A ring-mesh network architecture is provided for increasing the working/protection bandwidth ratio (W/PBR) of transport networks. The ring-mesh network has mesh connections between some nodes, the traffic on the mesh connections being unprotected. This increases the W/PBR from the current 1:2 value to (n−2)/(n−1), where n is the number of nodes, (n−1) is the number of connections on each node and (n−2) is the number of working connections on each node for one direction of traffic. Ring-mesh networks with add/drop multiplexers in the mesh connection are also provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to a network and in particular to an architecture for high-speed optical mesh networks.

2. Background Art

Network users and providers are looking for reliable networks at acceptable bandwidth (BW) cost. Reliability is the ability of the network to carry the information from source to destination with errors below a certain threshold.

Protection is a traffic preserving strategy for managing the usage of the working and the dedicated protection (redundant) bandwidth in the network. Automatic protection acts quickly enough to ensure that the client's connections remain unaffected by failures. SONET/SDH (synchronous optical network/ synchronous digital hierarchy) is provided with very effective and fast protection mechanisms, which make this technology a strong contender for the networks of the future.

SONET/SDH is a physical carrier technology for optical transmission, which can provide transport for services such as IP, ATM, Ethernet, SMDS, frame relay, DS-n, T1, E1, etc. The SONET/SDH standards define the physical interface, optical line rates known as optical carrier (OC) signals, a frame format, and an OAM&P protocol. The user signals are converted into a standard electrical format called the synchronous transport signal (STS). The optical carrier OC signals are named after the STS they carry. For example, and OC-3 carries an STS-3.

SONET/SDH protection protocols are designed for various network configurations, such as linear networks (1+1; 1:1 and 1:N protection schemes) and ring networks (unidirectional path switched rings UPSR and bidirectional line switched rings BLSR). As well known, the two digits used to define the type of protection refer to the number of “protection” (spare) fibers and the “working” fibers for a certain span. 1+1, UPSR and 1:1 schemes require 100% redundancy. 1:N, 2F (two-fiber)-BLSR and 4F-BLSR schemes require less than 100% network overbuild, as extra traffic (traffic of lower priority) may be carried between nodes on the protection bandwidth/fibers during normal operation conditions. The extra traffic is however lost when a protection switch occurs.

Typically, protection switching times are less than 50 ms for SONET. On the other hand, protection implies reserving bandwidth, and therefore transport networks are often 100% overbuilt.

SONET rings are currently the topology of choice in fiber deployment. The prime motivator for rings versus linear transport is higher survivability. A ring protects against simultaneous failure of the protection and working fibers and saves intra-ring and inter-ring pass-through traffic during node failure/isolation. In addition, while the traffic physically travels from node to node in a ring configuration, the services are practically connected in a mesh network, where each node exchanges services with any other node of the network.

The UPSRs are currently used in access networks and therefore they are not discussed herein.

The BLSR are extensively used in the backbone networks and therefore they are built for higher rates such as OC-48, OC-192, etc. Protection switching is done at the SONET line (multiplex section) sublayer. As indicated above, without extra traffic, 50% of the bandwidth available is used to protect against line or node failure conditions, i.e. 50% of the ring BW is used for the ‘working traffic’ and 50% for the ‘protection traffic’. This means that network owners must sell the protection bandwidth at a cheaper rate than the protected or working bandwidth price. Often the protection bandwidth sits completely unused and is therefore unavailable to produce income.

WDM (wavelength division multiplexing), dense WDM (DWDM) and the technical advances in the optical switching technologies resulted in an evolution of the transport network from ring to mesh configurations. Clearly, the most economical strategy for such an evolution is to adapt the existing BLSR's to mesh architectures, for preserving the huge HW and SW investment in the existing networks. However, current protection switching protocols are specifically designed for rings and are not readily applicable to mesh transport networks.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a network architecture that will allow use of more that 50% of the network capacity to transmit working traffic.

It is another object of the invention to create a ring-mesh network on top of a BLSR by adding some switching intelligence and one or more direct paths between the nodes of the BLSR.

According to one aspect of the invention, there is provided a ring-mesh network with a bandwidth BW on all lines, for transporting a traffic signal between a source and a destination node, comprising, a bidirectional line switched ring network, having a ring working bandwidth of 50% BW and a ring protection bandwidth of 50% BW, and a mesh connection between a first and a second node of said ring network, having a mesh working bandwidth of 100% BW allocated to a mesh working traffic.

According to another aspect of the invention, there is also provided a node connected on a ring network at an end on a mesh connection of a ring-mesh network with a bandwidth BW on all lines, comprising, means for routing, in an idle mode, a ring component of a forward traffic signal received from West direction over said ring network, into said mesh connection, means for routing, in said idle mode, a mesh component of a reverse traffic signal received from a further node connected on said ring network at another end of said mesh connection, into said ring network towards the East direction, wherein said ring network has 50% of said BW allocated to a ring working traffic, 50% of said BW allocated to a ring protection traffic, and said mesh connection has 100% of said BW allocated to a mesh working traffic.

In yet another aspect of the invention, there is provided a method for creating a ring-mesh network with a bandwidth BW on all lines, comprising, connecting a plurality of traffic nodes in a bidirectional line switched ring network, allocating to said ring network 50% of the BW for a ring working bandwidth and 50% of the BW to a ring protection bandwidth, providing a mesh connection between a first and a second node of said ring network, allocating 100% of the BW to a mesh working bandwidth, and transporting a traffic signal between a source and a destination node of said ring-mesh network, on a route including said mesh connection, said traffic signal using 50% of said mesh working bandwidth, wherein working/protection BW ratio for said traffic signal is higher than 0.5.

Advantageously, the present invention builds on the existing 4F-BLSR's and 2F-BLSR's. By allowing protection of more than 50% of the working BW, a network provider would earn more revenue per unit of BW.

In addition, the solution proposed herein is simple and is inexpensive to implement.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The term ‘mesh connection’ is used in this description to define a direct physical connection between two non-adjacent nodes of a ring network. The mesh connection may be a single fiber or a two-fiber line, accommodating bidirectional communication. The term ‘mesh component’ designates the traffic on a mesh connection. The term ‘ring component’ designates the traffic that travels along the original BLSR ring. For example, a hybrid component comprises a ring component, and a mesh component, indicating that the traffic signal of interest travels along both the ring and the mesh connections. The term ‘line’ refers to the connection between two add/drop nodes.

FIGS. 1Ato1C illustrate a 5-node ring-mesh network1according to the invention and the principle of operation of network1. InFIG. 1A, nodes A-E are connected in a BLSR ring, where the traffic in each span A-B, B-C, C-D, D-E and E-A) travels along two fibers (2F BLSR) or four fibers (4F-BLSR). The traffic is fully protected, which means that in the case of a span or node failure, the traffic is redirected to avoid the faulted section of the ring. To this end, the bandwidth (BW) on each span of the ring is allocated equally to the working traffic and protection traffic. It is evident that the protection BW is 50% of the total BW available on the ring.

We denote herein the ring working bandwidth/component with WR, and the ring protection bandwidth/ component with PR. The working and protection traffic on the mesh connection are denoted herein with WMand PMrespectively. We also define W/PBR as the ratio between the working and protection BW of the network. Furthermore, the working BW in the East direction with respect to a certain node (clockwise) is denoted herein with5, the working BW in the West direction (counter-clockwise) is denoted with6, the protection BW in the West direction with7, and the protection BW in the East direction with8. Similar notations are used for the respective working and protection components.

According to the invention, a mesh connection2is provided for example between nodes A and D. These nodes are also designated herein by terms ‘first node’ and ‘second node’. It is to be understood that connection2is by way of example, and that other nodes may be equally directly connected, and also that more than one mesh connection may be provided in network1, as it will be seen later.

As shown inFIG. 1A, the traffic on the ring is 100% protected, i.e. 50% of traffic is WRand 50% is PR. If we maintain the basic functionality of the BLSR, it is possible to run 100% working traffic (WM) on the mesh connection, while still having connection2protected by the protection BW (PR) of the ring. Mesh connection A-D divides the ring into two arms. We denote the arm A-E-D shown at the left side of the ring with11, and the arm A-B-C-D shown at the right side of the ring with13.

FIG. 1Bshows a ‘hybrid traffic’ from node A to nodes E and C of network1. The mesh component A-D of the A-E and A-C traffic is denoted with4, and is protected by the protection bandwidth of the ring1, as discussed above. At node D, the traffic is put into the ring and directed towards node E as shown by ring component5and towards node C as shown by ring component6. Ring components5and6are 50% protected, as they can use the protection BW of ring A-B-C-D-E-A. Nodes E and C are ‘destination nodes’, while node A is referred as the first node, and also as the ‘source node’ for the A-E and A-C traffic.

FIG. 1Cshows a protection switching operation for the case when mesh connection2is lost. In this case, for the direction A-D, the traffic is split at node A and one half is routed one way around the ring on arm11, and the other half the other way around on arm13, as shown by the dotted lines. More specifically, 50% of the traffic will be sent on the protection BW7and 50% of the traffic will be sent on the protection BW8However, if there is less than a full pipe's worth (100%) of bandwidth to be protected, the split could be arbitrary (e.g. 50%-20% or 10%-30%).

Once the traffic gets to node D, it is put back on the working BW and continues along the originally provisioned ring components5and6. In this way, the percentage of the working traffic protected by the network increases, while the network heals itself in the 50 ms time allowance to which SONET products adhere.

In case of a line failure on the ring, the ring will heal itself using the regular BLSR protection switching protocol. As well known, the working traffic on the ring is protected against single line failures for 2F-BLSR's and multiple line failures for 4F-BLSR's.

FIG. 2shows the maximum working traffic that can run on a 6-node ring-mesh network10(n=6). Again, all ring connections carry 50% working BW and all mesh connections carry 100% working traffic. A ring-mesh network is fully connected when each node is connected to every other node by a ring or a mesh connection. In the example ofFIG. 2, each node has three mesh connections and two ring connections to the adjacent East and West nodes.

The Working/Protection Bandwidth Ratio (W/PBR) of a ring-mesh network is proportional with the number of nodes of the BLSR. Thus, in the case of a fully connected ring network, W/PBR:

where n is the number of nodes, (n−1) is the number of connections on each node and (n−2) is the number of working connections on each node for one direction of traffic. This gives a W/PBR of 4/5, or 80% working traffic for network10.

In other words, this is an 1:N protection scheme. If the mesh line is four fiber, then span switches may be also performed in the mesh. When the ring is a 4F-BLSR, the ring components are protected by a 1:1 scheme, and the mesh component is protected by a 1:N protection scheme.

FIGS. 3A and 3Billustrate an example of a protection switch in case of a hybrid connection between nodes F and E of the 6-node ring-mesh network10. In this example, nodes E and F are on the same side of the mesh connection2. For the clockwise direction shown inFIG. 3Aby the arrows a, node F is the source node, E is the destination node, A is the first node and B is the second node. The hybrid path comprises two ring components5(F-A) and5′ (D-E), and mesh component4(A-D). If span2breaks as shown inFIG. 3Bfor direction A-D, node A will switch the traffic from node F into the protection BW7of the ring. The traffic will travel along protection BW7to D. Node D will receive this traffic and will switch it back on the working BW5′ where it will continue on to node E. It is to be noted that the switched traffic can travel towards West on the protection BW7along arm11, as shown inFIG. 3B, or toward East, along arm13on protection BW8. However, the shortest path is preferred.

It is also possible to implement a head-end ring switch (HERS), whereby node E will receive the traffic from A on the protection BW7, without it passing to node D and back.

When span2breaks on mesh component on the other direction of traffic (D-A), node D will perform a mesh protection switch, similar to the scenario described above for node A.

FIG. 4Ashows an example of a hybrid connection between two nodes E and C, andFIG. 4Billustrates a scenario for a failure of node A affecting connection E-C. In this example, nodes E and C are on different side of connection2. Node E is the source and node C is the destination. Node B is located downstream from the first node for the direction of traffic in this example. If node A fails, the failure affects both the ring components5and6, and the mesh component4. Again, the ring components will be protected using a BLSR ring switch. The mesh component4, as well as any other mesh component (not shown) travelling to or from node A will be squelched. Nodes adjacent to the failed node will go into a ring switched mode as defined by the BLSR protection switching protocol. Any nodes sending traffic through node A via the mesh connection (node D here and node B on direction E-C), will re-route this traffic on the protection BW available on ring10.

Namely, for direction E-C, shown by the arrows a, the working component6from E to D remains unaffected, traffic from D to C is sent in the protection BW7along arm13towards node B, from where it is inserted back into the working BW5towards node C. Node D must decide whether to re-route traffic onto protection BW8or protection BW7. Since in the idle state the traffic goes through node B after it passes node A, node D must re-route traffic to node B on the protection BW7when it does a ring-mesh protection switch.

For direction C to E, traffic from node C to node B remains unaffected, node B inserts the traffic into the East protection BW8towards node D, from where it is switched back on the working BW5and directed to destination node E. This scenario is shown inFIG. 4Bin brackets.

FIGS. 5A-5Eillustrate various traffic pattern constrains for ring-mesh networks, where traffic shown uses all working bandwidth available on the lines. An important requirement for the ring mesh networks is that that all lines have the same BW (i.e. OC192, or OC48, etc.)

As shown inFIG. 5A, it is not possible to provision traffic to run from one mesh line2-1directly onto another mesh line2—2. This is because it would be impossible to protect against losing node A if connection D-A-C uses 51%-100% of the available bandwidth. It is however possible to have hybrid connections between two nodes if they have distinct mesh connections as shown in FIG.5B. This is possible since the hybrid connections do not share a node.

There are scenarios where connections that pass from ring to mesh from both East and West ring components through a common hub node will interfere with each-other in the case of a node failure.FIG. 5Cillustrates one such scenario where connections F to C and E to B use more than 25% of the total bandwidth available on the ring. Nonetheless, node A may take traffic from East working bandwidth and switch it onto mesh connection2-4, or it may take traffic from the West working bandwidth and switch it into a mesh connection2—2.

FIGS. 5D and 5Epresent one possible solution to this problem where traffic is limited to entering the mesh for only the East or West ring components.

The next drawings illustrate various examples of ring-mesh networks where the mesh includes add/drop multiplexers (ADM).FIG. 6Aillustrates a ring-mesh network20with four ring nodes A, B, C and D, and a mesh connection3between nodes A and C, comprising ADM nodes E, F and G. We call the mesh connection3a mesh ADM connection, or an ADM arm. As indicated above, the arms of the ring connecting nodes A and C are designated by11and13respectively, and are called ring links or arms.

As in the previous examples, the BW on ring ABCD is 50% working and 50% protection, and the traffic on the mesh connection3is 100% working traffic. In addition, we distinguish within the working BW an ADM traffic component (Wadm), which is the working traffic between the adjacent nodes of arm3, and an passthrough traffic component (Wpt), which is for example the working traffic travelling all the way between hub nodes A and C on arm3.

In the case of a node or full line failure on the ADM arm3, the passthrough traffic is completely removed from the mesh arm and sent around the ring on one of the BLSR arms. This traffic may or may not be split at hub node A, C. Any add/drop traffic passing through mesh connection3affected by the fault has to be turned back to the hub node (node A for A-C direction and node C for C-A direction) where it can be sent on the BLSR protection bandwidth to node C. The bandwidth that was originally being used by the passthrough traffic is available for the add/drop traffic, since the passthrough traffic on the mesh connection A-C was switched off the mesh line onto the BLSR protection BW. The passthrough BW protects the add/drop BW and can add up to 100% of the total BW—therefore the ratio of PT/ADM traffic must be equal to one.

Thus, in the example ofFIG. 6A, 50% of the BW on the mesh component4is pass through traffic from node A destined to node C (or from node C to node A for the opposite direction). The remaining 50% is add/drop traffic between ADM's E, F and G, meaning that each of these ADM's removes 50% of the traffic on span3for its own use, and inserts 50% traffic on mesh connection3for the remaining nodes on the mesh connection.

FIG. 6Bshows re-distribution of the traffic in case of a failure in the mesh connection3, for example between ADM's F and G. Since the passthrough traffic between nodes A and C cannot use anymore link3, the add/drop traffic between the nodes A-E, E-F, F-G and G-C can be switched on the passthrough BW on the unaffected portions of the mesh connection3and routed back up to the hub node where the ring can protect it. Namely, for the direction A-C, the add/drop traffic between nodes A-E, E-F and G-C is moved on the passthrough BW12. For the direction C-A, the traffic between node C and G is moved on the passthrough BW for that direction.

The passthrough and ADM traffic between hub nodes A and C affected by the link3failure is switched around the ring. Namely, node A divides the passthrough and ADM traffic for node C into two equal ring components and switches each half onto the protection BW7and8on ring ABCD, towards West and East directions, respectively. Similarly, node C divides the passthrough traffic for node A into two equal components and switches each half onto the protection BW7,8on ring ABCD, towards East and West directions, respectively.

FIG. 6Cshows the traffic re-distribution in case of a node failure affecting the mesh connection3in network20. The scenario shown inFIG. 6Ccannot be applied to a ring-mesh network where node A has multiple mesh connections to different nodes on the ring other than C, as indicated in connection with FIG.5A. In this example, the passthrough traffic from A to C is lost, as well as the add/drop traffic from node A to node E. However, the add/drop traffic between nodes E-F, F-G and G-C is unaffected. The hybrid traffic that originally passed through node A to the nodes on the ring or the mesh, is divided by node C into a East and West component, as seen before, which are switched in the respective protection bandwidth7and8. For example, a connection B-A-E-F would now travel on protection bandwidth of connection B-C-G-F. It is to be noted that component12is accessible for all ADM nodes in the case of failure.

FIG. 7Aillustrates another architecture for a ring-mesh network, namely network40, comprising a ring A-H-B-J-C-K-D-I and mesh arms (or mesh connections)11,13,15,17,14,16and18. Each node on the ring40is allowed to connect to another node on the ring using one or multiple ADM mesh connections. For example, node A connects to node C using two ADM arms15and17. If a node does need to connect to multiple ring nodes, it must follow the rule described in connection with FIG.1B. When idle, all mesh connections (ADM arms)14,15,16,17and18run 100% working traffic with 50% available for add/drop and 50% for passthrough, and the ring itself (arms11and13) provides 50% working BW and 50% protection BW.

The network40ofFIG. 7Ahas, lets say, a working link failure or maintenance on two ADM arms, each provided with four fibers. For example, mesh connections17(A-G-L-C) and18(B-N-D) have either suffered working line only failures, or are being maintained. One or all of their legs on these lines are in a span switch mode. Failed lines will support 50% ADM traffic. The outer ring will carry 50% working traffic, 25% A-G-L-C passthrough traffic, and 25% B-N-D passthrough traffic in the protection BW.

Note that this type of network can suffer multiple span failures on up to two separate ADM chains, if the connections are four fiber.

FIG. 7Billustrates the network ofFIG. 7Awith a single ADM node failure, e.g. node E. This failure would be resolved using the strategy demonstrated in FIG.6C. Namely, the failed line cannot carry any passthrough traffic, but the add/drop traffic F to C. The ring40(A-H-J-C-K-D-I) will carry 50% working traffic, 25% passthrough traffic and 25% add/drop traffic from arm15.

The remaining mesh connections, idle ADM lines14,16,17and18carry as before the failure 50% passthrough traffic, and 50% add/drop traffic.

FIG. 7Cillustrates the network40ofFIG. 7Awith a hub failure, here node A. All passthrough traffic between nodes A and C is dropped in this case, since node A has failed. Any ring or mesh traffic that was trying to get to node A, travels back down the respective arm to node C and up the destination arm in the unused passthrough BW. Let's say for example that the passthrough traffic between nodes C and I used to travel before failure of node A along arm15(C-F-E-A-I). If hub A fails, the traffic for node C arrived at node E along arm15, is turned back to node C as shown in the dotted line41onFIG. 7C, and from node C to node I on the protection BW of ring arm13. The traffic on the unaffected mesh connections is as before, i.e. 50% passthrough traffic and 50% add/drop traffic. Similarly, the add/drop traffic between nodes E, F and C remains unaffected.

To summarize, the ring-mesh network has high working/protection bandwidth ratio, it can suffer a single node failure either hub or add/drop node, it can suffer multiple line failures on two separate arms, and can accommodate maintenance on all spans of two separate arms (this includes the ring).

The ring-mesh network has a number of constrains, as indicated above. Namely, if a node is connected to more than1other node through the mesh it must obey the East/West rule to ensure that the network can heal if it fails. The traffic composition must be limited to only 50% add/drop traffic.

While the invention has been described with reference to particular example embodiments, further modifications and improvements which will occur to those skilled in the art, may be made within the purview of the appended claims, without departing from the scope of the invention in its broader aspect.