WO2012038006A1

WO2012038006A1 - Method, device and telecommunication network for analyzing protecting routes in lower-layer paths over a sdh network

Info

Publication number: WO2012038006A1
Application number: PCT/EP2011/004018
Authority: WO
Inventors: Mary Luz Mouronte Lopez; Francisco Javier RAMOS GUTIÉRREZ
Original assignee: Telefonica, S.A.
Priority date: 2010-09-24
Filing date: 2011-08-11
Publication date: 2012-03-29
Also published as: AR083097A1; ES2385814B1; ES2385814A1

Abstract

The method comprises: - analysing one or more lower order layer trails considering its working and protecting routes; - obtaining, from said analysis, protected and unprotected working route segments, said unprotected segments defined as those not having protection in their protecting route or in higher-order layer paths that support the working route; - protecting, at said low order layer, said unprotected working route segments; and - generating a new protecting route including the protected working route segments found from said analysis and the ones protected after having been found as unprotected from said analysis. The device comprises the means to perform the method. The telecommunication network comprises the device. The invention refers to a method for maximizing protected segments in the lower-order path layer in Synchronous Digital Hierarchy (SDH) networks, minimizing the number of needed network resources.

Description

METHOD, DEVICE AND TELECOMMUNICATION NETWORK FOR ANALYZING

PROTECTING ROUTES IN LOWER-LAYER PATHS OVER A SDH NETWORK

State of the Art

The present invention relates, in a first aspect, to a method for analyzing routes that are assigned to a circuit in lower-path layer in SDH (Synchronous Digital Hierarchy) networks. The invention refers to a method for maximizing protected segments in the lower-order path layer in Synchronous Digital Hierarchy (SDH) networks, minimizing the number of needed network resources. The invention is based in the analysis of the route of a circuit in lower order path layer taking into account the protection in a higher order path layer in order to avoid redundancy. This analysis gets a new protecting route in lower-order path layer network for each unprotected segment using the minimum resources. It also gets a new protecting route for protected segments in LO layer which involves fewer resources than the initial one.

A second aspect of the invention relates to a device for analyzing protecting routes in lower-layer paths over a SDH network comprising the means to perform the method of the first aspect.

A third aspect of the invention relates to a telecommunication network comprising the device of the second aspect.

The invention belongs to telecommunication network area, specifically to the area of management, provisioning and planning of circuits over SDH networks.

Background art The requirement of more efficient and higher capabilities telecommunication services led standardization and network operators to search a solution to build synchronous transmission systems that allow developing more economic and flexible networks. The result was presented in a set of ITU-T recommendations [1 , 2, 3, 4, and 5] that established a standard for signal multiplexing and transmission called Synchronous Digital Hierarchy (SDH). ITU-T recommendations use two basic concepts to describe transport networks: layering and partitioning. A transport network can be broken down in a set of independent layers. A layer offers a service relationship to the immediately adjacent layer, which can be divided to reflect its internal structure and the way to manage it. From an architectural point of view, a transport network is composed by topological components (layer network, subnetwork, link and access groups), generic transport processing functions (adaptation, termination), transport entities (link connection, subnetwork connection, network connection, trail) and reference points. A layer network is defined by a set of topological components of the same type, which may get associated for transferring information. The transferred information is typical of the layer network. Three different layer networks can be distinguished: circuit layer network, path layer networks and transmission media layer network. A circuit layer network provides circuit and packets switching services and leased line services. A path layer network supports different types of circuit networks. A transmission media layer network supports one or more path layer networks and it depends on the media that finally transferred the signal. SDH defines two path layer networks: lower-order path layer network (LO) and higher-order path layer network (HO) that differ in the information structure (virtual container) used to support connections in the layer network. A lower-order path layer network supports 2 Mbit/s and 34/45 Mbit/s signals in virtual containers VC-12 and VC-3. A higher-order path layer supports lower-order path layer networks and 140 Mbit/s circuit networks. The topology of a layer network is described by subnetworks, links and access groups. In each layer, a subnetwork is defined as a set of access points that transfer characteristic information among them. Each subnetwork can be partitioned in smaller ones. A matrix in network equipment is the smallest subnetwork in SDH networks. A link represents a relationship that transfers information among subnetworks or access groups. An access group is defined as a set of termination functions which are connected to the same subnetwork or link. The architecture of a network distinguishes two generic processing functions: adaptation function and termination function. An adaptation function transforms characteristic information of a layer network in a suitable form for being transported over an adjacent layer network. A termination function adds new characteristics to the transferred information that allow the signal to be monitored in the layer network. A transport entity provides information transfer between reference points of a layer network. A reference point is the binding between inputs and outputs of transport processing functions and/or transport entities. A trail is a transport entity that transfers monitored information between reference points that support termination functions. It is capable of simultaneously transferring information in opposite directions between reference points. A link connection is a transport entity that transfers information across a link. It represents a pair of adaptation functions and a trail in a server layer network. A subnetwork connection is a transport entity that transfers information across a subnetwork. Trail termination reference points and link connection termination points delimit it. A subnetwork connection can be described as a concatenation of smaller subnetwork connections and link connections. A matrix connection is a special case of a single subnetwork connection. A network connection is a transport entity that transfers information across a network.

A main feature of transport networks is to establish instruments that can be used to enhance its availability. This enhancement consists in the detection and replacement of failed and degraded transport entities. There are two basic strategies to enhance the availability of a network. The first one is to generate protection. It makes use of pre- assigned capacity, where, in case of fail or degradation, the signal is switched and transferred across these pre-assigned entities. There are two types of protection: SDH trail protection and SDH subnetwork connection protection. The second strategy is to define restoration procedures. These procedures make use of any capacity available in the moment that a fail or degradation is detected for re-routing the signal. It is necessary that unused and reserved resources exist, which could be used for rerouting in case of fail or degradation. In SDH trail protections, a transferred signal through a working trail is replaced by the signal through the protection trail when a fail or degradation is detected in the working trail. The protection is applied in the layer network when a fail or degradation is detected in the same layer network. For the purpose of this invention, trail protection can be applied in SDH multiplex section. There are two basic protection schemes in SDH multiplex section layer: MSP (Multiplex Section Protection) and MS-SPRing (MS Shared Protection Rings).

MSP protections can be a dedicated or shared protection depending on the number of working SDH multiplex sections that are protected. A MSP 1 +1 protection establishes a dedicated protection of one working SDH multiplex section by other protecting SDH multiplex section. A MSP 1 : n protection establishes a shared protection. One protecting SDH multiplex section protects n different working SDH multiplex sections. A MSP protection cannot protect against node failures.

MS-SPRing protections are established over ring structures. A ring is a collection of network nodes that form a closed loop. Each node is connected with other two adjacent nodes. A ring provides redundant bandwidth, redundant network equipment, or both. This redundancy allows distributed services to be automatically restored in case of fail or degradation. When a MS-SPRing is established in a ring, the total payload of each multiplex section that connects two nodes is divided equally into working and protecting capacity. Working channels transfer the signal that has to be protected. Protection channels are reserved to transfer the signal in case of failure.

In Subnetwork Connection Protection (SNCP), a signal transferred through a working subnetwork connection, defined as a set of subnetwok connections and link connections, is switched to be transferred through a protection subnetwork when a defect is detected. It is a dedicated protection that can be used to protect a trail or segments of a trail. This type of protection typically applies to subnetworks in LO and HO layer networks. The strategies for establishing efficient protection and restoration mechanisms are ones of the most important features in the operation and support systems of telecommunication networks. In terms of client signals, it is necessary to guarantee quality of service in order to improve customer's trust and loyalty. In FIG.1 it is shown the existing solutions flowchart and its mechanisms wherein these mechanisms determine the source and target equipments where it is necessary to establish protection or restoration. These equipments are the input data to get the quality of service requirements for a leased line or to execute a recovery procedure when a failure occurs.

In addition, these mechanisms determine the boundary conditions. They have to establish the SDH resources (equipments and trails) to be used in the protection or restoration route. Typically, trails and equipments included in working route are banned. In case of restoration, faulty resources cannot be included in the restoration route. These mechanisms also determine the free resources which can be occupied depending on transferred client signal. Finally, these mechanisms search a new route between the equipments, keeping in mind the boundary conditions. There are different procedures to obtain routes between two network elements [6, 7, 8, and 9]. One of them is the Spanish patent application number P200930989 (Procedure for searching vacancy routes in complex networks with boundary conditions in a transport network).

The document US7542414 discloses a system and method for finding an optimal overall circuit path within a network, such as a synchronous optical network (SONET) using SDH technology. The protected and unprotected segments of the circuit path are identified. This document describes a method that obtains the working and protection routes between two nodes in unidirectional path-switch rings, which are included in time division multiple networks (TDM). It determines the primary path that includes a 1 +1 line-protected link. From this primary path, it searches for an alternative path to totally protect it, including the 1 +1 protected segment.

The present invention obtains a protection route from an initial route. Initial working route can include any protected or unprotected resources that support lower-order signals. It also can include a protection route. It is not necessary that working route includes protected segments, as the invention described in document US7542414. The present invention searches for an overall circuit protection and, if it is not possible to find it, the present invention intends to find routes to protect the maximum number of possible elements in the initial route. The PCT application WO2004/008685 from Nortel Networks Limited discloses a system and method for providing protection signaling between network elements in a SDH network. This document describes a method to provide shared protection in mesh networks and the way of switching in each network element. It is based on the specific characteristics in a mesh network, where all network elements are connected (directed or undirected) to each other.

Nevertheless, the present invention describes a method to obtain a no-shared protection in lower-order layer trail in SDH network. Although SDH networks can include mesh subnetworks, typical SDH networks are not mesh networks because they have different uncoupled network elements. The document EP2099172 describes a method for multicast traffic protection. It is applied on IP networks and treats the way of switching after a fault is detected. The present invention is applied to SDH networks. It searches a protection route based on topological components in SDH networks.

The document US20080144510 describes a method for establishing a path between two nodes that can include a protection route. It uses a mechanism to assign weights to links according to different conditions (bandwidth, protection, resilience class, degradation). It gets a path using these weights.

However, the present invention obtains a protection route from an initial route. It analyzes the initial route to get protected segments in function of the protections included in it. Protections can be included as a SNCP in a lower-layer layer or as protection schemes in server layers. Our invention gets a protected path for each unprotected segment using free resources in the network that can transfer a lower- order layer signal. Each free resource has the same weight. The search is restricted by a set of boundary conditions which establish the resources to be used in order to get a disjoint protecting route. It can use HO paths which offer free capacities and do not finish in any network equipment included in the initial working route, except the source and target equipments in the segment. It has to avoid the HO paths included in the working route and the HO paths supported by the same resources in the HO paths included in the working route.

The document US6813241 provides a method for configuring a network by mean of different devices to get a fast and accurate recovery in case of faults. On contrary, the present invention does not describe any configuration of SDH network elements and their equipments. It uses the topology of SDH networks, which includes all devices, to get a protection route. Finally, the document WO2007149886 describes techniques for routing data via lower layer paths and how packets have to be sent through a path, whilst the present invention provides a method to get an efficient protection route in order to transferred information when a fault in working route occurs. It does not establish a method for routing packets.

In conclusion, nowadays, there is an increasing demand of planning and provisioning tools. These tools must simplify the procedure to set up protecting routes. These routes must use a minimum number of resources and maximize the protected elements.

The existing solutions are usually applied when a fault is detected. These solutions determine a route between two equipments but they use free assignable resources ignoring other segments in the initial working route which are not affected by fault. To set up protecting routes efficiently, the solution must consider the whole route when it decides the segments in the working route (what segments must be protected explicitly with a protecting route and which can be protected implicitly in a server layer). The existing solutions do not provide a method which allows getting each unprotected segment involved in route, the protected segment in LO layer, and the protected segments in server layer, and searching a route for each unprotected segment. Consequently, they cannot find the redundant protections (segments protected in LO layer and server layer) included in a circuit route.

References:

[1] ITU-T Recommendation G.707: Synchronous Digital Hierarchy Bit Rates

[2] ITU-T Recommendation G.803: Architectures of Transport Networks Based on the Synchronous Digital Hierarchy (SDH)

[3] ITU-T Recommendation G.805: Generic functional architecture of transport networks

[4] ITU-T Recommendation G.841 : Types and characteristics of SDH network protection architectures

[5] ITU-T Recommendation G.842: Interworking of SDH network protection architectures

[6] A method of constructing independent routes and sections of network models,

V. V. Georgievskii and E. G. Davydov, 1974.

[7] The Bellman-Ford algorithm and "Distributed Bellman-Ford", D. Walden, 2003 [8] Algorithms for finding an optimal set of short disjoint path in a communication network, D. Torrieri, 1992.

[9] A dynamic routing procedure for connections with Quality of Service requirements, M. Nour, A. Hafid and M. Gendreau, 1997. Summary of the invention This invention provides, in a first aspect, a method for analyzing protecting routes in lower-layer paths over a SDH network, comprising obtaining one or more lower order layer trails and finding a protecting route therein.

On contrary to the known proposals, the method of the first aspect of the invention comprises:

- analysing said one or more lower order layer trails considering their working and protecting routes;

- obtaining, from said analysis, for each of said low order layer trails, protected and unprotected working route segments, said unprotected segments defined as those not having protection in their protecting route or in higher-order layer paths that support the working route;

- protecting, at said low order layer, said unprotected working route segments; and

- generating a new protecting route including the protected working route segments found from said analysis and the ones protected after having been found as unprotected from said analysis.

In other words, the method is intended for analyzing the route of a circuit in LO layer. It analyses the whole route, considers the SDH network topology and searches what segments are protected end-to-end in HO layer. These segments are treated as protected. It also obtains the segments in working route which can be protected. This analysis gets a new protecting route (SNCP protection) in lower-order path layer network for each unprotected segments using the minimum resources. It also gets a new protecting route for protected segments in LO layer which involves fewer resources than initial one.

Consequently, the objective technical problem that solves the present invention can be regarded as how to find a protecting route using minimum resources. The key idea in the present invention is to maximize protected segments in lower-order path layer network, minimizing the number of needed network resources. The final protecting route is different with others solutions. The invention is based on the analysis of each resource occupied by initial route in order to obtain unprotected and protected segments. The final goal is to get a protecting route which:

- reduces the unprotected segments in working routes;

- eliminates redundant protections; and uses minimum resources.

A protection is redundant when a resource in the server layer, which is assigned to the working route, is protected end-to-end and, furthermore, it is part of the protected route of the trail.

The assignment of the SNCP lower-order layer path without knowing the SDH network that supports can entail using higher resources that optimum. Elimination of redundant protection allows the network resource to use optimization. In that way, taken resources can be released for later use.

The reduction of unprotected segments allows increasing the quality of service, avoiding degradation in case of failures in working resources. From a resource collection assigned to a circuit layer trail, the procedure gets the different lower-order layer trails included in it. For this invention, a lower-order layer trail is composed by two ports that support termination and adaptation functions of lower- order layer network and an adjacent link connections collection, each of them included in a higher-order layer network trails that transfer signal between both ports. It can include another link connections collection for the protecting route, so they establish SNCP protections.

Once the procedure obtains the lower order layer trails, it considers the working and protecting routes for each one. The objective is to get a set of working route segments that does not have protection in its protecting route or in higher-order layer paths that support the working route.

This is the main difference between our invention and other solutions. The existing solutions determine the routes between the network elements. For example, the existing solutions obtain a route between SDH C and SDH H element, as answer to a specific request . But, they do not determine that segment between SDH B and SDH C is also unprotected. Also, if HO Path between SDH F and SDH H is protected, the existing solutions ignore that protection. In this case, the present invention determines that there are two LO trails where SNCP protections can be established. There is a protected segment between SDH C and SDH H which is a redundant protection between SDH F and SDH H because HO Path between SDH F and SDH H is protected. So, it must consider as unprotected the segment between SDH B and SDH F and segment between SDH I and SDH M. Those segments represent whole route of each LO trail. But, it could be that there are no routes between those network elements. The present invention also generates an unprotected segment for each ordered combination of network elements in each LO trail. So, it generates an unprotected segment between SDH B and SDH C, between SDH C and SDH F, between SDH I and SDH L, between SDH I and SDH K, between SDH K and SDH M, between SDH K and SDH L, between SDH L and SDH M. With these segments, it searches free resource routes for each segment. These routes are used to get a new protecting route for the circuit that in which the maximum number of network equipments assigned in the working route are included in the new protecting route, and what is more, protected segments in the initial route are also protected in the new route.

The present invention combines all segments where a route is found and generates a unique protecting route which reduces the number of unprotected segments. In a preferred embodiment, there are no unprotected segments. The method has found routes between SDH B and SDH F, between SDH I and SDH L, and between SDH L and SDH M. The segment between SDH F and SDH H is protected in HO layer. All equipments included in initial protecting route are protected in new route. The initial protecting route is released.

Throughout the description and claims the word "comprise" and variations of the word, are not intended to exclude other technical features, additives, components, or steps. Additional objects, advantages and features of the invention will become apparent to those skilled in the art upon examination of the description or may be learned by practice of the invention. The following examples and drawings are provided by way of illustration, and they are not intended to be limiting of the present invention. Furthermore, the present invention covers all possible combinations of particular and preferred embodiments described herein.

The method of the first aspect of the invention comprises several embodiments according to claims 2 to 10.

Brief description of the drawings

FIG 1. Shows the existing solutions flowchart.

FIG 2. Shows the main flowchart of the method for analyzing protecting routes in lower-layer paths over a SDH network, object of the present invention. FIG 3. Shows a schematic view of an example of a circuit route.

FIG 4. Shows a schematic view of the LO (low order) trails.

FIG 5. Shows a schematic view of a new route according with the method object of the present invention.

FIG 6. Shows the LO trail discovery flowchart, according with the method object of the present invention.

FIG 7. Shows the protecting route in LO trail flowchart.

FIG 8. Shows the protection analysis flowchart, according with the method object of the present invention.

FIG 9. Shows the route search flowchart, according with the method object of the present invention.

FIG 10. Shows the route treatment flowchart, according with the method object of the present invention.

FIG 11. Shows the segment treatment flowchart, according with the method object of the present invention.

FIG 12. Shows the segment with redundancy flowchart.

FIG 13. Shows the complete route flowchart.

Detailed description of particular embodiments

FIG. 2 shows the main flowchart of the method object of the present invention. The method for analyzing protecting routes in lower-layer paths over a SDH network comprising the steps of: (i) inputting the data; (ii) discovering the low order trail; (iii) analysis of the protection; (iv) selection of the route; and (v) outputting the data. 1 ) The first step is the operation collection called "input data" (100) that initiates the procedure. These operations define the needed data input:

a) Topological SDH network structure, that includes:

i) Paths that can support lower-order layer trail, including the capacities that these paths offer and information about their occupancy. It also includes the network elements where paths terminate.

ii) Ports that include termination functions for lower-order layer trail. It includes information about the network element where each port is located. iii) MS-SPring protections and resources involved in them: network elements, ports, higher-order layer paths and SDH multiplex section paths. iv) MSP protections including protected SDH multiplex section paths and higher-order layer paths they support.

v) SNCP higher-order path layer protections, including SDH multiplex section paths that support them in working and protecting route.

b) Circuit to be analyzed:

i) Signal rate;

ii) Assigned resources;

(1 ) Ports and link connections in working route;

(2) The link connections assigned when protecting route exists. c) Client/Server relationships between layers.

The FIG.3 shows an example of a circuit route for. The resources assigned to the route are six ports, wherein two are PDH (101 ,102) (Plesionchronous Digital Hierarchy), said ports are the first PDH port (101) in network equipment PDH A, and the second PDH port (102) in network equipment PDH B; and four ports are SDH ports (103,104, 105,106) in network equipments SDH B, SDH H, SDH I and SDH M respectively.

The circuit includes seven link connections in working route. One of them is a PDH link connection (LC1) whilst the other ones are SDH link connections (LC2, LC6, LC7, LC8, LC9 and LC10). The circuit also includes three link connections in protecting route (LC3, LC4 and LC5)

Two coaxial fibers that link border equipments of both technologies are also included in the circuit, but are omitted for the purposes of this invention. ) The second step of the invention is the operation called "Low order trail discovery" (200) wherein these operations define groups in terms of the circuit route resource, so the following steps can obtain the different LO trails implicitly included in the initial route. They also obtain the protected segments in each trail and the network equipment collection included in them. ) This information is the input data for the third step (300. The operation collection is called "protection analysis". The operation analyzes each LO trail to get the link connections supported by end-to-end protected paths, unprotected segments and redundant protections. For the search of the different unprotected segments, it considers protection in server layer in order to avoid including it as an unprotected segment. It also considers protecting assigned route to LO trail in the initial route. The final result of these operations is a collection of link connections in protecting route to be released, because they are redundant and a collection of unprotected segments. ) The fourth step (400) consists in the operation collection called "Route Selection" that takes the previous information as data input. These operations search a minimum length protecting route for each unprotected segment in a LO trail. The search is restricted by a set of boundary conditions that establish which resources can be used or not in order to get a disjoint protecting route. It can use HO paths which offer free capacities and do not finish in any network equipment included in the initial working route, except the source and target equipments in the segment. It also has to avoid HO paths included in the working route and those supported by the same resources than HO paths included in the working route. Once the segments get their own route, the procedure tries to find a route, or a minimum set of them, that protect the maximum number of network equipments assigned in the initial working route with the minimum resource use in the new protecting route. When a route is found, the procedure collects the link connections to establish the protecting route in the network and the link connections to release in the initial protecting route. ) Finally, the fifth step (500) is called "Output Data" which composes data output to get a set of link connections to be added and a set of link connections to be released in the circuit route. The intersection of both collections must be an empty set. FIG.6 and FIG.7 detail the second step (200). The low order trail discovery begins processing the ports in the initial working route, as can be shown in FIG.6. Therefore, firstly, it gets the first port in the route that implements LO trail termination function; secondly, it searches a link connection in the working route that ends in the network equipment where the port is located. If there is none, it obtains the next port assigned to the initial route that implements LO trail termination function and repeats the search using it. If a link connection was found, a new LO trail is created. Port is assigned as source port of LO trail and the link connection is included as a resource in LO trail route. After this, it repeats the link connection search, but now the end of the link connection must be in the network equipment where the previous link connection ends (and it is not the initial processed port).

If a new link connection is not found, it gets a port in the initial route which is located in the network equipment and implements LO trail termination function. Such port is included as LO trail port target. More concretely, the FIG.6 shows how the second step (200) starts getting the first port (201). Afterwards, if the port is a low order termination port (201), it gets the link connection in equipment (202), generating a low order trail (204) or getting the next port (203) if no exists link connection. If it exists, the link connection in the next equipment is achieved (205) and add the link connection to trail (21 1 ) or get the port in the equipment (206), finishing the LO trail (207) or discarding the LO trail (212).

If the port is not a LO termination port, the procedure looks for a next port (203) and if it does not exist then looks for a existing protecting link connection (208), establishing the protecting link connection treatment (209) or finishing the procedure (210).

The previous procedure is repeated until all the ports in the initial working route have been processed.

After the procedure where LO trails have been obtained, if there is a protecting route assigned to initial circuit route, the procedure will assign it to a LO trail, so it will repeat the next steps until all link connections are processed (see FIG.7). Firstly, it obtains the first link connection (213) which ends in a network equipment included in a LO trail working route. It creates a new protecting segment (214) and establishes the network equipment as the source network equipment in the new segment. The link connection is included in the LC collection (215). Afterwards, it gets the other network equipment of LC where the LC ends:

If the network equipment is included in the working route (216), it establishes this equipment as the target one in new segments and adds (217) the segment to the LO trail protecting segment collection. The network equipments among the source and target ones are included into protected equipment collection

(218).

If the network equipment is not included in the working route (219), it searches a link connection that ends in that equipment and adds (215) the link connection to the LC collection.

The procedure repeats the steps described above until it finds the segment target equipment or processes all the link connections.

FIG.4 shows the results after applying the aforementioned these operations to the initial route. Two new LO trails are obtained. The first one (LO trail 1 ) starts at SDH Port 1 in SDH B network equipment. Target port is SDH Port 2 in SDH H equipment. Link connections LC 2, LC 6, LC 7 are included into working route of LO trail. It also generates a protecting segment between SDH C and SDH H equipments. LC 3, LC 4 and LC 5 are included into the LO trail protecting route. The protecting route is assigned to LO trail 1 because LC3 terminates in SDH C equipment and LC5 terminates in SDH H and these equipments are included into working route of LO trail. Link connection LC4 completes the segment, as it allows the signal transmission between SDH D and SDH E equipments. SDH F is added to the protected equipment collection because it is included between SDH C and SDH H equipments in the working route. The second trail (LO trail 2) starts at SDH Port 3 in SDH I. The Target port is SDH Port 4 in SDH M. The link connections LC 8, LC 9, and LC 10 are included into the LO trail working route. There is no link connection included into initial protecting route that could be assigned to LO trail 2. On the other hand, PDH Port 1 , PDH Port 2 and link connection LC1 are not included in LO trails because they are PDH ports and do not implement LO trail termination function. FIG.8 shows detailed the third step (300) of protection analysis, wherein for each LO trail, the following steps are repeated: in the first step, it checks whether the HO (high order) paths that support the link connections included in the working route are protected end-to-end; then if a HO path is protected, the link connection supported by it is included in the server layer protected collection. In addition, if one of the network equipments where the link connection ends is included into the protected equipment collection or is source or target equipment in a protecting segment, the link connection is included into the redundant link connection collection. In the second step it defines the unprotected LO trail segments according to existing protections.

In the third step, if there is no server layer protection, it generates an unprotected segment between source and target equipments in the LO trail, trying to get an end-to- end protection.

In the fourth step if no protecting segment is included in the LO trail, it generates unprotected segments for all distinct combinations between the equipments included into working route, keeping the relative order between them. The total number of generated unprotected segments is determined by the expression (((n-1)*n))/2, where n is the number of equipments included into the working route.

In the fifth step, if any protecting segment is included in the LO trail, it fixes the trail source equipment. From there, it calculates the adjacent equipment. If the adjacent equipment is not included into the protected equipment collection, a new unprotected segment is added between the source equipment and the adjacent one. If the adjacent equipment is included into the protected equipments collection, it obtains the next adjacent equipment for it. These operations are repeated until the target equipment is reached. After the source equipment is processed, the procedure continues with the others equipments included in the working route. The total number of unprotected segments generated is determined by the expression (((n-(m+1)*(n-m))/2, where n is the number of equipments included into the working route and m is the number of protected equipments which are not the source and target equipments in the LO trail. In the sixth step, if there is server layer protection, it chooses the first equipment in the route where no link connection included in server layer protection the collection ends. From that source equipment, it repeats the following operations for all the equipments in the working route:

- It fixes the adjacent equipment as the current equipment.

If a link connection in the server layer protection collection ends in the current equipment, the procedure adds a new unprotected segment between the source equipment and the current equipment. Next, it chooses the equipment to continue. This equipment is the first adjacent one in the working route that is not the end equipment of a link connection in the server layer protection collection and is not included in the protected equipment collection.

- If it does not find a link connection in the server layer protection which ends in this equipment, and the equipment is not included in the protected equipment collection, the procedure adds a new unprotected segment between source equipment and current equipment. The total number of generated unprotected segments depends on where the server layer protections are located inside the working route.

In the example route (FIG.3 and FIG.4), if these operations are applied to LO 1 trail, the following result is obtained:

Case 1) There is no end-to-end protected HO path. The procedure obtains the following segments:

a) Segment between SDH B equipment and SDH H equipment. This segment is created for obtaining an end-to-end L01 trail protection.

b) Segment between SDH C equipment and SDH H equipment. This segment is created for obtaining an optimized route using fewer resources than the initial one.

c) Segment between SDH B equipment and SDH C equipment. This segment is unprotected in the initial route.

Case 2) HO Path F-H is end-to-end protected. The link connection that supports (LC 7) is added to the redundant link connection collection. The procedure obtains the following segments:

a) Segment between SDH B equipment and SDH F equipment. This segment is created for generating a SNCP that includes the remaining equipments in the working route.

b) Segment between SDH C equipment and SDH F equipment. This segment is a protected segment in the initial route after cleaning the redundancy,

c) Segment between SDH B equipment and SDH C equipment. This segment is unprotected in initial route. If these operations are applied to LO 2 trail, the following result is obtained:

a) Segment between SDH I and SDH M equipments.

b) Segment between SDH I and SDH L equipments.

c) Segment between SDH I and SDH K equipments.

d) Segment between SDH K and SDH M equipments.

e) Segment between SDH K and SDH L equipments.

f) Segment between SDH L and SDH M equipments.

Case 2) HO Path K-L is protected end-to-end. The link connection that supports (LC 9) is added to the redundant link connection collection. The procedure obtains the following segments:

a) Segment between SDH I and SDH K equipments.

b) Segment between SDH L and SDH M equipments.

In the FIG.9 it shown the details of the fourth step (400) of route selection, wherein for each LO trail, the procedure follows the next steps:

In the first step, for each unprotected segment that was found in the LO trail, for each link connection in the circuit working route, the procedure adds the HO path that supports the link connection to the unauthorized path collection. It also adds HO paths supported by same resources than HO path that support the link connection. If the link connection source equipment is different to source and target equipments of the segment, the source equipment is added to the unauthorized equipment collection. If the link connection target equipment is different to the source and target equipments of segment, the target equipment is added to the unauthorized equipment collection. Then, it searches an alternative route for the segment. The new route cannot include paths that are included in the unauthorized path collection or end in equipments included in the unauthorized equipment collection. If the procedure finds a route, it adds the route to the route collection. In the second step, if the route collection is not empty, the procedure continues with the treating of routes (see FIG.10), wherein if there exists any route that ends in the same source and target equipments than the LO trail, the procedure obtains the link connections supported by paths included in the route and adds them to the link connections added collection. If any protecting segment is included in the LO trail, the procedure adds the link connections included in those segments to the link connection released collection. Otherwise, the procedure binds routes by their source and target equipments and creates new segments. These segments are sorted by number of equipments in the LO trail working route. Therefore, if there is no redundant link connection, the procedure continues with the treatment of the segments (FIG.11). However, if there is any redundant link connection, the procedure continues with the treatment of segments with redundancy (FIG.12).

More concretely, the treatment of segments (FIG.10) processes the defined segments in the following way: firstly, it is selected the segments that include the maximum number of equipments in the LO trail working route. If more than one segment is selected, it searches the segments that include the minimum number of routes. If more than one segment is still selected, it searches the first segment with the minimum number of equipments included in the route.

Secondly, it continues with the complete route sub-process (FIG.13). From the route obtained in the above step, these operations try to complete the LO trail protecting route trail adding routes included in other segments. The procedure selects segments that end in equipments located before the route source equipment in the initial working route. It also selects segments which source equipment is situated after the target equipment in the working route. If more than one segment is selected, the procedure applies the above described criteria. These operations are repeated until the source and target equipment of LO are reached. Eventually, if any protecting segment is included in LO trail, the link connections belonging to the initial protecting route which protect the equipments that are protected in new route are added to the link connection released collection.

More concretely, the operation of treatment the segments with redundancy (see FIG.12) process segments in the following way: It selects segments that include the maximum number of equipments in the working route and which target equipment is equal to the source equipment of the first link connection included into redundant link connection collection. If the procedure does not find a segment, it removes the redundant link connection of the collection. It also removes the segments which source equipment is equal to source or target equipment of the redundant link connection. If the target equipment of redundant link connection is different than protecting segment in initial route, it removes segments which source equipment is equal to target equipment of redundant link connection. If there are more redundant link connections in the collection, the procedure repeats the operations for each one. Otherwise, the procedure selects a new route as is described in the above step of treatment segments.

If the procedure finds at least one segment, it searches the segments that include the minimum number of routes. If more than one segment is still selected, it searches the first segment with the minimum number of equipments included in the selected route. The procedure adds the segment link connections to added link connections collection.

It gets protecting segment in initial route which redundant link connection is included in. Procedure validates that resources protected in initial route are protected in new route. If target equipment of redundant link connection is different than target equipment of protecting segment:

Procedure searches segments that include maximum number of equipments in working route and which source equipment is the same than target equipment of redundant link connection.

If it finds any segment, procedure repeats the operations described in above step.

If it finds no segment, procedure validates if there is another redundant link connection in collection which source equipment is the same than target equipment of redundant link connection previously treated.

If it finds any link connection, the procedure repeats this step with the new link connection.

Otherwise, it means that new route does not protect resources that are protected in initial route. Procedure removes link connections previously added into link connections added collection and discards all segments that include protected equipments of protecting segmented in initial route. If the initial protected resources are also in the new route, the link connections included in the protecting segment are added to the released link connection collection. These operations are repeated until the redundant link connection collection is treated completely.

Finally, the procedure finishes treating the remaining segments as described in step of treatment segments.

In the example route, if these operations are applied to LO 1 trail, and HO Path F-H is protected end-to-end (case 2), the procedure searches an alternative route for the following segments:

Segment between SDH B equipment and SDH F equipment. Alternative route cannot include SDH C, SDH H, SDH I, SDH K, SDH L and SDH M equipments. Segment between SDH C equipment and SDH F equipment. Alternative route cannot include SDH B, SDH H, SDH I, SDH K, SDH L and SDH M equipments.

- Segment between SDH B equipment and SDH C equipment. Alternative route cannot include SDH H, SDH I, SDH K, SDH L and SDH M equipments. It also cannot include HO Path B-C.

As an example of a possible route search result, the following alternative routes could be obtained:

- Route between SDH B and SDH F equipments: Route includes HO Path B-N, HO Path N-0 and HO Path O-F

- Route between SDH C and SDH F equipments: Route includes HO Path C-0 and HO Path O-F.

- Route between SDH B and SDH C equipments: Route includes HO Path B-P and HO Path P-C.

Procedure searches a route combination that protects the maximum number of equipments in the working route:

- Segment between SDH B and SDH F equipment: One route is found. It includes HO Path B-N, HO Path N-0 and HO Path O-F.

- Segment between SDH B and SDH F equipment: It is formed by a concatenation: route between SDH B and SDH C and route between SDH C and SDH F. It includes HO Path B-P, HO Path P-C, HO Path C-0 and HO Path O-F.

Segment between SDH C and SDH F equipment: One route is found. It includes HO Path C-0 and HO Path O-F.

- Segment between SDH B and SDH C equipment: One route is found. It includes HO Path B-P and HO Path P-C.

The procedure selects first and second segments because they protect the maximum number of equipments in the working route. All the equipments included in the initial protecting route are protected in both protecting segments. SDH C equipment is protected because it is situated in the working route between source and target equipments of segments. SDH F and SDH H equipments are protected because HO Path F-H is protected end-to-end. The procedure obtains three link connections supported by HO Path B-N, HO Path N-0 and HO Path O-F, and adds them into added link connection collection. It also adds the link connections included in the initial protecting route (LC 3, LC 4 and LC 5) to the released link connection collection.

In the example route, if these operations are applied to LO 2 trail, and there is no HO path protected end-to-end (case 1), the procedure searches an alternative route for the following segments:

Segment between SDH I equipment and SDH M equipment. Alternative route cannot include SDH B, SDH C, SDH F, SDH H, SDH K, and SDH L equipments.

- Segment between SDH I equipment and SDH L equipment. Alternative route cannot include SDH B, SDH C, SDH F, SDH H, SDH K, and SDH M equipments.

Segment between SDH I equipment and SDH K equipment. Alternative route cannot include SDH B, SDH C, SDH F, SDH H, SDH L, and SDH M equipments. It also cannot include HO Path l-K.

Segment between SDH K equipment and SDH M equipment. Alternative route cannot include SDH B, SDH C, SDH F, SDH H, SDH I, and SDH L equipments. Segment between SDH K equipment and SDH L equipment. Alternative route cannot include SDH B, SDH C, SDH F, SDH H, SDH I, and SDH M equipments. It also cannot include HO Path K-L.

Segment between SDH L equipment and SDH M equipment. Alternative route cannot include SDH B, SDH C, SDH F, SDH H, SDH I, and SDH K equipments. It also cannot include HO Path L-M.

- Route between SDH I and SDH M equipments: No route is found.

- Route between SDH I and SDH L equipments: Route includes HO Path l-R, HO Path R-S and HO Path S-L.

- Route between SDH I and SDH K equipments: Route includes HO Path l-R and HO Path R-K.

- Route between SDH K and SDH M equipments: Route includes HO Path K-S, HO Path S-T, HO Path T-U and HO Path U-V.

- Route between SDH K and SDH L equipments: Route includes HO Path K-W, HO Path W-L.

- Route between SDH L and SDH M; equipments: Route includes HO Path L-V, HO Path V-M.

There is no alternative route that protects LO 2 trail end-to-end. Procedure searches a route combination that protects the maximum number of equipments in the working route. The following combinations protect LO trail end-to-end:

Segment between SDH I and SDH M equipments: It is a concatenation of route between SDH I and SDH L and route between SDH L and SDH M. It includes HO Path l-R, HO Path R-S, HO Path S-L, HO Path L-V and HO Path V-M. Six equipments are included in this route (SDH I, SDH R, SDH S, SDH L, SDH V and SDH M).

- Segment between SDH I and SDH M equipments: It is a concatenation of route between SDH I and SDH K and route between SDH K and SDH M. It includes HO Path l-R, HO Path R-K, HO Path K-S, HO Path S-T, HO Path T-U and HO Path U-M. Seven equipments are included in this route (SDH I, SDH R, SDH K, SDH S, SDH T, SDH U and SDH M).

Segment between SDH I and SDH M equipments: It is a concatenation of route between SDH I and SDH K, route between SDH K and SDH L and route between SDL and SDH M. It includes HO Path l-R, HO Path R-K, HO Path K- W, HO Path W-L, HO Path L-V and HO Path V-M

The last segment is discarded because it is the combination with maximum number or routes. The procedure selects the first segment because it includes the minimum number of equipments. Finally, the procedure obtains five link connections supported by HO Path l-R, HO Path R-S, HO Path S-L, HO Path L-V and HO V-M and adds them into link connections added collection

The FIG.5 shows the new circuit protecting route.

Example of implementation of the invention An example of implementation for the present invention is the following embodiment description. There are others possible implementations for the invention.

In the present embodiment, the invention is implemented in a multi-threading computational system composed of a processor unit, a memory unit, an input/output (I/O) unit, and a data storage unit. The topology of SDH network and the client/server relationships are stored in a database into data storage unit. The circuit to be analyzed can be provided by a human who uses I/O unit.

In the present embodiment, the second step (200) of low order trail discovery is implemented as a computer program. It receives data of the circuit from I/O unit and performs the operations described in figures 5 and 6. It obtains needed data from database in order to determine the resources restrictions. It stores LO trails data in the memory unit. The third step (300) of protection analysis is implemented as a computer program. It obtains LO trails data from memory unit. Each LO trail is analyzed in a different thread in order to minimize time required to perform the whole operation. For each HO link connection included into LO trail route, it accesses database to obtain HO paths route. For each link connection occupied by HO Path, it accesses to the database to get needed data which determine whether it is involved in SNCP, MSP or MS-SPring protection. If every link connection is protected then HO path is stored into the protected server layer collection in the memory unit. If HO link connection is protected in initial route then it is stored into the redundant link connection collection in the memory unit. It also calculates unprotected segments and stores them in the memory unit. In the present embodiment, the fourth step (400) of route selection is implemented as a computer program. It obtains LO trails and unprotected segments from memory unit. For each LO trail, it launches a thread to search a route for each unprotected segment. The search is based on Spanish patent application P200930989 (Procedure for searching vacancy routes in complex networks with boundary conditions in a transport network) and Dijkstra's algorithm. Available resources are stored in the memory unit.

Any topological change is notified for changing available resources. The search is limited by time (2 minutes) and by route length (12 equipments). The HO paths included into the initial working route, except source and target equipment of the segment, are considered as unavailable resources. HO paths supported by same resources than HO paths, which are included in initial working route, are also considered as unavailable resources. These paths are obtained from database. The routes and segments are stored in the memory unit.

The operation collections "Treat routes", "Treat segments" and "Complete route" are also implemented as a computer program. It reads routes and segments from the memory unit and generates a collection of link connections to be added to the set and a collection of link connections to be released. The link connections to be added are obtained from database. Finally, these collections are shown in the output unit.

Advantages of the Invention

This invention provides a method to analyze circuit protecting routes. The advantages obtained would be: it allows increasing efficiency in the design of new protected circuits, reducing the operations needed to get a protecting route that includes the maximum number of resources assigned in the working route. Also, it reduces the number of resources included in protecting routes, providing a new optimized route. Finally, it reduces the total network cost, releasing unnecessary resources in protecting route and avoiding adding new equipment to the network topology.

Claims

1.- A method for analyzing protecting routes in lower-layer paths over a SDH network, comprising obtaining at least one lower order layer trail and finding a protecting route therein, characterised in that it comprises:

- analysing said at least one lower order layer trail considering its working and protecting routes;

- obtaining, from said analysis, protected and unprotected working route segments, said unprotected segments defined as those not having protection in their protecting route or in higher-order layer paths that support the working route;

2 - Method according to claim 1 , comprising the steps of: (i) inputting data (100); (ii) discovering the low order trail (200); (iii) analysis of the protection (300); (iv) selection of the route (400); and (v) outputting the data (500), wherein:

the first step (100) of inputting data defines the needed data input including a topological SDH network structure, the circuit to be analyzed and the client/server relationships between layers;

the second step (200) of discovering the low order trail define groups in terms of the circuit route resource, and it is arranged to obtain the different low order trails implicitly included in the initial route and the protected segments in each trail and the network equipment collection included in them;

the third step (300) of protection analysis that is arranged to analyze each low order trail to get the link connections supported by end-to-end protected paths, unprotected segments and redundant protections; and wherein the final result of these operations is a collection of link connections in protecting route to be released, because they are redundant and a collection of unprotected segments;

the fourth step (400) of route selection that takes the previous information as data input and is arranged to search a minimum length protecting route for each unprotected segment in a low order trail, being the search restricted by a set of boundary conditions that establish which resources can be used or not in order to get a disjoint protecting route; and wherein the segments get their own route, the method starts to find a route, or a minimum set of them, that protect the maximum number of network equipments assigned in the initial working route with the minimum resource use in the new protecting route; and when a route is found, it collects the link connections to establish the protecting route in the network and the link connections to release in the initial protecting route; and

the fifth step (500) finally composes the data output to get a set of link connections to be added and a set of link connection be released in the circuit route.

3. - Method according to claim 2 wherein in the third step (300) for the search of the different unprotected segments, it is considered the protection in the server layer in order to avoid including it as an unprotected segment, and it is also considered to protect the assigned route to low order trail in the initial route.

4. - Method according to claim 2, wherein in the fourth step (400) for the route selection it can be used high order paths which offer free capacities and do not finish in any network equipment included in the initial working route, except the source and target equipments in the segment; and it also has to avoid high order paths included in the working route and those supported by the same resources than high order paths included in the working route.

5. - Method according to any of claims 2 to 4, wherein in the second step (200) the low order trail discovery begins processing the ports in the initial working route and, firstly, it gets the first port in the route that implements LO trail termination function; secondly, it searches a link connection in the working route that ends in the network equipment where the port is located; wherein if there is none, it obtains the next port assigned to the initial route that implements LO trail termination function and repeats the search using it.

6. - Method according to claim 5, wherein if a link connection if found, a new LO trail is created; and wherein the port assigned as source port of LO trail and the link connection is included as a resource in LO trail route; after this, it repeats the link connection search, but now the end of the link connection is in the network equipment where the previous link connection ends.

7.- Method according to claim 5, wherein if a new link connection is not found, it gets a port in the initial route which is located in the network equipment and implements LO trail termination function, wherein such port is included as LO trail port target.

8. - Method according to any of claims 5 to 7, wherein after the procedure where LO trails have been obtained, if there is a protecting route assigned to initial circuit route, the procedure will assign it to a LO trail according with the following steps: firstly, it obtains the first link connection (213) which ends in a network equipment included in a LO trail working route; then it creates a new protecting segment (214) and establishes the network equipment as the source network equipment in the new segment.; secondly, the link connection is included in the LC collection (215) and it gets the other network equipment of LC where the LC ends:

If the network equipment is included in the working route (216), it establishes this equipment as the target one in new segments and adds (217) the segment to the LO trail protecting segment collection; and the network equipments among the source and target ones are included into protected equipment collection (218); or

If the network equipment is not included in the working route (219), it searches a link connection that ends in that equipment and adds (215) the link connection to the LC collection;

and wherein these steps are repeated until it finds the segment target equipment or processes all the link connections.

9. - Method according to claim 2, wherein the third step (300) of protection analysis comprises the steps of: (i) checking whether the HO (high order) paths that support the link connections included in the working route are protected end-to-end; (ii) defining the unprotected LO trail segments according to existing protections; (iii) if there is no server layer protection, it generates an unprotected segment between source and target equipments in the LO trail, trying to get an end-to-end protection; (iv) if no protecting segment is included in the LO trail, it generates unprotected segments for all distinct combinations between the equipments included into working route, keeping the relative order between them; (v) if any protecting segment is included in the LO trail, it fixes the trail source equipment and calculates the adjacent equipment until it obtains an equipment which is included in protection equipment collection in order to add a new unprotected segment between source equipment and the obtained equipment, it stops when target equipment is reached; and (vi) if there is server layer protection, it chooses the first equipment in the route where no link connection included in server layer protection the collection ends and it generates unprotected segments which involves equipments not included into server layer protection; and wherein the total number of generated unprotected segments depends on where the server layer protections are located inside the working route.

10.- Method according to claim 2, wherein the fourth step (400) of route selection, for each LO trail, it comprises the following steps:

(i) for each unprotected segment that was found in the LO trail and for each link connection in the circuit working route, the procedure adds the HO path that supports the link connection to the unauthorized path collection, and also adds HO paths supported by same resources than HO path that support the link connection; and

(ii) if the route collection is not empty, the procedure continues with the treating of routes wherein if there exists any route that ends in the same source and target equipments than the LO trail, the procedure obtains the link connections supported by paths included in the route and adds them to the link connections added collection, and if there is no redundant link connection, the procedure continues with the treatment of the segments; or if there is any redundant link connection, the procedure continues with the treatment of segments with redundancy.

11.- Device for analyzing protecting routes in lower-layer paths over a SDH network comprising the means to perform the method of any of the claims 1 to 10.

12.- Telecommunication network comprising the device for analyzing protecting routes in lower-layer paths of claim 11.