WO1999011093A1

WO1999011093A1 - Method for transmitting user data that can be allocated to different applications

Info

Publication number: WO1999011093A1
Application number: PCT/DE1998/002191
Authority: WO
Inventors: Klaus Hünlich; Wolfgang Fraas
Original assignee: Siemens Aktiengesellschaft
Priority date: 1997-08-21
Filing date: 1998-07-31
Publication date: 1999-03-04
Also published as: EP1005778A1; CA2300965A1

Abstract

The invention relates to a method for transmitting user data, that can be allocated to different applications, between the A-side and the B-side of an ATM transmission path. The data allocated to the individual applications is transmitted in the substructures that can be allocated to the applications within an ATM adaptation layer frame containing several ATM cells. To this end, the A-side and the B-side allocation of the substructures of an ATM adaptation layer frame is determined by administration. Additional information such as the number of ATM cells containing an ATM adaptation layer frame or data indicating whether the individual substructures have the same size can also be determined by administration.

Description

Be honored

Method for transmitting user data that can be assigned to different applications

The invention relates to a method for transmitting user data, which can be assigned to different applications, between an A-side and B-side of an ATM transmission link, with data assigned to the individual applications in each case within an ATM containing a plurality of ATM cells. Adaptation layer frame are transmitted in the substructures contained in the ATM cells and the useful data of the substructures can each be forwarded differently depending on the receiver-side application assignments.

The interface, which enables access to the ATM network, the ATM adaptation layer, which is also called the AT adaptation layer or AAL, is of major importance.

The AAL is the interface between ATM and the higher protocol layers. It hides the ATM-specific properties of the transmission from the higher layers and adapts the ATM layer (bidirectionally) to them. For this purpose, the data of the higher layers are packed together with the protocol information of the AAL layer in the information fields of the ATM cells and transmitted as useful information, also known as payload. Since the AAL is responsible for adapting the services of higher layers to ATM, it plays no role in the network itself during the transmission. The AAL is for the user there. It establishes the connection between the subscriber and the network.

With an increasing number of applications, driver programs are used instead of special processors, which already use powerful processors in computers. This should also be done in order to adapt the data to be transmitted to the network requirements. This led to to use the AAL-5 specified in accordance with the international standard ITU-T 1.362, initially only intended for data transmission and for the transmission of signaling data, also in the speech area.

In order to meet the requirements placed on the AAL layer by different services, it is divided into sub-layers, so-called AAL sublayers, each with different tasks.

According to the international standard ITU-T 1.362, the possibility of a further breakdown is expressly possible. The functions are currently defined as follows: Seg entation and reassembly (SAR)

- Adaptation to the ATM structure by appropriate segmentation of the data to be transmitted into a size matched to the available information field of the ATM cell

- Recovery of the information content of the information fields of ATM cells for the higher layers Convergence Sublayer (CS)

- Adaptation to the requirements of the respective services by providing the service-specific properties of the

EEL Since AAL-specific protocol elements must be inserted into the data stream from the higher layers in order to implement the service-related properties, the CS function influences the operation of the SAR.

The demands placed on the transmission by individual services can be summarized in classes, so-called classes of services. The requirements are shown in ITU-T 1.362.

When classifying into service classes, the following aspects in particular must be taken into account:

Is "timing relation" between origin (source) and destination (destination) required or not; is the bit rate constant or variable; and a connection-oriented service or a connectionless service is provided.

AAL-5 has the advantage of a lower protocol overhead compared to other AALs. In addition, AAL-5 offers better opportunities to detect cell losses using CRC mechanisms across the entire information content. With voice transmission, AAL-5 fulfills most service requirements, namely synchronization of origin and destination (timing relation between source and destination), constant bit rate CBR (constant bit rate), variable bit rate VBR, connection-oriented service, connection pipes service, low protocol portion of the payload of the ATM cells (protocol overhead), favorable behavior with regard to "binary alignment". Only the delay in the transmission of compressed voice data due to the cell filling time is unfavorable. As long as the transfer of uncompressed ISDN data is concerned, the cell fill times do not play a special role. In the field of mobile radio, however, data compression is necessary in order to be able to optimally use the limited radio frequency bandwidth. Compression factors of 10 lead to the filling times for an ATM cell increasing up to 60 msec. It is therefore advisable in the case of mobile radio and, if necessary, also transmit more than one channel bundled via a VCI for other low bit rate applications such as ATM. For this purpose, a suitable substructure must be defined that can be embedded in ATM adaptation layers such as AAL-5.

At the AAL level, an integer multiple of ATM cells should be selected as a frame, for example based on AAL-5. AAL-5 would enable the security elements contained therein to be used.

It can be derived from the definition of AAL-5 that a substructure can also be chosen to be larger than the actual cell format and that it must be able to overlap the boundaries between two (or more) cells.

From the fact that in the case of mobile radio, data is compressed and thus there is no longer a constant data stream, there arises the requirement for the possibility of being able to define structural elements of different sizes in the substructure as well as structural elements whose size changes over time. In addition, there should be the possibility of being able to select the structural elements of the same size in order to support CBR. You should also be able to transfer elements to support synchronization.

It would also be desirable to be able to transmit data streams with different addressees within an AAL frame.

Therefore, additional properties of the structural elements should be known to the sender and receiver, namely the size of the AAL frame, the length of a structural element, the number of structural elements in a virtual channel, the assignment of individual structural elements to addresses, information regarding synchronicity or Asynchronicity and information regarding the constancy of the bit rate, i.e. CBR / VBR. If this information is transmitted in a known manner within AAL frames, the protocol overhead is greatly increased.

The object of the present invention is to provide a method for transmitting user data that can be assigned to different applications between an A side and a B side of an ATM transmission link, data assigned to the individual applications in each case within an ATM adaptation layer frame containing a plurality of ATM cells Substructures contained in the ATM cells are transmitted without the protocol overhead being greatly increased.

According to the invention, this is solved in that the A-side and B-side assignment of the substructures of an ATM Adjustment layer frame can be set via administration.

This means that the address information of the individual substructures is communicated administratively regardless of the information transfer from the A side and the B side. As a result, the protocol overhead is only increased very slightly on average, since the address information does not need to be transmitted and further information is not or only to be transmitted to a small extent.

In addition, additional information regarding the format of the substructures can be defined administratively or in the signaling phase via signaling. An administrative specification is recommended for transmission lines whose use does not change, for example a connection between a base station and a base station controller or a mobile radio switching center and a base station controller in a mobile radio system.

If, for example, in a development of the invention, the number of ATM cells which an ATM adaptation layer frame contains is determined administratively or in the signaling phase by signaling, this information need not be transmitted when there is an existing connection.

For example, in one embodiment of a method according to the invention, it can be determined administratively or in another embodiment in the signaling phase by signaling whether the individual substructures are the same size or not. In the method according to the invention, the start of the first substructure within a frame is preferably determined by the start of the frame.

In the case of substructure elements of different sizes, in particularly favorable embodiments of a method according to the invention, the first element of each substructure element specifies the length of the substructure element to which it belongs and thus when the next substructure begins.

In the case of substructures of different sizes, the length of a substructure element is preferably determined by the value range 1 of a length indicator field.

If 1 = 0, there is no longer any substructure element. The maximum length that a substructure element can assume is thus determined by L _^ - 1. If the length indicator field is eight bits, i.e. one octet long, up to 256 octets can be numbered. This means that an AAL-5 frame can have up to max. There are 5 ATM cells.

In the case of substructures of the same size, the length of the substructures can also be determined by administration.

The ATM adaptation layer frame can preferably correspond to the AAL-5 frame according to the ATM form. A connection between the A side and the B side can be bidirectional with respect to the substructures of an ATM adaptation layer frame.

A particularly advantageous embodiment of a method according to the invention provides that if no network data are to be transmitted within a substructure when using substructures of different sizes, the length of the substructure is shortened by the part intended for useful data.

If required, a substructure can also extend over the useful data area of two adjacent ATM cells and thus enclose the header information area of an ATM cell.

The invention is summarized below using an example.

An integer number of ATM cells is used as the structure of an AAL-5 frame. The number of cells per structure must be negotiated when signaling when establishing a connection. In the case of structural elements of flexible length, the length of a frame 5 should not exceed, as will be explained in more detail below.

Whether a fixed or flexible format should be selected is agreed by signaling. The same applies to the number of structure elements to be transferred in a frame, ie substructures. Substructures can be within an AAL-5 frame of one

ATM cell overlap in the next ATM cell.

The assignment of individual substructures to addresses is determined by administration. An additional burden on the substructures by the transport of addressing data is thus avoided.

So that structure elements of variable length can be linked together, each element contains a pointer as the first octet, which points to the beginning of the following element. This pointer is one octet long, so that up to 256 octets can be numbered consecutively. This means that an AAL-5 frame can have up to max. There are 5 cells. This restriction also makes sense because any lost pointers can be immediately recovered at the beginning of the next AAL-5 frame.

In the case of structural elements with a fixed length, the linkage can be omitted. The selected length must either be negotiated as part of the signaling or determined by administration. The length of the structural elements must always be specified in integer multiples of octets. Special processor or bus properties can be taken into account here.

The method described is characterized in that no address information has to be given to the individual structural elements. Synchronization measures that become necessary due to loss of frame can affect AAL-5 Support mechanisms. No additional agreements are necessary for this, which concern the formats used. Marking the last cell of a frame with AAL5 is sufficient.

Both sub-structures of flexible length and fixed sub-structures can be used.

Within a frame, information correlated in time along a path, such as related audio and video signals that are transmitted in different channels are always guaranteed to be transmitted simultaneously.

New formats can be defined and then negotiated via signaling without having to intervene in existing procedures.

To illustrate the implementation of information from higher layers in substructures of an AAL-5 frame, the

FIG shows an AAL-5 frame of layer two L2: AAL-5, consisting of four ATM cells, each with header H and not individually identified payload part. Data of a higher layer L3: PDU1, L3: PDU2 and L3: PDU3 are converted in this AAL-5 frame.

The conversion of the information L3: PDU1 leads to an equidistant substructure, the conversion of the information L3: PDU2 leads to a variable substructuring, the individual substructures being larger than cell formats and that Implementation of information L3: PDU3 leads to a variable

Substructuring, whereby the individual substructures are smaller than cell formats.

Claims

claims

1. A method for transmitting user data, which can be assigned to different applications, between an A-side and B-side of an ATM transmission link, with data assigned to the individual applications in each case within an ATM adaptation layer frame containing a plurality of ATM cells in the ATM cells contained substructures are transmitted and the user data of the substructures can be forwarded differently depending on the receiver-side application assignments, characterized in that the A-side and B-side assignment of the substructures of an ATM adaptation layer frame are determined by administration.

2. The method according to claim 1, characterized in that the number of ATM cells, which contains an ATM adaptation layer frame, is determined by administration.

3. The method according to any one of the preceding claims, characterized in that it is determined by administration whether the individual substructures are the same size or not.

4. The method according to any one of the preceding claims, characterized in that in the case of substructures of the same size, the size of the individual substructures is determined by administration.

5. The method according to any one of claims 1 to 3, characterized in that the start of the first substructure within a frame is determined by the start of the frame.

6. The method according to claim 3, characterized in that in the case of substructures of different sizes, the first element of each substructure indicates the length of the substructure element to which it belongs and thus when the next substructure begins.

7. The method according to any one of the preceding claims, characterized in that in the case of substructures of different sizes, the length of a substructure element is determined by the value range l of a length indicator field.

8. The method according to any one of the preceding claims, characterized in that the ATM adaptation layer frame corresponds to the AAL-5 frame according to the ATM form.

9. The method according to any one of the preceding claims, characterized in that the connection between the A side and the B side with respect to the substructures of an ATM adaptation layer frame is bidirectional.

10. The method according to any one of claims 5 to 9, characterized in that in the case of substructures of different sizes, if no network data are to be transmitted within a substructure, the length of the substructure is shortened by the portion provided for useful data.