Abstract:
This invention describes how combined session and resource tracking in a mobile node (MN) and/or basestation in a dynamic network resource environment can be used to control reactions to resource shortages. The session that is to experience a resource shortage is detected either by the MN, or communicated to the MN where session signaling is used to modify the session according to MN and basestation policy/configuration. The basestation can alternatively modify the session itself with all the session peers, on behalf of the MN. The specific new reaction to resource shortages that is then enabled is to place the session on hold such that the resources are freed, but so that the session state is maintained in the peers. This is preferable to dropping the session, as is generally the case in dynamic environments, if the likely period of resource loss is short and the session modifications require less overhead than restarting the session when the resources return after dropping the session. In addition, before having resources removed, the basestation can provide the MN with an opportunity to upgrade the priority of its resource request compared to other users in the cell, so that a resource auction is conducted to decide which MN actually loses its resources.

Description:
RELATED APPLICATIONS 
     The present application is a divisional of U.S. patent application Ser. No. 10/219,550, filed on Aug. 15, 2002 now U.S. Pat. No. 7,099,681 and titled “METHODS AND APPARATUS FOR CONTROLLING IP APPLICATIONS DURING RESOURCE SHORTAGES”, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/313,035, filed on Aug. 16, 2001 titled “A METHOD FOR CONTROLLING IP APPLICATIONS DURING NETWORK CHANGES THAT RESULT IN RESOURCE SHORTAGES” which is hereby expressly incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to communications session and resource management and, more particularly to methods and apparatus for enabling a mobile node to maintain a communications session despite a decrease in resources, e.g., temporary reduction or loss of bandwidth, used to support the communications session. 
     BACKGROUND OF THE INVENTION 
     Many user applications require a minimum amount of resources, e.g., communications bandwidth, to be useful. One example is traditional voice telephony that below either a target minimum bandwidth or above a maximum delay becomes unusable. During call set-up in traditional fixed telecom networks, a signaling channel first checks that sufficient resources exist between the caller and callee before admitting the call and ringing the callee in the case of voice. If there is insufficient resource then the call is refused with a network busy signal. Once admitted, calls are usually dropped by the network only if equipment fails or due to pre-emption mechanisms such as emergency over-rides. This model has continued into much of the traditional wireless industry where the resources are checked and then only dropped under network control as before. A new source of network failures though in wireless networks is that the hand-off between cells can result in a dynamic step-change in network conditions (new cell being fully occupied) that can cause the call to be dropped. 
     In existing cellular systems the media flow (e.g. voice and/or audio) and call control channel are tightly coupled resulting in both the call signaling and call media forcibly being dropped at the same time. This prevents the signaling channel from being used to advise the mobile node of the resource problem and give the MN options as to how things should proceed. In next generation IP data applications, the session control signaling, e.g., session signaling which may be implemented using, e.g., Session Initiation Protocol-“SIP” and media planes used to implement data-transfer and data application signal using, e.g., Realtime Transfer Protocol-“RTP”, are designed to be distinct and separable. This allows, in some IP based communications systems, session control signaling and data signaling to be controlled independently. 
     In IP based applications, multiple user of an IP device may interact as a group, e.g., as part of a group game session. Dropping group members due to the temporary loss of bandwidth by an individual member can result in an inconvenient and unenjoyable experience for the remaining group members. The sudden loss of a player may leave the other players without notice as to the dropped player&#39;s absence. Furthermore, the need for a dropped player to establish a new communications session in order to rejoin the group can result in relatively lengthy delays even after bandwidth has been restored to the dropped member. It would be far more desirable if a group member, e.g., player, subject to a sudden decrease in bandwidth could notify the other group members of a temporary absence and simply halt data communications without terminating the control portion of the group communications session. Thus, the other group members would be aware of the temporary absence of the group member subject to temporary bandwidth limitations and the group member can reestablish the data portion of the connection as soon as bandwidth is restored without having to establish an entirely new communications session. 
     In some cases, sudden decreases in bandwidth may be due to re-allocation of bandwidth in a cell in which a mobile node is operating or the previous allocation of bandwidth to other mobile communications users in a cell into which a mobile node is traveling. When confronted which such bandwidth problems, which would normally result in a connection being dropped, it would be nice to give the user who is about to have a connection dropped the opportunity to upgrade the user&#39;s priority, e.g., by paying a premium, to maintain an existing communications session. In this manner, a user could prevent the loss of the connection by selecting, e.g., to pay a premium to have the connection maintained. Unfortunatley, existing communications systems do not offer a mobile node user this opportunity. 
     In view of the above discussion, it is apparent that there is a need for methods and apparatus that would allow a communication session to be maintained even when changes in conditions, e.g., due to a mobile device&#39;s poor location or signal interference, result in insufficient resources to continue the data portion of the communications session. In addition, there is a need for providing users of mobile devices an opportunity upgrade their relative priority in terms of resource allocation before dropping a connection due to a resource request from a mobile device having a higher priority or because of the previous allocation of the required resources to another device. 
     SUMMARY OF THE INVENTION 
     The present invention relates to communications session and resource management and, more particularly to methods and apparatus for enabling a mobile node to maintain a communications session despite a decrease, e.g., temporary reduction or loss of bandwidth, used to support the communications session. 
     Control signaling often requires far less bandwidth than data transmission. In addition, in some system implementations, control signals used to support a communications session are transmitted on different channels than the channels used to transmit data, e.g., voice, text, game information, etc., as part of a communications session. Accordingly, even when there is insufficient resources to maintain the data portion of a communications session, it is possible to continue the control signaling and thus the communications session, e.g., at a reduced data rate or without the ability to transfer data for a period of time. When the bandwidth required to transfer data becomes available, the data portion of the communications session is restored to normal without the need to re-establish the session. This is in sharp contrast to having to close the session and later restart the session when resources are once more available, as done in the prior art systems. 
     Prior to dropping a connection, or placing a session into a hold or other state requiring reduced bandwidth, in accordance with one feature of the present invention a mobile node user is provided an option to upgrade the user&#39;s resource allocation priority. By selecting the upgrade option the user is provided with the resources, e.g., bandwidth, required to maintain the session and the communications network operator is provided the opportunity to generate revenue by charging a priority upgrade service charge or other type of fee. 
     Combining session and resource tracking is used in accordance with the invention in a mobile node (MN) and/or basestation in a dynamic network resource environment to control reactions to resource shortages. The session that is to experience a resource shortage is either detected by the MN, or communicated to the MN where session signaling is used to modify the session according to MN and basestation policy/configuration. The basestation can alternatively modify the session itself with all the session peers, on behalf of the MN. The specific new reaction to resource shortages, in accordance with the invention, is to place the session on hold thereby freeing network resources to be used by other nodes. However, as part of the session hold operation, the session state is maintained in the peers of the node subject to the resource shortage, and placed in a hold state where some form of local (to the MN) hold action can be performed for the user such as playing a tone, showing an advert, undertaking a local only game play phase etc. This is often preferable to dropping the session, as is generally the case in dynamic environments. This is particularly the case when the period of resource loss is likely to be short and the session modifications required to transition the session back into an on-state will require less overhead than restarting the session. 
     In accordance with one feature of the invention, before having resources removed, the basestation can provide the MN with an opportunity to upgrade the priority of its resource request compared to the resource allocation priority of other users in the same cell. In such embodiments a resource auction is conducted to decide which MN actually loses its resources. 
     While applicable to communications involving various types of data, e.g., voice, text, video, messaging, collaborative distributed applications such as game information, etc., the benefits of the present invention will be explained in various examples in the current application using a voice communications session, e.g., a telephone call, as an example. 
     Typically, in accordance with the invention, a communications session, e.g., IP telephone call, will be set-up with a minimum resource requirement, below which the session will be ineffective (e.g., (codec) coder/decoder bandwidth requirement). In the case of an IP telephone call communication session, this information would typically be communicated using SIP preconditions and installed using ReSerVation Protocol (RSVP) or similar signaling or preconfigured admission control techniques. During or following call set-up in a cell, a session may fail due to insufficient instantaneous resources although those resources might be available very shortly-due to a cell change or the action of other MNs in the cell. In addition, during hand-off into a congested cell, there may well be insufficient resource of the required type to admit the call/session into this cell. A number of existing processes can, and in various embodiments are, undertaken in accordance with the invention, for the MN and its various active sessions subject to sudden resource limitations. 
     For example, the cell (Quality of Service) QoS control can try to rebalance the existing resources in the cell being entered to release sufficient resources for the new MN using the well-known techniques of pre-emption or borrowing, or the affected sessions of the MN can be dropped at the cell base station. 
     In addition, according to this invention, if the basestation can maintain session or resource signaling independently of the media stream, and either the MN or the basestation can detect media resource shortages, then in the latter case the basestation can send a message to the MN indicting the media flows or resource requests that cannot be admitted at the new cell, or in the former case, the MN can detect this itself. Note that in either case this detection can also be done within a cell during a session when experiencing resource problems due to varying radio link conditions. The Receiving MN can then create a session signaling or resource message and send it to the other end of the affected sessions to inform them of the resource problem. Note that the basestation can alternatively send this message itself if it has end-to-end session knowledge of all participants and the session descriptions. Both ends are now aware of the problem and can then act on this knowledge to modify the session or resources. A number of alternatives are possible. 
     The MN communications application, e.g., voice application, in the congested cell can signal the other end (e.g. the voice application on the other end of a call) to put the new or ongoing call on hold, advising the other end that it is due to a temporary resource problem in an reason code. Once the resources become available, communications sessions, e.g., calls on ‘resource hold’ get access to the available bandwidth. The call is then taken off-hold by the call&#39;s participants when the network signals that the resources are available and have been allocated to the node on hold. This is better than losing the call, as in existing systems, because the MN does not immediately redial (creating wasteful signaling) and instead the call will be automatically re-connected at the earliest opportunity. During the break both ends can, and in some embodiments do, exchange messages to be played, e.g., using reduced bandwidth signaling such as text-messaging. In other embodiments the messages are signaled by the local BS to both ends and/or locally stored messages are played at the direction of the BS or MN. 
     As an alternative to the above described resource shortage handling technique, the two application endpoints, e.g., MNs, can renegotiate the session description to be used during resource problems or this information can be exchanged when the original call was being set-up during session description negotiation. The session description would describe how to react to resource failure and can include: drop to text chat, drop to a lower codec fidelity or bit rate, play a message, etc. 
     Alternatively, the reaction to insufficient resource could be to divert the session to a media recorder. In such an embodiment the unaffected application endpoint leaves a message which the affected user can listen to automatically when the resource becomes available and maybe then decide whether or not to call the unaffected user back. 
     Alternatively, the call can, and in various embodiments is, redirected to a third person (e.g. a manager&#39;s secretary)/another team member, or to another terminal for the affected user such as a fixed phone near the MN&#39;s current location. The new call location could be communicated to the affected user via the still functional signaling plane. 
     Alternatively, in various embodiments the payer for the call (normally the caller) or the affected user (additional payer for the local resource) is given the chance to increase the pre-emption level (resource priority) of the media flow, with an associated increase in ‘call’ cost, to enable the call to pre-empt an existing call and use its resource. In this case the message to the caller should include advice on the minimum required pre-emption level and the associated cost. In parallel, in some embodiments the caller on the identified call whose resources are to be removed (call to be pre-empted) is involved, e.g., notified of the impending interruption of service, so that an instantaneous ‘bidding war’, with a single bid per end-point, can be undertaken as to who gets the resource. Alternatively, such a bidding war can be avoided by a predetemined pre-emption ordering according to service level agreements (e.g., Gold users win over Silver users). 
     In addition to the session/resource signaling responses it can be beneficial to put a rate-limit on the number of renegotiations in a fixed period to avoid responding too quickly to resource changes. In accordance with one feature of the invention this is achieved by adding hysterisis to the session or resource transition, and by setting a minimum reconfiguration time for each session. This increases in importance as the rate of cell change increases (small cells, fast MNs) to the extent that the signaling round trips are a significant fraction of the cell transition time. In effect, the slower the cell change, the more opportunity there is for session renegotiation whilst faster transition times increase the importance and utility of the temporary call hold feature of the present invention. 
     Various features of the present invention such as a session holdmessage are particularly well suited to group communications sessions, e.g., multi-participant game communications sessions, where it is useful to convey temporary absence information to other group members. The signaled absence may be due, e.g., to being placed into a hold state due to resource shortages. In response to the absence message, the game application being executed by the group may take appropriate action to protect a players position in the game until such time as the player&#39;s bandwidth and connection are restored to normal. 
     Numerous additional features, benefits, applications and embodiments of the present invention are described in the detailed description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary communications system implemented in accordance with the present invention. 
         FIG. 2  is a block diagram of an exemplary base station that may be used in the communications system of  FIG. 1 . 
         FIG. 3  is a block diagram of an exemplary mobile node that may be used in the communications system of  FIG. 1 . 
         FIG. 4  is a flow diagram illustrating the steps of an exemplary routine that can be used by a basestation to control session hold transitions for mobile nodes in accordance with the present invention. 
         FIG. 5  is a flow diagram illustrating the steps of an exemplary routine that may be used to control resource re-allocation which can be used in conjunction with the method of  FIG. 4 . 
         FIG. 6  is a flow diagram illustrating the steps of an exemplary routine that may be used by a basestation to control resources while allowing session hold transitions to be managed by the mobile nodes. 
         FIG. 7  is a flow diagram illustrating the steps of an exemplary routine that may be used with the method of  FIG. 6  to control resource re-allocation. 
         FIG. 8  is a flow diagram illustrating the steps of an exemplary routine that may be used by a mobile node to control the transitioning into a session hold state in response to the occurrence of any one of a plurality of possible trigger events. 
         FIG. 9  is a flow diagram illustrating the steps of an exemplary routine that may be used by a mobile node to the transitioning from a session hold state into a session on state in response to any one of a plurality of possible trigger events. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates to communications session and resource management and, more particularly to methods and apparatus for enabling a mobile node to maintain a communications session despite a decrease in resources, e.g., temporary reduction or loss of bandwidth, used to support the communications session. 
     Various aspects of the present invention are directed to novel methods, apparatus and data structures for enabling a mobile node to roam in a foreign network, with multiple basestation handoffs, while permitting the basestation and mobile node to collaborate to enable the mobile node and its session peers to adapt to resource shortages, either as a result of hand-offs or due to changing channel, e.g., radio channel, conditions. This is achieved by placing particular sessions into a hold state in accordance with the invention as necessitated by resource shortages. The following description is presented to enable one skilled in the art to make and use the invention and is provided in the context of particular applications and their requirements. Various modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles set forth below may be applied to other embodiments and applications. Thus, the present invention is not intended to be limited to the embodiments shown and the inventor regards his invention as the following disclosed methods, apparatus and data structures and any other patentable subject matter and embodiments made obvious by the text of this application. 
     Various terms used in the present application will now be explained so that they can be properly interpreted in the description which follows. 
     Mobile Node: A host or router that can change its point of attachment from one network or sub-network to another. 
     Mobile nodes may have some or all of the following attributes. A mobile node may change its location without changing its IP address; it may continue to communicate with other Internet nodes at any location using its (constant or persistent) IP address, assuming link-layer connectivity to a point of attachment is available. In various embodiments a mobile node is given a long-term (or persistent) (e.g., IP) address on a home network. This home address may be administered in the same way as a “permanent” IP address is provided to a stationary host. When away from its home network, a “care-of address” is associated with the mobile node and reflects the mobile node&#39;s current point of attachment. The mobile node normally uses its home address as the source address of all IP datagrams that it sends. 
     Basestation: A node that serves as a network attachment point for one or more mobile nodes. 
     Cell: The area of wireless coverage resulting from radio propagation and system limits that extends out from a radio antenna on a basestation. 
     Session: A communication relationship that has a session description, which is negotiated and agreed between one or more session peers. The session description typically includes the time, duration and media types (voice/video codecs etc) for the session. 
     Session Peer: A peer with which a network node, e.g., a mobile node, has a negotiated session. Session peers can be mobile or stationary. 
     Link: A facility or medium over which nodes can communicate at the link layer. A link underlies the network layer. 
     Link-Layer Address: An address used to identify an endpoint of some communication over a physical link. Typically, the Link-Layer address is an interface&#39;s Media Access Control (MAC) address. 
     Node: A network element that serves as host or a forwarding device. A router is an example of one type of node. 
       FIG. 1  illustrates an exemplary communications system  100  implemented in accordance with the methods and apparatus of the present invention. The system  100  includes first and second cells  10 ,  10 ′ and a router  17 . The router  17  may be coupled to, e.g., the Internet. As shown, the cell  10  comprises a basestation  12  and a plurality of mobile nodes  14 ,  16 . The base station  12  manages mobile nodes (MNs)  14 ,  16  whilst in said cell, specifically providing bidirectional radio communications links  13 , 15  between the basestation and each mobile node. The basestation dynamically adjusts the bandwidth of the radio links  13 ,  15  to share the bandwidth between all mobile nodes in the cell  10  as a function of the mobile nodes resource requirements and, in some embodiments, resource allocation priority. Mobile node resource requirements are known as a result of resource and/or session signaling from the mobile node  14 ,  16  to the basestation  12 , and/or from mobile node specific configuration known to the basestation  12  independent of communications with the mobile nodes  14 ,  16 . Cellular networks are typically comprised of a multitude of such cells. In regard to  FIG. 1 , the second cell  10 ′ is another cell which is the same as or similar to cell  10 . Elements of the second cell are denoted using a to distinguish them from like numbered elements of the first cell. For example the base station in the second cell  10 ′ is indicated using reference number  12 ′. 
     In the  FIG. 1  example, mobile node  1 ,  14  appears in both the first and second cells. While this may occur in cases where cells overlap, in the  FIG. 1  example, the presence of the first mobile node  14  in the second cell  10 ′ occurs as the result of movement of the mobile node  14  from the first cell  10  to the second cell  10 ′ as represented by arrow  20 . Thus, in the  FIG. 1  example, mobile node  14  is present in second cell  10 ′ at a point in time subsequent to the time it is in the first cell  10 . 
     The base stations  12 ,  12 ′, of the first and second cells  10 ,  10 ′, are interconnected by network nodes such as IP router  17  which are coupled to the base stations by communications links. In the  FIG. 1  example, fixed communication links  18 ,  19  interconnect the router  17  and the basestation  12 ,  12 ′. This allows the base stations  12 ,  12 ′, and mobile nodes connected thereto, to interact with one another by way of communications links  18 ,  19  and router  17 . 
     Communications resources, e.g., bandwidth, available to a mobile node  14  may vary as a function of a variety of factors including demands of other nodes in a cell  10 ,  10 ′, resource demands of nodes entering and/or leaving the cell, and the quality of the radio link with the base station  12  or  12 ′ servicing the mobile node. 
     When a mobile node (MN)  14  moves geographically, the radio propagation between it and nearby basestations (BS)  12 ,  12 ′ varies. As a result of changes in radio communication due to movement, when moving into the second cell  10 ′ from the first cell  10 , the preferred BS changes from  12  to  12 ′. In order to allow communication through the preferred base station a hand-off will occur from the current base station to the new preferred base station. Thus, when a mobile node moves from the first cell  10  to the second cell  10 ′ a handoff will occur. As a result the mobile node, e.g., node  14 , entering the second cell  10 ′ will begin being served by BS  12 ′. This hand-off causes the resource and session information, sometime called “state” or “state information”, known in BS  12  to be transferred to BS  12 ′. As a result of the handoff, the resource demands in cell  10  are reduced while the demand for resources in cell  10 ′ increases due to the movement of the MN into the cell  10 ′. 
     As the MN  14  moves within the new cell  10 ′ the maximum potential radio link capacity in either direction between MN  14  and BS  12 ′ will vary as a function of the mobile node&#39;s,  14 , distance from the base station  12 ′. Changes in the maximum potential radio link capacity can affect the resources available to the MN  14 . Hand-offs for other MNs, e.g.,  16 , into the same cell  10 ′ can place additional demands on the resources in the cell  10 ′. The basestation  12 ′ is used to manage resources, and resource allocation requests, as mismatches occur between the total available resources in cell  10 ′ and the sum of the resource demands from MNs in the cell  10 ′. This management may result in the basestation requiring a node with allocated resources to discontinue, e.g., relinquish, some of the utilized resources before the mobile node completes an ongoing communications session. While in known systems this would normally result in a communication session being dropped, in accordance with the present invention a communications session may be placed into a hold state as will be discussed further below. 
       FIG. 2  is a block diagram of an exemplary BS  12  that may be used in the communications system of  FIG. 1  to permit a roaming mobile node to effectively manage sessions during resource shortages. As shown, the exemplary BS  12  includes a receiver circuit  202 , transmitter circuit  204 , processor  206 , memory  210  and a network interface  208  coupled together by a bus  207 . The receiver circuit  202  is coupled to an antenna  203  for receiving signals from mobile nodes. The transmitter circuit  204  is coupled to a transmitter antenna  205  which can be used to broadcast signals to mobile nodes. The network interface  208  is used to couple the base station  12  to one or more network elements, e.g., router  17  and/or the Internet. In this manner, the base station  12  can serve as a communications element between mobile nodes serviced by the base station  12  and other network elements. 
     Operation of the base station  12  is controlled by the processor  206  under direction of one or more routines stored in the memory  210 . Memory  210  includes communications routines  223 , data  220 , session management routine  222 , resource reallocation routine  225 , session signaling subroutine  224 , resource signaling subroutine  218 , messages  215 , and active user information  212 . Communications routines  223 , include various communications applications which may be used to provide particular services, e.g., IP telephony services or interactive gaming, to one or more mobile node users. Data  220  includes data to be transmitted to, or received from, one or more mobile nodes. Data  220  may include, e.g., voice data, E-mail messages, video images, game data, etc. Session management routine  222  is to oversee various communications sessions which may be supported by the base station  12  at any given time. Each mobile node in the cell serviced by the base station  12  may have any number of active communications sessions going on at any given time. Session management routine  222  is responsible, at least partially, for resolving conflicting resource requests that may be made by the various mobile nodes in a cell. Resource reallocation routine  225 , is used by the base station  12  to address resource allocation issues, specifically when there are insufficient resources available to satisfy the resource requests made by the various mobile nodes being serviced by the base station  12 . Session signaling subroutine  224  is responsible for controlling session signaling, e.g., SIP signaling, which is supported by the base station  12 . Resource signaling subroutine  218  is responsible for controlling resource signaling, e.g., RSVP signaling, which is supported by the base station  12 . Messages  215  may be stored messages sent to notify communications session participants of the temporary absence of a communications session participant and/or to notify the session participants that a communications session participant has been put on hold. Messages  215  may also be stored messages sent to notify communications session participants of the temporary absence or return of a session resource. Active user information  212  includes information for each active user and/or mobile node serviced by the base station  12 . For each mobile node and/or user it includes a set of state information  213 ,  213 ′. The state information  213 ,  213 ′ includes, e.g., a list of communications sessions in which the node and/or user are participating, the communications resources used by each listed communications session, and whether the session and/or resource is in an active, e.g., session on state, or a hold state as supported in accordance with the present invention. 
     In accordance with the present invention, resource shortages are handled by base station  12  under the direction of session management and/or resource allocation routines  222 ,  225  potentially in conjunction with the MN  14 , based on the relative importance of user sessions known from user data or via negotiation with MNs. Various exemplary session management and resource allocation routines which may be used as the base station routines  222 ,  225  will be discussed below. 
       FIG. 3  is a block diagram of an exemplary mobile node (MN)  14  that may be used as one of the mobile nodes  14 ,  16  of the communications system shown in  FIG. 1  along with the the exemplary base station (BS) of  FIG. 2 . When used in combination with the base station of  FIG. 2  in accordance with the present invention, mobile node  14  can support the maintenance of communications sessions during resource shortages, e.g., in a session hold state. 
     The exemplary MN  14  includes a receiver circuit  302 , transmitter circuit  304 , processor  306 , memory  310  coupled together by a bus  307 . The receiver circuit  302  is coupled to an antenna  303  for receiving signals from one or more basestations  12 ,  12 ′. The transmitter circuit  304  is coupled to a transmitter antenna  305  which can be used to broadcast signals to basestations  12 ,  12 ′. The mobile node  14  can interact with mobile nodes and other network elements by establishing communications sessions through a base station  12 ,  12 ′. 
     Operation of the mobile node  14  is controlled by the processor  306  under direction of one or more routines stored in the memory  310 . Memory  310  includes communications routines  323 , data  320 , mobile node processing routine  322 , resource reallocation routine  325 , session signaling subroutine  324 , resource signaling subroutine  318 , messages  315 , and information  312 . Communications routines  323 , include various communications applications which may be used to provide particular services, e.g., IP telephony, E-mail, video, games, etc. to a user of the mobile node  14 . Data  320  includes data to be transmitted to; or received from a base station  12 ,  12 ′. Data  320  may include, e.g., voice data, E-mail messages, video images, game data, etc. Mobile node processing routine  322  is used to oversee various communications sessions which may be supported by the base station  12  at any given time, to detect and to respond to various trigger events. In response to a trigger event, such as the receiving a particular message or detecting a resource shortage, the processing routine  322  can control the mobile node to transition a communications session between a session on state and a session hold state. It can also control a communications session to transition from a session hold state to a session on state, e.g., when an event such as the allocation of resources needed to restore a communications session to an on state is detected. Each mobile node  14  may have any number of active communications sessions going on at any given time. Resource reallocation routine  325  is used, in some embodiments, by mobile node  14  to address resource allocation issues when there are insufficient resources available to satisfy the resource requirements of the various communication sessions the mobile node  14  is involved in. Session signaling subroutine  324  is responsible for controlling session signaling, e.g., SIP signaling, which is supported by the mobile node  14 . Resource signaling subroutine  318  is responsible for controlling resource signaling, e.g., SIP preconditions or RSVP signaling, which is supported by the mobile node  14 . Messages  315  may be stored messages sent to notify communications session participants of the impending temporary absence of the mobile node from an on going communications session. This may include indicating that the mobile node  14  is being put on hold for a particular communications session. Information  312  includes information about the ongoing communications sessions supported by the device. It may list such sessions on a per user basis where the device can be used by multiple users. For each communications session, the information  312  includes resource and status information, e.g., the communications used and/or required for the session and whether the communications session is in a session on or a session hold state. An exemplary mobile node processing routine which may be used as the routine  322  will be discussed in detail below. 
       FIG. 4  is a flow diagram illustrating the steps of an exemplary base station session management routine  400  that can be used as the session management routine  222  of exemplary basestation  12 . The routine  400  starts in step  402  when the routine is executed by the base station&#39;s processor  206 , e.g., after the base station  12  is powered up. As indicated by input block  405 , the main acts of the method  400  are performed in response to trigger events  405 , which correspond to the receipt of messages or the detection of particular conditions. Trigger events are detected in step  410  and cause processing associated with the trigger event to proceed to step  415 . Monitoring is performed in step  410  on a continuous basis with each detected trigger event resulting in separate processing, e.g., by steps  415  etc sequence. Trigger events  405  include, for example, session request messages and session release messages. Such messages may be generated either by MNs  14 ,  16  in the cell or by the BS  12  in response to session state transitions within the BS  12  due to hand-off activity such as existing sessions leaving or arriving into the cell  10  with MNs  14 . In step  410 , a monitoring process looks for changes in the set of sessions employed by the plurality of MNs in the cell, along with the resources associated with those sessions. In response to detection of a session message, operation proceeds to step  415 . In step  415 , a test is conducted to determine if additional resources have been requested or existing resources released, e.g., whether a session request or release message was received. 
     If additional resources have been requested, operation proceeds from step  415  to step  420 . In step  420  the total amount of resources, including the new request, required for ongoing sessions at the BS  12  is compared to the total resources available in the cell  10 , to see if the new resource request can be granted in step  420 . This can simply be a comparison between the amount of free resource in the cell and the size in terms of resources of the additional session request. Note that a session request includes a change in the session description of an existing session that increases the required resources for that session. Thus, in step  420  the BS  12  decides whether or not there are sufficient resources, e.g., bandwidth, available to satisfy the request. If sufficient resources are available to satisfy the required operation proceeds to step  425  wherein the BS  12  grants the requested resource(s) to the requesting session. Step  425  leads to block  428  wherein the BS  12  allows a new session to be conducted using the granted resource or modifies an existing session to employ the new granted resources for the communication session. 
     If, in step  420  the BS  12  determines that there are insufficient resources available to satisfy the received resource request, operation proceeds from step  420  to step  430 . In step  430  a comparison between the priority of the requesting session is made to the priority of existing sessions to which the requested resource has been allocated. If in step  430  it is determined that the requesting session does not have higher priority, than an existing session which is using the requested resource, operation proceeds to step  439 . In step  439 , the requesting session is marked as a session hold candidate. Operation proceeds from step  439  to step  440 . 
     If in step  430  it was determined that the requesting session has a higher priority than a session to which the requested resource is already allocated, the resource will be reassigned to the requesting session. As part of the resource reallocation process, in step  435 , processing goes to the start of a resource re-allocation routine, e.g., the exemplary resource re-allocation routine  500  shown in  FIG. 5  (XX  500  was not marked in  FIG. 5  so I have updated). The resource re-allocation routine determines from which ongoing session the requested resource is to be reallocated. The existing session from which the resource is to be taken is identified and marked by the resource re-allocation routine as a session hold candidate. Once processing by the re-allocation routine is completed, i.e., a session is identified and marked as a session hold candidate, operation returns to the main processing routine  400  and continues from step  440 . 
     In step  440  a test is made against the user/device/session data  213 , to see if the device and session corresponding to the session marked as a hold candidate, supports a session hold state, whereby the marked session and the session participants can be put on hold temporarily until resources become available. If the device or session participants do not support a hold state, meaning the session hold candidate will have to be terminated to refuse the session request, or to permit the reallocation of requested resources, then operation proceeds from step  440  to step  445  where a signal is sent to the participants in the session hold candidate cancelling the session and the corresponding resource request (I have modified the text in  445  accordingly). Operation proceeds from step  445  to Stop step  470  wherein processing in response to the received session request is halted. 
     Referring once again to step  440 , if it was determined that the device and session corresponding to the session hold candidate did in fact support a session hold state, operation would proceed to step  428  via steps  455  and steps  460 . In step  455  the BS  12  signals the session peers to put the session hold candidate into session hold, and optionally includes a reason code to explain why this is happening, and a hold action instruction to be undertaken by the session software at the session peers during the hold period. Examples of such actions include the playing a tone, displaying a message to the screen, or in an interactive game invoking game play local to the node (game player and gaming server) that does not disadvantage the session peers in session hold compared to other session at the game server in the same game. Then, in step  460 , the held session is placed into a hold queue  219  with, e.g., session priority and time stamp information. Thus, the held session is put into a queue of held sessions at that BS  12  with a priority and locally generated timestamp. If the session request is from a held session that just transferred into this cell as part of a hand-off, then the priority and timestamp of that held session will not be updated at block  460 , but will be installed as is into the hold queue of this cell. This is so that handed off sessions do not lose their global place in the session hold queue at a particular cell, during a cell change, and requires a degree of time synchronization between basestations as is common in exemplary implementations. Accordingly, as the mobile node  14  passes from cell  10  to cell  10 ′ the hold queue  119  information corresponding to sessions being maintained by the mobile node  14  is passed along with other state information from BS  10  to BS  10 ′. As a result, the hold queue  219  may include hold information transferred from another cell as part of a handoff operation. 
     Operation proceeds from step  460  to step  428  wherein the BS  12  allows the communication session to which the resources were allocated to be conducted using the allocated resources. 
     The request message processing branch of the routine  400  has been described in detail. Processing of resource release messages will now be discussed. If in step  415 , it is determined that a resource release message was received, operation proceeds from step  415  to step  469 . The resource release message may be a result of a MN  14  and its sessions leaving the cell, the cessation or renegotiation for lower resources for a particular active session, or new resources becoming available in the cell  10  for other reasons such as capacity increases. In step  469 , a check is made-to-see if any sessions are presently in session hold and hence awaiting resources. If no sessions are in hold then processing of the received release message stops in stop step  465  but monitoring for resource messages at block  410  is allowed to continue. If in step  469  it is determined that there are sessions in hold then operation proceeds to step  470 . In step  470 , the available resources are allocated to held sessions in the queue, with the highest priority sessions being served first, and the length of time in session hold, determined from the global timestamp, being used to order allocations within the same priority level. Note that if the resources are insufficient for higher priority session to be taken out of session hold then a lower priority session with smaller resource requirements can still be allocated the resource to ensure maximum use of resources is made. Other well-known algorithms are also applicable for ordering the sessions in the hold queue, and for holding back partial resources for high priority sessions with large resource requirements, in preference to allocating such resources to lower priority sessions. 
     From allocation step  470 , operation proceeds to step  475 . In step  475 , a determination is made as to whether the released resources were allocated to a session in hold state. If the freed resources were insufficient to enable any session to be brought out of session hold, then the released resources are simply left spare at the input to step  475  and operation will proceed to step  485 . In step  485  the unused resources are made available for use in servicing future resource requests, or borrowed by elastic applications with resources allocated that are less than the peak resources possible for that application, or cam be consumed by best effort traffic for which no resource signaling is conducted. In contrast if in step  470  a session in hold has been granted sufficient resources then operation would proceed via step  475  to step  480 . In step  480  the basestation  12  signals the session peers to transition the session to which the resources were allocated from hold into an active state and then allows the session to use those resources in step  428  for purposes of a communication session. 
     The exemplary resource re-allocation routine  500 , shown in  FIG. 5 , may be used as the BS resource reallocation routine  225  shown in  FIG. 2 . It may be used in conjunction with routine  400 . The resource re-allocation routine starts in step  502 , e.g., in response to yes at block  430  and activation of step  435  of the routine  400  in  FIG. 4 . 
     Resource reallocation routine  500  is used to redistribute resources as a function of a priority level associated with each session that is using or requesting resources. In accordance with the invention, before being denied the use of its resources needed for an identified communication session of lower priority, an associated identified user and/or device may be presented with the opportunity to upgrade the priority associated with that particular identified communications session. 
     The routine  500  proceeds from start step  502  to step  505  where an existing session, having the requested resources, in the cell  10  with lowest priority is identified by the BS  12 . This session is henceforth called the identified session. In step  510  a test on the identified session data is undertaken to see if the mobile node  14  in the cell  10  corresponding to the identified session, i.e., is a member of the identified session, supports a dynamic priority upgrade option. In accordance with the invention, the dynamic priority upgrade option allows users corresponding to an identified session to dynamically increase the session&#39;s priority in an attempt to avoid resource reallocation to the requesting session, and having the identified session dropped or put on hold. The dynamic priority upgrade option may be presented to the mobile node user as part of a bidding war for the resource which occurs with other sessions whose individual resource is sufficient to satisfy the resource request. Note that whilst the exemplary routine in  FIGS. 4 and 5  covers the case of a one to one comparison between sessions, it will be obvious to someone skilled in the art that a suitably important requesting session with large resource requirements could result in resources being taken from more than one existing session of lower priority, resulting in a multitude of identified sessions. The requesting session may be included in the bidding processes and considered among the devices from which the requested resource may be taken. In this manner, if the requesting session&#39;s priority is exceed as the result of bidding by all the active devices to which the requested resource has already been allocated, the requesting session may be selected as the session to be put into a hold state. In step  510 , if the identified session does not support dynamic priority option then operation proceeds directly to step  569  which will be discussed below. 
     If, in step  510 , it is determined that the mobile node associated with the identified session supports the dynamic priority upgrade option, then a test at step  520  is executed to ensure that the number of upgrades in this pass of the routine has not exceeded some limit. If a limit has been exceeded then the routine settles on the present identified session with the lowest priority and proceeds to step  580 . If the limit has not been exceeded then another upgrade is allowed and a priority upgrade message is sent to the present identified session user in the cell, e.g., the BS  12  sends the mobile node  14  associated with the identified session a signal indicating that the mobile node should present the user of the mobile node  14 , with an upgrade option signal. This may be, e.g., a visible indicator, e.g., a light or text message, presenting the user of the mobile node  14  with a chance to select an upgrade in priority. Thus, the upgrade option message can be presented to the user on a display which is part of the MN  14 . Alternatively, the upgrade option signal can be processed by or interact with policy state/user agent processes, e.g., routines, in the MN  14  that automatically control such bidding for priority upgrades, e.g., in accordance with preprogrammed user selections. Such automated control may be based, at least in part, on the increase in priority required to maintain the session and the associated financial cost of increasing session priority to that level at the time the upgrade option signal is received. 
     In response to the upgrade option signal a mobile node  14  responds to the BS  12  with a signal indicating whether or not the upgrade has been selected, e.g., manually by the user of the mobile node  14  or automatically by the MN  14 . The response message is received by the BS  12  from the MN  14 . The response message is tested in step  540 . If the upgrade option has been refused then the identified session and user is will be left unchanged and processing will proceed from step  540  to step  569 . However, if the upgrade option has been accepted then processing passes from step  540  to step  550  where the user session state  212  is updated with the new priority for the session. Then, in step  560  the number of upgrades in this pass of the routine is incremented for the identified user, and for all users so that a limit on the number of bids per user, the signaling rate and latency can be applied to the process of selecting the final identified session. The routine  500  finally passes back to step  505  where the lowest priority session with sufficient resource for the requesting session user is once again identified, taking into consideration the upgrade in priority, for the next loop of the routine. Eventually the processing will proceed to step  569  with a final identified session. 
     In step  569  session resources are reallocated from the identified device to the requesting device. In this manner, resource reallocation occurs asynchronously from session management, e.g., placing the session from which the resources were reallocated into a hold state or terminating the session. This is consistent with the normal case of session signaling for a specific MN lagging cell resource changes, e.g., unpredictable changes due to radio environment, changes in number of active sessions for the MNs already in a cell, changes in number of active sessions as a result of hand-off of MNs. 
     From step  569 , operation proceeds to step  570  wherein the BS  12  transmits a session signal to the requesting MN  14  and its session peers granting the requested session resources. Then, in step  580 , the identified session is marked as a session hold candidate. From step  580  processing returns to the routine which called the resource reallocation routine  500  via return step  590 . In the case of a go to operation invoked by step  435  of  FIG. 4 , operation will be returned to step  440  of routine  400  which then used the session marked as a session hold candidate as part of further processing. 
     Note that an alternative exemplary method of signaling and receiving bids is to broadcast the requesting session priority out to all session users in the cell and to then collect bids from all users that wish to make a bid that will increase their present session priority, from a level that is lower than the priority of the requesting user. The basestation then selects the lowest resultant session as a session hold candidate. This minimizes the bandwidth and latency of the bidding process. 
       FIG. 6  shows a flowchart for an alternative basestation routine  600 , that employs an alternative a re-allocation routine shown in the flowchart of  FIG. 7 . In the  FIG. 6  embodiment, the basestation  12  identifies a session and corresponding mobile device from which the requested resources are to be reallocated, in the case where there are insufficient resources, to satisfy a request having a higher priority than the session from which the resources are to be reallocated. In the  FIG. 6  embodiment the base station notifies the corresponding mobile node  14 , from which the resources are to be taken, that the resources are unavailable and the mobile node  14  is given the opportunity to signal that the session using the resource is to be placed into a hold state, the session resources reduced down (not discussed further as this can be treated like a new session to the resource system), or terminated. In such an implementation, the basestation  12  does not have to keep track of a mobile node&#39;s ability to support a session hold state leaving the decision to drop a session or place a session into a hold state in response to resource shortages. In such an implementation, the dropping or placing of a session into a hold state is under the control of the mobile node  14 , which serves as the end node for the session subject to the resource shortage. 
     Many of the steps of the  FIG. 6  basestation routine  600  are the same as the steps of the previously described routine  400  shown in  FIG. 4 . For the purposes of brevity such steps are identified in  FIG. 6  using the same reference numbers as used in  FIG. 4 . Such steps will not be described again here. The steps of the basestation routine  600  which differ from the routine  400  are identified using reference numbers in the  600 &#39;s range. The routine  600  starts at step  602  but, in contrast to the  FIG. 4  implementation, the basestation  12  is interested in resource request/release messages that serve as trigger events rather than session release/request messages because in the  FIG. 6  embodiment session management is left primarily to the session users, e.g., users of nodes  14 . The resource messages  605  might come directly from user resource messages, e.g., RSVP messages, or can instead be derived by the BS  12  from received session messages, e.g., SIP messages. In step  610  the resource messages  605  are monitored. For each received resource message processing proceeds to step  615 . In step  615  messages that affect present resource allocations are tested to see if they are a request or a release message. 
     If the message is a resource request then steps  420 ,  425 ,  428 , and  430  are performed as in the case of the  FIG. 4  embodiment. Note that steps  425  and  430  use information identifying the session associated with a resource request and related priority information. This information is kept in the basestation  12  user session information  222  and is available for use on an as needed basis. With this information, in step  430  the priority of the resource request can be determined. If there is no existing session with the requested resources that has a lower priority, operation will proceed from step  430  to step  640  via step  639 . In step  639  the requesting device is marked as an identified device for subsequent processing and the requested resource is marked as unavailable. 
     If an existing session with lower priority exists, and is using the requested resources, operation will proceed from step  430  to step  640  via step  635 . Step  635  is a GOTO step which involves a jump to the alternate resource re-allocation routine  700  shown in  FIG. 7 . 
       FIG. 7  shows the alternate resource re-allocation routine with the modified steps being identified with numbers in the  700 &#39;s. The routine  700  is similar to the routine  500  with the exception of steps  730 ,  770  and  780 . As in the case of the routine  500 , the routine  700  seeks to determine, e.g., identify, a session and corresponding device whose resources can be given to the requesting session, whilst giving the session user at a MN  14  in the cell  10  an option to defend its resources by upgrading the priority of its session and hence the priority of its resource requests in the basestation  12 . The differences in the  FIGS. 5 and 7  embodiments are generally restricted to the signaling plane. In the  FIG. 7  embodiment a resource priority upgrade option message, rather than a session message is sent to the local MN in step  730 . In addition, in step  770 , a resource grant signal is sent to the device associated with a resource request as opposed to a session resource grant signal being transmitted. Finally, at block  780  it is the resource rather than the session that is marked as unavailable for the identified communications session, and it is therefore the resource request, i.e., the previously granted resource request that was canceled as a result of resource reallocation, that is therefore a candidate to be queued at the BS  12 . In step  590  the routine  700  returns to  FIG. 6  where step  640  is executed next. 
     As a result of processing in either step  635  or step  639 , an identified resource has been marked as unavailable and hence at block  640  a resource unavailable message, with a resource id identifying the specific resource and its relationship to a session at MN  14 , is sent to the identified device, e.g., MN  14 , in the cell  10 . This will cause the MN  14  to react to the resource change by noting the loss of resource, determining the associated session, and then modifying the associated session using session signaling, e.g., SIP. In step  645  the fact that a resource has become unavailable for a session, e.g., the identified session, as a result of a denial of the resource request or reallocation of the resource, is recorded in the hold queue  219  maintained in the basestation&#39;s memory  210 . This may be done by adding an appropriate resource request to the hold queue  219  with, e.g., a designated priority, a timestamp, the resource id and the associated session identifier. As in the previous example, the removal of resources from a session may occur asynchronously from changes in the session state. Thus, the loss of resources due2 to resource re-allocation will normally occur before the session state is placed into a hold state or the corresponding session from which the resources were take is terminated. A mobile node discovering the loss of resources may signal to the BS  12 , in accordance with the invention, whether the session from which the resources were taken should be placed in a hold state or terminated. With the placing of the resource request in the hold queue  219 , the associated session in the user session state  213  is marked as short of resources and will be converted in to a session hold state or terminated upon the MN  14  indicating the desired treatment. Following placement of the information in the hold queue  219 , processing the resource request message stops in step  450 . However, monitoring for additional resource messages continues on an ongoing basis in step  610 . 
     If a resource release message is detected in step  610 , instead of a resource request message, processing proceeds from step  610  to step  460  by way of step  615 . As in the  FIG. 4  example, in step  460  the BS  12  checks to see if there are any sessions on hold as a result of denial of previous resource requests or the reallocation of resources from existing communications sessions. This is accomplished by checking the contents of hold queue  219 . Steps  465 ,  470  and  475  are performed, with step  475  establishing if the freed resources are suitable, e.g., sufficient, for a current session (resource) on hold. If they are not, then the released resources are added to a free resource stack, which includes resources which can be utilized by existing and potential future sessions. If the resources are suitable, e.g., sufficient, for a session on hold, then at step  475  operation proceeds to step  680  where a resource available message is sent to the MN  14  that is a local member of the session to which the freed resources are being allocated. Processing then proceeds to step  428  where the communications session to which resources were allocated, can use the allocated resources for a communications session, e.g., allowing a communication session previously on hold to transition to an on state. Note that the resource available, e.g., resource grant, message could be refused by the MN  14  with a resource or session message due to it no longer wishing to pursue a session, e.g., because it choose to terminate a session as opposed to place it on hold. 
     The method shown in  FIG. 6 , enables the MN  14  in the cell  10  where the BS routine  600  is executed, to be informed of the available/unavailable resources for the user sessions at the mobiles  14 ,  16  in the cell  10 , and hence allow the MN  14  or  16  to locally react by sending session signals, e.g., SIP signals, in response to the resource changes. The MN  14  can then either change the session resource requirements (including putting the affected session on hold), borrow resources from another session that that MN  14  is involved in, or cancel the affected session altogether. In accordance with the present invention, the MN  14  issues session signals indicating its decision on how to handle an affected session to the peers and/or base station  12 . This mobile node based approach to session management is an alternative to the base station approach to session management described with regard to  FIGS. 4 and 5  wherein session signals used to control the termination or placing of sessions into a hold state are generated and transmitted by the basestation  12 . The basestation based session management method shown in  FIGS. 4 and 5  minimizes the amount of signaling between the MN  14  and its peers, but increases the amount of session knowledge needed at the basestation and ultimately removes or reduces the power from the MN  14  to manage its own sessions as it sees fit. This model is appropriate for simple, dumb mobile nodes  14  running simple sessions, or sessions that the basestation  12  will ultimately have to control. The methods illustrated in  FIGS. 6 and 7  in contrast to the  FIGS. 4 and 5  methods, minimize the basestation session knowledge requirements but increases the amount of signaling which is performed by the MNs  14 ,  16 . However, the benefit of such signaling is that MN  14  is in control of what it wishes for its communications sessions. This is more like the Internet model which assumes intelligent hosts, and is appropriate in applications where the basestation  12  can yield session control to the mobile nodes  14 ,  16 . 
     Having described the basestation processing for resource and session on hold management we now move on to the mobile node view of these interactions, which are described in the flowcharts shown in  FIGS. 8 and 9 . 
     For a mobile node  14  to be able to roam freely, it should be able to deal with basestations  12 , which implement either the method of  FIGS. 4 and 5  or the alternative method of  FIGS. 7 and 8 . This has the advantage of allowing a mobile node  14  to interact with multiple basestations  12 ,  12 ′ as it moves around or to deal with cases where a single session involves base stations  12 ,  12 ′ which support different techniques, e.g., the  FIG. 4  or  FIG. 6  techniques of handling session and resource control. 
     Exemplary mobile node processing routine  800 , comprising first and second parts,  800   a  and  800   b , is shown in  FIGS. 8 and 9 . The routine  800  may be used as the mobile node processing routine  322  of the mobile node  14 . 
       FIG. 8  illustrates a first portion  800   a  of the mobile node processing routine  800 . Portion  800   a  handles the processing of trigger events that have the potential to cause a transition of a MN communications session from an “on” state into a session “hold” state.  FIG. 9  illustrates the second portion  800   b  of the mobile node processing routine  800 . The second portion  800   b  handles the processing of trigger events that have the potential of allowing a transition of a MN session from a “hold” state to a “session on” state. A start step  802  of routine  800  is divided into parts  802   a  shown in  FIG. 8  and start step  802   b  in  FIG. 9  for purposes of illustration. However, both parts  802   a  and  802   b  represent part of the same step  802  which involves execution of the routine  800  by the mobile node  14 . Similarly trigger event detection step  810  is shown as two separate parts  810   a  and  810   b  but may be part of a single trigger event detection step. The processing performed following step  810  will depend on the type of trigger event that is detected. For purposes of illustration,  FIG. 8  deals with trigger events that may cause a mobile node communications session to transition into a hold state while  FIG. 9  deals with trigger events that may cause a mobile node communications session to transition from a hold state to an on state. 
     Referring to  FIG. 8 , the MN processing commences at block  800   a , in step  810   a  any one of four types of trigger events may be detected. The first trigger event is an upgrade option message that could either be a session or resource message, and which was issued by a BS  12  while executing a resource reallocation routine, e.g., as part of step  530 ,  730 . This causes processing to pass to step  815  where the upgrade option is presented to a user of the MN  14  or to a user agent process, e.g., automated MN routine. Then in step  820 , in accordance with the present invention, a user/user agent upgrade decision is received and in step  825  the received decision is returned, e.g., transmitted, to the basestation  12  as a session or resource upgrade reply message. In stop step  827  processing corresponding to the detected upgrade option message is halted however, step  810  continues to monitor for trigger events which may trigger additional processing by the routine  800 . 
     The second type of trigger event that may be detected in step  810   a  is a session hold signal received from a basestation  12  or from a session peer, e.g., MN  14  or  16 , that has itself decided to put a session on hold. This causes the processing to proceed from step  810   a  to step  880  where the session application implements the session hold action for that session which is either negotiated during session set-up, configured in the application or signaled, e.g., specified, in the detected session hold message. Processing then proceeds to step  885  where the MN  14  waits for a resource change for the session that has been put on hold. Monitoring in step  810   a  continues in an attempt to detect additional trigger events thought the processing of a hold signal. 
     The third trigger event that may be detected in step  810   a  is an internal resource unavailable message from a MN networking stack included in the MN  14  that indicates that the MN  14  is not getting sufficient resources for the MN&#39;s active sessions and hence below the resources previously promised by the basestation  12 . This trigger therefore implies a resource shortage (unavailability) at the basestation  12 . Detection of an explicit resource unavailable message received by the MN  14  from a basestation  12  will also result in operation proceeding from step  810   a  to step  830 . This represents the fourth and final trigger event that may be detected in step  810   a . Hence either of the last two triggers will cause processing to pass from block  810   a  to block  830 . The MN communication sessions affected by the detected trigger are determined, e.g., identified, in step  830 . Operation then proceeds to step  835 . 
     In step  835 , the MN session state information  312  is interrogated to see if the session signaling, the session peers and the application associated with the affected session(s), identified in step  830 , support session hold. If session hold is not supported then each affected session is cleared using session signaling with peers  14 ,  16  and the basestation  12 , as appropriate to the local basestation  12  processing, e.g., in accordance with the method of  FIGS. 6 and 7 . Note that the basestation  12  will see the session signaling messages and deduce that the affected session has been cancelled and that the associated resources have been released. Processing proceeds from step  890  to step  895  wherein processing of the detected trigger event stops. 
     If, however, in step  835  the it is determined that the affected application does support session hold then operation proceeds from step  835  to step  840 . In step  840  the MN  14  determines whether the affected session is a unicast or a multicast session. If it is a multicast session in step  850  a multicast session hold message is sent to the multicast session peers. However, if the affected session is a unicast session, operation proceeds instead to step  860  wherein one or more unicast session hold messages are sent to the unicast session peers. Note that a basestation  12  that initiates session hold messages should also be able to send both multicast and unicast session hold messages. The session hold reason in either case (unicast or multicast) should contain a reason code as well as an action code, so that each peer knows why the session is to go into session hold. This enables the peer to decide if it wishes to stay in the session waiting for resource to return, or to save resources at its basestation  12  by canceling its leg of the session with the MN  12 . Whether a multicast or unicast session hold message is sent, a response will be received back by the MN  14  indicating that the session hold was either accepted or rejected. If accepted then at step  880  the application and the application peers put the session into hold and implement a session hold action, e.g., an action communicated in the hold message, such as playing a tone. Then, operation proceeds to step  885 , wherein the MN  14  and its peers again wait for a resource change so that the session now in the hold state can be restored to an active, e.g., “on” state. 
     Note that while at step  835  the test is simply shown as whether the affected MN application supports session hold, the MN  14  could still choose to cancel an affected session rather than go into hold. This would cause the MN  14  to move to step  890 , cancel the session. Monitoring for trigger events would continue in step  810   a  despite cancellation of the affected session. Note also that one session end-point puts the session into session hold and out of session on, with a reason code to indicate the reason for this such as resource unavailable, and all peers implement the action code associated with that transition and reason. 
     Referring to  FIG. 9 , the MN processing commences at block  800   b , where in step  810   b  any one of three types of trigger events may be detected. The first trigger event that may be detected in step  810   b  is a session on signal (session out of hold/active) received from the basestation or a session peer. This causes the processing to proceed from step  810   b  to step  975  where the MN  14  sends a response accepting the session on message and associated reason/action, to the issuing peer/BS, and then passes the action code to step  980 , where the application implements the session on action. This could be, for example, to stop playing the tone and start sending/receiving media in the session. The processing then moves to the stop at step  995 . Processing of other trigger events continues at step  810   b  throughout the processing of each detected trigger event and despite stop step  995  being encountered. 
     The next potential trigger that may be detected in step  810   b  is a resource available message, from the MN  14  itself, and generated from its internal networking stack having detected that additional resources are now available. An equivalent trigger is the resource available message received from the local basestation which also signals the return of resources to the MN  14 . In either case, operation proceeds from step  810   b  to step  920  where the affected session is determined either as a result of an explicit resource_id in either received or detected resource message, which has a known local mapping to sessions, or as a result of the MN  14  prioritizing its sessions access to shared resources, using the session priority and timestamp state information that was similarly employed by the basestation in  FIGS. 4 ,  5 ,  6  and  7 . At step  930 , the selected session is checked to ensure it is still in hold and if it is not, and has already been cancelled, then the processing moves to step  990  where the selected session maybe restarted before we move to step  995 . If instead, the session is held at step  930  then we again check to determine if it is a multicast or unicast session in step  940 , so that the MN  14  can send the correct type of session on message to its session peers, with reason and action code, using step  950  or step  960 . At step  970  the MN  14  receives the session hold response and passes the action code to the application so that at step  980  the application implements the session on action, before processing of the particular detected event stops in step  995 . Therefore one session end-point puts the session out of session hold and into session on, with a reason code to indicate the reason for this such as resource now available, and all peers implement the action code associated with that transition and reason. 
     In summary, the combination of resource and session messages, plus the relationship between those messages and the associated session state being maintained in the basestations  12 ,  12 ′ and the MNs  14 ,  16 , enables the basestations  12 ,  12 ′ and the MNs  14 ,  16  to collaborate to enable sessions to be put into and out of session hold in the presence of resource shortages. The type of application processing whilst in session hold is dependent on both local application policy, session negotiated actions as well as action and reason codes specifically communicated in the session or resource messages that cause the session hold transition. The MN  14  while offered the option of going into session hold can instead cancel the session, or negotiate the session resource requirements lower to fit into remaining resources, or by rebalancing resources from other active sessions. When session hold is signaled by the basestation  12 , the flexibility of these choices at the MN  14  is reduced or lost but the complexity of managing such choices is moved to the basestation  12 . 
     As can be appreciated from the foregoing, the present invention permits a mobile host, e.g. mobile node  14 , to maintain session state with its session peers whilst the resources for the session are temporarily lost. The session response to a resource shortage can be signaled either by the basestation  12  of the affected mobile node  14 , or by the mobile node  14  itself. In addition, resource shortages can be detected both by the MN  14  and by the basestation  12 , and in the basestation  12  case a signaling exchange can be initiated with affected MNs  14 ,  16  to enable an auction of the available resource to be undertaken so the least important session from the users perspective is eventually deprived of resource. The MN  14  or basestation  12  can then respond to resource availability by allowing the session to once again access resources and continue with the session. During resource unavailability, affected sessions are put on hold and the session endpoints given an action to perform such as playing a tome or displaying a message. 
     The techniques of the present invention can be applied to a wide range of IP based mobile communications applications including E-mail, voice communications, and mobile game applications. Consider application of the invention to a game were a number of players are in a game with multiple players in the same cell. The game server multicasts out game play changes to the players and receives individual player actions via unicast from each player. 
     If a MN  14  loses uplink resources then the MN  14  can signal to the game server, e.g., basestation  12  in the case of this example, its absence and the game server will freeze the players activity in the game in such a way that the player is not harmed, e.g., the player goes invisible and/or is moved randomly by server so that return spot is unknown, protected from weapons, power stops waning etc. Meanwhile the game server  12  informs all other players of the status change through the multicast game play information, potentially periodically flashing the invisible user as it randomly moves the absent player through the game topology. 
     When the MN  14  returns, e.g., transitions from session hold to session on, the server  12  puts the player back in a safe spot in the game. If the MN  14  does not return then the absent status times out and the player is moved into a saved state. Meanwhile, the MN  14  can still see others progress in the game. 
     The MN  14  game software can include a special button that enables the MN  14  to increase its resource priority in the cell  10  which the MN  14 , e.g., incurring a higher price charge for services. It is pp to the MN  14  whether it uses the priority upgrade feature but when enabled it is applied for a fixed period of time, a bit like gaining more weapons in a game because better scheduling means lower latency and an advantage with respect to other players. 
     If the game play from the central server  12  is lost then the game instructions in the MN  14  become useless because the MN  14  cannot see the effects of its actions on the game play. Therefore, both uplink and downlink are lost together for the various players in the affected cell  10  and they go into the absent state by the basestation  12  sending the required session message stating the affected users. The basestation  12  also multicasts a single message to the MNs  14 ,  16  to indicate that they are in absent state. As they independently change cells so they independently can rejoin the game. If the players in the cell  10  press the improved resource button then they contribute to the resource flow being resurrected and share the cost for the upgrade in service priority. 
     The response to the absent message might include a trigger for the MN  14  to go into a local game play mode where the user can change configurations as part of the game (change car, weapons, pick a return spot etc) so that when gameplay returns the user has not be wasting time, twiddling thumbs and the new configuration can be sent to the server  12 . If only the uplink is lost then the MN  14  can still play within the static environment of the game by deciding where they will return and with what weapons etc so that when the uplink returns they can rejoin very quickly in a very active state. 
     In addition, it is possible to implement a very low bitrate gameplay channel still being available so that the user has some high-level sense of what is happening in the game even when full participation is not possible due to communications resource limitations. 
     The multi-user game example is just one exemplary application in which the methods and apparatus of the present invention can be used.