FR2748875A1 - METHOD AND DEVICE FOR ASYNCHRONOUS MULTIPLEXING AND DEMULTIPLEXING OF MICROCELLS FOR OPTIMIZING THE TRANSMISSION MEANS OF AN ATM NETWORK - Google Patents

Abstract

Asynchronous mode transmission for multiservice networks with a large bit rate range provides for digital data to be transported in standardized ATM cells with a fixed header and load of length. For low-speed services penalized as regards their transmission efficiency on the arteries of the networks, the method according to the invention provides, while performing all the switching and all the transmissions on cells in the standardized format, to multiplex and demultiplex microcells being able to belong to distinct communications thus avoiding the transmission of partially filled standard cells, and while admitting to pass through standardized ATM networks not having knowledge of these microcells. Application: tactical transmissions.

Description

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  The present invention relates to a method and a device for multiplexing and demultiplexing asynchronous microcells allowing

  the optimization of the transmission means of an ATM network.

  The invention relates to the field of telecommunications, and more particularly to Broadband Integrated Services Digital Networks, "Broadband ISDN" in the English terminology, ie multiservice networks with broad bandwidth, which can from television transmission to short spoken messages, for example for civilian or military applications where speech is coded using

linear prediction methods.

  For Broadband Integrated Services Digital Networks, an international conference has adopted asynchronous transfer mode, referred to as ATM (Asynchronous Transfer Mode). The information to be transported is segmented into cells of constant length to which is added a header for routing in the network. Such a cell then consists of a useful information field 48 bytes long, and a header field of 5 bytes. The need to wait for the source to produce 48 bytes of information before it can inject the cell into the network can degrade the quality of the service rendered, by unacceptably increasing transit delay across the network. This case is particularly critical in the case of low bit rate sources, such as vocoders at 2400 bit / s. The solution consisting in filling only partially the useful data fields of each transported cell has the effect of reducing by the same amount the actual utilization rate of the transmission means of the network. When these are rare, as is the case for tactical military networks, it is necessary to

  a compromise between these two opposing constraints.

  The invention aims to overcome this disadvantage.

  The purpose of the method according to the invention is to optimize both the delay of total transfer of information through the network, and the rate of use of the transmission means that support it, for low services. flow and real time. This method is fully compatible with the broadband ISDN architecture principles, and thus allows for interconnection with other ATM networks possibly called for.

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  participate in the transportation of information from end to end. On the other hand, it accepts multiplexing on the same route of transmission, low-speed and real-time services, with any other type of service, such as, non-real-time data, continuous flow services, etc. To this end, the subject of the invention is a method consisting, on the one hand, in receiving on an artery of an ATM network, of demultiplexing the microcells found inside a standardized ATM cell, so as to produce ATM cells, of standardized size but containing only a single microcell, which will then be introduced into a standardized ATM cell switching device, and secondly, to fill a standardized ATM cell with as much as possible, of microcells found in the cells coming out of the cell switching device

Standardized ATM.

  The invention also relates to a device for its implementation.

1 5 work.

  The method makes it possible to maintain ATM cells in standardized format both in the switch and on the transmission routes, which offers the advantage of being able to cross ATM networks not

not knowing the microcells.

  The invention will be better understood and other characteristics and

  advantages will become more apparent from the following description in

  FIG. 1, the structure of a standard cell loaded with two microcells, FIG. 2, a diagram of the architecture of a device according to the invention, FIG. functional diagram of the treatment of the cells coming from the transmission path carried out by the microcell demultiplexer of the device according to the invention; FIG. 4, a functional diagram of the processing of the cells leaving the standard switch of ATM cells, carried out by the microcell multiplexer device according to the invention, and - Figure 5 a block diagram summarizing the treatments performed on the cells emitted on an artery, made by the device

according to the invention.

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  The problematic treated here has already been addressed in the French patent N 2635242, filed by the Applicant and entitled "Method and device for transmission in asynchronous mode using microcells". The method according to the invention differs in that the microcells referred to here are directly generated by the information source, or by the ATM network adaptation device when it exists, and that the proposed device does not perform new segmentation of the processed information, but only statistical multiplexing / demultiplexing and translation of information

  routing in the header of the microcells and treated cells.

  On the other hand, the cells transmitted on the arteries are always in the format

standardized for ATM.

  The following description is based on a typical example of

  process, in which two or more microcells

  can be loaded inside a conventional ATM cell.

  Figure 1 illustrates the schematic structure of an ATM cell loaded with two microcells. If these were chosen to have a total length less than the length of the normalized cell, more could be put without questioning the process. The header of the normalized ATM cell is denoted OH, and its length is in this example 5 bytes. A control field K makes it possible to code among other things the number of microcells transported in the cell in question. It may contain other information related for example to the priority of the cell on transmission, or its priority to loss. It is therefore an essential parameter of

functions described in the following.

  Two functions are defined that are applicable to it: - K gives the number of microcells transported by the ATM cell, and - K and OH respectively give priority to the emission for the

microcell and the ATM cell.

  The fields E1, E2 and 11, 12 respectively designate the fields "header" and "useful information" of the first microcell and the second microcell. The fields OH and E carry information routing information. It should be noted that the actual structure of the interior of the

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  ATM cell may be different, provided that the information entered

here are present.

  In the following, the conventional ATM cells without microcells will be called CO type, those carrying a single microcell will be said to type CI and that containing two microcells will be said to type C2. FIG. 2 illustrates the architecture of the device according to the invention. It comprises, in the receiving direction of the cells in an artery, on a first artery A1, a microcell demultiplexer 1 whose output is coupled to the input of a standard ATM cell switch 2 and, on a second artery A2, a multiplexer of the microcells 3 coupled to the output of the switch 2. The multiplexer / demultiplexer are arranged

  physically in the junction cards from switches to arteries.

  In the receiving direction of the artery A1, the cells are of the type CO, C1 or C2 depending on their source. The microcells are exploded in standardized ATM cells created by the demultiplexer 1, so as to be isolated from their injection point. In the ATM cell switch 2, therefore, only cells of type CO and C1 appear. At the output of switch 2, at point X2, only cells of types CO and C1 appear. The role of the multiplexer 3 is to send on the A2 artery the maximum of type C2 cells mixed with CO cells.

  untreated, and a minimum of C1 cells, partially filled.

  Its role is therefore to maximize the rate of use of the transmission artery. FIG. 3 illustrates a functional diagram of the processing performed by the demultiplexer 1 on the C2 cells entering A1. The CO cells are transmitted without further action on the artery A1. The type C2 cells are divided into two type C1 cells, denoted A and B respectively, by applying translation rules previously recorded in the demultiplexer 1, respectively called Trad1, Trad2 and Trad3 and defined below: - OHA = Tradl (OH, K, E1) - E1A = Trad2 (OH, E1) - Priority (KA) = Trad3 (K, E1) - Number (KA) = 1 Similarly, the scheme is identical for the production of cell B. The cells A and B are injected into the switch 2 so as to respect the order of the microcells in the arrival cell. For proper operation, the physical flow at point Xl is twice that at point A1. Treatment of type C1 cells is identical with production of a cell A without producing a cell B. The operation is

  reduced to a pure translation.

  Figure 4 illustrates a block diagram of the treatment performed by

  the multiplexer 3 on the cells from the switch 2 of ATM cells.

  The rate at point X2 is greater than the rate at point A2 since the switching is asynchronous, and several cells from different routes may have to be routed simultaneously on the same output. For this, a first queue F1 is arranged between the switch 2 and the multiplexer 3. This allows the adaptation of the rates

entering and leaving.

  A second rate adaptation queue noted F2, is arranged between the output of the multiplexer 3 and the transmitter of cells 4 on

  the artery, the multiplexer 3 ensuring the translation of the microcells.

  The first queue F1 is emptied at a rate higher than that of the artery. The example described below considers a number of four cells, this number may be different. The treatments performed are as follows: In a first step, the four cells are transferred to the multiplexer and translator 3, if the first queue F1 is sufficiently full. In the opposite case two options are possible, either the multiplexer 3 only takes into account the number of cells present in the first queue F1, or it waits for others to arrive. This

  choice allows to set the compromise delay / transmission efficiency.

  These cells are of type C1 or CO, they are numbered I to IV on the

figure 4.

  In a second step, the microcells found inside the ATM cells are grouped in pairs in type C2 cells, keeping their order of extraction of the first queue F1, and applying rules of translation beforehand. recorded in the

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  multiplexer 3. In the proposed scheme, for example, cells I and III, each containing a microcell, are merged into a single "a", containing two. Cell IV is translationally transformed into a "b" cell of type C1. In this example, the microcells take precedence over the normal ATM cells CO, and the cell III is translated into a cell "c", which is inserted last in the second queue F2. This queue

  waiting F2 is then emptied at the rate of the artery A2 by the transmitter 4.

  Since it can happen that the first queue F1 contains only cells of type CO, the flow rate at point D2 must be equal to

the one at point D1.

  Figure 5 illustrates a block diagram summarizing the

  treatments carried out on the cells before their transmission on the artery A2.

  The translations TRADI, with i = 1 to 3, are performed by applying rules previously recorded in the multiplexer 3. A typical example is given below: OH.a = Tradl (OH.I, OH.lll, KI, Kil, E.I., E.I.I.) - E.al = Trad2 (OH.a, E.I) - E.a2 = Trad3 (OH.a, E.I.I.) Priority (Ka) = Max (Priority (KI) ), Priority (K.llI) - Number (Ka) = 2 The TRADi functions that appear above, have no

  relationship with the homonymous functions introduced in the description of the

  demultiplexer. It goes without saying that many configurations are imaginable depending on the size chosen for the microcells, and the respective length of their useful information fields, and their routing header. Likewise

  structure of the latter can be variable according to different criteria.

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Claims (4)

  1. A method for multiplexing and asynchronous demultiplexing microcells for optimizing the transmission means of an ATM network, characterized in that it consists, firstly in reception on an ATM network artery, in demultiplexing the microcells found within a normalized ATM cell, to produce ATM cells of standard size but containing only a single microcell, said cells being then introduced into a standardized ATM cell switching device, and secondly , to fill a standardized ATM cell with as many as possible, microcells found in the   outgoing cells of the standardized ATM cell switching device.   2. Method according to claim 1, characterized in that the header of the microcells and the header of the cells carrying them comprise the characteristics of the data stream to be transmitted in these microcells. 3. Device for carrying out the process according to the   1 and 2, characterized in that it comprises, on the arteries of the   network for transmitting low-speed and real-time communications in significant proportion, adapter circuits (1, 3) to at least one end of an artery, between at least two switches, and performing the multiplexing, demultiplexing and the translation of the transported microcells   in ATM cells in standardized format.   4. Device according to claim 3 characterized in that the adapter circuits (1, 3) are located in the junction cards of the switches to the arteries.