Classifications

• • 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
  • H04L2012/5647—Cell loss
• • 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
  • H04L2012/565—Sequence integrity
• • 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

Definitions

• the present invention relates to the field of digital communications, particularly in packet mode
• a transmitter sends messages, in the form of packets, to one or more receivers via one or more transport channels
• Each channel transport has imperfections, which can cause
• the packets of the sequence can be marked by respective numbers, or "time labels", generated by a counter and used for synchronization of the receiver
• the receiver detects the loss of a packet by the fact that a time tag is missing in the received sequence
• the receiver can include a buffer memory allowing it to reorder the packets of the sequence on the basis of the time labels received. After a complete interruption of communication on a channel, it is often useful. find out how many packets were lost by the time the channel is restored Time tags can also be used for this purpose
• a reliable transmission with small delays almost always uses either several channels, or the repetition of each packet at short intervals (for example three times) This is the case in particular in the sharing of AAL2 resources (“ATM Adaptation Layer No 2”) for the transmission of faxes If the delays introduced by the different channels differ notably, we need a time labeling method providing a good capacity for reordering over a large time range
• the time labels usually used are generated by a cyclic counter modulo 2 m , where m is the number of coding bits of the labels
• the reordering capacity of such a counter is 2 m , and its period is also 2 It is important that the counter has a large period, so that synchronization can be recovered after an interruption and a restoration of the channel
• the object of the present invention is to considerably increase the numbering period of the packets while limiting ambiguous cases for the receiver. Another aim is to maintain good reordering capacity if the packets are likely not to be received in their order. 'program
• the invention thus proposes a method of transmitting an ordered sequence of messages, in which a synchronization information item dependent on the rank n of the message in the sequence is inserted into a field of m bits of each message.
• N and A are two integers larger than 1 and such that NA ⁇ 2 m , • i is an integer such that 0 ⁇ ⁇ NA, representing the number n mod NA,
• • j is an integer such that 0 ⁇ j ⁇ N, representing the number n mod N, and
• F is a frame index such as 0 ⁇ F ⁇ A N "1 , representing the number (nd / v NA) t77 ⁇ o ⁇ N" 1 , and associated in a unique way with one (Nl) -uplet of integers designated by f k (F) for 1 ⁇ k ⁇ N and such that 0 ⁇ f k (F) ⁇ A
• x mod y and x div y denote respectively, for whole x and y such that y> 0, the remainder and the quotient of the Euclidean division of x by y
• 1 ⁇ k ⁇ N are chosen in such a way that for any frame index F, we have [f k ((F + 1) mo A N_1 ) - f k (F)] mod A ⁇ 1
• the method can then comprise the transmission of messages not belonging to the sequence, by replacing, in the field of m bits, the synchronization information by m bits representing a integer greater than or equal to NA
• Another aspect of the invention relates to a device for transmitting an ordered sequence of messages, comprising means for locating the messages in the sequence, for inserting into a field of m bits of each message an item of synchronization information. in accordance with the above process If NA ⁇ 2 m , the locating means can be arranged to place, in the field of a message to be sent which does not belong to the sequence, m bits representing an integer greater than or equal to NA
• a third aspect of the invention relates to a device for receiving messages sent in an orderly sequence in accordance with the above method, comprising synchronization means for extracting synchronization information from the m bit field of each message received, and for processing the synchronization information extracted from the received messages in order to synchronize means for processing the received messages
• the synchronization means are arranged to distribute the synchronization information extracted from the messages received successively in N classes as a function of the rest of the division Euclidean by N of the respective integers they represent, and to determine, modulo NA N , the rank
• FIGS. 1 and 2 are respectively block diagrams of an example of a transmitting device and an example of a receiving device according to the invention
• FIG. 3 is a flow diagram of a procedure for determining the synchronization information placed in the transmitted packets.
• FIGS. 4 and 5 show a flow diagram of a procedure for decoding the synchronization information received in the packets
• a counter generating, for each rank n of the packet numbered in the sequence an integer C (n ) between 0 and 2 -1 written in the m bit field reserved for the time label
• C (n ) between 0 and 2 -1 written in the m bit field reserved for the time label
• PERIOD For practical interest meters, PERIOD> 2 m ,
• - SYNC is the minimum number of consecutive messages the reception of which guarantees good synchronization in the period, assuming that the transmission never causes more REPET to be lost
• SYNC> m or jzj denotes the integer equal to or immediately greater than the real number z
• SYNC 1,
• - BAD_SYNC defined if SYNC> 1, is the minimum length of the transmitted sequences which, if received after the loss of one or more packets, can cause a bad synchronization of a receiver using
• SYNC consecutive packets to perform synchronization i.e. fk> SYNC / 3n, p, X 0 , X 1 , - I XsYNC- ⁇ n ⁇ P.
• a counter [P, Q] can be slightly modified to improve performance
• the value of the parameter BAD_SYNC 3 ⁇ 2 m "2
• the period of the counter ⁇ N * A ⁇ is very long
• NA is close to 2 m , so that the decrease in parameters REPET and BAD_SYNC compared to their maximum theoretical values (respectively 2 m and 2 m + SYNC) remains low
• N the preferred choice is to take A as the largest positive integer such that NA ⁇ 2 m
• the operations of Euclidean division and modulo in determining the time labels of the packets and their decoding are limited to simple shifts and bit extracts in binary representations of numbers, which simplifies the calculations performed by the transmitter and by the receiver
• N A ⁇ 2 m II certain counter values (which represent the integers of NA at 2 m -1) which are not valid time labels
• the transmitter can deliver messages to the receiver that do not belong to the labeled sequence, which allows for example to transmit signaling information
• the generalized counter ⁇ N * A ⁇ has properties close to those of the counter ⁇ N * A ⁇
• the receiver can distribute the values received successively in N classes according to the rest of the Euclidean division by N of these values Once at least one value has been placed in each of the N classes, the receiver can then determine the packet index, equal to n mod NA, from the value in class 0 and the frame index F from the numbers f k (F) deduced from the values in classes 1 to N-1 after having subtracted the packet index This allows, modulo NA N , the rank n of the message received in the sequence, and therefore synchronize the receiver
• FIG. 1 schematically shows a transmitter in which the information to be transmitted, delivered by a source 10, is subdivided into successive data units PDU, to which a numbering module 11 associates a time label formed by the value of a counter C
• PDU data units
• a numbering module 11 associates a time label formed by the value of a counter C
• the PDU data units and their C labels are assembled, at 12, to form packets or numbered messages, the C label being placed in a determined field of the message
• An interface 13 sets format messages for transmission on one or more channels
• the division and formatting of data units and messages depends on the transmission protocols used. For example, messages can be transmitted over virtual ATM connections. In the example shown in FIG. 1, the messages are duplicated. and sent in parallel on two separate ATM connections This redundancy secures the transmission of information
• the packets are formed from data units of the AAL5 protocol, which are each divided into several ATM cells for transmission.
• each ATM cell transmitted by the interface 13 contains several numbered packets, multiplexed according to the AAL2 protocol
• a corresponding receiver is illustrated diagrammatically in FIG. 2
• This receiver comprises two parallel reception channels up to a combination module 15
• Each channel includes a packet extraction module 16, which reconstitutes the packets received from the ATM cells received on the corresponding virtual connection
• a module 17 receives the successive messages, and extracts the m bits of the synchronization information M (t), supplied to a synchronization module 18
• This module 18 processes the synchronization information M (t) received successively for deliver to the combination module 15, with the data unit PDU, STATE information on the synchronization state of the receiver on the ATM connection concerned as well as, if this information indicates that the receiver is synchronized, the serial number n of the message in the sequence
• the module 15 selects one of the two channels to deliver the useful information processed in the upper protocol layers of the receiver.
• the combination module 15 can systematically select the most recent message received on one of the two channels If we prefer to favor the reliability of the transmission, we can modify the combination algorithm applied by the module 15, for example by providing a buffer memory in which the packets would be written to an address depending on their serial number n then read in order of these numbers, to limit the probability of information loss
• FIG. 3 shows the procedure applied by the dialing module 11 of the transmitter, using the counter ⁇ N * A ⁇
• the module 11 waits until 'a new message is to be sent (step 21)
• the module 1 1 calculates the indexes i and j in accordance with relations (3) and (4) in step 22.
• step 23 counter C takes the value of index i (step 23) Otherwise, index f is calculated in accordance with relation (5) and counter C receives the value (i + N f) mod NA in step 24
• step 25 the value of the counter C is supplied to the module 12 to be inserted in the m-bit field of the message to be sent.
• step 26 the message number n is incremented by a modulo NA unit, and the module 1 1 returns to wait for the next message
• FIG. 4 illustrates a corresponding procedure that the synchronization module 18 can implement in each channel of the receiver when the transmission channel does not modify the order of the packets, which is the case for an ATM virtual connection
• S denotes the number of messages received consecutively and containing synchronization information consistent with each other, which in particular succeed modulo N
• the coherent synchronization information received before the current message n is stored in a register R (0), R (1),, R (N-1)
• the location R (k) of this register (0 ⁇ k ⁇ N) contains the most recent value received from the counter equal to k modulo N
• the different locations of the register R therefore translate a classification of the values received on the basis of the rest of the Euclidean division by N
• a variable EXPECTED which corresponds to the next value of the counter that should be received if the sequence of messages sent is preserved, is initialized to an impossible value ( -1 in the example drawn) since the synchronization is not yet effective
• the module 18 then waits for the reception of a message on the ATM connection (step 31)
• the value M (t ) synchronization information is extracted therefrom (step 32)
• the class index j receives in step 33 the value M (t) mod N equal to the rest of the Euclidean division by N of the value M (t ), which is also loaded in location R (j) of the register
• test 34 and if the number S of previous consecutive messages containing coherent synchronization information does not reach the value of the parameter N '(test 35), the synchronization module 18 indicates to the module combination 15 that its reception channel is not synchronized, leaving the STATE information in the non-synchronized state In this case, the number S is simply incremented in step 36 If, at test 34 the current value M ( t) of the counter corresponds to that expected, and if S> N 'in test 35, the synchronization module 18 indicates by the information STATE that its reception channel is synchronized (step 37)
• the synchronization module 18 indicates by the STATE information that its reception channel is not synchronized (step 38), before compare the current class index j to the expected value j 'of this index at step 39
• the value given to the expected class index j' is arbitrary
• step 41 the module 18 returns to step 31 to wait for the reception of the next message
• the module 18 does not yet have enough counter values to be able to calculate the number n, and it proceeds to the abovementioned step 41
• S> N in test 45 module 18 is able to calculate a value for number n of the short message ant in the sequence produced by the transmitter This is carried out in step 47 in accordance
• steps 52 to 54 can be performed, which are equivalent to steps 22 to 24 executed by the transmitter to determine the value of the counter (FIG.
• the calculation 47 of the packet number from the values R (0), R (1), R (N-1) of the counter received in the current message and in the previous N-1 messages can be in accordance with the procedure represented on Figure 5 and described below
• the boolean variable RETENUE then receives the value TRUE in step 71 Otherwise, we stay in the same frame and the Boolean variable RETENUE receives the value FALSE in step 72
• the current value M (t) of the counter can be compared not with a single predicted value EXPECTED, but with H + K possible values EXPECTED. H + 1 ,, WHEREAS ..,, WHEREAS 0 , WHEREAS.,,, WHEREAS K corresponding to the counter values respectively for messages of ranks n-H + 1,
• the synchronization module commands the writing of the current message in a buffer memory, at an address determined by that of the values which coincided If no value coincides, the message is eliminated, and / or a loss of synchronization is decided
• the synchronization module also controls the output of the buffer of the message the older, of rank n-H + 1 A loss of synchronization can also be decided if several of the messages to be output consecutively miss
• the initial synchronization can for example be identical to what has been described with reference to FIGS. 4 and 5, until the variable S reaches the required value N 'In such an application, this value N' will generally be greater than N, since the possibility of a modification of the packet order entails a greater risk of false synchronization This implies that for the receiver to be able to synchronize, a sequence of a certain length is received in the order
• an interesting possibility for carrying out the initial synchronization is that the receiver distributes the counter values successively received in the modulo N classes, and detects the frame changes after accumulating a sufficiently large number of values.
• a missing value in class 1 makes it possible to locate a start of frame and to determine the index of modulo A frame
• the counter ⁇ N * A ⁇ presents the optimal performances measured by the parameters PERIOD, REPET and BAD_SYNC

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Data Exchanges In Wide-Area Networks (AREA)
• Synchronisation In Digital Transmission Systems (AREA)

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• 1999
  • 1999-03-31 FR FR9904023A patent/FR2791839B1/fr not_active Expired - Fee Related
• 2000
  • 2000-03-28 WO PCT/FR2000/000769 patent/WO2000059259A1/fr not_active Ceased
  • 2000-03-28 EP EP00915227A patent/EP1166593A1/de not_active Withdrawn

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