JP3565606B2 - Cell multiplexer - Google Patents

Description

すなわち、最終セル読出し時刻ｔｎ に最小セル間隔Ｔｐｅａｋ（ｎ） を加算することで、前回のセル送出時点から見てユーザ申告値である最小セル間隔Ｔｐｅａｋ（ｎ） を満たす最短時刻ｔｐｅａｋ（ｎ） を求め、この時刻ｔｐｅａｋ（ｎ） から現在時刻ｔｎｏｗ がどの程度経過しているかを評価値Ｓ（ｎ）とする。この評価値Ｓ（ｎ）が大きいことは、前回のセル送出から長時間の間セル送出を行なっていないことを意味し、従って、この評価値Ｓ（ｎ）が最大のものをセルを送出する入力バッファ１２−ｎに決定することにした。
【００２２】
なお、この第１実施例においては、評価値Ｓが同じものが２以上ある場合には、入力バッファ１２−１〜１２−ｍ間で固定的に定まっている優先順位（例えば最大評価値認識部１６ｃの構成によって一義的に定まる優先順位）に従ってセルを出力する入力バッファを決定する。
【００２３】
次に、図５のフローチャートを参照しながら、読出し制御部１９の動作を説明する。
【００２４】
読出しセル決定部１６は、タイマ１６ａの計時時刻が次のセル読出しタイミングになることを待機しており、タイマ１６ａの計時時刻がセル読出しタイミングになると（ステップ１００）、バッファアクセス制御部１５に、セルが到着している入力バッファがあるか否かを確認させる（ステップ１０１）。なお、バッファアクセス制御部１５は、このタイミングで入力バッファ１２−１〜１２−ｍの状態を見にいくようにしても良く、また、入力バッファ１２−１〜１２−ｍにセルが到着したときに到着信号をもらってそれを保持しておき、セルが到着している入力バッファを認識するようにしても良い。
【００２５】
読出しセル決定部１６は、セルが到着して滞留されている入力バッファが存在しなければ、次のセル読出しタイミングになることを待機する。一方、セルが到着して滞留されている入力バッファが存在すれば、読出しセル決定部１６はさらに、セルが滞留されている入力バッファが２以上存在するか否かを判定する（ステップ１０２）。
【００２６】
セルが滞留されている入力バッファが１個であれば、読出しセル決定部１６は、その入力バッファ（１２−ｎとする）をセルを読み出す入力バッファに決定して、バッファアクセス制御部１５にその入力バッファ１２−ｎからの読出しを指示すると共に、その入力バッファ１２−ｎについてのセル情報記録部１７の最終セル読出し時刻ｔｎ を現在時刻ｔｎｏｗ に更新させる（ステップ１０３）。そして、次のセル読出しタイミングになることを待機する。
【００２７】
一方、複数の入力バッファにセルが滞留されていると、読出しセル決定部１６は、内蔵する評価値計算部１６ｂに、それら入力バッファについての評価値Ｓを計算させ（ステップ１０４）、内蔵する最大評価値認識部１６ｃに評価値Ｓが最大の入力バッファ（１２−ｎとする）を選定させ、その入力バッファ１２−ｎをセルを読み出す入力バッファに決定して、バッファアクセス制御部１５にその入力バッファ１２−ｎからのセル読出しを指示すると共に、その入力バッファ１２−ｎについてのセル情報記録部１７の最終セル読出し時刻ｔｎ を現在時刻ｔｎｏｗ に更新させる（ステップ１０５）。そして、次のセル読出しタイミングになることを待機する。なお、この最大評価値の選定処理においては、上述した同一評価値の場合の調整も適宜なされる。
【００２８】
図６は、読出しセルの決定処理例の説明図である。あるセル読出しタイミング（時刻ｔｎｏｗ）において、入力バッファ１２−Ａ（Ａは１〜ｍ）及び１２−Ｂ（ＢはＡ以外の１〜ｍ）にセルＡ２ 、Ｂ２ が滞留されている場合である。これら入力バッファ１２−Ａ及び１２−Ｂからは、入力バッファ１２−Ｂ及び１２−Ａの順に直前セルＢ１ 、Ａ１ が読み出され、計算で求められた評価値Ｓ（Ａ）＝ｔｎｏｗ −ｔｐｅａｋ（Ａ） 及びＳ（Ｂ）＝ｔｎｏｗ −ｔｐｅａｋ（Ｂ） は、評価値Ｓ（Ｂ）が大きいので、このセル読出しタイミングでは入力バッファ１２−Ｂに滞留されているセルＢ２ を読み出すことに決定する。なお、次のセル読出しタイミングでは、他の入力バッファの状況が変わっていないならば、セルＡ２ が入力バッファ１２−Ａから読み出される。
【００２９】
以上のように、上記第１実施例によれば、セル読出しタイミングになったときに複数の入力バッファにセルが滞留されている場合には、前回の読出し時刻に最小セル間隔を加えた時刻から、時間が一番経過している入力バッファ中のセルから多重するようにしたので、多重後に、同一入力回線からのセル流のセル間隔が最小セル間隔以下に狭まりにくくすることができる。その結果、セルの転送品質を従来より高めることができる。
【００３０】
（Ｂ）第２実施例
次に、本発明の第２実施例を図面を参照しながら説明する。なお、第２実施例の機能ブロック図も、第１実施例に係る図１と同様に表すことができる。
【００３１】
第１実施例においては、複数の入力バッファについての評価値Ｓが同じ場合には、絶対的に定められている優先順位に従ってセルを読み出す入力バッファを決定していたが（図５のステップ１０５での処理）、この第２実施例においては、入力バッファの優先順位をセル読出しタイミング毎に可変させることとした。すなわち、図７に示すように、セル読出しタイミング毎に、各入力バッファの優先順位を１段階ずつ高めると共に、最上位の優先順位のものは次のセル読出しタイミングでは最下位の優先順位になるように、優先順位を可変させる。以上の点を除けば、第２実施例は第１実施例と同様である。
【００３２】
第２実施例の場合、このような優先順位情報もセル情報記録部１７に格納されており、読出し制御部１９は、ステップ１０５の処理において、複数の入力バッファについての評価値Ｓが同じ場合には、セル情報記録部１７に格納されている優先順位情報を参酌して、セルを読み出す入力バッファを決定する。
【００３３】
図８は、第２実施例における読出しセルの決定処理例の説明図である。あるセル読出しタイミング（時刻ｔｎｏｗ ：優先順位からのタイミングは２）において、入力バッファ１２−Ａ（Ａは１〜ｍ）、１２−Ｂ（ＢはＡ以外の１〜ｍ）及び１２−Ｃ（ＣはＡ、Ｂ以外の１〜ｍ）にセルＡ２ 、Ｂ２ 、Ｃ２ が滞留されている場合である。これら入力バッファ１２−Ａ、１２−Ｂ及び１２−Ｃからは、入力バッファ１２−Ｂ、１２−Ｃ及び１２−Ａの順に直前セルＢ１ 、Ｃ１ 、Ａ１ が読み出され、計算で求められた評価値Ｓ（Ａ）＝ｔｎｏｗ −ｔｐｅａｋ（Ａ） 及びＳ（Ｃ）＝ｔｎｏｗ −ｔｐｅａｋ（Ｃ） が等しく、評価値Ｓ（Ｂ）＝ｔｎｏｗ −ｔｐｅａｋ（Ｂ） がこれらより小さい場合である。
【００３４】
このセル読出しタイミングは優先順位から見たタイミングがｘであって、この優先順位タイミングｘでは入力バッファ１２−Ａより入力バッファ１２−Ｃを優先させるようになっていると、読出し制御部１９はその優先順位を認識し、このセル読出しタイミングでは入力バッファ１２−Ｃに滞留されているセルＣ２ を読み出すことに決定する。なお、次のセル読出しタイミング（優先順位タイミングｘ＋１）では、他の入力バッファの状況が変わっておらず、しかも入力バッファ１２−Ｂより入力バッファ１２−Ａの優先順位が高いならば、セルＡ２ が入力バッファ１２−Ａから読み出され、さらに次のセル読出しタイミングでは、他の入力バッファの状況が変わっていないならば、セルＢ２ が入力バッファ１２−Ｂから読み出される。
【００３５】
従って、この第２実施例によっても、セル読出しタイミングになったときに複数の入力バッファにセルが滞留している場合には、前回の読出し時刻に最小セル間隔を加えた時刻から、一番時間が経過している入力バッファ中のセルから多重するようにしたので、多重後に、同一入力回線からのセル流のセル間隔が最小セル間隔以下に狭まりにくくすることができる。その結果、セルの転送品質を従来より高めることができる。
【００３６】
また、この第２実施例によれば、複数の入力バッファについての評価値Ｓが同じときに読み出すセルを決定するための優先順位を、セル読出しタイミング毎に可変させるようにしたので、セル多重装置の統計多重効果をこの点からも有効に発揮させることができる。
【００３７】
（Ｃ）第３実施例
次に、本発明の第３実施例を図面を参照しながら説明する。なお、第３実施例の機能ブロック図も、第１実施例に係る図１と同様に表すことができる。
【００３８】
第１実施例及び第２実施例においては、最大評価値が負であってもその最大評価値に係る入力バッファからセルを読み出すものを示したが、この第３実施例においては、最大評価値が負であるときには入力バッファからセルを読み出すことを禁止するようにしたものである。
【００３９】
ここで、入力バッファ１２−ｎに係る評価値Ｓ（ｎ）が負である場合は、最終セル読出し時刻ｔｎ に最小セル間隔Ｔｐｅａｋ（ｎ） を加算して得られた、前回のセル送出時点から見てユーザ申告値である最小セル間隔Ｔｐｅａｋ（ｎ） を満たす最短時刻ｔｐｅａｋ（ｎ） より、現在時刻ｔｎｏｗ が早い場合であり、この場合にセルを読出すと、前回のセル送出時刻ｔｎ から最小セル間隔Ｔｐｅａｋ（ｎ） が経過する前に次のセル送出が実行され、これらのセルの間隔は最小セル間隔Ｔｐｅａｋ（ｎ） より短くなる。
【００４０】
第３実施例は、評価値Ｓが負の場合におけるセルの読出しを禁止することにより、常に、最小セル間隔以上の間隔をもってセルを送出することを補償したものである。
【００４１】
次に、図９のフローチャートを参照しながら、第３実施例の読出し制御部１９の動作を説明する。
【００４２】
読出しセル決定部１６は、タイマ１６ａの計時時刻が次のセル読出しタイミングになることを待機しており、タイマ１６ａの計時時刻がセル読出しタイミングになると（ステップ２００）、バッファアクセス制御部１５に、セルが到着している入力バッファがあるか否かを確認させる（ステップ２０１）。
【００４３】
読出しセル決定部１６は、セルが到着して滞留している入力バッファが存在しなければ、次のセル読出しタイミングになることを待機する。一方、セルが到着して滞留している入力バッファが存在すれば、読出しセル決定部１６は、内蔵する評価値計算部１６ｂに、セルが滞留されている全ての入力バッファについての評価値Ｓを計算させ（ステップ２０２）、内蔵する最大評価値認識部１６ｃに評価値Ｓが最大の入力バッファを認識させる（ステップ２０３）。
【００４４】
その後、読出しセル決定部１６は、最大評価値が負か否かを判定する（ステップ２０４）。負の場合には、次のセル読出しタイミングになることを待機する。一方、正又は０であると、最大評価値に係る入力バッファをセルを読み出す入力バッファに決定して、バッファアクセス制御部１５にその入力バッファからのセル読出しを指示すると共に、その入力バッファについてのセル情報記録部１７の最終セル読出し時刻を現在時刻ｔｎｏｗ に更新させ（ステップ２０５）、そして、次のセル読出しタイミングになることを待機する。
【００４５】
従って、この第３実施例によれば、セル読出しタイミングになったときに１以上の入力バッファにセルが滞留している場合には、前回の読出し時刻に最小セル間隔を加えた時刻から、時間が正方向に一番経過している入力バッファ中のセルから多重するようにしたので、多重後に、同一入力回線からのセル流のセル間隔が最小セル間隔未満になることを防止できる。その結果、セルの転送品質を従来より高めることができる。
【００４６】
（Ｄ）第４実施例
次に、本発明の第４実施例を説明する。なお、第４実施例の機能ブロック図も、第１実施例に係る図１と同様に表すことができる。
【００４７】
この第４実施例においては、上記第１〜第３実施例と、適用する評価値Ｓが異なっており、その他の点は同様である。なお、ユーザ申告の最小セル間隔Ｔｐｅａｋを評価値が利用している点では同様である。
【００４８】
すなわち、この第４実施例においては、入力バッファ１２−ｎに係る評価値Ｈ（ｎ）を（２） 式に示すように定めている。

最終セル読出し時刻ｔｎ に最小セル間隔Ｔｐｅａｋ（ｎ） を加算することで、前回のセル送出時点から見てユーザ申告値である最小セル間隔Ｔｐｅａｋ（ｎ） を満たす最短時刻ｔｐｅａｋ（ｎ） を求め、この時刻ｔｐｅａｋ（ｎ） から現在時刻ｔｎｏｗ がどの程度経過しているかを最小セル間隔Ｔｐｅａｋ（ｎ） で正規化して評価値Ｈ（ｎ）としている。この評価値Ｈ（ｎ）が大きいことは、前回のセル送出から長時間の間セル送出を行なっていないことを意味し、従って、この評価値Ｈ（ｎ）が最大のものをセルを送出する入力バッファ１２−ｎに決定することにした。
【００４９】
以上のように、第１〜第３実施例の評価値Ｓに比較した場合、この評価値Ｈは、最小セル間隔Ｔｐｅａｋで正規化している点が異なっている。仮に、第１〜第３実施例の評価値Ｓで同じものがあっても、最小セル間隔Ｔｐｅａｋが異なっていると、最小セル間隔Ｔｐｅａｋが小さい方がこの第４実施例の評価値Ｈが大きくなり、読出しセルとして選択される。そのため、最小セル間隔Ｔｐｅａｋに近いセル間隔でのセル送出が期待できる。
【００５０】
このように、評価値Ｈが異なるので、図５のフローチャートにおけるステップ１０４及び１０５の処理や、図９のフローチャートにおけるステップ３０２及び３０３の処理が上記実施例とは異なったものとなるが、第４実施例におけるこれらの処理を上記説明から類推できるので、その説明は省略する。
【００５１】
従って、この第４実施例によれば、セル読出しタイミングになったときに１以上の入力バッファにセルが滞留している場合には、前回の読出し時刻に最小セル間隔を加えた時刻から、最小セル間隔で正規化された時間が一番経過している入力バッファ中のセルから多重するようにしたので、多重後に、同一入力回線からのセル流のセル間隔が最小セル間隔以下に小さくなることをほとんど防止できる。その結果、セルの転送品質を従来より高めることができる。
【００５２】
（Ｅ）他の実施例
上記各実施例においては、図４に示すように、セル情報記録部１７に最小セル間隔及び最終セル読出し時刻を記録するものを示したが、上記評価値Ｓ又はＨを形成できる情報を格納しておけば良く、格納形式は図４に示すものに限定されない。例えば、最小セル間隔と最終セル読出し時刻とを加算した値（ｔpeak）を記録するようにしても良い。なお、特許請求の範囲のセル情報記録部についての表現は、この場合をも含むものとする。
【００５３】
また、上記各実施例においては、ＡＴＭセルを取り扱うセル多重装置を示したが、本発明は、これに限定されるものではなく、固定長のパケット（セル）を統計多重するセル多重装置であれば広く適用することもできる。
【００５４】
さらに、上記各実施例においては、出力回線上での１セル期間が入力回線上での１セル期間に等しい装置（統計多重する装置）を示したが、時間軸圧縮を伴うセル多重装置にも本発明を適用することができる。
【００５５】
【発明の効果】
以上のように、本発明によれば、多重後に、同一入力回線からのセル流のセル間隔が最小セル間隔以下に狭まり難くすることができ、セルの転送品質を従来より高めることができる。
【図面の簡単な説明】
【図１】第１実施例の構成を示すブロック図である。
【図２】従来の構成を示すブロック図である。
【図３】従来の課題の説明図である。
【図４】第１実施例のセル情報記録部の記録内容の説明図である。
【図５】第１実施例の読出し制御部の動作を示すフローチャートである。
【図６】第１実施例の多重例を示す説明図である。
【図７】第２実施例のセル情報記録部の一部記録内容の説明図である。
【図８】第２実施例の多重例を示す説明図である。
【図９】第３実施例の読出し制御部の動作を示すフローチャートである。
【符号の説明】
１０…セル多重装置、１１−１〜１１−ｍ…入力回線、１２−１〜１２−ｍ…入力バッファ、１３…多重部、１４…出力回線、１５…バッファアクセス制御部、１６…読出しセル決定部、１７…セル情報記録部、１９…読出し制御部。[0001]
[Industrial applications]
The present invention relates to a cell multiplexing apparatus, and can be applied to, for example, a line concentrator in an ATM (Asynchronous Transfer Mode) network.
[0002]
[Prior art]
In the ATM network, information is divided and transferred into fixed-length packets (hereinafter, referred to as cells). Therefore, various types of media such as voice and data can be multiplexed collectively. In addition, information at speeds of several kbit / s to several tens Mbit / s can be flexibly multiplexed. Further, according to the ATM network, a statistical multiplexing effect utilizing the burstiness of information can be expected, and efficient use of the ATM network is possible.
[0003]
2. Description of the Related Art Conventionally, as a cell multiplexing apparatus that exerts a statistical multiplexing effect, there is a cell multiplexing apparatus to which a polling method shown in FIG. In this method, cells from each input line are stored in input buffers 1-1,..., 1-m corresponding to the input lines, and a read control unit 3 corresponding to each input buffer 1-1,. -1,..., 3-m perform polling of the buffer groups 1-1 to 1-m in a predetermined order, and if there is a buffer having a cell, read out only one cell from the buffer and read out one cell. This is a method of outputting to an output line via the multiplexing unit 2.
[0004]
Literature "Toshio Soumiya, Naoto Watanabe, Mario Luoni, Masafumi Kato," A Study of Burst Traffic Characteristics in ATM Concentrator ", IEICE Technical Report SSE92-88, November 1992"
[0005]
[Problems to be solved by the invention]
However, in the conventional cell multiplexing device 4, even if the cell flow from the input line satisfies the declared speed (minimum cell interval) that the user has negotiated with the network provider, the cell flow on the output line is not sufficient. There is a problem that the speed of the vehicle may exceed the declared speed.
[0006]
This will be described in detail with reference to FIG. Consider a case where cells arrive from the input lines A, B, and C as shown in FIG. 3 and the multiplexer 4 multiplexes them. Here, it is assumed that when the cells A1 and C1 arrive at the same time, the cell A1 is selected by the cell multiplexer 4 first, and the cell C1 is selected after waiting for one cell period. Thereafter, when the cells A2 and C2 arrive at the same time, it is assumed that the cell C2 is selected by the cell multiplexing device 4 first, and the cell A2 is selected after waiting for one cell period. That is, looking at the cells C1 and C2 from the input line C, the cell interval before being input to the cell multiplexer 4 is T, which is reduced to T1 through the cell multiplexer 4. For example, if the input-side cell interval T is the declared minimum cell interval, the cell interval T1 does not satisfy the declaration via the cell multiplexer 4. Further, as the cell multiplexing device 4, there is a cell multiplexing device having a common buffer also on the output side of the multiplexing unit 2. In this case, the cell interval T1 becomes shorter.
[0007]
In the case of the polling method, generally, the buffer at the starting point of polling is sequentially changed at each cell read timing to prevent continuous reading of cells from the same buffer. The selection of the arrival cell may be different from the previous one.
[0008]
When the cell interval T1 thus narrowed is equal to or smaller than the minimum cell interval,
(1) The cell is discarded by a user declared cell rate control device (UPC: user parameter control),
(2) If a shaper is provided, the cell interval T1 is expanded until it becomes the minimum cell interval. In the case of (1), the cell discard rate increases, and in the case of (2), delay processing is involved, and the number of cells affected is large.
[0009]
Therefore, there is a demand for a cell multiplexing device that can compensate as much as possible that the cell interval of the cell stream after the multiplexing process is equal to or longer than the minimum cell interval.
[0010]
[Means for Solving the Problems]
In order to solve such a problem, in the present invention, m input buffers corresponding to each input line for buffering cells arriving from the m input lines, and cells stored in any of the input buffers are used. In a cell multiplexing apparatus having a read control unit for reading and a multiplexing unit for outputting read cells to a common output line, the read control unit is constituted by the following units.
[0011]
That is, the read control unit sets (I) a cell that records, for each input line, the declared minimum cell interval and the last cell read time at which the cell was read most recently from the input buffer associated with that input line. An information recording unit, (II) a buffer access control unit for observing whether a cell has arrived at each input buffer and outputting the cell from the designated input buffer, and (III) a cell access recording unit An evaluation value reflecting an elapsed time from a time obtained by adding the minimum cell interval to the last cell read time is read by a read cell determining unit used to determine a read cell.
[0012]
[Action]
In the cell multiplexing device of the present invention, the read cell determining unit appropriately uses the evaluation value reflecting the elapsed time from the time obtained by adding the minimum cell interval to the last cell read time recorded in the cell information recording unit. The read cell is determined, and the buffer access control unit causes the determined cell to be output from the stored input buffer.
[0013]
As a result, after multiplexing, it is possible to make it difficult for the cell interval of the cell flow from the same input line to be smaller than the minimum cell interval, and as a result, it is possible to improve the transfer quality of the cell as compared with the conventional case.
[0014]
【Example】
(A) First Embodiment Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. Here, FIG. 1 is a block diagram showing the cell multiplexer according to the first embodiment.
[0015]
In FIG. 1, the cell multiplexing apparatus 10 also basically has input buffers (FIFO memories) 12-1,..., 12- for buffering cells arriving from the input lines 11-1,. m, a read control unit 19 for reading out the cells stored in any of the input buffers 12-1,..., 12-m, and a multiplexing unit 13 for outputting the read out cells to a common output line 14. It is composed of
[0016]
Here, the read control unit 19 includes a buffer access control unit 15, a read cell determination unit 16, and a cell information recording unit 17.
[0017]
The buffer access control unit 15 checks whether a cell has arrived at each of the input buffers 12-1,..., 12-m. The input buffer 12-n determined by the read cell determination unit 16 (n is 1 to m) to output a cell.
[0018]
As shown in FIG. 4, the cell information recording unit 17 stores the minimum cell of the declared value for each of the input lines 11-1,..., 11-m (accordingly, for each of the input buffers 12-1,. , Tpeak (m) and the time at which the cell was read most immediately before for the input buffers 12-1,..., 12-m corresponding to the input line (hereinafter referred to as the last cell read time). , tm are stored. The final cell read times t1,..., Tm are provided from the read cell determination unit 16 and stored in the cell information recording unit 17.
[0019]
The read cell determination unit 16 determines a cell (accordingly, an input buffer) to be read at the cell read timing based on the cell arrival information from the buffer access control unit 15 and the record information of the cell information recording unit 17. The read cell determination unit 16 includes a timer 16a, an evaluation value calculation unit 16b, a maximum evaluation value recognition unit 16c, and the like. The evaluation value calculation unit 16b and the maximum evaluation value recognition unit 16c function when cells are accumulated in two or more input buffers, and the evaluation value calculation unit 16b calculates the evaluation value S for those input buffers. Then, the cell is output from the input buffer recognized as the maximum evaluation value by the maximum evaluation value recognition unit 16c.
[0020]
Here, in the first embodiment, the evaluation value S (n) relating to the input buffer 12-n is determined as shown in Expression (1). Note that tnow is the current time.
[0021]

That is, by adding the minimum cell interval Tpeak (n) to the last cell read time tn, the shortest time tpeak (n) that satisfies the minimum cell interval Tpeak (n), which is the user declared value from the previous cell transmission time point, is obtained. Then, how much the current time tnow has elapsed since the time tpeak (n) is defined as an evaluation value S (n). When the evaluation value S (n) is large, it means that the cell has not been transmitted for a long time since the previous cell transmission, and therefore, the cell having the maximum evaluation value S (n) is transmitted. The input buffer 12-n is determined.
[0022]
In the first embodiment, if two or more evaluation values S are the same, the priority (for example, the maximum evaluation value recognition unit) that is fixedly set among the input buffers 12-1 to 12-m. The input buffer for outputting the cell is determined according to the priority order uniquely determined by the configuration of FIG. 16c).
[0023]
Next, the operation of the read control unit 19 will be described with reference to the flowchart of FIG.
[0024]
The read cell determination unit 16 waits until the time counted by the timer 16a reaches the next cell read timing. When the time counted by the timer 16a reaches the cell read timing (step 100), the buffer access control unit 15 It is checked whether there is an input buffer in which a cell has arrived (step 101). Note that the buffer access control unit 15 may check the state of the input buffers 12-1 to 12-m at this timing, and when a cell arrives at the input buffers 12-1 to 12-m. May be received and held, and the input buffer at which the cell has arrived may be recognized.
[0025]
If there is no input buffer in which a cell arrives and stays, the read cell determination unit 16 waits for the next cell read timing. On the other hand, if there is an input buffer in which a cell arrives and stays, the read cell determination unit 16 further determines whether or not there are two or more input buffers in which the cell stays (step 102).
[0026]
If there is only one input buffer in which cells are retained, the read cell determining unit 16 determines the input buffer (referred to as 12-n) as an input buffer from which cells are read, and sends the input buffer to the buffer access control unit 15. Instructing reading from the input buffer 12-n, and updating the last cell read time tn of the cell information recording unit 17 for the input buffer 12-n to the current time tnow (step 103). Then, it waits for the next cell read timing.
[0027]
On the other hand, if the cells are stored in the plurality of input buffers, the read cell determination unit 16 causes the built-in evaluation value calculation unit 16b to calculate the evaluation value S for those input buffers (step 104), The evaluation value recognition unit 16c selects an input buffer (supposed to be 12-n) having the maximum evaluation value S, determines the input buffer 12-n as an input buffer from which cells are read, and inputs the input buffer to the buffer access control unit 15. The cell reading from the buffer 12-n is instructed, and the last cell reading time tn of the cell information recording unit 17 for the input buffer 12-n is updated to the current time tnow (step 105). Then, it waits for the next cell read timing. In the process of selecting the maximum evaluation value, the adjustment for the same evaluation value described above is appropriately performed.
[0028]
FIG. 6 is an explanatory diagram of an example of a read cell determination process. At a certain cell read timing (time tnow), the cells A2 and B2 are staying in the input buffers 12-A (A is 1 to m) and 12-B (B is 1 to m other than A). From the input buffers 12-A and 12-B, the immediately preceding cells B1 and A1 are read out in the order of the input buffers 12-B and 12-A, and the evaluation value S (A) = tnow-tpeak ( A) and S (B) = tnow−tpeak (B) Since the evaluation value S (B) is large, it is determined that the cell B2 staying in the input buffer 12-B is read at this cell read timing. At the next cell read timing, the cell A2 is read from the input buffer 12-A if the status of the other input buffers has not changed.
[0029]
As described above, according to the first embodiment, when cells are accumulated in a plurality of input buffers when the cell read timing comes, the time from the previous read time plus the minimum cell interval is used. Since the multiplexing is performed from the cell in the input buffer where the time has elapsed most, the cell interval of the cell flow from the same input line after the multiplexing can be hardly narrowed to the minimum cell interval or less. As a result, the transfer quality of the cell can be improved as compared with the related art.
[0030]
(B) Second Embodiment Next, a second embodiment of the present invention will be described with reference to the drawings. Note that the functional block diagram of the second embodiment can be represented in the same manner as FIG. 1 according to the first embodiment.
[0031]
In the first embodiment, when the evaluation values S of a plurality of input buffers are the same, the input buffer from which cells are read is determined in accordance with the absolutely determined priority (see step 105 in FIG. 5). In the second embodiment, the priority of the input buffer is varied at each cell read timing. That is, as shown in FIG. 7, the priority of each input buffer is increased by one step at each cell read timing, and the highest priority is given the lowest priority at the next cell read timing. Then, the priority is changed. Except for the above points, the second embodiment is the same as the first embodiment.
[0032]
In the case of the second embodiment, such priority information is also stored in the cell information recording unit 17, and the read control unit 19 determines in step 105 that the evaluation values S for the plurality of input buffers are the same. Determines the input buffer from which the cell is read, in consideration of the priority order information stored in the cell information recording unit 17.
[0033]
FIG. 8 is an explanatory diagram of an example of a read cell determination process in the second embodiment. At a certain cell read timing (time tnow: the timing from the priority order is 2), the input buffers 12-A (A is 1 to m), 12-B (B is 1 to m other than A) and 12-C (C In the case where the cells A2, B2, and C2 are retained in 1 to m) other than A and B. From these input buffers 12-A, 12-B and 12-C, the immediately preceding cells B1, C1 and A1 are read out in the order of the input buffers 12-B, 12-C and 12-A, and the evaluations obtained by calculation are obtained. The value S (A) = tnow-tpeak (A) and S (C) = tnow-tpeak (C) are equal, and the evaluation value S (B) = tnow-tpeak (B) is smaller than these.
[0034]
When the cell read timing is x in terms of priority, the read control unit 19 determines that the input buffer 12-C has priority over the input buffer 12-A at this priority timing x. The priority is recognized, and at this cell read timing, it is determined to read the cell C2 staying in the input buffer 12-C. At the next cell read timing (priority timing x + 1), if the status of the other input buffers has not changed and if the priority of the input buffer 12-A is higher than that of the input buffer 12-B, the cell A2 becomes the cell A2. The cell B2 is read from the input buffer 12-B at the next cell read timing, and if the status of the other input buffer has not changed, at the next cell read timing.
[0035]
Therefore, according to the second embodiment, when cells are accumulated in a plurality of input buffers at the cell read timing, the most read time is calculated from the time obtained by adding the minimum cell interval to the previous read time. Are multiplexed from the cells in the input buffer that have elapsed, so that after multiplexing, it is possible to prevent the cell interval of the cell flow from the same input line from becoming narrower than the minimum cell interval. As a result, the transfer quality of the cell can be improved as compared with the related art.
[0036]
Further, according to the second embodiment, the priority for determining the cell to be read when the evaluation values S of the plurality of input buffers are the same is varied at each cell read timing. The statistical multiplexing effect described above can also be effectively exerted from this point.
[0037]
(C) Third Embodiment Next, a third embodiment of the present invention will be described with reference to the drawings. Note that the functional block diagram of the third embodiment can be represented in the same manner as FIG. 1 according to the first embodiment.
[0038]
In the first embodiment and the second embodiment, the case where the cell is read from the input buffer relating to the maximum evaluation value even when the maximum evaluation value is negative is shown. In the third embodiment, the maximum evaluation value is read. There is negatively Oh Rutoki is obtained so as to prohibit the reading cells from the input buffer.
[0039]
Here, when the evaluation value S (n) relating to the input buffer 12-n is negative, since the last cell transmission time obtained by adding the minimum cell interval Tpeak (n) to the last cell read time tn, In this case, the current time tnow is earlier than the shortest time tpeak (n) that satisfies the minimum cell interval Tpeak (n), which is a user-reported value. The next cell transmission is performed before the cell interval Tpeak (n) has elapsed, and the interval between these cells is shorter than the minimum cell interval Tpeak (n).
[0040]
In the third embodiment, the reading of cells when the evaluation value S is negative is prohibited, thereby compensating for always transmitting cells at intervals equal to or longer than the minimum cell interval.
[0041]
Next, the operation of the read control unit 19 of the third embodiment will be described with reference to the flowchart of FIG.
[0042]
The read cell determination unit 16 waits until the time counted by the timer 16a reaches the next cell read timing. When the time counted by the timer 16a reaches the cell read timing (step 200), the buffer access control unit 15 It is checked whether there is an input buffer in which a cell has arrived (step 201).
[0043]
If there is no input buffer in which a cell arrives and stays, the read cell determination unit 16 waits for the next cell read timing. On the other hand, if there is an input buffer in which a cell arrives and stays, the read cell determination unit 16 sends the evaluation values S for all the input buffers in which the cell stays to the built-in evaluation value calculation unit 16b. Calculation is performed (step 202), and the built-in maximum evaluation value recognition unit 16c is made to recognize the input buffer having the maximum evaluation value S (step 203).
[0044]
Thereafter, the read cell determination unit 16 determines whether the maximum evaluation value is negative (Step 204). If negative, it waits for the next cell read timing. On the other hand, if the value is positive or 0, the input buffer relating to the maximum evaluation value is determined as the input buffer from which the cell is read, and the buffer access control unit 15 is instructed to read the cell from the input buffer. The last cell read time of the cell information recording unit 17 is updated to the current time tnow (step 205), and the process waits for the next cell read timing.
[0045]
Therefore, according to the third embodiment, when cells are accumulated in one or more input buffers at the cell read timing, the time is calculated from the time obtained by adding the minimum cell interval to the previous read time. Are multiplexed from the cell in the input buffer which has passed the most in the forward direction, so that after multiplexing, the cell interval of the cell flow from the same input line can be prevented from becoming smaller than the minimum cell interval. As a result, the transfer quality of the cell can be improved as compared with the related art.
[0046]
(D) Fourth Embodiment Next, a fourth embodiment of the present invention will be described. Note that the functional block diagram of the fourth embodiment can also be represented in the same manner as FIG. 1 according to the first embodiment.
[0047]
The fourth embodiment is different from the first to third embodiments in the evaluation value S to be applied, and the other points are the same. It is the same in that the evaluation value uses the minimum cell interval Tpeak reported by the user.
[0048]
That is, in the fourth embodiment, the evaluation value H (n) related to the input buffer 12-n is determined as shown in Expression (2).

By adding the minimum cell interval Tpeak (n) to the last cell read time tn, the shortest time tpeak (n) that satisfies the minimum cell interval Tpeak (n), which is the user report value from the previous cell transmission time, is obtained. The evaluation value H (n) is obtained by normalizing how much the current time tnow has elapsed from the time tpeak (n) by the minimum cell interval Tpeak (n). When the evaluation value H (n) is large, it means that the cell has not been transmitted for a long time since the previous cell transmission, and therefore, the cell having the maximum evaluation value H (n) is transmitted. The input buffer 12-n is determined.
[0049]
As described above, when compared with the evaluation value S of the first to third embodiments, the difference is that the evaluation value H is normalized by the minimum cell interval Tpeak. Even if the evaluation values S of the first to third embodiments are the same, if the minimum cell interval Tpeak is different, the smaller the minimum cell interval Tpeak, the larger the evaluation value H of the fourth embodiment. And is selected as a read cell. Therefore, cell transmission at a cell interval close to the minimum cell interval Tpeak can be expected.
[0050]
As described above, since the evaluation value H is different, the processing of steps 104 and 105 in the flowchart of FIG. 5 and the processing of steps 302 and 303 in the flowchart of FIG. 9 are different from those in the above embodiment. Since these processes in the embodiment can be inferred from the above description, the description is omitted.
[0051]
Therefore, according to the fourth embodiment, when cells are accumulated in one or more input buffers at the cell read timing, the minimum read time is added to the previous read time by adding the minimum cell interval. Since multiplexing is started from the cell in the input buffer where the time normalized by the cell interval is the longest, the cell interval of the cell flow from the same input line becomes smaller than the minimum cell interval after multiplexing. Can be almost completely prevented. As a result, the transfer quality of the cell can be improved as compared with the related art.
[0052]
(E) Other Embodiments In each of the above embodiments, the minimum cell interval and the last cell read time are recorded in the cell information recording section 17 as shown in FIG. May be stored, and the storage format is not limited to that shown in FIG. For example, a value (tpeak) obtained by adding the minimum cell interval and the last cell read time may be recorded. The expression of the cell information recording unit in the claims includes this case.
[0053]
Further, in each of the above embodiments, the cell multiplexing apparatus for handling ATM cells has been described. However, the present invention is not limited to this, and may be any cell multiplexing apparatus for statistically multiplexing fixed-length packets (cells). It can be widely applied.
[0054]
Furthermore, in each of the above embodiments, a device (statistical multiplexing device) in which one cell period on the output line is equal to one cell period on the input line has been described. The present invention can be applied.
[0055]
【The invention's effect】
As described above, according to the present invention, after multiplex, the cell spacing in the cell stream from the same input line can be difficult narrowing below the minimum cell interval, the transfer quality of the cell can be increased than before.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a first embodiment.
FIG. 2 is a block diagram showing a conventional configuration.
FIG. 3 is an explanatory diagram of a conventional problem.
FIG. 4 is an explanatory diagram of recorded contents of a cell information recording unit of the first embodiment.
FIG. 5 is a flowchart illustrating an operation of a read control unit according to the first embodiment.
FIG. 6 is an explanatory diagram showing a multiplexing example of the first embodiment.
FIG. 7 is an explanatory diagram of partially recorded contents of a cell information recording unit according to a second embodiment.
FIG. 8 is an explanatory diagram showing a multiplexing example of the second embodiment.
FIG. 9 is a flowchart illustrating an operation of a read control unit according to the third embodiment.
[Explanation of symbols]
10: Cell multiplexer, 11-1 to 11-m: input line, 12-1 to 12-m: input buffer, 13: multiplexing unit, 14: output line, 15: buffer access control unit, 16: read cell determination Unit, 17: cell information recording unit, 19: read control unit.

Claims (4)

m input buffers corresponding to each input line for buffering cells arriving from the m input lines, a read control unit for reading cells stored in any of the input buffers, A cell multiplexing device having a multiplexing unit for outputting cells to a common output line,
The read control unit includes:
For each of the input lines, a cell information recording unit that records the declared minimum cell interval and the last cell read time at which the cell was read most recently from the input buffer for that input line,
A buffer access control unit for observing whether a cell has arrived at each of the input buffers, and outputting a cell from the designated input buffer,
An evaluation value that reflects the elapsed time from the time obtained by adding the minimum cell interval to the last cell read time recorded in the cell information storage unit, Ri Na in the reading cell determination unit for use in determining the read cell,
The evaluation value calculated by the read cell determination unit is a value obtained by normalizing the difference value from the time obtained by adding the minimum cell interval to the last cell read time to the current time at the minimum cell interval.
A cell multiplexing device, characterized in that: m input buffers corresponding to each input line for buffering cells arriving from the m input lines, a read control unit for reading cells stored in any of the input buffers, A cell multiplexing device having a multiplexing unit for outputting cells to a common output line,
The read control unit includes:
For each of the input lines, the declared minimum cell interval, and a cell information recording unit that records the last cell read time at which the most recently read cell was read from the input buffer for the input line,
A buffer access control unit for observing whether a cell has arrived at each of the input buffers, and outputting a cell from the designated input buffer,
A read cell determining unit that uses an evaluation value reflecting an elapsed time from a time obtained by adding the minimum cell interval to the last cell read time recorded in the cell information recording unit to determine a read cell;
In the cell information recording unit, information for switching the priority among the input buffers when there are a plurality of input buffers related to the highest evaluation value is recorded at each cell read timing,
When there are a plurality of input buffers associated with the highest evaluation value, the read cell determination unit determines an input buffer from which a cell is to be read according to the recorded priority information.
A cell multiplexing device, characterized in that: 3. The cell multiplexing device according to claim 1, wherein the read cell determining unit does not read a cell from an input buffer associated with a negative evaluation value. The read cell determining unit determines the cell in the input buffer as a read cell without obtaining an evaluation value when there is only one input buffer in which the cell stays at the cell read timing. in the cell multiplexing device according to claim 1, the input buffer in which the cells are staying in the case of 2 or more and determines the read cell by comparing the evaluation value.

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