Multiplex communications – Fault recovery – Bypass an inoperative switch or inoperative element of a...
Reexamination Certificate
1999-08-03
2004-08-24
Patel, Ajit (Department: 2664)
Multiplex communications
Fault recovery
Bypass an inoperative switch or inoperative element of a...
C370S254000
Reexamination Certificate
active
06781953
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to communication networks and in particular to broadcast protocols in local area networks.
BACKGROUND OF THE INVENTION
Standard local communication networks comprise a plurality of bridging-devices and communication links. Each communication link connects between two or more bridging-devices or between a bridging-device and an end-station, e.g., a computer. Each bridging-device comprises a plurality of ports which serve as interfaces between the bridging-device and the links to which it is connected. When a source station sends a message to a destination station, the source station parses the message into frames and sends the frames to a nearest bridging-device which forwards the frames to one of its neighboring bridging-devices (bridging-devices which are directly connected by a common link are referred to herein as neighbors). The neighboring bridging-device forwards the frames to another bridging-device (which is its neighbor) until the frames finally reach the bridging-device connected to the destination station. In many cases, frames are broadcast to all the bridging-devices in a local network. In the context of the present application and claims the term “broadcast frames” refers to any frames which are to be distributed throughout the network, including broadcast and multicast frames and frames with a unicast address for which a bridging-device does not recognize the address.
One requirement imposed in many cases on bridging-devices is modularity, i.e., they do not require changes when the topology of the network changes, for example, by adding new bridging-devices. A standard broadcast scheme involves having a bridging-device, which receives a broadcast frame, forward the frame through all its ports, except for the port through which the frame was received. This broadcast scheme operates properly only if the bridging-devices and links do not form a loop in the network. If the network includes a loop, a single frame may be repeatedly sent through the network and the network will fail. Such a situation is commonly referred to as a broadcast storm. The term loop is taken to mean in the following description and claims, at least three bridging-devices connected by links which forward data, such that there are at least two different paths along non-parallel links between each pair of the bridging-devices.
In many cases redundant links are added to networks, to be used in case one or more of the bridging-devices and/or links fail. A spanning tree algorithm is commonly used to dynamically block the ports leading to the redundant links and thus prevent the formation of loops. One common spanning tree algorithm is the 802.1D standard spanning tree algorithm (STA) which is described in “Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Media access control (MAC) bridges”, International Standard ISO/IEC 15802-3, 1998, ANSI/IEEE Std 802.1D, 1998 edition, the disclosure of which is incorporated herein by reference.
However, blocking the redundant links is wasteful in bandwidth since the redundant links could be used to pass messages and thus speed up the network operation. The blocking of redundant links is especially wasteful in networks which have a full-mesh topology and therefore may have many blocked links.
Many modem LAN bridging-devices support a feature named virtual local area networks (VLANs). Some or all of the messages sent through the network are given a VLAN ID which represents the VLAN to which the messages belong. The ports of the bridging-devices of the network are configured as active or blocking for each VLAN separately. VLANs allow a single physical network to operate as a plurality of independent networks. For example, a station may be connected to a network through a port in which only a VLAN X is enabled. The station therefore can only forward packets to, and receive packets from, stations which are connected to VLAN X. An emerging standard for VLANs is described in “Draft Standard P802.1Q/D9, IEEE Standards for Local and Metropolitan Area Networks: Virtual Bridged Local Area Networks”, 1998, the disclosure of which is incorporated herein by reference.
“IEEE draft P802.3ad/D0.1, Supplement to Carrier Sense Multiple Access with Collision Depiction (CSMA/CD), Access Method and Physical Layer Specification: Link Aggregation”, Dec. 30, 1998, pages 1-62, the disclosure of which is incorporated herein by reference, describes a scheme in which a plurality of parallel links, referred to as a Link Aggregation Group (LAG), connect between a pair of bridging-devices (and/or end stations). Broadcast frames sent between the pair of bridging-devices are always sent on only one of the links of the LAG, regardless of the source of the frame. A broadcast frame received through one of the parallel links is not forwarded through any of the parallel links so as to prevent the occurrence of a broadcast storm. This draft, however, only discusses broadcasting through parallel point to point links and does not describe avoidance of broadcast storms in bridged networks which include a plurality of links which connect between more than two bridging-devices and/or end stations.
SUMMARY OF THE INVENTION
It is an object of some preferred embodiments of the invention to provide a method for forwarding broadcast frames in a full-mesh-topology network, which method does not require blocking of links.
It is an object of some preferred embodiments of the invention to provide a method for forwarding broadcast frames in a network which includes loops, which method is free of the possibility of a broadcast storm.
It is an object of some preferred embodiments of the invention to provide a method for forwarding broadcast frames in a network which includes loops, which method is modular.
It is an object of some preferred embodiments of the invention to provide a method for aggregation of non-parallel links.
One aspect of some preferred embodiments of the present invention relates to restricting the distribution of broadcast frames, in full-mesh-topology networks and/or full-mesh-topology sub-networks (referred to herein as clusters). Bridging-devices, belonging to the full-mesh-topology cluster, forward broadcast frames according to the origin of the frames. Broadcast frames received by a cluster bridging-device from another cluster bridging-device are forwarded only to non-cluster bridging-devices. On the other hand, broadcast frames received from external bridging-devices (not belonging to the cluster) are preferably forwarded as usual through substantially all the ports of the receiving bridging-device (except the port through which the frame was received). Since the cluster bridging-devices are all connected to each other, when a first cluster bridging-device forwards a frame to a second cluster bridging-device the frame is also forwarded to all the other cluster bridging-devices. Therefore, the second cluster bridging-device does not need to send the frame to any of the cluster bridging-devices. The broadcast method described above avoids the generation of broadcast storms although the network includes physical loops.
One aspect of some preferred embodiments of the present invention relates to a broadcast protocol which operates in a cluster of a frame based local area network (LAN) which includes loops. Each bridging-device in the network forwards broadcast frames to neighboring bridging-devices according to a specific distribution table of the bridging-device. The bridging-devices to which the broadcast frames are forwarded are preferably determined responsive to the bridging-device from which the frames were received. The distribution tables are planned such that broadcast frames are forwarded to each of the bridging-devices in the cluster only once.
There is therefore provided in accordance with a preferred embodiment of the present invention, a method of distributing a broadcast frame within a network, including receiving the broadcast frame in a bridging-device of t
Avaya Communication Israel Ltd.
Dinicola Brian K.
Patel Ajit
Shah Chirag
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