Patent Publication Number: US-2007104093-A1

Title: Method of inter-RPR-ring bridge redundancy

Description:
FIELD OF THE TECHNOLOGY  
      The present invention relates to Resilient Packet Ring (RPR) techniques, and more particularly, to a method of inter-RPR ring bridge redundancy.  
     BACKGROUND OF THE INVENTION  
      As the fast development of diversified Metropolitan Area Network (MAN) techniques, the RPR is used by more and more MANs for its advanced technique, effective investment, ascendant performance and diversity of services supported. The RPR, of which the architecture and technique are newly designed to satisfy the requirements of the packet MAN, is a ring network composed of packet switch devices. The network adopting the RPR technique is called an RPR ring network and can be called an RPR ring for short. The packet switch device on the RPR ring is called an RPR device. When the RPR device adopts a Media Access Control (MAC) address with 48 bits used in the Ethernet as an address identity (ID) to identify the RPR device uniquely, and bears a layer-two packet by way of Ethernet Over RPR, the RPR ring can also be called a bridge mode RPR. The device on the RPR ring can also be called an RPR bridge and the MAC address of the RPR bridge can be called an RPR MAC address. As shown in  FIG. 1 , the architecture of two RPR rings interconnecting at two RPR bridges is illustrated.  
      There are two RPR rings in  FIG. 1 , one is RPR ring  1  and the other is RPR ring  2 . There are four RPR bridges on each RPR ring. The RPR ring  1  and the RPR ring  2  interconnect at RPR inter-ring bridge  1  and RPR inter-ring bridge  2 . An RPR inter-ring bridge is an RPR bridge which is on at least two RPR rings at the same time and it is in charge of forwarding a data packet between the at least two RPR rings. To simplify the description, the RPR inter-ring bridge will be called an inter-ring bridge for short; the RPR bridge will be called a bridge for short hereinafter.  
      In the RPR ring, since layer-two Ethernet packets are carried and the packets between the RPR rings are forwarded according to an address analysis protocol (e.g. MAC), a loop would be brought between the two RPR inter-ring bridges interconnecting the two RPR rings. That is, there would be a broadcast storm phenomenon between the RPR inter-ring bridge  1  and the RPR inter-ring bridge  2  shown in  FIG. 1 . To avoid the loop and the broadcast storm problem, a minimum spanning tree without the loop is generated by prune branches through the Spanning Tree Protocol (STP) or Rapid Spanning Tree protocol (RSTP). And the layer-two Ethernet packets are forwarded along the minimum spanning tree to avoid a loop in the layer-two communication. In addition, when there is a failure in any device or link in the layer-two network, a new forwarding tree would be recalculated through the minimum spanning tree calculation of the STP or the RSTP to ensure the normal work after a failure appears.  
     SUMMARY OF THE INVENTION  
      The present invention provides a method of inter-RPR-ring bridge redundancy, by which the RPR ring may recover rapidly after a failure in the RPR ring, and the normal use of services on the RPR ring may be ensured.  
      The inter-RPR-ring bridge redundancy method includes: configuring a priority for each inter-ring bridge; constituting a redundancy group by more than one inter-ring bridge, which interconnects two RPR rings; configuring one inter-ring bridge in the redundancy group as a primary inter-ring bridge which is in charge of forwarding packets; configuring the other(s) as secondary inter-ring bridge(s); and electing an inter-ring bridge with the highest priority and having an inter-ring communication ability to be the primary inter-ring bridge, when the redundancy group changes.  
      The method of inter-RPR-ring bridge redundancy in accordance with the present invention makes inter-ring bridges constitute a redundancy group, elects one inter-ring bridge as a primary inter-ring bridge in the redundancy group which is in charge of forwarding packets and configuring the priority of every inter-ring bridge. When the redundancy group changes, the inter-ring bridge with the highest priority and having the ability of packet forwarding is elected to be the primary inter-ring bridge. According to the method provided by the present invention, an RPR ring may recover rapidly after the RPR ring changes. As a result, the services on the RPR ring may be ensured to be normal and the network communication delay and the burden of the network communication may be reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic diagram illustrating the architecture of two interconnecting RPR rings in the prior art;  
       FIG. 2  is a flow chart illustrating the redundancy of a primary inter-ring bridge in accordance with an embodiment of the present invention;  
       FIG. 3  is a flow chart illustrating the redundancy of a secondary inter-ring bridge in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      According to an embodiment of the present invention, more than one inter-ring bridge, which is the interconnection of the two RPR rings, is set to constitute a redundancy group. One inter-ring bridge in the redundancy group is configured as a primary inter-ring bridge, while the other(s) is (are) secondary inter-ring bridge(s). The primary inter-ring bridge is in charge of forwarding data packets between the two RPR rings. However, when the primary inter-ring bridge becomes invalid, a secondary inter-ring bridge upgrades to be the primary inter-ring bridge continuing to forward data packets between the two RPR rings.  
      Here, the step of transmitting the data packets between the two RPR rings can be implemented by that the primary inter-ring bridge takes charge of forwarding all packets or packets with the same characteristics according to specific configurations. And the secondary inter-ring bridge(s) is (are) not in charge of forwarding these data packets.  
      Whether the primary inter-ring bridge is invalid or whether a new primary inter-ring bridge needs to be elected can be reflected through the change of the topology of the RPR ring. As the topology detection and the topology convergence of the RPR ring only need 50 ms, after a change of the RPR ring topology, the time for electing a new primary inter-ring bridge through a special topology detection of the RPR ring will be less than 100 ms.  
      Therefore, both the primary inter-ring bridge and the secondary inter-ring bridge(s) in the present embodiment can use the special topology detection function of the RPR ring to obtain the topology information of other inter-ring bridge(s) in the redundancy group. In this way, a primary inter-ring bridge in the redundancy group can be elected in time when a change of the topology in the group takes place.  
      A node information table can be configured in each inter-ring bridge in the redundancy group, the node information including at least a bridge ID, a bridge priority, a current state of the bridge and RPR MAC information of the current two interfaces of the inter-ring bridge. Here, the reason that there are two interfaces in the inter-ring bridge is that the inter-ring bridge connects two RPR rings and the two interfaces of the inter-ring bridge are used to connect the two RPR rings respectively.  
      Here, the bridge priority can be configured according to actual needs, for example, the smaller value the higher priority, or the larger value the higher priority. In addition, if the priorities of the bridges are identical, the priority of the bridge can be determined according to value of the bridge ID.  
      As shown in  FIG. 2 , when there is a change on the topology of the RPR ring and the primary inter-ring bridge in the redundancy group receives a topology message, the following steps will be executed.  
      Step  201 : the primary inter-ring bridge recalculates the current the topology structure after receiving the topology message, and refresh a topology structure table stored in the primary inter-ring bridge after the topology is convergent.  
      Specifically, since the primary inter-ring bridge is on both the two RPR rings at the same time, there are two topology structure tables stored in the primary inter-ring bridge corresponding to the two RPR rings respectively. According to the topology structure of the network shown in  FIG. 1 , if a topology message is received from the RPR ring  1 , the primary inter-ring bridge will refresh the topology structure table of the RPR ring  1  stored in it. While, if a topology message is received from the RPR ring  2 , the primary inter-ring bridge will refresh the topology structure table of the RPR ring  2  stored in it.  
      Step  202 : the primary inter-ring bridge judges whether both its two RPR bridge interfaces have inter-ring communication ability, if both the two interfaces have the ability, proceeds to Step  203 ; and otherwise, proceeds to Step  206 .  
      Here, the step of judging whether both the two RPR bridge interfaces have the inter-ring communication ability can be implemented by that the primary inter-ring bridge judges whether the two RPR bridge interfaces of itself can forward packets normally, if they can forward packets normally, it means that they have the inter-ring communication ability; and otherwise, it means that they do not have the inter-ring communication ability.  
      Step  203 : the primary inter-ring bridge looks up the node information table stored in it and judges whether there is an inter-ring bridge with a higher priority in the redundancy group, if there is such an inter-ring bridge, proceeds to Step  204 ; and otherwise, proceeds to Step  205 .  
      The judging in Step  203  should be implemented in all the nodes in the redundancy group, no matter whether the previous state of the inter-ring bridge is invalid or not. In this way, it is ensured that none of the inter-ring bridge with a high priority will be neglected. Some inter-ring bridges on an RPR ring are invalid due to a link failure or other reasons. However, if the link is recovered, the inter-ring bridge with a higher priority will reappear on the RPR ring and it is eligible to be a primary inter-ring bridge.  
      Step  204 : the primary inter-ring bridge judges whether the inter-ring bridge with a higher priority has the inter-ring communication ability. If the inter-ring bridge has the inter-ring communication ability, proceeds to Step  206 ; otherwise, proceeds to Step  205 .  
      Here, there may be more than one inter-ring bridge with a higher priority in the redundancy group due to the change of the network topology. Step  206  will be performed as long as there is one inter-ring bridge with a higher priority and having the inter-ring communication ability.  
      Wherein, the step of the primary inter-ring bridge judging whether the inter-ring bridge with a higher priority has the inter-ring communication ability can be performed as follows: first, assume that the inter-ring bridge with a higher priority is bridge A, the two RPR bridge interfaces of bridge A on each of the two RPR rings are RPR bridge interface A 1  and RPR bridge interface A 2  respectively, the current primary inter-ring bridge is bridge B, and the two RPR bridge interfaces of bridge B on each of the two RPR rings are RPR bridge interface B 1  and RPR bridge interface B 2 . The step of the primary inter-ring bridge judging whether the inter-ring bridge with a higher priority has the inter-ring communication ability includes that judging whether the RPR bridge interface A 1  of the bridge A can communicate with the RPR bridge interface B 1  of the bridge B on the RPR ring  1  and whether the RPR bridge interface A 2  of the bridge A can communicate with the RPR bridge interface B 2  of the bridge B on the RPR bridge  2 . If the RPR bridge interface A 1  of the bridge A can communicate with the RPR bridge interface B 1  of the bridge B and the RPR bridge interface A 2  of the bridge A can communicate with the RPR bridge interface B 2  of the bridge B, the bridge A has the inter-ring communication ability.  
      Here, the step of judging whether the RPR bridge interface A 1  of the bridge A can communicate with the RPR bridge interface B 1  of the bridge B on the RPR ring  1  includes that the bridge B looks up the topology information table of the RPR ring  1  stored in it and determines whether there is the RPR bridge interface A 1 . If there is the RPR bridge interface A 1 , the RPR bridge interface A 1  of the bridge A can communicate with the RPR bridge interface B 1  of the bridge B on the RPR ring  1 . Otherwise, the RPR bridge interface A 1  of the bridge A can not communicate with the RPR bridge interface B 1  of the bridge B on the RPR ring  1 . A same method can be adopted to judge whether the RPR bridge interface A 2  of the bridge A can communicate with the RPR bridge interface B 2  of the bridge B or not. Hence, no more description will be given.  
      Step  205 : the primary inter-ring bridge terminates the current process.  
      This step shows that the current primary inter-ring bridge still works well and there is no inter-ring bridge with a higher priority and having the inter-ring communication ability.  
      Step  206 : the primary inter-ring bridge exits the primary state.  
      When a primary inter-ring bridge receives and processes a topology message, each secondary inter-ring bridge in the redundancy group receives and processes the topology message as well. The specific processing procedure of each secondary inter-ring bridge is shown in  FIG. 3 .  
      Step  301 : the secondary inter-ring bridge recalculates the current topology structure after receiving the topology message and refresh the topology structure table stored in it after the topology is convergent.  
      The specific refreshing method is the same as the refreshing method performed by the primary inter-ring bridge shown in Step  201 . Thus no more description will be given.  
      Step  302 : the secondary inter-ring bridge judges whether both its two RPR bridge interfaces have the inter-ring communication ability. If both the two interfaces have the inter-ring communication ability, proceeds to Step  303 ; and otherwise, proceeds to step  306 .  
      Here, the method of judging is the same as that shown in Step  202 . Thus no more description will be given.  
      Step  303 : the secondary inter-ring bridge looks up the node information table stored in it and judges whether there is an inter-ring bridge with a higher priority in the redundancy group. If there is such an inter-ring bridge, proceeds to Step  304 ; and otherwise, proceeds to Step  305 .  
      The judging in Step  303  should be implemented in all the nodes in the redundancy group, no matter whether the state of the inter-ring bridge is invalid or not.  
      Step  304 : the secondary inter-ring bridge judges whether the inter-ring bridge with a higher priority has the inter-ring communication ability. If the inter-ring bridge has the inter-ring communication ability, proceeds to Step  306 ; and otherwise, proceeds to Step  305 .  
      Here, there may be more than one inter-ring bridge with a higher priority in the redundancy group due to the change of the network topology. Step  306  will be performed as long as there is one inter-ring bridge with a higher priority and having the inter-ring communication ability.  
      Wherein, the step of the secondary inter-ring bridge judging whether the inter-ring bridge with a higher priority has the inter-ring communication ability can adopt the same method as that in Step  204 .  
      Step  305 : the secondary inter-ring bridge upgrades to the primary state.  
      Step  306 : the secondary inter-ring bridge terminates the current process.  
      Step  306  shows that in the redundancy group, there is an inter-ring bridge with a higher priority and having the inter-ring communication ability. So the secondary inter-ring bridge is not eligible to be a primary inter-ring bridge.  
      Generally speaking, the flows shown in  FIG. 2  and  FIG. 3  can both ensure that when the topologies of the two RPR rings where the redundancy group belongs change, the current primary inter-ring bridge in the redundancy group is the one with the highest priority and having the inter-ring communication ability.  
      A waiting time can be further configured in the primary inter-ring bridge and the secondary inter-ring bridge(s) in accordance with the present embodiment. The primary inter-ring bridge will wait the configured time when it is ready to exit the primary state, that is, between Step  204  and  206 . And the secondary inter-ring bridge which is ready to upgrade to the primary state will also wait the configured time before upgrading to the primary state, that is, between Step  304  and  305 . After determining that the state of the inter-ring bridge with the highest priority and having the inter-ring communication ability is steady, the corresponding Step  206  and Step  305  will be performed respectively. Otherwise, the corresponding Step  205  and Step  306  will be performed respectively.  
      A parameter of the number of topology messages to be waited can also be configured in the primary inter-ring bridge and the secondary inter-ring bridge(s), that is, the primary inter-ring bridge which is ready to exit the primary state and the secondary inter-ring bridge which is ready to upgrade to the primary state will first wait the configured number of topology messages. And then if the state of the inter-ring bridge with the highest priority and having the ability to forward is steady, corresponding implementations will be performed.  
      Each inter-ring bridge in the redundancy group can discover whether there is a new inter-ring bridge being added or deleted through the topology message received. However, the inter-ring bridge in the redundancy group can not discover the change of the priorities of other inter-ring bridges in the redundancy group. Therefore, a new control message can be added to the redundancy group to transmit the state of each inter-ring bridge. The control message carries at least a bridge ID of the inter-ring bridge, a bridge priority of the inter-ring bridge, the current state of the inter-ring bridge, RPR MAC information of the current two interfaces of the inter-ring bridge. Here, the information carried in the control message is called redundancy group information of the inter-ring bridge. When the protection information of an inter-ring bridge changes, the inter-ring bridge will broadcast a control message to other bridge(s) in the redundancy group informing the change of its state. The node information table of each inter-ring bridge in the redundancy group will be refreshed according to its current state and the received control message from other inter-ring bridge(s). Specifically, the redundancy group information of other inter-ring bridge(s) stored in this inter-ring bridge is refreshed according to the received control message. Well, the redundancy group information of this inter-ring bridge is refreshed according to its own configurations and its state which is calculated by the current RPR ring topology.  
      For example, the priority of one inter-ring bridge in the redundancy group is degraded due to such reasons as a manual configuration. After the priority of the inter-ring bridge is degraded, it will broadcast a control message carrying the changed redundancy group information to other inter-ring bridge(s) in the redundancy group. Other bridge(s) in the redundancy group will refresh its (their) own node information table(s) according to the received redundancy group information and perform corresponding processes. The specific processing procedure of the primary inter-ring bridge is the same as that shown in  FIG. 2 . The specific processing procedure of the secondary inter-ring bridge(s) is (are) the same as that shown in  FIG. 3 . So no more description will be given.  
      The control message may be broadcasted to other inter-ring bridge(s) in the redundancy group not only when the priority of the inter-ring bridge changes, but also when the state of the inter-ring bridge changes. Here, the change of the state may be a result from the change of the topology or the change caused by a manual configuration or other reasons.  
      In addition, the control message may be sent to other bridge(s) in the redundancy group not only when the redundancy group information changes, but also periodically. Under the circumstance that the control message is sent periodically, when receiving the control message each time, the primary inter-ring bridge will implement the flow showed in  FIG. 2 . And the secondary inter-ring bridge(s) will implement the flow showed in  FIG. 3 .  
      Under the circumstance that the control message is sent periodically, a parameter of the number of control messages to be waited can be configured. The primary inter-ring bridge which is ready to exit the primary state and the secondary inter-ring bridge which is ready to upgrade to the primary state, will wait the configured number of control messages first. After that, if the state of the inter-ring bridge with the highest priority and having the inter-ring communication ability is still steady, corresponding implementations will be performed.  
      The above embodiments introduce only the situation that a redundancy group is formed by two RPR rings. In real networks, the general situation is that one inter-ring bridge belongs to multiple redundancy groups. Here, one entry should be added to the node information table of each inter-ring bridge. The entry is call group ID, which is used to illustrate which redundancy group formed by which two RPR rings that the inter-ring bridge belongs to. The group ID entry should be added to the control message correspondingly.  
      The foregoing is only preferred embodiments of this invention. The protection scope of this invention, however, is not limited to the above description. Any change or substitution, within the technical scope disclosed by this invention, but those skilled in the art should be covered by the protection scope of this invention as set by the appended claims.