Multiplex communications – Channel assignment techniques – Details of circuit or interface for connecting user to the...
Reexamination Certificate
1998-03-17
2001-03-06
Chin, Wellington (Department: 2664)
Multiplex communications
Channel assignment techniques
Details of circuit or interface for connecting user to the...
C370S412000, C370S229000, C370S395430
Reexamination Certificate
active
06198750
ABSTRACT:
TECHNICAL FIELD
This invention relates to arrangements for controlling the flow of data traffic between users and a broad band data network.
PROBLEM
In a typical modern broad band data network, a plurality of users share a single high speed link to a broad band network, such as a broad band asynchronous transfer mode (ATM) network. Such network links are capable of accepting data rates as high as, for example, 155 megabits per second. A data concentrator, sometimes referred to as an access interface, is use to connect the multiplicity of users to a single 155 megabit per second network link. It is well known that data traffic is frequently very bursty, i.e., has very high data rate peaks whose magnitude far exceeds the average data rate of a user. To effectively use the bandwidth of the network link many users must be connected, through the access interface, to the network link. The data rate of the link between each user and the access interface can be as high as the data rate of the network link, 155 megabits per second, provided a means exists to handle periods of congestion, i.e., times when multiple users attempt to simultaneously send high bandwidths of data to the network for extended periods of time.
A modern broad band data network must be capable of handling real time data that is delay sensitive such as data representing speech, as well as data for which delay, although undesirable, can be tolerated to a greater extent, such as FAX, Internet web access , still video, and file system transfers. The method of handling periods of congestion must not introduce excessive delay in delay sensitive data.
The ATM standards provide a mechanism for limiting the flow of data from the user into the ATM network. Each user continuously sends and receives a complete 155 megabits per second or other standard data rate. When the user is idle, i.e., has no data to send, all the cells sent to the network are idle cells; when the user is transmitting at peak capacity, all of the cells are active. Usually, only a moderate fraction of the cells, that are transmitted from any one user, are active. A flow control mechanism for active cells transmitted to the network is provided by the standard through the use of tokens transmitted to the user via generic flow control (GFC) bits, sometimes referred to as the GFC field, contained in the ATM header, of each transmitted cell. When the flow control mechanism is invoked, a user may transmit an active cell only if that user has an available token. Tokens are transmitted to users in cells received by the users; if the network cannot accept more than a certain rate of active cells, the network will transmit to the user only enough tokens to allow that many cells to be transmitted.
A number of problems exist in the prior art. First, the mechanism for detecting that traffic into the network should be throttled by limiting the number of tokens is slow compared to the build up rate of bursty data traffic. Second, although it is possible to give transmission priority to cells containing high priority data, such as data representing speech or control cells, when the cells arrive at an ATM interface, a large number of low priority cells may already be in the pipeline and cause the high priority cells to be delayed; a problem know as “head of line blocking”. Both of these problems can be overcome at the access interface by the use of very large multiple priority data buffers to store all data and grant it access according to priority, the dropping of data cells, and/or the use of traffic projection algorithms that limit the aggregate of the peak traffic rates from all the users or limit the number of users connected to an ATM access interface. Such solutions, however, are undesirable and/or uneconomical.
In summary, a problem in the prior art is that there is no satisfactory arrangement for responding rapidly to bursty data traffic into the network by throttling that traffic before excessive queues are formed in the ATM access interface, and further for insuring the timely transmission of high priority data traffic, such as data representing speech, or data demanding immediate delivery, such as a stock purchase or sale request.
SOLUTION
The above problems are solved, and an advance is made over the teachings of the prior art in accordance with our invention wherein a first-in-first-out (FIFO) queue is connected to each user that is connected to the ATM access interface, and wherein a token is returned to that user only if its FIFO has fewer than n cells, and wherein the number of tokens that a user can accumulate is limited to m. With this arrangement, if its FIFO is not being emptied rapidly enough, the supply of tokens available to the user connected to that FIFO will be rapidly depleted. In Applicants' preferred embodiment, n and m, each of which can be set independently, are limited to either one or two. Advantageously, this allows for a very rapid detection of and response to overload. In Applicants' preferred embodiment, electronic circuit means are used to detect whether the FIFO contains more than n cells, and these circuit means are used to directly suspend the generation of further tokens by inserting the proper value in the standard ATM generic flow control (GFC) bits that are sent with each cell transmitted to the user.
In accordance with one feature of Applicants' invention, when a high priority cell, as defined by data in the GFC field of the transmitted cell, is received at the ATM access interface, this cell is sent to a different FIFO, a FIFO for receiving and storing high priority cells. The high priority FIFO is given preferential treatment over other FIFOs either by being polled more often for transmission of a cell into the ATM network or by being given absolute preference over the other, low priority, FIFOs. Only the low priority FIFO is tested to detect whether a token should be transmitted to the user. On the user side, high priority cells may be transmitted without requiring a token.
REFERENCES:
patent: 5696764 (1997-12-01), Soumiya et al.
patent: 5742765 (1998-04-01), Wong et al.
patent: 6122279 (2000-09-01), Milway et al.
Buchholz D. Bruce
Byers Charles Calvin
Loos James Stavert
Runyon James Philip
Yu Hsien-Chuen
Chin Wellington
Lucent Technologies - Inc.
Tran Maikhanh
Ulrich Werner
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