Port redundancy and backpressure translation table apparatus

Details Port redundancy and backpressure translation table apparatus Port redundancy and backpressure translation table apparatus

1998-05-28

2001-03-13

Ton, Dang (Department: 2732)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S395430, C370S401000, C370S466000

Reexamination Certificate

active

06201809

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to data communications equipment and more particularly relates to a port redundancy/backpressure translation table apparatus.
BACKGROUND OF THE INVENTION
More and more reliance is being placed on data communication networks to carry increasing amounts of data. In a data communications network, data is transmitted from end to end in groups of bits which are called packets, frames, cells, messages, etc. depending on the type of data communication network. For example, Ethernet networks transport frames, X.25 and TCP/IP networks transport packets and ATM networks transport cells. Regardless of what the data unit is called, each data unit is defined as part of the complete message that the higher level software application desires to send from a source to a destination. Alternatively, the application may wish to send the data unit to multiple destinations.
Asynchronous Transfer Mode
ATM originated as a telecommunication concept defined by the Comite Consulatif International Telegraphique et Telephonique (CCITT), now known as the ITU, and the American National Standards Institute (ANSI) for carrying user traffic on any User to Network Interface (UNI) and to facilitate multimedia networking between high speed devices at multi-megabit data rates. ATM is a method for transferring network traffic, including voice, video and data, at high speed. Using this connection oriented switched networking technology centered around a switch, a great number of virtual connections can be supported by multiple applications through the same physical connection. The switching technology enables bandwidth to be dedicated for each application, overcoming the problems that exist in a shared media networking technology, like Ethernet, Token Ring and Fiber Distributed Data Interface (FDDI). ATM allows different types of physical layer technology to share the same higher layer—the ATM layer.
More information on ATM networks can be found in the book “ATM: The New Paradigm for Internet. Intranet and Residential Broadband Services and Applications,” Timothy Kwok, Prentice Hail, 1998.
ATM uses very short, fixed length packets called cells. The first five bytes, called the header, of each cell contain the information necessary to deliver the cell to its destination. The cell header also provides the network with the ability to implement congestion control and traffic management mechanisms. The fixed length cells offer smaller and more predictable switching delays as cell switching is less complex than variable length packet switching and can be accomplished in hardware for many cells in parallel. The cell format also allows for multi-protocol transmissions. Since ATM is protocol transparent, the various protocols can be transported at the same time. With ATM, phone, fax, video, data and other information can be transported simultaneously.
ATM is a connection oriented transport service. To access the ATM network, a station requests a virtual circuit between itself and other end stations, using the signaling protocol to the ATM switch. ATM provides the User Network Interface (UNI) which is typically used to interconnect an ATM user with an ATM switch that is managed as part of the same network.
Cell Processing at the Ingress
A typical ATM switch comprises a plurality of port interface cards coupled to the ingress of a switching fabric. The egress of the switch is also coupled to a port interface card. The functions of the interface card includes translation from optical signal to electrical, performing error checking on the received cells, etc. The interface card also comprises a cell processor one of whose major functions is to determine the appropriate output destination port for each incoming cell. The cell processor makes this determination based on the destination ATM address in the received cell and on the contents of a lookup table (LUT). The LUT comprises destination entries for many possible VPI/VCI combinations.
As an example, the entry retrieved from the LUT can be used to generate a routing tag for the cell. The cell is then passed to the switching fabric which functions to steer the cell to the appropriate destination. Note that for a unicast cell, the routing tag has only a single destination port selected. For a multicast (MC) cell, however, the routing tag may have a plurality of destination ports indicated.
Currently, there is increasing concern over the reliability of networks including both the switches and the links used to connect them. As the amount and importance of the data traffic sent over networks increases, the reliability of networks become more and more important. When a link fails, it is desirable to have a redundancy capability within the switch which can provide recovery in the event of a port or link failure. When a port or link in a switch fails, a backup port can be assigned in its place. The original routing tag, however, remains unchanged as it is impractical to modify the contents of the LUT. The LUT typically contains a large number of entries, e.g., tens of thousands, wherein any combination of entries may contain the failed port.
One solution is to utilize a memory lookup table that contains the mappings from the old output ports designations to the new one. Access to the lookup table occurs in serial fashion which greatly slows down the process. Large time delays are generated as the number of parallel output port designations increases, e.g., multicast cells wit h large numbers of destinations.
Thus, a mechanism is needed to modify the routing tag before the cell is transferred to the switching fabric. The mechanism should preferably handle both unicast and multicast cells without incurring significant time delays.
SUMMARY OF THE INVENTION
The present invention comprises a translation table that can serve as both a forward translation table and as a backward translation table. The translation table can be used with bit vectors where it is desired to displace one or more bits to different bit positions in accordance with a configurable bitmap translation table. The translation of one bit vector to another can be performed in real time. Any number of bits can be moved simultaneously. In addition, both the bit vectors and the contents of the translation table can be changed on the fly. In practice, the translation table is typically more static that the bit vectors but the invention is not limited to this case. The translation table is accessible by a host application.
A typical application of the present invention includes a switch wherein the information units, e.g., frames, cells, etc., are queued at the ingress of the switch in accordance with their output destination ports. Each data unit has associated with it a routing tag which is a bitmap vector representing the output ports of a switch to which the data units are destined to.
Now assume, for example, that due to a link or port failure, the traffic originally destined to output port J is to be diverted to output port K. In this case, the bitmap representing the destination output ports should be modified such that when a data unit arrives with destination output port J selected, the translation table can be configured so as to inhibit traffic to port J and instead divert it to output port K. Note that the selection of an output port is indicated in the bitmap vector, i.e., routing tag, as a ‘1’. A ‘0’ indicates that the output port is not selected. Thus, to divert traffic from one port to another, the bit corresponding to the output port to be inhibited is set to a ‘0’ and the bit corresponding to the output port to receive the traffic is set to a ‘1’.
It is an important feature of the present invention that the above described operation can be performed on multiple bits simultaneously, i.e., several bits can be displaced at the same time in accordance with the translation table.
For example, assume that a multicast stream of data is destined to output ports K, L and M. In addition, assume that output ports K and M have failed. It is desirable to diver

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