Abstract:
The present invention provides a network architecture that interworks OA&amp;M (Operations, Administration and Maintenance) failure notification data from the ATM Domain to the Ethernet Domain and vice versa. Failure indications or notifications are typically routed from one domain to another within 1-2 seconds; providing service providers and customers the ability to react quickly to network faults. This enhances the overall quality of the Ethernet-to-ATM Interworking service and provides a similar level of reliability across the Ethernet/ATM/FR domains.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Application No. 60/489,716 filed Jul. 21, 2003. 

   The present application is related to United States utility patent applications, “ETHERNET TO ATM SERVICE INTERWORKING TECHNIQUE,” Ser. No. 10/016,019, filed on Dec. 12, 2001; “FAILURE NOTIFICATION METHOD AND SYSTEM IN AN ETHERNET DOMAIN,” Ser. No. 10/248,761, filed on Feb. 14, 2003; and “DISCOVERY AND INTEGRITY TESTING METHOD IN AN ETHERNET DOMAIN,” Ser. No. 10/248,858, filed on Feb. 25, 2003, the contents of which are incorporated by reference herein. 
   FIELD OF THE INVENTION 
   The present invention relates to interworking data between Ethernet domains and ATM/Frame Relay domains and, more particularly, to integrating operations, administration, management (OAM) traffic failure data. 
   BACKGROUND OF THE INVENTION 
   Traditionally, for customers running IP networks, they typically rely on routing protocols such as Border Gateway Protocol (BGP), Open Shortest Path First (OSPF), Routing Information Protocol (RIP) also known as layer 3 IP Routing Protocols, to detect a failure in the network and route around the problem. These routing protocols send systematic “hello” messages to their remote end points and when one isn&#39;t observed after a period of time, they assume there&#39;s a problem and route around it. So, these Layer 3 IP Routing Protocols are needed to re-route around failures, such as between two separate networks like Ethernet and ATM. Using these Layer 3 techniques takes about 30-60 seconds to detect and respond to a failure. This is inefficient and too slow but that is a limitation of the Layer 3 routing protocols. 
   Customers who rely on Frame Relay/ATM networks are used to failure notification response times of 1-2 seconds (or less). The FR/ATM network independently generates a failure notification towards customer premises equipment at the onset of failure. Customers of this new Ethernet to FR/ATM Interworking service require similar failure notification behavior from the network. Therefore, it is required to integrate automated Operations, Administration and Management traffic which can propagate failure indications end-to-end much faster, and does not require either a Layer 3 IP Routing Protocol or any type of “hello” or integration timer messages. 
   It is known that regular traffic can be interworked between Ethernet and ATM, e.g. using the technique described in the patent application Ser. No. 10/016,019. It is also known that there is a native OAM in the Ethernet domain, e.g. see the patent application Ser. No. 10/248,761 and Ser. No. 10/248,858. The difficulty involves implementing Ethernet OAM first, then bridging EOAM with ATM OAM. 
   So, besides integrating (interworking) regular traffic data between Ethernet and ATM, it is also advantageous to integrate OAM failure notification between the two separate networks. Moreover, it is also advantageous to provide failure indications by a much faster and more reliable means. 
   SUMMARY OF THE INVENTION 
   The present invention provides a method for notifying/communicating at least one failure message from at least one source to at least one destination, the source served by a first network and the destination served by a second network. The method includes receiving at an interworking facility a first frame which includes a failure notification message and a first destination address in a first format compatible with said first network, forming a second frame of a second format compatible with the second network, the second frame including the failure notification message and mapping the first destination address to a second destination address specifying in the second format the address of the destination in the second network so that the second network, upon receipt of the second destination address, can route the second frame to the destination. 
   The present invention also provides a network system for notifying/communicating at least one failure message from at least one source to at least one destination. The system includes a first network associated with the source, generates a first frame includes a failure notification message and a first destination address in a first format compatible with the first network. Also included is a second network associated with the destination having a destination address and an interworking facility. The interworking facility receives the first frame, forms a second frame of a second format compatible with the second network, and maps the first destination address to a second destination address specifying in the second format the destination address in the second network, so that the second-network upon receipt of the second destination address routes the second frame to the destination, wherein the second frame includes the failure notification message. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a block schematic diagram of a prior art network architecture for interworking regular traffic data between two networks. 
       FIG. 2  shows a block schematic diagram comprising part of the network architecture of  FIG. 1  and the manner in which the link failure notification is transmitted from a source to a destination. 
       FIG. 3  shows a block schematic diagram comprising part of the network architecture of  FIG. 1  and the manner in which the link failure notification is transmitted from a source to a destination. 
       FIG. 4  shows a block schematic diagram comprising part of the network architectures of  FIG. 1  and the manner in which the trunk failure detected in the Ethernet domain  14  is transmitted. 
       FIG. 5  shows a block schematic diagram comprising part of the network architecture of  FIG. 2  and the manner in which the link failure notification is transmitted from a source to a destination. 
       FIG. 6  shows a block schematic diagram comprising part of the network architecture of  FIG. 3  and the manner in which the link failure notification is transmitted from a source to a destination. 
       FIG. 7  shows a block schematic diagram comprising part of the network architecture of  FIG. 4  and the manner in which the trunk failure detected in the Ethernet domain  14  is transmitted. 
       FIG. 8  shows a block schematic diagram comprising part of the network architecture of  FIG. 1  and the manner in which the link failure notification is transmitted from a destination to a source. 
       FIG. 9  shows a block schematic diagram comprising part of the network architecture of  FIG. 1  and the manner in which the link failure notification is transmitted from a destination to a source. 
       FIG. 10  shows a block schematic diagram comprising part of the network architecture of  FIG. 1  and the manner in which the trunk failure detected in the ATM domain  18  is transmitted. 
       FIG. 11  shows a block schematic diagram comprising part of the network architecture of  FIG. 1  and the manner in which the link failing notification is transmitted from a destination to the source. 
       FIG. 12  shows a block schematic diagram comprising part of the network architecture of  FIG. 1  and the manner in which the trunk failure detected in the ATM domain  18  is transmitted. 
   

   DETAILED DESCRIPTION 
   The present invention provides a service that interworks two networking OAM protocols (Ethernet OAM and ATM OAM). It allows for failure notification of OAM packets observed in one domain (e.g. Ethernet) to be carried into the other domain (e.g. ATM) and vice versa. Specifically if a failure is detected in the Ethernet domain, OAM packets are forwarded on the failed VLAN in the Ethernet domain to the applicable PVC in the ATM domain. The Failure Notification scheme works essentially the same in the Ethernet-to-ATM direction. Customer equipment in either domain would get near Real Time notification of a failure independent of the domain. 
   Referring to  FIG. 1  depicts a block schematic diagram of a prior art network architecture 10 as shown in U.S. patent application Ser. No. 10/016,019 for interworking a source and destination that lie in first and second networks having different protocols to allow the source to send data using its own protocol by first establishing for the source a set of addresses in a format compatible with the destinations that lie in second network, and thereafter having an interworking facility act as a proxy between networks. In the embodiment of  FIG. 1 , the source  10  comprises a first router  10   a  and a second router  10   b  and the destination  12  comprises one of routers  12   a  and  12   b . Broadly stated, in the illustrated embodiment, either the first router  10   a  or the second router  10   b  routes data in the form of Ethernet-formatted information frames onto an Ethernet-based Metropolitan Area Network (MAN) or Ethernet Domain  14  which comprises a first network, the router  12   a  routes data in the form of ATM-formatted information frames onto an ATM domain  18 , which comprises a second network, and router  12   b  routes data in the form of Frame Relay formatted information frames which are converted [to ATM] at the edge of the ATM domain  18 . The Ethernet domain  14  as shown provides network services to a plurality of customers and/or customer sites. For illustration purposes,  FIG. 1  only shows two source routers  10   a  and  10   b  and two destination routers  12   a  and  12   b , although any number of sources and destination sites may be shown connected to the Ethernet domain  14  and the ATM domain  18  respectively. 
   To enable transmission of the data to one of the destination routers  12   a  and  12   b  that lie outside the first network, the Ethernet network  14  transmits each Ethernet-formatted information frame destined for one of the routers  12   a  and  12   b  to an Ethernet InterWorking Switch (EIWS)  16  for transmission to the Wide Area ATM core network  18  (a second) network that serves the routers  12   a  and  12   b  as discussed below. The EIWS  16  functions as an interworking facility typically comprising an Ethernet switch that serves as a proxy between the Ethernet network  14  and the ATM network  18  which services a plurality of edge devices that utilize one of a plurality of protocols, such as ATM or Frame Relay. 
   In practice, the interworking facility establishes a set of pseudo addresses in a format compatible with the first network that correspond to destinations in the second network so that the source can address an information frame using its own protocol for a destination that actually lies in the second network without concerning itself with the protocol employed in the second network. In the case where the first information frame comes from a source in an Ethernet-based network, the first information frame will have a Virtual Local Area Network (VLAN) tag associated with the address of the destination. On the other hand, if the information frame comes from a source in an ATM Virtual Private network (VPN), the frame will include a Virtual Path Identifier (VPI)/Virtual Channel Identifier (VCI), herein after referred to as a Permanent Virtual Circuit (PVC) that corresponds to the address of (e.g., the network path to) the destination in a format compatible with the ATM network, even though the destination lies in another network having a different protocol. 
   Upon receipt of the first traffic failure frame at the interworking facility, the facility forms a second frame compatible with the second network, the second frame including the traffic failure. The destination address of the first frame is mapped to a second destination address compatible with the second network. Thus, for example, the VLAN tag in an originating Ethernet frame is mapped to a VPN PVC for an ATM frame and vice versa. Mapping the destination address from a format compatible with the first traffic failure frame to a format compatible with the second traffic failure frame allows propagation of the second frame, including the information embodied in its traffic failure, to the destination. 
   Generally, two types of alarms are sent when error or failure is detected in the flow of traffic from one domain to the other domain. An alarm indication signal (AIS) is generated which sends a message in the same, i.e. forward direction as that of the signal to the effect that an error or failure has been detected. A Remote Defect Indication (RDI) is generated which sends a message back to a transmitting terminal that a failure (AIS) has been indicated, i.e. received. 
     FIGS. 2-12  show transmission of traffic failure notifications upon detection of traffic failures in different areas of the network architecture of  FIG. 1 . 
   Referring to  FIG. 2  of the present invention, there is shown a block schematic diagram comprising part of the network architecture of  FIG. 1  and the manner in which the link failure notification is transmitted from a source to a destination. Link failure l 1  occurs on a link in the Ethernet domain  14 . In this case, the failure is detected on a R x  port of Ethernet Edge Switch  20  facing the Ethernet router  10   a . The Ethernet edge switch  20  recognizes that this failure is on the Green VLAN, and generates an Ethernet OAM AIS (EOAM.AIS) message and forwards it towards the EIWS  16  on the Green VLAN. Upon receipt of the EOAM.AIS message, EIWS  16  performs two functions. One, EIWS  16  sends an EOAM.RDI message on the Green VLAN back towards the Ethernet router  10   a  notifying the router  10   a  of the link failure l 1  detection. Two, EIWS converts the EOAM.AIS message on the Green VLAN into an ATM.AIS message on the Green PVC as described below. AIS is in the same ‘forward direction’ as the traffic flow direction where the error was detected, it signals the detection of an outage condition. Whereas, the RDI is a response in the reverse direction to receiving the AIS error message (i.e. “I have received a message about an error condition”) rather than the actual error detection. 
   EIWS  16  operates to interwork the Ethernet frames with the ATM frames to facilitate the actual transmission of failure notification as described herein below. When EIWS  16  receives traffic failure message from the Ethernet Network  14 , it opens the message/packet to determine the VLAN tag embodied in the packet for the purpose of matching the VLAN tag to a PVC path of the ATM network  18 . To match the VLAN tag to an ATM PVC, the EIWS  16  uses a PVC-VLAN mapping table (not shown) that cross references VLAN tags to corresponding ATM PVC VPI/VCI values. By mapping the VLAN tag to the corresponding ATM PVC, the EIWS  16  effectively converts the Ethernet address into an ATM address. 
   Referring back to  FIG. 2 , when EIWS  16  receives the EOAM.AIS message on Green VLAN from Ethernet network  14 , it maps the Green VLAN to Green PVC of the ATM network  18 , using the PVC-VLAN mapping table. It recognizes this packet as an EOAM.AIS message, and converts it to an ATM.AIS message on the appropriate PVC. EIWS  16  then forwards the ATM.AIS message to the ATM network  18 . The ATM network  18  then forwards the ATM.AIS message towards the ATM router  12   a  on the Green PVC. The ATM router  12   a  receives the ATM.AIS message, processes the failure notification, and takes the subinterface corresponding to the Green PVC out of service. In other words, the IP address associated with Green PVC is no longer available for data transmission. Also, Cust  1  ATM Router  12   a , per ATM protocol, responds with an ATM.RDI packet on the Green PVC. This ATM.RDI packet is an acknowledgement by Cust  1  ATM Router  12   a  that it has successfully received the failure notification message. The ATM.RDI packet on the Green PVC is transmitted through the ATM domain  18  to the EIWS  16 . The EIWS  16  receives the ATM.RDI message for the Green PVC and converts into EOAM.RDI message for the Green VLAN and forwards it to the Ethernet router  10   a . Note that the EOAM.RDI message is a redundant message reiterating the link failure detection. The Ethernet domain  14  is not limited to a single Ethernet service provider and, for purposes of the present invention, may consist of multiple Ethernet service providers (ESPs). In such a case, the layer two device “facing” the edge router  10   a , namely switch  20  in  FIG. 2 , would aggregate traffic from multiple Ethernet service providers. 
   Referring to  FIG. 3  of the present invention, there is shown a block schematic diagram comprising part of the network architecture of  FIG. 1  and the manner in which the link failure notification is transmitted from a source to a destination. Link failure  12  occurs on a link in the Ethernet domain  14  between router  10   b  and edge switch  20  (Red VLAN). In this case, the failure is also detected on the R x  port Ethernet Edge Switch  20  facing the Ethernet router  10   b . An Ethernet OAM AIS (EOAM.AIS) message is generated by the Ethernet edge switch  20  and sent towards the EIWS  16  on the Red VLAN. Again, EIWS  16  performs two functions. One, EIWS  16  sends an EOAM.RDI message on the Red VLAN back towards the Ethernet router  10   b  notifying the router  10   b  of the link failure  12  detection. Second, EIWS  16  maps the EOAM.AIS message into an ATM.AIS message, and forwards the ATM.AIS message to the ATM domain  18  on to the applicable PVC (Red PVC) based on the PVC-VLAN mapping table. Since, in this case the network path is on the Red PVC, the ATM network  18  then forwards the ATM.AIS message towards the frame relay (FR) edge switch  22 . The FR edge switch  22  receives the ATM.AIS message and converts it into the equivalent frame relay (F.R.) OAM (a/k/a LMI—Link Management Interface) message indicating the Red PVC has gone into an inactive state. This state change is signaled in a message called an Asynchronous Status message, with the Activity bit (A-bit) set to 0. The Cust 2  F.R. router  12   b  receives this F.R. OAM message, and takes the subinterface associated with the Red PVC out of service. In other words the IP address of the Red PVC is no longer available for data transmission. The FR edge switch  22  also generates an ATM.RDI message on the Red PVC back towards the EIWS  16 . The EIWS  16  receives the ATM.RDI message for the Red PVC. It converts it into an EOAM.RDI message for the Red VLAN and forwards it to the Ethernet router  10   b.    
   Referring to  FIG. 4  of the present invention, there is shown a block schematic diagram comprising part of the network architectures of  FIG. 1  and the manner in which the trunk failure detected in the Ethernet domain  14  is transmitted. Trunk failure T 1  occurs in the Ethernet domain  14  that carries multiple VLANs as discussed above. T 1  indicates multiple customer traffic failures have occurred, since more than one customer circuit is carried on the trunk. In this case, the failure is detected on the R x  port of a switch in the Ethernet domain for traffic data being transmitted from the source, routers  10   a  and  10   b  to the destination, routers  12   a  and  12   b . An EOAM.AIS message is generated in the Ethernet domain  14  towards the EIWS  16  on both the Green and Red VLANs. The behavior of the network for Green VLANs is similar to the one described in  FIG. 2  and for the Red VLANs is similar to the one described in  FIG. 3 . 
   Referring to  FIG. 5  of the present invention, there is shown a block schematic diagram comprising part of the network architecture of  FIG. 2  and the manner in which the link failure notification is transmitted from a source to a destination. Link failure  13  occurs in the Ethernet domain  14  for router  10   a  (Green VLAN) similar to the one in  FIG. 2 , however, in this case the failure is detected on an Rx port of the Ethernet router  10   a . The Ethernet Cust 1  Router  10   a  generates an EOAM.RDI message and transmits the same from the Ethernet Domain  14  towards the EIWS  16  on the Green VLAN. The EIWS  16  maps the EOAM.RDI message into an ATM.RDI message, and forwards the ATM.RDI message to ATM network  18  on Green PVC based on the PVC-VLAN mapping table. The ATM network  18  then forwards the ATM.RDI message towards the ATM router  12   a . Upon receipt of the ATM.RDI message, the ATM router  12   a  processes the failure notification, and may take the subinterface associated with the Green PVC out of service. It is to be noted that because the link failure l 3  was detected by the Cust 1  Ethernet Router  10   a  itself, an AIS message was not generated simply because the function of the AIS message is to notify the Cust 1  Ethernet Routers of the link failure. 
   Referring to  FIG. 6  of the present invention, there is shown a block schematic diagram comprising part of the network architecture of  FIG. 3  and the manner in which the link failure notification is transmitted from a source to a destination. Link Failure l 4  occurs on a link in the Ethernet domain  14  for router  10   b  (Red VLAN) similar to the one in  FIG. 3 , however, in this case, the failure is detected on the Rx port of the Ethernet Router  10   b . An EOAM.RDI message is generated by the Ethernet Cust 2  Router  10   b  and transmitted towards the EIWS  16  on the Red VLAN. EIWS  16  maps the EOAM.RDI message into an ATM.RDI message, and forwards the ATM.RDI message on to the applicable PVC (Red PVC) based on the PVC-VLAN mapping table. The ATM network  18  then forwards the ATM.RDI message towards the Frame Relay Edge Switch  22 . The F.R. Edge Switch  22  receives the ATM.RDI message. It may create a Frame Relay LMI update on the Red PVC indicating Abit=FAIL as indicated in  FIG. 2  and forward the same to the F.R. router  12   b  notifying of the link failure l 4  detection. Again, note that since the link failure l 4  was detected by the Cust 2  Ethernet Router  10   b , the AIS message is not generated. 
   Referring to  FIG. 7  of the present invention, there is shown a block schematic diagram comprising part of the network architecture of  FIG. 4  and the manner in which the trunk failure detected in the Ethernet domain  14  is transmitted. A Trunk Failure (T 2 ) occurs in the Ethernet domain  14  that carries multiple VLANs. In this case, the failure is detected on the Rx port of the switch in the Ethernet domain  14  for traffic data being transmitted from the destination, routers  12   a  and  12   b  to the source routers  10   a  and  10   b . An EOAM.AIS message is generated in the Ethernet domain  14  both on the Green and Red VLANs towards the Ethernet Customer Routers  10   a  and  10   b  respectively. Both Customer Routers  10   a  and  10   b  receive the EOAM.AIS messages and in turn generate their own EOAM.RDI messages towards the EIWS domain  14 . The behavior of the network for Green VLAN is similar to the one described in  FIG. 5  and for the Red VLAN is similar to the one described in  FIG. 6 . 
   Referring to  FIG. 8  of the present invention, there is shown a block schematic diagram comprising part of the network architecture of  FIG. 1  and the manner in which the link failure notification is transmitted from a destination to a source. Link Failure (l 5 ) occurs on a link in the ATM domain  18  for ATM Router  12   a  (Green PVC). In this case, the failure is detected on the Rx port of the ATM Router  12   a . An ATM.RDI packet is generated by the ATM router  12   a  towards the EIWS  16  on the Green PVC. In this case, EIWS  16  interworks ATM frames to Ethernet frames. When EIWS  16  receives the ATM.RDI message on Green PVC from the ATM network  18 , it maps the Green PVC to Green VLAN of the Ethernet Domain  14  using the PVC-VLAN mapping table and converts the ATM.RDI message to EOAM.RDI message, thereby essentially reversing the process described previously with reference to  FIG. 3 . EIWS  16  then forwards the EOAM.RDI message to the Ethernet network  14  which is then forwarded to the Ethernet router  10   a.    
   Referring to  FIG. 9  of the present invention, there is shown a block schematic diagram comprising part of the network architecture of  FIG. 1  and the manner in which the link failure notification is transmitted from a destination to a source. Link Failure (l 6 ) occurs on the Frame Relay link for FR router  12   b  (Red PVC). The failure is detected at both the FR Edge Switch  22  and the FR Router  12   b . The F.R Edge Switch  22  generates an ATM.AIS message on the Red PVC towards the EIWS  14 . The EIWS  14  performs two functions. One, it generates an ATM.RDI message and sends it back to the ATM domain  18  which in turn forwards the ATM.RDI message towards the FR Router  12   b  on the Red PVC. Since the link failure occurred on both the FR edge switch and router  12   b , the router never receives this second LMI failure update. The ATM.RDI message is an acknowledgement by the EIWS  14  that it has successfully received the failure notification message. Second, the EIWS  16  receives the ATM.AIS message and maps it into an EOAM.AIS message. It then forwards the EOAM.AIS message on to the applicable VLAN (Red VLAN) based on the PVC-VLAN mapping table. The EOAM.AIS message is received at the Ethernet Router  10   b  via the Ethernet Domain  14 . The Ethernet router  10   b  receives the EOAM.AIS message, processes the failure, and takes the subinterface associated with the Red VLAN out of service. In other words, the IP address associated with Red VLAN is no longer available for data transmission. Also, the Ethernet Router  10   b  per Ethernet protocol responds with an EOAM.RDI message and sends the same into the Ethernet domain  14  on the Red VLAN. The Ethernet domain  14  forwards the message to the EIWS  16 . The EIWS  16  receives the EOAM.RDI message for the Red VLAN and generates an ATM.RDI message for the Red PVC and forwards it to the F.R. Edge Switch  22 . The F.R. Edge Switch  22  receives the ATM.RDI message. However, since the link between the FR Edge Switch  22  and the ATM router  10   b  has been disconnected, it does nothing with the RDI message. 
   Referring to  FIG. 10  of the present invention, there is shown block schematic diagram comprising part of the network architecture of  FIG. 1  and the manner in which the trunk failure detected in the ATM domain  18  is transmitted. A Trunk Failure (T 3 ) occurs in the ATM domain  18  that carries multiple PVCs. In this case, the failure is detected on the Rx port of an ATM switch in the ATM domain  18  for traffic data being submitted from the source routers  10   a  and  10   b  to the destination routers  12   a  and  12   b . The ATM Network  18  immediately generates ATM.AIS messages on both Green and Red PVCs towards the ATM/FR routers  12   a  and  12   b  respectively. The ATM router  12   a  receives the ATM.AIS message, processes the failure, and takes the subinterface associated with the Green PVC out of service. When the F.R. Edge Switch  22  (Red PVC) receives the ATM.AIS message, it converts it into an LMI message with Abit=Fail. It then forwards the LMI message to the F.R. router  12   b . The F.R. Router  12   b  receives the message, processes the failure, and takes the subinterface associated with the RED PVC out of service. The ATM router  12   a  responds with an ATM.RDI message for the Green PVC. Likewise, the F.R. Edge Switch  22  responds with an ATM.RDI message for the Red PVC. Both RDI messages are forwarded to the EIWS  16  via the ATM Domain  18  on their respective PVCs. The EIWS  16  maps the ATM.RDI messages into EOAM.RDI messages and forwards the EOAM.RDI messages on to the applicable VLANs based on the PVC-VLAN mapping table. 
   The EOAM messages of the trunk failure notification are received at the applicable Ethernet Routers  10   a  and  10   b  on the Green and Red VLANs respectively. 
   Referring to  FIG. 11  of the present invention, there is shown block schematic diagram comprising part of the network architecture of  FIG. 1  and the manner in which the link failure notification is transmitted from a destination to the source. Link Failure (l 7 ) occurs in the ATM domain  18  between ATM edge switch  24  and ATM router  12   a  (Green PVC). In this case, the failure is detected on the Rx port of an ATM Switch  24 . The ATM Domain  18  generates an ATM.AIS message on the Green PVC towards the EIWS  16 . The EIWS  16  performs two functions. One, it generates an ATM.RDI message back into the ATM domain  18  towards the ATM Router  12   a . Second, the EIWS  16  maps the ATM.AIS message into an EOAM.AIS message. It then forwards the EOAM.AIS message on to the applicable VLAN (Green VLAN) based on the PVC-VLAN mapping table. The EOAM.AIS message is received at the Ethernet Router  10   a . The Ethernet router  10   a  receives the EOAM message, processes the failure, and takes the subinterface associated with the Green VLAN out of service. The Ethernet Router  10   a  responds with an EOAM.RDI message on the Green VLAN. This EOAM.RDI message is an acknowledgement by Cust 1  Ethernet Router  10   a  that it has successfully received the failure notification message. The EOAM.RDI message on the Green VLAN is transmitted through the Ethernet domain  14  towards the EIWS  16 . The EIWS  16  receives the EOAM.RDI message and generates a ATM.RDI message into the ATM domain  18 . The ATM domain  18  then forwards the message to the ATM Router  12   a . Note that the ATM.RDI message is a redundant message reiterating the link failure detection. 
   Referring to  FIG. 12  of the present invention, there is shown a block schematic diagram comprising part of the network architecture of  FIG. 1  and the manner in which the trunk failure detected in the ATM domain  18  is transmitted. A Trunk Failure (T 4 ) occurs in the ATM domain  18  that carries multiple PVCs. In this case, the failure is detected on the Rx port of the ATM switch for traffic data flowing towards the EIWS. The ATM Network  18  generates ATM.AIS messages towards the EIWS  16  for both Green and Red PVCS. EIWS  16  converts the ATM.AIS messages into EOAM.AIS messages and transmits EOAM.AIS messages on both Green and Red VLANs. EIWS  16  also sends ATM.RDI messages back toward routers  12   a  and  12   b  (see  FIGS. 9 &amp; 11 ). 
   It will be apparent that the present invention has been described herein with reference to certain preferred or exemplary embodiments. The preferred or exemplary embodiments described herein may be modified, changed, added to, or deviated from without departing from the intent, spirit and scope of the present invention, and it is intended that all such additions, modifications, amendments and/or deviations be included within the scope of the following claims.