Bridging for SONET/SDH automatic protection switching

Bridging for Synchronous Optical NETwork (SONET)/Synchronous Digital Hierarchy (SDH) Automatic Protection Switching is disclosed. First and second apparatus in a redundant pair handle communication traffic that includes content for transmission on respective first and second SONET/SDH connections. Content received by each apparatus for transmission on a SONET/SDH connection is transmitted on the first and second SONET/SDH connections. Such content is also transmitted by each apparatus to the other apparatus in the redundant pair unless that content was received from the other apparatus. The content is thereby transmitted on both the first and second SONET/SDH connections even though the content is received directly by only one apparatus of the redundant pair. This avoids duplication of communication traffic that carries the content. Where the traffic is Ethernet traffic, the traffic may be bridged between the first apparatus and the second apparatus at the Media Access Control (MAC) layer.

FIELD OF THE INVENTION

This invention relates generally to redundancy protection and, in particular, to bridging of communication traffic between redundant components to enable Automatic Protection Switching (APS) for Ethernet connections.

BACKGROUND

APS for Synchronous Optical NETwork (SONET)/Synchronous Digital Hierarchy (SDH) technology according to the GR-253-CORE specification entitled “Synchronous Optical Network (SONET) Transport Systems: Common Generic Criteria”, for example, requires electrical bridging between components which support redundant network-side SONET/SDH connections to subtending equipment. Electrical bridging at the physical layer provides for transmission of the same SONET/SDH payloads on redundant network-side optical connections. In a 1+1 linear APS implementation, traffic is bridged from a working connection to a protection connection at transmitting equipment, and receiving equipment normally selects traffic from the working connection. A fault or other condition affecting the working connection causes an APS operation, and traffic is then selected from the protection connection.

Physical layer bridging tends to be implemented in a single equipment chassis. This can significantly limit the actual level of protection that is provided, in that a failure affecting one equipment installation would interrupt traffic flow.

Such bridging also provides protection only for the optical SONET/SDH connections, and not for further connections, such as access-side connections from which traffic for SONET/SDH connections originates.

SUMMARY

Some embodiments of the invention allow SONET/SDH payloads to be derived from other traffic, such as Ethernet frames which are destined for either one of two different Ethernet MAC addresses. This can provide redundancy protection for Ethernet traffic while still providing support for optical connection APS.

According to an aspect of the invention, an apparatus includes an optical interface that enables communications via a SONET/SDH connection; an interface that enables reception of communication traffic comprising content for transmission from the apparatus via the SONET/SDH connection; an inter-apparatus interface that enables communications between the apparatus and a further apparatus, the further apparatus including an optical interface that enables communications via a further SONET/SDH connection and an interface that enables reception of communication traffic comprising content for transmission from the further apparatus via the further SONET/SDH connection, the apparatus and the further apparatus forming a redundant pair; and a bridging module, operatively coupled to the optical interface, to the interface, and to the inter-apparatus interface. The bridging module provides content that is for transmission from the apparatus via the SONET/SDH connection and is received through the interface to the optical interface for transmission via the SONET/SDH connection, and transmits the content to the further apparatus through the inter-apparatus interface for transmission via the further SONET/SDH connection. The bridging module also provides content that is for transmission from the further apparatus via the further SONET/SDH connection and is received through the inter-apparatus interface to the optical interface for transmission via the SONET/SDH connection.

In some embodiments, the interface includes an Ethernet interface that enables reception of Ethernet traffic destined for a first Ethernet Media Access Control (MAC) address, and the interface of the further apparatus includes an Ethernet interface that enables reception of Ethernet traffic destined for a second Ethernet MAC address different from the first Ethernet MAC address.

Where the Ethernet traffic destined for the first Ethernet MAC address includes Ethernet frames, the bridging module may transmit content to the further apparatus through the inter-apparatus interface as Ethernet frames.

The apparatus may also include a traffic processor, operatively coupled to the bridging module and to the optical interface, that receives content from the bridging module, synthesizes a SONET/SDH payload comprising the content, and transmits the SONET/SDH payload via the SONET/SDH connection. Where the interface includes an Ethernet interface that enables reception of Ethernet traffic including Ethernet frames, the bridging module may provide content to the traffic processor as Ethernet frames, and the traffic processor then synthesizes the SONET/SDH payload from the Ethernet frames.

The bridging module itself synthesizes a SONET/SDH payload including received content and provides the SONET/SDH payload to the optical interface in some embodiments.

A state module may also be implemented in the apparatus. The state module determines whether the apparatus is in a first operating state or a second operating state in the redundancy pair.

The state module may determine whether the apparatus is in the first operating state or the second operating state on the basis of one or more of: communication traffic that is received through the interface, whether the content for, transmission via the SONET/SDH connection is received through the interface or the content for transmission from the further apparatus via the further SONET/SDH connection is received through the inter-apparatus interface, and a state indication received from the further apparatus through the inter-apparatus interface, the state indication providing an indication of a current operating state of the further apparatus in the redundancy pair.

In some embodiments, the state module further transmits a state indication to the further apparatus through the inter-apparatus interface, the state indication providing an indication of the determined operating state of the apparatus.

A method is also provided, and includes receiving, at a first apparatus that handles communication traffic including content for transmission via a first SONET/SDH connection, content for transmission from the first apparatus via the first SONET/SDH connection, the first apparatus forming a redundant pair with a second apparatus that handles communication traffic including content for transmission via a second SONET/SDH connection; determining whether the received content was received from the second apparatus; transmitting the received content via the first SONET/SDH connection; and where the received content was not received from the second apparatus, further transmitting the received content to the second apparatus for transmission via the second SONET/SDH connection.

In some embodiments, the first apparatus handles Ethernet traffic destined for a first Ethernet MAC address, and the second apparatus handles Ethernet traffic destined for a second Ethernet MAC address different from the first Ethernet MAC address. Where the Ethernet traffic destined for the first Ethernet MAC address including Ethernet frames, further transmitting the received content to the second apparatus may involve transmitting the received content as Ethernet frames.

The method may also include synthesizing a SONET/SDH payload comprising the received content, and in this case, transmitting the received content via the first SONET/SDH connection may involve transmitting the SONET/SDH payload. Where the communication traffic includes Ethernet frames, synthesizing may involve synthesizing the SONET/SDH payload from the Ethernet frames.

In some embodiments, the method also includes determining whether the first apparatus is in a first operating state or a second operating state on the basis of one or more of: communication traffic that is received at the apparatus, whether the received content was received at the first apparatus from the second apparatus, and a state indication received from the second apparatus, the state indication providing an indication of a current operating state of the second apparatus in the redundancy pair.

Such a method may be embodied, for example, in a computer-readable medium encoded with computer executable instructions which when executed cause a computer to perform the method.

A system is also provided, and includes a first apparatus, operatively coupled to a first SONET/SDH connection, for handling communication traffic including content for transmission from the first apparatus via the first SONET/SDH connection; and a second apparatus, operatively coupled to the first apparatus and to a second SONET/SDH connection, for handling communication traffic including content for transmission from the second apparatus via the second SONET/SDH connection. The first apparatus and the second apparatus form a redundant pair, and each of the first apparatus and the second apparatus includes a bridging module. The bridging module of the first apparatus transmits content on the first SONET/SDH connection and, where the content was not received from the second apparatus, further transmits the content to the second apparatus for transmission on the second SONET/SDH connection. The bridging module of the second apparatus transmits content on the second SONET/SDH connection and, where the content was not received from the first apparatus, further transmits the content to the first apparatus for transmission on the first SONET/SDH connection.

The first apparatus might handle Ethernet traffic including Ethernet frames that contain content for transmission via the first SONET/SDH connection, and the second apparatus might handle Ethernet traffic including Ethernet frames that contain content for transmission via the second SONET/SDH connection. In this case, the bridging module of each apparatus could further transmit the content to the other apparatus in Ethernet frames.

In some embodiments, the first apparatus handles Ethernet traffic destined for a first Ethernet MAC address, and the second apparatus handles Ethernet traffic destined for a second Ethernet MAC address different from the first Ethernet MAC address.

Each apparatus may also include a traffic processor operatively coupled to the bridging module of the apparatus, the traffic processor receiving from the bridging module the content for transmission from the apparatus via its SONET/SDH connection, synthesizing a SONET/SDH payload comprising the content, and transmitting the SONET/SDH payload via the SONET/SDH connection.

Other aspects and features of embodiments of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description.

DETAILED DESCRIPTION

Redundancy protection is provided in some embodiments through Ethernet MAC bridging. This type of Layer 2 bridging can be used, for example, to protect customer Ethernet traffic including content that is to be transferred over an APS-protected SONET/SDH connection. Ethernet MAC bridging provides for redundancy using two different MAC addresses but without duplicating Ethernet traffic in the subtending Ethernet network. The SONET/SDH payload can then be synthesized from Ethernet traffic that is bridged at the MAC layer, and thus the same SONET/SDH payload is presented to subtending SONET/SDH equipment via redundant optical links.

FIG. 1is a block diagram of an example communication network implementation. The example communication network10includes a SONET/SDH Add Drop Multiplexer (ADM)12coupled to head network elements14,16through respective optical links22,24. The head network elements14,16are also coupled to each other through a connection26, and to leaf network elements18,20through an Ethernet network17. Communications between the head network elements14,16and the leaf network elements18,20are represented inFIG. 1at28,30,32,34. It should be appreciated that the system ofFIG. 1, as well as the contents of the other drawings, are intended solely for illustrative purposes, and that the present invention is in no way limited to the particular example embodiments explicitly shown in the drawings and described herein.

In one common architecture, optical and multiplexer network elements convert and transfer communication traffic between access-side T1 connections, which are often leased lines, and network-side optical links. T1 connections might be leased to carry traffic from base stations in a wireless network back to an optical aggregation point and into a core network, for instance. Such leased connections, however, can significantly increase operating costs for an operator of the wireless network.

Although other technologies such as Ethernet might provide a much more cost efficient alternative to leased T1 connections, communication equipment that supports optical communications through SONET/SDH connections, for example, tends to be geared toward T1 implementations at the “electrical” connection side.

One possible application of the example communication network10would be to allow the Ethernet network17to be used as the transport mechanism between the SONET/SDH connections on the optical links22,24and access-side connections (not shown) at the leaf network elements18,20. For example, the leaf network elements18, might include T1 interfaces for connection to existing base station equipment which would otherwise communicate with a core network over T1 connections, and convert to Time Division Multiplexing over Ethernet (TDMoE) to transfer traffic in the Ethernet network17. At the head network elements14,16, traffic is further processed for transfer over the SONET/SDH connections on the optical links22,24. Thus, T1 leased lines can be avoided while still transporting traffic to and from a core network through optical links. The head network elements14,16and the leaf network elements18,20handle any interworking between SONET/SDH connections on the optical links22,24and the Ethernet network17, and between the Ethernet network and access-side T1 connections in this example.

The SONET/SDH ADM12may be implemented in substantially the same manner as existing SONET/SDH ADMs. It will become apparent as the present specification proceeds that embodiments of the invention need not affect the way in which optical links, SONET/SDH connections, and even 1+1 APS for SONET/SDH connections operate.

At least the optical side of the head network elements14,16may similarly be implemented in substantially the same way as existing network components, such as optical and multiplexer network elements. An illustrative example of an apparatus that might be implemented in a head network element14,16to provide additional features in accordance with embodiments of the invention is shown inFIG. 2and described in further detail below.

Each leaf network element18,20includes at least an Ethernet interface, an interface to other equipment with which it exchanges communication traffic, and traffic processing components. In one embodiment noted above, each leaf network element18,20includes a T1 interface and allows traffic to be transported through the Ethernet network17rather than T1 connections.

Operation of the network10can perhaps best be illustrated by considering an example. Suppose that the leaf network elements18,20include respective Ethernet interfaces that are addressable in the Ethernet network17and T1 interfaces for terminating access-side T1 connections. When traffic is received on a T1 connection, the corresponding leaf node18,20generates TDMoE frames destined for one of the head network elements14,16. These Ethernet frames carry voice information where the T1 connections at the leaf network elements18,20originate in a base station of a wireless voice communication network for instance. Although the head network elements14,16are intended to provide redundant protection for Ethernet communications in the example network10, in order to avoid duplicating traffic in the Ethernet network17the leaf network elements18,20forward the TDMoE frames to only one of the head network elements14,16, as represented at28,30.

In one embodiment, one of the head network elements14,16is in a first state and the other is in a second state at any time. For ease of reference, the first state is also described herein as an In-Service state, and the second state is described herein as a Standby state. It should be appreciated however, that embodiments are not limited to implementations using states which are characterized in this or any other particular manner. Operating states in redundancy groups are also often referred to as Active and Inactive, for example, and any designations or names may be used for such operating states.

The head network element14is in the In-Service state and the head network element16is in the Standby state in the example shown inFIG. 1. The leaf network elements18,20send TDMoE frames to the In-Service head network element14. This is represented inFIG. 1at28,30. Bridging of traffic at the In-Service head network element14as disclosed herein allows redundancy protection to be provided for communications in the Ethernet network17even though traffic is sent to only a single destination, namely the In-Service head network element, by the leaf network elements18,20. Duplicate Ethernet traffic need not be sent from the leaf network elements18,20to both of the head network elements14,16.

Keep-Alive signalling between the Standby head network element16and the leaf network elements18,20is represented at32,34, and is used in one embodiment to prevent the leaf network elements18,20and any intermediate routing nodes or components (not shown) in the Ethernet network17from aging the address of the Standby head network element out of their routing tables. For example, Keep-Alive signalling might include packets which are sent to the Standby head network element16by the leaf network elements18,20, and response packets which are echoed back to the leaf network elements by the Standby head network element16. A similar signalling scheme could be used during startup or initialization to enable the leaf network elements18,20to determine which head network element14,16is to be in the In-Service state.

In the event of a loss or possibly degradation of communications with the In-Service head network element14, the leaf network elements18,20begin sending traffic to the Standby head network element16. The Standby head network element16then enters the In-Service state, and the former In-Service head network element14transitions to the Standby state.

Embodiments of the present invention are directed primarily to bridging of traffic between redundant network elements. Further details regarding the management of In-Service and Standby states and the exchange of traffic and other signals such as Keep-Alive packets between head network elements such as14,16and leaf network elements such as18,20are provided in co-pending United States Patent Application Serial No. 12/382,031, entitled “OPERATING STATE CONTROL IN REDUNDANCY. PROTECTION SYSTEMS”, filed of even date herewith, which is incorporated in its entirety herein by reference.

In order to support redundancy protection for SONET/SDH connections on the optical links22,24, the same SONET/SDH payload is to be transmitted on both connections. As noted above for the example system10, however, duplicate Ethernet traffic is not transmitted through the Ethernet network17between the leaf network elements18,20and the head network elements14,16. The leaf network elements18,20send live TDMoE traffic to only the In-Service head network element, which is the head network element14in the example shown inFIG. 1. In accordance with one aspect of the invention, payload mirroring for the SONET/SDH connections on the optical links22,24is provided by bridging content, illustratively in the form of Ethernet frames, from the In-Service head network element14to the Standby head network element16using the connection26. In an implementation that bridges Ethernet frames between equipment such as the head network elements14,16, the connection26may be an Ethernet link. Other embodiments may use different types of connections between redundant equipment.

The In-Service head network element14receives and processes TDMoE frames to synthesize the SONET/SDH payload for transmission to the SONET/SDH ADM12, and also re-directs the received frames to the Standby head network element16through the connection26. The Standby head network element16receives the TDMoE frames, synthesizes the SONET/SDH payload, and presents it to subtending SONET/SDH equipment, which is the ADM12in the example system10. This provides mirrored SONET/SDH payloads for redundancy protection of communications on the optical links22,24, using GR-253 1+1 APS for instance.

FIG. 2is a block diagram of an example apparatus40according to an embodiment of the invention. The example apparatus40includes an optical interface42, a traffic processor44operatively coupled to the optical interface, and a bridging module46operatively coupled to the traffic processor, to a state module47, to an Ethernet interface48, and to an inter-apparatus interface49. The state module47is also operatively coupled to the optical interface42, to the traffic processor44, to the Ethernet interface48, and to the inter-apparatus interface49. Communication equipment in which the example apparatus40is implemented, such as a head network element14,16(FIG. 1) may include additional components that have not been explicitly shown inFIG. 2in order to avoid overly complicating the drawing. More generally, other embodiments may include further, fewer, or different components which may be interconnected in a similar or different order than shown.

The optical interface42includes components which support communications over an optical link, and in particular a SONET/SDH connection in one embodiment. Such components often include hardware at least in the form of a physical port or connector and an optical multiplexer. The exact structure of the optical interface42may, to at least some extent, be implementation-dependent, and could vary depending on the type of connection(s) and/or protocol(s) to be supported.

Other components which provide higher-level functions such as communication protocol support may also be implemented, in the optical interface42and/or in the traffic processor44. The traffic processor44is intended to represent a module that handles communication traffic that is received by the apparatus40. When implemented in a head network element14,16(FIG. 1), for example, the traffic processor44might process received Ethernet frames to extract content for transmission via a SONET/SDH connection. Hardware, firmware, components which execute software, or some combination thereof might be used in implementing the traffic processor44, and possibly other elements of the example apparatus40. Electronic devices that may be suitable for this purpose include, among others, microprocessors, microcontrollers, Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), Application Specific Integrated Circuits (ASICs), and other types of “intelligent” integrated circuits.

The bridging module46and the state module47may similarly be implemented using hardware, firmware, and/or components which execute software. These modules are defined moreso by their functions as set out below rather than a particular internal structure. The present disclosure would enable a skilled person to implement these modules in any of various ways to perform their respective functions.

The Ethernet interface48and the inter-apparatus interface49, like the optical interface42, include components such as physical ports or connectors and possibly other components which support communications over respective links. In the case of the Ethernet interface48, these components may include at least an Ethernet port and a MAC device. The structure of the inter-apparatus interface49may be dependent upon the type of connection(s) and/or protocol(s) over which information is to be exchanged between installations of apparatus in a redundant pair. In one embodiment, the inter-apparatus interface49is another Ethernet interface.

In operation, the optical interface42enables communications via a SONET/SDH connection, and the Ethernet interface48represents an example of an interface that enables reception of communication traffic that includes content for transmission from the apparatus40via the SONET/SDH connection. The content for transmission on the SONET/SDH connection might be voice information in TDMoE frames, for example. It should be appreciated that such content need not necessarily include the entirety of received traffic. The content to be transmitted from the apparatus40through the optical interface42might include only certain parts or fields in received traffic, such as only part of a received Ethernet frame.

The inter-apparatus interface49enables communications between the apparatus40and a further or second apparatus which, with the apparatus40, forms a redundant pair. For full redundancy, the second apparatus has the same structure as the example apparatus40, and the first apparatus and the second apparatus of a redundant pair communicate through their respective inter-apparatus interfaces49. The optical interface42of the second apparatus enables communications via a second SONET/SDH connection and the Ethernet interface48of the second apparatus represents an example of an interface that enables reception of communication traffic that includes content for transmission from the second apparatus via the second SONET/SDH connection. Thus, each apparatus of a redundant pair handles incoming communication traffic for transmission on its respective SONET/SDH connection.

An apparatus in a redundant pair performs slightly different operations in the In-Service state and the Standby state, since those states impact the interface at which content for transmission via its SONET/SDH connection would be received. During normal operation, only one apparatus in a redundant pair is in each operating state at any time.

When the example apparatus40is in the In-Service state, the bridging module46receives, through the Ethernet interface48, communication traffic that includes content for transmission from the apparatus via the SONET/SDH connection supported by the optical interface42. The content is provided to the optical interface42by the bridging module46, through the traffic processor44in the example shown, for transmission via the SONET/SDH connection. The bridging module46also transmits the content to the second apparatus through the inter-apparatus interface49for transmission via the second SONET/SDH connection.

In this scenario, the second apparatus is in the Standby state. At the second apparatus, the bridging module46receives, through the inter-apparatus interface49, content for transmission from the second apparatus via the SONET/SDH connection supported by its optical interface42, and provides that content to the optical interface for transmission via the second SONET/SDH connection.

It should be noted that the same apparatus can operate in either of the In-Service and Standby states. Therefore, the bridging module46of the example apparatus40might pass content that is received through the Ethernet interface48to both the optical interface42and the inter-apparatus interface49, which would be the case when the apparatus is in the In-Service state. In the Standby state, an apparatus40would not receive live communication traffic through its Ethernet interface48, since such traffic is sent to only the In-Service apparatus of a redundant pair. Thus, in the Standby state, an apparatus40would receive content for transmission on its SONET/SDH connection through its inter-apparatus interface49, and pass that content to the optical interface42.

A bridging module46in an apparatus thus transmits received content to a further apparatus in a redundant pair unless the content was received from that further apparatus.

In one embodiment, the Ethernet interface48enables reception of Ethernet traffic destined for a first Ethernet MAC address, and the Ethernet interface of the second apparatus in the redundant pair enables reception of Ethernet traffic destined for a second Ethernet MAC address that is different from the first Ethernet MAC address. However, only one apparatus of the pair actually receives Ethernet traffic, such as TDMoE traffic in one embodiment, from an Ethernet network at any time. If the example apparatus40were implemented at each head network element14,16(FIG. 1), for example, the leaf network elements18,20might have the MAC addresses of both of the head network elements, but send traffic through the Ethernet network17to only one of the head network elements. The different MAC addresses provide redundancy protection for communications in the Ethernet network17, but only one of those addresses is used by the leaf network elements18,20at a time in order to avoid duplicating Ethernet traffic.

Referring again toFIG. 2, any of several mechanisms could potentially be used by the bridging module46to bridge received content to a second apparatus of a redundant pair. For example, Ethernet frames received through the Ethernet interface48could be duplicated by the bridging module46and sent in their entirety to the traffic processor44and to the inter-apparatus interface49for transfer to the redundant apparatus. Another option would be to extract the content that is to be sent on the SONET/SDH connections of the apparatus and the redundant apparatus and forward that content to the local traffic processor44and to the redundant apparatus through the inter-apparatus interface49.

The traffic processor44receives from the bridging module46the content for transmission from the apparatus40via the SONET/SDH connection supported by the optical interface42. The content may be in the form of the traffic originally received, illustratively Ethernet frames, or in a modified form. A SONET/SDH payload including the content is synthesized by the traffic processor44, which also transmits the SONET/SDH payload via the SONET/SDH connection that is supported by the optical interface42. The form of the content may vary between the communication traffic in which it was originally received and the SONET/SDH payload synthesized by the traffic processor44. In one embodiment, content is mapped between the TDM payload of TDMoE frames and the SONET/SDH payload through jitter buffers. Various implementations of such mapping may be used to synthesize the same SONET/SDH payload at the traffic processors44of each apparatus in a redundant pair.

The preceding description relates primarily to communication traffic that includes content to be transmitted on SONET/SDH connections. Embodiments of the present invention may also be implemented in conjunction with bidirectional communications. In this case, the apparatus40may receive communication traffic through the optical interface42and transfer at least some content of that traffic to the Ethernet interface48for transmission in Ethernet traffic. In the example network10(FIG. 1), traffic received by the head network elements14,16over redundant SONET/SDH connections on the optical links22,24might include content that is to be forwarded on to the leaf network elements18,20.

In one implementation, the traffic processor44controls the flow of content received from the optical interface42to the Ethernet interface48. In order to avoid duplicating Ethernet traffic in the direction from the head network elements14,16to the leaf network elements18,20(FIG. 1), for instance, only the In-Service head network element14might be allowed to pass content from the optical interface42to the Ethernet interface48. The Standby head network element16in this case does not pass content from the optical interface42to the Ethernet interface48. In this example, the traffic processor44passes or blocks content on the basis of operating state, although this function could potentially be provided by the bridging module,46or another component in other embodiments.

Since an apparatus40operates differently depending on its current operating state in a redundant pair, the state module47is provided in some embodiments to determine whether the apparatus is in the In-Service operating state or the Standby operating state in the redundant pair. The determined state could be reported to the bridging module46and/or possibly other components, which then perform any state-dependent operations accordingly. The bridging module46, for example, might provide received content for transmission through the optical interface42and possibly the inter-apparatus interface49depending on whether the apparatus40is in the In-Service or Standby state. This function could instead be controlled on the basis of the interface through which content is received, as described above. Behaviour of the traffic processor44, at least in its handling of content received on a SONET/SDH connection, may similarly change between different operating states. An indication of current operating state could therefore also or instead be provided to the traffic processor44by the state module47.

Operating state indications could potentially be distributed to components of the apparatus40in any of various ways. For instance, a state indication might be provided to each component that performs state-dependent operations each time a change in state is detected by the state module47. An indication of current operating state could instead be stored in a memory (not shown) by the state module47for subsequent access by other components as those components are preparing to perform state-dependent operations. The state module47may also or instead support a query/response mechanism, whereby an indication of current state is provided to another component in response to a received query message. Embodiments of the invention are in no way limited to these or any other particular mechanisms for advising other components of the current operating state of the apparatus40.

A determination of the current operating state of an apparatus40may be made, for example, on the basis of communication traffic that is received through the Ethernet interface48. If communication traffic that includes content for transmission via the SONET/SDH connection through the optical interface42is received through the Ethernet interface48, then the apparatus40is in the In-Service state, since communication traffic is sent only to one apparatus in a redundant pair.

The state determination could also or instead be made on the basis of whether the content for transmission via the SONET/SDH connection is received through the Ethernet interface48or through the inter-apparatus interface49. In the In-Service state, content would be received through the Ethernet interface48in Ethernet traffic, whereas in the Standby state content would be received from the second apparatus through the inter-apparatus interface49.

Another possible option for determining the current operating state of an apparatus40might be a state indication received from the redundant apparatus through the inter-apparatus interface49. The inter-apparatus interface49could potentially be used to transfer other information than content that is to be transmitted via SONET/SDH connections. State indications that provide indications of a current operating state of each apparatus in the redundancy pair could be exchanged through the respective inter-apparatus interfaces49. Since only one apparatus in a redundant pair should be in each state at any time, a state indication from the redundant apparatus would advise an apparatus of the current state of its redundant apparatus. The apparatus that receives a state indication should be in the opposite operating state from its redundant “mate” apparatus.

Two-way state determination by each apparatus in a redundant pair could be supported where the state module47in each apparatus sends a state indication to the other apparatus. Such an indication could use a single bit if only two states are to be detected. In embodiments in which other states are possible, during startup or initialization for instance, additional bits could be used. Other forms of state information are also possible.

Current operating states could also be signalled to optical equipment at the far end of SONET/SDH connections, to coordinate the control of operating states between optical equipment and Ethernet equipment, for example. The state module47might provide state indications to the optical interface42and/or to the traffic processor44for this purpose. The head network elements14,16inFIG. 1, for instance, provide redundancy protection for optical communications on the links22,24, and accordingly an APS operation affecting the head network elements might be initiated due to an optical side fault or condition. Therefore, some form of coordination of operating state control might also be provided in some embodiments. Examples of such coordination mechanisms are disclosed in the co-pending application referenced above.

FIGS. 3 and 4are block diagrams illustrating a bridging function. The example system50which is shown inFIGS. 3 and 4is similar to the network side ofFIG. 1, and includes a SONET/SDH ADM52and two head network elements54,56which are operatively coupled together at58. Although the head network elements54,56may include other components, only their bridging modules60,62have been explicitly shown in order to avoid overly complicating the drawing. The head network elements54,56have respective MAC addresses ‘A’ and ‘B’.

InFIG. 3, the head network element54is in the In-Service state and the head network element56is in the Standby state. Ethernet frames64, illustratively TDMoE traffic, destined for MAC ‘A’ are received by the In-Service head network element54and also sent to the Standby head network element56by the bridging module60. Although the Standby head network element56has a different MAC address ‘B’, in accordance with an embodiment of the invention the bridging module62accepts two MAC addresses, including MAC ‘A’ and MAC ‘B’.

The bridging modules60,62, as well as the traffic processors (not shown) of the head network elements54,56, may accept both MAC addresses. In a modern Ethernet network containing switches or routers, traffic destined for MAC ‘A’ is sent only to the head network element54. Similarly, traffic for MAC ‘B’ would be routed only to the head network element56. This is the expected and desired behaviour of an Ethernet network, as it uses bandwidth efficiently by routing traffic only where necessary. In one embodiment, neither the Ethernet interface48(FIG. 2) nor the inter-apparatus interface49of a head network element filters traffic based on MAC address, and this function is instead handled by the bridging module46(60,62inFIG. 3) and the traffic processor44.

SONET/SDH payloads66,68are synthesized at each head network element54,56for transmission via redundant SONET/SDH connections. The SONET/SDH payloads66,68are identical, thereby providing the payload mirroring required for 1+1 APS between the SONET/SDH ADM52and the head network elements54,56. APS functions between the SONET/SDH ADM52and the head network elements54,56are thereby unaffected by the fact that Ethernet is used instead of the usual T1 connections. The head network elements54,56handle all interworking between SONET/SDH and Ethernet, which allows APS for the optical links to operate normally. No changes at the optical side of the head end network elements54,56are necessary.

The synthesis of identical SONET/SDH payloads66,68based on the same Ethernet frames is represented inFIG. 3by the dashed lines. It should be noted that while the SONET/SDH payloads66,68are identical, SONET/SDH frames transmitted by the head network elements54,56need not be entirely identical. Such frames include other information than payloads, and that other information may be different for the head network elements54,56.

Like the bridging module62of the Standby head network element56, the bridging module60of the In-Service head network element54also accepts two MAC addresses, including its own MAC ‘A’ and MAC ‘B’ of the Standby head network element. In the case of an APS switch-over event at the Ethernet side, such as loss of TDMoE traffic to the head network element54as shown inFIG. 4, the head network element56begins to receive Ethernet frames70and enters the In-Service state. Received Ethernet frames70that are destined for MAC ‘B’ are bridged from the new In-Service head network element56to head network element54, which is now in the Standby state. SONET/SDH payload mirroring is maintained, and identical SONET/SDH payloads are synthesized for transmission to the SONET/SDH ADM52as shown at72,74.

It can be seen perhaps most clearly fromFIGS. 3 and 4that an embodiment of the invention provides a system including a first apparatus and a second apparatus, such as the head network elements54,56, that form a redundant pair. The first apparatus is operatively coupled to a first SONET/SDH connection and handles communication traffic that includes content for transmission from the first apparatus via the first SONET/SDH connection, and the second apparatus is operatively coupled to the first apparatus and to a second SONET/SDH connection and handles communication traffic that includes content for transmission from the second apparatus via the second SONET/SDH connection. Each apparatus also includes a bridging module.

The bridging module of the first apparatus transmits content on the first SONET/SDH connection. As described in detail above, content may be received by a bridging module from an Ethernet network or from the second apparatus in a redundant pair in one embodiment. If the content was not received from the second apparatus, the bridging module further transmits the content to the second apparatus for transmission on the second SONET/SDH connection. The bridging module of the second apparatus similarly transmits content on the second SONET/SDH connection and, if the content was not received from the first apparatus, transmits the content to the first apparatus for transmission on the first SONET/SDH connection.

Embodiments of the invention have been described above primarily in the context of apparatus and systems. Aspects of the invention may also be embodied, for example, in method form.FIG. 5is a flow diagram illustrating an example method.

The example method80involves receiving content at82. The content is received at a first apparatus that handles communication traffic including content for transmission via a first SONET/SDH connection. The first apparatus and a second apparatus that handles communication traffic comprising content for transmission via a second SONET/SDH connection form a redundant pair. If it is determined at84that the content was not received from the second apparatus, then the content is not only transmitted via the first SONET/SDH connection at86, but is further transmitted to the second apparatus at88for transmission via the second SONET/SDH connection. If the content was received from the second apparatus, the content is transmitted via the first SONET/SDH connection at86.

FIG. 5represents an illustrative example of a method according to one embodiment. Various ways of performing the operations shown inFIG. 5, and examples of additional operations that may be performed, will be apparent from the description and drawings relating to apparatus and system implementations, for example. Operations may also or instead be performed in a different order than shown. The transmission of received content on a SONET/SDH connection and to the other apparatus in a redundant pair need not be in any particular order, although in embodiments where transmission of the same payloads on the first and second SONET/SDH connections should be synchronized, content could be transmitted to the second apparatus at88before it is transmitted on the first SONET/SDH connection at86. Further variations may be or become apparent to those skilled in the art.

Bridging as disclosed herein provides a mechanism other than traditional electrical bridging to present mirrored SONET/SDH signals to subtending equipment. Embodiments may also minimize Ethernet traffic, since remote leaf network elements need not send duplicate TDMoE traffic to both In-Service and Standby head network elements.

Thus, bridging as proposed herein is not just traditional SONET/SDH GR-253 electrical port bridging and mirroring. Embodiments may provide bridging at the Ethernet MAC layer, allowing for SONET/SDH payload and port mirroring.

What has been described is merely illustrative of the application of principles of embodiments of the invention. Other arrangements and methods can be implemented by those skilled in the art without departing from the scope of the present invention.

For example, the division of functions shown inFIG. 2is illustrative of an embodiment of the invention. Further, fewer, or different elements may be used to implement the techniques disclosed herein. Bridging and SONET/SDH payload synthesis could potentially be performed by a single physical component, for instance, such that a bridging module synthesizes a SONET/SDH payload that includes content for transmission via a SONET/SDH connection, and provides the SONET/SDH payload to an optical interface.

In addition, although described primarily in the context of methods and systems, other implementations of the invention are also contemplated, as executable instructions stored on a computer-readable medium, for example.