Reducing CC message transmission in a provider network

A method and apparatus for reducing the number of CC messages transmitted in a provider network. In one embodiment of the invention, a first service provider network element receives CC messages from a first customer network at a first periodicity rate. The first service provider network element stores the received CC messages and reduces the first periodicity rate to create a second periodicity rate that is smaller than the first periodicity rate. The first service provider network element transmits CC messages to a second service provider network element through the provider network at the second periodicity rate. Other methods and apparatus are also described.

BACKGROUND

Embodiments of the invention relate to the field of network processing; and more specifically to transmission of CC (Connectivity Check) messages.

CC (Connectivity Check) messages, described in Institute of Electrical and Electronics Engineers (IEEE) standard 802.1ag-2007 “IEEE Standard for Local and metropolitan area networks—Virtual Bridged Local Area Networks Amendment 5: Connectivity Fault Management”, Dec. 17, 2007, are used to detect the status between points in a network (e.g., Maintenance End Points (MEPs)). The CC messages are multicast messages that are sent between the end points at a periodic rate (e.g., every 3.3 milliseconds). CC messages are sent by each endpoint that is being monitored within each service instance in an Ethernet service network (e.g., Virtual Private LAN Service (VPLS), Provider Backbone Bridges (PBB) networks). The service instance may include endpoints across a wide area, such as in a Metro Area Network (MAN) or a Wide Area Network (WAN). CC messages for the service instance may be transmitted across MAN or WAN links to reach the corresponding end point.

Typically, CC messages in an Ethernet service network are transmitted over the transport network (e.g., over MAN or WAN links) in a similar fashion as any other frame received over the service network. Thus, since CC messages are typically sent at a high periodic rate, and as the number of service instances increases, bandwidth of the transport network may be used to transmit a large number of CC messages.

DETAILED DESCRIPTION

The techniques shown in the figures can be implemented using code and data stored and executed on one or more electronic devices (e.g., a computer end station, a network element, etc.). Such electronic devices store and communicate (internally and with other electronic devices over a network) code and data using machine-readable media, such as machine storage media (e.g., magnetic disks; optical disks; random access memory; read only memory; flash memory devices) and machine communication media (e.g., electrical, optical, acoustical or other form of propagated signals—such as carrier waves, infrared signals, digital signals, etc.). In addition, such electronic devices typically include a set of one or more processors coupled to one or more other components, such as a storage device, one or more user input/output devices (e.g., a keyboard, a touchscreen, and/or a display), and a network connection. The coupling of the set of processors and other components is typically through one or more busses and bridges (also termed as bus controllers). The storage device and signals carrying the network traffic respectively represent one or more machine storage media and machine communication media. Thus, the storage device of a given electronic device typically stores code and/or data for execution on the set of one or more processors of that electronic device. Of course, one or more parts of an embodiment of the invention may be implemented using different combinations of software, firmware, and/or hardware.

As used herein, a network element (e.g., a router, switch, bridge, etc.) is a piece of networking equipment, including hardware and software that communicatively interconnects other equipment on the network (e.g., other network elements, computer end stations, etc.). Some network elements are multiple services network elements which provide support for multiple networking functions (e.g., routing, bridging, switching, Layer 2 aggregation, and subscriber management, or any combination, and/or providing support for multiple services (e.g., data, voice, and video). Subscriber computer end stations (e.g., workstations, laptops, palm tops, mobile phones, smartphones, multimedia phones, portable media players, etc.) access content/services provided over the Internet and/or content/services provided on virtual private networks (VPNs) overlaid on the Internet. The content and/or services are typically provided by one or more server computing end stations belonging to a service or content provider, and may include public webpages (free content, store fronts, search services, etc.), private webpages (e.g., username/password accessed webpages providing email services, etc.), corporate networks over VPNs, etc. Typically, subscriber computing end stations are coupled (e.g., through customer premise equipment coupled to an access network (wired or wirelessly) to edge network elements, which are coupled through one or more core network elements to the server computing end stations.

Some network elements support the configuration of multiple contexts. As used herein, each context includes one or more instances of a virtual network element (e.g., a virtual router, virtual switch, or a virtual bridge). Each context typically shares one or more computing resources (e.g., memory, processing cycles, etc.) with other contexts configured on the network element, yet is independently administrable. For example, in the case of multiple virtual routers, each of the virtual routers shares computing resources, but is separate from those other virtual routers regarding its management domain, authentication, authorization, and accounting (AAA) name space, IP address, and routing database(es).

A method and apparatus for reducing the number of CC messages transmitted in an Ethernet service network is described. In one embodiment of the invention, a first Ethernet service provider network element (e.g., Provider Edge (PE) network element, Provider Backbone Edge Bridge (PBEB)) receives CC messages for a first end point of a service instance at a first periodicity rate. The first Ethernet service provider network element caches the received CC messages, and adds a repeat count to a CC message to be transmitted to a second Ethernet service provider network element across an intra-Ethernet service provider network link (e.g., MAN or WAN link). The first Ethernet service provider network element transmits the modified CC message to the second Ethernet service provider network element at a second periodicity rate that is less than the first periodicity rate. The second Ethernet service provider network element caches the modified CC message and generates and transmits a repeat count number of CC messages to a second end point of the service instance at the first periodicity rate.

In another embodiment of the invention, upon determining that CC messages have not been received from the first end point, the first Ethernet service provider network element triggers the second Ethernet service provider network element to stop transmitting CC messages to the second end point.

FIG. 1illustrates an exemplary network with a reduced periodicity transmission rate of CC messages in an Ethernet service network according to one embodiment of the invention.FIG. 1will be described with reference to the exemplary operations ofFIG. 4. However, it should be understood thatFIG. 1can be performed by embodiments of the invention other than those discussed with reference toFIG. 4, and the embodiments discussed with reference toFIG. 4can perform operations different than those discussed with reference to theFIG. 1.

FIG. 1illustrates an exemplary VPLS (Virtual Private LAN Service) network with two Ethernet services instances, the service instance125and the service instance135. WhileFIG. 1illustrates an exemplary VPLS network, it should be understood that other networks are within the scope of the invention (e.g., networks that include Provider Backbone Bridges (PBBs)). VPLS provides a framework for provisioning Layer 2 Virtual Private Networks (L2VPNs). For example, in a VPLS network, the Local Area Network (LAN) at each site is extended to the edge of the provider network. The provider network emulates a switch (or bridge) to connect the customer LANs to create a single bridged LAN. For example, the Customer Edge (CE) network element110and the CE network element130are connected by the provider network (e.g., the Provider Edge (PE) network element150and the PE network element160) to create a single service instance125. Similarly, the CE network element120and the CE network element140are connected by the provider network to create a single service instance135.

The Customer Edge (CE) network element110is coupled with the Provider Edge (PE) network element150through the attachment circuit170. While not shown for simplicity purposes, the CE network element110may be coupled with the PE network element150through one or more access network elements. The CE network element110is coupled with a bridge module of the PE network element150. The PE network element150connects the bridge module to an emulated LAN for the CE network element110. For example, the service instance125is an emulated LAN between the CE network element110and the CE network element130. The CE network element130is coupled with the PE network element160through the attachment circuit174. While not shown inFIG. 1for simplicity purposes, one or more subscriber computing end stations are coupled with the CE network element110, and the CE network element130. In addition, the CE network elements110and130may be geographically separate yet belong to the same organization (e.g., the CE network elements110and130are each at branch offices of the same company). For example, the CE network element110may be located at a branch office in San Francisco while the CE network element130may be located in a branch office in New York City.

In a similar fashion, the CE network element110is coupled with a bridge module of the PE network element150(through zero or more access network elements) through the attachment circuit172. The PE network element150connects the bridge module to an emulated LAN for the CE network element120. For example, the service instance135is an emulated LAN between the CE network element120and the CE network element140. The CE network element140is coupled with the PE network element160through the attachment circuit176. While not shown inFIG. 1for simplicity purposes, one or more subscriber computing end stations are coupled with the CE network element120, and the CE network element140.

The PE network element150is coupled with the PE network element160through the transport network connection180. The PE network elements150and160are each types of Ethernet service provider network elements. In addition, the CE network elements110,120,130, and140are each types of Ethernet customer network elements. According to one embodiment of the invention, Ethernet service provider network elements are under control of the Ethernet service provider, while the Ethernet customer network elements are under control of a customer of the service provider.

In one embodiment of the invention, the transport network connection180may include one or more intra-Ethernet service provider network links, such as MAN links and/or WAN links. In addition, the transport network connection180may include one or more links designated for the service instance125, and one or more links designated for the service instance135. According to one embodiment of the invention, the transport network connection180is more expensive than the attachment circuit170, the attachment circuit172, the attachment circuit174, or the attachment circuit176. The CE network element110transmits and receives network traffic and CC messages through the attachment circuit170. Similarly, the CE network element130transmits and receives network traffic and CC messages through the attachment circuit174.

A maintenance end point (MEP)112, which is associated with the service instance125, is configured on the CE network element110. Similarly, a MEP132, which is also associated with the service instance125, is configured on the CE network element130. Thus, the MEP112and the MEP132are part of the same service instance125. The CE network element110transmits CC messages to the PE network element150for the MEP112at a periodicity rate of R1(e.g., one MEP message transmitted per 3 milliseconds). In one embodiment of the invention, the CC messages transmitted are Connectivity Check Messages (CCMs) conforming to the IEEE standard 802.1ag (hereinafter “802.1ag”). Each CC message includes a transmission interval rate, hereinafter referred to as the periodicity rate. InFIG. 1, the periodicity rate between the CE network element110and the PE network element150is R1(e.g., one CC message transmitted every 3.3 milliseconds) (thus, the PE network element150expects a CC message from the CE network element at the rate R1).

The MEP122, which is associated with the service instance135, is configured on the CE network element120. Similarly, a MEP142, which is associated with the service instance135, is configured on the CE network element140. Thus, the MEP122and the MEP142are part of the same service instance135. The CE network element120transmits CC messages to the PE network element150for the MEP122at a periodicity rate of R2(e.g., one CC message transmitted every 10 milliseconds).

The PE network element150includes the ingress service delimiting module190and the transport module191. According to one embodiment of the invention, the ingress service delimiting module190reduces the transmission rate of CC messages sent through the transport network connection180. For example, the PE network element150transmits CC messages associated with the MEP112(of the CE network element110) and the MEP122(of the CE network element120) at a periodicity rate of (R1+R2)/RC (where RC is a repeat count, which will be described in greater detail later herein). Thus, the PE network element150transmits CC messages through the transport network connection180at a periodicity rate less than the periodicity rate of CC messages the PE network element150receives. In addition, as will be described in greater detail later herein, the PE network element160transmits CC messages to the endpoint of a service instance (e.g., MEP132of the CE network element130) at the same periodicity rate the CE network element110transmits CC messages to the PE network element150. Thus, even though the number of CC messages transmitted through the transport network is reduced, the nodes monitoring MEPs in a service instance are unaware of the reduction as CC messages continue to be transmitted and received at the endpoints (e.g., the MEP112and the MEP132) at the expected periodicity rate.

FIG. 3Ais an exploded view of the PE network element150according to one embodiment of the invention. The PE network element150includes the ingress service delimiting module190coupled with the transport module191. The ingress service delimiting module190includes the CCM module310and the memory312. The memory312stores the CCM data structure314, the CCM receipt counter316, and the CCM timeout timer318.FIG. 3Awill be described with reference to the exemplary operations ofFIG. 4. However, it should be understood thatFIG. 3Acan perform operation by embodiments of the invention other than those discussed with reference toFIG. 4, and the embodiments discussed with reference toFIG. 4can perform operations different than those discussed with reference to theFIG. 3A.

FIG. 4is a flow diagram illustrating an exemplary method for reducing the periodicity transmission rate of CC messages according to one embodiment of the invention. At block410, the ingress service delimiting module190of the PE network element150receives a CC message. For example, the ingress service delimiting module190receives a CC message from the CE network element110or the CE network element120. For illustration purposes, for further discussion ofFIG. 4, it will be assumed that the ingress service delimiting module190receives a CC message from the CE network element110associated with the MEP112. Referring toFIG. 3A, the CC module310receives the CC message from the MEP112of the CE network element110. According to one embodiment of the invention, the CC message includes a periodicity rate of R1(thus, CC messages are expected to be received from the CE network element110at the rate of R1). It should be understood that the received CC message may optionally include a sequence number.

Flow moves from block410to block412, where the ingress service delimiting module190caches the CC message. For example, referring toFIG. 3A, the CCM module310caches the CC message in the CCM data structure314. Any number of mechanisms may be used to manage the CCM data structure314including caching only a certain amount of messages for each MEP (e.g., according to each MEPID). In one embodiment of the invention, the CCM data structure314stores one or more CC messages associated with a single MEP. According to one embodiment of the invention, the CCM data structure314is a CCM database as defined in the 802.1ag standard. Flow moves from block412to block414.

At block414, the ingress service delimiting module190decrements a CCM receipt counter that is associated with the MEP112. For example, referring toFIG. 3A, the CCM module310decrements the CCM receipt counter316associated with the MEP112. Thus, according to one embodiment of the invention, each MEP transmitting CC messages to the PE network element150has a separate CCM receipt counter. According to one embodiment of the invention, the CCM receipt counter316is a value associated with a repeat count (RC), which is used to reduce the number of CC messages transmitted through the transport network. For example, according to one embodiment of the invention, the CCM receipt counter316is equivalent to the repeat count minus X (where RC>X>=1). According to one embodiment of the invention, the CCM receipt counter indicates the number of CC messages a PE network element receives (e.g., the ingress service delimiting module190on the PE network element150) from a particular MEP (e.g., MEP112on the CE network element110) prior to transmitting a CC message through the transport network for that MEP (e.g., prior to transmitting a CC message for MEP112to the PE network element160over the transport network connection180).

According to one embodiment of the invention, the repeat count is a value indicating the number of CC messages the egress service delimiting module192should transmit to a CE network element prior to receiving another CC message from the PE network element, which will be described in greater detail later herein. While in one embodiment of the invention the repeat count is configured (e.g., by a network administrator), in alternative embodiments of the invention the repeat count is automatically provisioned depending on the status of the network resources (e.g., depending on the load of the transport network).

Flow moves from block414to block416. At block416, the ingress service delimiting module190adds an explicit down notification (EDN) field (set to 0), a repeat count (RC), and a transaction ID (e.g., a MAC address of the PE network element150) to the CC message. In one embodiment of the invention, the CCM data structure314is extended to support the EDN field, the RC field and the transaction ID field. Each of these fields is used by the egress service delimiting module192, which will be described in greater detail later herein. Flow moves from block416to block418.

At block418, the ingress service delimiting module190determines whether the EDN field of the previous CC message sent to the PE network element160for the associated MEP (e.g., MEP112) was set (e.g., set to 1) (i.e., the last CC message that was sent to the PE network element160for the MEP112). If the received CC message was the first CC message received from CE network element110associated with the MEP112(e.g., the CCM data structure314does not include an entry for the MEP112), or the previous CC message sent to the PE network element160was not set (e.g., set to 0), then flow moves to block422. If the previous CC message sent to the PE network element160was set (e.g., set to 1) for the MEP, then flow moves to block420. With reference toFIG. 3A, in one embodiment of the invention, the CCM module310determines, from the CCM data structure314, whether the previous CC message included an EDN field of 1. As will be described in greater detail later herein, the CCM module310sets an EDN field to 1 if it detects a CCM receipt timeout (e.g., if the CCM module310does not receive any CC messages from the MEP112over the stated periodicity rate, the CCM module310sets the EDN field to 1). In addition, the CCM module310sets the EDN field to 1 if the ingress service delimiting module190determines that the MEP112is down and/or the connection between the PE network element150and the CE network element120is down. For example, if the port coupling the PE network element150and the CE network element120goes down and the MEP112is associated with that port, then the CCM module310sets the EDN field to 1.

At block420, a CC message with a cleared EDN field is transmitted (e.g., an EDN field of 0) through the transport network (e.g., through the transport network connection180). For example, with reference toFIG. 3A, the CCM module310generates a CC message from information in the CCM data structure314(e.g., from the CC message cached in block412and the fields added to the message in block416) and passes the generated CC message to the transport module191. According to one embodiment of the invention, the last CCM module310generates the CC message from the last CC message received and cached in the CCM data structure314. The transport module191adds any required encapsulations for the transport network (e.g., layer 2 encapsulations, tunnel encapsulations, etc.), performs any additional processing, and transmits the generated CC message (with an EDN of 0) to the PE network element160. In addition, it should be understood that if the cached CC message which was used to generate the transmitted CC message included a sequence number, the transmitted CC message includes that sequence number. Flow moves from block420to block430, where the CCM timeout timer is reset to its initial value (e.g., to the periodicity rate value included in the received CC message).

At block422, the ingress service delimiting module190determines whether the CCM receipt counter is at zero. For example, with reference toFIG. 3A, the CCM module310determines if the CCM receipt counter315is at zero for the MEP112. If the CCM receipt counter is at zero, then flow moves to block424, where a CC message with the additional fields (e.g., added in block416) is transmitted over the transport network. For example, with reference toFIG. 3A, if the CCM module310determines the CCM receipt counter315is at zero for the MEP112, the CCM module310generates a CC message from information in the CCM data structure314(e.g., from the CC message cached in block412and the fields added to the message in block416) and sends it to the transport module191. According to one embodiment of the invention, the last CCM module310generates the CC message from the last CC message received and cached in the CCM data structure314. In addition, it should be understood that if the cached CC message which was used to generate the transmitted CC message included a sequence number, the transmitted CC message includes that sequence number The transport module191adds any required encapsulations for the transport network (e.g., layer 2 encapsulations, tunnel encapsulations, etc.). For example, in a VPLS network, the transport module191may map the generated CC message to a particular pseudowire and a particular egress port of the PE network element150. It should be understood that different embodiments of the invention may use a different type of transport module191and the transport module191may perform operations differently in some embodiments of the invention. Thus, embodiments of the invention are independent of the type and function of the transport network.

If the CCM receipt counter is not at zero (e.g., it is greater than zero), then flow moves to block426where a CC message is not transmitted. It should be understood that in some embodiments of the invention, the PE network element150may continue to receive CC messages from a particular MEP (e.g., MEP112) yet it does not transmit a CC message associated with that MEP over the transport network unless the CCM receipt counter316is at zero. Thus, it should be understood that the number of CC messages the PE network element150transmits through the transport network (e.g., through the intra-Ethernet service provider network links (MAN and/or WAN links)) is reduced. For example, the PE network element150receives CC messages from the MEP112at a periodicity rate (e.g., R1) that is higher than the periodicity rate (e.g., R1/RC) of CC messages it transmits through the transport network connection180. Thus, the number of CC messages transmitted through the attachment circuit170for a particular end point of a service instance is greater than the number of CC messages transmitted through the transport network connection180for that end point of that service instance. Thus, it should be understood that bandwidth of the transport network is conserved. In addition, it should be understood that as the number of service instances increases (and thus the number of CC messages the PE network element150receives increases), the amount of bandwidth savings also increases. Thus, the scalability of increased service instances which employ CCM mechanisms is improved (e.g., the number of service instances may be increased without a corresponding increase in the CC message load on the provider network).

Flow moves from block424to block428, where the CCM receipt counter is reset to its initial value, and flow moves to block430. At block430, the CCM timeout timer is reset to its initial value (e.g., e.g., to the periodicity rate value included in the received CC message).

It should be understood that the PE network element150performs similar operations as described inFIG. 4for CC messages received from the MEP122of the CE network element120for the service instance135. For example, the PE network element150receives CC messages from the MEP122at a periodicity rate (e.g., R2) that is higher than the periodicity rate (e.g., R2/RC) of CC messages it transmits through the transport network connection180. Thus, according to one embodiment of the invention, the PE network element150transmits CC messages for the MEP112and the MEP122through the transport network connection180at a periodicity rate of (R1+R2)/RC.

FIG. 2illustrates an exemplary VPLS network with a reduced periodicity transmission rate of CC messages in a transport network connection where a CE network element is dual homed according to one embodiment of the invention.FIG. 2will be described with reference to the exemplary operations ofFIG. 5. However, it should be understood thatFIG. 2can perform operation by embodiments of the invention other than those discussed with reference toFIG. 5, and the embodiments discussed with reference toFIG. 5can perform operations different than those discussed with reference to theFIG. 2.

FIG. 2includes the CE network element110(and the MEP112) illustrated inFIG. 1. In addition, the CE network element110is coupled with the PE network element150via the attachment circuit170, and the PE network element150is coupled with the PE network element160via the transport network connection180. In addition, the CE network element110is dual homed to the PE network element250. For example, if the attachment circuit170fails for some reason (e.g., an incorrectly configured Spanning Tree Protocol operating on the PE network element incorrectly blocks the port coupling the attachment circuit170, the physical link carrying the attachment circuit170goes down, etc.), the CE network element110switches to the attachment circuit210to transmit data and CC messages to the PE network element150. In this manner, even if the attachment circuit170is disabled, the CE network element110has access to the VPLS network and has access to the CE network element130. The PE network element250includes the ingress service delimiting module290and the transport module291, which operate in a similar fashion as the ingress service delimiting module190and the transport module191. The PE network element250is coupled with the PE network element160over the transport network connection220.

InFIG. 2, the attachment circuit170has failed (as indicated by the large “X” on the attachment circuit170) and the CE network element110has switched to its secondary (e.g., backup) attachment circuit210to transmit and receive CC messages. Thus, the PE network element150does not receive CC messages from the MEP112over the attachment circuit170. It should be understood that although the PE network element150may detect a CC message timeout rather quickly (e.g., after not receiving a CC message at a time when the periodicity rate R1expires), the PE network element160does not detect a CC message timeout at the same rate. For example, the PE network element160expects to receive CC messages at the reduced periodicity rate (e.g., R1/RC). Therefore, in one embodiment of the invention, upon detecting a CC message timeout for a particular MEP, the ingress service delimiting module generates a CC message with an EDN field with a value of 1 for that MEP and transmits this message to the egress service delimiting module. A CC message with am EDN field set to a value of 1 notifies the egress service delimiting module of the CC message timeout and triggers the egress service delimiting module to stop transmitting CC messages for that MEP.

FIG. 5is a flow diagram illustrating an exemplary method for determining a CC message timeout and triggering an explicit service instance down CC message according to one embodiment of the invention. At block510, the PE network element150determines that the CC message has timed out. For example, the PE network element150has not received a CC message from the MEP112in the expected periodicity rate (e.g., rate R1). For example, with reference toFIG. 3A, the CCM module310determines that the CCM timeout timer318has expired. Flow moves from block510to block520.

At block520, the PE network element150reads a previously cached CC message associated with the timed out MEP (e.g., MEP112). For example, with reference toFIG. 3A, the CCM module310reads an entry of the CCM data structure314for a previously cached CC message for the MEP112. Flow moves from block520to block530, where one or more fields are added to the message. For example, an EDN field is added to the message and set to a value of 1. In addition, a transaction ID field is added to the message and populated with a unique identifier of the PE network element150(e.g., a MAC address of the PE network element150). Flow moves to block540where the CC message, with the additional fields, is transmitted to the PE network element160. For example, with reference toFIG. 3A, the CCM module310generates a CC message with an EDN field set to 1 and a transaction ID field uniquely identifying the PE network element150, and passes this message to the transport module191to be transmitted to the PE network element160.

Referring back toFIG. 2, since the CE network element110is dual homed (e.g., the CE network element110is coupled with a backup PE network element250in case of failure of the attachment circuit170and/or the PE network element150), the MEP112transmits CC messages through the attachment circuit210to the PE network element250. According to one embodiment of the invention, the ingress service delimiting module290and the transport module291of the PE network element250perform in a similar manner as the ingress service delimiting module190and the transport module191of the PE network element150. For example, the PE network element250transmits CC messages to the PE network element160via the transport network connection220, at a reduced rate (e.g., at the rate of R1/RC, where RC is a rate count value). In addition, each CC message the PE network element250transmits to the PE network element160includes a transaction ID uniquely identifying the source of the CC message (e.g., a MAC address of the PE network element250).

Thus, as illustrated inFIG. 2, the PE network element160receives a CC message from the PE network element150for the MEP112that includes an EDN field of 1. According to one embodiment of the invention, this CC message triggers the PE network element160to stop transmitting CC messages associated with the PE network element150to the CE network element130. In addition, the PE network element160also receives CC messages from the PE network element250for the MEP112(that do not include an EDN field of 1). According to one embodiment of the invention, the PE network element160treats CC messages received from different Ethernet service provider network elements (e.g., as identified by the transaction identifier) separately. For example, the explicit MEP down notification message sent by the PE network element150for the MEP112does not affect the CC messages sent by the PE network element250for the MEP112. In other words, even though the PE network element160receives a message which triggers the PE network element160to stop transmitting CC messages from the PE network element150for a particular MEP, this MEP down message only applies for those CC messages, and not to the CC messages received from the PE network element250for that MEP.

FIGS. 6A and 6Bare flow diagrams illustrating an exemplary method for processing CC messages received at the reduced periodicity transmission rate ofFIG. 4and processing the explicit service instance down CC message ofFIG. 5, according to one embodiment of the invention. For example, in one embodiment of the invention, the operations ofFIGS. 6A and 6Bmay be performed by the PE network element160. At operation610, an egress servicing delimiting module (e.g., the egress servicing delimiting module192) receives a CC message associated with a particular MEP. According to one embodiment of the invention, the received CC message includes the EDN field, the repeat count field, and the transaction identifier field, or any combination of the EDN field, the repeat count field, and the transaction identifier field. In addition, in some embodiments of the invention, the received CC message was transmitted at a reduced periodicity transmission rate (i.e., the received CC message was not transmitted at the original periodicity transmitted rate included in the CC message). Flow moves from block610to block612.

FIG. 3Bis a block diagram illustrating an exemplary Ethernet service provider network element receiving the reduced periodicity transmission rate of CC messages ofFIG. 3A, and transmitting CC messages at the original periodicity transmission rate according to one embodiment of the invention. The PE network element160ofFIG. 3Bincludes the egress service delimiting module192coupled with the transport module193. The egress service delimiting module192includes the CCM module370coupled with the memory352. The memory352stores the CCM data structure364, the CCM transmission timer366, and the CCM timeout timer368. According to one embodiment of the invention, the CCM transmission timer366indicates the amount of time between transmission of CC messages to a CE network element. For example, the CCM transmission timer366may be equivalent to the periodicity rate included in the CC message (thus, for example, if the periodicity rate is R1, then the CCM transmission timer366may expire at R1time). According to one embodiment of the invention, the CCM timeout timer368indicates the amount of time before the egress service delimiting module192determines a CC message timeout (e.g., the time to declare a CC message timeout for CC messages sent by the PE network element150).

At block612, the egress servicing delimiting module caches the received CC message. For example, with reference toFIG. 3B, the egress servicing delimiting module192caches the received CC message from the PE network element150(e.g., with the added fields) into the CCM data structure364. Flow then moves to block614, where the egress servicing delimiting module determines whether the EDN field of the received CC message is set (e.g., whether the EDN field has a value of 1). If the EDN field has a value of 1, flow moves to block616where the egress service delimiting module192stops the CCM transmission timer (e.g., the CCM module370stops the CCM transmission timer366), and does not transmit any CC messages for the transaction associated with the CC message. Thus, for example referring toFIG. 2, the PE network element160does not transmit any CC messages to the CE network element130for the MEP112from the PE network element150upon receiving a CC message from the PE network element150, for the MEP112, that includes an EDN field with a value of 1 and a transaction identifier uniquely identifying the PE network element150.

If the EDN field is not set (e.g., the EDN field has a value of 0), then flow moves to block618. At block618, in one embodiment of the invention, a repeat counter is set to the repeat count value in the CC message. In an alternative embodiment of the invention, the repeat count field of the cached CC message (e.g., cached during operation of block612) is used as the repeat counter. Flow moves from block618to block620.

At block620, the CCM transmission timer is configured according to the periodicity rate included in the CC message. For example, with reference toFIG. 3B, the CCM module370configures the CCM transmission timer366according to the periodicity rate (e.g., R1) included in the CC message. Flow moves to block622. At block622, it is determined whether the CCM transmission timer has expired. For example, with reference toFIG. 3B, the CCM module370determines whether the CCM transmission timer366has expired. If the CCM transmission timer has expired, flow moves to block624. If the CCM transmission timer has not expired, flow moves back to622.

At block624, a determination is made whether the cached CCM message includes a sequence number. For example, with reference toFIG. 3B, the CCM module370accesses the CCM data structure364to determine whether the latest cached CC message associated with the MEP includes a sequence number. If the cached CC message includes a sequence number, then flow moves to block626. However, if the cached CC message does not include a sequence number, then flow moves to block628. At block626, the sequence number is incremented and the cached message is updated to reflect the incremented sequence number. Flow moves from block626to block628.

At block628, a CC message is created from the cache where the extra fields (e.g., the EDN filed, the repeat count field, and the transaction identifier field) are stripped from the message. If the cached message includes a sequence number, the created CC message includes that sequence number. Flow moves from block628to block630, where the created CC message is transmitted. For example, with reference toFIG. 3B, the CCM module370accesses the CCM data structure364and generates a CC message without the extra fields and passes the generated CC message to the transport module193. The transport module193adds any required encapsulations for the attachment circuit (e.g., the attachment circuit174), performs any additional processing, and transmits the generated CC message to the CE network element130. Flow moves from block630to the block632.

At block632, the repeat counter is decremented. For example, in one embodiment of the invention the CCM module370decrements the value of the repeat count field by 1 upon transmitting each CC message. Flow moves to block634, where a determination is made whether the repeat counter is greater than zero. For example, the CCM module370determines if the repeat counter is greater than zero. If the repeat counter is not greater than zero, then flow moves to block636, where alternative action is taken (e.g., the PE network element160may determine a CC message timeout, the PE network element160may readjust the repeat counter, etc.). If the repeat counter is greater than zero, then flow moves back to622. Thus, for example, for a repeat count number of times (as indicated in the repeat count field of the received CC message), the PE network element160transmits a CC message to the MEP132(for the service instance125) at the original periodicity rate (e.g., rate R1). It should be noted that at any time during the operations of blocks622-636, the egress service delimiting module192may receive a CC message with an EDN field set (e.g., an EDN filed of 1) which overrides the operations of the blocks622-636. In other words, a CC message with an EDN field of 1 associated with a particular MEP and with a particular ingress service delimiting module, triggers the egress service delimiting module to stop transmitting CC messages for that MEP and ingress service delimiting module.

While embodiments of the invention have been described in relation to a VPLS network, in alternative embodiments of the invention a different network may be used (e.g., a standard Ethernet network, a Provider Backbone network, etc.). Additionally, while embodiments of the invention have described reducing the periodicity rate of CC messages transmitted through an Ethernet service provider network, in alternative embodiments of the invention the periodicity rate of CC messages may be reduced in an Ethernet customer network (e.g., within a LAN). In addition, while embodiments of the invention have been described with reducing the transmission rate of CC messages (e.g., 802.1ag CC messages), embodiments of the invention described herein may also be used for reducing the transmission rate of different types of messages (e.g., other keep-alive messages, control messages, operations, administration, and maintenance (OAM) messages, etc.).

It should be understood that the CE network elements130and140, via the MEPs132and142, transmit CC messages to the MEPs112and122respectively. In addition, the PE network element160supports an ingress service delimiting module and the PE network element150supports an egress service delimiting module.

In addition, in one embodiment of the invention, the PE network element150and the PE network element160agree to support the reduced periodicity rate and the added fields to the CC messages. For example, in some embodiments of the invention these capabilities are signaled (e.g., through Label Distribution Protocol (LDP), GMPLS, etc.). In other embodiments of the invention, a network administrator supporting the PE network elements150and160configures each PE network element to support the reduced periodicity rate and the added fields to the CC messages.