DE9304560U1 - Circuit arrangement for routing telecommunications connections in a meshed network - Google Patents

Description

6 1 1 3 7 EN

Siemens AG

Circuit arrangement for routing telecommunications connections in a meshed network

The term meshed network or mesh network refers to communications networks without a hierarchy of nodes, in which each node is connected to at least two other nodes. A fully meshed network exists when each node is directly connected to every other node in the network. In a meshed network configuration with routing of telecommunications connections, there is a risk of loops forming in the case of so-called bundle bottlenecks, which occur across several network nodes. If the bundle bottleneck that led to the loop formation is not eliminated, the telecommunications connection runs through the loop until all paths are occupied.

A method for searching for an alternative path in a communication network is already known from the published European patent application with the application number 90 125 088.6. In the context of the known method, the entire network must first be checked for the failure of one or more nodes and/or the failure of one or more connection paths between two nodes. Then, the nodes affected by the detected failures must be identified in each path. After that, a message called a "restoration message" must be created, which includes an identification number for the sender node and identification numbers for the nodes affected by the failures. It must also be checked whether one of the latter nodes represents the end node of an alternative path. Finally, an alternative path is determined by the communication network. Overall, the known method requires a large number of process steps, with the result that the controls involved in the method are subjected to considerable strain.

01 01

6 1 1 3 7 EN

A method called "telecommunications network route selection" is already known from the published European patent application with the application number 90 311 577.2. The selection of a route from a message source to a message destination is carried out, among other things, using so-called "busy/idle status information", which is to be created and managed network-wide. In this context, a so-called "source destination restriction map" is also created in each network node.

In such a table, for connections from certain source nodes to another network node, it is specified which connection routes outgoing from this network node are permissible. However, network loops are not excluded: for a connection from a source node (e.g. source "2") to the other node (e.g. "1"), a connection route (e.g. "20") can be specified as permissible, over which the connection has already been routed (FIG 1: 2-11-2-20-3,-20...).

Methods for setting up telecommunications connections are already known from the German patent DE 36 26 870 as well as from the explanatory documents 1 512 858 and 1 487 989, whereby it is partly provided that information identifying the originating switch is inserted into the signaling information. However, in the previously known methods, this information is not used to prevent loops from forming. In the method previously known from the German patent DE 36 26 870, a digital telecommunications network is divided into so-called routing cells, each of which consists of several signaling points. Within a routing cell, only certain signaling routes between the signaling points are released for selection from possible signaling routes, progressively in the destination direction, whereby the circulating of signaling messages within a routing cell is avoided. In the method previously known from the German explanatory document

01 02

6 1 1 3 7 EN

In the method known from German patent application 1,512,858, connections are made via a relay station designed as a satellite, whereby a free speech path is selected in the forward direction and whereby a occupancy signal with an identity symbol identifying the selected speech path and the originating exchange is transmitted to the destination exchange. In the method known from German patent application 1,487,989, additional information is provided about the suitability of the path to be taken and/or the path traversed. This method also provides for the creation of information which identifies the number of connection sections traversed, whereby test equipment is provided in transit exchanges to check this information and whereby further path searches are aborted when a maximum, predetermined number of connection sections traversed on the relevant path is reached.

A communication system ("HICOM 300") that can form a network node in a meshed network is already known from the Siemens product brochures "HICOM 300 System Product Data", Ordering No. A19100-K3161-430-X-7600, pages 55/56, and "Private Communication Systems, HICOM creates Connections", Order No. A19100-K3160-A302, page "HICOM 300 Networking". For telecommunications connections to be set up via transit nodes, it can be provided that transit nodes use a node number identifying the destination node to check whether a telecommunications connection to the destination node is permissible. However, when telecommunications connections are set up in this way, there is a risk of network loops forming.

From the Siemens product brochures "HICOM 300 System Product Data", Ordering No. A19100-K3161-430-X-7600, pages 55/56, and "Private communication systems, HICOM creates connections", Order No. A19100-K3160-A302,

01 03

G 1 1 3 7 EN

A communication system ("HICOM 300") is already known on the "HICOM 300 Networking" page that can form a network node in a meshed network. For telecommunications connections to be set up via transit nodes, it can be provided that transit nodes use a node number identifying the destination node to check whether a telecommunications connection to the destination node is permissible. However, with such a setup of telecommunications connections there is a risk of network loops forming.

The invention is therefore based on the object of specifying an arrangement for routing telecommunications connections in a meshed network in which the risk of loop formation is reduced.

This object is achieved according to the invention with the features of patent claim 1.

The solution according to the invention requires neither any modifications to the meshed network nor any intervention in the hardware structure of the network nodes, which are designed in particular as switching centers. The control program assigned to these network nodes only needs to be modified slightly. The solution according to the invention reduces or eliminates the risk of loop formation; this also creates the conditions for improved traffic utilization.

The embodiment of the invention according to claim 3 supports the measures according to claims 1 and 2 in particular also in meshed networks with a large number of nodes. By combining the measures according to claims 1 and 3, as well as the inventive arrangement according to claim 2, the risk of network loops forming can be completely eliminated.

01 OA

G 1 1 3 7 EN

Further advantageous embodiments of the invention are characterized in the subclaims.

The invention will now be described with reference to the drawings. It shows

FIG 1 a meshed network;

FIG 2 and 3 Tables showing transit nodes in the network according to

FIG 1 are assigned,

FIG A is a block diagram of the circuit arrangement according to the invention and FIG 5 shows the structure of the transit nodes according to the

FIG 1 to 3 formed signaling information

tions.

FIG 1 shows a meshed network with several nodes. A telecommunications connection is to be set up from a telecommunications device A (e.g. telephone terminal, fax machine, etc.) to a telecommunications device B. The network nodes have the function of an origin node ON, a transit node TNx and a destination node DN. For example, seven transit nodes TN 1 ... TN 7 are provided, which are connected to one another as shown in FIG 1. This allows a telecommunications connection to be set up between the telecommunications devices A and B in various ways: for example on the path 0N-TN6-DN, 0N-TN2-TN4-DN and 0N-TN2-TN3-TN5-TN7-TN6-DN.

These examples illustrate that telecommunications connections can be established in different ways, over a different number of nodes and distances between the source node ON and the destination node DN or between the facilities A and B. These possibilities arise due to the meshed structure of the network and a corresponding configuration of the network nodes, ON TN1,...TN7, DN, to which a node-specific number KON, KTN1, ... KTN7, KDN is assigned. For example,

01 05

G 1 1 3 7 EN

these nodes - as shown in FIG 1 - are assigned the node numbers 20...28. The method according to the invention is initiated by entering the telephone number of the receiving telecommunications terminal B into the transmitting telecommunications terminal A. This B telephone number, e.g. 95-1234, consists of a code number (here: 95), which designates, for example, an extension range "95", and an extension number 1234.

In addition to the B telephone number (95-1234), information identifying the originating node number KON (here: 20) is also inserted into the signaling information of the telecommunications connection to be set up. The telecommunications connection is now fed in a known manner according to the given network structure either to the transit node TN1, the transit node TN6 or the transit node TN2. It is now assumed that, due to the current traffic situation, the telecommunications connection is routed from the originating node ON to the transit node TN2. For this purpose, the corresponding signaling information, which - as already described - contains the B telephone number (95-1234) and the originating node number KON (20), is fed to the transit node TN2. The control (CTN, FIG 4) of the transit node TN2 assigns the code 95 contained in the B telephone number to the destination node number 28.

Each node is assigned a table that specifies permissible connections depending on the source node ON and destination node DN. These connections are identified, for example, by the numbers of the nodes through which the permissible connections are to be routed. Examples of such tables are shown in FIGS. 2 (embodiment of the invention according to claim 1) and 3 (embodiment of the invention according to claim 2). FIGS. 2a and 3a each show a table for the transit node TN2 and FIGS. 2b and 3b each show a table for the transit node TN4.

01 06

6 1 1 3 7 EN

If, as previously described, a telecommunications connection reaches the transit node TN2 with node number 22, the control of this node uses the table shown in FIG 2a) to determine which network nodes permissible connections can be established, depending on the node number (20) for the source node and depending on the node number (28) of the destination node. These are, as shown in the table in FIG 2a), network nodes 23 and 2A. In contrast, a connection from the node TN2 with node number KTN2 = 22 to the source node ON with node number KON = 20 is not permissible. The telecommunications connection is therefore routed either to node 23 or to node 2A. The process steps that were already carried out in node TN2 = 22 are then carried out in these nodes 23 and 2A.

In node 2A, the corresponding node control (FIG A: CC (CTN)) accesses the table shown in FIG 2b) and determines nodes 23, 26, 27 and 28 as permissible follow-on nodes. This prevents the telecommunications connection to be established from being returned to nodes 21 or 22.

The network node controllers check for permissible paths to neighboring nodes, as already described, based on the source node number transmitted in the signaling information. On the other hand, it is particularly intended that the destination node code (“direction code”, here: 95), which was selected on the transmitting side and is also transmitted in the signaling information, is converted by the network node controllers into the destination node number (here: 28).

The method described above with reference to FIG 2 thus reduces the risk of network loops forming. The risk of network loops forming is reduced by the following embodiment of the circuit according to the invention.

01 07

G 1 1 3 7 EN

arrangement is excluded. It is provided that, for the telecommunications connection to be set up, a node number identifying the respective node is inserted into the signaling information assigned to the telecommunications connection in each transit node through which the telecommunications connection passes. In the case of a telecommunications connection that is routed from the originating node ON = "20" to the transit node TN2 "22", the signaling information contains - apart from other information (FIG. 5) - only the node number of the originating node, but not the node number of a transit node passing through, as in the embodiment of the invention described with reference to FIG. 2a).

In the transit node "22", the node number of the permissible nodes is determined based on the node number "20" of the source node ON and the destination node number 28. These are nodes 23 and 24. For this first transit node 22, which is immediately downstream of the source node, the same permissible nodes 23 and 24 result as in the example shown in FIG 2a).

In FIG 3b), in which, as in FIG 3a), the permissible nodes are specified depending on the upstream network nodes and the destination node, exemplary combinations of source nodes and upstream nodes are specified for the network node TN4 (20, 20-22, 20-21-23, ...).

If, for example, the telecommunications connection was routed via nodes 20 and 22, where the node number information "20" and "22" was inserted into the signaling information, the connection can alternatively be routed via nodes 23, 26, 27 or 28. In contrast, connection paths via nodes 21 and 22 are excluded, so that network loops starting or continuing in these nodes are prevented.

01 08

G 1 1 3 7 OE

The nodes are in particular communication systems, which are disclosed in the published European patent applications EP 0 306 693 A1 (US-PS 4,903,258), EP 0 303 870 A2 (US-PS 5,018,097) and EP 0 303 869 A1 (US-PS 5,047,923). In FIG 4 only the components of the circuit arrangement required for understanding the invention are shown: This includes a controller CC (CTN), a switching network SN and connection units LTUl...LTUn. These connection units include subscriber connection circuits and line set circuits. The subscriber connection circuits are subscriber-oriented device connections, such as ISDN basic connections for digital mono- and multifunctional terminal devices. The line set circuits are used to connect to public and/or private networks and are, for example, ISDN basic connections for ISDN trunk traffic and ISDN cross-traffic.

The subscriber connection and line set circuits have the same system-internal interfaces. They couple the individual base channels on which user data, i.e. voice and/or data information, is transmitted to any selection of 2 multiplex channels with, for example, 32 channels of the switching network SN and transfer the signaling information transmitted in a control channel as an HDLC protocol to the control CC (CTN). This control is assigned a memory MEM in which the table information shown in FIGS. 2 and 3 is stored. The table information can be configured in particular via operational commands that are to be entered into an operational unit ADS. A first threshold value, which specifies a maximum number of paths to be traversed in the network, and optionally a second threshold value, which specifies a maximum number of satellite paths to be traversed, can also be entered into the ADS unit (cf. claims 3 and 4). The communication shown in FIG 4

01 09

G1137DE

&iacgr;&ogr;

nication system, which forms the node TNA, for example, establishes connections to neighboring nodes, for example to the nodes TN2 and TN7.

The meshed network shown in FIG 1 can, for example, be a network for which the well-known CorNet protocol is implemented (Siemens Aktiengesellschaft Private Communication Systems and Networks Division: "CorNet Signalling for ISDN Communication in Corporate networks", Ordering No. A19100-K3110-G284-X-7600, Berlin and Munich 1987; "CorNet functional specification"). The connection setup message can be structured as in FIG 5a). This message consists of the following information elements: Protocol discriminator, Call reference, Message type, ... Called party number, ... Calling party number, ... Transit Counter, ... Equipment Identification, ... Satellite Counter ...

The information element "Protocol discriminator" indicates the protocol type, e.g. CorNet; "Call reference" indicates a running process number and "message type" indicates the type of signaling message, here: "connection setup" (setup).

The "called party number" (B-number) contains, in addition to the actual telephone number as already described, the area code (95), which is assigned to the destination node DN (28).

The information element "Calling party number" refers to the α-number, which is supplemented by the code number assigned to the originating node in the case of number signaling in open numbering. If the originating node number is not contained in the signaling information in the method according to the invention or cannot be evaluated by a network node controller, this evaluates

01 10

6 1 1 3 7 OE

When evaluating the tables according to FIGS 2 and 3, the source node identification number is converted into the source node number.

The information element "Transit Counter" indicates the number of passing nodes (see claim 3).

The information element "equipment identification", which will be described with reference to FIG 5 b), indicates the node number (20) of the originating node ON and, if applicable, the numbers (e.g. -22-24-) of the nodes (TN2, TNA, ...) to which the telecommunications connection was routed (concatenation of the node numbers, FIG 3b)).

The information element "Satellite Counter" indicates the current number of routes that are routed between two network nodes via satellite, as well as the maximum permissible number of these routes ("second threshold").

FIG 5b) shows the structure of the information element "equipment identification", which consists of several parts, each with 8 bits (octet 1). In octet I (information element identifier), an information element-specific identifier is specified for the information element "equipment identification"; in octet 2, the length of the information element (number of octets) is specified. In octet 3, it is specified that node numbers are specified in the following octets. This is the original node number (claims 1 and 2) or the node numbers of further passing nodes (claim 2). "1 ext." or "0/1 Ext." in the 8th bit position indicates whether information specified in an octet is continued in the following octet.

Connections that originate in the public office and are to be routed to a receiving telecommunications terminal B connected to a network node receive

01 11

G U 37 OE

a fictitious originating node number, so that exchange connections can also be checked against the destination node number in each transit node using this node number. Connections from other nodes or networks that cannot signal the originating node number also receive a fictitious originating node number based on the setup of the incoming bundle. In general, any network node can be connected to a network-external transmitting telecommunications terminal A ¹ , whereby this network node forms a fictitious originating node number for A ¹ and inserts this corresponding information into the telecommunications connection.

In the circuit arrangement according to the invention, it is further provided that the number of nodes passing through, in particular transit nodes passing through, is counted and compared with a predeterminable first threshold value. The connection to be set up is only routed to another node if the number of nodes to be passed through is less than or equal to a predefined threshold value. To implement this function, the information element "Transit Counter" is provided in the connection setup information (FIG 5a). It can also be provided that the connection to be set up is routed between two nodes via satellite. Overall, a plurality of such connection paths can be provided between two network nodes. In order to limit the number of these satellite paths that can be occupied during the course of a connection setup, a so-called SATELLITE counter (FIG 5a) can be implemented using appropriate software procedures. The number of connection path sections between two nodes via satellite is counted. In the network nodes that are subordinate to the source node, this numerical value is compared with a second threshold value. The telecommunications connection to be established is only routed to another node via satellite if

01 12

92 G 1 1 3 7 EN

if the number of connection sections routed via satellite is less than or equal to a specified threshold.

222 01

Claims (5)

G 1 1 3 7 DE IA Protection claims 1. Circuit arrangement for routing telecommunications connections in a meshed network, whereby the telecommunications connections are routed from a transmitting-side telecommunications terminal (A) via an originating node (ON), via transit nodes (TN1,... TN7) and a destination node (DN) to a receiving-side telecommunications terminal (B), and whereby in transit nodes (TN1,... TN7) it is checked on the basis of first information identifying the destination node (DN) whether a telecommunications connection to the destination node (DN) is permissible, and wherein a second piece of information identifying the originating node (ON) is inserted into a piece of signaling information associated with the telecommunications connection to be established, characterized in that in transit nodes (TNx) the immediately following node (TNx+1, DN) to be traversed is determined on the basis of the second and first information. 2. Circuit arrangement according to claim 1, characterized in that for the telecommunications connection to be set up in each transit node (TN2, TN4) to which the telecommunications connection is routed, a third piece of information identifying the respective node (TN2, TNA) is inserted into the signaling information assigned to the telecommunications connection, and that in each transit node (TN2, TNA) the immediately following node to be traversed (e.g. TNA) is determined on the basis of the first, second and third pieces of information identifying the originating node (ON) and the transit nodes traversed (e.g. TN2). 03 01 G 3 7 EN 3. Circuit arrangement according to one of the preceding claims, characterized in that for a telecommunications connection to be set up, in each node to which the telecommunications connection to be set up is routed, the number of nodes previously passed through is increased by the number "1", that this number increased by "1" is compared with a predeterminable first threshold value, and that the connection to be set up is only routed to a further node if the number increased by "1" is less than or equal to the first. 4. Circuit arrangement according to one of the preceding claims, characterized in that the telecommunications connection to be established is routed via satellite between two nodes (ON, TN1; TN1, TN2; ...), that the number of connection path sections routed via satellite between two nodes (ON; TN1; TN1, TN2; ...) is counted and compared in the nodes (TN1,...TN7, DN) with a second threshold value, and that the telecommunications connection to be established is only routed via satellite to another node if the number of connection path sections routed via satellite is less than or equal to the second threshold value. 5. Circuit arrangement according to one of the preceding claims, characterized, that any node (ON, TN1, TN7, DN) of the network can be connected to a network-external transmitting telecommunications terminal (A ¹ ), that this node (ON, TN1, ... TN7, DN) inserts its own second information, designating a fictitious originating node, into the telecommunications connection for this telecommunications terminal (A ¹ ). 03 02