Abstract:
The Federal Communications Commission Order 05-116, E911 Requirements for IP-Enabled Service Providers, (FCC Order) requires interconnected Voice over Internet Protocol (VoIP) service providers to deliver all emergency service calls to a VoIP service user&#39;s local emergency service operator as a standard feature of the service. Under the FCC Order, VoIP service providers must supply emergency service if the VoIP service user accesses the VoIP service over broadband and if the VoIP service provider interconnects to and from the Public Switched Telephone Network (PSTN). Embodiments of the present invention guarantee compliance with the FCC Order by routing a call as either a VoIP call over the Internet or as a conventional call over the PSTN, verifying that at least one of the VoIP or PSTN telephony connections supports emergency service and routing calls over that connection or, if there is no connection supplying emergency service, restricting calling over the VoIP connection.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 11/450,137, filed on Jun. 9, 2006 now abandoned, which claims the benefit of U.S. Provisional Application No. 60/693,745, filed on Jun. 23, 2005 and U.S. Provisional Application No. 60/689,266, filed on Jun. 10, 2005. The entire teachings of the above applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The Federal Communications Commission (FCC) Order 05-116, E911 Requirements for IP-Enabled Service Providers, hereinafter referred to as the FCC Order, stipulates that interconnected Voice over Internet Protocol (VoIP) service providers must deliver 911 calls to a VoIP service user&#39;s local emergency service operator as a standard feature of the service. The term “interconnected” refers to the ability of the VoIP service provider to enable VoIP service users to receive calls from and terminate calls to the public switched telephone network (PSTN). 
     Under the FCC Order, VoIP service providers must supply 911 service if the VoIP service user accesses the VoIP service over broadband and if the VoIP service provider supplies interconnection both to and from the PSTN. Interconnected VoIP service providers must provide emergency service operators with the call back number and location information of the VoIP service users (i.e., E911) where the emergency service operator is capable of receiving it. If the VoIP service provider&#39;s approach requires some or all VoIP service users to provide location information, the VoIP requires some or all VoIP service users to provide location information, the VoIP service provider must supply the VoIP service user a means of providing and updating this information. 
     Interconnected VoIP service providers must also inform the VoIP service users, both new and existing, of the E911 capabilities and limitations of the VoIP service. To aid the VoIP service providers in implementing methods to conform to the FCC Order, the incumbent local exchange carriers are required to provide access to their E911 networks to any requesting telecommunications carrier, and must continue to provide access to trunks, selective routers, and E911 databases to competing carriers. 
     SUMMARY OF THE INVENTION 
     A VoIP service provider knows whether it operates under the conditions which would require it to supply emergency service to the VoIP service users (i.e., customer access over broadband and interconnectivity). However, it may be difficult for a VoIP service provider subject to the FCC Order to ensure that its VoIP service users are supplied with emergency service at all times. If a VoIP service provider is required to supply emergency service to its VoIP customers, then the VoIP service provider wants to be able to control its VoIP service users&#39; ability to place calls using the VoIP service depending on whether emergency service is available to the VoIP service user. 
     A VoIP service user might be supplied with emergency service by a means other than that by the VoIP service provider, such as over the PSTN. If the VoIP service provider knows that a VoIP service user has an active PSTN connection in addition to the VoIP service, and the VoIP service provider knows that the VoIP service user has a telephone endpoint device that automatically routes emergency service calls over that PSTN line, the VoIP service provider can operate under the assumption that the VoIP service user will have emergency service as long as the PSTN connection remains active, because emergency service is mandatory on active PSTN lines within the United States. Thus, the determination of an active PSTN line drastically simplifies complying with the FCC Order. However, if the VoIP service provider knows that the FCC Order is inapplicable or the requirements of the FCC Order are satisfied (i.e., the VoIP service provider is not interconnected to the PSTN or the VoIP service provider supplies emergency service operators with the call back number and location information of the VoIP service users), the status of a customer&#39;s PSTN line, if present, is irrelevant. 
     In an example embodiment of the present invention, an endpoint telephone device has a packet network interface, a telephone line interface, a telephone set interface and a controller. The packet network interface is to be connected to a packet network. The telephone line interface is to be connected to a telephone line. The telephone set interface is to be connected to a telephone set. One skilled in the art will understand that the telephone set could be, but is not limited to, a cordless telephone or a corded telephone. 
     The controller is configured to monitor a set of bits transmitted from the VoIP service provider that indicate whether a VoIP service provider is required to supply emergency service to the endpoint telephone device, sense access to emergency service on the packet network interface and the telephone line interface, and route or restrict calls depending on the sensed access. The emergency service may be 911 service. 
     The controller may disable all calling via the VoIP service over the packet network when the VoIP service provider is required to supply emergency service to the endpoint telephone device and the controller senses that emergency service is not available via the VoIP service over the packet network or via the PSTN over the telephone line. 
     The controller may route all calls, including emergency service calls, via the VoIP service over the packet network when the VoIP service provider is required to supply emergency service to the endpoint telephone device and the controller senses that emergency service is available via the VoIP service over the packet network and is not available via the PSTN over the telephone line. 
     The controller may route emergency service calls via the PSTN over the telephone line when the VoIP service provider is required to supply emergency service to the endpoint telephone device and the controller senses that emergency service is not available via the VoIP service over the packet network and is available via the PSTN over the telephone line. 
     The controller may route all calls, including emergency service calls, via the VoIP service over the packet network or via the PSTN over the telephone line according to information supplied to the controller when the VoIP service provider is required to supply emergency service to the endpoint telephone device and the controller senses that emergency service is available via the VoIP service over the packet network and via the PSTN over the telephone line. 
     The controller may route all calls via the VoIP service over the packet network or via the PSTN over the telephone line according to information supplied to the controller when the VoIP service provider is not required to supply emergency service to the endpoint telephone device. 
     The controller may also route VoIP calls, but only to other VoIP devices, if the VoIP service provider is not required to supply emergency service to the endpoint telephone device and the controller senses that emergency service is not available via the VoIP service over the packet network or via the PSTN over the telephone line. 
     More generally, we can think of the endpoint device as having some programmable bits that can be set by the VoIP service provider and used to determine the endpoint&#39;s behavior, including its decision about whether to route a call to a VoIP service provider. Further, the routing decision need not be made at the endpoint device, but may alternatively be made at the VoIP service provider&#39;s server, as long as the endpoint supplies the server with required information in relation to the status of the endpoint&#39;s PSTN connection. 
     The endpoint telephone device may contain a software switch to connect the telephone set interface to the telephone line interface or, alternatively, to the packet network interface. In another example embodiment, the switch may be a hardware switch or relay. In an example embodiment, the hardware relay automatically connects the telephone set interface to the telephone line interface when power is disrupted to the endpoint telephone device. The endpoint telephone device may also contain a switch that allows a user to specify whether the telephone line interface will be connected via a telephone line to the PSTN. 
     In operation of an example embodiment, a VoIP service user configures his or her account with the VoIP service provider to indicate information, such as the VoIP service user&#39;s street address. The VoIP service user then registers the endpoint telephone device with the VoIP service provider such that the endpoint telephone device is associated with the VoIP service user. The endpoint telephone device then notifies the VoIP service provider whether emergency service is available to the VoIP service user via the telephone line interface. In response, the VoIP service provider typically notifies the endpoint telephone device whether the VoIP service provider is required by the FCC Order to supply emergency service to the VoIP service user, whether the VoIP service user&#39;s account is configured for VoIP emergency service, and whether the VoIP service provider supplies emergency service to the VoIP service user. The endpoint telephone device then activates VoIP calling if emergency service is available via the PSTN. Otherwise, if the VoIP service provider is required by the FCC Order to supply emergency service, the VoIP service user&#39;s account is configured for VoIP emergency service, and the VoIP service provider provides emergency service to the VoIP service user, then the endpoint telephone device may also activate VoIP calling. 
     The endpoint telephone device may also notify the VoIP service provider whenever it detects a change in whether an active PSTN line is present. The endpoint telephone device may determine the status of emergency service via the PSTN line by determining whether the PSTN line is active. The determination of an active PSTN connection is taken to imply the availability of emergency service on the PSTN line because such emergency service is mandatory on active PSTN lines within the United States. 
     In addition to notifying the VoIP service provider when a change in status has occurred of a connection to a PSTN line, the endpoint telephone device may transmit status information on a periodic basis. Whenever the endpoint telephone device transmits such status information, whether because of a change in state or on a periodic basis, the endpoint telephone device expects a response from the VoIP service provider that indicates the current status of the VoIP service provider. The endpoint telephone device may disable VoIP calling if a number of successive such notifications from the VoIP service provider fail to arrive at the endpoint telephone device when expected, unless the PSTN connection is active. 
     The VoIP service provider may periodically notify the endpoint telephone device whether the VoIP service provider is required to supply emergency service, whether the VoIP service user&#39;s account is configured for VoIP emergency service, and whether the VoIP service provider supplies emergency service. Additionally, the VoIP service provider may immediately notify the endpoint telephone device whenever there is a change in the status any of these factors. 
     The endpoint telephone device may disable VoIP calling if emergency service is required by the FCC Order but is unavailable via either the PSTN line or VoIP service provider. The endpoint telephone device may then notify the VoIP service provider that VoIP calling has been disabled. 
     Note that, alternatively, the VoIP service provider may make routing decisions based on its own knowledge of requirements of emergency service call handling, together with the service&#39;s capabilities for handling emergency service calls from the particular subscriber, and information forwarded to the VoIP service provider from the endpoint, relative to the availability of a PSTN connection at the endpoint. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1C  are network diagrams illustrating different connections that may be implemented using an endpoint telephone device embodying the invention. 
         FIGS. 2A-2E  are block diagrams illustrating example embodiments of an endpoint telephone device. 
         FIG. 3  is a table illustrating four data fields used by a VoIP service provider to control a VoIP service user&#39;s endpoint telephone device. 
         FIGS. 4A-4B  are flow diagrams illustrating the mechanism used to communicate with the endpoint telephone device. 
         FIGS. 5A-5C  are flow diagrams illustrating the algorithm performed in determining whether the VoIP service provider complies with the FCC Order and allowing calling based on that compliance. 
         FIG. 6  is a flow diagram illustrating the algorithm performed in determining whether there is an active telephone line attached to the telephone line interface of the endpoint telephone device and, therefore, whether the telephone line interface supports emergency service. 
         FIG. 7  is a table illustrating four states of PSTN and VoIP emergency service availability. 
         FIG. 8  is a table illustrating two states of VoIP emergency service availability when the endpoint telephone device is in VoIP only mode. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A description of preferred embodiments of the invention follows. 
     Device Hardware 
       FIGS. 1A-1C  are network diagrams illustrating different connections that may be implemented using an endpoint telephone device embodying the invention.  FIG. 1A  is a network diagram  100   a  illustrating the connection of an endpoint telephone device  105  to a telephone set  110  for making a telephone call over a packet network  115  via VoIP service  120  over a packet network  125   a  to a VoIP service user  130   a .  FIG. 1B  is a network diagram  100   b  illustrating the connection of an endpoint telephone device  105  to a telephone set  110  for making a telephone call over a packet network  115  via VoIP service  120  over PSTN  125   b  to a telephone set  130   b .  FIG. 1C  is a network diagram  100   c  illustrating the connection of an endpoint telephone device  105  to a telephone set  110  for making a telephone call over PSTN  125   b  to a telephone set  130   b.    
       FIGS. 2A-2E  are block diagrams illustrating example embodiments of an endpoint telephone device  200 . In  FIGS. 2A-2D , the endpoint telephone device  200  includes a telephone set interface  205  for connecting to a telephone set  210 , a telephone line interface  215  for connecting to a telephone line  220 , and a packet network interface  225  for connecting to a packet network  230 , such as the Internet. In  FIGS. 2A and 2C , the endpoint telephone device  200  uses a software switch  235   a  to connect the telephone set interface  205  to the telephone line interface  215  or, alternatively, to the packet network interface  225 . In an alternate example embodiment, as illustrated by  FIGS. 2B and 2D , the endpoint telephone device can use a hardware switch or relay  235   b  to connect the telephone set interface  205  to the telephone line interface  215  or, alternatively, to the packet network interface  225 . 
     In the embodiment as illustrated by  FIG. 2E  the endpoint telephone device  200  includes a telephone set interface  205  for connecting to a telephone set  210  and a packet network interface  225  for connecting to a packet network  230 , such as the Internet. Because this embodiment does not provide a telephone line interface  215  for connecting to a telephone line  220 , the soft switch  235   a  or a hardware switch or relay  235   b  to connect the telephone set interface  205  to the packet network interface  225  or, alternatively, to the telephone line interface  215  are not required. 
     In the example embodiments illustrated by  FIGS. 2A-2D , the endpoint telephone device  200  communicates over a PSTN network  220  or over a packet network  230  with a VoIP service  235  stored on a VoIP server  240 . The VoIP service  235  facilitates initiating telephone calls from the telephone set  210  to be transmitted over the packet network  230 . The processor block  245  includes a VoIP controller  250  and a processor  255 , and is connected to the telephone set interface  205 , telephone line interface  215  and packet network interface  225 . In  FIG. 2E , the processor block  245  is connected to the telephone set interface  205  and the packet network interface  225 . 
     In an example embodiment, the processor  255  senses the availability of emergency service on both the PSTN and the VoIP network and runs a Session Initiation Protocol (SIP) stack that controls the VoIP telephony feature. In an alternate example embodiment, as illustrated by  FIGS. 2C and 2D , the endpoint telephone device can contain a switch  260  to control whether or not the processor  255  checks for an active PSTN connection at the telephone line interface  215  and allows only VoIP calls to be made over the packet network  230 . For example, if a VoIP service user knows that there is no PSTN line connected to the telephone line interface of the endpoint telephone device, such as when the VoIP service user does not have an active PSTN line with a PSTN carrier, the VoIP service user can indicate, via this switch, that the endpoint telephone device should place calls over only the packet network and not check for PSTN connectivity. Additionally, in another example embodiment, as illustrated by  FIG. 2E , because the endpoint telephone device does not contain a telephone line interface, the endpoint telephone device may only make calls over the packet network  230 . 
     In one embodiment, the packet network interface  225  is a WAN Ethernet port that can be connected to a broadband Internet access device such as a Digital Subscriber Line (DSL) modem or cable modem. In alternate embodiments, the packet network interface  130  can be an integrated DSL modem, integrated cable modem or other access medium, such as wireless or power line networking. In an alternate example embodiment, the packet network interface  225  may be an Asymmetric Digital Subscriber Line (ADSL) enabled telephone line, in which case the telephone line interface  215  and the packet network interface  225  may share the same physical interface, although they are logically distinct. 
     In one embodiment, the telephone line interface  215  is a DSL port with PSTN service enabled. In alternate embodiments, this can be an FXO port, or a variant that allows a telephone connected to the device to be switched, as by a relay, directly to the PSTN. 
     Device Operation—Eservice-Profile 
     In a process that is separate and distinct from the endpoint telephone device setup, the VoIP service provider configures a VoIP service user&#39;s account for VoIP emergency service. To do this, the VoIP service provider determines the physical location of the endpoint telephone device either by some automated means or by requiring that the VoIP service user provide and authenticate the location information. 
     The endpoint telephone device determines the status of emergency service through the VoIP connection or, more specifically, whether the VoIP service provider is required by the FCC Order to supply emergency service and whether the VoIP service provider supplies that service, by making use of the SIP mechanism called SUBSCRIBE/NOTIFY, as described in Internet Engineering Task Force (IETF) Request for Comments (RFC) 3265. The SUBSCRIBE/NOTIFY mechanism provides a means for a SIP service to convey specific information to the endpoint telephone device. 
       FIG. 3  is a table  300  illustrating four data fields in the SIP event Eservice-profile and the two values each field can have. Data field SIPProvider-Supports911 indicates whether the VoIP service provider supplies emergency service for VoIP service users and can take the value YES or NO. Data field UserAccountEnabledFor-911 indicates whether the VoIP service user&#39;s account is configured with certain data, including the physical location of the endpoint telephone device, and can take the value YES or NO. Data field Allow-VoIPToVoIPCalls indicates whether the VoIP service provider allows the VoIP service users, under certain circumstances, to make direct calls to other VoIP customers only, and can take the value YES or NO. Data field 911-ServiceNotRequired indicates whether the VoIP service user is among those not required under the FCC Order to be supplied emergency service by the VoIP service provider, and can take the value YES or NO. 
       FIG. 4A  is a flow diagram  400   a  illustrating the use of the SIP mechanism SUBSCRIBE/NOTIFY to convey specific information regarding emergency service supplied by the VoIP service provider to the endpoint telephone device. First, the endpoint telephone device REGISTERs  405  with the SIP service of the VoIP service provider using account information provisioned in the endpoint telephone device. This information is distinct from the emergency service location information, and the method for loading this information is beyond the scope of this description. Next the endpoint telephone device SUBSCRIBES  410  to the SIP event Eservice-profile. The SIP service returns a NOTIFY  415  packet for this event that tells the endpoint telephone device whether or not it can and should make emergency service calls through the VoIP service. The NOTIFY packet does this by indicating the values of the data fields in Eservice-profile as illustrated in  FIG. 3 . In general, the SIP service will send NOTIFY packets related to an event any time there is a change in the status described by the event. In the case of Eservice-profile, the SIP service will send NOTIFY packets as soon as the subscription is initiated to convey the initial status. The endpoint telephone device then stores  420  that data. In another example embodiment, as illustrated by  FIG. 4B , the SIP service may also repeat  425  sending NOTIFY packets  415  to the endpoint telephone device that indicate whether the service continues to support VoIP emergency service and whether the particular VoIP service user account is activated for VoIP emergency service. The endpoint telephone device stores  420  the status indication it receives via the Eservice-profile notification  415 . 
     Device Operation—Checking for Emergency Service 
       FIG. 5A  is a flow diagram illustrating an example embodiment of the algorithm performed in determining whether the VoIP service provider complies with the FCC Order and allowing calling based on that compliance. First, the endpoint telephone device checks the value of data field 911-ServiceNotRequired  505  in Eservice-profile to determine whether emergency service is required under the FCC Order. If the value of data field 911-ServiceNotRequired  505  is YES  507 , indicating that emergency service is not required by the FCC Order (implying that the VoIP service provider is not interconnected with the PSTN), then the endpoint telephone device enables all calls  535 . 
     If the value of data field 911-ServiceNotRequired is NO  508 , indicating that emergency service is required under the FCC Order (implying that the VoIP service provider is interconnected with the PSTN), then the endpoint telephone device must determine whether emergency service is provided over the PSTN connection. The endpoint telephone device checks whether the PSTN connection is active  520 . The determination of an active PSTN connection implies the availability of emergency service on the PSTN line because emergency service is mandatory on active PSTN lines within the United States. If the PSTN connection is active  522 , the FCC Order is satisfied because emergency service is available via the PSTN. The endpoint telephone device enables all calls  535 . 
     However, if the PSTN connection is not active  523 , the FCC Order is not yet satisfied and the endpoint telephone device must determine whether the VoIP service provider supplies emergency service. The endpoint telephone device checks the value of data field SIPProvider-Supports911  525  in Eservice-profile. If the value of data field SIPProvider-Supports911  525  is NO  527 , indicating that the VoIP service provider does not support emergency service, then there is no emergency service via either the PSTN or the VoIP service provider to satisfy the FCC Order. The endpoint telephone device disables all calls  540 . 
     If the value of data field SIPProvider-Supports911  525  is YES  528 , indicating that the VoIP service provider does support emergency service, then the endpoint telephone device must determine whether the VoIP service user&#39;s account is configured for VoIP emergency service. The endpoint telephone device checks the value of the data field UserAccountEnabledFor-911  530  in Eservice-profile. If the value of data field UserAccountEnabledFor-911  530  is YES  532 , indicating that the VoIP service user&#39;s account is enabled for VoIP emergency service, then the endpoint telephone device enables all calls  535 . Otherwise, if the value of data field UserAccountEnabledFor-911  530  is No  533 , indicating that the VoIP service user&#39;s account is not enabled for VoIP emergency service, then the endpoint telephone device disables all calls  540 . 
       FIG. 5B  is a flow diagram illustrating an example embodiment of the algorithm performed in determining whether an endpoint telephone device should enable calling over the packet network or PSTN. This example embodiment is identical to the example embodiment illustrated by  FIG. 5A  except that the endpoint telephone device contains a switch, as illustrated in  FIGS. 2C and 2D . Thus, in an example embodiment, the endpoint telephone device must first determine  510 , via the position of the switch, if it should or should not check whether the PSTN connection is active  520 . If the VoIP service user has indicated, via the switch, that the endpoint telephone device should check if the PSTN connection is active  512 , the endpoint telephone device then does so  520 . However, if the VoIP service user has indicated that the endpoint telephone device should not check if the PSTN connection is active  513 , then the endpoint telephone device may skip directly to checking whether the VoIP service provider supports emergency service  525 . 
       FIG. 5C  is a flow diagram illustrating an example embodiment identical to the example embodiment illustrated by  FIG. 5B , except that the endpoint telephone device must check whether the VoIP service provider allows VoIP-to-VoIP only calls to be made on the VoIP network. If there is no approved method for emergency service access via either the PSTN or the VoIP service provider, and such a method is required by the FCC Order, the endpoint telephone device may be enabled for VoIP-to-VoIP calling if the VoIP service provider supports this feature. In this case, the VoIP service provider would allow calls from the endpoint telephone device to be made only over the packet network and not over the PSTN. 
     Thus, in an example embodiment, before enabling VoIP-to-VoIP calls only, the endpoint telephone device must check the value of the data field Allow-VoIPToVoIPCalls  515  in Eservice-profile. If the value of data field Allow-VoIPToVoIPCalls  515  is NO  517 , indicating that the VoIP service provider does not support VoIP-to-VoIP only calls, then the endpoint telephone device disables all calls  540 . Otherwise, if the value of data field Allow-VoIPToVoIPCalls  515  is YES  518 , indicating that VoIP-to-VoIP only calls are permitted by the VoIP service provider and the VoIP service provider will not allow calls from the endpoint telephone device to be made over the PSTN, then the endpoint telephone device enables VoIP-to-VoIP calls only  545 . The endpoint telephone device can issue a special dial tone that indicates only VoIP-to-VoIP calls are supported. 
     Checking the PSTN Connection 
       FIG. 6  is a flow diagram  600  illustrating an example embodiment of the algorithm performed in determining whether there is an active telephone line attached to the telephone line interface of the endpoint telephone device and, therefore, whether the telephone line interface supports emergency service. The endpoint telephone device checks for the presence of an active PSTN line  615 . This check may involve, for example, testing for dial tone or other AC signals on the PSTN line, testing for PSTN loop current, testing the PSTN DC voltage level, or placing a call to a predetermined number and verifying ringback, a busy signal, or a successful connection. If the endpoint telephone device determines that there is not an active PSTN line connected to the telephone line interface  617 , the endpoint telephone device then checks whether the VoIP service provider complies with the FCC Order and supports emergency service  625 , corresponding to the same stage of the algorithm  525  as illustrated in  FIGS. 5A-5C . If there is an active PSTN line connected to the telephone line interface  618 , then PSTN emergency service is available  620 . The determination of an active PSTN connection is taken to imply the availability of emergency service on the PSTN line because such emergency service is mandatory on active PSTN lines within the United States. 
     If the endpoint telephone device detects an active PSTN connection  618 , it enables all calls  630  regardless of the value of data field SIPProvider-Supports911  625  in Eservice-profile. When it does this it sends an indication to the VoIP service provider indicating that PSTN emergency service is supported on the PSTN line  635 . In an example embodiment, the indication is sent in a SUBSCRIBE packet. In the case that a SUBSCRIBE packet is used to send the indication of PSTN emergency service support, the device re-subscribes when it detects a change in the PSTN emergency service status. 
     Similarly, the VoIP service provider may respond to each SUBSCRIBE packet with a NOTIFY packet that may include bit fields that the endpoint interprets to indicate how to route VoIP calls, as described previously. 
     Persistence 
     Once the endpoint telephone device activates VoIP calling, whether because it found a valid value of data field SIPProvider-Supports911 in Eservice-profile or because it detected an active PSTN connection, the endpoint telephone device maintains the VoIP feature in the active state. However, in an example embodiment, this is subject to continuing tests of the availability of emergency service over both the PSTN and packet network. If, at any time, emergency service becomes unavailable, the endpoint telephone device may disable VoIP calling if, for example, this is necessary in order to remain in compliance with the FCC Order. In an example embodiment, the endpoint telephone device notifies the VoIP service provider if VoIP calling becomes disabled. 
     The subscription to Eservice-profile results in notifications sent to the endpoint telephone device. Notifications may be sent in response to periodic resubscriptions, or if the VoIP service provider needs to report a change in state relative to EServices. If at any time a notification indicates that VoIP emergency service is no longer available for the account active on the endpoint telephone device or, if a number, such as two, successive notifications in response to periodic resubscriptions fail to arrive at the endpoint telephone device when expected, the endpoint telephone device will disable VoIP calling, unless the PSTN connection is active, in order to remain in compliance with the FCC Order. 
     Similarly, in an example embodiment, if the endpoint telephone device has detected an active PSTN connection, the endpoint telephone device continuously verifies the connection. In another example embodiment, the endpoint telephone device tests for an active PSTN connection when a user puts the telephone set connected to the telephone set interface in an off-hook condition. If at any time the endpoint telephone device determines that the PSTN connection is no longer active, the endpoint telephone device disables VoIP calling unless the value of the SIPProvider-Supports911 data field indicates that the VoIP service provider supports emergency service. 
     Device States and Emergency Service Routing 
       FIG. 7  is a table  700  illustrating four states of PSTN and VoIP emergency service availability. The endpoint telephone device configures default emergency service routing according to which state it is in. 
     In state A, VoIP emergency service is not available and PSTN emergency service is not available. Based on this availability, for a VoIP service provider required under the FCC Order to supply emergency service to the endpoint telephone device, the endpoint telephone device completely disables VoIP operations because the availability of emergency service does not comply with the FCC Order. When the telephone set connected to the endpoint telephone device comes off hook, the endpoint telephone device connects its telephone set interface to the VoIP circuitry and generates a distinctive tone, such as a reorder tone, indicating that calling is not available. If the VoIP service provider sets the value of data field Allow-VoIPToVoIPCalls in Eservice-profile to YES, indicating it will allow calls to be made from the endpoint telephone device over the packet network to another VoIP device and will not interconnect calls from the endpoint telephone device to the PSTN, then the endpoint telephone device may accept incoming and outgoing VoIP-to-VoIP calls only. In this case, the device generates a dial tone when the telephone set connected to the endpoint telephone device comes off hook. The device continuously loops through its initialization detection routine searching for either VoIP or PSTN emergency service. If the endpoint telephone device detects that VoIP emergency service is available, it proceeds to state B. If the endpoint telephone device detects PSTN connectivity, it proceeds to state C. If the endpoint telephone device detects both VoIP emergency service and PSTN connectivity it proceeds to state D. 
     In state B, VoIP emergency service is available and PSTN emergency service is not available. Based on this availability, for a VoIP service provider required under the FCC Order to supply emergency service to the endpoint telephone device, the endpoint telephone device routes all calls, including emergency service calls, via the VoIP connection. The endpoint telephone device checks for PSTN connectivity on the telephone line interface either periodically or whenever the telephone set connected to the telephone set interface comes off hook. If the endpoint telephone device detects PSTN connectivity, it proceeds to state D. The endpoint telephone device also continuously checks the availability of VoIP emergency service. If VoIP emergency service becomes unavailable, the endpoint telephone device proceeds to state A. If VoIP emergency service becomes unavailable and the endpoint telephone device detects PSTN connectivity, the endpoint telephone device proceeds to state C. 
     In state C VoIP emergency service is not available and PSTN emergency service is available. Based on this availability, for a VoIP service provider required under the FCC Order to supply emergency service to the endpoint telephone device, the endpoint telephone device routes emergency service calls via the PSTN and may route any or all other calls via VoIP according to information provided by the VoIP service provider. The endpoint telephone device continuously checks the availability of VoIP emergency service. If the endpoint telephone device detects that VoIP emergency service is available, it proceeds to state D. The endpoint telephone device also continuously checks for PSTN connectivity. If the endpoint telephone device detects that the PSTN is no longer connected, the endpoint telephone device proceeds to state A. If the endpoint telephone device detects that the PSTN is no longer connected and VoIP emergency service becomes available, the endpoint telephone device proceeds to state B. 
     In state D VoIP emergency service is available and PSTN emergency service is available. Based on this availability, for a VoIP service provider required under the FCC Order to supply emergency service to the endpoint telephone device, the endpoint telephone device routes emergency service calls, and any and all other calls, either via the PSTN or via VoIP according to information provided by the VoIP service provider. The endpoint telephone device continuously checks the availability of VoIP emergency service. If the endpoint telephone device detects that VoIP emergency service is not available, the endpoint telephone device proceeds to state C. The endpoint telephone device also continuously checks for PSTN connectivity. If the endpoint telephone device detects that the PSTN is no longer connected, the endpoint telephone device proceeds to state B. If the endpoint telephone device detects that the PSTN is no longer connected and VoIP emergency service becomes unavailable, the endpoint telephone device proceeds to state A. 
       FIG. 8  is a table  800  illustrating two states of VoIP emergency service availability when the endpoint telephone device is in VoIP only mode or does not include a telephone line interface. The endpoint telephone device enters VoIP only mode when the VoIP service user selects the switch position that indicates to the endpoint telephone device that a telephone line will not be connected to the telephone line interface of the endpoint telephone device. Similarly, if the endpoint telephone device does not include a telephone line interface, it is not possible for a user to connect a telephone line to the endpoint telephone device via its telephone line interface. Therefore, PSTN emergency service over the telephone line interface is not only not available, but is also not possible, making states C and D irrelevant such that the device may only operate in state A or B. 
     In state A (which is similar to state A in  FIG. 7  except that there is no PSTN line connected to the endpoint telephone device, rather than there being a lack of emergency service on a connected telephone line), VoIP emergency service is not available. Based on this availability, for a VoIP service provider required under the FCC Order to supply emergency service to the endpoint telephone device, the endpoint telephone device is disabled for VoIP calling because it does not comply with the FCC Order. In state B (which is similar to state B in  FIG. 7  except that there is no PSTN line connected to the endpoint telephone device rather than there being a lack of emergency service on a connected telephone line), VoIP emergency service is available. Based on this availability, for a VoIP service provider required under the FCC Order to supply emergency service to the endpoint telephone device, the endpoint telephone device is enabled for VoIP calling because it complies with the FCC Order. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.