Patent Description:
ITU-T ERP, which is defined in ITU-T G. <NUM>, is widely used in Ethernet transport networks. ERP is also used with Ethernet rings built with microwave nodes (using microwave links).

In Ethernet Rings one link in the network is configured, for instance by the operator, as Ring Protection Link (RPL). Under normal conditions, the RPL is blocked from forwarding data to avoid forwarding loops within the ERP network. If any link in the conventional ERP network of <FIG> fails, e.g. if the link BC between the nodes B and C fails and thus drops to zero bandwidth, then the nodes B and C are able to block this link BC, and the nodes F and E can unblock the RPL, which is used to recover the traffic. Thus, in spite of the failed link BC, traffic forwarding on the ring is recovered and the bandwidth of the ring network can be maintained at 400Mbps (since the RPL is also configured with 400Mbps).

Document <CIT> discloses a method for detecting a first current bandwidth of a first link in a network ring. The first current bandwidth indicates a signal degradation on the first link. In particular, the method further comprises determining whether the first current bandwidth has degraded more than a second current bandwidth of a second link in the network ring, and routing one or more network flows away from the first link if the first current bandwidth has degraded more than the second current bandwidth. In this case, the method further comprises sending control messages to other nodes in the network ring.

Document <CIT> discloses a method comprises: determining a bandwidth level associated with a link and compare the bandwidth level to a threshold level. A fail-over can be triggered for a selected one of a plurality of Ethernet ring protection elements if the bandwidth is below the threshold level.

Document <CIT> discloses an Ethernet ring protection switching method comprising determining whether a current link is a lower-bandwidth link based on bandwidth information of the current link and bandwidth of another link on a ring. If the current link is a lower-bandwidth link, the method further comprises blocking a port corresponding to the current link.

Microwave links between microwave nodes are bandwidth-variable. That means, degradation conditions may occur that reduce the bandwidth of the microwave links. This case is problematic in the conventional ERP network. For example, if there is bandwidth degradation (not fail) on a link, then this becomes the bottleneck of the entire ERP network and the ring throughput is decreased to the degraded bandwidth of the link. The RPL is not unblocked in this case. As a consequence the ring link bandwidth cannot be utilized maximally.

In view of the above-mentioned problem, the present invention aims to improve conventional ERP (networks).

The present invention has the object to enable ERP to take into account bandwidth degradation of microwave links in an Ethernet ring. To this end, the present invention has the goal to provide a microwave node and a method, which enable protecting an ERP network against microwave link degradation. Accordingly, also a bandwidth utilization of such a ring network should be improved. Thereby, multiple failure scenarios should be supported, including at least signal fail and microwave link degradation conditions on different links in the same ERP network. The solution of the invention should also be backward compatible with existing non-microwave nodes on the same ERP network. Finally, the solution of the invention should not require any modification of the protocol and state machines of G.

In particular, the present invention proposes generating the signal that indicates a fail of a local microwave link also when its bandwidth degrades (but not fails). ERP protection switching may then be triggered by inputting this signal to the ERP state machine as currently defined in G. Thus, no changes to the existing ERP protocol and state machine is necessary.

A first aspect of the present invention provides a microwave node for an ERP network. The ERP network is a hybrid network comprising the microwave node, at least one further microwave node, and at least one non-microwave node not sending a bandwidth notification message (BNM). The microwave node comprises at least one processor configured to receive a BNM from the at least one further microwave node, determine whether a degree of bandwidth degradation of a local link of the microwave node fulfils a degradation condition based on the received BNM, and generate a signal indicating a fail of the local link, if the degradation condition is fulfilled.

The signal indicating a fail of the local link is a signal fail (SF) or a manual switch (MS) signal for triggering an ERP protection switching.

When the microwave node receives a further SF or MS signal from the non-microwave node and does not receives any BNM from the non-microwave node, the degradation condition is not fulfilled, and the microwave node is configured not to trigger an ERP protection switching.

This may be the case, if a non-microwave node in the same ERP network sends a RAPS (SF) message notifying a failed link and it would not send any BNM. If a non-microwave link within the ring fails, degraded microwave links should not trigger any protection switching. Further, also microwave nodes in the same ERP network may be configured not to generate BNM with zero current bandwidth. Therefore, at least the microwave nodes attached to the microwave link with the lowest current bandwidth should check the information from received BNM and RAPS messages, in order to understand whether there is a failed microwave or non-microwave link within the ring. A RAPS (SF) messages but no BNM will be sent for this link. Accordingly, this implementation form avoids blocking degraded links, while other failed links are blocked.

As a consequence, the solution of the invention is backward compatible with existing non-microwave nodes, not supporting the present invention on the same ERP ring. For instance, this may occur in hybrid networks where microwave and non-microwave nodes co-exist on the same ERP-protected ring. The solution of the invention, when deployed in such hybrid ERP rings, enhances the ERP protection switching to be backward compatible with non-microwave ERP nodes assuming that these nodes implement ERP as described in G. <NUM> and G. <NUM> and therefore they do not generate BNM and ignore any received BNM.

The local link is a microwave link. The at least one processor may include at least two decision logics (or decision processes or decision units). The first decision logic may be implemented to determine the degree of bandwidth degradation of the local link of the node, and to further determine whether the degraded bandwidth fulfills the degradation condition. The second decision logic may be implemented to decide whether to generate the signal indicating a fail of the local link or not. The signal indicating a fail of the local link may be generated when the first decision logic determines that that the degradation condition is fulfilled. The first decision logic may indicate this to the second decision logic by generating a bandwidth degradation signal when the degradation condition is fulfilled. The signal indicating a fail of the local link generated by the second decision logic may be input into an ERP state machine (realized for instance by an ERP control process as defined in G. <NUM> and G. The state machine can then further decide whether and how to trigger ERP switching.

The microwave node of the first aspect thus enables protect an ERP network, in which it is included, against microwave link degradation. Accordingly, the bandwidth utilization of ERP network can be improved. With multiple such microwave nodes in the ERP network, multiple failure scenarios are supported, e.g. signal fail and microwave link degradation conditions on different links.

In an implementation form of the first aspect, the at least one processor is configured to determine that the local link is under bandwidth degradation, if the current bandwidth of the local link is smaller than its nominal bandwidth but larger than zero bandwidth.

That is, bandwidth degradation of a microwave link is different from a fail of said link.

In a further implementation of the first aspect, for determining whether the degree of bandwidth degradation of the local link fulfills the degradation condition, the at least one processor is configured to determine whether the local link is currently the link in the ERP network with the lowest bandwidth.

That means, protection is advantageously triggered on the link with the lowest bandwidth, in order to maximize the bandwidth utilization of the ERP network as much as possible.

In a further implementation of the first aspect, the BNM includes current bandwidth information of a remote link of the other microwave node, wherein for determining whether the local link is currently the link in the ERP network with the lowest bandwidth, the at least one processor is configured to compare the current bandwidth of the local link with the current bandwidth information of the remote link included in the received BNM.

For instance, all microwave nodes of the first aspect on the Ethernet ring may send, via the BNM, current bandwidth information of their respective link(s) to all the other microwave nodes on the same ring. Each microwave node may then use the received BNM and included information, in order to compare the current bandwidth of its local link with the current bandwidth of the remote links. ERP protection switching may be triggered, if the local link is determined to be the one with the lowest current bandwidth.

The current bandwidth of the local link may be obtained by the microwave node of the first aspect by its local microwave interface. The current bandwidths of the remote links are obtained via received BNMs as described above.

In a further implementation of the first aspect, for determining whether the local link is currently the link in the ERP network having the lowest bandwidth, the at least one processor is configured to apply a tiebreak condition, if the current bandwidth of the local link matches the current bandwidth information of the remote link included in the BNM message. In a possible implementation, matching of the current bandwidth of the local link with the current bandwidth information of the remote link is done by checking whether the current bandwidth of the local link is equal to the current bandwidth information of the remote link included in the received BNM message.

The tiebreak mechanism ensures that ERP protection switching is triggered only on one microwave link, in case that there are more microwave links having in common the lowest current bandwidth.

In a further implementation of the first aspect, for applying the tiebreak condition, the at least one processor is configured to determine the link of the node having the lowest MAC address as the link currently having the lowest bandwidth in the ERP network.

This provides an easy to implement but efficient tiebreak mechanism.

In a further implementation of the first aspect, the microwave node may send one or more BNM messages.

Accordingly, other microwave nodes according to the first aspect in the same ERP network are able to obtain the current bandwidth, and compare their local link bandwidth with the bandwidth information reported via BNM. If the local link of the microwave node fails, it is configured to generate a BNM (one or more messages) with a zero current bandwidth as the current bandwidth information. Therefore, any other degraded microwave link in the ERP network will not be considered the link with the lowest current bandwidth. This avoids blocking a degraded link while there is also a failed link on the same ring.

In a further implementation of the first aspect, the microwave node is further configured to send a message notifying a fail of the local link to the other nodes in the ERP network, and the message and the BNM, which are sent to the other nodes, include the same identifier of the microwave node and local link.

The message may be a Ring Automatic Protection Switching message indicating signal fail (RAPS (SF)). The common identifier allows the other nodes to determine that the microwave node sent the message and the BNM for the same link. This helps distinguishing from fail messages, e.g. RAPS (SF) messages, from non-microwave nodes (which do not generate BNM) or from microwave nodes configured not to generate a BNM (one or more messages) with zero current bandwidth during fail conditions.

In a further implementation of the first aspect, the microwave node further comprises an ERP control process configured to receive the signal indicating a fail of the local link generated by the at least one processor, and able to block the local link upon receiving said signal.

In an implementation the ERP control process may be implemented as an ERP controller.

That is, the ERP control process may trigger ERP switching also in case that there is a bandwidth degradation of the local link, not a failed link. Thus, the bandwidth utilization of the ring is improved.

In a further implementation of the first aspect, if the microwave node is an owner node or neighboring node of a RPL of the EPR network, the ERP control process is able to unblock the RPL upon receiving the signal indicating a fail of the local link from the at least one processor.

Opening the RPL, while the degraded link in the ERP network is blocked, increases the bandwidth throughput of the ring.

In a further implementation of the first aspect, the ERP control process is able to unblock the local link, if the at least one processor determines that the degree of bandwidth degradation of the local link does not anymore fulfill the degradation condition.

For instance, if the bandwidth degradation is overcome and the local link returns to its nominal bandwidth, blocking this local link is no longer necessary.

In a further implementation of the first aspect, the ERP control process is able to unblock the local link, if the at least one processor determines based on the received BNM that the local link is currently not anymore the link in the ERP network with the lowest bandwidth.

This avoids that a link is blocked that is not the bottleneck of the ring, thereby increasing the throughput of the ring and improving bandwidth utilization.

In a further implementation of the first aspect, for determining whether the degree of bandwidth degradation of the local link fulfills the degradation condition, the at least one processor is configured to determine whether the bandwidth of the local link of the microwave node is below a configured nominal bandwidth of a RPL of the ERP network.

This is particularly advantageous, if the RPL is a non-microwave link or if the RPL is a microwave link but no BNMs indicating current bandwidth are sent during normal conditions. In this case, the RPL nominal bandwidth may be configured on all the microwave nodes on the ring, in order to ensure that ERP protection switching is triggered only when the local link bandwidth degrades below the bandwidth of the RPL link, at which point a degradation of the bandwidth of the whole ring starts.

In a further implementation of the first aspect, the at least one processor is configured to generate the signal indicating a fail of the local link, if it determines that the degradation condition is fulfilled and/or that at least one local fail condition is fulfilled.

Thus the decision of the at least one processor (e.g. by the second decision logic) concerning a failure condition may base on different criteria (e.g. OAM protocols) as defined in G. The processor may generate the signal by applying a logical "or" between the degradation condition and the criteria defined in G.

A second aspect of the present invention provides a method for an ERP network, in which the ERP network comprises a microwave node, at least one further microwave node and at least one non-microwave node not sending a BNM. The method comprise:.

Further, when the microwave node receives a further SF or MS signal from the non-microwave node in the ERP network and does not receive any BNM from the non-microwave node, the degradation condition is not fulfilled, and the method comprises not triggering, by the microwave node, an ERP protection switching.

In an implementation form of the second aspect, the method comprises determining that the local link is under bandwidth degradation, if the current bandwidth of the local link is smaller than its nominal bandwidth but larger than zero bandwidth.

In a further implementation of the second aspect, for determining whether the degree of bandwidth degradation of the local link fulfills the degradation condition, the method comprises determining whether the local link is currently the link in the ERP network with the lowest bandwidth.

In a further implementation of the second aspect, the BNM includes current bandwidth information of a remote link of the microwave node, wherein for determining whether the local link is currently the link in the ERP network with the lowest bandwidth, the method comprises comparing the current bandwidth of the local link with the current bandwidth information of the remote link included in the BNM.

In a further implementation of the second aspect, for determining whether the local link is currently the link in the ERP network having the lowest bandwidth, the method comprises applying a tiebreak condition, if the current bandwidth of the local link matches (e.g. it is equal to) the current bandwidth information of the remote link included in the BNM message.

In a further implementation of the second aspect, for applying the tiebreak condition, the method comprises determining the link of the node having the lowest MAC address as the link currently having the lowest bandwidth in the ERP network.

In a further implementation of the second aspect, the method comprises sending a message notifying a fail of the local link to the nodes in the ERP network, and the message and the BNM, which are sent to the nodes, include the same identifier of a microwave node and a local link.

In a further implementation of the second aspect, the method further comprises receiving the signal indicating a fail of the local link, and blocking the local link upon receiving said signal.

In a further implementation of the second aspect, the method comprises unblocking an RPL upon receiving the signal indicating a fail of the local link.

In a further implementation of the second aspect, the method comprises unblocking the local link, if determining that the degree of bandwidth degradation of the local link does not anymore fulfill the degradation condition.

In a further implementation of the second aspect, method comprises unblocking the local link, if determining based on the received BNM that the local link is currently not anymore the link in the ERP network with the lowest bandwidth.

In a further implementation of the second aspect, for determining whether the degree of bandwidth degradation of the local link fulfills the degradation condition, the method comprises determining whether the bandwidth of the local link of the microwave node is below a configured nominal bandwidth of a RPL of the ERP network.

In a further implementation of the second aspect, the method further comprises generating the signal indicating a fail of the local link, if determining that the degradation condition is fulfilled and/or that at least one local fail condition is fulfilled.

The method of the second aspect and its implementation forms achieves all the advantages and effects described above for the microwave node of the first aspect and its respective implementation forms.

According to a third aspect, a computer program product is given storing instructions, which when executed on a processor perform the steps of the method according to the second aspect and any of the implementation forms of the second aspect.

<FIG> shows a microwave node <NUM> according to an embodiment of the invention. The microwave node <NUM> of <FIG> is configured for being used in an ERP network <NUM> (see e.g. <FIG>), and comprises at least one processor <NUM>. The at least one processor <NUM> may comprise one or more decision logics, or may be configured to carry out one or more decision processes.

In particular, the at least one processor <NUM> is configured to determine, whether a degree of bandwidth degradation of a local link <NUM> of the microwave node <NUM> fulfils a degradation condition. Notably, the microwave node <NUM> of <FIG> is shown to be connected to two microwave links <NUM>. However, a microwave node <NUM> in this document is one that is connected to at least one microwave link <NUM>. For instance, a first decision logic or first processor of the at least one processor <NUM> may decide whether the bandwidth is degraded and/or to what degree the bandwidth is degraded. The first decision logic or first processor may subsequently also decide whether the degree of the bandwidth degradation is such that it fulfills the degradation condition. In this case, it may generate a bandwidth degradation signal.

The at least one processor <NUM> is then further configured to generate a signal <NUM> indicating a fail of the local link <NUM>, i.e. if the degradation condition is fulfilled. The signal <NUM> may, for instance, be issued by a second decision logic or second processor of the at least one processor <NUM> based on the bandwidth degradation signal.

<FIG> shows a microwave node <NUM> according to an embodiment of the invention, which builds on the microwave node <NUM> shown in <FIG>. In particular, <FIG> shows an exemplary implementation for the microwave node <NUM>. <FIG> thereby shows a high-level block diagram of the microwave node <NUM>. The at least one processor <NUM> of the microwave node <NUM> is, or is included in, an Operation, Administration and Maintenance (OAM) unit <NUM>.

It is assumed that this microwave node <NUM> sends/receives traffic to/from at least two interfaces: one micro-wave interface <NUM>, here supporting a microwave link <NUM> as West ERP link, and one non-microwave interface <NUM>, here supporting a non-microwave link <NUM> (see <FIG>) as East ERP link. The microwave interface <NUM> is capable of reporting to the OAM unit <NUM> the nominal bandwidth and the current bandwidth of the microwave link <NUM> of the node <NUM>. This information may be used to generate BNMs and send them along the ring.

The traffic for the two interfaces <NUM> and <NUM> may be processed by a common processing unit <NUM>. The processing unit <NUM> may process the traffic (e.g. Ethernet frames) received from the line (i.e. one of the West ERP link and East ERP link), as specified in relevant standards, to understand to which connection the traffic belongs to, and to decide how it has to be further processed.

The traffic to be forwarded may be passed to a switching unit <NUM>, together with the information needed to properly forward it toward the egress. Some of the traffic received from the line can contain OAM information (e.g. Ethernet OAM frames) to be processed locally by the microwave node <NUM>. This information may be sent to the OAM unit <NUM>, together with the information identifying the associated maintenance entity.

The processing unit <NUM> may also be responsible for properly formatting the egress traffic, as received from the switching unit <NUM>, for being transmitted toward the line. The processing unit <NUM> may also receive OAM information from the OAM unit <NUM> to be forwarded either toward the line (likewise the traffic received from the switching unit <NUM>) or toward the switching unit <NUM> (likewise the traffic received from the line).

The microwave node <NUM> <FIG> further includes an ERP control process <NUM> (as defined in G. <NUM> and G. <NUM>), which may implement an ERP state machine, e.g. as defined in G. <NUM> and G. It receives the signal <NUM> indicating a fail of the microwave link <NUM>, e.g. implemented as SF, and may optionally receive RAPS information from the OAM unit <NUM>. The ERP control process may be implemented by a hardware controller, such as an EPR controller, or may be executed by a processor, which may be the processor <NUM> or another dedicated or shared processor.

The OAM unit <NUM> of this exemplary microwave node <NUM> of <FIG> is shown in more detail in <FIG>, and may be composed of different functional blocks implementing different OAM functions and by one multiplexer/demultiplexer <NUM>, which may multiplex OAM information generated by the OAM functional blocks toward the processing unit <NUM>, and demultiplex the OAM information received from the processing unit <NUM> toward the proper OAM functional block. In case of Ethernet, the demultiplexing of received OAM frames toward different OAM processing units may be based on the OpCode field in the Ethernet OAM PDU, as defined in ITU-T Recommendation G.

A BNM block <NUM> processes received BNMs and reports current bandwidth information (e.g. current bandwidths) of remote microwave links <NUM> of other microwave nodes <NUM> using, for instance, the MI_BWReport information defined in ITU-T G. It may also generate BNMs to be sent along the ring, in order to notify current bandwidth information (for instance the current bandwidth and the nominal bandwidth of the local microwave link <NUM>) as received from the microwave interface <NUM>.

A CCM block <NUM> generates CCM frames and processes received CCM frames on a given maintenance entity, implementing CCM state machines as defined in ITU-T Recommendation G. It may support many instances of these state machines, e.g. one for each maintenance entity. It may also provide, for each maintenance entity, dLOC (and other CCM-related defect) information to the at least one processor <NUM>, e.g. a Consequent Action block <NUM> (see below) as defined in ITU-T Recommendation G.

A RAPS block <NUM> generates RAPS OAM messages to carry the RAPS information received from the ERP control process <NUM> and report back the RAPS information carried by the RAPS OAM messages, which it receives from the processing unit <NUM>.

The at least one processor <NUM> includes in <FIG> a Bandwidth Degrade Decision block <NUM> (first decision logic mentioned above) and a Consequent Action block <NUM> (second decision logic mentioned above). The Bandwidth Degrade Decision block <NUM> is configured to determine whether a degree of bandwidth degradation of the local microwave link <NUM> of the microwave node <NUM> fulfils the degradation condition. If the degradation condition is fulfilled, it may output a bandwidth degradation signal (BwD) to the Consequent Action block <NUM>. The Consequent Action block <NUM> can then decide based on this bandwidth degradation signal (and optionally based on further input from the CCM block <NUM>) whether to generate the signal <NUM> indicating a fail of the local link. In particular, the Consequent Action block <NUM> may report via aTSF[] signal <NUM> a failure of the microwave link <NUM> (both in case of a real failure and also in case of a microwave bandwidth degradation that fulfils the degradation condition) to the ERP control process <NUM>. To this end, the Bandwidth Degrade Decision block <NUM> may further receive from the RAPS block <NUM> the RAPS information carried by the RAPS OAM messages received from the processing unit <NUM>.

<FIG> shows a plurality of the microwave nodes <NUM> as described with respect to <FIG> and/or <FIG> and <FIG> in an ERP network <NUM> (which is similar to the conventional ERP network shown in <FIG>).

<FIG> particularly illustrates the effect that can be achieved with using such microwave nodes <NUM> according to embodiments of the invention, instead of conventional microwave nodes as are used in <FIG>. Namely, with these nodes <NUM> it is possible also in case of a bandwidth degradation to enable an ERP protection switching. For instance, if the link BC between node B and node C exhibits bandwidth degradation - here the bandwidth of the link <NUM> degrades from its nominal bandwidth of 400Mbps to a degraded bandwidth of 100Mbps - it can be blocked by the nodes B and C, and the RPL link <NUM> can be opened instead. The RPL link <NUM> is maintained by an RPL owner <NUM> (here Node E) and an RPL neighbor <NUM> (here Node F). These nodes are responsible for blocking/unblocking the RPL <NUM>. This leads to an increase of the whole ring network throughput (to be kept at 400Mbps). ERP protection switching means blocking a failed or degraded link <NUM> and switching instead to the RPL <NUM>, in order to protect the ring bandwidth.

In the following, further advantages are illustrated, which are achievable when using microwave nodes <NUM> according to embodiments of the invention. To this end, different ERP networks <NUM> and different scenarios are shown.

<FIG> shows an ERP network <NUM> comprising microwave nodes <NUM> according to an embodiment of the invention, for instance, as in <FIG>, <FIG> and/or <NUM>. Specifically, the ERP network <NUM> is a microwave ERP ring with only microwave nodes <NUM> and microwave links <NUM>.

When an ERP port of a microwave node <NUM> (here e.g. node B or node C) detects a bandwidth degradation on the local link <NUM> (here the link BC), it can compare its current bandwidth with current bandwidth information of all the other remote microwave links <NUM> on the same ring. To this end, it may use bandwidth information from received BNMs. If the local link BC is the one with lowest current bandwidth on the ring, the degradation condition is fulfilled and ERP protection switching may be triggered by generating the signal <NUM> regarding the local link <NUM>, for instance a SF signal. Notably, it is also possible to generate a manual switch (MS) signal, rather than SF, as the signal <NUM>, in order to trigger ERP protection switching. However, in the following description of specific embodiment, SF is always assumed to be the signal <NUM>.

In the scenario of <FIG>, two links <NUM> are degraded. Namely, the bandwidth of the link BC is degraded from 400Mbps to 100Mbps, and the bandwidth of the link ED is degraded from 400Mbps to 200Mbps. At least some of the nodes and advantageously all the microwave nodes <NUM> in the network are aware of the current bandwidth of all the links <NUM> on the ring, and know that the link with the lowest current bandwidth is the BC link. The nodes B and C have therefore enough information to trigger ERP protection switching, thereby also signaling RAPS (SF) for the BC link <NUM> to other nodes <NUM>. Further, the nodes D and E have enough information to not trigger ERP protection switching for the link DE.

If the DE link degrades after the nodes B and C have triggered ERP protection switching for the BC link degradation, the nodes D and E do not trigger the ERP protection switching. If the BC link <NUM> recovers from bandwidth degradation before the DE link, the nodes D and E may trigger ERP protection switching for the DE link <NUM> as soon as they receive BNMs indicating that the current bandwidth of the BC link <NUM> has increased, and therefore the local DE link <NUM> has become the one with the lowest current bandwidth in the network <NUM>.

If the BC link <NUM> degrades after the nodes D and E have triggered ERP protection switching for the DE link degradation, the nodes D and E may clear ERP protection switching, as soon as they receive BNMs indicating that the current bandwidth of the BC link <NUM> has decreased below the current bandwidth of the DE link <NUM>, and therefore the local DE link <NUM> is no longer the one with the lowest current bandwidth.

In case that there is more than one link <NUM> having the lowest current bandwidth, a tiebreak mechanism may be applied. For example, the MAC addresses of the nodes <NUM> attached to the links <NUM> having the lowest current bandwidths can be used as tiebreaker. That is, ERP protection switching is triggered only for the link <NUM> attached to the node <NUM> that has the lowest MAC address. Other tiebreak criteria can also be defined. For the following description, while it is possible to use other tiebreak criteria, it is assumed that the MAC address is used as a tiebreaker.

<FIG> also shows an ERP network <NUM> with microwave nodes <NUM> and links <NUM>. In the scenario of <FIG>, both the link BC and the link DE have a degraded bandwidth of 100Mbps, lowered from a nominal bandwidth of 400Mbps. At least some of the nodes and advantageously all the microwave nodes <NUM> are aware of the current bandwidth of all the links <NUM>, and know that the links <NUM> with the lowest bandwidth are the BC and DE links. Since node B is the node <NUM> with the lowest MAC address among those with the links <NUM> showing the lowest current bandwidth, the nodes B, C, D and E have enough information to trigger ERP protection switching for the BC link <NUM> but not for the DE link <NUM>.

The microwave nodes <NUM> may be aware of the MAC address of at least their adjacent node <NUM>. If a node <NUM> does not know its neighbors MAC address, ERP protection switching may only be triggered by a node <NUM> at one end of the link <NUM> having the lowest current bandwidth (i.e. by the node <NUM> with the lowest MAC address) and not by its adjacent node <NUM>. For example, in the scenario of <FIG>, only node B may in this case trigger ERP protection switching, not node C.

The present invention allows also deployment of hybrid ERP networks <NUM> (rings), where microwave nodes <NUM> and non-microwave nodes <NUM> and microwave links <NUM> and non-microwave links <NUM> are deployed (e.g. <FIG>). Within this network <NUM>, microwave nodes <NUM> (i.e. nodes having at least one microwave port attached to a microwave link <NUM>) and non-microwave nodes <NUM> (i.e. nodes having two non-microwave ports attached to two non-microwave links <NUM>) may co-exist. Accordingly, the present invention is backward compatible with existing non-microwave nodes <NUM>, since it needs to be implemented only on microwave ports of microwave nodes <NUM>. Non-microwave ports implementations may only be compliant with current ITU-T G. <NUM> and G. This means that they do not generate BNMs, they ignore any received BNMs, and trigger ERP protection only when their non-microwave link <NUM> fails.

If the RPL <NUM> is a microwave link <NUM> maintained by two microwave nodes <NUM>, the solution of the invention works as discussed above for the pure microwave networks <NUM>. If all the non-microwave links <NUM> have a bandwidth higher or equal to the nominal bandwidth of the microwave RPL <NUM>, it is ensured that in case of link bandwidth degradation, ERP protection switching is triggered only for the microwave link <NUM> with the lowest current bandwidth. Instead, if the RPL <NUM> is a non-microwave link <NUM> - maintained by two non-microwave nodes <NUM> or two non-microwave ports of microwave nodes <NUM> - the information of the RPL bandwidth may be configured in all the microwave ports to make sure that microwave ports do not trigger ERP protection switching, until the current bandwidth of their link <NUM> degrades below the RPL bandwidth.

It is moreover also possible to configure the microwave ports of microwave nodes <NUM> such that they do not generate BNMs during normal conditions. In this case, the information of the RPL nominal bandwidth should be configured for microwave RPL <NUM> and non-microwave RPL <NUM>.

It is worth noting that the RPL may be chosen among the links <NUM>/<NUM> with the lowest nominal bandwidth, in order to have the highest possible ring throughput during normal conditions. The solution of this invention allows having the highest possible throughput also during bandwidth degradation conditions of microwave links <NUM>.

<FIG> shows a network <NUM> including exemplarily two microwave nodes <NUM> (B and C) connected by a microwave link <NUM> (BC), and several non-microwave nodes <NUM> and links <NUM>. In the scenario of <FIG>, the nodes B and C are configured with the RPL bandwidth such that they do not trigger ERP protection switching, until the BC link <NUM> bandwidth degrades below the RPL bandwidth, i.e. before the nominal bandwidth of <NUM>. 5Gbps drops below the bandwidth of 1Gbps of the RPL <NUM>. Accordingly - as illustrated in <FIG> - ERP protection switching is not yet triggered, and the link BC is still unblocked, while the RPL <NUM> is still blocked.

<FIG> shows the same network <NUM>. <FIG> illustrates that when the bandwidth of the link BC drops further from 1Gbps to 400Mbps, i.e. below the RPL bandwidth of 1Gbps, the ERP protection switching is triggered. Accordingly, the BC link <NUM> is blocked and the RPL <NUM> is unblocked.

In case one or more microwave links <NUM> or non-microwave links <NUM> fail, and one or more other microwave links <NUM> degrade, ERP protection switching may not be triggered for the degraded microwave links <NUM>. This behavior may "emulate" other protection switching technologies, where SF has higher priority than signal degrade (SD). If microware links <NUM> fail, BNMs indicating that their current bandwidth is zero could be sent, such that failed microwave links <NUM> will inevitably be considered as those with the lowest current bandwidth. Accordingly, ERP protection switching will not be triggered for degraded links <NUM> having a current bandwidth greater than zero.

However, this mechanism does not work when a non-microwave link <NUM> fails. Typically, if a non-microwave link <NUM> fails, a RAPS (SF) messages (signaling SF conditions) is sent by the non-microwave node <NUM>. However, a RAPS (SF) message may also be used by a microwave node <NUM> to signal link bandwidth degradation conditions to other microwave nodes <NUM>. Thus, detecting a RAPS (SF) message is not sufficient to understand for a microwave node <NUM> that a microwave link <NUM> failed. However, since non-microwave nodes <NUM> do not generate BNMs, a microwave node <NUM> can understand that a non-microwave link <NUM> has failed, when an RAPS (SF) message for that link <NUM> is received, but no BNM for the same link <NUM> is received.

It is moreover also possible to configure the microwave ports of microwave nodes <NUM> such that they do not generate BNMs during a signal failure condition. In this case, detection of signal failure conditions for microwave links <NUM> and non-microwave links <NUM> will follow the same procedure.

Due to the above, microwave nodes <NUM> advantageously generate RAPS messages and BNMs using consistent identifiers to allow other microwave nodes <NUM> to understand that they are reporting RAPS and current bandwidth information for the same link <NUM>. One possibility is that the MAC address used for a BNM is the same as the node-id used in the RAPS message and that the port-id used in a BNM is the same as the Block Port Reference (BPR) used in the RAPS message.

<FIG> shows the same network <NUM> as <FIG>. In the scenario of <FIG>, the microwave nodes B and C can understand from the RAPS (SF) messages received from the non-microwave nodes D and E, and from the lack of BNMs received from these nodes D and E, that the DE link (a non-microwave link <NUM>) failed. Therefore, the nodes B and C do not trigger ERP protection switching when the BC link (a microwave link <NUM>) is only degraded. Consequently, only the DE link <NUM> is blocked by the ERP protocol and state machine.

<FIG> shows a method <NUM> according to an embodiment of the invention. The method <NUM> is for ERP, and comprises: a first step <NUM> of determining, whether a degree of a bandwidth degradation of a local link <NUM> of a microwave node <NUM> fulfils a degradation condition, and a step <NUM> of generating a signal <NUM> indicating a fail of the local link <NUM>, if the degradation condition is fulfilled.

The method <NUM> may be carried out in a node <NUM> according to an embodiment of the present invention, for instance in the at least one processor <NUM>, for example by at least one decision logic. The first step <NUM> of the method <NUM> as carried out in the at least one processor <NUM> - as e.g. implemented by the Bandwidth Degrade Decision block <NUM> in <FIG> - is outlined in <FIG> in exemplary detail.

First, it is determined at <NUM> whether a local link <NUM> of the microwave node <NUM> is degraded. If no link <NUM> is degraded, then it is determined at <NUM> that the degradation condition is not fulfilled. If a link <NUM> is degraded, then it is further checked at <NUM> whether a RAPS message is received from another node <NUM> or <NUM>. If a RAPS message is received, then it is checked at <NUM> whether a BNM (one or more messages) is received with the same identifier, i.e. from another microwave node <NUM>. If such BNM is not received, then this indicates that e.g. a non-microwave link <NUM> has failed, and it is determined at <NUM> that the degradation condition is not fulfilled.

If at <NUM> it is determined that a BNM (one or more messages) with the same identifier is received, or if at <NUM> no RAPS message is received, then it is further determined at <NUM>, whether a RPL nominal bandwidth is configured on all microwave nodes on the ring or whether a RPL nominal bandwidth is signaled. If a RPL nominal bandwidth is configured, then the RPL <NUM> may be non-microwave link <NUM> (or a microwave link <NUM> that is configured not to generate BNM during normal condition), and it is further checked at <NUM> whether a bandwidth of the local link <NUM> is below the configured RPL nominal bandwidth. If it is not below the configured RPL nominal bandwidth, then it is further determined at <NUM> that the degradation condition is not fulfilled.

If it is determined at <NUM> that the bandwidth of the local link <NUM> is below the configured RPL nominal bandwidth, or if it is determined at <NUM> that no RPL nominal bandwidth is configured but is signaled (i.e. the RPL <NUM> is a microwave link <NUM> reporting via BNM in normal conditions the current bandwidth equal to the RPL nominal bandwidth), then it is further determined at <NUM> whether any BNM from another microwave node <NUM> is received. If no BNM is received, then it is further determined at <NUM> that the bandwidth degradation condition is fulfilled. Accordingly, the signal <NUM> is generated.

If a BNM (one or more messages) is received at <NUM>, then it is further checked at <NUM>, whether the bandwidth of the local link <NUM> is lower than all bandwidth information reported in all received BNM(s). If it is lower, and thus is the lowest link bandwidth in the network <NUM>, then it is further determined at <NUM> that the bandwidth degradation condition is fulfilled. Accordingly, the signal <NUM> is generated.

If it is determined at <NUM> that the bandwidth of the local link <NUM> is not lower than all the bandwidth information reported with all the BNM(s), then it is further determined whether it is at least equally low than the lowest reported bandwidth (information). If it is not equally low (i.e. higher), then it is not the lowest bandwidth in the network <NUM>, and it is further determined at <NUM> that the degradation condition is not fulfilled.

Claim 1:
Microwave node (<NUM>) for an Ethernet Ring Protection, ERP, network (<NUM>), wherein the ERP network (<NUM>) is a hybrid network comprising the microwave node (<NUM>), at least one further microwave node, and at least one non-microwave node (<NUM>) that does not generate a bandwidth notification message, BNM, wherein the microwave node (<NUM>) comprises at least one processor (<NUM>) configured to:
receive a BNM from the at least one further microwave node;
determine whether a degree of bandwidth degradation of a local link (<NUM>) of the microwave node (<NUM>) fulfils a degradation condition based on the received BNM, and
generate a signal (<NUM>) indicating a fail of the local link (<NUM>) if the degradation condition is fulfilled, wherein the signal (<NUM>) indicating a fail of the local link is a signal fail, SF, or a manual switch, MS, signal for triggering an ERP protection switching, and
if the microwave node (<NUM>) receives a further SF or MS signal from the non-microwave node (<NUM>) and does not receive any BNM from the non-microwave node (<NUM>), the degradation condition is not fulfilled, and the microwave node (<NUM>) is configured not to trigger the ERP protection switching.