WO2006051033A1

WO2006051033A1 - Method of protecting engineering order wire

Info

Publication number: WO2006051033A1
Application number: PCT/EP2005/055357
Authority: WO
Inventors: David Cornish; Ian Bullock
Original assignee: Ericsson Ab
Priority date: 2004-11-11
Filing date: 2005-10-19
Publication date: 2006-05-18
Also published as: GB0424866D0; GB2420243A

Abstract

A method of protecting Engineering Order Wire in a network with a ring topology the network comprising a master node and at least one slave node. The method comprises the following steps: inserting (302) artificial breaks on the incoming and outgoing speech lines on one port of the master node. In the next step a first Ring Integrity Check code signal is periodically transmitted by said master node (402) in two opposite directions and if the first and a second Ring Integrity Check code signal are not received (306, 312) on either or both ports at a slave node, the slave node transmits (314) the second Ring Integrity Check code signal in two, opposite directions.

Description

METHOD OF PROTECTING ENGINEERING ®RDER WTRF.

Field of the Invention

The present invention relates to telecommunications networks, in general, and in particular to protection of Engineering Order Wire in a network, said Engineering Order Wire having a ring topology.

Background of the Invention

In a typical telecommunications network a plurality of nodes are interconnected by communications paths also referred to as network spans. The nodes incorporate various hardware and software that is responsible for correct routing and switching of communication within the network. The hardware and software installed at the nodes require periodic maintenance and other engineering operations like software upgrades^¹ repairs, etc. For the purpose of facilitating said operations a special voice communication channel between nodes of the network is provide to allow engineers working on different nodes of the network to communicate with each other. This special communication channel is referred to as Engineering Order Wire (EOW). EOW is independent of the main body of the telecommunications network and is for exclusive use of service engineers.

In communication networks known in the art, one example of such network 100 is with great simplification depicted on FIG. 1 and FIG. 2, if EOW is set up in a network 100 with Ring Topology the ring provides a feedback loop for speech, which causes "howlround". To handle this, one and only one artificial break must be made to the speech circuit in each ring. This is done by configuring one node in each ring as "master" 102 and all the others 104, 106, 108 as "slaves". The slaves, 104, 106, 108, each provide a speech bridge between the local handset 112, 114, 116 and both ring ports. The master 102 normally provides a speech bridge only between the local handset 110 and one ring port, isolating the other ring port's input and output. This makes the EOW network look like a straight line. However, a drawback of this solution is that any network failure 220 and 222 between two nodes will break this line in two, disrupting the EOW service. If the master 102 knows about the break, it can reinstate its isolated port by removing the artificial breaks 120, 122 and thereby reconnect all the nodes.

In solution known in the art the master node 102 periodically sends short bursts of a Ring Integrity Check code (RIC) from one of its ports, in the EOW speech path. If a slave 104, 106, 108 receives this code on either port, it simply repeats it on the other. (This logic effectively forms a "shell" around the normal speech-processing element.) Therefore, this propagates around the ring. So if the master node 102 does not detect this code being returned on its other port within a timeout, it knows the ring is broken and reinstates its isolated port. In consequence every node in the network can hear all remaining ports of the network, which is reflected by the following equations and also illustrated on FIG. 2:

A <= B + C + D B <= A + C + D C <= A + B + D D <= A + B + C

These equations describe the sources of speech from handsets at nodes on the right, heard by handsets at the nodes on the left.

The limitation on this design is that it only works for rings where a failure is bi¬ directional, as depicted on FIG. 2. This is generally only guaranteed for two-fibre optics with Automatic Laser Safety (ALS) circuitry, or single-fibre optics, or rings with a mix of these two span types. It does not work in rings where a failure can be unidirectional. This is generally true for two-fibre optics without Automatic Laser Safety circuitry, or non-optical circuits such as electrical STM-I. Summary of the Invention

Accordingly, the present invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

According to a first aspect of the present invention there is provided a method of protecting Engineering Order Wire in a network with a ring topology as claimed in claim 1.

According to a second aspect of the present invention there is provided a network with a ring topology as claimed in claim 8.

According to a third aspect of the present invention there is provided a network node for use in a network with a ring topology as claimed in claim 14.

Further aspects of the present invention are as claimed in the dependent claims.

The present invention beneficially allows for reinstating connection in EOW if the failure is unidirectional, for example in two-fibre optics networks without Automatic Laser Safety circuitry, or non-optical circuits such as electrical STM-I. The invention is also applicable to the types of network that the prior art solution was limited to (i.e. rings where a failure is bi-directional - this is generally only guaranteed for two-fibre optics with ALS circuitry, or single-fibre optics, or rings with a mix of these two span types). Additional advantage of the present invention is that it allows for identification of the faulty network span and providing this information to the network management.

Brief description of the drawings

The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

FIG. 1 is a diagram illustrating network with a ring topology and an Engineering Order Wire known in the art, FIG. 2 is a diagram illustrating network with a ring topology and an Engineering Order Wire known in the art,

FIG. 3 is a flowchart illustrating method of protecting Engineering Order Wire in a network with a ring topology in accordance with one embodiment of the present invention,

FIG. 4 is a diagram illustrating network with a ring topology and an Engineering Order Wire in accordance with one embodiment of the present invention,

FIG. 5 is a diagram illustrating a master node for use in a network with a ring topology in accordance with one embodiment of the present invention,

FIG. 6 is a diagram illustrating a slave node for use in a network with a ring topology in accordance with one embodiment of the present invention.

Description of an embodiment of the invention

The following description focuses on an embodiment of the invention applicable to optical networks. However, it will be appreciated that the invention is not limited to this application but may be applied to any other types of networks with ring topology (such as electrical STM-I).

Referring to FIG. 3 and FIG. 4 one embodiment of a method of protecting Engineering Order Wire in a communications network 100 with a ring topology according to the present invention is shown.

In the telecommunications network 100 with a ring topology that comprises a master node 402 and slave nodes 404, 406, 408 the master node 402 inserts 302 first artificial break 120 on the incoming and second artificial break 122 on the outgoing speech lines on one port of the master node 402. In the next step the master node 402 transmits 304 periodically a first Ring Integrity Check (RIC) code signal in two, opposite directions. In one embodiment the RIC code signal is sent every second. The slave nodes 404, 406, 408, when receive 306 the RIC code signal on incoming line of one port, repeat 308 this RIC code signal on outgoing line of the opposite port with the same timing. In this way the RIC code signal is propagated in the network and if there is no real break of the speech line of the EOW the RIC code signal is detected 310 on both ports of the master node 402.

One of the slave nodes 404, 406, 408 transmits 314 in two opposite directions a second Ring Integrity Check code signal (RIC2) if neither RIC 306 nor RIC2 is detected 312 on one of its ports. The RIC2 code signal is sent periodically using internal timing of the transmitting slave node. In one embodiment the RIC2 code signal is sent every second. If neither RIC nor RIC2 is detected on the slave it means that the incoming line is broken 422. Once the RIC2 code signal is detected 312 on either port of the slave node 404, 408 it is repeated 322 on the opposite port of that slave node in the same way as is done with the RIC code signal. If RIC2 code signal is detected it means that another node of the network has detected break of the incoming line. Once the RIC2 code signal is detected 316 on the master node 402, the master node 402 removes 318 the two artificial breaks 120, 122 and the slave node 406 that detected the broken network span (broken incoming line) inserts 320 an artificial break 420 on the outgoing line of the broken, 422, network span. After this operation EOW service is restored, which is reflected by the following equations and also illustrated on FIG. 4:

A <= B + C + D B <= A + C + D C <= A + B + D D <= A + B + C

Again, as in previously explained, these equations describe the sources of speech from handsets at nodes on the right, heard by handsets at the nodes on the left. Alternatively, the slave node 406 that detected the broken network span (broken incoming line) inserts 320 an artificial break 420 on the outgoing line of the broken, 422, network span just after transmitting the RIC2 and after this step the master node 402 removes 318 the two artificial breaks 120 and 122.

In one embodiment, if the input failure is detected at the non-isolatable port of the master node 402 (the port without said artificial breaks), i.e. neither RIC nor RIC2 is detected at this port, the master node 402 transmits said RIC2 code signal from the port without said artificial breaks and said RIC code signal from the opposite port.

In yet another embodiment, if the input failure is detected at the isolatable port of the master node 402, i.e. neither RIC nor RIC2 is detected at this port no action is taken as the artificial breaks are already in the right place.

In yet another embodiment the node that inserted the artificial break in response to the input failure identifies to the network management the span of the network where the artificial break is inserted. This allows for quick reaction of the service engineers and fixing the broken line without necessity of time-consuming operation of identification of the broken span.

Referring to FIG. 5 one embodiment of the network 100 node according to the present invention is shown. In this particular embodiment the presented node is the master node 402.

The master node 402 comprises speech processing unit 502 with codec & bridge and with two ports for connecting the EOW and a port for connecting a local handset 410. In more detail, in this particular embodiment in the speech processing unit 502, the incoming A-law encoded PCM speech samples from each port are converted to linear PCM. The linear PCM samples from each pair of ports are summed, re-encoded to A- law and sent to the third port. The master node 402 further comprises two Ring Integrity Check code receivers 504, 508 on the incoming lines of the two opposite EOW ports and two Ring Integrity Check code transmitters 506, 510 on the outgoing lines of the two opposite EOW ports. The master node 402 comprises also two switches 520 and 522 on both lines of one of its ports and a switch 524 on the outgoing line of the opposite port. The switches 520, 522, 524 are used to isolate port, or line, of the master node and act as the artificial breaks that prevent from development of the "howlround" effect. Another two switches 530 and 532 connect RIC or RIC2 to outputs P and Q instead of speech as required. Thus, from a user's perspective, there are short gaps in the speech. The gaps, however, are short enough that they have little effect on intelligibility.

Referring to FIG. 6 one embodiment of the network 100 node according to the present invention is shown. In this particular embodiment the presented node is the slave node 404.

The slave node 404 comprises speech processing unit 602 with codec & bridge similar to that in the master node and with two ports for connecting the EOW and a port for connecting a local handset 412. The slave node 404 further comprises two Ring Integrity Check code receivers 604, 608 on the incoming lines of the two opposite EOW ports and two Ring Integrity Check code transmitters 606, 610 on the outgoing lines of the two opposite EOW ports. RIC receiver and RIC transmitter connected to the same line but on the opposite ports of the slave node 404 are connected with control lines 612 and 614. The control line is used to trigger repetition of the RIC or RIC2 on the outgoing line once the RIC or RIC2 is received at the RIC receiver, 604, 608. The slave node comprises also switch 620 on the outgoing line of one of its ports and a switch 624 on the outgoing line of the opposite port.

The switches 620, 624 are used to isolate line, of the slave node and act as the artificial breaks that prevent from development of the "howlround" effect. Another two switches 630 and 632 connect RIC or RIC2 to outputs P and Q instead of speech as required. Again, as in case of the master node, from a user' s perspective, there are short gaps in the speech. The gaps, however, are short enough that they have little effect on intelligibility.

The RIC transmitters 510, 606, 610, on master 402 and slave nodes 404, 406, 408 are further adapted to transmit said RIC2 code signal with its own, local timing. In one embodiment the RIC2 is sent every second. On slave nodes, the RIC2 is generated and transmitted by the RIC transmitters 606, 610 only if such code signal is not received at the RIC receivers 604, 608.

In operation, the slave network node 404, 406 or 408 is adapted to transmit using the RIC transmitter 606, 610 a second Ring Integrity Check code signal in two, opposite directions if neither the first nor the second Ring Integrity Check code signal is received on either or both ports at said node. Further, if neither RIC nor RIC2 is received the node 404, 406 or 408 is adapted to insert one artificial break on the output line of a port where an input failure has been detected. The master network node 402 is adapted to transmit using the RIC transmitter 510 a second Ring Integrity Check code signal if neither the first nor the second Ring Integrity Check code signal is received on the non-isolatable port 504 at said node. Further, if neither RIC nor RIC2 is received the node 402 is adapted to insert one artificial break 524 on the output line of the same port. The master node, in addition, is adapted to remove the two artificial breaks 520, 522 on the isolated port if it receives RIC2 on said port 508.

In one embodiment the node, either master or slave, in case of input failure detected informs the network management about the failure and about the network span where the line is broken.

Operation of the master node 402 and the slave node 404 is in more detailed manner explained with reference to FIG. 5 and FIG. 6. Under no fault conditions at the master node 402, switches 520 and 522 are open and switch 524 is closed. Port P would hear R, port Q would hear nothing and port R would hear P. RIC code signal is sent to P and Q once per second.

Under no fault conditions at the slave node 404 switches 620 and 624 are closed. Port P would hear R+Q, port Q would hear P+R and port R would hear P+Q. RIC code signal or RIC2 code signal received at P would be regenerated at Q and vice versa.

In one embodiment, an input failure is reported if neither RIC nor RIC2 is received in 1 Vi seconds. However, it is clear for those skilled in the art that the time-out may have different value and it has to be longer then the time period between two consecutive RIC code signals.

If input P failed at the slave node 404 (neither RIC nor RIC2 code signals received), switch 624 is opened. RIC2 code signal is sent to Q with local one second timing. RIC2 is sent to P whenever RIC (not RIC2) was received at port Q, unless input Q had failed as well, when local one second timing would again have to be used. This prevents RIC2 recirculating via the Master, when switches 520 and 522 are closed. The RIC logic never regenerates RIC or RIC2 across a Master.

If input Q failed at a Slave, switch 620 is opened. RIC2 code signal is sent to P with local one second timing. RIC2 is sent to Q whenever RIC (not RIC2) was received at the port P, unless input P had failed as well, when local, one second timing would again have to be used. As in the example above this prevents RIC2 recirculating via the Master, when switches 520 and 522 are closed. The RIC logic never regenerates RIC or RIC2 across a Master.

If input P failed at the master node 402, switch 524 is opened. RIC2 is sent to P once a second instead of RIC. Port Q continues to send RIC. If input Q failed at the master node 402, no change is required, though the failure would still be reported.

If RIC2 is received at Q at the master node, switches 520 and 522 would be closed.

As it was mentioned earlier, operation of the switches on the master and slave nodes causes that the speech circuit experiences small disturbances once per second. RIC and RIC2 code signals are in-band signals whose effect has to be minimised. In one embodiment, RIC is equivalent to the second quietest possible 4kHz speech signal (i.e. alternating 0xD4 & 0x54 for A-law PCM with ADI) and RIC2 the third quietest (0xD7 & 0x57). Though in-band in the digital code, these are effectively out-of-band in the analogue parts of an A-law codec. Each node will send either sequence for fourteen contiguous frames and the detector at the next node persists the signal for eight. As a result, the maximum disturbance to speech is lms per node in the ring plus 0.75ms. It was found to be acceptable to have the disturbance up to around 40 ms, which is more than would occur in any ring size implemented in practice.

The invention can be implemented in any suitable form including hardware, software, software embedded in hardware or any combination of these. The functionality defined in the present invention may be implemented in a plurality of units or as part of other functional units. In consequence, the invention may be physically and functionally distributed between different units and processors. Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Singular references do not exclude a plurality. Thus references to "a", "an", "first", "second" etc do not preclude a plurality.

Claims

1. A method of protecting an Engineering Order Wire in a network, said Engineering Order Wire having a ring topology, a master node and at least one slave node, the method comprising the steps of

- inserting (302) artificial breaks on the incoming and outgoing speech lines on one port of the master node;

- transmitting (304) periodically by said master node a first Ring Integrity Check code signal in two, opposite directions; transmitting (314) by one of the slave nodes a second Ring Integrity Check code signal in two, opposite directions if the first and the second Ring Integrity Check code signal are not received (306, 312) on either or both ports at said slave node.

2. The method according to claim 1 further comprising the following steps: if neither said first Ring Integrity Check code signal nor said second Ring Integrity Check code signal are detected at the port without said artificial breaks, the master node transmits said second Ring Integrity Check code signal from the port without said artificial breaks and said first Ring Integrity Check code signal from the opposite port.

3. The method according to claim 1 or claim 2 further comprising the steps of: removing (318) the artificial breaks from said one port of the master node; inserting (320) by said one of the nodes one artificial break on the output line of a port where an input failure has been detected.

4. The method according to claim 1 or claim 2 or claim 3, wherein said input failure is detected on either said master node or said one of the slave nodes.

5. The method according to any one of preceding claims, wherein said slave nodes repeat (308, 322) on their other port the received first or second Ring Integrity Check code signal with the same timing as the timing of the received code signal.

6. The method according to claim 1 or claim 2, wherein the second Ring Integrity Check code signal is transmitted with local timing provided by said node transmitting said second Ring Integrity Check code signal.

7. The method according to any one of preceding claims, wherein the node that inserted the artificial break in response to the input failure identifies to the network management the span of the network where the artificial break is inserted.

8. A network (100) with an Engineering Order Wire having a ring topology, a master node (402) and at least one slave node (404, 406, 408), wherein in order to protect said Engineering Order Wire the network is adapted to:

- insert artificial breaks on the incoming and outgoing speech lines on one port of the master node (402); transmit periodically by said master node (402) a first Ring Integrity Check code signal in two, opposite directions; transmit by one of the slave nodes (404, 406, 408) a second Ring Integrity Check code signal in two, opposite directions if the first and the second Ring Integrity Check code signal are not received on either or both ports at said slave node (404, 406, 408).

9. The network (100) according to claim 8, wherein the master node (402) is further adapted to transmit said second Ring Integrity Check code signal from the port without said artificial breaks and said first Ring Integrity Check code signal from the opposite port if said first Ring Integrity Check code signal and said second Ring Integrity Check code signal are not detected at the port without said artificial breaks of said master node (402).

10. The network (100) according to claim 8 or 9, further adapted to:

- remove the artificial breaks from said one port of the master node (402); - insert by said one of the nodes (402, 404, 406, 408) one artificial break (420) on the output line of a port where an input failure has been detected.

11. The network (100) according to claim 8 or claim 9, or claim 10, wherein said slave nodes (404, 406, 408) are adapted to repeat on their other port the received first or second Ring Integrity Check code signal with the same timing as the timing of the received code signal.

12. The network (100) according to claim 8 or claim 9, wherein said node (402, 404, 406, 408) transmitting said second Ring Integrity Check code signal is adapted to transmit said second Ring Integrity Check code signal with its own, local timing.

13. The network (100) according to claim 9 further adapted to identify, to the network management, the span of the network where the artificial break is inserted as the span where the failure (422) has developed.

14. A network node (402, 404, 406, 408) for use in a network, wherein, in order to protect an Engineering Order Wire with a ring topology, the node is adapted to transmit a second Ring Integrity Check code signal in two, opposite directions if the first and the second Ring Integrity Check code signal is not received on either or both ports at said node.

15. The node (402, 404, 406, 408) according to claim 14, wherein said network node is further adapted to insert one artificial break on the output line of a port where an input failure has been detected.

16. The node (402, 404, 406, 408) according to claim 14 or claim 15 further adapted to repeat the received first or second Ring Integrity Check code signal, on its other port, with the same timing as the timing of the received code signal.

17. The node (402, 404, 406, 408) according to claim 14 further adapted to transmit said second Ring Integrity Check code signal with its own, local timing.

18. The node (402, 404, 406, 408) according to claim 15, further adapted to identify, to the network management, the span of the network where the artificial break is inserted as the span where the failure (422) has developed.