Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Reexamination Certificate
1998-10-20
2003-08-12
Marcelo, Melvin (Department: 2663)
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
C370S395430
Reexamination Certificate
active
06606302
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for the control of flows for point-to-point, point-to-multipoint, multipoint-to-point and multipoint-to-multipoint non-real time connections within an ATM switch with distributed architecture and storage at input.
2. Discussion of the Background
The communication networks known as ATM or asynchronous transfer mode networks enable the circulation of fixed length packets known as ATM cells consisting of a 5-byte header and a 48-byte body. The header contains in particular a logic channel identifier known as a VPI/VCI (or virtual path identification and virtual channel identifier) field that enables the routing of the cells in the switches that it encounters on its path between the sender user and the addressee user.
The applications capable of using ATM networks for the communication of their data are highly varied. Most of the applications capable of using ATM networks have their own format for their data elements: these may be for example IP format frames of the Internet protocol or else frames using the format of the MPEG (moving picture export group) format. The adaptation between the format of these application frames and the format of the ATM cells is done in a layer called an ATM adaptation layer or AAL. In particular, this layer is responsible for segmenting the frames into cells and conversely reassembling the cells received from the network into frames.
Some of the data flows conveyed, known as “real time flows” require that the transit time and the jitter to which the network subjects their cells should be the minimum. This case relates for example to telephone data. Other data flows, hereinafter called non-real time flows, for example electronic mail, do not have these constraints. The real time flows must benefit from a certain degree of priority within the network and, for this purpose, they are subjected to a preventive congestion control mechanism by means of the reservation of resources.
Several major classes of flows known as “service categories” are defined in the standards ([UIT-T.I.371], [AF TM4.0]) to take account of the different demands that users may make as regards the quality of the service that they seek for a desired flow, defined by service quality parameters such as: cell loss rate, transfer time, jitter, minimum bit rate, etc. and to take account of the different characteristics of the bit rate of this flow, formed by traffic parameters such as peak bit rate, mean bit rate, maximum size of a burst, etc.
The real-time flow comes within one of the categories known as CBR (constant bit rate) or VBRrt (variable bit rate—real time). The non-real-time flows come within one of the following categories known as UBR (unspecified bit rate) whose service quality is not the object of any requirement on the part of the user, VBRnrt (variable bit rate—non-real-time) whose statistical characteristics are known with sufficient precision to enable a guarantee with respect to the loss rate or available bit rate (ABR) for which a minimum bit rate is guaranteed or a low loss rate as a trade-off for an end-to-end flow control according to the indications of the network.
Any ATM switch, in the manner shown in
FIG. 1
a,
implements four major sets of functions, an access function
1
to each port of an ATM switch, an ATM layer function
2
, a switch fabric function
3
and a management function
4
.
The access function
1
provides for the conversion of the ATM cells into the format that is suited to the transmission medium connected to said port and vice versa. This function makes it possible to present incoming cells to the ATM layer in a single format that is independent of the bit rate and the optical, electrical, radio or other type of technology of the transmission medium from which they come. The ports of a switch enable the connection of several switches together but they also enable the connection of a user of ATM services to a switch.
The processing operations to be implemented in the access function are described in a huge volume of standard-setting literature on the ANSI as well as the UIT and ATM Forum systems. The major classes of interface defined in these documents are:
The PDH (plesiochronous digital hierarchy) interface defined in the document UIT-T G.804, G.703.
The SDH (synchronous digital hierarchy) interface defined in the document UIT-T G.708, etc.
The SONET (synchronous optical network) interface defined in the document ANSI-T 1.105, etc.
The 25.6 Mbit/s IBM interface defined in the document af-phy-0040.000.
The ATM layer function
2
combines several functions and especially the management of the cell headers, the translation of the VPI/VCI (virtual path identification and virtual channel identifier) logic channels, the processing of the OAM (operations, administration and maintenance) management cells, a major part of the management of the traffic known as traffic management including sub-functions known as UPC (usage parameter control), SCD (selective cell discard), EPD (early PDU discard), RM (resource management) cells, etc.
The processing operations to be implemented in the ATM layer function are described especially in the following standard documents of the UIT and the ATM Forum:
B-ISDN ATN Layer Specification [UIT-T I.361]
B-ISDN Operation and Maintenance Principles and Functions [UIT-T I.610]
Traffic Management Specification Version 4.0 [AF-TM 4.0]
The switching or scrambling function
3
switches the cells from an input direction to one or more output directions, as a function of indications prepared by the ATM layer during the translation of the logic channels.
The management function
4
includes sub-functions such as: the local supervision of the switch (alarms, discovery of the configuration of the switch and of the local topology, management of versions, etc.), interfacing with the centralized supervision entity of the network, the interfacing needed to set up switched virtual circuits, etc.
For a more detailed description of some of these sub-functions, reference will be made to the standard-setting literature of the ATM Forum:
ATM User-Network Interface (UNI) Signalling Specification Version 4.0 (af-sig-0061.000)
Private Network-Network Interface Specification Version 1.0 (af-pnni-0055.000)
Integrated Layer Management Interface (af-ilmi-0065.000)
These different functions are mutually interfaced as indicated here below. It must be noted that the management function behaves exactly like a user except that its connection to the ATM layer does not go through an external port of the switch and therefore does not require any access function. By contrast, the management function does process ATM cells alone but also messages which it must therefore segment and reassemble by means of an AAL (ATM adaptation layer) which is therefore an additional function: the adaptation function.
The ATM switches are often switches with centralized architecture or weakly distributed architecture, that is to say the functions of the switch itself are performed by a single hardware element that combines computation capacities formed by microprocessors, storage capacities formed by memories and capacities for routing the cells in the switch fabric. However, this concentration adversely affects the modular nature of the switch and its ability to remain functional when one of its constituent elements goes out of order.
According to a standard solution, the functions are distributed among distinct hardware elements that may, if necessary, be doubled to enable the pack-up of a faulty element of the same nature. These hardware elements are installed in the switch in sufficient numbers to cope with the processing load that is foreseeable as a function of the configuration of the network at this place. In practice, these elements are electronic component boards assembled in a tray and interfacing with one another by means of one or more data buses placed at the bottom of the tray. They define what is common called a
Bavant Marc
Delattre Michel
Guerin Didier
Herau Philippe
"Thomson-CSF"
Marcelo Melvin
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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