FR2673786A1 - METHOD FOR SWITCHING DATA STREAMS. - Google Patents

Abstract

The invention relates to a method for switching data streams in synchronous transmission mode with a switch in asynchronous transmission mode. It relates to a method of switching data streams which comprises dividing the data stream into blocks which fill the header and information fields, and inhibiting the translation unit (48 '). header of the header decoding unit (40 ') of the switch in asynchronous transmission mode, so that the data block can be reconstructed in the output channel. Application to the transmission of data streams.

Description

The present invention relates to a method for switching large flows

  synchronous transmission mode (STM) data using a switch operating in asynchronous transmission mode (ATM) as a synchronous transmission mode space switch 5 for payloads such as an auxiliary unit 4 (AU 4 ) of a synchronous digital hierarchy (SDH) synchronous transport module 1 (STM-1), this switch also being able to switch the virtual container NO 4 (VC 4) or any other complete payload into existing systems.

transmission (non-SDH).

  This type of cross connection function is used

  for the reconfiguration of high level transmissions.

  The application of this type of switching corresponds to a reduced condition of switching AU 4 to a node which

has an ATM switch.

  The conventional method of managing this type of switch is the spatial switching of data between the channels, using STM method. This is an efficient method for switching as long as the switch performs only this type of switch. Cross-connect operation The conventional method is probably less expensive when used intensively However, when only occasional use is required, the following method may

suit.

  In an ATM mode, all information is transmitted in small, fixed-size packets called "cells", which have a five-byte header

  which identifies the cell, and forty-eight bytes of information

  which are transported end-to-end in the network.

  A function called "ATM adaptation layer" (AAL) is used for the adaptation of services to the ATM mode There are a number of AAL layer types for different types of services, for example there is the AAL type 1 layer which is used for transporting data streams and which uses a byte of the information part of the cell This byte is used for the

  transport of a sequence number and some protection

  This number allows the cell to carry

  forty-seven bytes of the data stream.

  An SDH stream at 155 megabits per second, carrying 150 megabits per second in ATM mode, could carry up to 132 megabits of data at full load, given the cell headers and the AAL type 1 layer. given the statistical nature of the ATM mode, loading can only be done at about 80%, so that 106 megabits per second of

  data only are transported.

  Given these restrictions, ATM switching

  can not be used in a traditional way for

  at 155 megabits per second.

  A method of switching STM data streams with an ATM switch, including separating the data stream into blocks that fill the header and information fields and inhibiting the translation set. in the ATM switch header decoding unit, so that the block of

  data can be restored by the way out.

  It further relates to an ATM switch for a telecommunications system, comprising an ATM switch and a header decoding unit comprising an inhibition device of the header translation unit.

of the decoding unit.

  Other features and advantages of the invention

  tion will become more apparent from the following description,

  with reference to the accompanying drawings in which: Figure 1 schematically shows a functional model of an ATM switch; Fig. 2 shows the structure of a sixty-two-octet cell used with an ATM switch; Fig. 3 is a block diagram of an exemplary header decoding unit; and FIG. 4 is a block diagram of an exemplary header decoding unit modified to be used.

according to the present invention.

  The use of an ATM switch as a space switch, and its use for the transport of data between the channels by using the full capacity of the fifty-three bytes in ATM mode is ensured so that the cells are fully filled, at the information and header capacity Since all data can be conveyed in the same way and do not require separate identification, it is not necessary to use the header to give Identity to data Since the data is not mixed with other traffic, there is no need for statistical multiplexing so the load can be around 100% An ATM switch capable of handling traffic at 155 , 52 megabits per second can switch AU units 4 to 155.52 megabits per second Simply inhibit the header translation that would normally

performed in the cells.

  The functions of an ATM switch can be divided into three main elements as shown in FIG. 1, any embodiment of switching

  having one or more of each of these functions.

The functions are as follows.

  a) 11, 12, 1 N header decoder units of each channel that transform the incoming circuit identity

  into an outgoing circuit identity and a channel number.

  This unit also allows the maintenance of the order for the use of a particular circuit according to the negotiated traffic level limits and, if necessary, it removes cells in order to avoid a switch overload which could have a effect on the rest of the traffic. (b) The transfer of cells from incoming channels to

  outgoing routes based on routing information.

  physical pathway derived from the decoder unit of

  head This is basically a routing function

Space 20.

  c Static multiplexing of the cells transferred by the routing function on the designated flows of the outgoing channel traffic 31, 32, 3 N Given the peaks of the traffic that exceed the capacity of the outgoing flow, it is necessary to form a queue with some of

  cells in sets 21, 22, 2 N with an output queue.

  This outgoing multiplexing and queuing function can be compared to the operation of a time switch in synchronous circuit switching, but does not obey a predetermined cyclic assignment of

  virtual circuit in the time domain.

  For this type of traffic, the functions of transfer and multiplexing of the cells can be used without change, the function 11, 12, 1 N of header decoder to be performed with invalidation of the translation function, and with derivation local track number

  Outgoing Law enforcement can also be inhibited.

  The described method allows the transmission of data in the switch, but has no protection, such as that given by the AAL layer La

  following description shows how this feature

  can be obtained with a particular embodiment of switch in ATM mode, this being however not the only

  process because other switch implementations per-

  put the execution of an AAL layer equivalent in another way, for example the CRC code layout by

  cell and the use of several synchronous planes.

  An example of a fundamental switch in ATM mode and its use in broadcast services are described in British Patent Applications No. 90 19340 0 and

89.17530 1.

  Inside the switch, a cell is routed as a sixty-two-byte cell with routing information and a sequence number (with protection) error detection and the complete cell of fifty-three bytes as shown

in Figure 2.

  The service byte is equivalent to the protection of the sequence number given by the AAL layer type, but has a longer sequence and is therefore better than

  the protection of the AAL type 1 layer.

  The cell completes to fifty-three octets trans-

puts the information.

  The verification sum byte FCS is equivalent to the protection of the sequence number given by the AAL type 1 layer, but it is a larger field and is

  therefore better than the protection of the AAL type 1 layer.

  The realization of the ATM switch that is used implements this internal sixty-two octet cell to allow information routing and protection so that two planes of the switch can

work with reliability.

  The system then works as follows.

  (a) The data stream at the switch input is divided into fifty-three-octet chunks, it has a sequence number, and the routing information is added. This flow is then switched to the exchange switch.

  the same way as ordinary traffic in ATM mode.

  (b) The switch output data is retrieved from the internal sixty-two-byte cells,

  verified by using the sequence number and protecting

  checked by FCS and then transmitted outside the switch. FIG. 3 shows an exemplary header decoding unit 40. A signal from line 42 is verified in a cell reception and verification unit 44, and the cell header is removed and transmitted to a set of 46 policing and a

  Header Translation Unit 48 Unit 48 picks up the

  existing head and produces the identity and the channel number of the outgoing circuit The identity and the channel number are then combined with the contents of the cell in the cell unit 40

  internal construction before transmission to the switch.

  FIG. 4 shows an alternative header decoding unit shown in FIG. 3. During normal operation, the unit 40 'works in the same manner as the unit 40 shown in FIG. , the policing unit 46 'and the header translation unit 48' are inhibited by a signal 52 of a

  central control unit, not shown.

  quence, the cell header is transmitted to the internal construction cell unit 50 'in unmodified form and is combined again with the contents of the front cell

  transmission to the switch, so that the cell originally

data is restored.

  ATM switches usually create

  instability as a function of the load of the data flow

  because of the statistical multiplexing of the traffic.

  However, in this case, the bandwidth used is so large that the flow must be routed on its own without any other traffic. This has the effect of creating instability.

  very small, and the delay can also be minimal.

  This application of an ATM switch would be effective in ensuring a limited AU-4 cross-connection amplitude through the use of an ATM switch requiring only minimal modification of the ATM switch.

track behavior.

  The provision of an ATM switch only for this function is unlikely and unreasonable, but the occasional use of an existing switch of

this way would be advantageous.

  The description relates to a particular form of

  ATM switch, but a similar approach can be

  used for other forms of ATM switches.

Claims (3)

  A method for switching data streams in synchronous transmission mode with a switch in asynchronous transmission mode, characterized in that it comprises dividing the data stream into blocks that fill the header and information fields. , and inhibiting the head translation unit (40 ') of the header header decoding unit (40') in transmission mode   asynchronous, so that the data block can be recognized stitué in the way of exit.   Method according to claim 1, characterized in that it further comprises inhibiting the unit (46 ') of   maintaining order in the header decoding unit.   3 switch in asynchronous transmission mode for a telecommunications system, characterized in that it comprises a switch in transmission mode   asynchronous and a header decoding unit (40 ') comprising   a device for inhibiting its unit (48 ') from header translation.