Technical Field

The present disclosure relates to a method for determining a signalling delay associated with each of a plurality of signalling connections between first and second devices. The present disclosure also relates to a management node for determining a signalling delay associated with each of a plurality of signalling connections, and to a computer program product configured, when run on a computer, to carry out such a method.

Background

An accurate estimate of the delays in a radio access network is of paramount importance for several reasons. These reasons include: meeting the requirements of latency-critical services or time-sensitive fronthaul interfaces, ensuring accurate phase synchronization, and guaranteeing time deterministic and symmetric end-to-end delay in uplink and downlink. In order to satisfy these requirements, an estimate of delay to sub-ns accuracy is required.

Optical fibers are widely used in radio transport, and represent one of the major delay sources in radio access networks. One kilometre of fiber introduces a delay of approximately 5 ps, meaning that the delay of one meter of fiber is 5 ns. This optical fiber delay means that estimating delay in radio access networks with the sub-ns accuracy discussed above is extremely difficult. One meter of optical fiber is comparable to the average length of patch-cords used to connect the various equipment units during installation. The precise length of the patch-cords depends on the specific installation environment and cannot be calculated in advance. Similarly, the exact length of the optical cable is also not known in advance as it depends on local bending and splicing points that are unforeseeable before its deployment. Another source of uncertainty comes from the chromatic dispersion of the optical fiber, which is a propagation effect whereby different wavelengths travels at different speed.

The propagation delay difference, AT, between two wavelengths, i and i, is: Equation 1 Where D( ) is the chromatic dispersion coefficient, measured in psZ(nm-km). Good analytical approximations exist for D( ) that enable a solution to the integral in Equation 1 in closed form. In C band (that is the wavelength region between 1530 and 1565 nm) the following linear law holds, where A is a reference wavelength within the considered band:

D(A) = £>(A) + s( )(A - A) Equation 2

A more general approximation, valid also in O band (1260-1360 nm) is given by the equation:

D(A) = [1 - g) ⁴ ] Equation 3

Where So is the dispersion slope coefficient, in in ps/(nm ² -km), at the zero-dispersion wavelength, A _o .

The above equations require the knowledge of dispersion and dispersion slope coefficients. These coefficients are known with a certain tolerance; however this tolerance is often incompatible with accurate delay calculations.

Finally, even without considering the chromatic dispersion effect, the fiber effective refractive index, (typically assumed equal to 1 .5, which gives about 200,000 km/s of light speed in the fiber) is a “nominal” value, which may be slightly different for different cables, and changes with temperature.

The consequence of the above discussed limitations to analytical methods of determining delay, is that only direct measurement of the delay in an installed system can give the sub-ns accuracy required for radio access network use cases.

Direct measurements of fiber delay are typically performed by diving by two the round trip propagation delay. This requires either that the signal be reflected back at one of the fiber terminations, or that the signal be received and retransmitted back at the same termination. Optical Time Domain Reflectometers (OTDR) use the first principle of reflecting the signal back but, in order to avoid causing traffic interruption, OTDR transmit at a wavelength different from the signal, and so suffer from delay measurement inaccuracy owing to the chromatic dispersion. Measurements can be made one-shot using the same signal wavelength, but this means it is impossible to estimate delay variations caused by temperature changes during system operation. The effect on delay of temperature changes is not negligible: for every 1 °C change in temperature, an optical signal's propagation time through a kilometer of standard solid-core fiber can change by 40 picoseconds. In addition, OTDRs are relatively expensive items of equipment, as they must be sensitive to the weak signal naturally reflected by the fiber due to Rayleigh backscattering, as shown in Figure 1. Figure 1 illustrates the Power Ratio of Rayleigh backscattered light vs. transmitted light (reproduced form: F. Cavaliere, A. D’Errico, Photonic applications for radio systems and networks, Artech House, 2019). Finally, with respect to OTDR, a lumped reflector at the fiber termination is far from ideal, owing to the risk of penalising the signal during normal operation.

As discussed above, an alternative method for measuring delay is to receive and retransmit the signal. In order to avoid any inaccuracy caused by chromatic dispersion effects, the retransmitted signal should be at the same wavelength as the transmitted signal. This is not compatible with the normal system operation, owing to the significant interferometric cross-talk penalty that the reflected signal would cause. In addition, in order to make efficient use of the deployed fiber, it would be desirable to use both propagation directions for data transmission while remaining capable of monitoring the fiber delay in real time, when the data are transmitted.

It will be appreciated that in addition to the practical difficulties discussed above when measuring signalling delay, current measurement methods rely on timing a round trip and dividing the measured time by two. These methods thus assume that the delay on each fiber of the round trip is symmetrical, which may not be the case.

Summary

It is an aim of the present invention to provide a method, management node and computer program product which at least partially address one or more of the challenges discussed above. It is a further aim of the present disclosure to provide a method, management node and computer program product which enable accurate measurement of signalling delay in a manner that is compatible with normal system operation. According to a first aspect of the present disclosure, there is provided a method for determining a signalling delay associated with each of one or more of a plurality of signalling connections between first and second devices. Each of the first and second devices comprises a plurality of transmit ports and a plurality of receive ports, and each signalling connection comprises a transport medium connecting a transmit port on one of the first or second devices to a receive port on the other of the first or second devices. The method comprises causing a message to be transmitted on a plurality of different signalling paths between the first and second devices, wherein each signalling path comprises a combination of two signalling connections, and extends from any one of the transmit ports on the first device, via receive and transmit ports on the second device, to terminate at any one of the receive ports on the first device. The method further comprises obtaining, for each signalling path, a time delay between transmission of the message from the first device and reception of the message at the first device. The method further comprises assembling a plurality of linear equations, each linear equation of the plurality representing an obtained time delay as a summation of the signalling delays associated with each of the signalling connections of the signalling path for which the time delay was obtained. The method further comprises solving the plurality of linear equations to determine the signalling delay associated with one or more individual signalling connections of the plurality.

According to another aspect of the present disclosure, there is provided a computer program product comprising a computer readable non-transitory medium, the computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform a method according to any one of the aspects or examples of the present disclosure.

According to another aspect of the present disclosure, there is provided a management node for determining a signalling delay associated with each of one or more of a plurality of signalling connections between first and second devices. Each of the first and second devices comprises a plurality of transmit ports and a plurality of receive ports, and each signalling connection comprises a transport medium connecting a transmit port on one of the first or second devices to a receive port on the other of the first or second devices. The management node comprises processing circuitry configured to cause the management node to cause a message to be transmitted on a plurality of different signalling paths between the first and second devices, wherein each signalling path comprises a combination of two signalling connections, and extends from any one of the transmit ports on the first device, via receive and transmit ports on the second device, to terminate at any one of the receive ports on the first device. The processing circuitry is further configured to cause the management node to obtain, for each signalling path, a time delay between transmission of the message from the first device and reception of the message at the first device. The processing circuitry is further configured to cause the management node to assemble a plurality of linear equations, each linear equation of the plurality representing an obtained time delay as a summation of the signalling delays associated with each of the signalling connections of the signalling path for which the time delay was obtained. The processing circuitry is further configured to cause the management node to solve the plurality of linear equations to determine the signalling delay associated with one or more individual signalling connections of the plurality.

Aspects of the present disclosure thus provide a method and management node that exploit multiple possible signalling paths between devices each having a plurality of transmit and receive ports, in order to determine asymmetric signalling delay in individual connections between the devices. This provides an accurate representation of signalling delay that can be measured during network operation and without traffic disruption.

Brief Description of the Drawings

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

Figure 1 illustrates the Power Ratio of Rayleigh backscattered light to transmitted light;

Figure 2 is a flow chart illustrating process steps in a method for determining a signalling delay associated with each of a plurality of signalling connections between first and second devices;

Figures 3a and 3b show flow charts illustrating another example of a method for determining a signalling delay associated with each of a plurality of signalling connections between first and second devices; Figure 4 illustrates example first and second devices having multiple transmit and receive ports;

Figure 5 illustrates the same example devices as Figure 4, with the addition of a Dense Wavelength Division Multiplexing (DWDM) connection between the devices;

Figure 6 illustrates further example first and second devices;

Figure 7 is a flow chart illustrating PTP message flow with reference to the devices illustrated in Figures 4 and 5;

Figure 8 is a block diagram illustrating functional modules in a management node;

Detailed Description

Examples of the present disclosure propose to exploit the availability in many devices of multiple transmit (Tx) and receive (Rx) ports, via which devices may be connected together. In many deployment situations, multiple individual signalling connections may extend between Tx and Rx ports on first and second devices. These signalling connections give rise to a number of potential signalling paths via which a message may be sent on a round trip from one device to the other and then back again. Examples of the present disclosure propose to measure round trip times on a plurality of these signalling paths, and then combine measurements from these paths in order to assemble a plurality of linear equations which may be solved to determine signalling delay on individual connections.

In some examples, the messages sent on the signalling paths may be Precision Time Protocol (PTP) peer delay messages. The current IEEE 1588-2019 standard for the Precision Time Protocol (PTP), "IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems," is IEEE Std 1588-2019 (Revision of IEEE Std 1588-2008), vol., no., pp.1-499, 16 June 2020, doi: 10.1109/IEEESTD.2020.9120376. This protocol is built upon exchanging packets between a slave port and a master port. Implementations of PTP exist in which devices are connected with multiple ports. However, in such a scenario only one of the possible combination of ports is chosen to perform synchronization according to the standard. For PTP transparent clocks operating in the peer to peer mode, the transport delay is measured per link, however it is still only one of the links that is used for synchronization. Examples of the present disclosure take advantage of the multiple signalling paths available as a consequence of the multiple Tx and Rx ports via which the devices are connected, and allow for the combination of measurements to determine an accurate delay measurement for individual signalling connections.

Figure 2 is a flow chart illustrating process steps in a method 200 for determining a signalling delay associated with each of one or more of a plurality of signalling connections between first and second devices. Each of the first and second devices comprises a plurality of transmit ports and a plurality of receive ports, and each signalling connection comprises a transport medium connecting a transmit port on one of the first or second devices to a receive port on the other of the first or second devices. The method may be performed by a management node, which may in some examples be a logical function, such as a virtual function, and may be instantiated for example in the first device or in any part of a network comprising the first and second devices.

Referring to Figure 2, the method 200 first comprises causing a message to be transmitted on each of a plurality of different signalling paths between the first and second devices as step 210. As illustrated in Figure 2, each signalling path comprises a combination of two signalling connections, and extends from any one of the transmit ports on the first device, via receive and transmit ports on the second device, to terminate at any one of the receive ports on the first device. In step 220, the method 200 comprises obtaining, for each signalling path, a time delay between transmission of the message from the first device and reception of the message at the first device. The method 200 then comprises, at step 230, assembling a plurality of linear equations, each linear equation of the plurality representing an obtained time delay as a summation of the signalling delays associated with each of the signalling connections of the signalling path for which the time delay was obtained. Finally, at step 240, the method comprises solving the plurality of linear equations to determine the signalling delay associated with one or more individual signalling connections of the plurality.

It will be appreciated that the signalling connections to which the method 200 refers may be optical connections in the form of optical fibers, or may be copper connections or any other connections operable to connect a transmit port on one device to a receive port on the other device, and to transfer a signal between the devices. The method 200 allows for the determination of asymmetrical delay in connections between devices without requiring the use of expensive additional equipment or intervention. Instead of dividing a round trip time by two, the method 200 takes advantage of the multiple paths offered by a plurality of physical connections between devices, and uses measurements from multiple paths to assemble a system of linear equations which can be solved to provide accurate representations of delay associated with individual connections. The signalling connections for which the delay is determined may include all or a subset of the plurality of signalling connections between the first and second devices.

Figures 3a and 3b show flow charts illustrating another example of a method 300 for determining a signalling delay associated with each of a plurality of signalling connections between first and second devices. As for the method 200 discussed above, each of the first and second devices comprises a plurality of transmit ports and a plurality of receive ports, and each signalling connection comprises a transport medium connecting a transmit port on one of the first or second devices to a receive port on the other of the first or second devices. The method 300 may be performed by a management node, which may in some examples be a logical function, such as a virtual function, and may be instantiated for example in the first device or in any part of a network comprising the first and second devices. The method 300 illustrates examples of how the steps of the method 200 may be implemented and supplemented to provide the above discussed and additional functionality.

Referring initially to Figure 3a, the method 300 first comprises causing a message to be transmitted on a plurality of different signalling paths between the first and second devices, as illustrated at step 310. As discussed above, each signalling path comprises a combination of two signalling connections, and extends from any one of the transmit ports on the first device, via receive and transmit ports on the second device, to terminate at any one of the receive ports on the first device.

As illustrated at 310a, step 310 may comprise causing a message to be transmitted over a number of different signalling paths that is at least equal to the number of the plurality of signalling connections. In some examples, step 310 may comprise causing a message to be transmitted over all possible signalling paths between the first and second devices, as illustrated at 310b. All possible signalling paths refers to all possible combinations of the plurality of signalling connections that allow a round trip to be made by a message starting and finishing at the first device. As illustrated at 310c, each signalling path of the plurality of paths over which the message is transmitted may share a signalling connection with at least one other signalling path of the plurality.

In some examples, as illustrated at 31 Od, each message transmitted over a signalling path may be a time stamped message. Step 310 may comprise transmitting the messages on each of the plurality of different signalling paths at the same time, or may comprise causing a Layer 1 Forward Error Correction (FEC) codeword and Cord Word Marker to be aligned in time for the message sent on all the different signalling paths, as illustrated at 31 Oe.

As illustrated at 31 Of and discussed above, in some examples the messages transmitted over the plurality of signalling paths may comprise PTP peer delay messages.

In further examples, the plurality of transmit ports and the plurality of receive ports on the first device may be comprised within a single logical port entity on the first device, and the plurality of transmit ports and the plurality of receive ports on the second device may be comprised within a single logical port entity on the second device, as shown at 310g. The logical port entity may comprise a logical port, a media independent interface as defined in IEEE 1588-2019, a logical port controller, etc. Each pair of transmit and receive ports on each of the first and second devices may comprise an identified physical port, and the logical port entity on each of the first and second devices may encompass a plurality of these physical ports. In such examples, each signalling path between the first and second devices originates at a physical port on the first device and terminates at a physical port that is either the same as or different to the physical port at which it originated. Thus if physical ports P1 , P2.... Pn on the first device each comprise a respective transmit and receive port (transmit port Tx1 and receive port Rx1 , transmit port Tx2 and receive port Rx2, transmit port Txn and receive port Rxn, etc.), then a message transmitted from Tx1 may be returned to the first device over a signalling connection to Rx1 , or may be returned to the first device over a signalling connection to any of Rx2, Rxn, etc.

Referring now to Figure 3b, the method 300 further comprises, at step 320, obtaining, for each signalling path, a time delay between transmission of the message from the first device and reception of the message at the first device. This may comprise calculating a difference between a transmission timestamp of the message from the first device and a reception time stamp of the message at the first device, as shown at 320a. As illustrated at 320b, obtaining a time delay at step 320 may further comprise subtracting from the obtained time delay an interconnect delay between the receive and transmit ports of the second device. Thus, in the example discussed above of multiple physical ports P1 , P2, Pn, if the message is received at the second device at port Rx1 , and retransmitted back to the first device from port Txn, there may be an interconnect time delay between ports Rx1 and Txn, and this interconnect time delay may be subtracted from the obtained total time delay between transmission and reception of the message from/at the first device.

The method 300 further comprises, at step 330, assembling a plurality of linear equations, each linear equation of the plurality representing an obtained time delay as a summation of the signalling delays associated with each of the signalling connections of the signalling path for which the time delay was obtained. The method then comprises solving the plurality of linear equations to determine the signalling delay associated with individual signalling connections of the plurality.

Figures 2 to 3b discussed above provide an overview of methods which may be performed according to different examples of the present disclosure. These methods may be performed by a management node, as illustrated in Figures 8 and 9 discussed below. The methods enable the determination of asymmetric delay in a plurality of signalling connections between first and second devices. There now follows a detailed discussion of how different process steps illustrated in Figures 2 to 3b and discussed above may be implemented.

Figure 4 illustrates example first and second devices 410 and 420. The devices 410, 420 are connected by multiple signalling connections 430, 440, 450, 460. Each signalling connection extends between a transmit port on one device and a receive port on the other device. Each device 410, 420 comprises two transmit ports 411 , 413, 421 , 423, and two receive ports 412, 414, 422, 424. On each device 410, 412, a first transmit port 411 , 421 and first receive port 412, 422 form a first physical port: Port 1 415, 425, and a second transmit port 413, 423 and second receive port 412, 424 form a second physical port: Port 2416, 426. The physical ports on each device are further assembled into a single logical port entity: the Logical PTP master port 417 on Device 1 410, and the logical PTP slave port 427 on device 2 420. Implementations of the methods 200 and 300 exploit the presence of multiple Tx and Rx ports on each device to create a plurality of overlapping but different signalling paths starting and finishing at the first device 410. The signalling paths are illustrated as dashed arrows and travel via the ports as follows:

Signalling path 1 : Tx1 411 , Rx1 421 , Tx1 422, Rx1 412

Signalling path 2: Tx1 411 , Rx1 421 , Tx2 424, Rx2 414

Signalling path 3: Tx2 413, Rx2 423, Tx1 422, Rx1 412

Signalling path 4: Tx2 413, Rx2 423, Tx2 424, Rx2 414

It will be appreciated that paths 1 and 3 originate and terminate in the same physical port of the first device (port 1 415 and port 2 416 respectively), while paths 2 and 4 terminate at a different physical port on the first device to the physical port at which they originate. Each signalling connection in Figure 4 carries two different signalling paths in the same direction, so connection 430 carries the outbound parts of paths 1 and 2, while connection 440 carries the inbound parts of paths 1 and 3, etc.

In the case of optical fibers, each signalling connection (i.e. each fiber) may carry paths using slightly different wavelengths or physically separated fibers, so that any inaccuracy due to the chromatic dispersion is negligible. For example, if D=5 ps/nm/km (upper bound for the O-band), and the difference between the two wavelengths is 4.6 nm (corresponding to the 800 GHz frequency spacing of the LAN WDM grid) the delay difference between the paths equals to 0.2 ns for a 10 km link, which is within an appropriate range.

With the above assumptions, a system of linear independent equations can be written based on the round-trip delays measured on each path (step 230 or 330). There is one equation per signalling connection (fiber) for which delay is to be calculated. The equations can then be solved for the delay in each connection. For example, with reference to Figure 4, and numbering the signalling connections as follows: connection 1 430 connection 2 440 connection 3 460 connection 4 450 The following equations can be generated (the subscripts referring to the signalling connection numbers)

TI + T = delay_path 2 TI + T ₂ = delay_path 1 T3 + T2= delay_path 3 T ₃ + T4= delay_path 4

With the measured values of delay for the four signalling paths (and with port interconnect delays on device 2 subtracted as appropriate), it is possible to solve the above linear equations to arrive at a value for the delay associated with each of the four signalling connections 430, 440, 450, 460.

The logical port entities of Logical PTP master port 417 and Logical PTP slave port 427 encompass the physical ports on each device. For PTP clocks using delay request mechanism and having multiple PTP slave ports, these multiple PTP slave ports are encompassed within the Logical PTP slave port. Similarly, multiple PTP master ports are encompassed within the Logical PTP master port. In this manner, the capability of a current PTP client may be amended to allow it to exchange synchronization messages over the logical port entities, and leverage the information gain from using the multiple signalling paths existing between the logical port entities. One way of amending the capability of a current PTP client is to use the existing peer delay messages and delay request mechanism to send the message on the plurality of signalling paths, to obtain time information from the signalling links and then use that information as discussed above to set up the linear equations. This represents a different use of available time information, compared to the existing peer delay mechanism.

It may be assumed that a common reference within each device is used to timestamp any event messages passed between them, enabling link and interconnect delay to be isolated. SYNC messages may be transmitted from multiple physical master ports at the same time and/or the Layer 1 FEC codeword and Code Word Marker I Alignment marker may be allowed to be aligned in time from the master side. By performing the roundtrips Port 1 to roundtrip Port N and up to all possible permutations of Port 1 to Port N delay measurements within the logic port, a set of linear equations can be assembled representing measured roundtrip delays as sums of individual signalling connection delays, and those equations can be solved for individual connection (fiber or copper) and interconnect asymmetry.

Figure 5 illustrates the same example devices as Figure 4, with the addition of a Dense Wavelength Division Multiplexing (DWDM) connection between the devices. The same signalling paths as discussed above can still be used for the devices of Figure 5. The only difference is that the transport media of the individual signalling connections now includes sections connecting directly to each of a Tx and Rx port, and a DWDM section in the middle. The methods 200 and 300 can be used as described above to solve for individual signalling delays associated with each signalling connection. The delay will encompass the signalling delay of the entire connection, from Tx to Rx and including the effects of the DWDM section.

Figure 6 illustrates another way in which the existing PTP protocol may be used to implement methods of the present disclosure. In the scenario illustrated in Figure 6, instead of a single logical PTP master port, and a single logical PTP slave port, multiple PTP ports run standard PTP, with only one of the ports being a PTP slave port. Each port is configured to use the peer delay mechanism. In this example, the logical port entity that is defined over the physical PTP ports ins a PTP logical port controller, 618, 628. The logical PTP port controllers gather the measured time delays from the individual ports to enable the combination of measurements that allows the formation of the plurality of linear equations, and solving for asymmetrical delays in individual signalling connections.

Figure 7 is a flow chart illustrating PTP message flow with reference to the devices illustrated in Figures 4 and 5. As discussed above with reference to Figure 4, the four signalling paths between the first and second devices travel via the following Tx and Rx ports:

Signalling path 1 : Tx1 411 , Rx1 421 , Tx1 422, Rx1 412

Signalling path 2: Tx1 411 , Rx1 421 , Tx2 424, Rx2 414

Signalling path 3: Tx2 413, Rx2 423, Tx1 422, Rx1 412

Signalling path 4: Tx2 413, Rx2 423, Tx2 424, Rx2 414

Paths 1 and 4 thus originate and terminate in the same physical port on the first device, while paths 2 and 3 involve passing a message between physical ports on the second device, allowing the path to terminate at a different physical port on the first device to that at which the path originated.

Referring to Figure 7, and considering the signalling paths in turn:

Path 1 : The message is transmitted from Tx 411 on Device 1 Port 1 at time T1 ml , and received at Rx 421 on Device 2 Port 1 at T2s1. The message is then transmitted from Tx 422 on Device 2 Port 1 at time T3s1 , and received on Rx 412 on Device 1 Port 1 at time T4m1.

Path 2: The message is transmitted from Tx 411 on Device 1 Port 1 at time T1 ml , and received at Rx421 on Device 2 Port 1 at T2s1. The message is then transferred between ports on Device 2, to be transmitted from Tx 424 on Device 2 Port N at time T3s2(m1), and received on Rx 414 on Device 1 Port N.

Path 3: The message is transmitted from Tx 413 on Device 1 Port N at time T 1 m2, and received at Rx 423 on Device 2 Port N at T2s2. The message is then transferred between ports on Device 2, to be transmitted from Tx 422 on Device 2 Port 1 at time T2s2(m1), and received on Rx 412 on Device 1 Port 1.

Path 4: The message is transmitted from Tx 413 on Device 1 Port N at time T 1 m2, and received at Rx 423 on Device 2 Port N at T2s2. The message is then transmitted from Tx 424 on Device 2 Port N at time T3s2, and received on Rx 414 on Device 1 Port N at time T4m2.

As discussed above, the methods 200 and 300 are performed by a management node, and the present disclosure provides a management node that is adapted to perform any or all of the steps of the above discussed methods. The management node may comprise a physical node such as a computing device, server etc., or may comprise a virtual entity. A virtual entity may comprise any logical entity, such as a Virtualized Network Function (VNF) which may itself be running in a cloud, edge cloud or fog deployment.

Figure 8 is a block diagram illustrating an example management node which may implement the method 200 and/or 300, as illustrated in Figures 2 to 3b, according to examples of the present disclosure, for example on receipt of suitable instructions from a computer program 850. Referring to Figure 8, the management node 800 comprises a processor or processing circuitry 802, and may comprise a memory 804 and interfaces 806. The processing circuitry 802 is operable to perform some or all of the steps of the method 200 and/or 300 as discussed above with reference to Figures 2 to 3b. The memory 804 may contain instructions executable by the processing circuitry 802 such that the management node 800 is operable to perform some or all of the steps of the method 200 and/or 300, as illustrated in Figures 2 to 3b. The instructions may also include instructions for executing one or more telecommunications and/or data communications protocols. The instructions may be stored in the form of the computer program 850. In some examples, the processor or processing circuitry 802 may include one or more microprocessors or microcontrollers, as well as other digital hardware, which may include digital signal processors (DSPs), special-purpose digital logic, etc. The processor or processing circuitry 802 may be implemented by any type of integrated circuit, such as an Application Specific Integrated Circuit (ASIC), Field Programmable Gate Array (FPGA) etc. The memory 804 may include one or several types of memory suitable for the processor, such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, solid state disk, hard disk drive, etc.

Examples of the present disclosure thus provide a method and management node that exploit multiple possible signalling paths between devices each having a plurality of transmit and receive ports, in order to determine asymmetric signalling delay in individual connections between the devices. In some examples, a logical PTP port may be defined that contains multiple physical PTP ports, all of which provide delay information to the PTP client. In other examples, the currently available IEE 1588-2008 delay mechanism may be used in combination with a logical PTP port controller to collect and use the delay measurements. Measurements of multiple interconnect paths can then be combined to assemble a set of linear equations and solve for individual signalling delays introduced by transport media such as fibers and by interconnections. The logical port entities also implement a layer of robustness according to which a single or multiple port or ports may be added or removed without affecting the performance of the logical port entity.

Examples of the present disclosure provide a more accurate representation of individual signalling connection delays, and the asymmetry in such delays, when compared with current IEEE 1588-2008 methods, in which fibers and interconnect are assumed to be fully symmetrical. Methods according to the present disclosure can be implemented using existing PTP messages, and can be implemented so as to be interoperable with a PTP standard compliant device that does not support methods according to the present disclosure. It will be appreciated that example methods according to the present disclosure use the same pluggable transceivers as are used for data connections, without any need of special equipment or network intervention. Methods according to the present disclosure enable monitoring of delay variation (for example caused by temperature variation) in real time and with no traffic interruption

The methods of the present disclosure may be implemented in hardware, or as software modules running on one or more processors. The methods may also be carried out according to the instructions of a computer program, and the present disclosure also provides a computer readable medium having stored thereon a program for carrying out any of the methods described herein. A computer program embodying the disclosure may be stored on a computer readable medium, or it could, for example, be in the form of a signal such as a downloadable data signal provided from an Internet website, or it could be in any other form.

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