WO2013034200A1

WO2013034200A1 - Apparatus and method for traffic routing

Info

Publication number: WO2013034200A1
Application number: PCT/EP2011/067815
Authority: WO
Inventors: Paola Iovanna; Giulio Bottari; Gianpaolo Oriolo
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2011-09-05
Filing date: 2011-10-12
Publication date: 2013-03-14

Abstract

Embodiments of the invention relate to a method (400) for routing traffic through a network having a plurality of nodes, at least one of said plurality of nodes being an integrated node including first and second technologies integrated inside the same node platform, the method comprising: applying (402) a transformation algorithm to the plurality of nodes for determining at least one virtual link between at least two ports of the plurality of nodes; and performing (404) a routing algorithm using the at least one virtual link to determine an optimal virtual route for the traffic through the network based on at least one cost parameter associated with the at least one virtual link. By applying a transformation algorithm to a plurality of nodes in a network, virtual links can be created between virtual ports in the nodes, which are homogenous and allow all routes through the network to be considered concurrently during a routing algorithm. This allows an optimal route to be determined based on cost parameters associated with each virtual link.

Description

Apparatus and Method for Traffic Routing

Technical Field The invention relates to a method and apparatus for traffic routing through a network, in particular it relates to a method and apparatus for routing client traffic across a network having nodes which include multiple technologies integrated inside the same node platform. Background

The communication landscape is evolving with the increasing bit rates needed to cope with high definition video streaming, web multimedia explosion, increased demand for broadband mobile access (LTE and WiMAX), cloud computing, data center backhauling. This evolution is occurring in parallel with the constant demand for reduction of the Total Cost of Ownership (TCO) to the communication operator.

In order to satisfy the requirement of reducing TCO, a consideration of the combination of two aspects may be given, namely: the availability of flexible nodes that can be dynamically and remotely re-configured; and the availability of an intelligence that is able to exploit such flexibility to maximize resource sharing and dynamically adjust the network according to traffic load and required service levels.

One way of providing more flexible nodes is to combine packet switching technologies and circuit switching, for example Optical Transport Network (OTN), which is optical switching based on Optical-Electrical-Optical (OEO) technology, to provide equipments able to use both technologies where appropriate. This provides the ability to off-load packet traffic to the circuit switching and to reduce the number of packet switch ports thus eliminating unnecessary packet processing. Furthermore, the recent introduction of photonic integrated component technologies (PIC), silicon photonics integrated transceiver, and very high capacity cross-point electrical switches, allows the reduction in the cost of OEO conversion and a low cost optical switching subsystem is possible. OEO technology is natively directionless, avoids impairments accumulation and provides a wavelength conversion facility at each node. Optical technology is no longer just a "physical transparent layer" and is becoming integral to a network solution needed to increase operator competitive advantages.

Nodes in which packet switching and optical circuit switching, so called packet- opto nodes, can be exploited using a Generalized Multi-Protocol Swithcing (GMPLS) control plane which provides a protocol toolbox to automate part of the network operations. The control plane solution utilises a Path Computation Element (PCE), which is a key differentiator among different vendors and operators and which provides the real network intelligence.

It may be anticipated that a full off-load of packet traffic towards the optical layer, may be desirable. However, several real use cases indicate that multi- hop optical paths, having intermediate traffic add/drop, are also possible according to considered traffic patterns and network topology. An efficient resource usage is crucial to achieve a cost and power reduction and to achieve a cost per bit that preserves the operator's revenues. The PCE is used to optimize the resource usage.

From an operator point a view, the desired overall goal is to optimize traffic provisioning and recovery at each layer, so as to globally optimize network resources.

However, multi-layer routing is a very complex task because heterogeneous technologies, having different behaviours and granularities, need to be considered. In addition only the concurrent consideration of all the involved technologies brings to an optimal resource allocation. It is known to use a "layer by layer" approach, in which routing in an upper layer, for example a Multi Label Switching Transport Profile (MPLS-TP) induces routing in a lower layer, for example Wavelength Switched Optical Network (WSON) or vice versa, and optical by-passes are created and then packet traffic is sent over such pre-established tunnels. However, this layer by layer approach results in sub-optimal resource usage.

Scalability, relative simplicity, efficiency are the key requirements of a PCE, in particular when the PCE is required to operate in a dynamic scenario. Such requirements are difficult to achieve, especially in a multi layer dimension, where multiple needs and constraints must be considered. The function of the PCE may be even more complex if a mixture of packet-opto integrated nodes and single technology nodes are considered inside the same network cloud. The PCE must also optimally route traffic with consideration to minimizing the power consumption of the network as a whole.

Operators are looking for solutions and technologies to deal with this extremely heterogeneous and flexible service level demands at lower cost. Summary

It is an aim of embodiments of the present invention to provide a method, routing system, routing unit and integrated node for routing traffic through a network that obviate or reduce at least one or more of the disadvantages mentioned above.

It is a further aim of embodiments of the present invention to provide a method for routing, a routing system, a routing unit and an integrated node for routing traffic through a network with heterogeneous and flexible service level demands at lower cost.

According to an aspect of the invention, there is provided a method for routing traffic through a network having a plurality of nodes, at least one of said plurality of nodes being an integrated node including first and second technologies integrated inside the same node platform, the method comprising: applying a transformation algorithm to the plurality of nodes for determining at least one virtual link between at least two ports of the plurality of nodes; and performing a routing algorithm using the at least one virtual link to determine an optimal virtual route for the traffic through the network based on at least one cost parameter associated with the at least one virtual link.

According to another aspect of the invention there is provided a routing system, for routing traffic through a network, comprising: a plurality of nodes, wherein at least one of said plurality of nodes is an integrated node including first and second technologies integrated inside the same node platform; and a routing unit comprising: a transformer arranged to apply a transformation algorithm to the plurality of nodes for transforming at least two ports of the plurality of nodes to provide at least one virtual link; and a processor arranged to perform a routing algorithm using the at least one virtual link to determine an optimal virtual route for the traffic through the network based on at least one cost parameter associated with the at least one virtual link.

According to another aspect of the present invention, there is provided a routing unit for routing client traffic across a network having a plurality of nodes, which nodes include first and second technologies integrated inside the same node platform, comprising: a transformer arranged to apply a transformation algorithm to the plurality of nodes for transforming at least two ports of the plurality of nodes to provide at least one virtual link; and a processor arranged to perform a routing algorithm using the at least one virtual link to determine an optimal virtual route for the traffic through the network based on at least one cost parameter associated with the at least one virtual link.

According to another aspect of the present invention, there is provided an integrated node, comprising: a packet switching capability module; and an optical switching capability module linked to the packet switching capability module, wherein the optical switching capability module is a digital

reconfigurable optical add-drop multiplexer, DROADM, having a N optical ports. Brief description of the drawings

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the following drawings in which:

Figure 1 shows an integrated node according to an embodiment of the invention;

Figure 2 shows an integrated node with a plurality of ports;

Figure 3 shows the integrated node of figure 2 after transformation; Figure 4 shows the steps performed by an embodiment of the present invention;

Figure 5 shows a routing unit according to an embodiment of the present invention; Figure 6 shows a routing system according to an embodiment of the present invention;

Figure 7 shows an example showing virtual links between integrated and non- integrated nodes; and

Figure 8 shows another example showing virtual links between integrated nodes.

Detailed description

Reconfigurable Add-Drop Multiplexers (ROADMs) are currently deployed in nodes in a communication network. These ROADMs are all optical. In other words, they receive optical signals, perform optical switching on the optical signals based on Wavelength Selective Switches (WSS), and output optical signals.

Recently, technological advances have made the integration of optical and electronic components and Optical-Electrical-Optical (OEO) conversion, possible at acceptable costs. These advances include, but are not limited to the development of the following devices.

• P hoton i c I nteg rated C om po nents ( P I C ) for WD M m u lt i-channel transceivers working at 10 Gbps with 10/12 channels and implemented as hybrid devices that include InP lasers and photodiode arrays, silica AWG and CMOS arrays of modulator drivers and Trans-Impedance Amplifiers (TIA). Application will be on optical line interfaces. · Silicon photonics integrated transceiver with multiple parallel channels, 4x10 Gbps and 12x10 Gbps. They are hybrid devices with all the optical and electronic parts monolithically integrated on the same CMOS die but the laser that is flip-chip bonded to the CMOS. Application will be on intra- system interconnection and client interfaces.

• Very high capacity cross-point electrical switches with capacity beyond 1 Tbps.

• High capacity OTN processor with capacity in the range 40-120 Gbps.

The Photonic Integrated Components and silicon photonics ensure a significant reduction in both the cost and power consumption in an OEO conversion. By using a combination of some or all of the above mentioned technologies, a Digital Reconfigurable Optical Add-Drop Multiplexer (DROADM) is proposed for use in an integrated node in which packet switching technologies and optical switching technologies are combined. Figure 1 shows an integrated packet-opto node 104 according to an

embodiment of the present invention. The integrated node 104 of figure 1 comprises a Packet Switching Capability (PSC) module 106 connected with an optical switching capability module 108. The optical switching capability module 108 comprises a Digital Reconfigurable Add-Drop Multiplexer (DROADM) having a plurality of optical ports 122. The DROADM 108 may also comprise an OEO flexible LSC (Lambda Switching Capability) module. The LSC may be integrally provided or may be provided in different units. The DROADM operates as an optical switch, however as opposed to

conventional ROADMs, the switching in the DROADM is performed in the digital domain. In other words, data is received by optical switching capability module 108, an optical-electrical conversion takes place and the switching is performed on the digital packets. After the switching, an electrical-optical conversion is performed before the packets are transmitted into the network.

At least one client ports 124, which may be Gigabit Ethernet client port, is connected to the PSC matrix 106, and acts as a packet traffic feeder for the node 104. As will be appreciated, one or more packet client ports 124 may be provided for input into the OSC 106 and a plurality of client ports 124 may be provided.

The PSC 106 has the ability to groom the traffic before switching it towards the LSC. Grooming, sometimes indicated also with pre-grooming, is the action of collecting packet traffic in order to fill as much as possible the optical container that will transport such packet traffic to the destination.

The bandwidth of packet clients varies in a continuous range of values while optical bandwidth (wavelengths) ranges according to discrete values (i.e. 10 Gbit/s for each wavelength). Therefore, in order to better exploit the optical bandwidth it's desirable to "pack" packet traffic (if directed from a common node A to a common destination node B) in order to fill an optical channel as much as possible. For example, collecting 9.9 Gbit/s of traffic directed from node A to node B would be successful grooming because the optical channel would be near to be completely filled.

The connection between PSC 106 and optical switching capability 108 is provided by internal connectivity within the node. In other words, the packet switching capability and the optical switching capability are vertically integrated within the integrated node 104.

In an embodiment of the present invention, multiple traffic clients, if directed to a common destination and with a common service level requirement, can be collected together at the PSC level and sent to the optical layer for immediate forwarding across the fibre infrastructure, with the minimum waste of bandwidth.

Figure 1 shows the integrated node 104 having four optical ports 122. At least one of the optical ports may be arranged on the Dense Wavelength Division Multiplexing (DWDM) line. Although figure 1 shows the integrated node having four optical ports, it should be appreciated that N optical ports may be provided, where 2 < N > 9. In embodiments of the invention, in order to optimise routing of traffic through a network that includes integrated nodes, such as integrated node 104 of figure 1 that includes heterogeneous technologies, a transformation algorithm is performed on the node such that the different granularity of the packet layer and circuit layer can be considered concurrently.

Figure 2 shows an integrated node 204 that includes a packet switching capability 206 and an optical switching capability 208 in which internal ports are shown. The PSC 206 has one or more client ports 224 for receiving packet clients. The optical switching capability module 208, comprises an

LSC/DROADM, as in figure 1 , and is provided with a plurality of optical ports 222, at least one of which is provided on the DWDM line. Although figure 2 shows the integrated node having four optical ports, it should be appreciated that N optical ports may be provided, where 2 < N > 9. A plurality of internal links 220 are provided within the node for coupling the PSC 206 to the LSC/DROADM 208. In the integrated node 204, the overall bandwidth of the internal links, divided by the overall bandwidth of the optical line connectivity, is defined as the add/drop ratio, i.e. the percentage of traffic which can be added/dropped by the node (e.g. 25%). Figure 3 shows the integrated node of figure 2, after a transformation algorithm has been applied to the node.

As can be seen in figure 3, all the internal ports, located on the PSC side, are transformed to be represented by two virtual ports 320, representing each direction. Each optical port is transformed to be represented with two virtual ports 322, one for reception and one for transmission. Clients ports 324 are unaffected by the transformation algorithm.

As can be seen in figure 3, the N optical ports of the optical switching module are transformed upon application of the transformation algorithm to provide 2xN virtual ports between which internal virtual links are provided. In other words, at least one of the N optical ports of the optical switching module may be transformed to provide a receiving port and a transmitting port, denoted by "R" and "T" in the figures.

The virtual internal ports 320 are connected with the respective virtual optical ports 322 by virtual links, and the virtual optical ports are connected with each other by virtual links. In other words, all virtual ports of the transformed node are connected together by virtual links in a full mesh.

The virtual links representing the internal connectivity between the packet switching module and the optical switching module summarizes all the internal bandwidth even if physically provided by a bundle of real links. Such cumulated bandwidth is however usable with a well defined granularity (e.g. 10Gbit/s).

The transformation algorithm acts to transform the ports in the integrated node, including both the internal PSC ports and the optical ports, to provide a plurality of virtual links between the transformed virtual ports. The virtual links are homogenous such that all the virtual links can be considered concurrently during a path computation/routing operation. The transformed node in figure 3 is shown with the dashed lines provided around the exterior of the physical components. These dashed lines represent the virtual nature of the transformed node and indicate that in the transformed state, the path computation need only be concerned with the homogeneous transformed virtual links provided between the virtual nodes and not the physical structure of the integrated node.

In an embodiment of the present invention, a method is provided for routing traffic through a network which comprises a plurality of nodes, at least one node of the plurality of nodes being and integrated node as shown in figure 1 or 2. The steps of the method are shown in figure 4.

Step 402 comprises applying a transformation algorithm to the plurality of nodes for determining at least one virtual link between at least two ports of the plurality of nodes.

In step 402, the transformation algorithm is arranged to transform the plurality of nodes to provide at least one virtual link, as shown in the transformed node of figure 3. It should be noted that not every node of the network may be an integrated node as shown in figure 1 and 2. One or more of the plurality of nodes may only contain a single technology platform. In other words, one or more of the nodes may be either a packet switching node or an optical switching node. It should also be noted that the at least one virtual link may be an internal virtual link that is provided between ports of the packet switching module and optical switching module of an integrated node. The at least one virtual link may be provided between the optical ports of an optical switching module. Further, the at least one virtual node may be an external virtual link between two nodes of the plurality of nodes.

Step 404 comprises performing a routing algorithm using the virtual link to determine an optimal virtual route based on at least one cost parameter associated with the at least one virtual link.

A cost parameter may be calculated for each virtual link. Therefore, by determining the total cost of a particular virtual route based on which virtual links are used in that virtual route, an optimal virtual route can be determined.

The cost parameter for each virtual link may be calculated based on a traffic engineering parameter, a power consumption parameter or an administrative weight parameter, or any combination thereof. The combination may be a linear combination, a weighted combination, or any other combination of all or some of traffic engineering, power consumption or administrative weight parameters.

In an embodiment of the present invention, the optimal route may be

determined such that in the optical layer, an already activated optical channel is filled. In the packet layer, the optimal route may be determined to distribute the traffic in a homogeneous way among the nodes and to avoid a packet node to work in saturation area. Furthermore, the optimal route may be determined to find traffic paths at the lower possible power consumption. Step 406 comprises applying a re-transformation algorithm to the at least one virtual link used in the optimal virtual route to determine which ports of the plurality of nodes the traffic should be routed. In step 406, after the optimal virtual route through the network has been determined for the traffic, virtual links used in the determined optimal route may be re-transformed to determine which physical ports in the nodes the traffic should be routed. This re-transformation provides the optimal physical route for the traffic through the network.

Step 408 comprises routing the traffic through the determined physical ports.

Figure 5 shows a routing unit 510 that is configured to perform the method steps of figure 4.

The routing unit 510 comprises a transformer 512 that is arranged to apply a transformation algorithm to the plurality of nodes for transforming at least two ports of the plurality of nodes to provide at least one virtual link. The

transformer 512 is arranged to apply the transformation step 402 of the method of figure 4.

The routing unit also comprises a processor 514 arranged to perform a routing algorithm using the at least one virtual link to determine an optimal virtual route for the traffic through the network based on at least one cost parameter associated with the at least one virtual link.

It should be noted that the transformer 512 may be arranged to perform the re- transformation step 406 of figure 4. Alternatively, a re-transformer (not shown), may be provided in the routing unit to perform the re-transformation step.

The routing unit 510 may further comprise a router 516 that is arranged to route the traffic through the determined physical ports. Figure 6 shows a routing system 600 according to an embodiment of the present invention. The routing system 600 comprises a network 602 comprising a plurality of nodes 604. Figure 6 shows a network having m nodes, where m may be any number greater than or equal to 2. As can be seen in figure 6, the plurality of nodes 604 may contain nodes that contain only a single technology platform, so-called non-integrated nodes such as node 604i, and integrated nodes such as node 604₂, which containing a packet switching module 606 and an optical switching module 608. It should be noted that the plurality of nodes may comprise any combination of non- integrated and integrated nodes. Also, in an embodiment, each node of the plurality of nodes may be an integrated node such as node 604₂. The routing system 600 also comprises a routing unit 610, which comprises a transformer 612, a processor 614 and a router 616, and operates in the same manner as the routing unit 510 of figure 5.

Figure 7 illustrates an example network 700 comprising a plurality of nodes A to E. Figure 7 shows the nodes after the transformation algorithm has been applied to the nodes to provide the virtual links between the nodes.

As can be seen in figure 7, network 700 comprises node A 701 , which is a non- integrated node that has only a packet switching capability. Node B 702, like node A is also a non-integrated node that has only a packet switching capability. Node C 703 is a non-integrated node having an optical switching capability. Node D 704 is an integrated node having a packet switching module 706 and an optical switching module 706. Node E 705, like node D is an integrated node having a packet switching module 712 and an optical switching module 714. Nodes D and E may be the integrated nodes of figures 1 and 2.

As shown in figure 7, after the transformation algorithm is applied to the plurality of nodes, as described above, each DWDM line port is

represented with two virtual ports, labeled "T" and "R", and each client port of the packet switching modules is represented with a virtual port. Further, as described above, internal ports between packet and optical switching modules are represented in an aggregated way in which all the internal connectivity within a particular node is collected in two virtual ports (labeled as "+" and "-"), at the PSC level.

The plurality of virtual nodes are fully meshed with a plurality of virtual links provided between the virtual ports. There are a number of different virtual link types defined.

A first virtual link type is an external virtual link 1 between two packet switching modules of different nodes, for example the virtual link between node A 701 and node B 702 or the virtual link between node B 702 and the packet switching module 706 of Node D 704.

A second link type is an external virtual link 2 between two optical switching modules of different nodes, for example the virtual link between node C 703 and the optical switching module 708 of node D 704.

A third virtual link type is an internal virtual link 3 between a client port of a packet switching module and an internal port of a packet switching module, for example the links shown in the packet switching modules 706 and 712 of node D 704 and node 705, respectively. This virtual link 3 represents the packet processing needed to setup a new lightpath.

An addition virtual link type 3.1 is shown in figure 7. This virtual link represents the packet processing needed to connect to an already established lightpath.

A fourth virtual link type is an internal virtual link 4 between a packet switching module and an optical switching module in an integrated node, for example, the virtual links between the packet switching module 706 and the optical switching module 708 of node D 704 and the virtual links between the packet switching module 712 and the optical switching module 714 of node E 705. A fifth virtual link type is an internal virtual link 5 within a packet switching module of a particular node in electrical mode. This virtual link represents the capability of a PSC module to connect two external ports. In other words if a first external port of a PSC module can be cross-connected with a second external port of the PSC module, a virtual link 5 is provided to represent this possibility. The maximum bandwidth that can flow between the two external ports is assigned to the virtual link. See for example virtual link 5 in node B 702. A sixth virtual link type is an internal virtual link 6 within a packet switching module of a particular node, for example within the optical switching module 708 of node D 704 and within the optical switching module 714 of node E 705. The above virtual link types are defined during the transformation process of the nodes. In other words, these virtual links are defined prior to any routing algorithm being applied.

A seventh virtual link type will now be described in relation to figure 8.

Figure 8 shows a network 800 comprising three nodes. Node A 802, node B, 804 and node C 806 are shown as integrated nodes comprising packet switching modules 808, 812, 816 and optical switching modules 810, 814, 818. It should be noted that although figure 8 only shows integrated nodes provided in the network, non-integrated nodes could also be provided, as in figure 7.

Figure 8 shows the network after the transformation algorithm has been applied to the nodes, as described above. As described in relation to figure 7, figure 8 shows the plurality of nodes comprising a plurality of virtual ports that are connected together with various types of virtual link. In figure 8, the seventh type of virtual link 830 is shown. This type of virtual link represents a virtual lightpath that passes directly from one node to another.

Consider an example in which a client signal at 1 Gbps would like to go from node A to node C. A wavelength at 10 Gbps may be switched on and the client traffic is sent through this wavelength. If another client traffic at 1 Gbps would like to go from A to node C, it is not necessary to activate another wavelength, because a residual 9 Gbps is available in the virtual link 830. This virtual link 830 can be used as an already available (optical) bypass between node A and node C. In other words, if a wavelength is activated (transparently) from a node A to node C, to provide optical connectivity between node A and node C in response to a packet traffic demand between these two nodes, this wavelength is then represented in the virtual topology as a virtual link 830 connecting node A and node C.

As can be seen, virtual link 830 is provided when an optical channel is activated between two end nodes. The virtual lightpath is provided to simplify further traffic forwarding between the same pair of end nodes. The virtual light path may for example directly connect the packet switching module 808 of node A 802 with the packet switching module 812 of node B or the packet switching module 816 of node C 806. Also a virtual lightpath may be provided to directly connect the packet switching module 812 of node B 804 with the packet switching module 816 of node C 806.

Virtual link 7 is different to the other virtual links in that is defined during the routing algorithm, rather than during the transformation algorithm. It should be noted that this virtual link is not a physical link. As soon as a peer-to-peer optical connection has been established

between two nodes, it is no longer required, for the purpose of routing of packet traffic, to preserve the details of the real collection of ports/links which is used to provide such optical connectivity. In other words, virtual link 7 is the "logical" representation of an optical connectivity established between two nodes. By aggregating several links in single virtual link, the routing of packet traffic can be simplified.

The behavior of each of the link types shown in figures 7 and 8 are defined with a cost formula. As described above, there are three different considerations that may be taken into account when evaluating the cost of a particular virtual link within path calculation:

The first consideration is based on traffic engineering parameters, which takes into account several considerations aimed at optimizing bandwidth and resources allocation in the network. This cost, in the optical layer, is defined with the purpose to completely fill an already activated optical channel. In the packet layer, the cost formula is defined to distribute the traffic in a homogeneous way among the nodes and to avoid the packet node to work in saturation area.

The second consideration is based on power consumption and this cost drives the routing engine to find traffic paths at the lower possible power consumption.

The third consideration (only defined for external links for example virtual l i nks 1 and 2) is based on the link Administrative Weight. This is a configurable parameter which is not affected by dynamic evolution and status of the network.

By calculating a cost for each virtual link and hence each traffic route through the network, an optimal virtual rotue can be determined. This virtual route may then be retransformed to provide the optimal physical route through the network.

In embodiments of the present invention, by applying a transformation algorithm to a plurality of nodes in a network, virtual links can be created between virtual ports in the nodes. The virtual links are homogenous in nature and allow all routes through the network to be considered concurrently during a routing algorithm. This allows an optimal route to be determined based on cost parameters associated with each virtual link.

The following is a pseudocode example of a particular implementation of the present invention.

INPUT

• Traffic Matrix K, where a vector (s_{k l}t_k, d_k) is given for each

commodity k, respectively representing the commodity source, destination and required capacity;

Real Network H (V,F);

· Virtual Network G (N, E), where:

♦ N= (ΛΡ² U N^{h b} U ΛΡΡ), where Ν·¹ represents the nodes set composed by electric ports, N°^p is twice the number of optical ports and N^ht, s twice the number of hybrid nodes;

♦ E= ζβ^β1 U E^hb U E^ep) represents the edges set, where E^el is the set of edges with label 1 ,3,3.1 and 5, E^hb is the set of edges with label 4 and E^op is the set of edges with label 2 and 6.

1 .1 DEFINITION AND INITIALIZATION

The Virtual Network connectivity is described by the following matrix: ADJACENCY AND LABEL MATRIX Ay V (i, j) e E, whose elements are:

♦ a(i,j) = k, if there is an oriented edge from the node i to the node j with label k, where k belongs to {1 ,2,3,3.1 ,4,5,6,7}.

♦ a(i,j) = 0, if there is not an oriented edge from the node i to the node j.

Let us observe that k=7 is the lightpath label, i.e. represents virtual link 7. At first step there is not any a(i,j)=7.

Now, for each (i,j) belonging to E, let us introduce a set of parameters that must be defined, according to the label of (i,j): if a (i,j)=1 we have:

♦ U(i,j) is the total bandwidth on the edge (i,j);

♦ b_u(i,j) is the used bandwidth on the edge (i,j); a (i,j)=2 we have:

U(i,j) is the bandwidth related to a wavelength of the edge (i,j); A(i,j) is the number of wavelengths associated with the edge (i,j); A _u(i,j) is the number of used wavelengths on the edge (i,j); a (i,j)=3 we have:

U(i,j) is the total bandwidth on the edge (i,j);

b_u(i,j) is the used bandwidth on the edge (i,j); a (i,j)=3.1 we have:

U(i,j) is the total bandwidth on the edge (i,j);

b_u(i,j) is the used bandwidth on the edge (i,j); · a (i,j)=4 we have:

U(i,j) is the bandwidth related to each grey fiber of the edge (i,j); f(i,j) is the number of grey fibers associated with the edge (i,j) ♦ fu(i j) is the number of used grey fibers on the edge (i,j); if a (i,j)=5 we have:

♦ U(i,j) is the total bandwidth on the edge (i,j);

♦ bu(ij) is the used bandwidth on the edge (i,j); if a (i,j)=6 we have:

♦ U(i,j) is the bandwidth related to a wavelength of the edge (i,j);

♦ λ (i,j) is the number of wavelengths associated with the edge (i,j);

♦ λ u(i,j) is the number of used wavelengths on the edge (i,j); The COST MATRIX Cy V (i, j) e E is defined as following: c(ij) = infinity if a(ij)=0; c(i,j) = Cadm(i,j)+ a_con ^* C_Con(i,j)+ a_pow ^* Cpow(iJ) if a(i,j)=[1 ;6];

As a preliminary assumption, a linear combination of the three costs is assumed. Other combinations can be considered. The a parameters are also used to have the same dimension (unit of measurement) for all the cost contributions.

2. COMMODITIES SORTING

In the context of this invention commodities are Traffic demands or Traffic requests, which are the entries of a traffic matrix. They will be submitted to the routing algorithm to be routed across the network.

Sort the commodities in increasing order according to the value (NH_k ^*d_k), where d_k is the bandwidth required by the commodity k and NH_k is calculated as follows:

- Consider the real Network H=(V,F) assigning unit cost to each edge belonging to F; - For each commodity k (s_k,, t_k, d_k):

{ - use Dijkstra Algorithm to find the minimum cost path C_k between s_k and t_k;

- put NH_k = the number of edges making up C_k }.

3. ROUTING AND UPDATING

Let COST_TOT be the total cost of the solution of the routing problem; For each commodity k {^*

3.1 SEARCH FIRST PATH

Set s= s_k t= t_k; Let P_k be the path associated to the commodity k; Find P_k (Dijkstra Algorithm): function Dijkstra(G, s): for each vertex v in G: dist[v] := infinity pred[v] := undefined dist[s] := 0

Q := the set of all nodes in G

while (Q is not empty or u≠t): u := vertex in Q with smallest dist[] if dist[y] = infinity: break remove u from Q for each neighbor v of u: alt := dist[y] + c (u, v) if d_k < U(u,v) if alt < d\st[v] d si[v] := alt pred[v] := u return dist[] if P_k exists Add ∑ c i,j) to COST_TOT;

3.1 .1 LIGHTPATH CREATION

if P_k exists

- Scan the edges, from s_k to t_k , belonging to P_k and for each time you find sequentially two edges (h,x),(y,z) such that a(h,x)=a(y,z)=4: create a lightpath putting a(h,z)=7;

Enter in the vector L^k _hz all the edges making up the lightpath just created;

- Put c(h,z)=0

- Put U(h,z)=U(i,j)-d_k, where (i,j) χ L^k _h2 .

3.1 .2 UPDATING ists ch (i,j) χ P_k if a(i,j)=1

if a(i,j)=2

if the edge (x,i) χ P_k preceding (i,j) is such that a(x,i)=3 for all y such that a(i,y)=4

then if the edge (x,i) χ P_k preceding (i,j) is such that

for all y such that a(y,j)=4

fu(yj) = fu(yj) + ; if a(i,j)=5

if a(i j )=6

if a(ij)=7

U(i,j)=U(i,j)-d_k;

end for

Let P'k be the path associated to the symmetric commodity (t_k,, s_k, d_k);

Built P'k as follows:

-Scan P_k from his last edge (i,j) to the first one.

For each edge (i,j): if a(i,j)= 1 enter (j,i) in P'_k; if a(i,j)=2 enter twin[(i,j)] in P'_k; if a(i,j)=3 enter twin[(i,j)] in P'_k; if a(i,j)=4 enter twin[(i,j)] in P'_k;

if a(i,j)=5 enter (j,i) in P'_k; if a(i,j)=6 enter twin[(i,j)] in P'_k; if a(i,j)=7 enter (j,i) in P'_k;

end for

Repeat the LIGHTPATH CREATION and UPDATING step for P'_k

3.2 SEARCH SECOND PATH

Q = set of nodes with the same physical label of the nodes belonging to P_k

Z = set of edges (i,j) such that a(i,j)=1 or a(i,j)=2 and with an endpoint belonging to Q We introduce a NEW CAPACITY MATRIX U'(iJ) whose generic element is defined as follows:

U'(i,j) = U(i,j) if CM) € z

U'(iJ) =0 if (i,j) e z

We find the second path p^²⁾ in the same way we found the first one, bearing in mind that now the capacity matrix is no longer U(i,j) , but IT

Find Ρχ²⁾ (Dijkstra Algorithm):

function Dijkstra(G, s):

for each vertex v in G:

dist[v] := infinity

pred[v] := undefined

dist[s] := 0

Q := the set of all nodes in G

while (Q is not empty or u≠t):

u := vertex in Q with smallest dist[]

if dist[y] = infinity:

break

remove u from Q

for each neighbor v of u:

alt := dist[y] + c (u, v)

if d_k < U'(u.v)

if alt < d\st[v]

d si[v] := alt pred[v] := u

return dist[] if P^²¹ exists

Add∑. _{j ep} c(i_rj) to COST TOT;

K

3.2.1 LIGHTPATH CREATION

if pj²⁾ exists

- Scan the edges, from s_k to t_k , belonging to / ~ and for each time you find two edges (h,x),(y,z) such that a(h,x)=a(y,z)=4:

create a lightpath putting a(h,z)=7;

Enter in the vector L^k _hz a\\ the edges making up the lightpath just created;

- Put c(h,z)=0

- Put U(h,z)=U(i,j)-d_k, where (i,j) χ L^k _h2 .

3.2.2 UPDATING

i^{f p} _j?³ exists

for each (i,j) χ p∞

if a(i,j)=1

if a(i ,j)=2

if a(i,j)=4

if the edge (x,i) % preceding (i,j) is such that a(x,i)=3

for all y such that a(i,y)=4

then if the edge (x,i) χ ρ^' preceding (i,j) is such that a(x, i)=2

for all y such that a(y,j)=4

fu(yj) = fu(yj) + ;

if a(i,j)=5

bu(i j) = bu(i j) + d_k;

if a(i,j)=6

if a(i,j)=7

U(i,j)=U(i,j)-d_k;

end for

Let pi ^l be the path associated to the symmetric commodity (t_k, s_k, d_k);

Built as follows:

-Scan Pg^*} from his last edge (i,j) to the first one.

For each edge (i,j): if a(i,j)=1 .

enter (j, i) in P (2)'

if a(i,j)=2 enter twin[(ij)] in p.J²⁾ⁱ; if a(i,j)=3 enter twin[(i,j)] in P^²'"; if a(i,j)=4 enter twin[(i,j)] in

if a(i,j)=5 enter (j,i) in P. if a(i,j)=6 enter twin[(i,j)] in Ρ.ί^{2) ί}; if a(i,j)=7 enter in p

end for

Repeat the LIGHTPATH CREATION and UPDATING step for

( 25 '

p -

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim, "a" or "an" does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the claims. Any reference signs in the claims shall not be construed so as to limit their scope.

Claims

1 . A method for routing traffic through a network having a plurality of nodes, at least one of said plurality of nodes being an integrated node including first and second technologies integrated inside the same node platform, the method comprising:

applying a transformation algorithm to the plurality of nodes for

determining at least one virtual link between at least two ports of the plurality of nodes; and

performing a routing algorithm using the at least one virtual link to determine an optimal virtual route for the traffic through the network based on at least one cost parameter associated with the at least one virtual link.

2. A method according to claim 1 , further comprising:

applying a re-transformation algorithm to the at least one virtual link used in the optimal virtual route to determine through which ports of the plurality of nodes the traffic should be routed; and

routing the traffic through the determined ports.

3. A method according to claim 1 or claim 2, wherein the transformation algorithm is applied prior to the routing algorithm being performed.

4. A method according to any preceding claim, wherein the at least one cost parameter is a traffic engineering parameter, power consumption or an administrative weight or a combination of any of said parameters.

5. A method according to any preceding claim, wherein at least one node of the plurality of nodes comprises an optical switching capability having N optical ports and the transformation algorithm transforms the N optical ports by providing 2xN virtual ports between which internal virtual links are provided.

6. A method according to any preceding claim, wherein the at least one integrated node of the plurality of nodes comprises a packet switching capability having at least one internal port and an optical switching capability having at least one optical port, and the transformation algorithm transforms the at least one internal packet switching port and the at least one optical port by providing virtual ports between which internal virtual links are provided.

7. A method according to claim 6, wherein the packet switching capability has a plurality of internal ports and the transformation algorithm transforms the plurality of internal ports by providing a virtual port, to which virtual links are provided.

8. A method according to any of claims 5 to 7, wherein the transformation algorithm provides an external virtual link between optical switching capabilities of two nodes of the plurality of nodes.

9. A method according to any of claim 6, 7 or 8, wherein the transformation algorithm provides an external virtual link between packet switching capabilities of two nodes of the plurality of nodes.

10. A method according to any of claims 5 to 9, wherein during the routing algorithm, a virtual light path is provided between two nodes of the plurality of nodes.

1 1 . A method for routing traffic through an integrated network node including first and second technologies integrated inside the same node platform, the method comprising:

applying a transformation algorithm for determining at least one virtual link between at least two ports of the node; and

performing a routing algorithm using the at least one virtual link to determine an optimal virtual route for the traffic through the node based on at least one cost parameter associated with the at least one virtual link.

12. A method according to claim 1 1 , further comprising: applying a re-transformation algorithm to the at least one virtual link used in the optimal virtual route to determine through which ports of the plurality of nodes the traffic should be routed; and

routing the traffic through the determined ports.

13. A method according to claim 1 1 or claim 12, wherein the transformation algorithm is applied prior to the routing algorithm being performed.

14. A method according to any one of claims 1 1 - 13, wherein the integrated network node comprises an optical switching capability having N optical ports and the transformation algorithm transforms the N optical ports by providing 2xN virtual ports between which internal virtual links are provided.

15. A method according to any one of claims 1 1 - 14, wherein the integrated network node comprises a packet switching capability having at least one internal port and an optical switching capability having at least one optical port, and the transformation algorithm transforms the at least one internal packet switching port and the at least one optical port by providing virtual ports between which internal virtual links are provided.

16. A method according to claim 15, wherein the packet switching capability has a plurality of internal ports and the transformation algorithm transforms the plurality of internal ports by providing a virtual port, to which virtual links are provided.

17. A method according to any of claims 15 to 16, wherein the transformation algorithm provides an external virtual link between the optical switching capability of the integrated network node and the optical switching capability of another node.

18. A method according to any of claim 15, 16 or 19, wherein the

transformation algorithm provides an external virtual link between the packet switching capability of the integrated network node and the packet switching capability of another node.

19. A routing system, for routing traffic through a network, comprising:

a plurality of nodes, wherein at least one of said plurality of nodes is an integrated node including first and second technologies integrated inside the same node platform; and

a routing unit comprising:

a transformer arranged to apply a transformation algorithm to the plurality of nodes for transforming at least two ports of the plurality of nodes to provide at least one virtual link; and

a processor arranged to perform a routing algorithm using the at least one virtual link to determine an optimal virtual route for the traffic through the network based on at least one cost parameter associated with the at least one virtual link.

20. A routing system according to claim 19, wherein the processor is arranged to applying a re-transformation algorithm to the at least one virtual link used in the optimal virtual route to determine through which ports of the plurality of nodes the traffic should be routed; the routing unit further comprising:

a router for routing the traffic through the determined ports.

21 . A routing system according to claim 19 or 20, wherein the transformer is arranged to apply the transformation algorithm prior to the processor performing the routing algorithm.

22. A routing system according to any of claims 19 to 21 , wherein the at least one cost parameter is a traffic engineering parameter, power consumption or an administrative weight.

23. A routing system according claim 22, wherein the cost parameter is a combination of the traffic engineering parameter, power consumption and administrative weight.

24. A routing system according to any of claim 19 to 23, wherein at least one node of the plurality of nodes comprises an optical switching capability having N optical ports; and

the transformer is arranged to transform the N optical ports by providing

2xN virtual ports between which internal virtual links are provided.

25. A routing system according to any of claims 19 to 23, wherein the at least one integrated node comprises a packet switching capability having at least one internal port and an optical switching capability having at least one optical port; and

the transformer is arranged to transform the at least one internal packet switching port and the at least one optical port by providing virtual ports between which internal virtual links are provided.

26. A routing system according to claim 25, wherein the packet switching capability has a plurality of internal ports; and

the transformer is arranged to transform the plurality of internal ports by providing a virtual port, to which virtual links are provided.

27. A routing system according to any of claims 24 to 26, wherein the transformer is arranged to provide an external virtual link between optical switching capabilities of two nodes of the plurality of nodes.

28. A routing system according to any of claim 25, 26 or 27, wherein the transformer is arranged to provide an external virtual link between packet switching capabilities of two nodes of the plurality of nodes.

29. A routing system according to any of claims 24 to 28, wherein during the routing algorithm, a virtual light path is provided between two nodes of the plurality of nodes.

30. A routing unit for routing client traffic across a network having a plurality of nodes, which nodes include first and second technologies integrated inside the same node platform, comprising:

31 . A routing unit according to claim 30, wherein the processor is arranged to applying a re-transformation algorithm to the at least one virtual link used in the optimal virtual route to determine through which ports of the plurality of nodes the traffic should be routed; the routing unit further comprising:

a router for routing the traffic through the determined ports.

32. An integrated node, comprising:

a packet switching capability module; and

an optical switching capability module linked to the packet switching capability module,

wherein the optical switching capability module is a digital reconfigurable optical add-drop multiplexer, DROADM, having a N optical ports.