Abstract: A method for measuring asymmetry in propagation delay of first and second links which connect a first node to a second node of a communication network. The method comprises measuring (101) a round trip delay of the first link. The round trip delay can be measured by transmitting (102) a test signal from the first node to the second node over the first link and receiving a reply to the test signal from the second node over the first link. The method further comprises measuring (105) a round trip delay of the second link. The round trip delay can be measured by transmitting (106) a test signal to the second node over the second link and receiving a reply to the test signal from the second node over the second link. A difference in the propagation delay of the first link with respect to the second link is determined (109) using the measured round trip delays of the first link and the second link.

Abstract: A synchronization module is associated with a network node of a communication network which comprises at least one Synchronization Master entity. The synchronization module has knowledge of a plurality of Synchronization Master references. Endpoints of paths of the plurality of Synchronization Master references are obtained. Each of the paths extends between one Synchronization Master Entity and the first or the second access network node. The paths are obtained from a synchronization report module based on the obtained endpoints. For each of the Synchronization Master references, a first path and a second path of the obtained paths are selected. A time synchronization inaccuracy value between the first and the second access network node is calculated based on the selected paths. A Synchronization Master reference is selected based on the calculated time synchronization inaccuracy values, and the first and the second access network node are notified which Synchronization Master reference was selected.

Abstract: A pluggable transceiver module (200) comprising a line receiver (208) connected to a unit interface transmitter (202), a line transmitter (206) connected to a unit interface receiver (204) and a timestamp counter (210) adapted to generate counter values based on clock signals received from an external source and to send the counter values to the line transmitter (206) and to the line receiver (208). The line transmitter (206) and the line receiver (208) are adapted to associate timing packets in a stream of data packets transmitted and received by the pluggable transceiver module (200) with counter values output by the timestamp counter (210).

Abstract: A connection-oriented communications network comprises a plurality of interconnected nodes. A traffic path can be set up across the network. Path delay data is obtained for the traffic path by using control plane signalling messages (e.g. a Resource Reservation Protocol-Traffic Engineering, RSVP-TE signalling message) between nodes of the traffic path. The path delay data can be path delay asymmetry data indicative of an asymmetry in path delay between a forward transmission direction and a reverse transmission direction of the traffic path. Each intermediate node along the traffic path can form a signalling message for forwarding to the downstream node which includes one or more values of path delay incurred by that node, or an accumulated path delay value. The path delay can result from one or more of mapping delay, Forward Error Correction (FEC) coding and propagation delay.

Abstract: A method for measuring asymmetry in propagation delay of first and second links which connect a first node to a second node of a communication network. The method comprises measuring (101) a round trip delay of the first link. The round trip delay can be measured by transmitting (102) a test signal from the first node to the second node over the first link and receiving a reply to the test signal from the second node over the first link. The method further comprises measuring (105) a round trip delay of the second link. The round trip delay can be measured by transmitting (106) a test signal to the second node over the second link and receiving a reply to the test signal from the second node over the second link. A difference in the propagation delay of the first link with respect to the second link is determined (109) using the measured round trip delays of the first link and the second link.

Abstract: A method of providing a path delay asymmetry for time synchronization between a master clock at a first client node and a slave clock at a second client node. The method comprises: mapping a first time protocol signal (TPS) carrying master clock time protocol data (TPD) onto a first signal; determining a forward mapping delay (dmf); mapping a second TPS carrying slave clock TPD onto a second signal; determining a reverse mapping delay (dmr); applying FEC to the first signal, determining a forward FEC delay (dfecf); applying FEC to the second signal; determining a reverse FEC delay (dfecr); providing dmf, dmr, dfecf and dfecr to a calculation element; calculating a path delay asymmetry in dependence on dmf, dmr, dfecf and dfecr; and providing it to a time protocol client at the second client node.

Abstract: Configuring a node (410) of a synchronization network involves identifying (10) possible alternative time synchronization trails arranged to carry time synchronization information for time synchronization at the node, and possible alternative frequency trails, arranged to carry frequency synchronization information for frequency synchronization at the node. Using information about the sources (20), a comparison of the trails (30) is biased to increase a likelihood of choosing time synchronization and frequency trails which share the same source, over a likelihood of choosing trails with different sources. This can help avoid divergence and consequent bit errors arising from phase errors, resulting from trails having different sources. It can encompass for example changing both to a new common source, or changing one or both trails while still using the old common source.

Abstract: A method 10 of providing a path delay asymmetry for time synchronization between a master clock at a first client node and a slave clock at a second client node across a server communications network.

Abstract: Communication between a Radio Equipment Control (REC) and a Radio Equipment (RE) in a wireless network uses a Common Public Radio Interface connection. When the Radio Equipment Control and the Radio Equipment are located remote from each other, and are connected by an asymmetric transport network, such as an Optical Transport Network, path delay data is transmitted in the Common Public Radio Interface data frames. This allows the CPRI end nodes to correct for path delay asymmetry using the path delay data.

Abstract: A method distributes clock synchronization information within an optical communications network having a plurality of network elements. The method receives an ingress clock synchronization message at a first said network element. The ingress clock synchronization message includes a clock synchronisation message identifier and a correction field. The clock synchronisation message identifier is inserted into an optical channel frame overhead and the ingress clock synchronisation message is inserted into an optical channel frame payload. The optical channel frame overhead and the optical channel frame payload are transmitted across the first network element, across the network to a second said network element, and across the second network element. A transit time of the clock synchronisation message identifier is determined across each of the network elements.

Abstract: A method of determining properties of an optical communications path between a first optical network node (A) and a second optical network node (B) determines, at the second optical network node (B), a time difference between respective first and second optical test signals received on different wavelengths (?1, ?2) from the first optical network node. The method also determines, at the second optical network node (B), a real-time chromatic dispersion parameter for each of the wavelengths using a respective coherent receiver at the second optical network node. The method can be used to determine length of the path between the nodes (A, B). The method can be used to determine propagation delay between the nodes (A, B), or asymmetry in propagation delay between the nodes (A, B). Where separate paths are used for forward and reverse transmission directions, measurements can be made of each path.

Abstract: There is provided a method of optimizing timing packet transport in a network node, the method comprising using a locally available stable frequency reference at the network node to provide a pre-determined network node transit time for timing packets in at least one direction into or out of the network node. There is also provided a network node comprising a locally available stable frequency reference and circuitry adapted to apply a pre-determined network node transit time, L, to all timing packets transiting the network node in at least one direction into or out of a network node dependent on the locally available stable frequency reference.

Abstract: A method and system of distributing clock synchronization information within an optical communications network including a plurality of network elements, in which a first network element receives an ingress clock synchronization message, the ingress clock synchronization message including a clock synchronization message identifier and a correction field. The first network element inserts the clock synchronization message identifier into an optical channel frame overhead and inserts the ingress clock synchronization message into an optical channel frame payload. The first network element transmits the optical channel frame overhead and the optical channel frame payload to a second network element, and determines a transit time of the clock synchronization message identifier across each of the network elements. The second network element updates the correction field of the ingress clock synchronization message with said transit times to form an egress clock synchronization message.

Abstract: A passive optical network comprises a first node configured to transmit a downlink data signal over a communication channel of an optical link, the communication channel having a first wavelength, and a second node configured to transmit an uplink data signal over the optical link using the communication channel having the first wavelength. The first node and/or the second node is adapted to perform at least one monitoring measurement on the communication channel having the first wavelength, and provide monitoring information, comprising the at least one monitoring measurement, in a monitoring channel. Common public radio interface (CPRI) traffic can therefore be transported over an optical transport network (OTN), by using a frequency reuse technique to provide a symmetrical bi-directional communication link between a first node and a second node, and using a frame structure of the optical transport network to provide a monitoring channel.

Abstract: A method 10 of providing a path delay asymmetry for time synchronization between a master clock at a first client node and a slave clock at a second client node across a server communications network.

Abstract: A method and system of distributing clock synchronization information within an optical communications network including a plurality of network elements, in which a first network element receives an ingress clock synchronization message, the ingress clock synchronization message including a clock synchronisation message identifier and a correction field. The first network element inserts the clock synchronisation message identifier into an optical channel frame overhead and inserts the ingress clock synchronisation message into an optical channel frame payload. The first network element transmits the optical channel frame overhead and the optical channel frame payload to a second network element, and determines a transit time of the clock synchronisation message identifier across each of the network elements. The second network element updates the correction field of the ingress clock synchronisation message with said transit times to form an egress clock synchronisation message.

Abstract: A method for measuring asymmetry in propagation delay of first and second links which connect a first node to a second node of a communication network. The method comprises measuring (101) a round trip delay of the first link. The round trip delay can be measured by transmitting (102) a test signal from the first node to the second node over the first link and receiving a reply to the test signal from the second node over the first link. The method further comprises measuring (105) a round trip delay of the second link. The round trip delay can be measured by transmitting (106) a test signal to the second node over the second link and receiving a reply to the test signal from the second node over the second link. A difference in the propagation delay of the first link with respect to the second link is determined (109) using the measured round trip delays of the first link and the second link.

Abstract: The invention relates to networking in general and in particular to an improved packet timing transport mechanism. The present invention provides a method of optimizing timing packet transport in a network comprising a first network node connected to a second network node. The method comprises forwarding a timing packet received at the first network node to the second network node, and transmitting the timing packet from the second network node a pre-determined duration K after receiving the timing packet at the first network node.

Abstract: Configuring a node (410) of a synchronization network involves identifying (10) possible alternative time synchronization trails arranged to carry time synchronization information for time synchronization at the node, and possible alternative frequency trails, arranged to carry frequency synchronization information for frequency synchronization at the node. Using information about the sources (20), a comparison of the trails (30) is biased to increase a likelihood of choosing time synchronization and frequency trails which share the same source, over a likelihood of choosing trails with different sources. This can help avoid divergence and consequent bit errors arising from phase errors, resulting from trails having different sources. It can encompass for example changing both to a new common source, or changing one or both trails while still using the old common source.

Abstract: There is provided a method of optimizing timing packet transport in a network node, the method comprising using a locally available stable frequency reference at the network node to provide a pre-determined network node transit time for timing packets in at least one direction into or out of the network node. There is also provided a network node comprising a locally available stable frequency reference and circuitry adapted to apply a pre-determined network node transit time, L, to all timing packets transiting the network node in at least one direction into or out of a network node dependent on the locally available stable frequency reference.