Abstract:
A method for configuring Internet Protocol Security (IPsec) protocol. The method includes configuring IPsec phase 1 Security Associations (SA) lifetimes and soft phase 2 SA lifetimes in a manner enabling efficient Dead Peer Detection recovery of secure communication between client and server in the event of a communication disruption and thereby preventing undesirable sustained periods of non-communication between client and server.

Description:
BACKGROUND 
     This invention relates to the field of communication protocols for authenticating, encrypting and decrypting digital information transferred via a stream of data packets. 
       FIG. 1  illustrates a communication system  100 . 
     As illustrated in the figure, communication system  100  includes a server  102 , a client  104 , a client  106  a client  108  and a router  110 . 
     Server  102  is arranged to be in two-way communication with router  110  by way of communication channel  112 . Client  104  is arranged to be in two-way communication with router  110  by way of communication channel  114 . Client  106  is arranged to be in two-way communication with router  110  by way of communication channel  116 . Client  108  is arranged to be in two-way communication with router  110  by way of communication channel  118 . 
     Server  102 , client  104 , client  106  and client  108  are any device operable to communicate with another device within an Internet Protocol (IP) communication system. Non-limiting examples of such devices include computers and phones. Router  110  manages communication between server  102  and clients  104 ,  106 , and  108  within an Internet Protocol (IP) communication system. Communication channels  112 ,  114 ,  116  and  118  may be wired or wireless communication channels. 
     Internet Protocol Security (IPsec) is a suite of industry standard protocols for securing Internet Protocol (IP) communications by authenticating, encrypting and decrypting each IP packet transferred between communication nodes. IPsec is being standardized by the Internet Engineering Task Force to incorporate secure communications to the widely used IP protocol. 
     IPsec provides cryptographic authentication and secure communications between two communication network nodes. IPsec supports communication between hosts, between Virtual Private Networks (VPNs) or between host and VPN. A VPN is a computer network in which communication is enabled via virtual circuits. A virtual circuit delivers communication information via packets of information. The packets of information can be routed and delivered to each destination independently from the all the other packets of information. 
     IPsec defines a set of operations for performing authentication, encryption and decryption for a stream of data comprised of packets. IPsec operates by adding new protocol headers to each transmitted packet. An authentication code is calculated for each packet using a secret key which is only known by the communicating parties and is transmitted within the packet. 
     IPsec implements Internet Security Association and Key Management Protocol (ISAKMP) for authentication, creation and management of Security Associations (SA), generation of keys and mitigation of threats. ISAKMP does not specify a specific key exchange, however, IPsec implements Internet Key Exchange (IKE) for creating SAs between communicating nodes. An IPsec SA determines the operations to be performed on each packet. Appropriate authentication, encryption and decryptions methods are determined by an SA. Additionally, an SA determines the parameters necessary for securely communicating between the nodes using cryptographic algorithms and cryptographic keys. 
     To simplify an explanation of conventional secure communication between two devices, an example of conventional secure communication between server  102  and client  104  will now be provided with reference to  FIGS. 2-5 . 
       FIG. 2  is a functional level diagram of conventional communication between server  102  and client  104 . 
     As illustrated in the figure, server  102  includes an application  202  and an IP kernel operating system stack  204 , which includes a Security Policy Database (SPD)  206 , a Security Association Database (SADB)  208 , an Internet Key Exchange (IKE) protocol portion  210  and an Internet Protocol security (IPsec) portion  212 . Client  104  includes an application  214  and an IP kernel operating system stack  216 , which includes a SPD  218 , a SADB  220 , an IKE protocol portion  222  and an IPsec portion  226 . 
     SADB  208  is a database that contains parameters associated with each active SA, as will be explained in more detail below, and is populated automatically from IKE protocol portion  210 . Similarly, SADB  220  is a database that contains parameters associated with each active SA, and is populated automatically from IKE protocol portion  222 . 
     SPD  206  is a database that specifies filter lists and associated settings that determine the status of all inbound or outbound IP traffic for server  102 . Inbound packets are checked to ensure that they have been secured according to policy. Outbound packets are permitted, blocked, or secured, according to policy. For secured traffic, the security policy that is used is a negotiated SA, which is stored in SADB  208 . Similarly, SPD  218  is a database that specifies filter lists and associated settings that determine the status of all inbound or outbound IP traffic for client  104 . Inbound packets are checked to ensure that they have been secured according to policy. Outbound packets are permitted, blocked, or secured, according to policy. For secured traffic, the security policy that is used is the negotiated SA, as will be described in greater detail below, and which is stored in SADB  220 . 
     IKE protocol portion  210  receives authentication and security settings from IPsec portion  212  and waits for requests to negotiate SAs for server  102 . When IKE protocol portion  210  receives a request to negotiate an SA from IPsec portion  212 , IKE protocol portion  210  negotiates both phase 1 SAs and phase 2 SAs with IKE protocol potion  222  based on the request of IPsec portion  212 . After IKE protocol portion  210  has negotiated an SA, IKE protocol portion  210  sends the SA settings to IPsec portion  212 . IKE protocol portion  222  is operable to perform the same functions for client  104 . 
     IPsec portion  212  retrieves IPSec policy from an Active Directory domain (not shown), a configured set of local policies (not shown), or a local cache (not shown) for server  102 . IPsec portion  212  then distributes authentication and security settings to IKE protocol portion  210 . IPsec portion  226  is operable to perform the same functions for client  104 . 
     Before client  104  can securely communicate with server  102 , a secure communication link must be established. A conventional method of establishing a secure communication link between client  104  and server  102  will now be discussed. 
     Presume, in this example, that client  104  initiates communication with server  102 . First application  214  sends a first packet to OS stack  216 . IPsec portion  226  intercepts the packet and initiates a negotiation with server  102 . IKE protocol portion  222  of client  104  then performs negotiation with IKE protocol portion  210  of server  102 . A more detailed discussion of secure communication will now be described. 
     IPsec includes two phases of setup during the establishment of a link between communication nodes. In a phase 1 SA, the security protocol and IKE are negotiated between peers for protecting all SAs and ISAKMP. Following the phase 1 SA, phase 2 SAs are implemented. A single phase 2 SA may be implemented or multiple simultaneous phase 2 SAs may be implemented. In a phase 2 SA, an SA is established between peers. 
     The lifetime of phase 1 SA is controlled by a finite timer. In phase 2 SA, the lifetime of SAs are controlled by either a finite timer or by an amount of data transferred between peers. 
     The finite timer methodology for controlling SAs is most commonly implemented for IPsec. A finite timer is initialized to a specific time value with the expiration of the timer indicating a specific action is to be performed by the communicating peers. Two types of finite timers are implemented for phase 2 SA: soft-lifetime timers and hard-lifetime timers. These timers are generated in the IPsec portion of the device initiating the communication, in this example, IPsec portion  226  of client  104 . Further, once generated and negotiated, these timers are stored in the IPsec portions of each device, in this example, IPsec portion  226  of client  104  and IPsec portion  212  of server  102 . 
     Phase 2 SA hard-lifetime timer and the initial soft-lifetime timer start at approximately the same time. In general, the time value of the hard-lifetime timer is configured to be longer than the time value of the soft-lifetime timer. Therefore, when the initial soft-lifetime timer expires, the hard-lifetime timer continues for a predetermined amount of time. Subsequent soft-lifetime timers may be initiated following the expiration of a soft-lifetime timer. Termination of the first soft-lifetime timer while the hard-lifetime timer continues, enables establishment of a new phase 2 SA between peers. Termination of a hard-lifetime timer of a phase 2 SA while a phase 1 SA is active, results in the replacement of the existing phase 2 SA with a new phase 2 SA. 
     Expiration of a phase 1 SA does not automatically result in the creation of a new SA, as a new SA may only be established after a request to establish a new phase 1 SA. 
     To facilitate discussion,  FIG. 3  illustrates a conventional IPsec communication process  300 . 
     In the figure, a y-axis  302  represents units of time increasing with progression from the top of the figure to the bottom of the figure. An x-axis  304  represents exchanges of communication between a client  104  and a server  102  via a communication channel  310 . 
     Before conventional IPsec communication process  300  is discussed in detail, please consider the following introduction to some aspects. 
     Bi-directional vertical arrows  320 ,  322 ,  376  and  378  represent phase 1 SA timers. A phase 1 SA timer counts down the time value of a phase 1 SA. In the figure, bi-directional vertical arrows  320 ,  322 ,  376  and  378  are illustrated with the same weight to represent a similar function. 
     Bi-directional vertical arrows  332 ,  334 ,  352 ,  354 ,  388  and  390  represent soft phase 2 SA timers. A phase 2 SA timer is timer that counts down the time value of a phase 2 SA. A soft-lifetime timer is conventionally set to a portion of the phase 2 SA timer, e.g., 80%. In the figure, bi-directional vertical arrows  332 ,  334 ,  352 ,  354 ,  388  and  390  are illustrated with the same weight to represent a similar function. 
     Unidirectional horizontal arrows  314  and  374  represent phase 1 SA negotiation initiations. A phase 1 SA negotiation initiation is a communication protocol wherein client  104  contacts server  102  to exchange security keys, authentication information and phase 1 SA time values. In the figure, unidirectional horizontal arrows  314  and  374  are illustrated with the same weight to represent a similar function. 
     Bi-directional horizontal arrows  326  and  382  represent phase 1 SA negotiation completions. In the figure, bi-directional horizontal arrows  326  and  382  are illustrated with the same weight to represent a similar function. 
     Unidirectional horizontal arrows  328 ,  350  and  386  represent phase 2 SA negotiation initiations. A phase 2 SA negotiation initiation is a communication protocol wherein client  104  contacts server  102  to exchange updated security keys, updated authentication information and phase 2 SA hard-lifetime values. In the figure, unidirectional horizontal arrows  328 ,  350  and  386  are illustrated with the same weight to represent a similar function. 
     Bi-directional horizontal arrows  338 ,  358  and  393  represent phase 2 SA negotiation completions. In the figure, bi-directional horizontal arrows  338 ,  358  and  393  are illustrated with the same weight to represent a similar function. 
     Bi-directional horizontal arrows  340 ,  362  and  394  represent link initiations. A link initiation is the start of a secure communication channel, wherein client  104  and server  102  may communicate with one another in an encrypted manner. In the figure, bi-directional horizontal arrows  340 ,  362  and  394  are illustrated with the same weight to represent a similar function. 
     Bi-directional dotted horizontal arrows  346  and  366  represent link completions. A link completion is the end of a secure communication channel, wherein client  104  and server  102  may no longer securely communicate with one another. In the figure, bi-directional horizontal dotted arrows  346  and  366  are illustrated with the same weight to represent a similar function. 
     Communication between client  104  and server  102  is bi-directional, i.e., client  104  can initiate and transfer data to server  102 , and server  102  can initiate and transfer data to client  104 . 
     Now for a more detailed discussion of conventional IPsec communication process  300 . 
     Client  104  seeking to communicate securely with server  102  transmits a phase 1 SA negotiation initiation  314  to server  102  via communication channel  310  at a time  312 . Phase 1 SA negotiation initiation  314  will arrive at server  102  at a time  316  after experiencing a channel path delay  318 . To simplify  FIG. 3 , the channel path delays between client  104  and server  102  are not shown for every instance of communication between client  104  and server  102 . 
     Following phase 1 SA negotiation initiation  314 , client  104  and server  102  negotiate the value of a phase 1 SA timer  320  and a phase 1 SA timer  322 . The values for phase 1 SA timer  320  and phase 1 SA timer  322  are identical and client  104  is responsible for maintaining phase 1 SA timer  320  and server  102  is responsible for maintaining phase 1 SA timer  322 . 
     Following phase 1 SA negotiation initiation  314 , client  104  and server  102  negotiate a method for Internet Key Exchange (IKE) for performing secure communication between client  104  and server  102  via communication channel  310 . The phase 1 SA negotiation between client  104  and server  102  is completed at a time  324  and is represented by a phase 1 SA negotiation completion  326 . In conjunction with phase 1 SA negotiation completion  326 , client  104  initializes phase 1 SA timer  320  and server  102  initializes phase 1 SA timer  322 . 
     Following phase 1 SA negotiation completion  326 , client  104  communicates a phase 2 SA negotiation initiation  328  to server  102  at a time  330 . Phase 2 SA negotiation initiation  328  begins the process of negotiating an IPsec SA. 
     During the negotiation of IPsec SA, client  104  and server  102  agree on the protocol for communication between client  104  and server  102 . 
     In one conventional communication method, the hard lifetime of phase 2 SA is determined during the IPSec SA negotiation. The value of a soft phase 2 SA timer  332  and a soft phase 2 SA timer  334  are derived from the hard lifetime later. For example, in one example IPsec-tool that implements IKE, the soft lifetime of phase 2 SA is set to 80% of the hard phase 2 SA lifetime. The values for soft phase 2 SA timer  332  and soft phase 2 SA timer  334  are identical. 
     During the negotiation of IPsec SA, client  104  and server  102  agree on a shared Data Encryption Standard (DES) or Triple Data Encryption Algorithm (TDEA) key. 
     DES is a methodology or algorithm for encrypting data. DES is based on a secret key algorithm using a 56-bit key. TDEA performs three iterations of DES methodology to each set of data to be communicated for increased security between communication nodes. 
     Negotiation of IPsec SA is completed at a time  336  and is represented by a phase 2 SA negotiation completion  338 . Client  104  initiates soft phase 2 SA timer  332  and server  102  initiates soft phase 2 SA timer  334  in conjunction with phase 2 SA negotiation completion  338 . 
     Following phase 2 SA negotiation completion  338 , a link initiation  340  occurs at a time  342  initiating secure data communication between client  104  and server  102  until a time  344  as represented by a link completion  346 . 
     At a time  348 , client  104  seeks to negotiate a new IPsec SA with server  102  and communicates a phase 2 SA negotiation initiation  350  to server  102 . 
     During the negotiation of the new IPsec SA, client  104  and server  102  agree on the protocol for communication and a shared DES or TDEA key. At a time  356 , IPsec SA negotiation is complete and is represented by a phase 2 SA negotiation completion  358 . After phase 2 SA negotiation completion  358 , client  104  derives and implements soft phase 2 SA timer  352  and server  102  derives and implements soft phase 2 SA timer  354 . 
     Between a time  360 , as represented by a link initiation  362 , and a time  364 , as represented by a link completion  366 , secure data communication occurs between client  104  and server  102 . 
     At a time  368 , phase 2 SA communications between client  104  and server  102  are terminated with the expiration of soft phase 2 SA timer  352  and soft phase 2 SA timer  354 . 
     At a time  370 , client  104  seeks to communicate with server  102 . At this point, since phase 1 SA timer  320  and phase 1 SA timer  322  both expired previously at a time  372 , client  104  must seek to communicate with server  102  via a new phase 1 SA as represented by a phase 1 SA negotiation initiation  374 . Following phase 1 SA negotiation initiation  374 , client  104  and server  102  negotiate the value of a new phase 1 SA timer  376  and a phase 1 SA timer  378 . At a time  380 , phase 1 SA is complete as represented by a phase 1 SA negotiation completion  382 , and client  104  initiates phase 1 SA timer  376  and server  102  initiates phase 1 SA timer  378 . 
     At a time  384 , client  104  communicates a phase 2 SA negotiation initiation  386  with server  102  initiating negotiation of IPsec SA. During the negotiation of IPsec SA, client  104  and server  102  agree on the protocol for communication. At a time  392 , negotiation of IPsec SA is complete and is represented by a phase 2 SA negotiation completion  393 . After phase 2 SA negotiation completion  393 , client  104  derives and implements soft phase 2 SA timer  388  and server  102  derives and implements soft phase 2 SA timer  390 . The values for soft phase 2 SA timer  388  and soft phase 2 SA timer  390  are identical. 
     Following phase 2 SA negotiation completion  393 , a link initiation  394  occurs at a time  396  and secure data communication between client  104  and server  102  ensues. 
     From the discussion above, in this example, client  104  and server  102  may communicate over a secure channel between link initiation  340  at time  342  and link completion  346  at time  344 . Further, in this example, client  104  and server  102  may communicate over a secure channel between link initiation  362  at time  360  and link completion  366  at time  364 . 
     At time  364 , although soft phase 2 SA timer  352  and soft phase 2 SA timer  354  continue, phase 1 SA timer  320  and phase 1 SA timer  322  have timed out. Accordingly client  104  and server  102  may not communicate over a secure channel until a new phase 1 SA and a new phase 2 SA are negotiated and completed. In other words, in this example, after time  364 , client  104  and server  102  may not communicate over a secure channel until after link initiation  394  at time  396 . 
       FIG. 3  illustrates a conventional implementation of secure communication between client  104  and server  102  via IPsec. The interaction and related timing necessary for client  104  and server  102  to communicate in a secure manner via IPsec is illustrated. The communication between client  104  and server  102  is not disrupted in any manner and completes communication successfully. 
     IPsec provides an optional mechanism, Dead Peer Detection (DPD), for recovering an SA which has been interrupted as a result of the loss of a peer. DPD relies on the IKE Notify messages via phase 1 SA for detecting the interruption of an SA. IKE Notify messages provide a mechanism for IPsec nodes to query and communicate status information. 
     A common occurrence for a disruption in communication results after the re-initialization of a peer. A node detecting the interruption or re-initialization of a peer via DPD can re-initialize the SA between the peers with recovery of secure communication occurring very quickly. 
     However, a problem with IPsec has been observed when a peer is reinitialized during the process of secure communication via an SA in which a phase 1 SA no longer exists as a result of the expiration of a phase 1 SA timer. Since a phase 1 SA does not exist, DPD cannot be implemented and the secure communications between the peers cannot be recovered until the soft phase 2 SA timer expires, which in some instances can be several hours. 
     To facilitate discussion of the loss of synchronization between peers with respect to phase 1 SA and phase 2 SA,  FIG. 4  illustrates the conventional relationship of phase 1 SAs, phase 2 SAs, phase 1 SA timers, soft phase 2 SA timers and hard phase 2 SA timers between a client and a server.  FIG. 4  illustrates how sustained and long periods of time can be experienced in which DPD mechanism cannot be used for detecting and restoring communication between peers as a result of the non-existence or expiration of a phase 1 SA. 
     Negotiation of independent phase 1 SA timers and soft phase 2 SA timers may create periods during which a phase 1 SA does not exist between peers. In the event a peer attempts to reinitialize, after communication is disrupted and a phase 1 SA does not exist, the re-initialization event cannot be consummated and resulting in extended interruptions of secure communication between the peers for an extended period of time. 
     There is a problem associated with conventional implementation of IPsec discussed above with respect to  FIG. 1 , which will now be described with reference to  FIG. 4  and  FIG. 5 . 
     An x-axis  400  of  FIG. 4  represents units of time, increasing with progression from left to right on the figure. 
     Before  FIG. 4  is discussed in detail, please consider the following introduction to some aspects. 
     The area below x-axis  400  illustrates phase 1 SAs between client  104  and server  102 . The area above x-axis  400  illustrates phase 2 SAs between client  104  and server  102 . 
     Rectangular blocks  404 ,  410 ,  424  and  434  represent phase 2 SAs. Horizontal arrows  334 ,  412 ,  428  and  440  represent soft phase 2 SA timers. Horizontal arrows  406 ,  414 ,  432  and  436  represent hard phase 2 SA timers. 
     Rectangular blocks  402 ,  420  and  448  represent phase 1 SAs. Horizontal arrows  322 ,  422  and  450  represent phase 1 SA timers. Horizontal arrows  418  and  446  represent unavailable DPD. 
     In order to simplify  FIG. 4 , all timers will be referenced with respect to server  102  illustrated in  FIG. 3 . 
     Now for a more detailed discussion of  FIG. 4 . 
     At time  324 , a phase 1 SA  402  is initiated between client  104  and server  102 . The lifetime of phase 1 SA  402  is negotiated between client  104  and server  102  and is represented by phase 1 SA timer  322 . 
     At time  336 , following initiation of phase 1 SA  402 , a phase 2 SA  404  is initiated between client  104  and server  102 . The lifetime of phase 2 SA  404  is negotiated between client  104  and server  102 . During negotiation of phase 2 SA  404 , the time value of hard phase 2 SA timer  406  is negotiated and the time value of soft phase 2 SA timer  334  is derived from hard phase 2 SA timer  406 . In this example, phase 2 SA  404  has a hard phase 2 SA timer  406  and soft phase 2 SA timer  334 . 
     Soft phase 2 SA timer  334  is initiated at time  336  and expires at a time  408 . Soft phase 2 SA timer  334  determines the time at which a new phase 2 SA must be initiated to retain secure communication between client  104  and server  102 . Hard phase 2 SA timer  406  is initiated at time  336  and expires at a time  407 . Hard phase 2 SA timer  406  determines the lifetime of phase 2 SA  404 . 
     At time  408 , soft phase 2 SA timer  334  expires. At time  408 , and prior to the expiration of hard phase 2 SA timer  406 , a phase 2 SA  410  is initiated between client  104  and server  102 . Phase 2 SA  410  has a soft phase 2 SA timer  412  and a hard phase 2 SA timer  414 . During the negotiation of phase 2 SA  410 , the time value for soft phase 2 SA timer  412  and the time value for hard phase 2 SA timer  414  are determined. 
     Soft phase 2 SA timer  412  is initiated at time  408  and expires at a time  416 . Soft phase 2 SA timer  412  determines the time at which a new phase 2 SA must be initiated to retain secure communication between client  104  and server  102 . Hard phase 2 SA timer  414  is initiated at time  408  and expires at a time  409 . Hard phase 2 SA timer  414  determines the lifetime of phase 2 SA  410 . 
     At time  372 , phase 1 SA timer  322  expires, resulting in the termination of phase 1 SA  402 . The time period between the expiration of phase 1 SA timer  322  at time  372  and time  416  represented as the initiation of a new phase 1 SA  420  is denoted as an unavailable DPD  418 . During the time period as referenced by unavailable DPD  418 , an interruption occurring between client  104  and server  102  will result in a lack of secure communication occurring between client  104  and server  102  until the start of phase 1 SA  420  initiated at time  416 . 
     The lifetime of phase 1 SA  420  is negotiated between client  104  and server  102  and is represented by a phase 1 SA timer  422 . 
     Following the initiation of phase 1 SA  420  at time  416 , a phase 2 SA  424  is initiated between client  104  and server  102  at a time  426 . Phase 2 SA  424  has a soft phase 2 SA timer  428  and a hard phase 2 SA timer  432 . During the negotiation of phase 2 SA  424 , the time value for hard phase 2 SA timer  432  is negotiated. The time value for soft phase 2 SA timer  428  is derived from the negotiated time value from hard phase 2 SA timer  432 . 
     Soft phase 2 SA timer  428  is initiated at time  426  and expires at a time  430 . Soft phase 2 SA timer  428  determines the time at which a new phase 2 SA must be initiated to retain secure communication between client  104  and server  102 . Hard phase 2 SA timer  432  is initiated at time  426  and expires at a time  444 . Hard phase 2 SA timer  432  determines the lifetime of phase 2 SA  424 . 
     At time  430 , soft phase 2 SA timer  428  of phase 2 SA  424  expires, enabling initiation between client  104  and server  102  of a phase 2 SA  434 . Phase 2 SA  434  has a soft phase 2 SA timer  440  and a hard phase 2 SA timer  436 . During the negotiation of phase 2 SA  434 , the time value for hard phase 2 SA timer  436  is negotiated. Then the time value for soft phase 2 SA timer  440  is derived from the time value for hard phase 2 SA timer  436 . 
     Soft phase 2 SA timer  440  is initiated at time  430  and expires at a time  442 . Soft phase 2 SA timer  440  determines the time at which a new phase 2 SA must be initiated to retain secure communication between client  104  and server  102 . Hard phase 2 SA timer  436  is initiated at time  430  and expires at a time  438 . Hard phase 2 SA timer  436  determines the lifetime of phase 2 SA  434 . 
     At time  444 , phase 1 SA timer  422  expires terminating phase 1 SA  420 . The time period from time  444  to time  442  represents a period in which a disruption between client  104  and server  102  cannot be resolved via DPD. The disruption cannot be resolved between time  444  and time  442  since a phase 1 SA is not available. The time period during which the disruption cannot be resolved is designated as an unavailable DPD  446 . A disruption occurring during unavailable DPD  446  results in a loss of secure communication between client  104  and server  102  which cannot be restored until initiation of a new phase 1 SA as represented by a phase 1 SA  448  starting at time  442  and expiring at a time  452 . The lifetime of phase 1 SA  448  is negotiated by client  104  and server  102  and is denoted as a phase 1 SA timer  450  which starts at time  442  and expires at time  452 . 
       FIG. 4  illustrates the relationship between phase 1 SA and phase 2 SA of a communications exchange between client  104  and server  102 .  FIG. 4  highlights periods of time denoted as unavailable DPD  418  and unavailable DPD  446  during which an occurrence of a communication disruption would result loss of secure communication between client  104  and server  102 . A disruption during which DPD was not available could cause the communication between client  104  and server  102  to be severely impeded and could require a significant amount of time for recovery. 
     To facilitate discussion of a loss of secure communication between client  104  and server  102 ,  FIG. 5  illustrates a link interruption  500 , a simplified IPsec communication exchange experiencing an occurrence of communication disruption. 
     A y-axis  502  of  FIG. 5  is illustrated by variable t in units of time with an increase in variable t as movement progresses from the top of the page to the bottom of the page. An x-axis  504  represents exchanges of communication between client  104  and server  102  via communication channel  310 . Communication channel may include two channels. One channel is used to transmit user data and uses a phase 2 SA. The other channel depends on the phase 1 SA for a phase 2 SA negotiation message and DPD messages. 
     Before conventional IPsec link interruption  500  is discussed in detail, please consider the following introduction to some aspects. 
     Bi-directional vertical arrows  522  and  524  represent phase 1 SA timers. A phase 1 SA timer counts down the time value of a phase 1 SA. In the figure, bi-directional vertical arrows  522  and  524  are illustrated with the same weight to represent a similar function. 
     Bi-directional vertical arrows  534  and  536  represent soft phase 2 SA timers. A soft phase 2 SA timer is a lifetime timer that counts down the time value of a phase 2 SA. A soft-lifetime timer is conventionally set to a portion of the phase 1 SA timer, e.g., 80%. In the figure, bi-directional vertical arrows  534  and  536  are illustrated with the same weight to represent a similar function. 
     Unidirectional horizontal arrow  520  represents phase 1 SA negotiation initiation. A phase 1 SA negotiation initiation is a communication protocol wherein client  104  contacts server  102  to exchange security keys, authentication information and phase 1 SA time values. 
     Bi-directional horizontal arrow  528  represents phase 1 SA negotiation completion. 
     Unidirectional horizontal arrow  530  represents phase 2 SA negotiation initiation. A phase 2 SA negotiation initiation is a communication protocol wherein client  104  contacts server  102  to exchange updated security keys, updated authentication information, phase 2 SA soft-lifetime time values and phase 2 SA hard-lifetime time values. 
     Bi-directional horizontal arrow  540  represents a phase 2 SA negotiation completion. 
     Bi-directional horizontal arrow  542  represents a link initiation. A link initiation is the start of a secure communication channel, wherein client  104  and server  102  may securely communicate with one another. 
     Bi-directional horizontal dotted arrow  514  represents an unsuccessful link completion. An unsuccessful link completion is the end of a secure communication channel, wherein communication between client  104  and server  102  was unsuccessful and incomplete and client  104  and server  102  may no longer securely communicate with one another until communication has been reestablished. 
     The loss of secure communication is due to the disruption for server  102  occurring at a time  506  designated as a communication disruption  508 . 
     The operation of  FIG. 5  is identical to  FIG. 3  until the occurrence of communication disruption  508  at time  506 . Communication disruption  508  occurs after the expiration of phase 1 SA timer  322  maintained by server  102 . Communication disruption  508  also occurs after the expiration of phase 1 SA timer  320  maintained by client  104 . Communication disruption  508  results in the premature termination of a soft phase 2 SA timer  510 . 
     Since a phase 1 SA does not exist at time  506  with the occurrence of communication disruption  508 , client  104  is not aware of communication disruption  508  and continues to transmit data via communication channel  310 . Server  102  ignores or discards the secure information transmitted by client  104  since server  102  does not have a phase 1 SA and phase 2 SA in operation due to communication disruption  508 . At a time  512 , client  104  completes transmitting secure data to server  102  which is designated as an unsuccessful link completion  514 . The time period between time  506  and time  512 , during which server  102  discards the data transmitted by client  104 , is designated as a discarded data  516 . 
     Following the expiration of soft phase 2 SA timer  352  at time  368 , a new phase 1 SA is initiated at a time  518  and is designated as a phase 1 SA negotiation initiation  520 . 
     Following phase 1 SA negotiation initiation  520 , client  104  and server  102  negotiate the value of a phase 1 SA timer  522  and a phase 1 SA timer  524 . The values for phase 1 SA timer  522  and phase 1 SA timer  524  are identical and client  104  is responsible for maintaining phase 1 SA timer  522  and server  102  is responsible for maintaining phase 1 SA timer  524 . 
     Following phase 1 SA negotiation initiation  520 , client  104  and server  102  negotiate a method for Internet Key Exchange (IKE) to perform secure communication between client  104  and server  102  via communication channel  310 . The phase 1 SA negotiation between client  104  and server  102  is completed at a time  526  and is represented by a phase 1 SA negotiation completion  528 . 
     Following phase 1 SA negotiation completion  528 , client  104  communicates a phase 2 SA negotiation initiation  530  to server  102  at a time  532 . Phase 2 SA negotiation initiation  530  begins the process of negotiating an IPsec SA. 
     During the negotiation of IPsec SA, client  104  and server  102  agree on the protocol for communication to occur between client  104  and server  102 . 
     The value of a soft phase 2 SA timer  534  and a soft phase 2 SA timer  536  are derived after the negotiation of hard phase 2 SA timers of IPsec SA. The values for soft phase 2 SA timer  534  and soft phase 2 SA timer  536  are identical. 
     During the negotiation of IPsec SA, client  104  and server  102  agree on a shared DES or TDEA key. 
     Negotiation of IPsec SA is completed at a time  538  and is represented by a phase 2 SA negotiation completion  540 . Client  104  initiates soft phase 2 SA timer  534  and server  102  initiates soft phase 2 SA timer  536  upon phase 2 SA negotiation completion  540 . 
     Following phase 2 SA negotiation completion  540 , a link initiation  542  occurs at a time  544  with secure data communication occurring between client  104  and server  102  following link initiation  542 . 
     As illustrated in  FIG. 5 , a disruption in service during secure communications via IPsec can result in prolonged periods of time in which communication cannot be performed between client  104  and server  102  as represented by discarded data  516 . 
     When server  102  crashes, there is a disruption of service. If client  104  crashes or reboots, client  104  will try to establish phase 1 and phase 2 SAs immediately when it comes back. In the case where server  102  crashes, client  104  will continue to use the existing phase 2 SAs to transmit data until the existing phase 2 SAs reach their soft lifetime and new phase 1 and phase 2 SAs are established. 
     A problem with conventional IPsec methods occurs when a service disruption occurs, e.g., the server  102  crashes, and there is no phase 1 SA available on server  102  for recovery of communications. If the lifetimes of phase 1 and phase 2 are chosen independently, there may be times in which a phase 1 SA does not exist and secure communications cannot be recovered until an existing phase 2 SA reaches a soft-lifetime termination. Following the soft-lifetime termination, client  104  and server  102  can renegotiate, resynchronize and continue with secure communication. 
     What is needed is a method for communication via IPsec that prevents prolonged periods of non-communication due to service disruptions. 
     BRIEF SUMMARY 
     An aspect of the present invention provides a system and method for communication via IPsec that prevents prolonged periods of non-communication due to service disruptions. 
     In accordance with an aspect of the present invention, a method is provided for communicating between a first communication device and a second communication device. The method comprises establishing a phase 1 security association between the first communication device and the second communication device and establishing a phase 2 security association between the first communication device and the second communication device. The phase 1 security association has a phase 1 SA timer corresponding to a time value of the phase 1 security association. The phase 2 security association has a soft phase 2 security association timer and a hard phase 2 security association timer. The soft phase 2 security association timer corresponds to a time value of the soft phase 2 security association. The hard phase 2 security association timer corresponds to a time value of the hard phase 2 security association. The time value of the soft phase 2 security association is less than the time value of the hard phase 2 security association. The time value of the phase 1 security association is an integer multiple of the time value of the soft phase 2 security association. 
     Additional advantages and novel features of the invention are set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate an exemplary embodiment of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
         FIG. 1  illustrates a prior art communication system; 
         FIG. 2  is a functional level diagram of a prior art communication between a server and a client; 
         FIG. 3  illustrates a prior art IPsec communication link protocol; 
         FIG. 4  illustrates a prior art relationship diagram between phase 1 SA and phase 2 SA resulting in periods of time when DPD is unavailable for secure communication recovery; 
         FIG. 5  illustrates a prior art IPsec link communication protocol with a disruption of secure communication resulting in a prolonged period of non-communication; 
         FIG. 6  is a functional level diagram of communication between a server and a client in accordance with an aspect of the present invention; 
         FIG. 7  illustrates, in accordance with an embodiment of the present invention, the recovery of secure communications for an IPsec link communication protocol via DPD in the event of a communication disruption; and 
         FIG. 8  illustrates, in accordance with an embodiment of the present invention, a relationship diagram between phase 1 SA and phase 2 SA in which DPD is always available for recovery of secure communications in the event of a communication disruption. 
     
    
    
     DETAILED DESCRIPTION 
     An aspect of the present invention provides a method for configuring phase 1 SA and phase 2 SA timing agreements between server and client which prevents prolonged service disruptions. These prolonged service disruptions are avoided by initializing timing agreements between server and client in such a way to uniformly enable the existence of a phase 1 SA during secure communication which allows recovery from a service disruption via DPD. 
     In accordance with an aspect of the present invention, phase 1 and phase 2 lifetimes are configured using the following equation:
 
Phase 1 lifetime=(Phase 2 soft-lifetime)* N,   (1)
 
where N is a positive integer.
 
     Equation (1) configures the expiration of phase 1 SA and phase 2 SA soft-lifetimes to occur simultaneously, which enables a phase 1 SA to be uniformly available during secure communications, thus enabling efficient recovery from service disruptions via DPD and further enabling the continuation of secure communications. 
     In an example embodiment, the expiration of phase 1 SA and phase 2 SA soft-lifetimes are configured in accordance with equation (1) after every phase 2 negotiation between a client and a server. A client and a server may configure the expiration of phase 1 SA and phase 2 SA soft-lifetimes in accordance with equation (1) and adjust timing agreements as necessary. 
     An aspect of the present invention will now be discussed below with reference to  FIGS. 6-8 . 
       FIG. 6  is a functional level diagram of communication between server  606  and client  604  in accordance with an aspect of the present invention. 
       FIG. 6  differs from the functional level diagram of the convention communication discussed above with reference to  FIG. 4 , in that IPsec portion  412  and IPsec portion  426  have been replaced with IPsec portion  608  and IPsec portion  610 , respectively. More specifically, in accordance with an aspect of the present invention, at least one of IPsec portion  608  and IPsec portion  610  will be operable to configure phase 1 and phase 2 lifetimes using equation (1) discussed above. 
     Before client  604  can securely communicate with server  602 , a secure communication link must be established. A method of establishing a secure communication link between client  604  and server  602  in accordance with an aspect of the present invention will now be discussed. 
     Presume, in this example, that client  604  initiates communication with server  602 . First application  214  sends a first packet to OS stack  216 . IPsec portion  608  intercepts the packet and initiates a negotiation with server  602 . IKE protocol portion  222  of client  604  then performs negotiation with IKE protocol portion  210  of server  602 . A more detailed discussion of secure communication will now be described. 
       FIG. 7  illustrates, in accordance with an embodiment of the present invention, a link communication  700 , a simplified IPsec communication exchange. A y-axis  702  represents the variable t in units of time with variable t increasing with progression from the top of the page to the bottom of the page. An x-axis  704  represents exchanges of communication between client  604  and server  602  via communication channel  310 . 
     Before conventional IPsec link communication  700  is discussed in detail, please consider the following introduction to some aspects. 
     Bi-directional vertical arrows  708 ,  710 ,  734  and  736  represent phase 1 SA timers. A phase 1 SA timer counts down the time value of a phase 1 SA. In the figure, bi-directional vertical arrows  708 ,  710 ,  734  and  736  are illustrated with the same weight to represent a similar function. 
     Bi-directional vertical arrows  738  and  740  represent soft phase 2 SA timers. A phase 2 SA timer is a hard-lifetime timer that counts down the time value of a phase 2 SA. A soft-lifetime timer is conventionally set to a portion of the hard-lifetime timer, e.g., 80%. In the figure, bi-directional vertical arrows  738  and  740  are illustrated with the same weight to represent a similar function. 
     Unidirectional horizontal arrows  706  and  732  represent phase 1 SA negotiation initiations. A phase 1 SA negotiation initiation is a communication protocol wherein client  604  contacts server  602  to exchange security keys, authentication information and phase 1 SA time values. In the figure, unidirectional horizontal arrows  706  and  732  are illustrated with the same weight to represent a similar function. 
     Bi-directional horizontal arrows  712  and  744  represent phase 1 SA negotiation completions. In the figure, bi-directional horizontal arrows  712  and  744  are illustrated with the same weight to represent a similar function. 
     Unidirectional horizontal arrow  748  represents a phase 2 SA negotiation initiation. A phase 2 SA negotiation initiation is a communication protocol, wherein client  604  contacts server  602  to exchange updated security keys, updated authentication information, phase 2 SA soft-lifetime time values and phase 2 SA hard-lifetime time values. 
     Bi-directional horizontal arrow  752  represents a phase 2 SA negotiation completion. 
     Bi-directional horizontal arrow  754  represents a link initiation. A link initiation is the start of a secure communication channel, wherein client  604  and server  602  may securely communicate with one another. 
     Bi-directional horizontal dotted arrow  726  represents a link completion. A link completion is the end of a secure communication channel, wherein client  604  and server  602  may no longer securely communicate with one another. 
     A large portion of the elements of  FIG. 7  are identical to  FIG. 3 . Some of the identical elements between  FIG. 3  and  FIG. 7  are not be included in the discussion of  FIG. 7 . At time  312 , client  604  communicates a phase 1 SA negotiation initiation  706  to server  602 . Following phase 1 SA negotiation initiation  706 , an embodiment of this invention is deployed during the negotiation of phase 1 SA, as client  604  configures a phase 1 SA timer  708  as a positive integer multiple of soft phase 2 SA timer  332 . For this particular embodiment of the invention, phase 1 SA timer  708  is configured as two times the value, or N equal to 2, of soft phase 2 SA timer  332 . Additionally, an embodiment of this invention is deployed during the negotiation of first SA, as server  602  configures a phase 1 SA timer  710  as a positive integer multiple of soft phase 2 SA timer  334 . For this particular embodiment of the invention, phase 1 SA timer  710  is configured as two times the value, or N equal to 2, of soft phase 2 SA timer  334 . 
     The illustration of link communication  700  as shown in  FIG. 7  is not to scale. The value of phase 1 SA timer  708  does not appear to be twice the value of soft phase 2 SA timer  332 , however, the period of time between time  324  and time  336  is very small relative to the length of time between time  336  and time  348  as represented by soft phase 2 SA timer  332 . 
     The phase 1 SA negotiation between client  604  and server  602  is completed at time  324  and is represented by a phase 1 SA negotiation completion  712 . In conjunction with phase 1 SA negotiation completion  712 , client  604  initiates phase 1 SA timer  708  and server  602  initiates phase 1 SA timer  710 . 
     At time  506 , communication disruption  508  is experienced by server  602 . After server  602  recovers or reinitializes, client  604  detects communication disruption  508  using IKE Notify messages via phase 1 SA protocol. As a result of the IKE Notify messages, client  604  and server  602  initiate a DPD  714  at a time  716  in order to restore server  602  to its state or condition prior to communication disruption  508 . At a time  718  secure communications are restored between client  604  and server  602  as represented by a communication restoration  720 . 
     During the time period between time  506  and time  718 , secure data is not communicated between client  604  and server  602  and is represented as a discarded data  722 . The length of time for discarded data  722  is significantly smaller than the length of time as represented by discarded data  516  as illustrated in  FIG. 5 . The reduction in time between discarded data  722  and discarded data  516  is a direct result of an implementation of an embodiment of this invention. 
     Following communication restoration  720 , the secure transmission of the data between client  604  and server  602  is completed at a time  724  as referenced by a successful link completion  726 . 
     Following the simultaneous expiration of phase 1 SA timer  708 , phase 1 SA timer  710 , soft phase 2 SA timer  352  and soft phase 2 SA timer  354  at a time  728 , client  604  seeks to communicate with server  602  at a time  730 . Since neither a phase 1 SA nor a phase 2 SA exists at time  730 , a phase 1 SA is initiated between client  604  and server  602  at time  730  as represented by a phase 1 SA negotiation initiation  732 . 
     Following phase 1 SA negotiation initiation  732 , client  604  and server  602  negotiate the value of a phase 1 SA timer  734  and a phase 1 SA timer  736 . Phase 1 SA timer  734  and phase 1 SA timer  736  are configured per an embodiment of this invention with N equal to 2, or the value of phase 1 SA timer  734  being configured as twice the value of a soft phase 2 SA timer  738  and the value of phase 1 SA timer  736  being configured as twice the value of a soft phase 2 SA timer  740 . The initial values of phase 1 SA timer  734  and phase 1 SA timer  736  are identical. At a time  742 , phase 1 SA negotiation is complete as represented by a phase 1 SA negotiation completion  744  and client  604  initiates phase 1 SA timer  734  and server  602  initiates phase 1 SA timer  736 . 
     At a time  746 , client  604  communicates a phase 2 SA negotiation initiation  748  with server  602  initiating negotiation of IPsec SA. During the negotiation of IPsec SA, client  604  and server  602  agree on the protocol for communication, the value for soft phase 2 SA timer  738  and soft phase 2 SA timer  740 . The values for soft phase 2 SA timer  738  and soft phase 2 SA timer  740  are identical and are determined per an embodiment of this invention with N equal to 2. At a time  750  negotiation of IPsec SA is complete and is represented by a phase 2 SA negotiation completion  752 . In conjunction with phase 2 SA negotiation completion  752 , client  604  implements soft phase 2 SA timer  738  and server  602  implements soft phase 2 SA timer  740 . 
     Following phase 2 SA negotiation completion  752 , a link initiation  754  occurs at a time  756  and secure data communication between client  604  and server  602  ensues. 
     As illustrated in  FIG. 7 , this invention prevents extended time periods of non-communication by rapidly reestablishing secure communication in the event of a communication disruption. The amount of time required for recovery of secure communications as a result of an embodiment of this invention as illustrated by discarded data  722  in  FIG. 7  is significantly less than the time required for recovery as illustrated in  FIG. 5  by discarded data  516 . 
     By configuring the expiration of phase 1 SA and phase 2 SA soft-lifetimes in accordance with equation (1), the uniform recovery of secure communications is enabled. The phase 1 SA and phase 2 SA timing agreements between server and client in accordance with the present invention enable the uniform existence of phase 1 SA, thereby enabling uniform recovery from service disruptions via DPD. This eliminates time periods during which a phase 1 SA is not available for recovery of secure communications via DPD. 
       FIG. 8  illustrates, in accordance with an embodiment of the present invention, a simplified relationship diagram representing the synchronization between peers with respect to phase 1 SA and phase 2 SA.  FIG. 8  illustrates the relationship between phase 1 SA, phase 2 SA, phase 1 SA timer, soft phase 2 SA timer and hard phase 2 SA timer as embodied by this invention.  FIG. 8  illustrates how this invention enables the uniform implementation of DPD for recovery of secure communications thereby avoiding sustained periods of non-communication as a result of communication disruptions. 
     An x-axis  800  of  FIG. 8  represents the variable t in units of time with variable t increasing with progression from left to right on the page. 
     Before  FIG. 8  is discussed in detail, please consider the following introduction to some aspects. 
     The area located below x-axis  800  is represented by phase 1 SAs. The area located above x-axis  800  is represented by phase 2 SAs. 
     Rectangular blocks  804 ,  810 ,  822 ,  832  and  846  represent phase 2 SAs. Horizontal arrows  816 ,  826 ,  836  and  852  represent soft phase 2 SA timers. Horizontal arrows  806 ,  812 ,  824 ,  834  and  850  represent hard phase 2 SA timers. 
     Rectangular blocks  802 ,  818  and  842  represent phase 1 SAs. Horizontal arrows  710 ,  736  and  840  represent phase 1 SA timers. 
     In order to simplify  FIG. 8 , all timers will be referenced with respect to server  602  illustrated in  FIG. 7 . 
     At time  324 , a phase 1 SA  802  is initiated between client  604  and server  602 . The lifetime of phase 1 SA  802  is negotiated between client  604  and server  602  and is represented by phase 1 SA timer  710 . The lifetime of phase 1 SA  802  and the value for phase 1 SA timer  710  are determined via an embodiment of this invention with N equal to 2 or twice the value of soft phase 2 SA timer  334 . 
     At time  336 , a phase 2 SA  804  is initiated between client  604  and server  602 . The lifetime of phase 2 SA  804  is negotiated between client  604  and server  602  and is represented by a hard phase 2 SA timer  806  which initiates at time  336  and expires at a time  807 . 
     The value for soft phase 2 SA timer  334  is derived from hard phase 2 SA timer  806 , which is negotiated between client  604  and server  602  during the negotiation of phase 2 SA  804 . The expiration of soft phase 2 SA timer  334  determines when a subsequent phase 2 SA may be initiated. The value of soft phase 2 SA timer  334  is determined via an embodiment of this invention with N equal to 2. 
     At a time  808 , soft phase 2 SA timer  334  expires enabling the start of a phase 2 SA  810 . During the negotiation of phase 2 SA  810 , client  604  and server  602  negotiate the values for a hard phase 2 SA timer  812 , expiring at a time  814 , and a soft phase 2 SA timer  816 . The value of soft phase 2 SA timer  816  is determined by an embodiment of this invention with N equal to 2. 
     Phase 1 SA  802  terminates after the expiration of phase 1 SA timer  710  at time  728 . Soft phase 2 SA timer  816  expires at a time  817  and since a phase 1 SA does not exist, a phase 1 SA  818  is negotiated and the value for phase 1 SA timer  736  is determined during the negotiation of phase 1 SA  818 . The lifetime of phase 1 SA  818  and the value for a phase 1 SA timer  736  are determined via an embodiment of this invention with N equal to 2. 
     At a time  820 , a phase 2 SA  822  is negotiated, wherein the value for hard phase 2 SA timer  824  is negotiated and wherein a value for soft phase 2 SA timer  826  is derived from the negotiated value for hard phase 2 SA timer  824 . Hard phase 2 SA timer  824  determines the lifetime of phase 2 SA  822 , which expires at a time  828 . Soft phase 2 SA timer  826  determines the time after which a new phase 2 SA may be initiated. In an example embodiment, the value for soft phase 2 SA timer  826  is set as N equal to 2. 
     Soft phase 2 SA timer  826  expires at a time  830  enabling the initiation of a phase 2 SA  832 . The value for hard phase 2 SA timer  834  is negotiated during the negotiation of phase 2 SA  832 . A value for soft phase 2 SA timer  836  is derived from the negotiated value for hard phase 2 SA timer  834 . Hard phase 2 SA timer  834  determines the lifetime of phase 2 SA  832  and soft phase 2 SA timer  836  determines the time after which a new phase 2 SA may be initiated. The value for soft phase 2 SA timer  836  is determined via an embodiment of this invention with N equal to 2. 
     Phase 1 SA timer  736  expires at a time  838  terminating phase 1 SA  818 . In conjunction with the expiration of phase 1 SA  818 , soft phase 2 SA timer  836  expires enabling the initiation of a new phase 2 SA. However, since a phase 1 SA does not exist, a phase 1 SA  842  is initiated at time  838  and the value for a phase 1 SA timer  840  is negotiated. Phase 1 SA timer  840  determines the lifetime of phase 1 SA  842  and expires at a time  844 . The value for phase 1 SA timer  840  is determined via an embodiment of this invention with N equal to 2. 
     A phase 2 SA  846  is negotiated between client  604  and server  602  at a time  848  and the value for hard phase 2 SA timer  850  is negotiated during the negotiation of phase 2 SA  846 . A value for soft phase 2 SA timer  852  is derived from the negotiated value for hard phase 2 SA timer  850 . Hard phase 2 SA timer  850 , expiring at a time  854 , determines the lifetime of phase 2 SA  846  and soft phase 2 SA timer  852 , expiring at a time  856 , determines the time after which a new phase 2 SA may be initiated. The value for soft phase 2 SA timer  852  is determined via an embodiment of this invention with N equal to 2. 
     As illustrated in  FIG. 8 , this invention prevents periods of time during which a communication disruption would cause an extended period of time for non-communication. The time periods during which a communication disruption can cause non-communication as illustrated for a conventional system in  FIG. 2  and represented by unavailable DPD  218  and unavailable DPD  246  are not experienced in  FIG. 8  as a result of an embodiment of this invention. 
     By configuring the expiration of phase 1 SA and phase 2 SA soft-lifetimes in accordance with equation (1), the relationship between phase 1 SA and phase 2 SA is configured in order to provide the uniform existence of phase 1 SA during secure communications. The uniform existence of phase 1 SA provides the ability to uniformly recover from service disruptions between server and client via DPD, as DPD can only be implemented during the existence of a phase 1 SA. 
     A device in accordance with the present invention may be any device operable to communicate with another device within an Internet Protocol (IP) communication system. Non-limiting examples of such devices include computers and phones, for example as discussed above with reference to  FIG. 1 . 
     A communication device in accordance with the present invention may include an IKE protocol portion  222  and an IPsec portion  608 . In some embodiments, IKE protocol portion  222  and an IPsec portion  608  may be implemented as individual processing portions. In some embodiments, IKE protocol portion  222  and an IPsec portion  608  may be implemented as a unitary processing portion. 
     A communication device in accordance with the present invention may additionally include a transmitter portion that can transmit wireless or wireline signals. Non-limiting examples of transmitter portions include transmitter portions that can transmit wireless or wireline public switched telephone network signals and transmitter portions that transmit wireless or wireline broadband Internet access signals, e.g., WiMax signals. 
     Further, in accordance with an aspect of the present invention, a device readable media for use with a communication device may have device-readable instructions stored thereon. In particular, the device-readable instructions may be capable of instructing the communication device to communicate with another device within an Internet Protocol (IP) communication system such that the time value of the phase 1 security association is an integer multiple of the time value of the soft phase 2 security association in accordance with the present invention. A non-limiting example of such a device readable media includes a hardware memory portion of a processing unit, wherein the processing unit is operable to process the instructions within the hardware memory portion. 
     The foregoing description of various preferred embodiments of the invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments, as described above, were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.