Multiplex communications – Fault recovery – Bypass an inoperative switch or inoperative element of a...
Reexamination Certificate
1998-05-28
2001-04-24
Vincent, David R. (Department: 2732)
Multiplex communications
Fault recovery
Bypass an inoperative switch or inoperative element of a...
C370S228000
Reexamination Certificate
active
06222820
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to data communication networks and more particularly relates to a method of providing redundancy or VCC/VPC virtual connections in an Asynchronous Transfer Mode (ATM) network.
BACKGROUND OF THE INVENTION
Currently, there is a growing trend to make Asynchronous Transfer Mode (ATM) networking technology the base of future global communications. ATM has already been adopted as a standard for broadband communications by the International Telecommunications Union (ITU) and by the ATM Forum, a networking industry consortium.
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 Hall, 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.
Prior Art Redundancy Schemes
Many of today's high end applications require a high degree of fault recovery capability from the communications networks which carry their data from one point to another. Traditionally, fault recovery was achieved by placing extra physical resources in the network to insure a backup path from any point to any point across the network. Examples include backup links, backup network elements such as switches, routers, bridges, etc.
The recovery capability requirement also includes quick recovery response times. For example, an FDDI physical layer includes a backup ring which is used immediately, on the order of milliseconds, when a physical connection problem is detected by a loss of signal on the primary ring.
In ATM networks, the architecture of the network is based on point to point links which function to carry many point to point and point to multipoint virtual circuits or connections (VCs). Since the routing of these numerous virtual connections is dynamic, there is no way to determine a priori a redundancy connection which will actually be redundant, i.e., a connection that does not use any part of the original path for the redundant path.
In addition, there is no implicit mechanism provided for in the ATM standards. Prior art attempts to recover from faults in ATM networks take a relatively long time to execute, e.g., tens of seconds, which may be long enough to cause any connected applications to crash. Also, the prior art techniques require network users to re-setup their connections that were broken as a result of the failure. The switchover time was also dependent on a variety of different timeouts associated with the user application, rather than a deterministic means that provides fast detection and switchover times.
There are some technologies that can potentially provide redundancy, such as Ethernet, Token Ring, FDDI, etc. A characteristic feature, however, of all these protocols is that it is very complex and costly to implement redundancy in any shared media such as these. In particular, the FDDI standard is the only shared media standard that defines a redundant recovery path. The standard, however, defines the redundant recovery path for all entities and all connections connected to the media without making it selective. Thus, it is all or nothing without leaving the choice up to only the entities that desire a redundant connection.
SUMMARY OF THE INVENTION
The present invention is a method of selectively providing redundancy on a dynamic basis to those end users that desire it. The method provides a redundancy feature that can be used on a call by call basis by end users at the time a call setup is requested to be established. The method functions to establish both a primary and a redundant connection for each connection requested to be redundant.
The method has the advantages of being quick with fast fault detection and subsequent fast switchover of traffic to the redundant path. Note that although some data may be lost until the switchover to the redundant connection is complete, this should not pose a major problem as the upper layers in the protocol stack at the end station, i.e., the Transport Layer, are able to compensate for the data loss. In most applications there is a higher priority on having a redundant link with the consequent potential loss of some data. In these applications, there is likely upper protocol layers in the communication stack that can handle the necessary retransmission, re-ordering, etc. required.
The redundancy method of the present invention has application to PNNI networks, B-ICI networks and to any public network that uses signaling and routing in its operation, i.e., ISDN, frame relay, networks utilizing general signaling, voice networks, etc.
The method functions to establish a primary connection from the source end user to the destination end user. A unique call reference number is generated by the end user and is carried unchanged from switch to switch along the path. In response to indicators that the call is a primary portion of a redundant call, each switch registers the call as a primary call in its database.
Subsequently, once the primary connection is established successfully, the redundant connection is established. Each switch along the redundant path checks to see if the primary path already includes the switch itself. If it does, then either the call can be rejected or it can be permitted with the condition that a link be used to the next hop that is not in use on the primary path.
Once established, the originator and the destination of the redundant path continuously monitor the primary connection for failures. If a failure is detected, data traffic is switched from the primary connection to the redundant connection with the loss of cells being handled by the upper communication protocol layers.
If the redundant connection cannot be established, then depending on options set by the user or network management entity, the primary call can be permitted without the redundant path or the entire call can be rejected.
There is thus provided in accordance with the present invention a method of providin
3Com Corporation
Vincent David R.
Weitz David J.
Wilson Sonsini Goodrich & Rosati
Zaretsky Howard
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