, within the framework of mobile radio telephony. Given a compression of 1:10, the filling time for an ATM cell thus amounts to 60 msec, the echo problems being yet further intensified as a result thereof.
Given the employment of compression algorithms that leave the information to be communicated unmodified due to the removal of redundant information sequences, a variable data stream arises from the continuous data stream dependent on the existing redundancy. Given a data transmission with a constant transmission rate such as, for example, given a packet-oriented data transmission according to ATM
adaption layer AAL Type 1, this leads to problems. For this reason, compression algorithms are preferably employed that generate a continuous stream; for example, on the basis of statistical predictions. Currently, however, non-compression algorithms can lead to a falsification of the information to be communicated in certain situations, so that these compression algorithms can, in fact, be employed for a transmission of speech but are unsuitable for a transmission of facsimile or data.
A critical advantage of the present invention, therefore, is that only sub-structure elements are transmitted via the ATM network whose allocated channels are currently occupied. This leads to an improved utilization of the existing network resources.
A further advantage of the present invention is that, due to the transmission of an individually adjustable plurality of payload data bytes allocated to a terminal equipment connection in a sub-structure element of a data packet, a data transmission with a variable transmission rate can be realized. This enables the employment of compression algorithms that, dependent on the redundancy present in the data to be transmitted, generate a variable data stream without falsification of the information from a continuous data stream.
Due to the definition of the first payload data segment of an ATM cell as a pointer that references the starting address of a first sub-structure element located in the payload area of the ATM cell, a synchronization of the communication system given a loss of one or more ATM cells can be realized in a simple way.
Additional features and advantages of the present invention are described in, and will be apparent from, the Detailed Description of the Preferred Embodiments and the Drawings.
DESCRIPTION OF THE DRAWINGS
Fig. 1 shows a schematic illustration of the data format according to the TDM
method and of the corresponding ATM data format according to the ATM adaption layer AAL Type 1;
Fig. 2 shows a schematic illustration of the corresponding ATM data format and of the data format of a sub-structure element according to the ATM adaption layer AAL
Type 2; and Fig. 3 shows a schematic illustration of the corresponding ATM data format, according to the ATM adaption layer AAL Type 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 shows a schematic illustration of two TDM frames R1, R2 and of two corresponding ATM cells ATM-Z1, ATM-Z2 according to the ATM adaption layer AAL
Type 1. A TDM frame R1, R2 includes 32 channels via which a data transmission is possible in the framework of 30 terminal equipment connections, and wherein an allocation of 30 channels for a transmission of payload information and of two channels far a transmission of signaling information exists. Given a conversion of a continuous data stream based on the TDM method onto the ATM format according to the ATM
adaption layer AAL Type 1, all 32 channels succeeding one another in time in a TDM
frame, with respect to the one byte payload data information, are converted onto the ATM cell format in the following way.
In addition to the cell header H of the ATM cell ATM- Z1, ATM-Z2, the first byte within the payload area, referred to below as payload data area, is defined as pointer Z. This pointer Z points to the first byte of a TDM frame R1, R2 beginning within the payload data area of an ATM cell ATM-Z1, ATM-Z2. With this pointer Z, a restoration of the synchronization between transmitter and receiver is possible in case one or more ATM cells ATM-Z1, ATM-Z2 have been lost due, for example, to a transmission error.
The transmission of the payload data information contained in a TDM frame R1, occurs beginning with the second byte of the payload data area of an ATM cell ATM-Z1, ATM-Z2. The payload data bytes allocated to the individual channels of the TDM
frame R1, R2 are thereby communicated in sequence. Immediately after a transmission of the last byte (the byte allocated to channel 31 ) of a TDM frame R1, a transmission of the first byte (the byte allocated to the channel 0) of the TDM successor frame R2 occurs. An allocation of the payload data bytes of an ATM cell ATM-Z1, ATM-Z2 to a channel of a TDM frame R1, R2 thus occurs via the position of the byte in the payload data area of the ATM cell ATM-Z1, ATM-Z2.
Fig. 2 shows a schematic illustration of two ATM cells ATM-Z1, ATM-Z2 and of a sub-structure element SE according to the ATM adaption layer AAL Type 2.
Within the framework of the ATM adaption layer AAL Type 2, there is the possibility of subdividing the payload data area of an ATM cell ATM-Z1, ATM-Z2 into sub-structure elements SE. A sub-structure element SE according to the ATM adaption layer AAL
type 2 is composed of a cell header SH that is 3 bytes long and of a payload data area I of variable length (0 through 64 bytes). The cell header of a sub-structure element SE
according to the ATM adaption layer AAL Type 2 is subdivided into a channel identification CID (Channel Identifier) that is 8 bits long, into a length indicator LI
(Length Indicator) that is 6 bits long, a sender-receiver identification UUI
(User-to-User Indication) that is 5 bits long and a 5 bit long cell header checksum HEC
(Header Error Control).
Corresponding to an ATM cell ATM-Z1, ATM-Z2 according to the ATM adaption layer AAL Type 1, the first byte in the payload data area of an ATM cell ATM-Z1, ATM-Z2 is defined as pointer Z. This pointer Z indicates the starting address of the first sub-structure element SE whose cell header SH lies in the payload data area of the ATM
cell ATM-Z1, ATM-Z2. A restoration of the synchronization between transmitter and receiver is possible with this pointer Z in case one or more ATM cells ATM-Z1, have been lost due, for example, to a transmission error.
Due to the sub-division of an ATM cell ATM-Z1, ATM-Z2 into sub-structure elements SE, a plurality of channels that are all addressed with the same ATM
address, composed of a VPI _ _ -(Virtual Path Identifier) and of a VCI (Virtual Channel Identifier), can be defined within an ATM connection on the basis of the channel identification CID.
Within the framework of an interworking of communication systems, thus, there is the possibility of defining a sub-structure element SE for a transmission of signaling information; i.e., for a transmission of D-channel data. A further sub-structure element SE can be defined for every required B-channel for a transmission of payload data information, i.e. for a transmission of B-channel data, so that the transmission capacity can be exactly adapted to the current requirements. In Fig. 2, for example, only sub-structure elements SEO, SE4, and SE9 are defined for the channels 0, 4 and 9;
i.e., that data are currently communicated between the communication systems only via three existing terminal equipment connections. In contrast to an ATM cell ATM-Z1, according to the ATM adaption layer AAL Type 1, an allocation of a useful data byte to a channel of a TDM frame R1, R2 given an ATM cell ATM-Z1, ATM-Z2 according to the ATM adaption layer AAL Type 2 does not occur via the position of the payload data byte in the payload data area of the ATM cell ATM-Z1, ATM-Z2 but via the channel identifier CID.
A payload data field I of variable length (0 through 26) can be defined by the six-bit long length identifier LI in the cell header of a sub-structure element.
The possibility connected therewith of realizing a data transmission with variable transmission capacity allows the employment of compression algorithms that, due to a removal of redundant information, generate a variable data stream from a constant data stream.
Given a conversion of a continuous data stream based on the TDM method onto the ATM data format according to ATM adaption layer AAL Type 2, the payload data field I with a constant length of 8 bytes is employed for the sub-structure elements SE.
A sub-structure element SE according to ATM adaption layer AAL Type 2 is thus bytes long, a cell header with a length of 3 bytes and 8 bytes of payload data. In this case, the cell overhang, which is often referred to as "overhead" in the references, of a sub-structure element SE according to ATM adaption layer AAL Type 2 is more than 37% of the payload. In order to reduce this cell overhead, a data transmission can be realized with the assistance of the ATM adaption layer AAL Type 5.
Fig. 3 shows a schematic illustration of an AAL Type 5 frame R5 and of two ATM
cells ATM-Z1, ATM-Z2 according to the ATM adaption layer AAL Type 5. An AAL
type frame R5 has a length of 0 through 2'6 bytes. The information contained in an AAL
Type 5 frame R5 is divided into one or more ATM cells ATM-Z1, ATM-Z2 according to the length of the AAL type 5 frame R5. For a restoration of the synchronization between transmitter and receiver if one or more ATM cells ATM-Z1, ATM-Z2 have been lost due, for example, to a transmission error, the data contained in an AAL
Type 5 frame R5 is divided such into one or more ATM cells ATM-Z1, ATM-Z2 that the first byte of the AAL Type 5 R5 is allocated to the first byte of the payload data area of an ATM
cell ATM-Z1. As a result of a marking F in the cell header of the last ATM
cell ATM-Z2 allocated to an AAL Type 5 frame R5) it can be recognized that the next-following ATM
cell that contains the same ATM address, composed of VPI and VCI, in the cell header H is the first ATM cell allocated to the AAL Type 5 successive frame.
For a subdivision of an AAL Type 5 frame R5 into sub-structure elements SE, sub-structure element-individual pointers L (with a length of one byte) are defined which indicate the length of the individual sub-structure elements SE. Sub-structure elements SE up to a length of 2a = 256 bytes therefore can be realized. Within the framework of an interworking of communication systems, there is the possibility, via a separate signaling, of defining an allocation between the channels of a TDM frame and individual sub-structure elements SE; for example, via the length of the sub-structure element SE
or via the sequence of the individual sub-structure elements SE. In Fig. 3, for example, only sub-structure elements SEO, SE4 and SE9 for the channel 0, 4 and 9 are defined;
i.e., that data is being currently communicated between the communication systems only via three existing terminal equipment connections.
Given a conversion of the data format according to the TDM method onto the ATM data format according to ATM adaption layer AAL Type 5, a payload data field having constant length of 8 bytes is employed for the sub-structure elements SE. A
sub-structure element SE according to ATM adaption layer AAL Type 5 is thus 9 bytes long, a pointer Z having a length of 1 byte and 8 bytes of payload data. In this case, the cell overhead of a sub-structure element SE according to ATM adaption layer AAL
Type 5 only amounts to 12.5% of the payload.
Although the present invention has been described with reference to specific embodiments, those of skill in the art will recognize that changes may be made thereto without departing from the spirit and scope of the invention as set forth in the hereafter appended claims.
Fig. 1 shows a schematic illustration of two TDM frames R1, R2 and of two corresponding ATM cells ATM-Z1, ATM-Z2 according to the ATM adaption layer AAL
Type 1. A TDM frame R1, R2 includes 32 channels via which a data transmission is possible in the framework of 30 terminal equipment connections, and wherein an allocation of 30 channels for a transmission of payload information and of two channels far a transmission of signaling information exists. Given a conversion of a continuous data stream based on the TDM method onto the ATM format according to the ATM
adaption layer AAL Type 1, all 32 channels succeeding one another in time in a TDM
frame, with respect to the one byte payload data information, are converted onto the ATM cell format in the following way.
In addition to the cell header H of the ATM cell ATM- Z1, ATM-Z2, the first byte within the payload area, referred to below as payload data area, is defined as pointer Z. This pointer Z points to the first byte of a TDM frame R1, R2 beginning within the payload data area of an ATM cell ATM-Z1, ATM-Z2. With this pointer Z, a restoration of the synchronization between transmitter and receiver is possible in case one or more ATM cells ATM-Z1, ATM-Z2 have been lost due, for example, to a transmission error.
The transmission of the payload data information contained in a TDM frame R1, occurs beginning with the second byte of the payload data area of an ATM cell ATM-Z1, ATM-Z2. The payload data bytes allocated to the individual channels of the TDM
frame R1, R2 are thereby communicated in sequence. Immediately after a transmission of the last byte (the byte allocated to channel 31 ) of a TDM frame R1, a transmission of the first byte (the byte allocated to the channel 0) of the TDM successor frame R2 occurs. An allocation of the payload data bytes of an ATM cell ATM-Z1, ATM-Z2 to a channel of a TDM frame R1, R2 thus occurs via the position of the byte in the payload data area of the ATM cell ATM-Z1, ATM-Z2.
Fig. 2 shows a schematic illustration of two ATM cells ATM-Z1, ATM-Z2 and of a sub-structure element SE according to the ATM adaption layer AAL Type 2.
Within the framework of the ATM adaption layer AAL Type 2, there is the possibility of subdividing the payload data area of an ATM cell ATM-Z1, ATM-Z2 into sub-structure elements SE. A sub-structure element SE according to the ATM adaption layer AAL
type 2 is composed of a cell header SH that is 3 bytes long and of a payload data area I of variable length (0 through 64 bytes). The cell header of a sub-structure element SE
according to the ATM adaption layer AAL Type 2 is subdivided into a channel identification CID (Channel Identifier) that is 8 bits long, into a length indicator LI
(Length Indicator) that is 6 bits long, a sender-receiver identification UUI
(User-to-User Indication) that is 5 bits long and a 5 bit long cell header checksum HEC
(Header Error Control).
Corresponding to an ATM cell ATM-Z1, ATM-Z2 according to the ATM adaption layer AAL Type 1, the first byte in the payload data area of an ATM cell ATM-Z1, ATM-Z2 is defined as pointer Z. This pointer Z indicates the starting address of the first sub-structure element SE whose cell header SH lies in the payload data area of the ATM
cell ATM-Z1, ATM-Z2. A restoration of the synchronization between transmitter and receiver is possible with this pointer Z in case one or more ATM cells ATM-Z1, have been lost due, for example, to a transmission error.
Due to the sub-division of an ATM cell ATM-Z1, ATM-Z2 into sub-structure elements SE, a plurality of channels that are all addressed with the same ATM
address, composed of a VPI _ _ -(Virtual Path Identifier) and of a VCI (Virtual Channel Identifier), can be defined within an ATM connection on the basis of the channel identification CID.
Within the framework of an interworking of communication systems, thus, there is the possibility of defining a sub-structure element SE for a transmission of signaling information; i.e., for a transmission of D-channel data. A further sub-structure element SE can be defined for every required B-channel for a transmission of payload data information, i.e. for a transmission of B-channel data, so that the transmission capacity can be exactly adapted to the current requirements. In Fig. 2, for example, only sub-structure elements SEO, SE4, and SE9 are defined for the channels 0, 4 and 9;
i.e., that data are currently communicated between the communication systems only via three existing terminal equipment connections. In contrast to an ATM cell ATM-Z1, according to the ATM adaption layer AAL Type 1, an allocation of a useful data byte to a channel of a TDM frame R1, R2 given an ATM cell ATM-Z1, ATM-Z2 according to the ATM adaption layer AAL Type 2 does not occur via the position of the payload data byte in the payload data area of the ATM cell ATM-Z1, ATM-Z2 but via the channel identifier CID.
A payload data field I of variable length (0 through 26) can be defined by the six-bit long length identifier LI in the cell header of a sub-structure element.
The possibility connected therewith of realizing a data transmission with variable transmission capacity allows the employment of compression algorithms that, due to a removal of redundant information, generate a variable data stream from a constant data stream.
Given a conversion of a continuous data stream based on the TDM method onto the ATM data format according to ATM adaption layer AAL Type 2, the payload data field I with a constant length of 8 bytes is employed for the sub-structure elements SE.
A sub-structure element SE according to ATM adaption layer AAL Type 2 is thus bytes long, a cell header with a length of 3 bytes and 8 bytes of payload data. In this case, the cell overhang, which is often referred to as "overhead" in the references, of a sub-structure element SE according to ATM adaption layer AAL Type 2 is more than 37% of the payload. In order to reduce this cell overhead, a data transmission can be realized with the assistance of the ATM adaption layer AAL Type 5.
Fig. 3 shows a schematic illustration of an AAL Type 5 frame R5 and of two ATM
cells ATM-Z1, ATM-Z2 according to the ATM adaption layer AAL Type 5. An AAL
type frame R5 has a length of 0 through 2'6 bytes. The information contained in an AAL
Type 5 frame R5 is divided into one or more ATM cells ATM-Z1, ATM-Z2 according to the length of the AAL type 5 frame R5. For a restoration of the synchronization between transmitter and receiver if one or more ATM cells ATM-Z1, ATM-Z2 have been lost due, for example, to a transmission error, the data contained in an AAL
Type 5 frame R5 is divided such into one or more ATM cells ATM-Z1, ATM-Z2 that the first byte of the AAL Type 5 R5 is allocated to the first byte of the payload data area of an ATM
cell ATM-Z1. As a result of a marking F in the cell header of the last ATM
cell ATM-Z2 allocated to an AAL Type 5 frame R5) it can be recognized that the next-following ATM
cell that contains the same ATM address, composed of VPI and VCI, in the cell header H is the first ATM cell allocated to the AAL Type 5 successive frame.
For a subdivision of an AAL Type 5 frame R5 into sub-structure elements SE, sub-structure element-individual pointers L (with a length of one byte) are defined which indicate the length of the individual sub-structure elements SE. Sub-structure elements SE up to a length of 2a = 256 bytes therefore can be realized. Within the framework of an interworking of communication systems, there is the possibility, via a separate signaling, of defining an allocation between the channels of a TDM frame and individual sub-structure elements SE; for example, via the length of the sub-structure element SE
or via the sequence of the individual sub-structure elements SE. In Fig. 3, for example, only sub-structure elements SEO, SE4 and SE9 for the channel 0, 4 and 9 are defined;
i.e., that data is being currently communicated between the communication systems only via three existing terminal equipment connections.
Given a conversion of the data format according to the TDM method onto the ATM data format according to ATM adaption layer AAL Type 5, a payload data field having constant length of 8 bytes is employed for the sub-structure elements SE. A
sub-structure element SE according to ATM adaption layer AAL Type 5 is thus 9 bytes long, a pointer Z having a length of 1 byte and 8 bytes of payload data. In this case, the cell overhead of a sub-structure element SE according to ATM adaption layer AAL
Type 5 only amounts to 12.5% of the payload.
Although the present invention has been described with reference to specific embodiments, those of skill in the art will recognize that changes may be made thereto without departing from the spirit and scope of the invention as set forth in the hereafter appended claims.
Claims (11)
1. A method for connecting communication systems via a packet-oriented data transmission link, wherein the communication systems provide multiplex connections respectively formed of a periodic sequence of channel-individual information segments, the method comprising the steps of:
forming data packets subdivided into a plurality of sub-structure elements for a data transmission;
allocating one of the plurality of sub-structure elements to a channel of a respective multiplex connection;
inserting into the sub-structure element an individually adjustable plurality of information segments successively arriving via the allocated channel; and suppressing a transmission of the plurality of sub-structure elements dependent on information contained in the plurality of information segments.
forming data packets subdivided into a plurality of sub-structure elements for a data transmission;
allocating one of the plurality of sub-structure elements to a channel of a respective multiplex connection;
inserting into the sub-structure element an individually adjustable plurality of information segments successively arriving via the allocated channel; and suppressing a transmission of the plurality of sub-structure elements dependent on information contained in the plurality of information segments.
2. A method for connecting communication systems as claimed in claim 1, further comprising the steps of:
providing in common a plurality of channels for a respective multiplex connection;
and inserting into the sub-structure element an individually adjustable plurality of information segments successively arriving via the plurality of channels.
providing in common a plurality of channels for a respective multiplex connection;
and inserting into the sub-structure element an individually adjustable plurality of information segments successively arriving via the plurality of channels.
3. A method for connecting communication systems as claimed in claim 1, wherein the data packets are formed as ATM cells.
4. A method for connecting communication systems as claimed in claim 2, further comprising the steps of:
providing a respective cell header for each of the plurality of sub-structure elements;
storing a channel identifier in the cell header for indicating an allocation of the sub-structure elements to the corresponding channels; and storing length information for indicating the plurality of information segments inserted in the sub-structure element.
providing a respective cell header for each of the plurality of sub-structure elements;
storing a channel identifier in the cell header for indicating an allocation of the sub-structure elements to the corresponding channels; and storing length information for indicating the plurality of information segments inserted in the sub-structure element.
5. A method for connecting communication systems as claimed in claim 1, wherein only information segments of at least one signalization channel are inserted into the sub-structure element.
6. A method for connecting communication systems as claimed in claim 3, further comprising the steps of:
defining a payload data segment of an ATM cell as a first payload data segment;
defining a pointer in the first payload data segment; and indicating with the pointer a starting address of the sub-structure element located in the first payload data segment.
defining a payload data segment of an ATM cell as a first payload data segment;
defining a pointer in the first payload data segment; and indicating with the pointer a starting address of the sub-structure element located in the first payload data segment.
7. A method for connecting communication systems as claimed in claim 1, further comprising the steps of:
forming, in each of the plurality of sub-structure elements, a sub-structure element-individual pointer as a cell header; and indicating by the sub-structure element-individual pointer the plurality of information segments inserted in the respective sub-structure element.
forming, in each of the plurality of sub-structure elements, a sub-structure element-individual pointer as a cell header; and indicating by the sub-structure element-individual pointer the plurality of information segments inserted in the respective sub-structure element.
8. A method for connecting communication systems as claimed in claim 7, further comprising the step of:
communicating via a separate signaling connection an allocation information allocating sub-structure elements to one or more channels.
communicating via a separate signaling connection an allocation information allocating sub-structure elements to one or more channels.
9. A method for connecting communication systems as claimed in claim 8, wherein the allocation information indicates a channel on the basis of the plurality of information segments inserted in a respective sub-structure element.
10. A method for connecting communication systems as claimed in claim 8, wherein the allocation information references a channel on the basis of the sequence of the sub-structure element.
11
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE1998118776 DE19818776A1 (en) | 1998-04-27 | 1998-04-27 | Method for connecting communication systems over a packet-oriented data transmission path |
| DE19818776.9 | 1998-04-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2270100A1 true CA2270100A1 (en) | 1999-10-27 |
Family
ID=7865930
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2270100 Abandoned CA2270100A1 (en) | 1998-04-27 | 1999-04-23 | Method for connecting communication systems via a packet-oriented data transmission link |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0954198A3 (en) |
| CA (1) | CA2270100A1 (en) |
| DE (1) | DE19818776A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19832999C2 (en) * | 1998-07-22 | 2001-10-11 | Siemens Ag | Method for switching data received via a packet-oriented data transmission link |
| DE10065514A1 (en) * | 2000-12-28 | 2002-07-18 | Siemens Ag | Transferring data between different units of radio communications system involves combining data transferred in different channels into packet transferred between two different units |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5761197A (en) * | 1994-11-14 | 1998-06-02 | Northern Telecom Limited | Communications in a distribution network |
| SE515588C2 (en) * | 1996-01-25 | 2001-09-03 | Ericsson Telefon Ab L M | Mini cells with variable for size of payload in a mobile phone network |
| DE19604245C2 (en) * | 1996-02-06 | 2000-07-06 | Siemens Ag | Method for transmitting time-division multiplex channel shape digital signals via an ATM transmission device |
| US5946309A (en) * | 1996-08-21 | 1999-08-31 | Telefonaktiebolaget Lm Ericsson | Hybrid ATM adaptation layer |
-
1998
- 1998-04-27 DE DE1998118776 patent/DE19818776A1/en not_active Withdrawn
-
1999
- 1999-01-28 EP EP99101559A patent/EP0954198A3/en not_active Withdrawn
- 1999-04-23 CA CA 2270100 patent/CA2270100A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| DE19818776A1 (en) | 1999-11-04 |
| EP0954198A2 (en) | 1999-11-03 |
| EP0954198A3 (en) | 2000-02-02 |
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