Abstract: A method (10) of configuring a synchronous optical switch to route received data cells. The synchronous optical switch comprises optical switch transmitter modules, each comprising tunable optical transmitters, optical switch receiver modules, each comprising optical receivers, and optical connections between the transmitter modules and receiver modules. For each optical switch transmitter module, the method: assigns (12) wavelengths associated with the received data cells to the transmitters such that each wavelength is assigned to a different transmitter; and generates (14) a control signal for controlling the operating wavelength of each transmitter.

Abstract: Systems, methods, media, and means for hiding network topology are provided. In some embodiments, methods for hiding network topology are provided, the methods including: receiving a message including topology information from a sender; removing at least part of the topology information; associating the removed topology information with an identifier; saving the topology information; sending the message to a receiver; receiving a response from the receiver; retrieving the removed topology information based on the identifier; inserting the removed topology information into the response; and sending the response to the sender.

Abstract: A distributed fabric system comprises a plurality of independent network elements interconnected by inter-switch links and assigned to a same group. Each network element includes one or more switching chips, a processor, and memory storing program code that is executed by the processor. The program code of each network element includes a switch discovery protocol (SDP) module. The SDP module of each network element, when executed, periodically multicasts SDP data units (SDPDUs) using one of a plurality of transmission rates. The plurality of transmission rates includes a fast transmission rate and a slow transmission rate. The transmission rate used by the SDP module of each network element is the fast transmission rate until the SDP module of that network element determines a criterion is met, in response to which the transmission rate used by the SDP module of that network element changes to the slow transmission rate.

Abstract: A negotiation process is conducted between a controller and a target forwarding or switching device with respect to an abstract candidate device model for a forwarding plane. The abstract candidate device model is provided by a controller and indicates intended forwarding or switching behavior for the target device that a controller desires to have implemented on the target device. The intended behavior is specified in terms of mandatory and non-mandatory behavior. A hardware abstraction layer (HAL) for the target device analyzes the abstract candidate device model and decides whether the mandatory and optional behavior that is specified by the model is supported given the architecture of the target. The HAL informs the controller whether the intended behavior is supported by the target. Additional behavior may be proposed and accepted or not before the model is finalized. The finalized model may then be implemented and used to control forwarding behavior on the target device.

Abstract: A network switch including a port receiving a first frame. A memory includes first buffers available to store frames and second buffers reserved for the port. A pointer module stores first pointers for the first buffers. A reserve module includes a counter, requests from the pointer module some of the first pointers, and increments the counter to count a number of pointers reserved for the first port. The pointers received from the pointer module are deemed reserved and as a result the first buffers, pointed to by the pointers received from the pointer module, are included in the second buffers. An ingress module stores the first frame in some of the second buffers and determines a destination channel for the first frame. The counter is incremented for each of the second buffers used to store the first frame. An egress module transmits the frame on the destination channel.

Abstract: A new type of Provider Edge (PE) device is used to support BGP-based IP-VPNs. Each VRF instance in a PE device is associated with a dedicated IP address (Service IP address). Each service IP address is dedicated to a VRF in a PE device. The service IP address is distributed by BGP for VPN route association. Customer/VRF IP packets can be sent to a VRF instance in the egress PE device using service IP header encapsulation (with IP Destination Address=Service IP address of egress PE's VRF & IP Source Address=Service IP address of ingress PE's VRF). This obviates the need for explicit tunnels in the core.

Abstract: Fault-tolerant multicast networks via network coding comprises a digital signal operator that combines data signals multicast from multiple sources and transmits the combined data signal via a link to the next or destination node. In one aspect, the digital signal operator includes an exclusive-OR operator that performs a Boolean exclusive-OR function on the received bit streams of the multicast data from the plurality of sources.

Abstract: The method that is disclosed enables specific information network traffic flows to retain packet ordering in a packet network in which multipath techniques are used. In a common network usage a plurality of traffic flows may be aggregated into a larger traffic flow. In such a situation, a finest granularity of individual traffic flow is referred to as a microflow and an aggregation of traffic flows is referred to as a traffic aggregate. The traffic aggregate may take a path from an ordered set of nodes including a first network element referred to as an ingress node through zero or more intermediate network elements referred to as midpoint nodes, to a final network known as the egress node. The ordered set of nodes traversed by such a traffic aggregate is referred to as the path taken by that traffic flow. At any node prior to the egress, the traffic aggregate may be split among multiple links or lower layer paths in reaching the next node in the path.

Abstract: Methods and apparatus to dynamically control connectivity within VPNs are disclosed. A disclosed example route server to control connectivity within a VPN comprises a memory to implement a database, a border gateway protocol (BGP) engine to process BGP advertisements, a network interface to receive a first BGP advertisement, which a first route target (RT) associated with the first PE router, from a first provider edge (PE) router associated with the VPN, and an intra-VPN connectivity controller to, in response to the first BGP advertisement, query the database to determine whether the first PE router is to be communicatively coupled to a second PE router of the VPN and when the first and second PE routers of the VPN are to be communicatively coupled, direct the BGP engine to form a second BGP advertisement that includes a second RT associated with the second PE router based on the first BGP advertisement.

Abstract: A control method of virtual link discovery and a system for Fiber Channel over Ethernet (FCoE) protocol allocates some Ethernet Nodes (ENodes) and FCoE Forwarders (FCFs) to different virtual networks during networking, and provides a Virtual Node (VN) port of each ENode and a Virtual Fiber Channel (VFC) port of each FCF with a Virtual Network Identification (VN ID) of a virtual network to which they belong. In this way, a VN port of an ENode may establish a virtual link with a VFC port that belongs to the same virtual network in preference, so that some ENodes are made to access FCFs that belong to the same virtual networks as the ENodes.

Abstract: A method and computer program product for defining a multicast group within a local area network. The multicast group includes a storage initiator device and a plurality of mirrored targets. Each mirrored target includes a plurality of storage targets. A write request for storing a data segment within the multicast group is received on the storage initiator device. The data segment is multicast to the plurality of mirrored targets included within the multicast group. A unique data chunk of the data segment is stored on each of the plurality of mirrored targets.

Abstract: A method, apparatus and computer program product for efficiently transmitting tunnel keep-alive messages is presented. A tunnel keep-alive trigger message is provided from a control processor of a multi-processor network switching device to at least one forwarding engine of the network switching device. The at least one of the forwarding engines produces a tunnel keep-alive packet as a result of receiving the tunnel keep-alive trigger message from the control processor. The at least one forwarding engine forwards the tunnel keep-alive packet on all tunnels the forwarding engine is servicing.

Abstract: A first header-attaching unit attaches to data of a low speed bit rate A, a header of the bit rate A. A second header-attaching unit attaches the header of the bit rate A to data of a high speed bit rate B. A combining unit combines outputs of the first and the second header-attaching units. A low speed scrambling unit performs a scrambling process on combined data by using a clock corresponding to the bit rate A. A high speed scrambling unit performs a scrambling process on the data of the bit rate B by using a clock corresponding to the bit rate B. During a timing corresponding to the bit rate A in the frame, a selector selects an output of the low speed scrambling unit. During a timing corresponding to the bit rate B in the frame, the selector selects an output of the high speed scrambling unit.

Abstract: A grid router includes a plurality of external interface units to receive packets of services from one point and to provide packets of services to another point and a second plurality of mailbox units to store and forward the packets associated with mailboxes, one per service. Each mailbox unit is connected to each external interface unit. The units are implemented on PCs (personal computers) having memory controllers and move the packets through the router close to or at the I/O (input/output) rate of the memory controllers.

Abstract: In one embodiment, the present invention is directed to method for receiving a packet in a first agent, where the packet includes a first packet header with an expanded header indicator. Based on this indicator, the agent can determine if the packet includes one or more additional packet headers. If so, the agent can next determining if it supports information in the additional packet header based on a header identifier of the additional header. Other embodiments are described and claimed.

Abstract: A system and method for handling a digital electronic flow between a first and second entity in which a flow policy is determined that is to be applied to the flow and the flow is then directed along a path in accordance with the policy. An ID is supplied for each flow and a tag associated with each flow which indicates the policy to be applied to its associated flow. Flows are also associated with one another, with associated flows having associated policies. In particular the flow may be processed or forwarded. The path may include a graph structure and virtual applications.

Abstract: When stored identifying information of a transmission target frame and identifying information of a received frame are equal, a node apparatus updates transmission feasibility information stored in association with the final destination of the received frame. The transmission feasibility information indicates feasibility of transmission to each of a plurality of adjacent node apparatuses being a transmission destination, and is updated so that feasibility of transmission to the transmission destination associated with the identifying information of the received frame indicates that “the transmission is infeasible”. The node apparatus transmits the received frame, when there is no adjacent apparatus to which transmission is feasible, and when the stored identifying information of the transmission target frame is equal to the identifying information of the received frame, to the adjacent node apparatus recognized as the origin in association with the identifying information of the received frame.

Abstract: An island-based network flow processor (IB-NFP) integrated circuit includes islands organized in rows. A configurable mesh event bus extends through the islands and is configured to form a local event ring. The configurable mesh event bus is configured with configuration information received via a configurable mesh control bus. The local event ring involves event ring circuits and event ring segments. In one example, a packet is received onto a first island. If an amount of a processing resource (for example, memory buffer space) available to the first island is below a threshold, then an event packet is communicated from the first island to a second island via the local event ring. In response, the second island causes a third island to communicate via a command/push/pull data bus with the first island, thereby increasing the amount of the processing resource available to the first island for handing incoming packets.

Abstract: An embodiment system and method to provide rack awareness for a virtual machine running on a data center server. The virtual machine sends an address resolution protocol request message to a top-of-rack switch to identify a MAC address of the server physical port. The virtual machine receives a reply containing the MAC address of the top-of-rack switch physical port. The virtual machine sends an ICMP packet to the top-of-rack switch with a pre-selected un-routable IP address using the identified physical port MAC address. The virtual machine then receives a message from the top-of-rack switch providing a top-of-rack IP address. The virtual machine employs the top-of-rack IP address to identify the rack location of the server.

Abstract: An apparatus and method for analyzing a data packet, where the first and second information is derived relating to the data packet. The first information relates to a type of the data packet, a standard to which the data packet conforms and/or which data item(s) is/are present in the data packet. The first information is used for identifying a function into which the second information is input to generate third, and this third information is output together with at least part of the data packet.

Abstract: A method of routing internal network traffic within a computing system comprises receiving a network packet at a configurable logic device (CLD), parsing the network packet to obtain a destination address, searching a predetermined range of a routing table wherein each row of the routing table specifies a range of possible destination addresses and routing information, identifying a matching row of the routing table wherein the destination address falls within the range of possible destination addresses of the matching row, and routing the packet according to the routing information.

Abstract: A system for matching data using flow based packet data storage includes a communications interface and a processor. A communications interface receives a packet between a source and a destination. The processor identifies a flow between the source and the destination based on the packet. The processor determines whether some of packet data of the packet indicates a potential match to data in storage using hashes. The processor then stores the data from the most likely data match and second most likely data match without a packet header in a block of memory in the storage based on the flow.

Abstract: In one embodiment, a method is provided. The method of this embodiment provides storing a packet header at a set of at least one page of memory allocated to storing packet headers, and storing the packet header and a packet payload at a location not in the set of at least one page of memory allocated to storing packet headers.

Abstract: A method, device, and program for determining states in a flow of packets are provided. A flow of transmitted packets is received. When the difference between the sequence number of the arriving packet and the next expected sequence number is equal to zero and when the TTL number of the arriving packet is equal to the TTL number of the previous packet, there is a stable state beginning with the first of the consecutively received packets. If a difference between the sequence number of an arriving packet and a next expected sequence number is greater than 1, or TTL of the arriving packet is not equal to the TTL number of the previous packet, there is a not stable state. Time between end of one stable state and start of the next stable state is the hole, and the states and holes correlate to events for analysis of the network.

Abstract: A content capability clearing house that can act as a trusted and neutral mediator among network providers to manage rich content capabilities among multiple networks is provided. Content capabilities that can be brokered include, but are not limited to, quality of service and content screening. In an embodiment, a content capability clearing house includes a receiver that receives content capability request messages and other messages from network providers. A content capability request message includes a quality of service request and/or a subscriber profile request for use with content screening and subscriber specific advertisements. The present invention includes a series of methods for determining content capabilities for data transmission over a transaction between a content provider and a subscriber in which a content capability clearing house is used to efficiently broker and manage the capability among multiple network providers.

Abstract: A network device or user equipment (UE) may manage the transmission and retransmission of radio link control (RLC) data protocol data units (PDUs). An indication is received that an RLC data PDU was not successfully received by a receiving device. The RLC data PDU, that was not successfully received, is retransmitted, and prioritized over non-retransmitted RLC data PDUs. A number of times that the RLC data PDU was retransmitted is determined.

Abstract: A method of establishing a multipath in a heterogeneous interface environment among wireless nodes including a source node, a relay node, and a destination node which receives a message from the source node via the relay node, the method including: receiving a route request message by a wireless node; and associating at least two heterogeneous interfaces of the wireless node by using a destination node address in the route request message.

Abstract: A cognitive radio communication network is provided. The cognitive radio communication network includes a cloud and a wireless communication network. A communication system accessing to a backbone network is provided. The communication system includes a cloud and a wireless communication network connected to the cloud, and having a plurality of cognitive radio access points and a plurality of users, wherein the cloud performs the functions of network management, power control, and radio resource management.

Abstract: An allocation technique is operable to allocate communication resources in multi-hop networks under the joint consideration of communication requirements and fairness. Embodiments operate to provide allocation of time slot resources in TDMA based multi-hop wireless networks under the joint consideration of QoS and fairness. Embodiments operate with respect to information regarding maximal common slot set flow contention. An iterative process is applied with respect to the information regarding maximal common slot set flow contention to allocate communication resources providing a balance between meeting communication requirements and fairness. According to embodiments, an inter-graph process iteratively selects a maximal common slot set for which resource allocation with respect to various flows is to be performed and an intra-graph process assigns communication resources in the maximal common slot set providing a balancing between meeting communication requirements (e.g., QoS) and providing fairness.

Abstract: A reference signal transmission method in a downlink MIMO system is disclosed. The downlink MIMO system supports a first UE supporting N transmission antennas among a total of M transmission antennas (where M>N) and a second UE supporting the M transmission antennas. The method includes transmitting, by a base station (BS), subframe-associated information which designates a first subframe in which data for the first UE and the second UE is transmitted and a second subframe in which data only for the second UE can be transmitted within a radio frame having a plurality of subframes, and transmitting the first subframe and the second subframe. Reference signals corresponding to antenna ports ‘0’ to ‘N?1’ of the N antennas are mapped to the first subframe, and reference signals corresponding to antenna ports ‘0’ to ‘M?1’ of the M antennas are mapped to the second subframe.

Abstract: In a method for estimating a channel at a receiver in a wireless communications network, the receiver obtains channel model parameters for a received signal based on raw channel estimates for the received signal, where each raw channel estimate corresponds to an antenna at the receiver. The receiver combines, for each of a plurality of contiguous subcarriers in the wireless communications network, the channel model parameters to generate a first plurality of combined channel model parameters. The receiver then chooses a first set of indices corresponding to combined channel model parameters from among the first plurality of combined channel model parameters having magnitudes passing a combined channel model parameter threshold. The receiver then estimates the channel in a sparse domain based on the first set of indices.

Abstract: According to various embodiments, a communication switch may create and/or manage a variety of configurable network relationships between intelligent electronic devices (IEDs) connected via disparate network interfaces using a variety of communication protocols. Accordingly, a communication switch may provide media translation between various types of physical network ports and communication protocol conversion between various communication protocols. For example, a communication switch may be used to create a networked group of IEDs in which some IEDs are connected via Ethernet ports and other IEDs are connected via D-subminiature ports and/or optical ports. The communication switch may create and/or manage network relationships such as publisher/subscriber, master/slave, multidrop configurations, star configurations, and/or other complex network relationships between two or more IEDs or groups of IEDs.

Abstract: A method and apparatus for implementing a protocol-neutral middleware interface in a home area network. The method comprises receiving one or more data packets from a client device using a first communication protocol, and decoding the data packets into a set of platform independent data objects. The data packets are decoded into the platform independent data objects by utilizing a metadata mapping located within one or more field classes. The apparatus comprises a frame engine, and one or more field classes. The frame engine receives a data packet in a first communication protocol. The frame engine decodes the data packet into a set of platform independent data objects. The frame engine uses a metadata map contained within the one or more field classes to decode the data packet into the set of platform independent data objects.

Abstract: Techniques for addressing high interference observed by a receiver in a wireless communication system are disclosed. The receiver may observe different interference power levels across a transmission symbol. In an aspect, the receiver applies different weights to different portions of the transmission symbol to account for fluctuation of interference power across the transmission symbol. In another aspect, a transmitter may send a transmission symbol such that a receiver can ignore a portion of a symbol period with high interference. In one design, the transmitter generates a transmission symbol including at least two copies of a signal component. The transmitter transmits at least one copy of the signal component in a portion of the symbol period in which the receiver does not observe high interference. The receiver processes the at least one copy of the signal component to recover data sent in the transmission symbol.

Abstract: Apparatus and methods are provided for delivering end-to-end Quality of Service (QoS) over Internet Protocol (IP) networks. According to one embodiment, a portion of available bandwidth between a first and second network device is reserved as a Quality of Service (QoS) resource pool for real-time communication sessions among users of a first and second user community. The first network device is communicatively coupled with a packet network and associated with the first user community. The second network device is communicatively coupled with the packet network and associated with the second user community.

Abstract: Disclosed is a multicast system and a multicast method using a shortened address and an apparatus applied to the same. The multicast system using the shortened address according to the present disclosure has a address configuration for supporting a multicast in an IEEE 802.15.4 MAC (Medium Access Control) layer. Accordingly, when a device processes a multicast through an address configuration of the MAC layer, the device receives the multicast through a simple scheduling such as receiving a beacon signal of a coordinator device only when there is a broadcast of a group including the device. As a result, the device can efficiently perform the multicast in a power managing process or a power processing process.

Abstract: An apparatus comprising a data framer configured to frame a Media Access Control (MAC) control message for transmission, the MAC control message comprising an organization specific identifier (OUI) and at least one type-length-value (TLV) comprising a type field, a length field, and a value field, wherein a format of the TLV is specified by the OUI, and wherein the value field comprises information related to operation, administration, and maintenance (OAM) features of a network. Also included is an apparatus comprising at least one component configured to implement a method comprising compiling an OAM message comprising a plurality of organization-specific TLVs and an organization unique identifier (OUI) that indicates an organization responsible for the format of the TLV, and transmitting the OAM message.

Abstract: A transmitter device includes a controller configured to generate a first field and a second field. The first field is at least one of a packet synchronization information field or a frame boundary indication field, the second field is a channel estimation field starting after the first field ends. The controller is configured to generate the second field at least in part by generating a first channel estimation sequence (CES) symbol and a second CES symbol. At least one of i) a sequence in the first field serves as a cyclic prefix of the first CES symbol, ii) a beginning portion of the second CES symbol serves as a cyclic postfix of the first CES symbol, or iii) an ending portion of the first CES symbol serves as a cyclic prefix of the second CES symbol.

Abstract: A method of powerline communications including a first node and at least a second node on a PLC channel in a PLC network. The first node sends a physical layer (PHY) data frame on the PLC channel including a preamble, PHY header, a MAC header and a MAC payload. The PHY header includes a destination address field having a destination address therein. The second node receives the data frame. The second node compares its network address to the destination address before decoding the MAC header and MAC payload, providing power savings by allowing the second node to not decode the MAC header or MAC payload if its network address does not match the destination address in the PHY header of the data frame.

Abstract: In an embodiment, a network device obtains a plurality of data packets that are each associated with one of a plurality of different streams, wherein each of the plurality of obtained data packets includes a header portion with stream-specific routing information. The network device strips the stream-specific routing information from the plurality of obtained data packets to produce a plurality of stream-specific payload portions, which are merged into a shared payload portion of a stream-multiplexed data packet that includes common routing information for the plurality of streams in a common header portion. The network device transmits the stream-multiplexed packet to a target device, and the target device determines whether any of the plurality of different streams are relevant to the target UE based on stream-mapping information contained in the stream-multiplexed packet, and selectively decodes and processes the stream-specific payload portions corresponding based on the determination.

Abstract: A physical layer (PL) frame generation method is provided. A PL payload is generated by encoding and modulating source data based on a first modcod of a first set. A synchronization header (a unique word (UW) of a UW set) is appended to the PL payload. The UWs of the set respectively correspond to different modcods of the first set, and the UW corresponds to the first modcod. A PL header is appended to the synchronization header and PL payload to form the PL frame. The PL header comprises a second UW and physical layer signaling (PLS). The PLS comprises encoded data fields reflecting a length of the PL frame, where the data fields are encoded based on a second modcod scheme of a second set. The first modcod set is designed for an SNR operating range relatively lower than the SNR operating range of the second modcod set.

Abstract: The present invention relates to a physical layer signalling in a digital broadcast network. In particular, for a digital broadcast network supporting a configuration with a plurality of physical layer pipes, a type indicator is signalled on physical layer for a pipe, the type indicator indicates the format of the input stream which may specify a transport stream, a generic stream or an IP stream. In addition, per physical layer pipe application of header and/or content compression to the user packet headers of the input stream is signalled. Another physical layer parameters are advantageously provided or extended in order to increase the flexibility and efficiency of the layer 1 signalling.

Abstract: A system, method, and computer program for compressing packet data is provided. In exemplary embodiments, one or more prefix arrays may be generated for retrieved data, and used as the basis for predicting subsequent data. The packet data may be compressed based, at least partially, on the predicted subsequent data. Accordingly, the compressed packet data may be transferred over a communication network.

Abstract: The disclosed embodiments relate to a system for providing remote tuning and clock synchronization in a network. The system includes a device that receives a signal that includes a plurality of channels, a device that receives a user request indicative of a desire to view at least one of the plurality of channels, and a filter that filters the received signal and transmits a user signal corresponding to the at least one of the plurality of channels to the user.

Abstract: Disclosed herein is a reception apparatus, including: a reception section configured to receive an OFDM (orthogonal frequency division multiplexed) signal obtained by modulating a common packet sequence configured from a packet common to a plurality of streams and a data packet sequence configured from packets individually unique to the plural streams; a buffer configured to accumulate packets of the common packet sequence and the data packet sequence obtained by demodulating the received OFDM signal; a retaining section configured to retain correction information for correcting out-of-synchronism between the common packet sequence and the data packet sequence obtained from particular packets of the common packet sequence and the data packet sequence upon reading out of the packets accumulated in the buffer; and a correction section configured to correct the out-of-synchronism of the packet which suffers from the out-of-synchronism of the packets based on the correction information retained in the retaining s

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 laser for generating an output wavelength of approximately 193.4 nm includes a fundamental laser, an optical parametric generator, a fourth harmonic generator, and a frequency mixing module. The optical parametric generator, which is coupled to the fundamental laser, can generate a down-converted signal. The fourth harmonic generator, which may be coupled to the optical parametric generator or the fundamental laser, can generate a fourth harmonic. The frequency mixing module, which is coupled to the optical parametric generator and the fourth harmonic generator, can generate a laser output at a frequency equal to a sum of the fourth harmonic and twice a frequency of the down-converted signal.

Abstract: Optical pump modules comprising VCSEL and VCSEL array devices provide high optical power for configuring fiber optic gain systems such as fiber laser and fiber amplifier particularly suited for high power operation. Pump modules may be constructed using two reflector or three reflector VCSEL devices optionally integrated with microlens arrays and other optical components, to couple high power pump beams to an optical fiber output port, particularly suited to couple light to an inner cladding of a double-clad fiber suitable for a high power gain element. Multiple-pumps may be combined to increase pump power in a modular fashion without significant distortion to signal, particularly for short pulse operation. The pump modules may be operated in CW, QCW and pulse modes to configure fiber lasers and amplifiers using single end, dual end, and regenerative optical pumping modes.

Abstract: Apparatus, systems, and methods of generating multi combs can be used in a variety of applications. In various embodiments, an etalon can be disposed in the laser cavity of a mode-locked laser to adjust frequency combs. Additional apparatus, systems, and methods are disclosed.

Abstract: A tunable narrow linewidth laser is provided, wherein an adjustable etalon structure is employed to simultaneously tune the wavelength of the laser transmission and the length of the laser cavity. The etalon structure is an effective, relatively thick shear plate comprised of transparent matched wedge-shaped substrates and a pair of parallel, partially transmissive mirrors with a space therebetween. Rotation of the etalon structure relative to the laser input changes the angle of incidence to the first substrate and the etalon angle, thereby changing the wavelength of the laser light and also changing the length of the external laser cavity. Thus, reliable frequency tuning is achieved, without mode hopping.