WO2000074317A1

WO2000074317A1 - Multi-atm layer, multi-phy layer bus architecture

Info

Publication number: WO2000074317A1
Application number: PCT/US2000/007340
Authority: WO
Inventors: Randall B. Sharpe
Original assignee: Pliant Systems, Inc.
Priority date: 1999-06-02
Filing date: 2000-03-20
Publication date: 2000-12-07
Also published as: AU3763500A

Abstract

An Asynchronous Transfer Mode (ATM) cell architecture overcomes the inability of a Universal Test and Operations PHY Interface for ATM Level 2 (UTOPIA L2) standard to service more than a limited number of ports and conduct cell transfers across a backplane. The invention provides both ATM-PHY layer (41) and PHY-ATM layer transport capability. The ATM layer is part of an ATM layer-containing circuit card, including a master multiple ATM layer (45), multiple Phy layer (MAMP) backplane interface unit (55), that provides ATM cell connectivity between a first UTOPIA L2 based bus (43) and the backplane. Each PHY layer-containing port card (50) includes a second UTOPIA L2 based bus coupled to multiple PHY ports, the number of which is less than the total PHY port capacity of the first UTOPIA L2 based bus.

Description

MULTI-ATM LAYER, MULTI-PHY LAYER BUS ARCHITECTURE

FIELD OF THE INVENTION

The present invention relates in general to communication systems and is particularly directed to a new and improved asynchronous transfer mode (ATM) bus architecture for telecommunication systems in which ATM connectivity is provided across the backplane of an equipment shelf. In ATM systems, physical (PHY) layer functionality is associated with every ATM port. ATM layer functionality may be associated with a group of ports. There is a standard interface between the ATM layer and multiple PHY layers known as the Universal Test and Operations PHY Interface for ATM Level 2 (UTOPIA L2) . The UTOPIA L2 interface is not appropriate for transmission across a backplane and is limited in the number of PHY ports supported. The ATM bus architecture of the present invention overcomes both of these limitations without including ATM layer functionality in the port cards, and allows the ATM layer functionality to be shared across all port cards. The high utilization and scalability of the ATM layer functionality in the fabric card(s) and the simplicity of the port cards result in a low cost solution. BACKGROUND OF THE INVENTION

Since the introduction of asynchronous transfer mode (ATM) protocol for cell switched communications, the specification for handling the flow of ATM digital cells or packets between devices has been refined to a prescribed set of parameters with which an ATM interface must conform. In particular, the telecommunication industry's ATM Forum defined the functionality of an ATM layer and a physical (PHY) layer, as well as a UTOPIA (universal test and operations PHY interface for ATM) interface therebetween, which manages the flow of ATM cells or packets from the ATM layer to the PHY layer, and from the PHY layer to the ATM layer. As an extension to this original interface, there currently exists a UTOPIA L2 interface specification, diagrammatically illustrated in Figure 1, which defines connectivity conditions between a single ATM layer 10 across a UTOPIA L2 bus 15 to a prescribed number N of ports (e.g., thirty-one ports 0-30) of PHY layers 20-1, ...20-N. In a UTOPIA L2 architecture, the ATM layer 10 polls the PHY layer ports 20 to determine whether or not space is available in their transmit cell (first-in, first-out

(FIFO)) buffers 21. If space is available, and the ATM layer has data to send, it transmits an ATM cell over the

UTOPIA L2 bus 15 to the 'downstream' destination PHY layer port buffer. The destination PHY layer 20 then forwards the ATM cells it has stored in its transmit FIFO buffer 21 from the UTOPIA L2 bus 30, via its transmit output port to a destination ATM site.

In the 'upstream' direction (from the PHY layer to the ATM layer) , the PHY layer ports are periodically polled by the ATM layer, in order to determine whether their upstream buffers 22 contain cells that have been received from the ATM site. Via a handshake routine, a PHY layer having ATM cells to transmit is selectively granted permission to transmit cells stored in its transmit buffer 22 over the UTOPIA L2 bus 15 to the ATM layer 10.

Unfortunately, the UTOPIA L2 interface specification suffers from two major shortcomings that limit its incorporation into an equipment shelf of a typical communication system site. The first is the fact that a typical equipment shelf serves a much larger number of ports (e.g., 90 - 120 ports) than the size of the available port address space defined in the UTOPIA L2 specification (thirty-one ports) , and therefore must be replicated. Secondly, being a self-contained architecture, the UTOPIA L2 specification is not configured to allow ATM-PHY layer transport across a backplane. SUMMARY OF THE INVENTION

In accordance with the present invention, these shortcomings are successfully obviated by a new and improved multi-ATM layer, multi-PHY layer (MAMP) bus architecture, that is configured for use with an equipment shelf of a communication installation. The functionality of the UTOPIA L2 interface is effectively 'modularized' into a 'downstream' -directed ATM-PHY layer transport portion, and an 'upstream' -directed PHY-ATM transport portion, that enable the MAMP backplane to separately provide ATM-PHY layer transport and PHY-ATM layer transport, in which the ATM layer's PHY layer port address capability (currently limited to thirty-one ports) is available to the total port capacity of a telecommunication service provider's equipment shelf . As the number of ports installed increases, addition ATM layer functionality can be added and made available to all system ports.

For this purpose, the MAMP bus of the invention comprises one or more ATM layer-associated interface modules, or 'ATM fabric' printed circuit cards, and one or more PHY layer-associated interface modules, or 'PHY port' printed circuit cards, that are coupled with each of the respective transmit (or downstream transport direction) and receive (or upstream transport direction) portions of the MAMP backplane. A fabric card includes an ATM layer, that is coupled by way of a UTOPIA L2 bus to a 'master' multiple ATM layer, multiple PHY layer (MAMP) backplane interface unit installed on the fabric card.

The master MAMP backplane interface unit provides ATM cell connectivity between the ATM layer-associated UTOPIA L2 bus and the respective transmit and receive portions of the MAMP backplane. Its backplane interface capability allows the master unit to transmit cells to and receive cells from any slave MAMP backplane interface unit on any port card, so that the address capability of its ATM layer can be associated with any port of any port card. When the total capacity of a master MAMP backplane interface unit is exceeded, additional master MAMP backplane interface units may be added. The transmit portion of the MAMP backplane includes a clock signal that is used for the downstream and upstream portions of the backplane, and a transmit end-of-cell signal that establishes ATM cell framing. Transmit data signal lines are used to transport data from the master MAMP backplane interface unit to any slave MAMP backplane interface unit. A transmit full signal has a plurality of lines respectively associated with each of the ports of a slave MAMP backplane interface unit. During its assigned clock cycle, a slave MAMP backplane interface unit of a PHY layer port card will drive the lines of this signal to logic states that indicate whether its PHY layer port buffers can accept a downstream-directed cell transfer from the ATM layer of a fabric card.

The transmit portion of the MAMP backplane also includes signal lines for parity and arbitration. The arbitration signal line is used to award access to the MAMP bus among contending fabric card master MAMP backplane. The master unit's backplane arbitration mechanism is an internal ' backpressure' -based round robin arbitration routine, that is carried out for a respective fabric card's master unit backplane transmit buffers that have cells to transmit, and an external priority/fairness based arbitration routine for handling contending master MAMP backplane interface units. A master MAMP interface unit comprises a transmitter section coupled to the transmit portion of the backplane, a receiver section coupled to the receive portion of the backplane, and a communication control processor section, which controls the operation of the transmitter and receiver sections. The transmitter section interfaces ATM cells from the fabric card' s UTOPIA L2 bus to the transmit portion of the backplane for delivery to a destination PHY layer port/device. The receiver section interfaces ATM cells sourced from a PHY layer port of a port card, and supplied by its associated slave MAMP backplane interface unit over the receive portion of the MAMP backplane to the fabric card's UTOPIA L2 bus for delivery to the ATM layer. The transmitter section of a master MAMP interface unit includes a transmit UTOPIA L2 interface that operates as a PHY layer to the fabric and interfaces the UTOPIA L2 bus with an ATM cell processor, which maps the cell's port address to a routing tag in a routing tag look-up table. A routing tag byte, which is the same for both the downstream (ATM layer - PHY layer) and upstream (PHY layer - ATM layer) directions, is prepended to the ATM cell, and contains routing information for assigning incoming ATM cells via the UTOPIA L2 bus to an associated PHY layer port of a port card. A transmit buffer controller generates read and write address pointers and contains backplane transmit buffers that are coupled through a transmit MAMP bus interface to the transmit portion of the backplane. The receive portion of the MAMP backplane includes a receive end-of-cell signal line for ATM cell framing, and a receive data signal lines for transporting data. The master MAMP backplane interface unit of each fabric card monitors routing tag/address information on these signal lines to determine whether it is the intended recipient of an ATM cell that has been placed on the backplane by a slave MAMP backplane interface unit of a port card. The receive portion of the MAMP backplane also contains parity and arbitration signal lines. The receiver section of a master MAMP interface unit contains a receive MAMP bus interface, into buffers of which ATM cells from a PHY layer device of a port card are buffered off the receive portion of the backplane. The receive MAMP bus interface is coupled to an ATM cell processor, which is also coupled the routing tag look-up table. The ATM cell processor examines routing information prepended to each cell on the receive portion of the backplane to determine if it is the intended recipient of the cell. The receive buffers are interfaced with the ATM layer's UTOPIA L2 bus by a receive UTOPIA L2 interface.

A PHY layer port circuit card contains plural PHY layers that are coupled by way of a UTOPIA L2 bus to a slave MAMP backplane interface unit, through which connectivity between the UTOPIA L2 bus and the MAMP backplane is conducted. Each PHY layer port card contains M ports associated with a fraction of the total number of ports served by the shelf. To furnish backplane-PHY layer connectivity for these M PHY layer ports, the slave MAMP backplane interface unit contains M pairs of backplane transmit and receive buffers.

A slave MAMP backplane interface unit is configured generally the same as, but is connected to the MAMP backplane in a manner complementary to that of the master MAMP backplane interface unit. Namely, the slave MAMP backplane interface unit's receive direction section interfaces ATM cells sourced from a PHY layer port of a port card via the UTOPIA L2 bus for delivery to an upstream

ATM layer of a fabric card, while a slave unit's transmit direction section interfaces ATM cells received via the transmit section of the MAMP backplane from a master MAMP backplane interface unit associated with a sourcing fabric card ATM layer, for delivery to a PHY port layer of a port card.

The slave MAMP backplane interface unit's receive direction section has a receive UTOPIA L2 interface that operates as a ATM layer and interfaces the UTOPIA L2 bus with an ATM cell processor. From the UTOPIA L2 interface the ATM cell processor receives a respective 53 -byte ATM cell 181, together with the cell's address, which is based upon receive direction address signals driven from the ATM layer. The ATM cell processor maps the cell's address to one of eight PHY entries in a routing tag look-up table

(LUT) . A routing tag byte is prepended to the ATM cell, and sent with the cell to a receive or upstream direction

(FIFO) cell buffer. The upstream direction cell buffer contains a set of receive direction backplane buffers through which the ATM cells are interfaced with the upstream transmission direction portion of the MAMP backplane. Receive MAMP bus arbitration logic is coupled to an upstream direction arbitration line, a receive MAMP bus interface and a performance monitoring controller for arbitrating access to the upstream transport portion of the MAMP bus.

Arbitration among contending slave MAMP backplane interface units for access to the upstream portion of the MAMP backplane is carried out using an arbitration line, to which the bus arbitration mechanism of the slave unit bus arbitration logic is coupled. As in the master MAMP backplane interface unit, the slave unit bus arbitration mechanism also executes a two-step (internal-external) pre- transmission arbitration sequence, comprised of an internal round robin arbitration routine and an external arbitration routine among contending slave MAMP backplane interface units. However, since the upstream path to the ATM layer is sufficiently fast so that cell loss will not occur during transport between a PHY layer port of a port card and its destination ATM layer in a fabric card, there is no (backpressure-based) traffic control in the upstream direction.

The slave MAMP backplane interface unit's transmit (downstream direction) section includes a transmit MAMP bus interface into which ATM cells received via the transmit portion of the MAMP backplane from an upstream master backplane interface unit are buffered. The transmit MAMP bus interface is coupled to an ATM cell processor routing address information for which is provided by way of a routing tag look-up table (LUT) interfaced with the control processor. The ATM cell processor compares the prepended byte of each incoming cell on the transmit portion of the MAMP backplane with the routing tag information stored in the routing tag LUT. If the two match, the cell is routed to a transmit FIFO and stored in the appropriate backplane transmit cell buffer. The transmit backplane buffers are interfaced with the UTOPIA L2 bus 53 by means of a transmit UTOPIA L2 interface in accordance with the UTOPIA L2 specification.

In the course of downstream ATM cell transport, the ATM layer of a respective fabric card repeatedly polls its master MAMP interface unit to determine whether it's backplane transmit buffers contains available cell storage space for ATM cells associated with a destination PHY layer ports of the port cards. When a logical port in the ATM layer has a cell to transmit to a port and space is available in the master MAMP interface unit's backplane transmit buffer associated with that port, the ATM cell is transferred across the UTOPIA L2 bus and stored in the master unit's backplane transmit buffer. The master MAMP backplane interface unit also monitors the bits of the transmit full signal lines to determine whether there is space available for a potential ATM layer - PHY layer cell transfer across the MAMP bus, for each of its associate PHY ports. A cell backpressure condition exists for a respective PHY port, if the slave MAMP backplane interface unit of the port card containing that PHY port has no buffer space available to receive an ATM cell from the fabric card. Backpressure indicates to the ATM fabric card that queuing and traffic management in the fabric is needed. If there is traffic congestion problem, cells with various qualities of service attributes can be readily buffered in large shared buffers of appropriate size and priority in the ATM layer on the fabric card.

When a master MAMP backplane interface unit has a cell ready for transport, it is controllably awarded access to the backplane in accordance with the backplane arbitration mechanism. Once a master MAMP interface unit with a cell ready for transport has been awarded the bus, an ATM cell transfer takes place across the transmit section of the backplane. Within the port card, the slave MAMP backplane interface unit repeatedly polls port buffers of its M PHY layers to determine whether they have available storage space for transferring cells that have been received from the fabric card and buffered on the backplane side of the port card's UTOPIA L2 bus.

When a backplane buffer in the slave MAMP backplane interface unit has received a cell and space is available in its associated PHY layer's port buffer, the cell is sent across the service card's UTOPIA L2 bus and stored in the PHY layer port buffer for delivery to customer premises equipment (CPE) or other ATM device. Because the frequency and density of traffic flow in the upstream direction for any particular PHY port is unpredictable, there is no simple way to quickly handle upstream ATM cell traffic flow control. This potential problem is obviated by using a high speed path and arbitration-based transport control mechanism on the upstream portion of the backplane, rather than polling. The receive portion of the MAMP backplane has sufficient capacity so that, even for a worst case traffic load, no backpressure mechanism is required. When a PHY layer port buffer receives cells received from its associated CPE or other ATM device, those cells are transferred across the port card's UTOPIA L2 bus and stored in the larger capacity receive buffer of the MAMP slave backplane interface unit . As in the downstream direction, upstream (PHY-ATM layer) directed ATM cells are prepended with a routing tag byte, that allows the ATM cell processor in the master MAMP interface unit of the destination fabric layer card to associate the cell- sourcing PHY layer port with the destination ATM layer device . As a respective port card having cells to send is granted access by the arbitration signal of the receive portion of the backplane, a cell is transferred across the backplane and coupled to the receive MAMP bus interface of the fabric card. As described above, the ATM cell processor of a fabric card examines the routing tag byte to determine if it's ATM layer is the intended recipient of the cell. Once it has been buffered in the master MAMP interface unit, the cell is interfaced with the fabric card's UTOPIA L2 bus for delivery to the ATM layer. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 diagrammatically illustrates a conventional UTOPIA Level 2 interface;

Figure 2 diagrammatically illustrates the MAMP backplane architecture of the present invention;

Figures 3 and 4 show logical configurations of the respective transmit (downstream) and receive (upstream) portions of the MAMP backplane architecture of Figure 2;

Figure 5 diagrammatically illustrates the configuration of a master MAMP backplane interface unit;

Figure 6 shows the format of an ATM cell for a three- byte wide data bus;

Figure 7 shows the format of an ATM cell for an eight bit (single byte) wide data bus; Figure 8 shows a non-limiting example of a routing tag byte;

Figure 9 is a timing diagram of the relationship among BpCLK, TxEOC, TxData and TxFull signal lines of the transmit portion of the MAMP backplane; Figure 10 shows a two-step (internal-external) pre- transmission bus arbitration mechanism used for the granting access to the MAMP backplane;

Figure 11 shows the steps of the pre-transmission arbitration routine of Figure 10 for a master MAMP backplane interface unit;

Figures 12 and 13 are timing diagrams associated with the pre-transmission arbitration routine of Figure 11; Figure 14 shows a non-limiting example of an arbitration frame employed for the transmit portion of a MAMP backplane;

Figure 15 diagrammatically illustrates the configuration of a slave MAMP backplane interface unit;

Figure 16 shows the steps of the pre-transmission arbitration routine of Figure 10 for a slave MAMP backplane interface unit;

Figures 17 and 18 are timing diagrams associated with the pre-transmission arbitration routine of Figure 16. DETAILED DESCRIPTION

Before describing in detail the new and improved multi-ATM layer, multi-PHY layer (MAMP) backplane architecture of the present invention, it should be observed that the invention resides primarily in prescribed modular arrangements of conventional digital communication circuits and associated digital signal processing components and attendant supervisory control circuitry therefor, that controls the operations of such circuits and components. In a practical implementation that facilitates their incorporation into existing printed circuit telephony cards of a telecommunication equipment shelf, these modular arrangements may be readily implemented as field programmable gate array (FPGA) -implemented, or application specific integrated circuit (ASIC) chip sets.

Consequently, the configuration of such arrangements of circuits and components and the manner in which they are interfaced with other telecommunication equipment have, for the most part, been illustrated in the drawings by readily understandable block diagrams, which show only those specific details that are pertinent to the present invention, so as not to obscure the disclosure with details which will be readily apparent to those skilled in the art having the benefit of the description herein. Thus, the block diagram illustrations are primarily intended to show the major components of the invention in a convenient functional grouping, whereby the present invention may be more readily understood.

Attention is now directed to Figures 2, 3 and 4, wherein the overall architecture of the multi-ATM layer, multi-PHY layer (MAMP) backplane architecture of the present invention is diagrammatically illustrated. Figure 2 shows the MAMP backplane architecture in a diagrammatic format that facilitates contrasting differences between the invention and the conventional UTOPIA Level 2 architecture of Figure 1, described above. Figures 3 and 4 show logical configurations of the respective transmit and receive bus structures of the MAMP backplane engaged by equipment shelf cards containing the ATM layer and PHY layer modules of the invention, for respectively providing ' downstream' -directed ATM-PHY layer transport, and 'upstream' -directed PHY-ATM transport connectivity, as will be described.

As shown in Figures 2-4, the MAMP backplane architecture of the present invention comprises one or more ATM layer-associated interface modules, or 'ATM fabric' printed circuit cards 40, and one or more PHY layer- associated interface modules, or 'PHY port' printed circuit cards 50, each of which is configured to be mechanically and electrically engaged with a MAMP backplane 60, for use in an equipment shelf of an industry standard telecommunication installation (e.g., telephony central office switch, as a non-limiting example) .

In addition to customary components for providing signaling and management of ATM connections, a respective ATM fabric card 40 is augmented to include an ATM layer 41, that is coupled by way of a UTOPIA L2 bus 43 to a 'master' multiple ATM layer, multiple PHY layer (MAMP) backplane interface unit 45 (shown in Figure 5 to be described) . Each of ATM layer 41 and UTOPIA L2 bus 43 is of conventional configuration and operation, as described above with reference to Figure 1. As will be described, the master MAMP backplane interface unit 45 is operative to provide ATM cell connectivity between the ATM layer-associated UTOPIA L2 bus 43 and transmit and receive portions of the MAMP backplane 60.

In a complementary fashion, a respective PHY layer port card 50 includes a plurality M of PHY layer ports 51- 1, ..., 51-M, that are coupled by way of a UTOPIA L2 bus 53 to a 'slave' MAMP backplane interface unit 55, through which communications between PHY port-associated UTOPIA L2 bus 53 and the MAMP backplane 60 are conducted. As pointed out above, because its interface capability with the MAMP backplane 60 allows the master MAMP backplane interface unit 45 of an ATM fabric card 40 to transmit cells to and receive cells from any slave MAMP backplane interface unit 55, the functionality of its ATM layer 51 is not limited to serving only (CPE or ATM) devices which are directly connected to its UTOPIA L2 -defined (N=31) PHY layer ports, as in the conventional architecture of Figure 1. Instead, the PHY layer (N=31) port address capacity of the ATM layer of a respective fabric card 40 is available to the all of the port card slots of the backplane. This ATM-PHY port extension capability means that the ATM layers' costs can be divided over the total number of ports served by the shelf, rather than by the number of ports that can fit on a card. Also, augmented fabric cards 40 and port cards 50 of the present invention need only be added as additional ATM-PHY service capacity is required. As will be described, the non-limiting parameters of the present embodiment readily conform with the service capability of a typical equipment shelf, which may be configured for up to four fabric cards and eighteen port cards, as a non- limiting example.

Similar to a PHY layer 20 of the conventional UTOPIA L2 interface of Figure 1, the master MAMP backplane interface unit 45 of each ATM fabric card 40 contains transmit and receive cell (FIFO) buffers for buffering cell transfers between the ATM layer 41 and MAMP bus 60. In order to conform with the UTOPIA L2 specification, a respective master MAMP backplane interface unit 45 contains N pairs or sets of transmit FIFO backplane buffers 45T1, ..., 45TN, and receive FIFO backplane buffers 45R1, ..., 45RN, where N conforms or is defined in accordance with the PHY address parameters of the UTOPIA L2 specification (N=31 in the present example) .

Since the ATM layer 41 possesses substantial cell buffering capacity and queue management functionality, the capacity of a transmit buffer 45Ti requires only a limited number of cell buffers for ATM-PHY layer cell transport, and therefore may be smaller than that each receive buffer 45Ri. From a practical standpoint of hardware component population capacity, a respective PHY layer port card 50 may be configured to provide PHY layer connectivity for a prescribed fraction of the total number of ports served by the equipment shelf. As a non-limiting example, equipping each of the eighteen port cards 50 of a typical shelf with M=8 PHY layer ports will provide PHY layer connectivity for up to (8X18=144) ATM ports, and thereby can quite amply accommodate the typical range of shelf service capability for 90-120 ATM equipments, referenced above.

For the present example of providing M=8 PHY layer ports per port card, Figure 2 shows a respective PHY layer port card 50 providing PHY layer connectivity to M=8 pairs of transmit, receive PHY layer ports 52T0, 52R0, .... 52T7, 52R7 of the M=8 PHY layers 51-1, ..., 51-M. To furnish backplane-PHY layer connectivity for PHY layer ports, the slave MAMP backplane interface unit 55 of a port card 50 contains M pairs or sets of transmit backplane buffers 55T1, ..., 55TM, and receive backplane buffers 55R2 - 55RM.

As in the case of a master MAMP backplane interface unit 45, for the ATM layer to PHY layer (downstream) transport direction, the capacity of a backplane transmit buffer 55Ti within a slave MAMP backplane interface unit 55 requires only a small cell buffer and therefore may be of a reduced size relative to each backplane receive cell buffer 55Ri. The logical structure of the transmit or 'downstream' transport portion 60T of the MAMP backplane 60, through which downstream-directed ATM-PHY layer cell transport (from an ATM fabric card 40 to a PHY port card 50) is effected, is shown in Figure 3. This logical structure of the transmit portion of the backplane includes a backplane clock (BpCLK) signal 61, which provides centralized bus timing and is common to both the downstream and upstream portions of the backplane. The BpCLK clock signals may be supplied by clock circuitry resident on any one of the backplane cards, such as fabric card 40, as a non-limiting example .

The transmit bus structure 60T further includes a transmit end-of-cell (TxEOC) signal 62, that is used to maintain ATM cell framing on the transmit bus. The TxEOC signal 62 is asserted in an active logical state for one complete cycle of the BpCLK, once every number of BpCLK cycles that corresponds to the total number of clock cycles for transmitting a cell (eighteen in the present example) . A multibit wide transmit data (TxData) signal 63 is used to transport data from a master MAMP backplane interface unit 45 to any MAMP slave MAMP backplane interface unit 55 along the bus. The TxData signal 63 includes routing tag/address information that is monitored by each slave MAMP backplane interface unit 55 to determine whether that slave MAMP backplane interface unit is the intended recipient of an ATM cell placed on the bus by a master MAMP backplane interface unit.

A transmit full (TxFull) signal 64 is a multibit signal, the respective bits of which are associated with the M ports of the polled slave MAMP backplane interface unit. Thus, for the present example of employing M=8 ports per port card, the TxFull signal 64 is eight bits wide. During its associated cycle of the (eighteen) BpCLK cycles, a polled slave MAMP backplane interface unit 55 will drive each bit of the TxFull signal 64 with a prescribed logical state representative of whether or not that signal line's associated backplane transmit buffer is full (i.e. whether or not it has storage capacity available to accept a cell transfer from the master MAMP backplane interface unit of a fabric card 40. In addition to the cell transport signals described above, the transmit portion 60T of the MAMP backplane includes logic signals that are used for arbitration and parity.

For this purpose, a transmit arbitration (TxArb) signal 65 is distributed among multiple master MAMP interface units 45 for arbitrating access to the bus, as will be described below with reference to Figures 10-14. Also, a transmit parity (TxParity) signal 66 provides performance monitoring of the transmit bus 60T as the odd parity bit over the TxData signal 63 in a conventional manner.

Figure 4 shows the logical structure of the receive or 'upstream' transport portion 60R of the MAMP backplane 60, through which upstream-directed PHY-ATM layer cell transport (from a PHY layer port card 50 to an ATM fabric card 40) is effected. In addition to the backplane clock (BpCLK) signal 61, the upstream-directed receive bus structure 60R includes a receive end-of-cell (RxEOC) signal 67, which is used to maintain ATM cell framing on the receive bus. The RxEOC signal 67 is asserted in an active logical state for one complete cycle of the BpCLK, once every integral multiple of the number of BpCLK cycles that corresponds to the number (e.g., 18) of clock cycles required to transfer a cell.

This integral multiple depends upon the width of a multibit wide receive data (RxData) signal bus 68 that is used to transport cells from a slave MAMP backplane interface unit 55 to a master MAMP interface unit 45. For a three bytes (24 bits) wide RXData signal bus 68, the receive RxEOC signal 67 will be asserted once every eighteen BpCLK cycles. For an eight bit wide RxData signal, the RxEOC signal 67 will be asserted once every fifty-four BpCLK cycles . Although only one slave MAMP backplane interface unit 55 drives the RxData signal bus 68 at any time, each master MAMP backplane interface unit 45 monitors routing tag/address information on the signal bus 68 to determine whether it is the intended recipient of an ATM cell that has been placed on the upstream bus by a slave MAMP backplane interface unit 55.

In addition to the upstream cell transport signals described above, like the transmit portion of the backplane, the receive portion also includes logic signals employed for arbitration and parity. A receive arbitration

(RxArb) signal 69 is distributed among multiple slave MAMP backplane interface units for performing arbitration using a serial protocol mechanism. Also, a receive parity

(RxParity) signal 70 provides performance monitoring of the receive bus 60R as the odd parity bit over the RxData signal bus 68 in a conventional manner.

The configuration of a master MAMP backplane interface unit 45 is shown diagrammatically in Figure 5 as comprising a transmitter section 80, a receiver section 90, and a communication control processor section 100. The control processor section 100, which contains a microprocessor interface and associated registers 101, and a performance monitoring controller 102, controls the operation of the transmitter and receiver sections, in accordance a supervisory control routine executed by the fabric card's control processor.

The transmitter section 80 interfaces ATM cells from the UTOPIA L2 bus 43 to the transmit portion 60T of the backplane for delivery to a slave MAMP backplane interface unit 55 associated with the destination PHY layer port. The receiver section 90 interfaces ATM cells that have been sourced from a PHY layer port of a port card, and supplied by its associated slave MAMP backplane interface unit 55 over the receive portion 60R of the MAMP backplane 60 to the UTOPIA L2 bus 43 for delivery to an ATM layer 41 of a fabric card. The transmitter section 80 includes a transmit (Tx) UTOPIA L2 interface 81 that operates as a PHY layer and interfaces the UTOPIA L2 bus 43 with an ATM cell processor 82. The ATM cell processor 82 receives a respective ATM cell from the UTOPIA L2 interface 81, together with the cell's PHY address driven from the ATM layer. The ATM cell processor 82 maps the cell's UTOPIA L2 PHY address to an associated MAMP address (card plus port) using a routing tag look-up table (LUT) 83. The routing tag byte is prepended to the ATM cell, and sent with the cell to a transmit (FIFO) cell buffer 84, containing transmit backplane buffers 45T1-45TN through which ATM cells are interfaced with the backplane 60.

Figure 6 shows the format of an ATM cell for a three- byte wide data bus; Figure 7 shows the format for an eight bit (single byte) wide data bus. The routing tag LUT 83 contains routing information for assigning incoming ATM cells via the UTOPIA L2 bus 43 to a specified port card 50, under the control of the control processor 100. The backplane transmit cell buffers 45T are coupled through a transmit Tx MAMP bus interface 85 to the transmit portion 60T of the backplane. Transmit Tx MAMP bus arbitration logic 86 is coupled to the TxArb arbitration signal 65, Tx MAMP bus interface 85 and a performance monitoring controller 102, for arbitrating access to the bus, described below with reference to Figures 10-14)

The receiver section 90 of a master MAMP backplane interface unit 45 includes a receive RX MAMP bus interface 91, into which ATM cells from a sourcing the slave backplane interface unit associated with a PHY layer port of a port card 50 are buffered from the receive portion 60R of the backplane. The receive RX MAMP bus interface 91 is coupled to an ATM cell processor 92, routing address information for which is provided by way of a routing tag look-up table (LUT) 93, interfaced with the control processor 100. As described previously, the routing tag byte, a non-limiting example of which is shown in detail in Figure 8, is the same for both the transmit (ATM layer -

PHY layer) and (PHY layer - ATM layer) receive directions.

The ATM cell processor 92 compares the prepended byte of each cell on the receive portion 60R of the backplane 60 with the routing tag information stored in the routing tag

LUT 93 to determine if it is the intended recipient of the cell. If so, that cell is routed to the RxFIFO and stored in the appropriate backplane receive cell buffer (RxFIFO)

45Ri of a receive FIFO 94, which may be configured essentially the same as the transmit FIFO 84, described above, and contains (N=31) receive backplane cell buffers

(RxFIFOs) 45R1, ... , 45RN for N PHY layer ports of the port cards 50. Otherwise, the cell is ignored. The receive backplane buffers 45R are interfaced with the UTOPIA L2 bus 43 by means of a receive (Rx) UTOPIA L2 interface 95 in accordance with the UTOPIA L2 specification.

Figure 9 is a timing diagram of the relationship among the BpCLK, TxEOC, TxData and TxFull signals referenced above. As shown in Figures 6 and 7, referenced previously, each data cell contains fifty-four bytes, containing fifty- three ATM bytes plus one prepended routing tag byte. The routing tag byte is the most significant byte and is transmitted first, while the ATM payload byte 48 is the least significant byte and is transmitted last. In the non- limiting example of a routing tag byte shown in Figure 8, the upper five bits (7-3) specify one of the eighteen 'slave' port cards 50, while the three LSBs (2-0) identify one of the (M=8) eight ports of the addressed port card.

Arbitration among contending master MAMP backplane interface units 45 for access to the transmit portion 60T of the backplane is carried out using the TxArb arbitration signal 65, to which the bus arbitration mechanism of the bus arbitration logic 85 is coupled. As a non-limiting example, the bus arbitration mechanism may execute a two- step (internal-external) pre-transmission arbitration sequence, as diagrammatically illustrated in Figure 10. This two step arbitration mechanism is comprised of an internal round robin arbitration routine 103 among any of the (N=31) transmit FIFO cell buffers 45T1, ..., 45TN that have cells to transmit for a respective master MAMP backplane interface units 40, and an external arbitration routine 104 among contending master MAMP backplane interface units.

Figure 11 shows the steps of the pre-transmission arbitration processing routine, associated timing diagrams for which are shown in Figures 12 and 13. Pursuant to the pre-transmission arbitration processing routine, beginning with one of the N transmit backplane buffers 45TN, shown as a 'buffer N' in query step 111N, the internal round robin arbitration among the transmit backplane buffers of a respective master MAMP backplane interface unit 45 checks to see if that 'buffer N' contains a cell awaiting transmission to a PHY port. If the answer to query step 111N is YES (i.e., 'buffer N' has a cell to transmit), the routine transitions to step 112N and examines its backpressure indicator or TxFull bit on TxFull signal 64. If the answer to query step 111N is NO, (indicating that 'buffer N' has no cell awaiting transmission) , the routine steps to query step 111N+1 to check whether the next buffer N+l contains a cell awaiting transmission to a PHY port. This process continues for all (N=31) buffers and then loops back to the buffer N and repeats continuously, until a backplane transmit buffer is found with a cell to transmit .

Once a backplane transmit buffer having a cell to transmit has been found, its TxFull bit for the destination PHY port is checked to determine whether the slave transmit buffer associated with the destination PHY port can accept the cell awaiting transmission. If the TxFull bit has not been asserted active (the answer to query step 112N here is NO) , an external arbitration request is submitted at step 113. However, if the TxFull bit for the destination PHY port has been asserted active (the answer to query step 112N is YES) , then the routine will transition to step 111N+1 for the next buffer, as described above. In the external arbitration request step 113, the master MAMP backplane interface unit asserts a multibit arbitration frame on the TxArb line, synchronized with respect to the TxEOC pulse, as shown in the timing diagrams. In query step 114, it monitors the bits of an arbitration cell to see if it continues to contend or loses the arbitration. A master MAMP backplane interface unit that was not eliminated from contention by the end of the contention cycle is granted opportunity to transmit in the next cell period.

As shown in the arbitration cell diagram of Figure 14, a representative arbitration frame includes a two-bit priority field, a single 'fairness' bit, a five-bit address field, and an idle bit. The fairness bit is used to ensure that each of the master MAMP units of a given priority level receives an equal opportunity to gain access to the bus, and thereby prevents an individual master MAMP unit from unduly monopolizing the bus.

As a non-limiting example, the fairness bit may award access to the bus in an order from the fabric card containing a master MAMP unit with the highest shelf address to the fabric card containing the lowest master MAMP unit address. A fairness cycle is initiated when one or more fabric cards of the same priority level having a cell to transmit assert their fairness bits to a prescribed (e.g., '1') state. Once a respective master MAMP unit has won its arbitration, it transmits a cell in the next cell period. At step 115 in the routine of Figure 11, it clears its fairness bit, which allows other master MAMP units of the same priority level to gain access to the bus. If that master MAMP unit has more cells to send, it must again set its fairness bit. This will grant that master MAMP unit preference over a lower priority fabric card, but it will lose arbitration to another card having the same priority. This process is carried out until all fairness bits have been cleared for all fabric cards of the same priority. The arbitration then steps to the next lower priority level and the routine is executed for that level of priority.

The configuration of a slave MAMP backplane interface unit 55, which is generally the same as, but is connected to the MAMP backplane 60 in a manner complementary to that of the master MAMP backplane interface unit 45 of Figure 5, is diagrammatically illustrated in Figure 15. As shown therein, the slave MAMP backplane interface unit 55 comprises a receive (upstream direction) section 180, a transmit (downstream direction) section 190, and a communication control processor section 200. Control processor section 200 contains a microprocessor interface and associated registers 201, and a performance monitoring controller 202, and serves to control the operation of the upstream section 180, and the downstream section 190, in accordance a supervisory control routine executed by the port card's control processor.

The slave MAMP backplane interface unit's receive direction section 180 interfaces ATM cells sourced from a PHY layer port 51 of a port card 50 via the UTOPIA L2 bus 53 for delivery to an upstream ATM layer 41 of a fabric card 40. The slave unit's transmit direction section 190 interfaces ATM cells received via the transmit section 60T of the MAMP backplane 60 from a master MAMP backplane interface unit 45 associated with a sourcing fabric card

ATM layer, for delivery to a PHY port layer of a port card.

For this purpose, the slave MAMP backplane interface unit's receive direction section 180 includes a receive (Rx) UTOPIA L2 interface 181 that operates as a ATM layer and interfaces the UTOPIA L2 bus 53 with an ATM cell processor 182. The ATM cell processor 182 receives a respective 53 -byte ATM cell from the UTOPIA L2 interface 181, together with the cell's address which is based upon receive direction address signals driven from the ATM layer. The ATM cell processor 182 maps the cell's address to one of eight PHY entries in a routing tag look-up table (LUT) 183. A routing tag byte is prepended to the ATM cell, and sent with the cell to a receive direction (FIFO) cell buffer 184, containing receive direction backplane buffers 55R1-55RN through which the ATM cells are interfaced with the upstream transmission direction portion 60R of the backplane 60. The backplane receive direction cell buffers 55R are coupled through a receive direction Rx MAMP bus interface 185 to the upstream direction portion 60R of the backplane. Receive Rx MAMP bus arbitration logic 186 is coupled to the RxArb arbitration line 69, Rx MAMP bus interface 185 and performance monitoring controller 202, for arbitrating access to the bus. Arbitration among contending slave MAMP backplane interface units 55 for access to the receive portion 60R of the MAMP backplane 60 is carried out using the RxArb arbitration signal 69, to which the bus arbitration mechanism of the bus arbitration logic 185 is coupled.

As in the case of the master MAMP backplane interface unit, the bus arbitration mechanism employed by a slave MAMP backplane interface unit may execute a two-step

(internal-external) pre-transmission arbitration sequence, comprised of an internal round robin arbitration routine and an external arbitration routine among contending slave

MAMP backplane interface units, as shown generally at steps 103 and 104 in Figure 10, described above.

However, as pointed out above, the upstream path to the ATM layer is sufficiently fast so that cell loss will not occur during transport between a PHY layer port of a port card 50 and its destination ATM layer in a fabric card 40. Consequently, there is no traffic control in the upstream direction, in view of the asymmetrical nature of the data traffic, as more data cells are sent in the downstream (ATM-PHY layer) direction than in the upstream

(PHY-ATM layer) direction. As noted above, the receive portion 60R of the backplane 60 is engineered to sustain even a worst case traffic load, so that no backpressure mechanism is required, and there is no polling. Instead, port card access to the MAMP bus is granted in accordance with the upstream arbitration scheme shown in Figure 16, associated timing diagrams for which are shown in Figures 17 and 18. In the arbitration routine of Figure 16, beginning with one of the N transmit backplane buffers 55RN, shown as a 'buffer N' in query step 2UN, an internal round robin arbitration among the receive (upstream direction) backplane buffers of a respective slave MAMP backplane interface unit 55 checks to see if that 'buffer N' contains a cell awaiting upstream transmission to an ATM port. If the answer to query step 211N is YES (i.e., 'buffer N' has a cell to transmit), the routine transitions to 212, wherein an external arbitration request is submitted. In the external arbitration request step 212, the slave MAMP backplane interface unit asserts a multibit arbitration frame on the RxArb line 69, synchronized with respect to the RxEOC pulse, as shown in the timing diagram of Figure 17. In query step 213, it monitors the bits of an arbitration cell to see if it continues to contend or loses the arbitration. A slave MAMP backplane interface unit that was not eliminated from contention by the end of the contention cycle is granted opportunity to transmit on the receive portion 60R of the MAMP bus 60 in the next cell period.

If the answer to query step 111N is NO, (indicating that the buffer of interest ('buffer N' ) has no cell to transmit) , the routine steps to query step 111N+1 to check whether the next buffer N+l contains a cell. This process continues for all (N=8) buffers and then loops back to the buffer N and repeats continuously, until a backplane receive section buffer is found with a cell to transmit.

As in the case of a downstream cell transmission, an arbitration frame for an upstream transmission includes a two-bit priority field, a single 'fairness' bit, a five-bit address field, and an idle bit, shown in the arbitration cell diagram of Figure 14, described previously. The fairness bit may be used to grant access to the upstream portion 60R of the MAMP bus 60, in an order from the PHY port card containing a slave MAMP unit with the highest shelf address to the PHY port card containing the lowest slave MAMP unit address. Again, a fairness cycle is initiated when one or more PHY port cards of the same priority level having a cell to transmit assert their fairness bits to a prescribed logic state (e.g., ' 1 ' ) . Once a respective slave MAMP unit has won its arbitration, it transmits a cell in the next cell period. At step 214 in the arbitration routine of Figure 16, it clears its fairness bit, which allows other slave MAMP units of the same priority level to gain access to the upstream portion of the MAMP bus. If the slave MAMP unit has more cells to send, it again sets its fairness bit; this will grant that slave MAMP unit preference over a lower priority PHY port card, but it will lose arbitration to another PHY port card having the same priority. This process is carried out until all fairness bits have been cleared for all PHY port cards of the same priority. The arbitration then steps to the next lower priority level and the routine is executed for that level of priority.

The slave MAMP backplane interface unit's transmit (downstream direction) section 190 includes a transmit Tx MAMP bus interface 191, into which ATM cells received via the transmit portion 60T of the MAMP backplane 60 from an upstream master backplane interface unit are buffered. The transmit Tx MAMP bus interface 191 is coupled to an ATM cell processor 192, routing address information for which is provided by way of a routing tag look-up table (LUT)

193, interfaced with the control processor 200. As described previously, the routing tag byte is the same for both the transmit (ATM layer - PHY layer) and (PHY layer - ATM layer) receive directions. The ATM cell processor 192 compares the prepended byte of each incoming cell on the transmit portion 60T of the MAMP backplane 60 with the routing tag information stored in the routing tag LUT 193 to determine if it is the intended recipient of the cell. If so, that cell is routed to a transmit FIFO 194 and stored in the appropriate backplane transmit cell buffer (TxFIFO) 55Ti. Otherwise, the cell is ignored. The transmit backplane buffers 55T are interfaced with the UTOPIA L2 bus 53 by means of a transmit (Tx) UTOPIA L2 interface 195 in accordance with the UTOPIA L2 specification. OPERATION DOWNSTREAM (ATM-PHY Layer) Cell Transport

As described briefly above, in the course of an ATM- PHY layer transmission, using its UTOPIA L2 mechanism, the ATM layer 41 of a respective fabric card 40 will poll (repeatedly) the master MAMP interface unit 45, in order to determine whether there is cell storage space available in that one of the (N=31) transmit buffers 45T1-45T31, which is associated with the PHY layer port 52T of the port card 50 for whom an ATM cell is intended. When a logical port in the ATM layer 41 has a cell to transmit and space is available in the associated transmit buffer 45i, the ATM cell is transferred across the UTOPIA L2 bus 43 and stored in a master MAMP interface unit's backplane transmit buffer 45Ti.

Independent of this operation by the UTOPIA L2 portion of the fabric card, and before transmitting a cell over the transmit portion 60T of the backplane 60, the master MAMP interface unit 45 determines whether cell buffer space is available in the associated slave MAMP interface unit for each PHY port. A cell backpressure condition exists if the transmit backplane buffer within the slave MAMP backplane interface unit 55 of the port card 50 containing the destination PHY port has no space for an ATM cell from the fabric card. Backpressure indicates to the ATM fabric card that queuing and traffic management, which is more sophisticated and more readily executed at the ATM layer, may be needed as the PHY layer port is becoming congested. If the data traffic is 'bursty' and causes congestion, cells with various quality of service attributes can be readily buffered in large shared buffers of appropriate size and priority of the ATM layer on the fabric card. This facilitates the intelligent discard of cells at the ATM layer, when necessary, using techniques such as early packet discard and partial packet discard. If cells could be potentially lost downstream of the ATM layer, such as crossing the backplane, or on the port card, installing equally sophisticated buffer management beyond the fabric card's ATM layer would be too complex and costly.

As described briefly above, in order to determine whether a potential backpressure condition exits, the master MAMP interface unit 45 polls the slave MAMP backplane interface units 55 of the port cards 50 for the status of their transmit FIFO buffers 55T1, ..., 55TN. If the master MAMP interface unit 45 has a cell ready for transport to a destination PHY layer port 52T, and the transmit buffer 55T within the slave MAMP backplane interface unit 55 of the port card 50 containing that destination port has space available, namely its associated TxFull signal line of the TxFull signal 64, described above, has not been asserted at a logical state representative that its cell buffer is full, then for that PHY layer port there is no backpressure condition, and an ATM cell transfer is allowed to take place across the transmit section 60T of the backplane in accordance with the transmission arbitration routine described above.

In order that the respective bits of the TxFull signal 64 will accurately reflect the status of each of the M transmit buffers 55T, the contents of a counter within the control processor of the slave MAMP backplane interface unit 55 of a port fabric card 50 is incrementally changed

(e.g., incremented or decremented) at each BpCLK from a prescribed value, after detecting the TxEOC pulse, and continues for each BpCLK through a count sequence that covers the total number of port cards (e.g., eighteen in the present example) , as shown in the timing diagram of Figure 12. When the counter reaches a prescribed value associated with the identification of the port card, for example, being incremented to a count value that is numerically equal to a value between the values of '1' and '18' (respectively associated with the identifications or shelf addresses of the eighteen port cards) , then that port card's slave MAMP interface unit 55 will report the state of its buffers 55T1-55TM on the TxFull signal 64. Independently of this polling of the status of its transmit buffers 55T for establishing the state of lines of the TxFull signal 64 during its designated one of the eighteen port card time slots shown in the timing diagram of Figure 12, using its UTOPIA L2 mechanism, the port card's slave MAMP backplane interface unit 55 will repeatedly poll the transmit buffers 51T1-51TM of its M PHY ports 51-1, ..., 51-M, to determine whether there is cell storage space available for transferring cells that have been buffered in associated transmit buffers 55T1-55TM. When a buffer 55Tj in the slave MAMP backplane interface unit 55 has a cell to transmit and space is available in its associated transmit buffer 51Tj, the cell is transferred across the UTOPIA L2 bus 53 and stored in the PHY layer transmit buffer 51Tj for delivery to its associated CPE or other ATM device.

UPSTREAM (PHY-ATM Layer) Cell Transport

Unlike downstream-directed communications on the transmit section 60T of the MAMP bus 60, where the substantial buffering capability of the ATM layer of a fabric card makes it possible to effect reasonable control over the flow of traffic to the various ports served by the backplane, in the upstream direction of the receive section 60R of the MAMP bus 60, the frequency and density of traffic flow at any particular port is unpredictable, so there is no simple way to quickly handle traffic flow.

SUBSTTTUTE SHEET (RULE 26) As noted above, systems are generally traffic- engineered so that (PHY layer associated) user devices are may transmit at the line rate, and the path to the ATM layer is sufficiently fast, so that cell loss will not occur during transport between a PHY layer port and its destination ATM layer. At the ATM layer, traffic control may be carried out to ensure that the PHY port devices do not violate their traffic contracts and create problems deeper into the network. Traffic flow violating such contracts may causes non-conforming cells to be tagged or discarded. An inherent shortcoming with this 'traffic policing' approach is its prohibitive cost when applied on each port card.

Fortunately, in the upstream direction this potential deficiency is effectively obviated by the asymmetrical nature of the data traffic, where more data cells are transported in the downstream (ATM-PHY layer) direction on the transmit portion 60T of the MAMP backplane 60, than in the upstream (PHY-ATM layer) direction on the receive portion 60R of the MAMP backplane bus. The receive portion 60R of the MAMP backplane bus 60 is engineered to sustain even a worst case traffic load, so that no backpressure mechanism is required, and there is no polling. Instead, the upstream arbitration scheme described above with reference to Figures 16 - 18 is used to grant port card access to the bus.

More particularly, as a PHY layer port 52R receives cells from its associated sourcing ATM device, and buffers those cells in its receive PHY port buffer 55R, the cells are transferred across the port card's UTOPIA L2 bus 53 and stored in the larger capacity receive buffer 51R of its associated slave MAMP backplane interface unit 50. As in the downstream direction, upstream (PHY-ATM layer) directed cells stored in the receive buffer 51R are prepended with a routing tag byte, to allow the ATM cell processor 82 in the master MAMP interface unit 45 of the destination fabric layer card to associate the cell-sourcing PHY layer port with the destination ATM layer device.

When a respective port card having cells to send is granted access by the RxArb signal 69 to the receive portion 60R of the backplane, as described above with reference to Figures 16 - 18, a cell is transferred across the upstream portion 60R of the MAMP backplane 60 and coupled to the receive RX MAMP bus interface 91 of a fabric card 40. The ATM cell processor 92 of the fabric card compares the (prepended) first byte of the received cell with routing tag information stored in its associated routing tag LUT 93, to determine if it's ATM layer is the intended recipient of the cell. If it is, the cell is stored in the appropriate receive buffer 45Ri within Rx FIFO controller 94. Otherwise, the cell is ignored. Once it has been buffered in a receive buffer of the master MAMP interface unit 45, the cell is interfaced with the UTOPIA L2 bus 43 and transferred to its destination ATM layer by the receive (Rx) UTOPIA L2 interface 95 using the UTOPIA L2 specification.

As will be appreciated from the foregoing description, shortcomings of a conventional UTOPIA L2 interface for ATM cell transport are successfully obviated by the multi-ATM layer, multi-PHY layer (MAMP) bus architecture of the invention, in which the functionality of a UTOPIA L2 interface is modularized into ATM-PHY layer transport and PHY-ATM layer transport portions. The ATM layer's PHY layer port address capability (currently limited to thirty-one ports) is made available to all of the ports the shelf.

The number of PHY layer ports per port card is a fraction of the total number of ports of the shelf, and is less than the maximum number of ports specified for a UTOPIA L2 based bus. This MAMP backplane allows the ATM layer-containing fabric card to monitor whether there is an ATM layer - PHY layer backpressure condition associated with a destination PHY port, before sending an ATM cell over the backplane . While we have shown and described an embodiment in accordance with the present invention, it is to be understood that the same is not limited thereto but is susceptible to numerous changes and modifications as known to a person skilled in the art, and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are obvious to one of ordinary skill in the art .

Claims

WHAT IS CLAIMED 1. A communication bus architecture for transporting ATM cells between an asynchronous transfer mode (ATM) layer and physical (PHY) layer ports of a plurality of port cards through which telecommunication service is provided to ATM equipments comprising: a backplane that is configured to provide ATM-PHY layer and PHY-ATM layer transport capability thereover; and an ATM layer-containing circuit card containing said ATM layer and an first backplane interface that is operative to provide ATM cell connectivity between said ATM layer and said backplane; and wherein each port card contains multiple PHY layer ports, and includes a second backplane interface that is operative to provide ATM cell connectivity between said backplane and any of said multiple PHY layer ports.

2. A communication bus architecture according to claim 1, wherein said ATM layer-containing circuit card includes a first ATM bus to which said ATM layer thereof is coupled, and a master multiple ATM layer, multiple PHY layer (MAMP) backplane interface unit coupled to and being operative to provide ATM cell connectivity between said first ATM bus and said backplane; and wherein each of said plurality of PHY layer-containing port cards includes a second ATM bus to which a slave MAMP backplane interface unit is coupled, said slave MAMP backplane interface unit being operative to provide ATM cell connectivity between said second ATM bus and said backplane, and wherein each of said multiple PHY layer ports is interfaced with said second ATM bus.

3. A communication bus architecture according to claim 2, wherein each of said first and second ATM buses comprises a Universal Test and Operations PHY Interface for ATM Level 2 (UTOPIA L2 ) based bus.

4. A communication bus architecture according to claim 2, wherein said master MAMP backplane interface unit is operative to determine whether there is an ATM layer - PHY layer backpressure condition for a PHY port to whom an ATM cell is to be transported from said ATM layer- containing circuit card.

5. A communication bus architecture according to claim 1, wherein said backplane includes an ATM-PHY layer transport portion for transporting ATM cells from said ATM layer-containing circuit card to any PHY layer port of any of said plurality of port cards, and a PHY-ATM layer transport portion for transporting ATM cells to said ATM layer-containing circuit card from any PHY layer port of any of said plurality of port cards.

6. A communication bus architecture according to claim 2, wherein said backplane is configured to indicate whether the slave MAMP backplane interface unit of a port card has available storage space for ATM cells to be transported from said ATM layer-containing circuit card to any PHY port of said port card.

7. A communication bus architecture according to claim 2, wherein said backplane is configured to indicate whether the slave MAMP backplane interface unit of the port card containing a PHY port to whom an ATM cell is to be transported from said ATM layer-containing circuit card has available storage space for said ATM cell.

8. A communication bus architecture according to claim 7, wherein said master MAMP backplane interface unit is operative to examine said backplane to determine whether the slave MAMP backplane interface unit of the port card containing a PHY port to whom an ATM cell is to be transported from said ATM layer-containing circuit card has storage space for said ATM cell.

9. A communication bus architecture according to claim 5, wherein said PHY-ATM layer transport portion includes an arbitration portion through which said slave MAMP backplane interface unit gains access to said backplane, in order to provide ATM cell transport from said second ATM bus over said backplane to said master MAMP backplane interface unit .

10. A communication bus architecture according to claim 2, wherein said master MAMP backplane interface unit is operative to incorporate, within an ATM cell transported over said backplane to a port card, routing information that is capable of associating an available port of said first ATM bus to any PHY layer port of said plurality of port cards .

11. A communication bus architecture according to claim 2, wherein said slave MAMP backplane interface unit is operative to incorporate, in an ATM cell transported over said backplane to said ATM layer-containing circuit card, routing information that is capable of associating any PHY layer port of the port card containing said slave MAMP backplane interface unit with any port of said first ATM bus of said ATM layer-containing circuit card.

12. A communication bus architecture according to claim 1, wherein said plurality of PHY layer ports of said PHY layer of a port card corresponds to a fraction of the total number of ATM equipments ported to said communication bus architecture.

13. A method of providing for the transport of ATM cells between an asynchronous transfer mode (ATM) layer and physical (PHY) layer ports of a plurality of port cards through which telecommunication service is provided to ATM equipments comprising the steps of: (a) providing a backplane that is configured to provide ATM-PHY layer and PHY-ATM layer transport capability thereover; (b) incorporating said ATM layer as part of an ATM layer-containing circuit card, and providing ATM cell connectivity between said ATM layer and said backplane; and (c) configuring each PHY layer-containing port card to include multiple PHY layer ports, and providing ATM cell connectivity between said backplane and any of the multiple PHY layer ports of said plurality of port cards.

14. A method according to claim 13, wherein step (b) comprises configuring said ATM layer- containing circuit card to include a master multiple ATM layer, multiple PHY layer (MAMP) backplane interface unit that is coupled to and is operative to provide ATM cell connectivity between said first ATM bus and said backplane; and wherein step (c) comprises configuring each PHY layer- containing port card to include a slave MAMP backplane interface unit that is operative to provide ATM cell connectivity between said second ATM bus and said backplane .

15. A method according to claim 14, wherein each of said first and second ATM buses comprises a Universal Test and Operations PHY Interface for ATM Level 2 (UTOPIA L2) based bus .

16. A method according to claim 14, wherein said master MAMP backplane interface unit is configured to determine whether there is an ATM layer - PHY layer backpressure condition for a PHY port of any port card to whom an ATM cell is to be transported from said ATM layer- containing circuit card.

17. A method according to claim 14, wherein said backplane is configured to indicate whether the slave MAMP backplane interface unit of a port card has available storage space for ATM cells to be transported from said ATM layer-containing circuit card to any PHY port of said port card.

18. A method according to claim 17, wherein said backplane is configured to indicate whether the slave MAMP backplane interface unit of the port card containing a PHY port to whom an ATM cell is to be transported from said ATM layer-containing circuit card has available storage space for said ATM cell.

19. A method according to claim 18, wherein said master MAMP backplane interface unit is operative to examine said backplane to determine whether the slave MAMP backplane interface unit of the port card containing a PHY port to whom an ATM cell is to be transported from said ATM layer-containing circuit card has storage space available for said ATM cell.

20. A method according to claim 14, wherein said backplane includes an ATM-PHY layer transport portion for transporting ATM cells from said ATM layer-containing circuit card to any PHY layer port of any of said plurality of port cards, and a PHY-ATM layer transport portion for transporting ATM cells to said ATM layer-containing circuit card from any PHY layer port of any of said plurality of port cards .

21. A method according to claim 20, wherein said PHY- ATM layer transport portion of said backplane includes an arbitration portion through which said slave MAMP backplane interface unit gains access to said backplane, in order to provide ATM cell transport from said second ATM bus over said backplane to said master MAMP backplane interface unit .

22. A method according to claim 14, wherein said master MAMP backplane interface unit is operative to incorporate, within an ATM cell transported over said backplane to a port card, routing information that is capable of associating an available port of said first ATM bus to any PHY layer port of said plurality of port cards.

23. A method according to claim 14, wherein said slave MAMP backplane interface unit is operative to incorporate, within an ATM cell transported over said backplane to said ATM layer-containing circuit card, routing information that is capable of associating any PHY layer port of the port card containing said slave MAMP backplane interface unit with any available port of the first ATM bus of said ATM layer-containing circuit card.

24. A method according to claim 13, wherein the number of said multiple PHY layer ports of said port card is a fraction of the total number of said plurality of ports associated with an ATM layer containing card.

25. A method of providing for the transport of ATM cells between an asynchronous transfer mode (ATM) layer and physical (PHY) layer ports of a plurality of port cards through which telecommunication service is provided to ATM equipments comprising the steps of: (a) providing a backplane that is configured to provide ATM-PHY layer and PHY-ATM layer transport capability thereover; (b) incorporating said ATM layer as part of an ATM layer-containing circuit card, and configuring said ATM layer-containing circuit card to include a master multiple ATM layer, multiple PHY layer (MAMP) backplane interface unit that is coupled to and is operative to provide ATM cell connectivity between a first Universal Test and Operations PHY Interface for ATM Level 2 (UTOPIA L2) based bus and said backplane; and (c) configuring each PHY layer-containing port card to include a second UTOPIA L2 based bus coupled to multiple PHY layer ports, the number of which is less than the total PHY port capacity of said first UTOPIA L2 based bus, and to include a slave MAMP backplane interface unit that is operative to provide ATM cell connectivity between said second UTOPIA L2 based bus and said backplane, and providing ATM cell connectivity between said backplane and any of said multiple PHY layer ports.

26. A method according to claim 25, wherein said backplane is configured to indicate whether a port card has available storage space for ATM cells to be transported from said ATM layer-containing circuit card to any of said multiple PHY ports.

27. A method according to claim 25, wherein said backplane includes an arbitration portion through which said slave MAMP backplane interface unit gains access to said backplane, in order to provide ATM cell transport from said second UTOPIA L2 based bus over said backplane to said master MAMP backplane interface unit.

28. A method according to claim 25, wherein said master MAMP backplane interface unit is operative to controllably enable the transport of an ATM cell over said backplane to a port card in accordance with whether there is an ATM layer - PHY layer backpressure condition for a PHY port of said port card for whom said ATM cell is intended.