Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Reexamination Certificate
1999-12-30
2003-10-14
Ngo, Ricky (Department: 2697)
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
C370S395100, C370S468000, C398S168000
Reexamination Certificate
active
06633541
ABSTRACT:
BACKGROUND OF THE INVENTION
(1 ) Field of the Invention
The present invention relates to a technique for controlling cell communication in an asynchronous transfer mode (ATM) in an access network in which an optical subscriber line is shared by a plurality of subscribers, and particularly to a method for controlling an ascending transmission speed from a plurality of optical network units to an optical line termination, and a communication system therefor in case of providing a best effort type service which does not guarantee a subscriber's available communication speed in a congested state of the network in a passive optical network (PON) system constituted of an optical line termination at a base station side. and of a plurality of optical network units.
(2) Related Art
FIG. 8
is a block diagram showing a constitution of a common PON system to be connected to an ATM network.
The PON system shown in
FIG. 8
is an access network in which optical subscriber lines provided by branching a single optical fiber such as by an optical splitter are shared by a plurality of subscribers. Namely, the system has a basic constitution including a single optical line termination (OLT)
2
connected to an ATM network
1
, and a plurality of optical network units (ONU's)
4
connected to the optical line termination
2
via optical splitter
3
. The OLT
2
accommodates a plurality of ONU's by a single PON interface, while each of the ONU's
4
accommodates a single or plural user terminal(s)
5
.
In the above described PON system, those descending data from the OLT
2
are broadcast toward the respective ONU's
4
in a time-division multiplexing manner, and each of the applicable ONU's
4
takes out relevant information addressed to itself from the descending data. Meanwhile, concerning the ascending data from the respective ONU's
4
to the OLT
2
, in order to avoid collision among cells transmitted from the respective ONU's
4
, the OLT
2
transmits PLOAM (Physical Layer Operation, Administration, and Maintenance) cells to the ONU's
4
, respectively, and each of the ONU's
4
transmits cells at relevant timings in ascending frames as specified by a transmission granting information included in the PLOAM cells. As such, ascending transmission speeds of the respective ONU's
4
in the common PON system have been determined by a transmission period of the transmission granting information included in PLOAM cells to be transmitted from the OLT
2
to the respective ONU's
4
.
FIG. 9
shows frame formats of data to be transmitted on the PON system of FIG.
8
.
As shown in
FIG. 9
, first and second PLOAM cells are included in a descending frame. The first PLOAM cell includes transmission granting informations for 1st through 27th cells in an ascending frame, while the second PLOAM cell includes transmission granting informations for 28th through 53rd cells in the ascending frame. Each of the PLOAM cells has a pay load including the contents as shown in the following Table 1.
TABLE 1
The GRANTn (n=1 to 27) in Table 1 is a transmission granting information corresponding to an n-th cell of the ascending frame (it is noted that the GRANT
27
of the second PLOAM cell is an idle GRANT which does not request any transmission from ONU). The ascending transmission speed of each of ONU's
4
is allocated with a fixed rate based on a peak cell rate (PCR) of each communication channel, irrespectively of a relevant service category and an active/inactive state of the channel.
Each cell in the ascending frame has an overhead comprising a guard time field G for avoiding collision on the transmission line due to transmission fluctuation of ONU's
4
, a clock supplying field PR for supplying a clock in an ascending direction, and a field DL for detecting a heading of the ATM cell.
In the ATM-PON type communication system as described above, a band (ascending transmission speed) has been fixedly allocated to each communication channel on the PON, possibly resulting in such a situation that more bands on the PON are allocated than actually used, thereby causing waste of bands. To. avoid such a situation, there has been known a conventional technique for conducting effective allocation of bands, such as disclosed in Japanese Unexamined Patent Publication No. 10-224368 or No. 10-145386.
In an “ATM cell communication method in a passive double star network” disclosed in the former publication, a main device (corresponding to the OLT
2
) exchanges control slots with subsidiary devices (corresponding to ONU's
4
), to thereby decide activated states of subsidiary devices. During activation of any one of the subsidiary devices, the main device allocates an ascending communication band to the activated one. Conversely, during inactivation of any one of the subsidiary devices, the main device allocates the band, which has been allocated to the inactivated one, to a variable capacity ATM service accommodated in another subsidiary device, to thereby realize an effective band allocation control.
In a “connection setting method in an ATM line concentrator” disclosed in the latter publication, there is established a common path in, which data from subscribers flow between an ATM line concentrator and an ATM switchboard. When the ATM switchboard has received a call from a subscriber accommodated in the ATM line concentrator, the ATM switchboard notifies a band available in the common path to the ATM line concentrator, to thereby simplify setting treatment of connection.
However, there exists a problem as follows, in the aforementioned conventional techniques. Namely, in the method disclosed in the former Japanese Unexamined Patent Publication No. 10-224368, those bands, which have been allocated to the inactivated subsidiary devices, are allocated irrespectively of the traffic amounts (presence/absence of data, bands) of a virtual path (VP) of the variable capacity ATM service being a subject of allocation. Namely, the bands are allocated equally to those VP's of variable capacity ATM service of less traffic amount and to those VP's of variable capacity ATM service of large traffic amount, resulting in that an effective band allocation may not be fully realized. Further, in the method disclosed in the latter Japanese Unexamined Patent Publication No. 10-145386, there may be caused a situation that an actual traffic amount does not exist so much as that of the band established between the ATM line concentrator and the ATM switchboard such as due to congestion of the ATM network, resulting in waste of the difference between the established band and the actual traffic amount.
Meanwhile, there is a best effort type service which does not guarantee a user's available communication speed in a congested state of a network in an ATM communication system. As categories of this service, there are known such as available bit rate (ABR) service, unspecified bit rate (UBR) service, and guaranteed frame rate (GFR) service.
The ABR service means a service in which an ATM network conducts a flow control in response to a congestion state of the network, such that a wide transmission band is allocated to a user terminal in a range between a minimum cell rate (MCR) and a peak cell rate (PCR) when a network resource is not fully used, and the thus allocated transmission band is notified to the user terminal, and a transmission restriction is imposed on a transmitting user terminal when a congestion has occurred in the ATM network. The UBR service means a service in which a band guarantee is not given, but data can be transmitted at a rate up to the PCR when the network resource is not fully used. The GFR service means a service in which the MCR is guaranteed, and data can be transmitted at a rate up to the PCR when the network resource is not fully used.
In the se best effort type services, the transmission speed is increased up to the PCR at the maximum in a situation where the ATM network is not fully used. How ever, in case of occurrence of
Hijikata Toshiyuki
Irie Toshio
Matsunaga Yoshinori
Nobuyasu Kosuke
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Lee Timothy
Ngo Ricky
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