Abstract:
Methods and apparatus improving availability of voice services controlled via IP signaling links provisioned over converged ATM and Ethernet converged network infrastructure are provided. A media gateway network element implements a Layer-2 signaling link end-to-end monitoring via heartbeat messages formulated at the ATM end to traverse the converged network infrastructure to the Ethernet end. The media gateway is provided with SPVC connectivity information and is made aware of network bridging in order to perform a Layer-2 switchover to a standby signaling link in re-establishing signaling link connectivity with a media gateway controller should a communications fault be detected. The advantages include codeployment with previous media gateway controller implemented techniques, and providing a reduction of overheads for media gateway controller implemented techniques while increasing availability by reducing exposure to service outages.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to connectivity monitoring across converged packet-switched communications networks, and in particular to monitoring Internet Protocol (IP) link integrity over a hybrid path traversing Asynchronous Transfer Mode (ATM) and Ethernet packet-switched infrastructure of converged communications networks.  
       BACKGROUND OF THE INVENTION  
       [0002]     In the field of packet-switched communications there is a need to ensure end-to-end link connectivity. For services, such as packet voice services provisioned over a converged ATM/Ethernet network infrastructure, link connectivity monitoring is important specifically for IP links employed in conveying signaling traffic.  
         [0003]     Recently, particular importance has been given to the use of the H.248 Megaco protocol for conveying signaling traffic between a Media Gateway (MG) and a Media Gateway Controller (MGC) network elements in support of packet voice applications. The H.248 protocol provides a framework enabling an MGC to control multiple redundant MGs. The H.248 Megaco protocol is described in RFC3015 published on the Internet by the Internet Engineering Task Force (IETF) at www.ietf.org/rfc/rfc3015.txt, and is incorporated herein by reference. MGs convert the format of media content received from one type of network to a format suitable for transmission over another type of network. For packet voice applications, MGs are employed to terminate bearer channels (e.g., DS 0 s), typically provisioned over the distribution portion of a circuit-switched network, and. media streams from a packet-switched network such as, but not limited to, Real-Time Transport Protocol (RTP) streams provisioned over an IP network. MGs are intended for use in processing audio, video and T.120 media content streams alone or in any combination, and capable of performing full duplex media content translation. MGCs control portions of the call connection that pertain to connection control for media channels in a MG.  
         [0004]      FIG. 1  shows an exemplary deployment of packet-switched communications network infrastructure employed in provisioning packet voice services. At the top of the connectivity hierarchy is a Call Server (CS) entity  100 , a class 4 switch, with logical signaling links  102  to class 5 Central Office (CO) switches  104  such as an Originating Central Office (OCO)  104 -O and a Terminating Central Office (TCO)  104 -T using Signaling System 7 signaling. In provisioning voice services over a packet-switched communications network infrastructure, the CS  100  uses an associated MGC  106  which employs the H.248 protocol to communicate over signaling links  108 , also known as media gateway signaling links, with corresponding redundant Originating MGs (MG-O)  110 -O and redundant Terminating MGs (MG-T)  110 -T.  
         [0005]     In accordance with typical prior art approaches, MGC  106  regularly polls each signaling connection defined by a pair of signaling links  108  to corresponding redundant MGs  110 , to detect signaling link failures. Failing to confirm connectivity over the active signaling link  108 , the MGC  106  performs a switchover to the backup signaling link  108  of the pair. The polling frequency for large numbers of MGs  110  varies inversely with the number of MGs  110  deployed, thereby leading to scalability problems.  
         [0006]     Typically, in the event that the MGC  106  fails to detect the signaling link failure affecting a signaling link  108 , failure detection and switchover would be handled at the application layer, wherein the CS  100  coordinates heartbeat monitoring with the COs  104  over logical signaling links  102 .  
         [0007]     Due to very high connection densities, high bandwidths, and high availability requirements, every moment counts when it comes to detecting and taking the necessary steps to recover from failure. It would be advantageous to detect and recover from such failures as quickly as possible. However, the centralized link failure detection performed by the MGC  106  and the centralized heartbeat monitoring performed by the CS  100 , become increasingly inadequate as the number of MGs  110  deployed in the packet-switched communications network  120  increases, the MGC  106 /CS  100  having to devote significant operational resources to connectivity monitoring.  
         [0008]     It is apparent that in accordance with the prior art centralized connectivity monitoring provided, the MGC  106 /CS  100  represents a single point of failure. An outage affecting the MGC  106 /CS  100 , impacts all MGs  110  registered therewith. Therefore practical deployments require the use of redundant MGC  106 /CS  100  (not shown). Typically, because of the poor scalability performance described above, more than two MGC  106 /CS  100  are used.  
         [0009]     Another relevant issue, relates to network management wherein it is highly desired that network elements such as MGCs  106 /CS  100  employed by the service provider to provisioning packet voice services, connect to an Ethernet management network  122  which introduces compatibility issues as typically the core of the packet-switched communications network provisioning packet-voice services  120  is an ATM network. Using Ethernet in the management network  122  provides cost advantages particularly in view of the recent rapid development and deployment of new services, while the use of ATM payload transport in the service provider&#39;s network  120  provides high bandwidth and high service quality advantages. At least one bridge  124  is used to provide interconnectivity between the Ethernet management network  122  and the ATM transport network  120 . The bridge  124  provides interoperability by employing the Internet Protocol (IP) at the network layer on both sides of the bridge  124 . The interconnectivity and interoperability between Ethernet and ATM networks, which have been, are, and continue to be the subject of intense research and development is referred to as convergence, while such hybrid deployments are referred to as convergent applications.  
         [0010]     Service providers are looking for convergent solutions to packet voice applications; because of the disparate technologies employed in the management and the transport networks, ensuring availability is becoming increasingly important. Service providers are looking for ways to ensure a high level of availability of convergent applications and therefore there is a need to address the above mentioned issues.  
       SUMMARY OF THE INVENTION  
       [0011]     In accordance with an aspect of the invention, a method of monitoring signaling link viability from a media gateway for a multitude of signaling links between the media gateway and a multitude of media gateway controllers is provided. The method includes a sequence of steps. A heartbeat message destined for a selected one of the multitude of media gateway controllers is formulated. The heartbeat message is sent towards the media gateway controller via a selected one of the multitude of signaling links. The viability of the signaling link is ascertained based on whether the heartbeat message is returned. And, a different standby signaling link is selected if the currently selected signaling link is no longer viable.  
         [0012]     In accordance with another aspect of the invention, a media gateway providing interworking between circuit-switched channels and packet voice media streams provisioned over a packet-switched communications network is provided. The media gateway is controlled by one of a multitude of redundant media gateway controllers via a corresponding signaling connection. Each signaling connection is provisioned over redundant signaling links over a packet-switched communications infrastructure. The media gateway includes a signaling link lookup table for storing, in a multitude of signaling link table entries, signaling link connectivity information in respect of a multitude of redundant signaling links, each signaling link table entry further specifying one of the multitude of redundant media gateway controllers. The media gateway also includes a heartbeat message generator for generating a heartbeat message destined for a selected one of the multitude of redundant media gateway controllers. The media gateway further includes transmission means for sending the heartbeat message towards the selected media gateway controller via a selected signaling link. The media gateway further includes reception means for receiving heartbeat messages from the selected media gateway controller via the selected signaling link. And, the media gateway controller further includes media gateway logic for selecting another signaling link from the multitude of signaling links should a sent heartbeat message not be received.  
         [0013]     In accordance with a further aspect of the invention, a system for monitoring signaling link viability for a multitude of signaling links between a multitude of media gateways and a multitude of media gateway controllers is provided. Each media gateway includes a signaling link lookup table having a multitude of signaling link table entries, and heartbeat message generator for generating OSI Layer-2 heartbeat messages employing signaling link connectivity information held in a selected one of the multitude of signaling link table entries. Each media gateway also includes transmission means for sending the heartbeat message via a signaling link corresponding to the selected signaling link table entry towards a corresponding media gateway controller specified in the selected signaling link table entry, and reception means for receiving the heartbeat message via the signaling link. And, the media gateway further includes media gateway logic for selecting another signaling link from the multitude of signaling links specified in the multitude of signaling link table entries should a sent heartbeat message not be received. Each media gateway controller includes at least one input port configured to reply to each heartbeat message.  
         [0014]     Accordingly, while the media gateway can, in accordance with the exemplary embodiment of the invention described herein, perform connectivity monitoring of signaling links, the media gateway may also continue to perform connectivity monitoring however only as necessary since the stringent requirement of a short polling cycle is relaxed allowing the number of media gateways deployed to be less dependent on the processing bandwidth of the media gateway controller.  
         [0015]     Accordingly, an improved Layer-2 fault detection and signaling link switchover method has been presented which increases service availability above current service availability levels. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The features and advantages of the invention will become more apparent from the following detailed description of the exemplary embodiment(s) with reference to the attached diagrams wherein:  
         [0017]      FIG. 1  is a network diagram showing cooperating convergent network elements employed in provisioning packet voice services over a packet-switched communications network;  
         [0018]      FIG. 2  is a network diagram showing cooperating convergent network elements employed, in accordance with an exemplary embodiment of the invention, in provisioning packet voice services using a convergent packet-switched communications network signaling infrastructure at an improved level of service availability;  
         [0019]      FIG. 3  is an exemplary signaling link connectivity information lookup table employed in accordance with the exemplary embodiment of the invention to provide an improved level of service availability for packet voice services employing signaling provisioned over a convergent communications network infrastructure;  
         [0020]      FIG. 4  is a flow diagram showing, in accordance with the exemplary embodiment of the invention, steps performed by a media gateway actively monitoring hybrid connectivity to a media gateway controller; and  
         [0021]      FIG. 5  is an exemplary state diagram of a signaling link. 
     
    
       [0022]     It will be noted that in the attached diagrams like features bear similar labels.  
       DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0023]     It is recognized that given the mean failure rate of deployed equipment, even if centralized failover functionality is employed in accordance with prior art practices at the Media Gateway Controller (MGC), increasing the level of availability is dependent on the detection of infrastructure failure as fast as possible. In particular, prior art deployments typically quote a level of 99.99% availability, in order to increase this level ten fold to 99.999% availability, faster signaling link failure detection and faster initiation of signaling link switchover to a standby signaling link is required.  
         [0024]     It is realized that service availability in packet voice applications, operator assisted calls aside, is largely predicated on the ability of a MG  110  to connect to an MGC  106  at the control layer to convey service connection setup messages in order for service connectivity to be established at the application layer. It is too late for an MGC  106  to realize that it can no longer receive service requests nor send control messages to a particular MG  110 , because, since the last polling cycle, the corresponding CO  104  may have been unsuccessfully requesting the services of the CS  100 .  
         [0025]     In accordance with an exemplary embodiment of the invention, a distributed Layer-2 heartbeat monitoring technique is provided, wherein multiple deployed MGs  210  are adapted to perform distributed signaling link connectivity monitoring in parallel, as shown in  FIG. 2 .  
         [0026]     In accordance with the exemplary embodiment of the invention, MGs  210  register with multiple MGCs  206 , and at least with a primary and a secondary MGC  206 . In accordance with the exemplary embodiment of the invention, signaling link monitoring and switchover on failure is performed in a distributed fashion by each MG  210  at Layer-2 based on the success of receiving ( 410 ) heartbeat messages previously sent by the MG  210 .  
         [0027]     In accordance with the exemplary embodiment of the invention, each MG  210  is provided with a signaling link connectivity information lookup table  300  exemplary shown in  FIG. 3 , storing signaling link provisioning information for at least two redundant signaling links  208 . Each signaling link lookup table entry  302  includes: 
        an originating interface specification  310 , typically a network address specification, of a corresponding core-side interface of the MG  210 , typically a trunk port, on which a Switched Permanent Virtual Circuit (SPVC) signaling link originates in the uplink direction;     optionally an outgoing interface identifier  312 , typically, but not limited to, a port specification, on one of a redundant group of bridges  224 , of an interface to the management network  122  on which the SPVC signaling link terminates in the uplink direction; and     an MGC  206  identifier  314 , typically, but not limited to, a fully qualified host name or a network address, in accordance with the exemplary embodiment of the invention, each redundant MGC  206  having redundant connections to the Ethernet management network  122  therefore being addressed redundantly via a pair of redundant identifiers  314 . 
 
 Redundancy is ensured to the extent to which entry fields  310 ,  312 , and  314 ; or the entries  302  are unique—fully redundant signaling links  208  employing different physical network elements on both the ATM transport network  120  and Ethernet management network  122 . 
       
 
         [0031]     Making reference to  FIG. 4 , at setup, the entries  302  of the signaling link lookup table  300  are consulted to establish  402  at least a pair of redundant SPVCs between an MG  210  and a corresponding pair of bridges  224 . For example the first signaling link lookup table entry  302  corresponds to the default active signaling link  208  and the second signaling link lookup table entry  302  corresponds to the default standby signaling link  208 . Respective portions of the signaling links  208  traverse the ATM transport network  120  are carried over the SPVCs.  
         [0032]     Failure of transport network  120  infrastructure between the MG  210  and each bridge  224  is detected by the ATM network  120 , and addressed by autonomous rerouting the SPVCs within the ATM network  120 .  
         [0033]     Failure of the originating interface ( 310 ) of each SPVC at the MG  210 , failure of the bridge  224  proper, failure of the outgoing interface ( 312 ), and/or of the specified ( 314 ) MGC  206  are addressed, in accordance with the exemplary embodiment of the invention, via the Layer-2 heartbeat monitoring as exemplary shown in  FIG. 4 . In accordance with the exemplary embodiment of the invention, heartbeat monitoring is initiated at the ATM side of the signaling link  208 , the MG  210  formulating  406  and sending  408  an Internet Control Message Protocol (ICMP) echo message to traverse both the ATM transport network  120  and Ethernet management network  122  via the specified interfaces, to arrive at the specified  314  MGC  206  to which the Ethernet side of the signaling link  208  connects. The ICMP protocol is employed for conveying control and error messages used to manage the behavior of the Internet protocol stack. The ICMP protocol is defined in RFC 792 and RFC 950 published by the IETF on the Internet at www.ietf.org/rfc/rfc792.txt and www.ietf.org/rfc/rfc950, both of which are incorporated herein by reference.  
         [0034]     In accordance with the exemplary embodiment of the invention, MGC  206  interfaces  314  are configured to return each echo message upon receipt without intervention of the MGC  206  itself, the MGC  206  proper being relived of intensive ICMP echo message return processing. For greater certainty, the MGC  206  proper is unaware of the signaling link connectivity monitoring performed by MGs  210 . The MGC  206  becomes aware of whether an MG  210  relies thereupon for signaling through MG  210  registration therewith, and as signaling is received from the MG  210 . Incidentally, while the MGC  206  proper is not actively involved in returning the ICMP echo messages to the MG  210  at the link layer, successful registration with the MGC  206  and continued successful exchange of H.248 messages between the MG  210  and the MGC  206  at the application layer provide an indication to the MGC  206  that the MC  210  is operational, otherwise that a switchover at the MGC  206  would be in order.  
         [0035]     Repeating process steps  406 ,  408 , and  410  periodically after a link integrity check interval provides a Layer-2 heartbeat for monitoring end-to-end signaling link  208  connectivity over the convergent deployment. Persons of ordinary skill in the art understand the propagation of heartbeat messages between the MG  210  and the MGC  206  is not instantaneous. In accordance with an exemplary implementation of the exemplary embodiment of the invention, a transit delay register is employed by the MG  210  to specify a time duration during which a sent heartbeat message is respected to be received at the MG  210 .  
         [0036]     In the event that the ICMP echo message sent in accordance with the signaling link provisioning information specified in the first signaling link lookup table entry  302  fails  410  to be returned to the MG  210 , the MG  210  autonomously performs a switchover to a standby signaling link  208  by employing  416  signaling link provisioning information specified in another signaling link lookup table entry  302  thereby ensuring end-to-end connectivity through the convergent deployment. In practice however, considering the fact that the IP protocol does not guarantee successful transport end-to-end, the switchover  416  is delayed until a MaxRetry number of sent ICMP echo messages, for example two, are not received. The MG  210  tracks the number of retries in a retry register.  
         [0037]     In accordance with the exemplary embodiment of the invention, should the services of a CS  100  be required, service connection setup and teardown messages are sent by the MG  210  over the signaling link  208  via which the Layer-2 heartbeat messages are successfully ( 412 ) being sent  408  and returned  410 .  
         [0038]     Making reference to  FIG. 4 , in accordance with an exemplary implementation of the exemplary embodiment of the invention, the OSI Layer-2 monitoring process  400  is performed only when application layer H.248 messages have not been exchanged between the MG  210  and MGC  206  for a period of time, thereby reducing the introduced overhead to the minimum necessary. In accordance with another exemplary implementation of the exemplary embodiment of the invention, the link integrity check interval is adjustable, the interval being adjusted based on relevant statistical variables affecting the service availability. In accordance with an exemplary implementation of the exemplary embodiment of the invention, the link integrity check interval, which also corresponds to a monitoring frequency, is specified at the MG  210  via a register.  
         [0039]     It was mentioned above that the level of redundancy provided is dependent on the degree to which the signaling link entries  302  are unique. Whenever the same interface  310  or  312  is used in multiple entries  302  for the same signaling connection  102 , redundancy is reduced and therefore availability is reduced as that common interface associated with the corresponding signaling links  208  represents a common point of failure for the same signaling connection  102 . While redundant engineered SPVCs following disparate paths in the ATM transport network  120  can be controllably provisioned, the nature of packet switching in the Ethernet management network  122  requires careful selection of MGCs  206  specified in the entries  302  in order to ensure adequate redundancy via the provisioning redundant Ethernet signaling links following disparate paths. Added redundancy is provided by multiply connecting each MGC  206  to the management network  122  via multiple interfaces ( 314 ).  
         [0040]     In view of the fact that each MG  210  can only be registered with a single MGC  206  and in view of the fact that the registration process is not instantaneous, the multitude of entries  302  may be employed to delay the need for incurring MGC registration overheads by specifying multiple redundant signaling links  208  to each of a group redundant MGCs  206 . For brevity, steps registering the MG  210  with an MGC  206  are not show in  FIG. 4  however the information in the signaling link configuration information table  300  is also used for this purpose. However, redundancy is reduced when multiple entries  302  exclusively specify the same MGC  206 , and therefore availability is reduced as the specified MGC  206  represents a common point of failure for a given signaling connection  102 .  
         [0041]     In the above description, it was assumed for brevity that the first signaling link lookup table entry  302  corresponds to the active signaling link  208 , the second entry  302  corresponding to the standby signaling link  208 . The invention is not limited to such an assumption. In accordance with an exemplary implementation of the exemplary embodiment of the invention, at setup, after the SPVCs are established, the MG  210  may perform a selection process which sends Layer-2 heartbeat messages, as described above, in respect of each entry  302 , the signaling link  208  corresponding to the first returned heartbeat message becoming ( 412 ) the active signaling link  208 .  
         [0042]     For greater certainty, while process  400  concentrates on selecting a viable signaling link  208 , parallel processes pace each signaling link  208 , as any other SPVC, through a series of states in accordance with network conditions and configuration/management steps including the raising and clearing of alarms as appropriate. An exemplary state diagram is shown in  FIG. 5 .  
         [0043]     Therefore, in accordance with the exemplary embodiment of the invention, the MG  210 , typically an ATM network element, is adapted to formulate, convey and receive ICMP echo messages intended to traverse both the ATM transport network  120  and the Ethernet management network  122 . The MG  210  and bridge  224  implement RFC 1483 and RFC 2684 as appropriate, both published by the IETF on the Internet at www.ietf.org/rfc/rfc1483.txt, and www.ietf.org/rfc/rfc2684.txt and are incorporated herein by reference.  
         [0044]     Accordingly, while the MG  210  can, in accordance with the exemplary embodiment of the invention described herein, perform all necessary connectivity monitoring of signaling links  208 , the MGC  206  may also continue to perform connectivity monitoring however only as required since the stringent requirement of a short polling cycle is relaxed allowing the number of MGs  210  deployed to be less dependent on the processing bandwidth of the MGC  206 .  
         [0045]     Accordingly, an improved Layer-2 fault detection and signaling link switchover method has been presented which improves service availability above current service availability levels.  
         [0046]     For greater certainty, as the process  400  relates to signaling link  208  monitoring and switchover, all service call connections already established over the transport network  120  between originating and terminating CO  104  pairs are unaffected by signaling link switchovers, and service call connection control is independent of which one of the redundant signaling links  208  is employed. It is understood that at least two redundant MGs  210  are associated with each CO  104 .  
         [0047]     The embodiments presented are exemplary only and persons skilled in the art would appreciate that variations to the above described embodiments may be made without departing from the spirit of the invention. The scope of the invention is solely defined by the appended claims.