Method and system for time-sharing transmission frequencies in an optical network

An optical communication system includes an optical ring that couples a hub node and a plurality of local nodes. The hub node is capable of receiving traffic over the optical ring from the plurality of local nodes on a transmitting wavelength and transmitting traffic over the optical ring to the local nodes on a receiving wavelength. At least one local node is capable of adding traffic to the optical ring by determining whether any other local node is transmitting at the transmitting wavelength and, in response to determining that no other local node is transmitting at the transmitting wavelength, transmitting a request message to the hub node requesting use of the transmitting wavelength. The local node adding traffic is further capable of receiving a grant message from the hub node and, in response to receiving the grant message from the hub node, transmitting traffic at the transmitting wavelength.

TECHNICAL FIELD

The present invention relates generally to optical networks and, more particularly, to a method and system for time-sharing transmission frequencies in an optical network.

BACKGROUND

Telecommunication systems, cable television systems, and data communication networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical fibers comprise thin strands of glass capable of transmitting optical signals over long distances with very low loss of signal strength.

Recent years have seen an explosion in the use of telecommunication services. As the demand for telecommunication services continues to grow, optical networks are quickly becoming overburdened by the increasing amount of information communicated over such networks. The addition of new networks or the expansion of existing networks may however be too costly to be practical solutions to this problem. Thus, efficient use of network resources has become an important goal in developing and operating optical networks.

SUMMARY

According to a particular embodiment of the present invention, an optical communication system includes an optical ring, a hub node, and a plurality of local nodes. The hub node and the plurality of local nodes are coupled to the optical ring. The hub node is capable of receiving traffic over the optical ring from the plurality of local nodes on a transmitting wavelength and of transmitting traffic over the optical ring to the local nodes on a receiving wavelength.

The plurality of local nodes are capable of adding traffic to and drop traffic from the optical ring and at least one local node is capable of adding traffic to the optical ring by determining whether any other local node is transmitting at the transmitting wavelength. The local node adding traffic is also capable of transmitting a request message to the hub node requesting use of the transmitting wavelength, in response to determining that no other local node is transmitting at the transmitting wavelength. Additionally, the local node adding traffic is further capable of receiving a grant message from the hub node and, in response to receiving the grant message from the hub node, transmitting traffic at the transmitting wavelength.

Technical advantages of certain embodiments of the present invention include centralized data storage and processing in an optical network that utilizes wavelength-sharing to increase overall network capacity. Another technical advantage of one or more embodiments may include the ability to prioritize transmissions by particular network components on shared transmitting wavelengths.

It will be understood that the various embodiments of the present invention may include some, all, or none of the enumerated technical advantages. In addition other technical advantages of the present invention may be readily apparent to one skilled in the art from the figures, description, and claims included herein.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1illustrates an optical network10in accordance with one embodiment of the present invention. Optical network10includes a hub node12and a plurality of local nodes14coupled to an optical ring20. During operation, local nodes14transmit traffic using one or more transmitting wavelengths and receive traffic propagating on optical ring20at one or more receiving wavelengths, while hub node12facilitates communication of information to local nodes14. Moreover, in particular embodiments of network10, hub node12manages the use of transmitting wavelengths utilized by local nodes14and facilitates sharing of one or more of the transmitting wavelengths. AlthoughFIG. 1, illustrates one embodiment of network10that includes a particular number of local nodes14and hub nodes12, network10may include any appropriate number of local nodes14and hub nodes12configured in any appropriate manner.

AlthoughFIG. 1illustrates a particular embodiment and configuration of network10, other suitable types of optical networks may be used in accordance with the present invention. In the illustrated embodiment, network10is an optical network in which a number of optical channels are carried over a common path at different wavelengths. Network10may be a wavelength division multiplexed (WDM) network, a dense wavelength division multiplexed (DWDM) network, or any other suitable multi-channel network. Network10may be represent all or a portion of a short-haul metropolitan network, long-haul intercity network, or any other suitable network or combination of networks. Ring20may include, as appropriate, a single unidirectional fiber, a single bi-directional fiber, or a plurality of uni- or bi-directional fibers.

As shown, optical ring20comprises a pair of uni-directional fibers, first fiber16and second fiber18, transporting traffic in counterclockwise and clockwise directions, respectively. Optical ring20optically connects the plurality of local nodes14a-14dand hub node12, and optical traffic propagates between nodes12and14over optical ring20. As used herein, “traffic” means information transmitted, stored, or sorted in the network, including any request for services as discussed in more detail below. Such traffic may comprise optical signals having at least one characteristic modulated to encode audio, video, textual, real-time, non-real-time and/or other suitable data. Modulation may be based on phase shift keying (PSK), intensity modulation (IM), and other suitable methodologies. Additionally, the information carried by this traffic may be structured in any suitable manner. Although the description below focuses on an embodiment of network10that communicates traffic on optical ring20in the form of optical frames, network10may be configured to communicate traffic structured in the form of frames, as packets, or in any other appropriate manner.

Local nodes14are each operable to add and drop traffic to and from optical ring20to facilitate communication between a plurality of client devices (not shown) coupled to each local node14through a plurality of client ports. As used herein, the term “each” means every one of at least a subset of the identified items. More specifically, each local node14may receive traffic from the client devices coupled to that local node14and add this traffic to the optical ring20by inserting the added traffic into the traffic currently being transmitted by hub node12and local nodes14on optical ring20. Concurrently, each local node14receives traffic from optical ring20and drops traffic destined for client devices of that local node14. For the purposes of this description, local nodes14may “drop” traffic by transmitting a copy of the traffic to any appropriate components coupled to the relevant local node14. As a result, local nodes14may drop traffic from optical ring20by transmitting the traffic to components coupled to the relevant local node14while allowing the traffic to continue to downstream components on optical ring20.

The client devices may represent any devices appropriate for the communication or storage of information on optical network10. Examples of client devices may include, but are not networked personal computers (PCs), telephones, fax machines, hard drives, and web servers. The contents and operation of local node14, according to a particular embodiment, are discussed in greater detail below with respect toFIG. 2.

Hub node12receives optical traffic from local nodes14and other components of optical network20and transmits optical traffic to local nodes14at a receiving wavelength. In the illustrated embodiment, hub node12includes a demultiplexer30, a plurality of receivers32, a data center40, a transmitter28, and a multiplexer22. The demultiplexer30demultiplexes WDM or other multichannel optical signals transmitted over the optical ring20into constituent channels and sends each optical signal24to an optical receiver32. Each optical receiver32electrically recovers the encoded data from the corresponding traffic. The data is then forwarded to the data center40. Although, for the sake of simplicity, only one demultiplexer30, one multiplexer22, one set of transmitters28, and one set of receivers32are shown inFIG. 1, the illustrated embodiment of hub node12is assumed to have a demultiplexer30, a multiplexer22, and an appropriate number of transmitters28and receivers32for each of fibers16and18.

Data center40receives traffic, sorts traffic based on one or more destination nodes associated with the traffic, and passes the sorted traffic to transmitter28for transmitting the traffic to local nodes14at one or more wavelengths on fiber16or18or, if appropriate, to external devices coupled to hub node12through external connections26. As used herein, a “destination node” associated with particular traffic is the local node14to which the client device that is the intended destination of the traffic is coupled. In the illustrated embodiment, data center40includes an electrical switch36, and a controller44.

Switch36is coupled to controller44and services module38. Although not illustrated, data center40, in a particular embodiment, may include a Layer 3 (L3) switch or other suitable component for passing traffic to and from an Internet Protocol (IP) or other network coupled to optical network10via hub node12. Switch36passes traffic received from the receivers32, transmitters28, and/or other components of hub node12. Switch36may comprise a Layer 2 switch such as an Ethernet switch, IP switch, fiber channel (FC) switch, a router or other suitable devices for selectively directing traffic.

Controller44manages operation of electrical switch36and/or other components of hub node12, and may comprise logic stored in memory. This logic may comprise computer disks, a hard disk memory or other suitable computer-readable media, and application specific integrated circuits (ASIC), field programmable gate arrays (FPGA), digital signal processors (DSP), or other suitable specific or general purpose processors, transmission media, or other suitable media in which logic may be encoded and utilized. In one embodiment, controller44comprises a server. Controller44is operable to send a command signal to the electrical switch36to facilitate the sorting of both inter- and intra-network traffic. In particular embodiments, hub node12may include a traffic buffer (not shown) for receiving and buffering traffic received from external networks and destined for local nodes14of optical network10. In such embodiments, controller44may control operation and access to the traffic buffer for purposes of buffering, sorting, and transmitting traffic to appropriate local nodes14.

Additionally, controller44may control operation of one or more components responsible for generating control signals to be transmitted to local nodes14on an optical supervisory channel (OSC). In a particular embodiment, this OSC represents one or more wavelengths, among a plurality of wavelengths utilized by optical network10, that are dedicated to control signals. Alternatively, the OSC may represent a separate fiber in optical ring20on which hub node12transmits control signals.

In operation, local nodes14are operable to receive and drop traffic from optical ring20. Once traffic is dropped from the optical ring20, local nodes14may provide optical-to-electrical conversion of the dropped traffic for extracting data based on headers or tags associating portions of the traffic with a destination node and/or port. In a particular embodiment, each local node14is operable to drop traffic transmitted at one or more designated wavelengths, referred to here as “receiving wavelengths.” Although the description below focuses on embodiments of optical network10in which local nodes14receive all optical traffic on a single receiving wavelength, particular embodiments of optical network10may be configured such that local nodes14receive optical traffic at a plurality of receiving wavelengths.

Each local node14electrically converts traffic received on the receiving wavelengths, discarding traffic transmitted at other wavelengths. Local nodes14then extract, based on addressing information in the traffic, portions of this traffic destined for client devices coupled to that local node14. Addressing information may include a header, a VLAN tag, and/or any other suitable addressing information. In certain embodiments, each local node14comprises a switch element (not shown inFIG. 1) which may forward the traffic, or a portion thereof, to one of a plurality of client devices based on addressing information. In particular embodiments, the switch element comprises a Layer 2 (L2) switch. Additionally, the switch element may be configured, where appropriate, to determine a local port to which traffic should be forwarded based on a header or VLAN tag in the addressing information.FIG. 2illustrates the contents and operation of a particular embodiment of local node14in greater detail.

In a particular embodiment, each local node14is also operable to generate optical traffic at one or more wavelengths, referred to here as “transmitting wavelengths.” Local nodes14are operable to add this optical traffic to optical network20. Although the description below focuses, for purposes of simplicity, on embodiments of optical network10in which each local node14transmits at a single transmitting wavelength, particular embodiments of optical network10may be configured such that each local node14transmits at a plurality of transmitting wavelengths.

Furthermore, one or more of these transmitting wavelengths may be shared by two or more local nodes14on optical network10. In particular embodiments, all local nodes14may share one or more transmitting wavelengths utilized in optical network10. In alternative embodiments, one or more of the transmitting wavelengths may be utilized by only a particular subset of local nodes14, as appropriate based on the characteristics and configuration of that embodiment of optical network10. As a result of this sharing of transmitting wavelengths, certain elements of optical network10may be responsible for managing the use of transmitting wavelengths to ensure that only a single component is transmitting on a particular transmitting wavelength at any given time and to prevent optical interference between the transmissions of different local nodes14.

Meanwhile, during operation, hub node12receives optical traffic transmitted by local nodes14, processes the received optical traffic in any appropriate manner, and transmits this optical traffic at one or more receiving wavelengths to appropriate local nodes14and/or to components on external networks coupled to hub node12through external connections26. Hub node12may also receive optical traffic from external networks through external connections26and may transmit this optical traffic to local nodes14at one or more receiving wavelengths. In a particular embodiment of optical network10, hub node12also manages use of shared transmitting wavelengths to prevent optical interference between local nodes14.FIGS. 3A-3Eand4A-4D below illustrate examples of the operation of hub node12in facilitating the sharing of a common transmitting wavelengths between multiple local nodes14. Hub node12may also store data locally or have access to remotely-stored data, and hub node12may transmit this data to local nodes14in response to requests from local nodes14. For example, hub node12may have access to video data stored in an appropriate location within optical network10and may support Video on Demand (VOD) service to local nodes14by transmitting this video data to local nodes14in response to requests from these local nodes14.

Thus, optical network10supports optical communication between local nodes14and/or other components of optical network10or other network coupled to optical network10. Because local nodes14share a common transmitting wavelength, particular embodiments of optical network10may be able to make efficient use of the spectrum of wavelengths supported by those embodiments of optical network10. As a result, such embodiments may provide greater data transmission rates and/or other additional benefits.

FIG. 2illustrates a particular embodiment of local node14that may be utilized in the example optical network10shown inFIG. 1. As illustrated, local node14comprises a first transport element62, a second transport element64, a transmitting element68, a receiving element66and a managing element120. In a particular embodiment, local node14receives electrical signals from client devices (not shown) coupled to local node14, generates optical traffic from these electrical signals, and adds the optical traffic to optical traffic propagating on fiber16and/or fiber18. Additionally, local node14may also receive optical traffic on fiber16and/or fiber18and convert this optical traffic to electrical signals that are transmitted to an appropriate client device. AlthoughFIG. 2illustrates an example embodiment of local node14in which local node14couples to both fibers16and18, particular embodiments of optical network10may include only a single fiber and local node14may be modified as appropriate to operate in such an embodiment of optical network10.

Transport element62and64couple optical signals generated by local node14to fibers16and18and drop a copy of optical signals propagating on fibers16and18for use by other components of local node14. Additionally, transport elements62and64each include an OSC ingress filter66athat processes an ingress optical signal from its respective fiber16or18. Each OSC filter66afilters the OSC signal from the optical signal and forwards the OSC signal to managing element120. Each OSC filter66aalso forwards or lets the remaining optical signal pass to other components of the relevant transport element. Transport elements62and64each also include an OSC egress filter66bthat adds an OSC signal from managing element120to the optical signal from an amplifier70and forwards the combined signal as an egress transport signal to the associated fiber16or18of optical network10. The added OSC signal may be locally generated data or may be received OSC data passed through by managing element120.

Managing element120may comprise OSC receivers112, OSC interfaces114, OSC transmitters116, and an element management system (EMS)124.FIG. 2illustrates an embodiment of local node14configured for use in an optical network10in which the OSC represents a particular wavelength of optical traffic propagating on fibers16and18and received as a component of the aggregate optical traffic on fibers16and18. As a result, the illustrated embodiment of local node14includes an OSC unit for each of fiber16and18that includes an OSC receiver112, an OSC interface114, and an OSC transmitter116. The OSC units receive OSC signals from and transmit OSC signals to EMS124.

EMS124monitors and/or controls any appropriate elements in local node14based, in part, on information received by local node14in the OSC signal. For example, EMS124may determine based on information received from hub node12in the OSC signal to begin transmitting optical traffic on the shared transmitting wavelength. As described in greater detail below with respect toFIGS. 3A-3Eand4A-4D, this data may represent control signals that manage the use of one or more shared transmitting wavelengths by local node14. In general, EMS124may include any combination of hardware and/or software appropriate for providing the functionality described below. In a particular embodiment, EMS124comprises logic encoded in media for performing the described functions. This logic may comprise software encoded in a disk or other computer-readable medium, such as a memory associated with EMS124, and/or instructions encoded in an application-specific integrated circuit (ASIC), field programmable gate array (FPGA), or other processor or hardware.

Transmitting element68generates local add traffic to be added to fibers16and18by transport elements62and64. In particular embodiments, transmitting element68generates this local add traffic based on electrical signals received by local node14from client devices coupled to local node14. As shown, transmitting element68includes one or more couplers92and one or more transmitters94.

Receiving element66receives a copy of optical traffic that is dropped from fibers16and18by transport elements62and64. In particular embodiments, receiving element66transmits portions of this local drop traffic to appropriate client devices coupled to local node14. As shown, receiving element66includes one or more couplers76, one or more tunable filter80, one or more selectors82, one or more switches84, one or more receivers86, and a switch element88.

In particular embodiments, the transport, transmitting, and receiving elements62,64,68, and66may each be implemented as a discrete card and interconnected through a backplane of a card shelf of the node14. Alternatively, the functionality of one or more elements62,64,68, and66may be distributed across a plurality of discrete cards. In this way, the node14is modular, upgradeable, and provides a “pay-as-you-grow” architecture. The components of node14may be coupled by direct, indirect or other suitable connection or association. In the illustrated embodiment, the elements62,64,68, and66and devices in the elements are connected with optical fiber connections; however, other embodiments may be implemented in part or otherwise with planar wave guide circuits and/or free space optics.

In operation, transport elements62and64receive optical traffic that is propagating on fibers16and18. In one embodiment, transport elements62and64each comprise amplifiers70, a drop coupler72, and an add coupler74. Amplifiers70amplify the optical signals. Drop coupler72is operable to split the optical signal into a drop signal and a pass-through signal, wherein both signals are substantially the same. In addition, the transport elements62and64each comprise an add coupler74operable to combine both the traffic generated at transmitting element68and the pass-through signal.

Drop couplers72and74may each comprise an optical fiber coupler or other optical splitter operable to combine and/or split an optical signal. As used herein, an optical splitter or an optical coupler is any device operable to combine or otherwise generate a combined optical signal based on two or more optical signals and/or to split or divide an optical signal into discrete optical signals or otherwise passively discrete optical signals based on the optical signal. The discrete signals may be similar or identical in frequency, form, and/or content. For example, the discrete signals may be identical in content and identical or substantially similar in power, may be identical in content and differ substantially in power, or may differ slightly or otherwise in content. In one embodiment, each drop coupler72may split the signal into two copies with substantially different power.

Amplifiers70may be Erbium-doped fiber amplifiers (EDFAs) or other suitable amplifiers capable of receiving and amplifying an optical signal. To reduce the optical power variations of the clockwise ring18and of the counterclockwise ring20, amplifiers70may use an automatic level control (ALC) function with wide input dynamic-range. Hence amplifiers70may deploy automatic gain control (AGC) to realize gain-flatness against input power variation, as well as variable optical attenuators (VOAs) to realize ALC function.

During operation of local node14, amplifier70of each transport element62and64receives a signal from the connected fiber16or18and amplifies the signal. The amplified signal is forwarded to the drop coupler72. The drop coupler72splits the signal into a pass-through signal and a drop signal. The drop signal includes at least a subset of the set of wavelengths assigned to local node14. The pass-through signal is forwarded to the add filter74. The local drop signal is forwarded from the drop coupler72to receiving element66, which selectively passes traffic in one or more λSof the drop signal to a receiver86. The add filter74combines the pass-through signal and signals generated by the transmitting element68.

In the illustrated embodiment, receiving element66includes 1×n couplers76, a plurality of tunable (or fixed) filters80, a plurality of selectors82, a plurality of 2×1 switches84, one or more receivers86, and switch element88. The 1×n couplers76may comprise one optical fiber lead and a plurality of optical fiber leads which serve as drop leads78. Drop leads78may be connected to the plurality of tunable filters80operable to pass traffic in a selected wavelength and reject other wavelengths. In the illustrated embodiment, drop lead78aassociated with fiber16and drop lead78bassociated with fiber18are coupled to tunable filters80aand80b, respectively.

The selected wavelengths from80aand80bare passed to the selector82and switch84, which allows selective connection of the receiver86with either an associated drop signal coming from optical ring20or an associated drop signal coming from the ring18. Such selective switching may be used to implement Optical Unidirectional Path-Switched Ring (OUPSR) protection switching. In a particular embodiment, the selector82is initially configured to forward to the client device(s) traffic from a fiber16or18that has the lower Bit Error Rate (BER). A threshold value is established such that the switch remains in its initial state as long as the BER does not exceed the threshold. Another threshold or range may be established for power levels. For example, if the BER exceeds the BER threshold or if the power falls above or below the preferred power range, the switch selects the other signal. Commands for switching may be transmitted via connection90. This results in local control of switching and simple and fast protection. After optical-to-electrical conversion of the signal, receiver86transmits data segments, to switch element88. Although the description below focus on an embodiment of hub node12in which receiver86forwards data segments to switch element88as frames, receiver86may forward data segments to switch element88in any appropriate form. Additionally, althoughFIG. 2shows only a single receiver86, local node14may include any number of receivers86with appropriate numbers of all associated equipment including filters80, selectors82, and switches84. As a result, local node14may be capable of receiving optical signals on one or more receiving wavelengths.

Switch element88may comprise any appropriate switch such as, for example, an L2 switch, an L3 switch, or any other suitable switch. Upon receiving frames, switch element88determines a destination client device for frames based on addressing information and transmits frames to a client port108coupled to the destination client device. Some or all frames may contain addressing information such as IP addresses, VLAN tags, or any other suitable information identifying the destination client in any appropriate manner. Switch element88may determine an appropriate port108for the frames based on this addressing information and/or any other appropriate information.

Switch element88also receives, through client ports108, frames or data segments of another suitable form from client devices for transmission on network10. Switch element88transmits frames to transmitting element68. In the illustrated embodiment, transmitting element68comprises a 2×n coupler92and a transmitter94that transmit the frames into a plurality of optical signals transmitted in one or more wavelengths assigned to the node14. The 2×n coupler92comprises a plurality of leads which serve as add leads and may be connected to the one or more transmitters94(which may be tunable or fixed-wavelength). The transmitters94are operable to transmit add signals at selected wavelengths. The coupler92splits the add signal into two substantially similar signals, wherein one signal is added to the fiber16and the other signal is added to the fiber18. The add signals are forwarded to the add filters74for addition to the associated fiber16or18, as described above. The add filters74rejects signals transmitted at the assigned subband and combines the pass-through signal with the add signals transmitted at the assigned subband by the transmitting element68. AlthoughFIG. 2shows only a single transmitter94, local node14may include any number of transmitters94with appropriate numbers of all associated equipment. As a result, local node14may be capable of transmitting optical signals on one or more transmitting wavelengths.

In the illustrated embodiment, the same or substantially the same signals are communicated over both the fibers16and18. Therefore, a single set of the receivers86may be used to receive signals from the fibers16or18(one or the other are received, depending on the position of switch84and selector82), the same set of the transmitters94may be used to transmit the same signals to both the fibers16and18. Such a configuration is appropriate when providing OUPSR protection. However, in other embodiments, local node14may include a separate set of the receivers86associated with each of fibers16and18, and a separate set of the transmitters94associated with each of fibers16and18. In this case, no switch84and selector82are needed. Instead, the drop signals associated with each fiber16or18are coupled to the set of the receivers86associated with each ring. Therefore, different signals may be received from the fibers16and18.

Similarly, instead of splitting the signal from one or more transmitters94using a coupler92and providing this signal to both the fibers16and18, a different signal may be generated by one or more transmitters94associated with the fiber16and one or more transmitters94associated with the fiber18. Therefore, different signals may be communicated over each fiber16and18. For example, a first signal can be added in a particular channel on the fiber16at the node14, and an entirely different signal can be added in the same channel on the fiber18by the same node14.

FIGS.3A-3E[?] illustrate operation of a particular embodiment of optical network10in transmitting optical traffic from local node14dto local node14a. In the illustrated embodiment of optical network10, all local nodes14share a common transmitting wavelength, λT, for transmitting optical traffic to hub node12and hub node12utilizes a receiving wavelength, λR, to transmit traffic to all local nodes14. Furthermore, in this example embodiment, local nodes14are configured to determine whether another local node14is currently using the shared transmitting wavelength before transmitting optical traffic. If another local node14is transmitting, local node14will wait until the transmitting local node14has finished transmitting before being using λTand/or requesting use of λT. By contrast, as described in greater detail below,FIGS. 4A-4Dillustrate operation of an alternative embodiment of optical network10in which local nodes14request use of λTfrom hub node12and hub node12determines, based on a priority level of the requesting local node14, whether to grant the requesting local node14use of λT.

FIG. 3Aillustrates operation of optical network10as local node14dreceives traffic (as electrical signals) from a client device to be transmitted on optical ring20in λT. In the illustrated example, however, local node14cis already transmitting optical traffic to local node14b. As a result, in this example embodiment of optical network10, local node14ddetermines that local node14dcan not transmit on λTand local node14waits until λTis free before transmitting the traffic to local node14a.

More specifically, local node14dreceives client traffic310from a client device coupled to local node14d. Client traffic310may represent any appropriate electrical signal to be transmitted to hub node12or another local node14on optical network10, in this case local node14a. Upon receiving client traffic310, local node14ddetermines whether another local node14is currently transmitting on λT. Local node14dmay determine whether λTis currently being used in any appropriate manner. As one example, hub node12or a transmitting local node14may transmit a control signal in the OSC while the transmitting local node14is transmitting. In such an embodiment, EMS124or another appropriate component of local node14dmay sample the OSC signal when local node14dreceives client traffic310and may determine based on this sampling whether λTis currently being used. As another example, hub node12may transmit a control signal in the OSC to all local nodes14when a particular local node14requests use of λTor begins using λTand may transmit another control signal when that local node14is done transmitting. EMS124may set a flag or otherwise store information in memory or EMS indicating the current status of λTand local node14dmay, upon receiving client traffic310, check memory to determine whether λTis currently being used. In general, however, local nodes14may determine in any appropriate manner whether another local node14is currently transmitting traffic on λT.

If no other local node14is transmitting on λT, local node14d, in the illustrated embodiment, requests use of λTfrom hub node12and/or begins using λT. If another local node14is transmitting on λT, local node14, in the illustrated embodiment, waits until the transmitting local node14finishes its use of λT. During this period, local node14dmay monitor control signals transmitted by hub node12on the OSC channel to determine when the transmitting local node14has completed its transmission. Additionally, in a particular embodiment, local node14dmay include a buffer and local node14dmay buffer client traffic310until λTis available for use by local node14d. In the illustrated example, local node14cis currently transmitting on λT, so local node14dwaits until local node14cfinishes transmitting.

FIG. 3Billustrates operation of optical network10after local node14cfinishes transmitting on λT. At an appropriate point after local node14chas finished transmitting, local node14ddetermines that λTis available. As noted above, local node14may determine that λTis available in any appropriate manner, including by monitoring the OSC and by accessing information stored in memory. For example, in the illustrated embodiment, hub node12transmits an idle message312on the OSC to all local nodes14when local node14cfinishes transmitting and local node14ddetermines that λTis available in response to receiving idle message312. As used in this description and the associated claims, a “message” may represent one or more signal pulses, packets, or frames, or information structured in any other suitable format. Idle message312may include any appropriate information indicating that a particular local node14previously transmitting on λThas completed its transmission or that λTis otherwise available. In this example, idle message312is transmitted to local nodes14a-d, as indicated by the “A-D” label inside idle message312.

After determining that λTis available, local node14d, in the illustrated embodiment, requests use of λTfrom hub node12. In the illustrated embodiment, local node14drequests use of λTby transmitting a request message320to hub node12on the OSC. Request message320identifies a destination node12or14to which local node14dis attempting to transmit optical traffic and any other appropriate information.

In an alternative embodiment, local node14dmay be allowed to use λTunconditionally as long as no other local node14is transmitting. In such an embodiment, local node14dmay be configured to, once λTis available, begin using λTwithout requesting use from hub node12. In such an embodiment, local node14dmay begin transmitting optical traffic on λT, as described below with respect toFIG. 3D, without transmitting request message320and/or receiving any further messages from hub node12.

FIG. 3Cillustrates operation of a particular embodiment of optical network10after hub node12receives request message320. Upon receiving request message320, if no other local node14has requested use of λT, hub node12may unconditionally grant local node14duse of λT. Alternatively, hub node12may determine, based on any appropriate information, whether to grant local node14duse of λT. For example, hub node12may determine based on access rights of local node14dwhether local node14dshould be granted use of λTto communicate with the intended destination local node14.

Hub node12then transmits a grant message330to the requesting local node14, local node14d, on the OSC. Grant message330indicates to local node14dthat local node14dhas been granted use of λTfor transmitting traffic to the destination local node14specified in request message320. Grant message330may represent a single pulse, a packet, a frame, and/or information structured in any other suitable format.

In a particular embodiment, hub node12may also transmit an intimation message340to the intended destination, in this case local node14a, on the OSC. Intimation message340may include any appropriate information to facilitate reception of optical traffic by local node14afrom local node14d. As one example, intimation message340may specify the source local node14, local node14d, from which local node14ashould expect to receive traffic. As another example, in an embodiment of optical network10in which optical traffic is transmitted to local nodes14on multiple receiving wavelengths, intimation message340may indicate to local node14awhich the particular receiving wavelength on which optical traffic from local node14dwill be transmitted to local node14a. In such an embodiment, local node14amay use the information in intimation message340to retune one or more tunable filters and/or receivers of local node14a.

Additionally, hub node12may notify, in any suitable manner, other local nodes14that local node14dhas been granted use of λT. As one example, hub node12may transmit grant message330, intimation message340, or some other appropriate form of messages on the OSC to all local nodes14to indicate that local node14dhas been granted use of λT. Other local nodes14may update information stored in their memory as a result of receiving such notification. Furthermore, in alternative embodiments, local node14dmay instead notify the other local nodes14that local node14dwill be using λTby sending any appropriate messages to other local nodes14on the OSC after receiving grant message330from hub node12.

FIG. 3Dillustrates operation of optical network10after local node14dreceives grant message330. Upon receiving grant message330, local node14dbegins transmitting optical traffic on λT. More specifically, local node14dgenerates optical signals at a wavelength of λT, based on the electrical signals of client traffic310, and transmits these optical signals on optical ring20as optical traffic350. AlthoughFIG. 3Dshows, for the purposes of simplicity, local node14dtransmitting optical traffic counterclockwise on first fiber16, local node14dmay transmit optical traffic350as appropriate on either or both of fibers16and18. For example, in a particular embodiment of network10, local node14dmay transmit identical copies of optical traffic350on each of first fiber16and second fiber18to ensure delivery of optical traffic350to destination local node14a.

In the illustrated example, local node14dtransmits optical traffic350along first fiber16in a counterclockwise direction at a wavelength of λT. When hub node12receives optical traffic350in this embodiment, hub node12performs any appropriate processing, such as buffering optical traffic350or modifying header information included in optical traffic350, and regenerates optical traffic350at wavelength λR. The regenerated optical traffic350′ is transmitted on first fiber16.

Each of local nodes14may receive regenerated optical traffic350′ and drop a copy of regenerated optical traffic350′. Each local node14may then forward the dropped copy of regenerated optical traffic350′ to appropriate client devices, if any, from among the client devices coupled to local node14. For example, in the illustrated embodiment, local node14adetermines, based on addressing information within regenerated optical traffic350′ or any other appropriate information and/or considerations, that a client device coupled to local node14ais the destination of regenerated optical traffic350′ and routes the dropped copy of regenerated optical traffic350′ to that client device. Meanwhile, each of the remaining local nodes14drops a copy of regenerated optical traffic350′ and determines, based on addressing information or other appropriate considerations, that none of the client devices attached to that local node14is the destination for regenerated optical traffic350′. As a result, in the illustrated embodiment, each of these local nodes14discards their dropped copy of regenerated optical traffic350′.

FIG. 3Eillustrates operation of optical network10after local node14dhas completed its transmission to local node14a. In the illustrated example, local node14dtransmits a termination message360to hub node12on the OSC after local node14dhas transmitted all of optical traffic350to local node14a. Termination message360may include any suitable information local node14dhas completed transmission of optical traffic350and/or no longer requires the use of λT. Upon receiving termination message360from local node14d, hub node12indicates to local nodes14that the transmitting wavelength is again available for use. In the illustrated example, hub node12indicates that λTis now available by transmitting another idle message312to local nodes14.

Thus,FIGS. 3A-3Eillustrate a particular embodiment of optical network10that supports sharing of a transmitting wavelength by two or more local nodes14. Furthermore, the illustrated embodiment of optical network10supports decentralized decision-making that allows each local node14to determine whether the transmitting wavelength is currently available and to request use of the transmitting wavelength from hub node12only when no other local node14is transmitting. Such an embodiment may reduce the workload of hub node12and/or congestion on the OSC.

AlthoughFIGS. 3A-3Eshow, for the purposes of simplicity, an embodiment of optical network10in which messages between two components are transmitted on the OSC along the shortest path on optical ring20between the relevant components, particular embodiments of optical network10may utilize only a single direction for OSC signals and all OSC messages may be transmitted around optical ring20in the same direction. Alternatively, in particular embodiments of optical network10, each message may be transmitted on optical ring20in both directions, with a first copy transmitted in one direction between the relevant components on first fiber16and a second copy transmitted in the other direction on second fiber18. Additionally, althoughFIGS. 3A-3Eillustrate a specific embodiment of optical network10that utilizes specific types of messages to facilitate sharing of the transmitting wavelength, alternative embodiments of optical network10may utilize some, none, or all of these messages to provide the describe functionality. For example, instead of transmitting idle messages312to local nodes14to indicate that λTis available for use, hub node12may periodically transmit a refresh message indicating that λTis currently being used by a particular local node14and a particular local node14may determine that λTis available based on whether that local node14has received a refresh message from hub node12within a particular amount of time.

FIGS. 4A-4Dillustrate another embodiment of optical network10in which a local node14may request use of the transmitting wavelength, λT, while another local node14is transmitting. In the embodiment of optical network10illustrated inFIGS. 4A-4D, hub node12determines, based on suitable criteria, whether a particular requesting local node14should be granted use of λTwhen a particular transmitting local node14is already transmitting on λT. In particular, the illustrated embodiment of optical network, determines whether to grant use of λTto a requesting local node14based on the priority statuses of the requesting local node14and the currently transmitting local node14. Consequently, the embodiment of optical network10illustrated byFIGS. 4A-4Dmay provide more efficient use of λTby allowing particular nodes preferred access to λT.

FIG. 4Aillustrates operation of optical network10as local node14dreceives client traffic410(as electrical signals) from a client device to be transmitted on optical ring20. In the illustrated example, however, local node14cis already transmitting optical traffic at λTto local node14b. In this example embodiment of optical network10, local node14dmay still request use of λT. More specifically, in response to receiving client traffic410, local node14dtransmits a request message420to hub node12on the OSC. Request message420identifies a destination node12or14to which local node14dis attempting to transmit optical traffic.

Request message420may also identify a priority status associated with local node14d. Each local node14of optical network10is associated with a priority status. Each local node14or transmission may be associated with a particular priority status based on any appropriate characteristic of that local node14, the information that local node14is attempting to transmit, and/or other characteristics, considerations, or factors associated with the requesting local node14. Furthermore, the priority status of a particular local node14may change over time or based on the particular information that local node14is transmitting. For example, a particular transmission may be associated with a quality of service (QoS) requirement and hub node12may prefer that transmission over transmissions that are not associated with any QoS requirement. Alternatively, request message420may not include any priority status and hub node12may itself determine the priority status in any appropriate manner.

FIG. 4Billustrates operation of optical network10after local node14dtransmits request message420to hub node12. In response to receiving request message420, hub node12determines whether to allow local node14dto interrupt the transmission by local node14c. In particular, in the illustrated example, hub node12determines whether to allow local node14dto interrupt the transmission based on the priority status of local node14dand the priority status of local node14c.

If hub node12decides not to allow local node14dto interrupt the transmission by local node14c, hub node12transmits a negation message (not shown). The negation message may include any appropriate information indicating to local node14dthat local node14dhas not been granted use of λT. If local node14receives the negation message, local node14dmay wait until local node14ccompletes transmission, abort its own transmission, or take any other appropriate action. For example, local node14dmay buffer client traffic410in a buffer of local node14dand wait a predetermined amount of time before requesting use of λTagain. In such an embodiment, the priority status of the transmission associated with client traffic410may be based, in part, on how long local node14dhas been waiting to transmit client traffic410on optical ring20and thus the priority status may change as local node14dwaits.

If instead hub node12decides to allow local node14dto interrupt the transmission by local node14c, hub node12may transmit an interruption message440to the currently transmitting local node14, local node14c, as shown. In response to interruption message440, local node14cterminates its current transmission. Hub node12also transmits an acknowledgement message450to the requesting local node14, local node14d. Acknowledgement message450may include any appropriate information indicating to local node14dthat local node14dmay use λT.

Hub node12may also transmit an intimation message460to the intended destination, local node14a, on the OSC. Intimation message460may include any appropriate information to facilitate reception of optical traffic by local node14afrom local node14d. In response to intimation message460, local node14amay configure local node14ain any appropriate manner to facilitate receipt of optical traffic from local node14d.

FIG. 4Cillustrates operation of local node14dafter receiving acknowledgement message450. In response to receiving acknowledgement message450, local node14begins transmitting optical traffic on λT. More specifically, local node14dgenerates optical signals at a wavelength of λT, based on the electrical signals of client traffic410, and transmits these optical signals on optical ring20as optical traffic470. AlthoughFIG. 4Cshows, for the purposes of simplicity, local node14dtransmitting optical traffic counterclockwise on first fiber16, local node14dmay transmit optical traffic470as appropriate on either or both of fibers16and18. For example, in a particular embodiment of network10, local node14dmay transmit identical copies of optical traffic470on each of first fiber16and second fiber18to ensure delivery of optical traffic470to destination local node14a.

In the illustrated example, local node14dtransmits optical traffic470along first fiber16in a counterclockwise direction at a wavelength of λT. When hub node12receives optical traffic470in this embodiment, hub node12performs any appropriate processing, such as buffering optical traffic470or modifying header information included in optical traffic470, and regenerates optical traffic470at wavelength λR. The regenerated optical traffic470′ is transmitted on first fiber16.

Each of local nodes14may receive regenerated optical traffic470′ and drop a copy of regenerated optical traffic470′. Each local node14may then forward the dropped copy of regenerated optical traffic470′ to appropriate client devices, if any, from among the client devices coupled to local node14. For example, in the illustrated embodiment, local node14adetermines, based on addressing information within regenerated optical traffic470′ or any other appropriate information and/or considerations, that a client device coupled to local node14ais the destination of regenerated optical traffic470′ and routes the dropped copy of regenerated optical traffic470′ to that client device. Meanwhile, each of the remaining local nodes14drops a copy of regenerated optical traffic470′ and determines, based on addressing information or other appropriate considerations, that none of the client devices attached to that local node14is the destination for regenerated optical traffic470′. As a result, in the illustrated embodiment, each of these local nodes14discards their dropped copy of regenerated optical traffic470′.

Additionally, another local node14may interrupt the transmission by local node14d. If another local node14requests use of λTfor a transmission that has a priority status higher than that associated with client traffic410, hub node12may decide to interrupt the transmission of optical traffic470. Hub node12may interrupt transmission of optical traffic470by transmitting interruption message440to local node14d, as described above.

FIG. 4Dillustrates operation of optical network10after local node14dhas completed its transmission to local node14a. In the illustrated example, local node14dtransmits a termination message480to hub node12on the OSC after local node14dhas transmitted all of optical traffic470to local node14a. Termination message480may include any suitable information indicating local node14dhas completed transmission of optical traffic470and/or no longer requires the use of λT. Upon receiving termination message480from local node14d, hub node12indicates to local nodes14that the transmitting wavelength is again available for use. In the illustrated example, hub node12indicates that λTis now available by transmitting an idle message412to local nodes14.

FIGS. 5A-5Dillustrate another embodiment of optical network10in which a local node14may request use of the transmitting wavelength to transmit directly to another local node14that lies between the requesting local node14and hub node12. The illustrated techniques allow a requesting local node14to request use of a particular wavelength over the portion of optical ring20that connects the requesting local node14to the destination local node14. Because these techniques eliminate the need for traffic to be transmitted to hub node12before being transmitted to the destination local node14, these techniques may reduce traffic on other portions of optical ring20and may reduce the workload of hub node12.

In the illustrated example, local node14brequests direct communication at a particular wavelength, λS. The requested wavelength may be a currently unused receiving wavelength, a currently unused transmitting wavelength, or any other appropriate wavelength. In alternative embodiments of optical network10, local node14bmay not specify a requested wavelength, and hub node12may instead select a wavelength for direct communication and transmit information identifying the selected wavelength to local node14band/or local node14c.

FIG. 5Aillustrates operation of optical network10as local node14breceives client traffic510(as electrical signals) from a client device to be transmitted to local node14con optical ring20. In this example, local node14bdecides based on appropriate criteria to request use of λSfor direct communication to node14c. For example, in a particular embodiment, local node14bdetermines whether to request use of λSfor direct communication to local node14cbased on whether the amount of traffic being transmitted to local node14cis greater than a predetermined threshold.

If local node14bdecides to request use of λSfor direct communication, local node14btransmits a request message520to hub node12. Request message520indicates to hub node12that local node14bis requesting use of λSfor direct communication with local node14c. Request message520may include information identifying requesting local node14band/or destination local node14cand/or any other appropriate information. Local node14may also transmit an intimation message530to local node14c.

Local node14may also transmit an intimation message530to local node14c. Intimation message530indicates to local node14cthat local node14bwill be transmitting information directly to local node14c. Intimation message530may include information identifying requesting local node14b, the transmitting wavelength on which requesting local node14bwill be transmitting, and/or any other appropriate information to be used by local node14cto facilitate receipt of optical traffic from local node14c.

FIG. 5Billustrates operation of optical network10after local node14btransmits intimation message530to local node14c. In response to receiving intimation message530, local node14cmay configure itself in any appropriate manner to facilitate reception of optical traffic from local node14b. For example, in particular embodiment, intimation message530specifies the wavelength at which local node14bwill communicate optical traffic to local node14c, and local node14cmay retune tunable filters and/or tunable receivers of local node14cto receive optical traffic at the specified wavelength.

After configuring itself to receive optical traffic on the appropriate wavelength, local node14cmay inform both local node14band hub node12that local node14cis ready to receive traffic from local node14bdirectly. For example, in the illustrated example, local node14ctransmits a confirmation message540to hub node12and to local node14b. Confirmation message530indicates to hub node12and local node14bthat local node14cis ready to receive traffic directly from local node14bat the selected wavelength and may include any appropriate information.

In response to receiving request message520, hub node12may initiate any appropriate procedures to reserve use of λSover the span of optical ring20between local node14band local node14cfor direct communication between local node14band local node14c. For example, in the illustrated embodiment, hub node12may maintain a table of available wavelengths and may update this table to indicate that λSis currently in use by local node14b.

FIG. 5Cillustrates operation of optical network10after local node14breceives confirmation message540from local node14c. In response to receiving confirmation message540from local node14c, local node14bbegins generating optical traffic540from client traffic510and transmitting optical traffic540to local node14cat λS. Because λSis reserved for direct communication between local node14band local node14cand because local node14chas be tuned to receive optical traffic on λS, optical traffic540can be transmitted by local node14bto local node14cdirectly, as shown, without optical traffic540having to propagate around optical ring20to hub node12and/or be switched by hub node12.

FIG. 5Dillustrates operation of optical network10after local node14bfinishes transmitting optical traffic540. After finishing transmission of optical traffic540, local node14bmay transmit a termination message550to hub node12. Termination message550indicates to hub node12that local node14bhas finished transmitting to local node14con λS. Termination message550may include information identifying local node14band/or the selected wavelength, and/or any other appropriate information to be used by hub node12to release λSfor other uses.

Additionally, local node14bmay also transmit termination message550to local node14c. Alternatively, local node14cmay determine based on the loss of optical signal on λSthat local node14bhas finished transmitting optical traffic540. In response to receiving termination message550or otherwise determining that local node14bhas finished transmitting optical traffic540, local node14cmay reconfigure itself to return to operating in the same or a similar manner as local node14cwas operating before receiving intimation message530. For example, local node14cmay retune a tunable filter or tunable receiver of local node14cso that this filter or receiver receives optical traffic transmitted at a default receiving wavelength.

Using these techniques, local nodes14in particular embodiments of optical network10may improve efficiency of communication between local nodes14. As optical traffic between two local nodes14communicated via node12approaches the full capacity of a particular wavelength, these embodiments of optical network10may enhance efficiency by switching to direct communication between the nodes14. Direct communication can limit traffic on other portions of optical network10, reduce traffic at hub node12, and limit transmission times between local nodes14by both eliminating switching delay at hub node12and round-trip travel delay.