Title of Invention

SYSTEM FOR PROTECTION LINK SUPERVISION

Abstract To ensure that the distributed restoration process of a DRA provisioned network proceeds only in response to true failures, the present invention DRA network provisions to each of the ports of the nodes a timer mechanism for ascertaining whether an alarm is a genuine alarm. This is done by presetting the timer with an expiration period so that an alarm is validated as a failure only upon the expiration of the timer. When validated, the value of a counter is incremented. The value of the counter is reflective of the sum of validated alarms, and is compared against a preset threshold value. And it is only when the value of the summed validated alarms exceeds the preset threshold value would the DRA process be initiated. When a validated alarm ceases, the reverse process takes place. That is, the ending of the alarm has to be validated by another timer, which could be the same timer as used for validating an alarm. The counter is decremented for each validated non-alarm, so that when the value of the defect counter falls below the threshold value, the DRA process is reset.
Full Text Technical Field
The present invention relates to a system of performing protection link fault supervision in a Synchronous Digital Hierarchical (SDH) based network. The principles of the SDH protocol are described in International Telecommunication Union recommendation ITU G. 707.
Technical Background
To connect Radio Network Controller nodes to form a Radio Access Network, there is a need to protect the physical lines connecting these nodes against failure. A common architecture to achieve line protection in an SDH based network uses two physical lines to connect two nodes of the network. The node that is sending the data traffic, sends the data on two lines to the receiving node. If one of the lines breaks, the receiving node can extract the traffic from the other line.
The RNC node includes two line termination boards, of which one is active and the other is in standby mode. A link supervision block supervises the function of the lines and termination boards, and performs a switchover from the active to the standby board should a fault occur on one of the connections.
In the AXE system manufactured by Telefonaktiebolaget LM Ericsson such a supervision system is implemented. Faults detected on the active board are sent towards the supervision block spontaneously when they are detected. The supervision block then reads out state information from the standby board. The results are correlated to achieve information about a fault cause (failure in the active board or the connected line, failure in the standby board or the connected line, failure in the internal link between the boards, no failure).
Such a system is prone to some problems:
We can imagine that an identical fault is detected on both boards. Due to varying detection and signal transmission times, it is undetermined which fault (i.e. from which board) that will be reported first. Then the correlation result might not reflect the true physical situation, and the supervision block may misunderstand the situation. Varying detection times is caused by
the standby board not reporting faults immediately, but instead checks the situation at fixed time intervals.
Even a single short disturbance can lead to a failure being reported without being justified. In addition, the active and standby boards have two rather different functions. In case of failure, the functions must be swapped, without loosing information on the faults that has occurred. This might be complicated to implement in a computer program.
Statement of the invention
A system for protection link fault supervision between two nodes (1, 11) in a transmission network, wherein the nodes are connected by first (6) and second (8) transmission lines, which carry identical data traffic between the nodes (1, 11). Each node (1, 11) includes a first, active or working line transmission board (2), terminating the first transmission line (6), a second passive or standby line termination board (3), terminating the second transmission line (8), and a node core (4) including a link supervision block (10). The line termination boards (2, 3) are adapted to report faults to the link supervision block (10). The node core (4) is adapted to switch traffic between the line termination boards (2, 3) in case of a fault. The system comprises a fault detector (12) residing in the line termination boards (2, 3), configured to detect fault in the transmission lines (6, 8). A persistency timer means (13) residing in the line termination boards (2, 3) when triggered by the line termination boards (2, 3) on detection of fault, supervises the persistence of the detected fault. The line termination boards (2, 3) are adapted to report the fault to the link supervision block (10), if the fault persists beyond the persistency timer period. The link supervision block (10) is adapted to store received fault causes and correlate the latest received fault causes from the line termination boards (2, 3) with the latest received fault cause from the other line termination board (2, 3). A correlation result persistency timer means (14) residing in a link supervision block (10) when triggered by the link supervision block (10) supervises the persistence of a correlation result. The link supervision block (10) is configured to request the node core (4) to switch traffic between the line termination boards (2, 3), if the correlation result persists beyond the correlation result persistency timer period.
Summary of the Invention
It is an object of the present invention to provide a supervision system for protecting
transmission paths in radio access networks, which is more reliable in deciding the true cause
of a fault.
Another object of the invention is to provide a system that is nearly immune against random
disturbances.
Still another object is to provide a system that is less costly to implement than prior art
systems.
These and other objects are achieved in a system as defined in the appended patent claims.
Brief description of the drawings
The invention will now be described in detail in reference to the appended drawings, in which
Fig. 1 gives a schematic overview of the circuitry used in current radio access network nodes
in order to protect against line faults,
Fig. 2 is a sequence diagram showing the detection of a fault in the system outlined in Fig. 1
(prior art),
Fig. 3 shows a similar diagram and the detection of faults in a system according to the present
invention.
Detailed description of the invention
Fig. 1 shows two radio access network nodes, 11 and 1, with redundant lines, 6 and 8, between the nodes for securing a reliable connection between them.
The node 1 has an active Line Termination Board 2 that carries the data traffic, a passive Line Termination Board 3 that can be used as a replacement and a Node Core 4 that switches the data traffic and contains a Link Supervision instance 10. The Line Termination Boards (2,3) further comprises a fault detector (12) to detect fault in the transmission lines (6, 8) and a persistency timer means (13) residing in the line termination boards (2, 3) when triggered by the line termination boards (2, 3) are adapted to report the fault to the link supervision block (10), if the fault persists beyond the persistency timer period. Further, a correlation result
persistency timer means (14) residing in a link supervision block (10) supervises the persistence of a correlation result.
The incoming data traffic is sent from a source node 11. The data source 5a sends via link 6 towards the active board 2. The same data traffic is sent by the data source 5b via link 8 to the passive board 3 and further via the internal link 9 to the active board 2 that selects one of the two external links as an input and sends the data further via internal link 7 towards the core 4. In normal operation the active board 2 has the role of the working board, it takes the data traffic from link 6. Board 3 has the role of the standby board, it forwards the incoming traffic to the active board.
When link 6 becomes unusable, the data traffic is taken from internal link 9 (protected operation). The Link Supervision Block 10 controls the switch between these two modes. The roles of the boards are swapped.
Essential for the usability of the protected operation mode is the absence of faults that might disturb data traffic on internal link 9. Therefore the supervision block 10 needs information about the transmitter state from board 3 and about the receiver state from board 2. Information from both boards is needed to be able to decide about the cause of a possible fault to determine if a switch is possible or needed.
As explained earlier, faults detected on the working board 2 will be sent towards the supervision block 10 spontaneously when they are detected. The supervision block then reads out the state information from the standby board 3. The results are correlated to achieve information about a fault cause (failure in board 2, failure in board 3, link failure, no failure).
In one instance one class of faults is detected on both boards. Due to varying detection and signal transmission times, it is not determined which fault will be reported first {t3 t2}. It is possible that the fault on board 3 is detected after the information was read out {t3-tr > 0}. Then the correlation result at {tf} does not reflect the physical situation.
Varying detection times can e.g. be caused by checks that are triggered by expiry of a fixed-period timer. Since these faults cannot be detected between the checks, the detection time may vary from 0 up to a time period.
The correlation result is not checked for persistency in a defined period. This might lead to unjustified failure from the supervision block towards an operator in case of a single short disturbance.
The implementation of this method as a software program is expensive because the two different roles of the board imply different reactions upon fault detection. Only the working one reports spontaneously, the functionality to switch between the two roles must be implemented in a way that secures that knowledge on initial faults of the standby board are preserved.
Fig. 3 shows the timing diagram for a system according to the invention. The hardware is as described in Fig. 1. However, several new functions are implemented in the line boards 2,3 and the supervision block 10.
According to a first embodiment of the invention, the following actions are performed when
each of the boards 2,3 detect a fault state change:
Both boards report all fault state changes spontaneously when they are detected to the
supervision block.
The supervision block stores the received faults causes.
The received fault cause is correlated with the latest received fault cause of the board
terminating the other end of the link.
A correlation result persistency timer means (14) is started to supervise the persistency of the
correlation result.
When the result has not disappeared during the persistency timer period, it can be reported.
If the correlation result shows that a traffic-disturbing fault on the link has occurred and that
the traffic can be reestablished by some actions is the node, e. g. re-routing, then these actions
can be started.
One advantage of this system is that the result of the supervision block is as accurate as
possible since all fault changes are reported immediately after detection. This overcomes the
timing problems of the known solution.
The persistency check ensures that the correlation result is correct and stable.
The timeout can be selected to fulfill system requirements for a specified detection time.
The timeout can be selected to suppress short time disturbances.
The method is inexpensive and can thereby easily be implemented as a computer program because the fault detection mechanism in both boards is independent of the board's role (working/standby).
In an alternative embodiment of the invention an additional persistency check is implemented by the persistency timer means (13) before the correlation is done. If this check is done by the reporting board, the amount of signaling towards the supervision block can be reduced in case of faults that change state with a high frequency. With this pre-correlation check, the persistency check after correlation could be left out under certain circumstances. While the present invention has been described in relation to SDH based networks, the applicability is not restricted to this particular type of network. All transmission techniques can be used that support error detection. Thus, this system can be used for general link supervision, when information about the sender of data traffic as well as information about the receiver of data traffic is available at different locations and needs to be correlated to gain information about the state of the link.







We Claim:
1. A system for protection link fault supervision between two nodes (1, 11) in a
transmission network, the nodes (1, 11) being connected by first (6) and second (8)
transmission lines carrying identical data traffic between the nodes (1, 11), each node (1, 11)
comprising a first, active or working line transmission board (2), terminating said first
transmission line (6), a second passive or standby line termination board (3), terminating said
second transmission line (8), and a node core (4) including a link supervision block (10), said
line termination boards (2, 3) being adapted to report faults to the link supervision block (10),
said node core (4) being adapted to switch traffic between the line termination boards (2, 3)
in case of a fault, characterized in that comprising:
fault detector (12) configured to detect fault in said transmission lines (6, 8), said fault detector (12) residing in said line termination boards (2, 3);
a persistency timer means (13) residing in said line termination boards (2, 3) when triggered by said line termination boards (2, 3) on detection of fault supervises the persistence of the detected fault, the line termination boards (2, 3) adapted to report the fault to said link supervision block (10), if the fault persists beyond the persistency timer period, the link supervision block (10) is adapted to store received fault causes and correlate the latest received fault causes from said line termination boards (2, 3) with the latest received fault cause from the other line termination board (2, 3); and
a correlation result persistency timer means (14) residing in the link supervision block (10) when triggered by said link supervision block (10) supervises the persistence of a correlation result, said link supervision block (10) configured to request the node core (4) to switch traffic between the line termination boards (2, 3), if the correlation result persists beyond the correlation result persistency timer period.
2. The system as claimed in claim 1, said transmission network is a synchronous
digital hierarchical based network.


Documents:

4005-delnp-2004-abstract.pdf

4005-delnp-2004-claims.pdf

4005-delnp-2004-correspondence-others.pdf

4005-delnp-2004-correspondence-po.pdf

4005-delnp-2004-description (complete).pdf

4005-delnp-2004-drawings.pdf

4005-delnp-2004-form-1.pdf

4005-delnp-2004-form-13.pdf

4005-delnp-2004-form-19.pdf

4005-delnp-2004-form-2.pdf

4005-delnp-2004-form-26.pdf

4005-delnp-2004-form-3.pdf

4005-delnp-2004-form-4.pdf

4005-delnp-2004-form-5.pdf

4005-delnp-2004-gpa.pdf

4005-delnp-2004-pct-210.pdf

4005-delnp-2004-pct-308.pdf

4005-delnp-2004-pct-408.pdf

4005-delnp-2004-pct-409.pdf

4005-delnp-2004-pct-416.pdf

4005-delnp-2004-petition-137.pdf

4005-delnp-2004-petition-138.pdf


Patent Number 241488
Indian Patent Application Number 4005/DELNP/2004
PG Journal Number 29/2010
Publication Date 16-Jul-2010
Grant Date 07-Jul-2010
Date of Filing 16-Dec-2004
Name of Patentee TELEFONAKTIEBOLAGET LM ERICSSON(PUBL)
Applicant Address S-164 83 STOCKHOLM, SWEDEN
Inventors:
# Inventor's Name Inventor's Address
1 JOCHEN CHRISTOF SCHIRDEWAHN VELLIVEIEN 11B, N-1358 JAR, NORWAY
PCT International Classification Number H04B 1/74
PCT International Application Number PCT/NO2002/00318
PCT International Filing date 2002-09-10
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 PCT/NO2002/00318 2002-09-10 PCT