Abstract: A method of determining a round trip delay time in a network comprising receiving a gate message allocating a transmission time window; retrieving a first timestamp from the gate message; setting a first clock to the time corresponding to the first timestamp, and wherein the first clock runs synchronously with a second clock recovered from a received data stream; sending upstream, after a time interval comprising a grant start time included in the transmission time window offset by a random delay time, a registration request message, wherein the registration request message includes a second timestamp obtained from the first clock; and determining a round trip delay (RTT) from a time the registration request message is received and the second timestamp.

Abstract: A remote socket apparatus comprises a socket to receive a remote electronics unit. The socket is configured to house multiple media to connect to remote electronics housed in the remote electronics unit. The socket includes a socket interface configured to mate with a remote electronics unit interface. At least one of the socket and remote electronics unit further includes an actuation mechanism configured to connect the multiple media simultaneously. The remote socket apparatus can be utilized in a network that provides in-building wireless (IBW) communications and in a converged network that also provides wired in-building telecommunications.

Abstract: In general, techniques are described for automatically discovering services in computer networks. A service node comprising a control unit and an interface may implement the techniques. The control unit determines services provided by the service node and generates a routing protocol message that includes service discovery information related to the services. The interface transmits the routing protocol message to enable network devices of the network to discover the services provided by the service node based on the service discovery information. The interface then receives traffic via a path established based on the service discovery information included in the routing protocol message and configured so that the service node applies at least one of the services to the traffic received via the path. The control unit then applies the one or more services to the traffic received via the path.

Abstract: In one embodiment, a network switch includes multiple chips communicably coupled together and a buffered crossbar. Each chip is coupled to every other chip with two bi-directional serial channels and includes a slice of the buffered crossbar. One or more input ports, one or more output ports, and an input logic module are coupled to the plurality of chips, and the input logic module is configured to receive a packet of data, allocate the packet of data into one or more data fragments, and distribute the packet of data to the buffered crossbar. An output logic module is coupled to the chips and configured to retrieve the packet of data from the buffered crossbar, reconstruct the packet of data from the data fragments according to a gather scheme, and transmit the packet of data.

Abstract: The present invention concerns an AFDX network which is extended by a passive optical network or PON. The AFDX network comprises an AFDX switch to which are connected a plurality of equipments. The AFDX switch constitutes the optical line termination and said equipments constitute the optical network terminations of the PON. The PON broadcasts over the downlink, to all said equipments, every AFDX frame output by said AFDX switch. It also multiplexes over the uplink the AFDX frames transmitted by the same equipments. The invention also concerns an ?AFDX network using a PON.

Abstract: A device that may include a router and may also include narrowband generators arranged to generate samples of narrowband channels, a digital up converter (DUC). The DUC may include multiple DUC inputs. Different DUC inputs are associated with different frequency ranges. The router may include multiple router inputs, multiple router outputs and a routing circuit. The multiple router outputs are coupled to the multiple DUC inputs. The multiple router inputs are coupled to the narrowband generators. The routing circuit may include a re-sequencing memory module that is arranged to receive the samples of narrowband channels from the narrowband generator according to an input order and to output the samples of the narrowband channels to the multiple router outputs according to an output order that is responsive to an allocation of frequencies to the samples of the narrowband channels.

Abstract: A method for communication includes configuring a multi-level fat-tree network to include at least three levels of switches, including multiple modules arranged externally in a tree topology. Each module contains a respective group of the switches arranged in an internal tree extending over at least two of the levels of the network. A subset of the modules is selected to be active in carrying the communication traffic. The network is operated so as to convey communication traffic among the switches via the active modules, while the modules that are not in the selected subset remain inactive.

Abstract: A system, method and apparatus is provided for optimizing network data communications. At an extender device, a data signal is received at a host link port across a data cable that is interfaced with the host link port. The host link port is configured to receive the data signal. The data cable is configured to carry management communications and data communications between a switch host device and the extender unit device. The data signal is split into data signal components. Each of the data signal components comprises a ten gigabit per second portion of the data signal. The data signal components are sent to one or more network devices via one or more corresponding data transmission ports.

Abstract: A method for automatic topology discovery implemented in a wavelength division multiplexing (WDM) network is disclosed. The WDM network contains a number of wavelength switching devices, and the method starts with selecting an unassigned wavelength between a pair of wavelength switching devices. For a first port of a first wavelength switching device, a pass through state is configured between the first port and a coupling port of the first wavelength switching device, and a first probing signal is sent at the unassigned wavelength to the first wavelength switching device. The method continues with detecting iteratively the first probing signal at the unassigned wavelength through each of a set of ports of a second wavelength switching device during a time period, and recording a connection between the first port of the first wavelength switching device and a port of the second wavelength switching devices when the first probing signal is detected.

Abstract: A system, method, and optical switch for communicating timing. A determination is made whether one of a number of data streams are available. Packets are received at a remote node in response to determining one of the number of data streams is available. A timing characteristic of the at least one of the packets is associated with a tick of a reference clock. The tick of the reference clock is extracted utilizing the timing characteristic of the at least one of the packets. A secondary clock is disciplined with the reference clock by adjusting the secondary clock based on a difference between times measured by the reference clock and the secondary clock to generate a clock signal. The clock signal is communicated to one or more interfaces for distributing.

Abstract: A method and system for static routing in a TRILL network is disclosed. Routing bridges in the TRILL network use LLDP discovery to identify their next hop routing bridges. A data packet, with an inner header specifying a MAC address of a destination host, is sent by a source host and received by an ingress routing bridge. The ingress routing bridge encapsulates the data packet with a TRILL header and an outer header and sends the data packet to a next hop routing bridge on path to the destination host. The next hop routing bridge determines it is not the egress routing bridge for the data packet and sends the data packet onward to the egress routing bridge. The egress routing bridge decapsulates the data packet and forwards the data packet to the destination host specified in the inner header.

Abstract: A reconfigurable optical add-drop multiplexer (ROADM) transport network comprising a plurality of optical fan-out devices and a first plurality and a second plurality of demultiplexers for locally dropping selected wavelengths; and first plurality and a second plurality of multiplexers for locally adding selected wavelengths, the first and second plurality disposed in a cascaded relationship to enable selective coupling between network degrees.

Abstract: Techniques for placing a first fibre channel (FC) switch into maintenance mode in a virtualized computing environment in which each data store is connected to at least one host computing system via at least two FC switches are described. In one embodiment, a first active input/output (I/O) path from a data store to a host computing system via the first FC switch is identified. Further, a path change is initiated from the data store to the host computing system via any other FC switch coupled to the data store and the host computing system.

Abstract: A hybrid electro-optical data center system includes multiple tiers. A bottom tier has one or more bottom tier instances, with each bottom tier instance including one or more racks, an electro-optical switch corresponding to each rack, and a first bottom tier optical loop providing optical connectivity between the electro-optical switches of the respective bottom tier instance. At least one server within each rack is electrically connected to the respective electro-optical switch and at least one super-server within each rack is electrically and optically connected to the respective electro-optical switch. A top tier includes electro-optical switches, each electrically connected to an electro-optical switch in a respective bottom tier instance, a first top tier optical loop providing optical connectivity between the electro-optical switches of the top tier, and one or more optical add/drop modules providing optical connectivity between the first bottom tier optical loop and the first top tier optical loop.

Abstract: An optical switch includes: a first birefringent element; a first Faraday rotator; a first half-wave plate; a second birefringent element; a second half-wave plate; a second Faraday rotator; and a third birefringent element, which are arranged in a forward direction from the front, wherein the first birefringent element splits light in the forward direction from a first optical port into ordinary and extraordinary lights emitted onto first and second optical paths, respectively, the first and second half-wave plates are arranged on the first and second optical paths, respectively, and in the first and second Faraday rotators, a permanent magnetic field in a left-right direction and an external magnetic field in a front-back direction in an on state are applied to a Faraday element, a bidirectional optical path is formed between the first and second optical ports in an off state, and the optical path is interrupted in the on state.

Abstract: Apparatuses are disclosed including a node having a switch for communicating traffic from input interface to output interface; and a control module, located proximate to the input interface, output interface and switch, comprising a communication interface configured to connect to a third communication link external to the node and having a processor accessing network node configuration information and being configured to compute a path to a destination node through the output interface with the network node configuration information and also configured to be switched from a first state in which the processor provides first instructions to the switch to configure the switch to communicate the traffic from the input interface to the output interface, to a second state in which the processor provides second instructions, received via the communication interface, to the switch to configure the switch to communicate traffic from the input interface to the output interface.

Abstract: The present disclosure discloses data vortex architecture with bidirectional links in which the packets are routed both in forward as well as in reverse directions through a single node. The disclosed arrangement avoids any packet congestion in the network and improves the BER characteristics.

Abstract: An apparatus comprising an optical multiplexer/demultiplexer having a set of input ports and a set of output ports, the optical multiplexer/demultiplexer configured to demultiplex a wavelength division multiplexed optical signal to one port of the set of input ports, and to output a plurality of demultiplexed wavelength channels to one of a plurality of subsets of output ports within the set of output ports. The apparatus comprises an optical switch configured to route the wavelength division multiplexed signal to a selected one of the input ports, thereby causing the plurality of demultiplexed wavelength channels to be output by the optical multiplexer/demultiplexer to selected ones of the plurality of subsets of output ports.

Abstract: The disclosure relates to a method and apparatus for implementing self-adaption of cross granularity in an Optical Transport Network (OTN). The method includes: acquiring an optical interface side OTN service signal which has been processed by a frame-forming chip, and performing determination on the frame header of an Optical channel Data Unit (ODU) frame of the current level in the OTN service signal; when frame-alignment is determined to be successful, performing level-by-level de-multiplexing processing on the ODU frame of the current level to obtain cross granularities of different levels, selecting output channels for the cross granularities of different levels, performing mapping processing on the output cross granularities of different levels to form fixed rate service signals, and outputting the fixed rate service signals to back board ports, where the signals are transmitted to a cross board.

Abstract: A system for routing signals in a Distributed Antenna System includes a plurality of local Digital Access Units (DAUs) located at a Local location. Each of the plurality of local DAUs is coupled to each other and operable to route signals between the plurality of local DAUs. Each of the plurality of local DAUs includes one or more Base Transceiver Station (BTS) RF connections. Each of the plurality of BTS RF connections is operable to be coupled to one of one or more sectors of a BTS. The system also includes a plurality of remote DAUs located at a Remote location. The plurality of remote DAUs are coupled to each other and operable to transport signals between the plurality of remote DAUs.

Abstract: A unified network and elements thereof, including a switch fabric, is provided. The switch fabric may include a plurality of transport elements and a first signal-communication media. The transport elements may be adapted to communicatively couple and to communicate, via the first signal-communication media, transport signals adapted for communication among any of the plurality of transport elements. At least one transport element may be further adapted to communicate, via a second signal-communication media, signals and/or sets of signal originating from and/or terminating to one or more network nodes. Each of the electrical signals may be formatted in accordance with a protocol for electrical signals. And one or more of the transport signals may include the electrical signals in adapted form. Additionally and/or alternatively, one or more of the transport signals may be formed from, or as a function of, the electrical signals.

Abstract: The present invention is directed to communication system and methods. More specifically, various embodiments of the present invention provide a communication interface that is configured to transfer data at high bandwidth using PAM format(s) over optical communication networks. In certain embodiments, the communication interface is used by various devices within a spine-leaf network architecture, which allows large amount of data to be shared among servers.

Abstract: A method for establishing an end-to-end service is provided in the present invention, which includes: acquiring link information in a network and multi-stage multiplexing capability constraint information supported by gateway network elements; when an end-to-end path computation request is received, according to the link information and the multi-stage multiplexing capability constraint information, performing an end-to-end routing computation to acquire an end-to-end routing, and selecting a multi-stage multiplexing capability used on a gateway network element passed by the end-to-end routing; and configuring the end-to-end service, and configuring the selected multi-stage multiplexing capability on the gateway network element passed by the end-to-end routing. A system for establishing the end-to-end service, an optical transport network and a signal transmission method thereof are also provided in the present invention, which can all implement the interconnection between new networks and old networks.

Abstract: A network is described in which a base optical point-to-point (P2P) network can be reconfigured to a target network topology. This reconfigurable architecture customizes the network topology for different classes of applications to maximize throughput. In particular, the network can function efficiently at high-radix and low-radix traffic patterns. This capability is obtained using configurable electrical circuit switches at each node in the network. These configurable electrical circuit switches can be set so that incoming packets are directly routed to a specified output (either a local destination or an outgoing optical link) without: delay, contention, or buffers. In this way, predefined network topologies can be configured with improved node-to-node bandwidths when compared to the original P2P network by leveraging unused optical links. Furthermore, because the electrical circuit switches can be reconfigured, the network topology can be dynamically reconfigured to suit applications or application phases.

Abstract: A configurable Clos network includes leafs and spines and a switch fabric that connects the leafs and the spines. The switch fabric couples each leaf port of each leaf to at least one spine port of each spine.

Abstract: Techniques are provided for distributing a fabric name to switching elements of a distributed switch configured to forward Fibre Channel over Ethernet (FCoE) frames. A distributed switch membership distributed (DMFD) message is transmitted that includes names of all switching elements in the distributed switch, and further includes a fabric descriptor that contains the fabric name.

Abstract: An optical intensity control system for use with an optical switch providing individual signal paths between input and output ports. The system has optical splitters connectable to output multiplexers of the switch and has variable optical intensity controllers (VOICs) for insertion into the individual signal paths to individually control the intensity of optical signals present in the signal paths via intensity control signals. An equalizer is connected to the splitters and to the VOICs produces an estimate of the optical power of each individual switched optical signal and generates the intensity control signals. The equalizer is adapted to controllably isolate individual switched optical signals. In this way, individual and independent control of the power on each optical channel is provided.

Abstract: A wavelength division multiplexed optical communication system includes a plurality of optical line terminals which may be part of separate in service networks, each having a line interface and an all-optical pass-through interface including a plurality of pass-through optical ports, and each also including a plurality of local optical ports which are connectable to client equipment and an optical multiplexer/demultiplexer for multiplexing/demultiplexing optical wavelengths. The optical multiplexer/demultiplexer may include one or more stages for inputting/outputting individual wavelengths or bands of a predetermined number of wavelengths, or a combination of bands and individual wavelengths.

Abstract: A method and apparatus for low-rate traffic signal transmission on Optical Transport Networks (OTN). The method includes: defining a frame format of the low-rate traffic optical channel data unit (ODU) signal for bearing the low-rate traffic signal; mapping the low-rate traffic signal to the low-rate traffic optical channel payload unit (OPU) of the low-rate traffic ODU signal, generating overhead bytes and filling the bytes in an overhead section of the low-rate traffic ODU to obtain the low-rate traffic ODU signal; multiplexing low-rate traffic ODU signals to an ODUk signal of which the rate matches the transmission rate rank of the OTN where the signal is transmitted, and transmitting the signal via the OTN. Based on this method, the invention provides an apparatus for the low-rate traffic signal transmission in the OTN as well. With this invention, the low-rate traffic signal transmission in the OTN can be implemented conveniently.

Abstract: Bandwidth translation may be provided. First, data may be transceived at a first data port. Next, the data may be transceived at a plurality of second data ports. The bandwidth of a path for the data between the first port and the plurality of second ports may be translated.

Abstract: Example embodiments of the present invention relate to An optical node comprising of at least two optical degrees; a plurality of directionless add/drop ports; and at least one wavelength equalizing array, wherein the at least one wavelength equalizing array is used to both select wavelengths for each degree, and to perform directionless steering for the add/drop ports.

Abstract: Embodiments provide a methodology for designing a large-scale non-blocking OCS using a multi-stage folded CLOS switch architecture for use in datacenter networks and fiber-rich backbone network POPs. One aspect employs a folded CLOS architecture because of its ease of implementation, enabling the topology to scale arbitrarily with increasing number of stages. The fraction of ports allocated for internal switch wiring (overhead) also increases with the number of stages. Design decisions are made to carefully optimize the insertion loss per module, number of ports per module, number of stages and the total scale required. Other embodiments include folded CLOS switch architectures having at least two stages. In one example, power monitoring may be included only on the leaf switches.

Abstract: The invention discloses a system, a method and an apparatus for optical network protection. The system includes: an output control apparatus for obtaining protection mode information configured by a system and controlling an input signal to be output from a set line corresponding to said protection mode information; and a detection control apparatus for detecting powers of signals transmitted on an active line and on a standby line, if it is determined that the active line is abnormal and the standby line is normal according to detection results, then controlling the input signal to be output from a protection line corresponding to the protection mode information; if it is determined that the active line is normal, or that the active line and the standby line are abnormal according to the detection result, then controlling the input signal to be output from a set line corresponding to the protection mode information.

Abstract: An automated, robotic patch-panel system in a highly compact form factor implementing Knots and Braids switching algorithms is disclosed. This system incorporates stacked layers of connector ports, each row of connector ports defining an arc with a radius of curvature, wherein the radius of curvature is substantially larger than the total height of the stacked layers. A synchronized gripper pair on a three axis actuation system is used to disconnect, weave and connect fibers arbitrarily across an array of dense connector ports on a curvilinear surface. Each row of connector ports is independently translatable by slight rotation to generate the proper relationship between surrounding fibers and the individual fiber undergoing the multi-step reconfiguration process.

Abstract: The present invention relates to a method and apparatus for reducing the resource utilization of the switching fabric in a SONET/SDH multiplexer by switching data on a TU level instead of byte or column level.

Abstract: A multi-path provisioning scheme is provided to ensure full protection while reducing or minimizing resource overbuild. A signal to be provisioned is divided at a source node into a plurality of sub-signals that are independently routed from the source node to a destination node. Bandwidth for back-up traffic B is allocated in addition to bandwidth for primary traffic T. In some embodiments, the initial bandwidth B of the backup traffic equals the bandwidth of the primary traffic. The T+B traffic is initially distributed so that no link carries more than B traffic. The traffic distribution pattern is then iteratively revised to reduce the bandwidth requirements for the backup traffic while still meeting requirements for protection.

Abstract: A transparent clock converter is interposed between a non-precision time protocol (non-PTP) enabled network node and other portions of the network. The transparent clock converter effectively converts the non-PTP node into a transparent clock node. In some embodiments the transparent clock converter includes physical layer devices, but not media access controllers.

Abstract: The present principles are directed to a transponder aggregator-based optical loopback in a multi-degree colorless, directionless, contention-less, reconfigurable optical add/drop multiplexer. The multiplexer includes a reconfigurable optical add/drop multiplexer section for performing connect operations for wavelength division multiplexing signals among all degrees. The section has a plurality of subsections. Each of the subsections corresponds to a respective one of the degrees and has an optical separator at an input side and an optical combiner at an output side. The multiplexer further includes a transponder aggregator section having a split-and-select switch-based transponder aggregator. The multiplexer also includes an optical line loopback having a connection path between the optical separator at the input side and the optical combiner at the output side of at least one of the subsections.

Abstract: A system and method for connectivity configuration of a network node permits an optical signal to be passed through the node and shifted from a first connector position to a second connector position that is offset from the first connector position. The shifted optical signal permits a number of distant nodes in the network to be reached with a direct optical connection, which can be configured to be bidirectional. The disclosed connectivity configuration reduces the cabling requirements for the network and simplifies the interconnections.

Abstract: An optical line terminal (OLT) device and an implementation method thereof, relate to the field of a passive optical network (PON). The OLT device includes an interface unit for receiving data in an Ethernet format sent by a service processing apparatus, performing protocol processing on the received data in the Ethernet format, converting the data after the protocol processing into a transmission signal corresponding to a sending interface, and then transmitting the transmission signal to an external device, as well as receiving message data sent by the external device, converting the message data for protocol processing corresponding to the service processing apparatus, converting the signal after the protocol processing into data in the Ethernet format, and transmitting the data to the service processing apparatus; the service processing apparatus performing service processing on the data transmitted by the interface unit, and transmitting the processed data to the interface unit.

Abstract: A system and method for designing and constructing optical networks is provided. The system comprises: a server, and interactive software program residing on the server, an interactive input device—capable of accessing the interactive software program residing on the server, and a communication network—used to connect the interactive input device to the server. The method comprises: entering network topology information and service demands for a plurality of nodes into the interactive software program residing on the server, having the interactive software program determine the required optical equipment for the nodes, and ordering the required optical equipment for the nodes using the interactive software program.

Abstract: The present invention is directed to data communication system and methods. More specifically, various embodiments of the present invention provide a communication interface that is configured to transfer data at high bandwidth using PAM format(s) over optical communication networks. In various embodiments, amplitude and phase of the optical wave are modulated. There are other embodiments as well.

Abstract: A packet switch 40 comprises wavelength tunable optical transmitters 12, an optical switch fabric 42, optical detectors 30 and a controller 32. The transmitters 12 are arranged to receive at least one electrical signal packet to be switched and convert it into a corresponding optical signal packet at an input wavelength. The optical switch fabric 42 comprises an ingress stage 44 comprising wavelength selective routers 46 and an egress stage 50 comprising wavelength selective routers 54 and tunable wavelength converters 26 arranged to receive an optical signal at the input wavelength and to output an optical signal at an output wavelength. The controller 32 is arranged to set the input wavelength of a transmitter 12 and the output wavelength of a wavelength converter to configure a path across the switch fabric 42 connecting the transmitter 12 to a detector 30. A communications network router 90 comprises an input module 92, a packet switch 40, an output module 96 and a scheduler 94.

Abstract: A network is described in which a base optical point-to-point (P2P) network can be reconfigured to a target network topology. This reconfigurable architecture customizes the network topology for different classes of applications to maximize throughput. In particular, the network can function efficiently at high-radix and low-radix traffic patterns. This capability is obtained using configurable electrical circuit switches at each node in the network. These configurable electrical circuit switches can be set so that incoming packets are directly routed to a specified output (either a local destination or an outgoing optical link) without: delay, contention, or buffers. In this way, predefined network topologies can be configured with improved node-to-node bandwidths when compared to the original P2P network by leveraging unused optical links. Furthermore, because the electrical circuit switches can be reconfigured, the network topology can be dynamically reconfigured to suit applications or application phases.

Abstract: Methods and systems for variable rate control include determining a new communications rate in response to measured data traffic patterns. A receive change message is transmitted to a receiver that triggers the receiver to wait for an end of transmission (EoT) message and to set a new communications rate. A transmit change message is transmitted to a transmitter that triggers the transmitter to send the EoT message to the receiver, to set the new communications rate, and to send a start of transmission (SoT) message to the receiver before resuming data communications.

Abstract: A system and method for optical switching of networks in a multi-node computing system with programmable magneto-optical switches that enable optical signal routing on optical pathways. The system includes a network of optical links interconnecting nodes with switching elements that are controlled by electrical control signals. Data transmission is along the optical links and an optical pathway is determined by the electrical control signals which are launched ahead of optical signal. If links are available, an optical pathway is reserved, and the electrical signal sets the necessary optical switches for the particular optical pathway. There is thereby eliminated the need for optical-electrical-optical conversion at each node in order to route data packets through the network. If a link or optical pathway is not available the system tries to find an alternative path. If no alternative path is available, the system reserves buffering. After transmission, all reservations are released.

Abstract: Various architectures of a multi-degree reconfigurable optical add-drop multiplexer with reduced contention are provided. These architectures allow the degree of contention reduction to be managed in a flexible and modular way. The degree of the node and the amount of add/drop at the node can also be managed in a flexible and modular way. This Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Abstract: A network device includes a plurality of optical input/output (I/O) units to exchange one or more optical signals with the optical network. The network device further includes a switch fabric to process one or more optical signals exchanged with an optical network. The network device also includes a connector configured to receive a connector to couple the network device to another device. The network device also includes a base layer connecting to the plurality of optical I/O units and the switch fabric. The base layer is included in a connection that does not include a back plane and that enables communications between the plurality of I/O units, the switch fabric, and the connector.

Abstract: The disclosure claims a bandwidth adjustment method and system for Optical channel Data Unit flexible (ODUflex) based on a Generic Framing Procedure (GFP), wherein, the method includes that: (501) a source end sends a bandwidth adjustment control frame which contains bandwidth adjustment parameters; (503) a plurality of intermediate nodes forward the bandwidth adjustment control frame to a sink end via an ODUflex link, during the forwarding process, the plurality of intermediate nodes determine that resource thereof can satisfy the bandwidth adjustment parameters, and then reserve the bandwidth adjustment resource; (505) after receiving the bandwidth adjustment control frame, the sink end feeds back an adjustment acknowledgment frame which contains adjustment acknowledgment information to the source end via the plurality of intermediate nodes; (507) the plurality of intermediate nodes use the reserved bandwidth adjustment resource to implement adjustment for the bandwidth of the ODUflex link according to the

Abstract: A method is provided for detecting the skew between parallel light signals generated from a serial data stream. The method can be used with polarization multiplexed signal, as well as with wavelength division multiplexed signals, spatial division multiplexed signals, phase modulated signals, or intensity modulated signals. The method can be used with direct detection schemes as well as with coherent detection schemes. The method is provided with: imprinting dips between a fixed number of transmitted symbols of the parallel signals; detecting an electrical signal related to the dips for each parallel signal; and comparing the electrical signals in delay.