Abstract:
A method and system for media independent handover (MIH) using an Ethernet operation, administration and maintenance (OAM) protocol are disclosed. Link connectivity between a user equipment (UE) and an MIH point of service (PoS) is monitored by using an OAM protocol. An OAM trigger indicating a link status is mapped to an MIH event and the MIH event is reported for potential handover. The OAM protocol may be IEEE 802.3ah or 802.1ag.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. provisional application No. 60/735,275 filed Nov. 10, 2005, which is incorporated by reference as if fully set forth. 
    
    
     FIELD OF INVENTION 
     The present invention is related to communication systems. More particularly, the present invention is related to a method and system for media independent handover (MIH) using an Ethernet operation, administration and maintenance (OAM) protocol. 
     BACKGROUND 
     IEEE 802.21 provides architecture to enable a seamless handover process based on measurements and triggers supplied from link layers. IEEE 802.21 defines media independent event service (ES), command service (CS) and information service (IS). IEEE 802.21 also defines medium access control (MAC) layer service access points (SAPs) and associated primitives for each specific access technology. 
     IEEE 802.21 MIH event and information service (EIS) requires MAC or physical layer-based event notification for link status updates between a user equipment (UE) and an MIH point of service (PoS). The MIH EIS events include link up, link down, link parameters change, link going down, service data unit (SDU) transmission status, link event rollback, pre trigger (L2 handoff imminent), and the like. Currently, link layer extensions required to support MIH EIS are under consideration for various technologies. 
     For Ethernet networks, link monitoring using continuity messages is necessitated where physical layer signaling is inadequate to detect a connectivity status between two communication peers. IEEE 802.3ah Ethernet first mile (EFM) provides an extension to the 802.3 physical layer signaling to facilitate a connectivity status determination. IEEE 802.3ah provides link monitoring, fault signaling and remote loopback. Link monitoring serves for detecting and indicating link faults under a variety of conditions so entities can detect failed and degraded connections. Fault signaling provides mechanisms for one entity to signal another that it has detected an error. Remote loopback, which is often used for troubleshooting, allows one entity to put another entity into a state whereby all inbound traffic is immediately reflected back onto the link. 
     IEEE 802.1ag, (also known as connectivity fault management (CFM)), specifies protocols, procedures and managed objects to support transport fault management for end to end Ethernet networks at the customer, operator and service provider levels. These allow discovery and verification of the path through bridges and local area networks (LANs) and detection and isolation of connectivity fault to a specific bridge or LAN. 
     CFM mechanisms for fault detection include continuity check, traceroute, loopback (ping), alarm indication, and the like, at different OAM domains, (e.g., operator domain, provider domain and customer domain). Each maintenance domain carries CFM messages using destination address and EtherType. CFM messages are sourced or received at maintenance end points (MEPs) after traversing zero or more maintenance intermediate points (MIPs). The CFM messages pass transparently through 802.1Q or 802.1ad bridges. Multiple instances of CFM can operate at multiple levels on the same bridge port simultaneously. 
     Although conventional arts provide a mechanism to detect link problems and provide this information to the link end-points, there is currently no means to make use of this information for the purpose of triggering handover operation towards an alternative link. 
     SUMMARY 
     The present invention is related to a method and system for MIH using an Ethernet OAM protocol. Link connectivity between a UE and an MIH PoS is monitored by using an OAM protocol. An OAM trigger indicating a link status is mapped to an MIH event and the MIH event is reported for potential handover. The OAM protocol may be IEEE 802.3ah or 802.1ag. The access networks may be 802.1D-bridged network or 802.1Q-bridged network. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows functional entities of a UE in accordance with the present invention. 
         FIG. 2  shows a UE and an MIH PoS monitoring a link status using 802.3ah OAM messages in accordance with the present invention. 
         FIG. 3  shows an exemplary system for supporting MIH using 802.3ah OAM messages in accordance with a first embodiment of the present invention. 
         FIG. 4  shows a UE and an MIH PoS connected through an 802.1D-bridged network and monitoring a link status using 802.1ag OAM messages in accordance with the present invention. 
         FIG. 5  shows a UE and an MIH PoS connected through an 802.1Q bridged network and monitoring a link status using 802.1ag OAM messages in accordance with the present invention. 
         FIG. 6  shows an exemplary system for supporting MIH using 802.1ag OAM messages in accordance with a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereafter, the terminology “UE” includes but is not limited to a wireless and/or wired transmit/receive unit (TRU), a mobile station (STA), a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless and/or wired environment. 
     The features of the present invention may be incorporated into an integrated circuit (IC) or be configured in a circuit comprising a multitude of interconnecting components. 
     In accordance with the present invention, MIH endpoints, (i.e., an UE and an MIH PoS), are made as OAM peer entities and a link status between the UE and the MIH PoS is monitored by using an OAM protocol, (such as 802.3ag or 802.1ag). An OAM trigger indicating a detected link status is mapped to an MIH event. The MIH event is reported to higher layers for potential handover. The MIH PoS is a network entity providing MIH services. The MIH PoS may reside in any place in the network. For example, the MIH PoS may reside in a point of attachment (PoA) or in a core network. In accordance with the present invention, the current link status information is made available to an 802.21 PoS with MIH capabilities, and the PoS may use it to trigger a handover towards an alternate link whenever a problem with the current link is reported. The present invention provides a mechanism to generically use the 802.1 link detection mechanism for handover decision over 802.3 and 802.11 networks. 
       FIG. 1  shows functional entities of the UE  100  in accordance with the present invention. The UE  100  includes a higher layer  110 , an MIH entity  120  and a lower layer  130 . The higher layer  110  includes a session initiation protocol (SIP) entity  112 , a mobile Internet protocol version 4 (MIP v.4) entity  114 , a mobile Internet protocol version 6 (MIP v.6) entity  116 , and the like. The lower layer  130 , (i.e., layer 2 and layer 1), includes an IEEE 802.3 entity  132 , an IEEE 802.11 entity  134 , an IEEE 802.16 entity  136 , a third generation partnership project (3GPP) entity  138 , a 3GPP2 entity  140 , and the like. The MIH entity  120  receives link events and link information from the lower layer  130 . Based on the reported link events and information from the lower layer  130 , the MIH entity  120  generates MIH events and information and sends them to the higher layer  110 . The MIH entity  120  receives MIH commands and information from the higher layer  110 . Based on the MIH commands and information received from the higher layer  110 , the MIH entity  120  generates link commands and link information and sends them to the lower layer  130 . 
       FIG. 2  shows a UE  202  and an MIH PoS  208  monitoring a link status using 802.3ah OAM messages in accordance with the present invention. A connection between the UE  202  and the MIH PoS  208  is established via a network  210  including one or more hubs (or repeaters)  204 ,  206 . The first hub (or repeater)  204  is a PoA. When the UE  202  and the MIH PoS  208  are connected through a hub (or repeater)  204 ,  206 , the 802.3 physical layer signaling at the layer 1 interface of the UE  202  is unable to detect the link event change between the hub (or repeater)  204 ,  206  and the MIH PoS  208 . Therefore, the end to end semantics required for a handover decision are lost as loss of connectivity between the hubs (or repeaters)  204 ,  206  is not visible to either the UE  202  or the MIH PoS  208 . It should be noted that the loss of connectivity beyond the MIH PoS  208  is beyond the scope of what can be accomplished by IEEE 802.21. 
     In accordance with a first embodiment of the present invention, the MIH endpoints, (i.e., the UE  202  and the MIH PoS  208 ), are made as OAM peer entities and the link status between the UE  202  and the MIH PoS  208  are monitored by using an IEEE 802.3ah protocol. Both the UE  202  and the MIH PoS  208  include an MIH entity. The PoA  204  may include an MIH entity. In such case, the PoA  204  works as an MIH capable PoA. The MIH entities of the UE  202  and the MIH PoS  208 , (optionally, an MIH entity of the MIH PoA  204 ), use this link status information to generate an 802.21 MIH event notification about the link status. 
     When a link status is detected using an 802.3ah protocol, an OAM trigger is forwarded to the MIH entity of the UE  202  (or the MIH PoS  208  and the MIH PoA  204 ). The OAM triggers are then mapped to MIH events by the MIH entity of the UE  202  (or the MIH PoS  208  and the MIH PoA  204 ) and reported to higher layers for triggering a handover. 
     Table 1 shows mapping of 802.3ah triggers to 802.21 events. Some of the currently defined MIH events can be associated with 802.3ah triggers. The 802.3ah framework allows extension of this subset by a vendor using custom type-length-value (TLV) specification. An 802.3ah link up event indicating that the physical layer has determined that the link is up and the OAM remote entity is up is mapped to an 802.21 link up event. An 802.3ah link fault event indicating that the physical layer has determined a fault has occurred in the receive direction of the local data terminal equipment (DTE) is mapped to an 802.21 link down event. An 802.3ah dying gasp event indicting that an unrecoverable local failure condition has occurred is mapped to an 802.21 link going down event. 
     
       
         
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                   
                 802.3ah Triggers 
               
             
          
           
               
                 MIH Event 
                 Event 
                 Description 
               
               
                   
               
               
                 Link Up 
                 Link Up 
                 The PHY has determined that the link is up 
               
               
                   
                   
                 AND the OAM Remote Entity is up. 
               
               
                 Link Down 
                 Link fault 
                 The PHY has determined a fault has occurred 
               
               
                   
                   
                 in the receive direction of the local DTE 
               
               
                 Link Going 
                 Dying 
                 An unrecoverable local failure condition has 
               
               
                 Down 
                 Gasp 
                 occurred. 
               
               
                   
               
             
          
         
       
     
       FIG. 3  shows an exemplary system  300  for supporting MIH services using 802.3ah OAM in accordance with the present invention. The system  300  includes a UE  302 , a wireless local area network (WLAN)  310 , an 802.3 network 320 and an MIH PoS  330 . The 802.3 network  320  includes a plurality of inter-connected hubs (or repeaters)  322 ,  324 . The UE  302  is MIH capable and supports both the WLAN access technology and 802.3 access technology. The UE  302  and the MIH PoS  330  are two OAM peer entities and the link status between the UE  302  and the MIH PoS  330  are monitored by using an IEEE 802.3ah protocol. Upon detection of one of the 802.3ah triggers, an MIH entity of the UE  302  (or the MIH PoS  330 ) maps the 802.3ah trigger to an 802.21 event. Therefore, MIH communication between the UE  302  and the MIH PoS  308  is established through one of the WLAN  310  and the 802.3 network  320  as shown in  FIG. 3 . Based on the reported MIH event, a handover may be triggered between the WLAN  310  and the 802.3 network  320 . 
     In accordance with a second embodiment of the present invention, the link status between a UE and an MIH PoS is monitored by using an IEEE 802.1ag protocol. If the UE is connected to the MIH PoS through an 802.1D or 802.1Q-bridged network as shown in  FIGS. 4 and 5 , an 802.3 layer 1 event notification or 802.3ah OAM messages are insufficient to detect loss of connectivity between the UE and the MIH PoS. 
       FIG. 4  shows an UE  402  and an MIH PoS  408  connected through an 802.1D-bridged network  410  and monitoring a link status using 802.1ag OAM messages in accordance with the present invention. The 802.1D-bridged network  410  includes hubs  404  and bridges/switches  405 , 406 . The connection between the UE  402  to the MIH PoS  408  is established via one or more 802.1D bridges or switches. When the UE  402  and the MIH PoS  408  are connected through an 802.1D-bridged network  410 , an 802.3 level physical layer link status notification is insufficient to detect a link connectivity to the MIH PoS  408  and IEEE 802.3ah OAM messages do not traverse 802.1D bridges/switches  405 ,  406 . 
       FIG. 5  shows an UE  502  and an MIH PoS  508  connected through an 802.1Q bridged network and monitoring a link status using 802.1ag OAM messages in accordance with the present invention. The UE  502  is connected to a hub, (i.e., PoA),  504 . The connection between the PoA  504  to the MIH PoS  508  is established via one or more 802.1Q bridges or switches  512 ,  522 . When the bridges or switches  512 ,  522  are 802.1Q bridges or switches, the reachability to the MIH PoS  508  may be through different links for different virtual local area networks (VLANs)  510 ,  520 , either due to static configuration or through configuration of spanning tree running on each bridge. In such case, the MIH connectivity between the UE  502  and the MIH PoS  508  needs to be established and monitored on a per VLAN identity (ID) basis. 
     In accordance with the second embodiment of the present invention, the 802.1ag protocol for customer level OAM is used to detect the end to end link status by mapping the 802.1ag management information base (MIB) objects to the 802.21 events. Table 2 shows a mapping of 802.1ag MIB objects to the 802.21 events. 
     An 802.1ag MIB object indicating that a connectivity is detected or has been restored is mapped to an 802.21 link up event. An 802.1ag MIB object indicating that a management end point (MEP) has lost contact with one or more MEPs is mapped to an 802.21 link down event. A new 802.1ag MIB object is defined to indicate the number of connectivity check frames that can be lost before indicating a fault has occurred to map 802.21 link going down event to 802.1ag dying gasp. 
     A link going down event is used whenever there is a possibility that a link might fail, (e.g., due to poor radio conditions). Where the current link is supported via 802.3, the link going down status may be flagged when it is determined that the connection would likely be down within a short period of time after looking at the amount of frames that have been lost. For example, if a threshold is set to ten (10) frame losses before the link is deemed faulty, then a link going down indication may be sent on the 9th frame check has failed. 
     
       
         
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                   
                 802.1ag MIB objects 
               
             
          
           
               
                 MIH 
                   
                 Present/ 
                   
               
               
                 event 
                 Object 
                 Extension 
                 Description 
               
               
                   
               
               
                 Link Up 
                 Dot1agCfmCCheckRestoredEvent 
                 Present 
                 Detected connectivity or connectivity 
               
               
                   
                   
                   
                 has been restored. 
               
               
                 Link 
                 Dot1agCfgCCheckLossEvent 
                 Present 
                 A MEP has lost contact with one or 
               
               
                 Down 
                   
                   
                 more MEPs. A notification (fault 
               
               
                   
                   
                   
                 alarm) is sent to the management 
               
               
                   
                   
                   
                 entity with the MEPID of the MEP 
               
               
                   
                   
                   
                 which detected the problem. 
               
               
                 Link 
                 X 
                 Extension 
                 Number of connectivity check frames 
               
               
                 Going 
                   
                   
                 that can be lost before indicating 
               
               
                 Down 
                   
                   
                 fault is defined. “Link Going Down” 
               
               
                   
                   
                   
                 signal is generated for one or more 
               
               
                   
                   
                   
                 less than the count. 
               
               
                   
               
             
          
         
       
     
       FIG. 6  shows an exemplary system  600  for supporting MIH services using 802.1ag OAM in accordance with the second embodiment of the present invention. The system  600  includes a UE  602 , an 802.11 network  604 , an 802.16 network (WIMAX)  606 , an 802.3 network  608 , a home network  614  and an MIH PoS  616 . The 802.11 network  604  and the 802.3 network are connected to the home network  614  via 802.1Q bridges  610 ,  612 , respectively. The UE  602  is MIH capable and supports the 802.11, 802.16 and 802.3 access technologies. The UE  602  and the MIH PoS  616  are two OAM peer entities and the link status between the UE  602  and the MIH PoS  616  are monitored by using an IEEE 802.1ag protocol as stated above. Upon detection of the 802.1ag events, an MIH entity of the UE  602 , (or the MIH PoS  616  or PoAs in the 802.11 network  604 , the 802.16 network  606  and the 802.3 network  608 ), maps the 802.1ag MIB object to an 802.21 event and may trigger an inter-technology handover between the 802.11 network 604, the 802.16 network 606 and the 802.3 network  608 , or intra-technology handover may be triggered within the currently connected network, based on the MIH event. An IEEE 802.1Q VLAN traffic can be carried over 802.3, 802.11 and 802.16 frames through the associated convergence sublayer. Thus, the end-to-end 802.1ag based connectivity is valuable to make inter-technology or intra-technology handover decisions. 
     Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention.