Abstract:
A method and system are disclosed that enable performance improvements by reallocating to client endpoints at least some of the feature functionality of a server. Each logical user in the system is represented by his own private domain of endpoint entities, from which an endpoint is selected to serve as a super peer to represent the user to the centralized server. Furthermore, one or more endpoints in the private domain of endpoints handle some of the telecommunications features that the server otherwise would have handled. An endpoint that needs to access a particular feature determines the best endpoint to handle the feature, in part by querying the other endpoints in the private domain. If the querying endpoint wants to subscribe to a feature that is located at an endpoint in the private domain, the querying endpoint interacts with the relevant endpoint without requiring the further assistance of a server.

Description:
FIELD OF THE INVENTION 
     The present invention relates to telecommunications in general, and, more particularly, to a hybrid peer-to-peer system of telecommunications endpoints that handles one or more telecommunications features for the endpoints. 
     BACKGROUND OF THE INVENTION 
       FIG. 1  depicts telecommunications system  100  in the prior art. System  100  comprises telecommunications network  101 ; client endpoints  102 - 1  through  102 -H, wherein H is a positive integer; and servers  103 - 1  through  103 -L, wherein L is a positive integer. The elements of system  100  are interconnected as shown. System  100  enables calls, via network  101 , between endpoints  102 - 1  through  102 -H and servers  103 - 1  through  103 -L. Network  101  comprises one or more of the Internet, the Public Switched Telephone Network (PSTN), a local area network (LAN), and so forth. 
     Client endpoints  102 - 1  through  102 -H are telecommunications devices such as an Internet-protocol telephone, a notebook computer, a personal digital assistant (PDA), a tablet computer, and so forth. Each endpoint is capable of originating outgoing calls and receiving incoming calls, in well-known fashion. In addition, each endpoint is capable of one or more communication modes that comprise but are not limited to voice, video, data, email, and instant messaging. 
     Servers  103 - 1  through  103 -L are data-processing systems that handle telecommunications features that can be subscribed to by the endpoints. The servers are capable of handling features such as voice calling, video streaming, data retrieval, email, instant messaging, availability and presence monitoring, and so forth. 
     Telecommunications system  100  operates in accordance with the Session Initiation Protocol (SIP), a set of standardized communication rules for initiating and maintaining communication for telephony, presence-based systems, instant messaging, and other telecommunications applications. The increasing use of SIP-based systems represents a fundamental shift in telecommunications, in which a user can be addressed as a logical entity that might possess one or more devices, with each device going in and out of service based on the usage patterns of the user. 
     As new telecommunications features are built onto the SIP infrastructure, issues are emerging that affect performance throughout telecommunications system  100  and, in particular, servers  103 - 1  through  103 -L. One such issue is an increase in network traffic. For example, as features that are related to monitoring the client endpoints are introduced at a centralized server that also handles call processing, the number of SIP-related events that the server must handle also increases, and consequently the server&#39;s capacity to process calls becomes severely degraded. 
     In some techniques in the prior art, the scalability issue that arises in a centralized server architecture is partially mitigated by partitioning the client endpoint users across multiple servers. Doing so, however, often has the effect of spreading out the call processing-related resource utilization, but not necessarily the SIP events-related utilization. Consequently, there are various issues with the centralized server architecture in the long run that are related to diminishing scalability, increasing complexity of the centralized server, and increasing complexity of feature development. 
     Moreover, as systems evolve in which the constituent endpoints migrate out into the Internet Protocol network and become relatively autonomous, the centralized server loses its complete authority over the control of the migrated endpoints. Often, as is the case with a SIP-based system, the server might not even have an active connection to an endpoint. This causes the initialization sequence between server and endpoint to be more intensive than before and requires an increased amount of bandwidth as each endpoint executes potentially numerous, different message sequences to fully initialize. Consequently, the time to service as perceived by an endpoint user can become unacceptably long. 
     What is needed is a way to mitigate the server scalability and time-to-service issues, without some of the disadvantages in the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention enables improvements in the scalability of a centralized server and in the perceived time to service by reallocating at least some of the feature functionality of the server to the client endpoints. In accordance with the illustrative embodiment of the present invention, each logical user in the system is represented by a private domain of endpoint entities, from which an endpoint is selected to serve as a super peer to represent the user to the centralized server, as is the case in a hybrid peer-to-peer system. Those endpoint entities can be physical devices; logical instances of the user&#39;s capability in shared software systems, applications, and services; or a combination of the two. Furthermore, one or more endpoints in the private domain of endpoints handle some of the telecommunications features that the server otherwise would have handled. The super-peer endpoint can be one of the feature-providing endpoints, but is not required to be. 
     As part of an initialization sequence, when a client endpoint of the illustrative embodiment registers with its telecommunications system, it receives a list of contact addresses of endpoints that are members of the same private domain as the registering client endpoint. In accordance with the illustrative embodiment, the client endpoint then queries one or more of the fellow member endpoints on the received list of contact addresses, in order to determine the capabilities of those endpoints. Capabilities that can be made available at one or more endpoints include, but are not limited to, the following:
         i. the ability to communicate in a particular manner (e.g., at a specific level of service, via a specific protocol, in a specific format, etc.);   ii. the ability to process or store information in a particular manner;   iii. the ability to present information to an endpoint user in a particular manner; and   iv. the ability to provide a particular telecommunications feature to another endpoint or endpoints.
 
One or more endpoints in the private domain then respond to the querying endpoint by reporting on the capabilities that are available. Based on the available capabilities, the querying endpoint can then determine the best endpoint or subset of endpoints to handle a particular feature on behalf of the querying endpoint. If the querying endpoint wants to subscribe to a feature that is located at a second endpoint in the same private domain, the querying endpoint interacts with the second endpoint without requiring the further assistance of a server with respect to accessing the feature. Conversely, if the querying endpoint wants to subscribe to a feature that is still being handled at a server, the endpoint can still subscribe to the feature via the server in well-known fashion.
       

     The illustrative embodiment of the present invention is advantageous over some techniques in the prior art for various reasons. First, the illustrative embodiment enables a mitigation of the server scalability issue, in terms of reducing the amount of associated messaging from order (n*k*m) to roughly order (n), where n is the number of users in the system, k is the number of endpoints per user, and m is the number of messages per endpoint. In addition to improving the server scalability, the illustrative embodiment enables a reduction in the number of messages that each client endpoint has to initially exchange with a server, thereby improving the time to service as perceived by the user. 
     The illustrative embodiment of the present invention comprises: a first client endpoint that subscribes to a first telecommunications feature; and a second client endpoint that handles the first telecommunications feature; wherein the first client endpoint and the second client endpoint are associated with a first user; and wherein at least one endpoint in the plurality of endpoints communicates with a server data-processing system as an agent of at least one other endpoint in the plurality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts telecommunications system  100  in the prior art. 
         FIG. 2  depicts a first diagram of telecommunications system  200  that comprises private domain  220 . 
         FIG. 3  depicts a second diagram of telecommunications system  200  that comprises private domain  320 , in accordance with the illustrative embodiment of the present invention. 
         FIG. 4  depicts a third diagram of telecommunications system  200  that comprises private domains  420  and  430 , in accordance with the illustrative embodiment of the present invention. 
         FIG. 5  depicts a fourth diagram of telecommunications system  200  that comprises private domain  520 , in accordance with the illustrative embodiment of the present invention. 
         FIG. 6  depicts a block diagram of the salient components of client endpoint  202 - m  in system  200 . 
         FIG. 7  depicts a block diagram of the salient components of server data-processing system  203 - n  in system  200 . 
         FIG. 8  depicts a flowchart of the salient tasks that are executed by client endpoint  202 - m , in accordance with the illustrative embodiment of the present invention. 
         FIG. 9  depicts a flowchart of the salient tasks that are executed by server data-processing system  203 - n , in accordance with the illustrative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following terms are defined for use in this Specification, including the appended
         The term “call,” and its inflected forms, is defined as a communication of user information between two or more telecommunications endpoints. Examples of a call are a voice telephone call (including interactive voice response [IVR] sessions), an emailing, a text-based instant message [IM] session, a video conference, and so forth. In a Session Initiation Protocol (or “SIP”) context, a call is a type of session.   The term “private domain,” and its inflected forms, is defined as a group of networked telecommunications endpoints (either physical devices or logical instances, or both) that share at least one particular attribute such as being associated with the same user, being in physical proximity with each other, and so forth.   The term “user domain,” and its inflected forms, is defined as a private domain in which all of the endpoints in the domain are associated with the same user and which comprises all of the endpoints at which the user is currently registered, regardless of location. For example, the contact address, as is known in the art, of each endpoint in a particular user domain maps to the public address of the particular user.   The term “member endpoint,” and its inflected forms, is defined as a telecommunications endpoint that belongs to (i.e., is a member of) a private domain, such as a user domain or a domain based on endpoint proximity.   The term “designated endpoint,” and its inflected forms, is defined as a telecommunications endpoint that has been designated to handle (i.e., have the responsibility for providing) a telecommunications feature in a private domain for one or more endpoints in that domain. There can be more than one designated endpoint in a private domain.       

       FIG. 2  depicts telecommunications system  200 , a hybrid peer-to-peer system, as is known in the art, which comprises telecommunications network  201 ; client endpoints  202 - 1  through  202 -M, wherein M is a positive integer; and servers  203 - 1  through  203 -N, wherein N is a positive integer. Although M is depicted as being equal to 3, the number of endpoints can be different from that depicted, as those who are skilled in the art will appreciate. The depicted elements in system  200  are interconnected as shown. System  200  is capable of handling calls between endpoints via Session Initiation Protocol-based (SIP-based) signaling, in accordance with the illustrative embodiment. Nevertheless, it will be clear to those who are skilled in the art how to apply the present invention to some alternative embodiments that use other types of call-control signaling, such as H.323, as is known in the art. As depicted, system  200  comprises endpoints  202 - 1  through  202 -M and servers  203 - 1  through  203 -N in the illustrative embodiment; however, it will also be clear to those skilled in the art how to apply the present invention to some alternative embodiments that further comprise legacy endpoints or servers, or both, in which those legacy endpoints and servers do not embody the tasks described below and with respect to  FIGS. 8 and 9 . 
     Telecommunications network  201  is a network that comprises one or more of the Internet, the Public Switched Telephone Network (PSTN), a local area network (LAN), and so forth. Network  201  comprises or is connected to one or more transmission-related nodes such as gateways, routers, or switches that are used to direct packets from one or more sources to their correct destinations. Network  201  is capable of handling SIP-based messages in well-known fashion that are transmitted among two or more SIP-capable processing systems. 
     Each client endpoint  202 - m , for m=1 through M, is a telecommunications device such as an Internet-protocol telephone, a notebook computer, a personal digital assistant (PDA), a tablet computer, and so forth. The salient components of endpoint  202 - m  are described below and with respect to  FIG. 6 . Endpoint  202 - m  is capable of originating outgoing calls and receiving incoming calls, in well-known fashion. In addition, endpoint  202 - m  is capable of one or more communication modes that comprise but are not limited to voice, video, data, email, and instant messaging. In accordance with the illustrative embodiment, endpoint  202 - m  is SIP-capable, but as those who are skilled in the art will appreciate, in some alternative embodiments endpoint  202 - m  can operate in accordance with a different type of call-control protocol. 
     Endpoint  202 - m  is able to provide access to telecommunications features to its user. As a client device, endpoint  202 - m  is able to access one or more servers  203 - 1  through  203 -N for the purpose of providing server-based telecommunications features to its user. Endpoint  202 - m  is also able to communicate with other endpoints for the purpose of subscribing to endpoint-based, telecommunications features; in turn, one or more of endpoints  202 - 1  through  202 -M are able to handle those telecommunications features on behalf of the subscribing endpoints. Moreover, endpoint  202 - m  executes the tasks described below and with respect to  FIG. 8  in supporting the distributed feature functionality of the illustrative embodiment. 
     Each endpoint  202 - m  is identified by a unique contact address, as is known in the art. The contact addresses for endpoints  202 - 1  through  202 -M are associated with a public address of the particular user. The public address, as is known in the art, is an identifier that is used to represent the user publicly. It is an address that might, for example, appear on the user&#39;s business card. When calling parties specify the user&#39;s public address, it is up to the SIP network to resolve the address down to one or more of several endpoint devices that the user might possess. Each of endpoints  202 - 1  through  202 -M registers its contact address and its association with a particular public address, at which point the endpoint becomes a contact for a particular user. 
     For example, a user named Carol Q. Jones might have a public address of cjones@company.com and four endpoints that are identified by the following contact addresses:
         i. sip:cjones@111.111.111.111:5061; transport=tls;   ii. sip:cqj@111.111.111.222:5061; transport=tls;   iii. sip:19735551212@company.com; and   iv. sip: cjones@research.company.com.       

     In the example, each of Carol&#39;s four endpoints is considered to be a contact for the purpose of reaching her. When Carol is called by another party, the public address that is used to specify the destination is cjones@company.com. System  200  routes the incoming call that was placed to cjones@company.com to one or more of endpoints  202 - 1  through  202 -M. 
     Endpoints  202 - 1  through  202 -M are all depicted as wireless devices in the illustrative embodiment. As those who are skilled in the art will appreciate, some alternative embodiments of the present invention can comprise endpoints that are all wired or can comprise a mix of wireless and wired endpoints. Furthermore, as those who are skilled in the art will appreciate, the wireless communication protocol can be cellular-based, WiFi-based, Bluetooth-based, or based on yet a different set of rules. 
     Endpoints  202 - 1  through  202 -M are all depicted also as physical devices in the illustrative embodiment. As those who are skilled in the art will appreciate, however, some alternative embodiments of the present invention can comprise endpoint entities that are instead logical instances of a user&#39;s capability in shared software systems, applications, and services. A logical instance can be resident at one device, such as a shared computing system, even though that logical instance was created as the result of the user logging into telecommunications system  200  by using a different device. In other words, the Session Initiation Protocol enables the user to log in via a first device and be represented by an addressable endpoint entity virtually anywhere throughout system  200 , such as in a first application (e.g., conferencing, etc.) that is not necessarily resident at the first device. The same user could then log into system  200  via a second device—with or without having logged out of the first application—and be represented by an addressable endpoint entity in another place, such as in a different application (e.g., one with screen pops and an instant messaging interface, etc.). 
     In the illustrative embodiment, endpoints  202 - 1  through  202 -M are associated with to a specific human user. As those who are skilled in the art will appreciate, however, endpoints  202 - 1  through  202 -M might be associated with a user that is itself a telecommunications device, such as an automated call distributor (ACD). In this case, incoming calls have as their destination address the address of the ACD system, where the individual contact addresses, as are known in the art, correspond to the various endpoints in the ACD system. 
     In any event, it will be clear to those skilled in the art, after reading this specification, how to make and use endpoints  202 - 1  through  202 -M. 
     Server  203 - n , for n=1 through N, is a data-processing system that handles one or more server-based, telecommunications features that can be subscribed to by the endpoints, and operates in accordance with the Session Initiation Protocol. The salient components of server  203 - n  are described below and with respect to  FIG. 7 . The server-based features that server  203 - n  handles can include but are not limited to SIP event packages (e.g., as a SIP event server, etc.), call processing (e.g., as a SIP proxy, etc.), voice calling, video streaming, email, voice mail, instant messaging, web access, other data retrieval, and presence-based services (e.g., availability and presence monitoring, etc.). Note that some of the features that server  203 - n  is able to handle are also referred to as “services.” Each server  203 - n  is able to handle its own set of server-based telecommunications features. Moreover, server  203 - n  executes the tasks described below and with respect to  FIG. 9  in supporting the distributed feature functionality of the illustrative embodiment. 
     Although server data-processing system  203 - n  executes the tasks of the illustrative embodiment, in some alternative embodiments another data-processing system can be used to execute those tasks, as those who are skilled in the art will appreciate. Furthermore, in accordance with the illustrative embodiment, server  203 - n  is SIP-capable, but as those who are skilled in the art will appreciate, in some alternative embodiments server  203 - n  can operate in accordance with a different type of call-control protocol. In any event, it will be clear to those skilled in the art, after reading this specification, how to make and use server  203 - n.    
     Private domain  220  comprises client endpoints  203 - 1  through  203 -N, each of which is said to belong to domain  220 . In accordance with the illustrative embodiment, private domain  220  is a user domain. As those who are skilled in the art will appreciate, however, in some alternative embodiments private domain  220  can be defined based on a different attribute than endpoints that are associated with the same user. For example, domain  220  can be defined as comprising those endpoints that are in close physical proximity to each other or are in direct communication range of each other. 
     Within domain  220 , client endpoints  202 - 1  through  202 -M are able to function as either equal peers or super peers. An “equal peer” is able to communicate peer-to-peer with other endpoints in the same private domain, in well-known fashion. A “super peer,” in addition to being able to communicate peer-to-peer with the other endpoints, communicates with servers  203 - 1  through  203 -N, as an agent of itself and its peers. As depicted in  FIG. 2 , for example, endpoint  202 - 2  is the super peer, while the other endpoints depicted are not; therefore, endpoints other than  202 - 2  communicate with servers  203 - 1  through  203 -N through the super-peer endpoint and communication path  214 . Regardless of peer status, each of endpoints  202 - 1  through  202 -M runs an onboard software agent, wherein the agent is responsible for peer-to-peer routing and communication, as well as possibly other telecommunications features to be described later. 
     Communication paths  211 ,  212 , and  213  enable the peer-to-peer communication exchanges between endpoints  202 - 1  through  202 -M. As depicted in  FIG. 2 , in some situations the transmission between two endpoints occurs directly. For example, endpoint  202 - 1  might be within direct communication range of endpoint  202 - 2  and, as a result, transmits signals via path  211  (i.e., a wireless medium) directly to endpoint  202 - 2  in well-known fashion and without assistance from any other endpoint. 
     In some situations, the transmission between two endpoints occurs indirectly through one or more networks, such as a wireline network. For example, endpoints  202 - 1  through  202 -M might communicate with each other through one or more intermediate systems, such as base stations and switching centers. This can be either because the endpoints are scattered across widely-separated geographic regions that are out of direct communication range with each other or because the endpoints receive service via different service providers (e.g., Boingo for WiFi, Verizon for cellular, etc.) and cannot communicate directly with each other. 
     As depicted in  FIG. 3 , the relationship between endpoints and the rest of telecommunications system  200  can be different than the relationship described with respect to  FIG. 2 .  FIG. 3  depicts private domain  320 , which is similar to private domain  220 , except that one or more of the peer endpoints other than super-peer endpoint  202 - 2  are both able and allowed to access telecommunications network  201  directly (i.e., not requiring an intermediary super-peer endpoint). As depicted in  FIG. 3 , for example, client endpoint  202 - 2  is the super peer, yet client endpoint  202 - 1  is allowed to access network  201  directly via communication path  315 , instead of having to go through endpoint  202 - 2 . 
     As depicted in  FIG. 4 , each private domain can be defined by an attribute other than comprising all of the endpoints that belong to a particular user. For example,  FIG. 4  depicts private domain  420 , which is defined as comprising all of the endpoints that are in close physical proximity in a first area (i.e., endpoints  202 - 2  and  202 - 3 ), and private domain  430 , which is defined as comprising all of the endpoints that are in close physical proximity in a second area (i.e., endpoints  202 - 1  only). Client endpoint  202 - 2  is the super-peer endpoint in private domain  420 . Client endpoint  202 - 1  is the super-peer endpoint in private domain  430 , as well as the only endpoint in domain  430  until another endpoint comes along. 
       FIG. 5  depicts a plurality of endpoints within private domain  520 . In this example, all of the endpoints depicted are associated with a particular user. The plurality of endpoints comprises a super-peer endpoint  202 - 2 , as well as other client endpoints that are members of domain  520 . As a super-peer, endpoint  202 - 2  communicates with one or more servers  203 - n  as an agent of one or more other endpoints in the plurality. In accordance with the illustrative embodiment, at least some of the endpoints, such as endpoints  202 - 1  and  202 - 4 , are capable of subscribing to telecommunications features via one or more servers  203 - n . Moreover, at least some of the endpoints, such as endpoints  202 - 3  and  202 - 5 , are capable of handling one or more telecommunications features, though not necessarily those features to which some endpoints attempt to subscribe via the servers. In some embodiments, some of the client endpoints are allowed to access network  201  without having to go through super-peer endpoint  202 - 2 . 
     At least some of the endpoints in domain  520 —as well as in some of the other depicted domains, for that matter—are capable of inquiring about one or more capabilities that are present among the endpoints. For example, endpoint  202 - 1  might query the other endpoints about their abilities to communicate at or above a predetermined quality-of-service level (e.g., bandwidth, error rate, latency, etc.). As a result of the inquiry, endpoint  202 - 1  might find that endpoints  202 - 1 ,  202 - 2 , and  202 - 3  are able to support voice services (i.e., by being able to communicate above a specified quality-of-service level), while endpoints  202 - 4  and  202 - 5  are not able to support voice services but are still able to support instant messaging services, along with endpoint  202 - 2 . As a result, endpoints  202 - 1 ,  202 - 2 , and  202 - 3  will be able to transfer voice packets directly with each other, or at least without involving network  201 , via paths  511 ,  512 , and  513 ; at the same time, endpoints  202 - 2 ,  202 - 4 , and  202 - 5  will be able to transfer instant messaging packets directly with each other via paths  515 ,  516 , and  517 . 
     In addition to communication-related capability, other types of capabilities that might be present at one or more endpoints in domain  520  can be related to storage capability, processing capability, and user presentation (e.g., display, etc.) capability, as well as the ability to provide one or more specified telecommunications features. For example, one such capability might be an endpoint&#39;s capability to display the HTML-based content of messages. In fact, a particular telecommunications feature might comprise the ability to select an endpoint to present media content to a user. As those who are skilled in the art will appreciate, each given endpoint in the plurality of endpoints associated with domain  520  can inquire about, report on, or handle other capabilities than those already mentioned. 
       FIG. 6  depicts the salient components of client endpoint  202 - m  in accordance with the illustrative embodiment of the present invention. Endpoint  202 - m  comprises receiver  601 , processor  602 , memory  603 , and transmitter  604 , interconnected as shown. 
     Receiver  601  is part of a network interface that is capable of receiving signals from other client endpoints in the same private domain, as well as signals from one or more of server data-processing systems  203 - 1  through  203 -N via network  201 , and forwards the information encoded in the signals to processor  602 , in well-known fashion. It will be clear to those skilled in the art, after reading this specification, how to make and use receiver  601 . 
     Processor  602  is a general-purpose processor that is capable of receiving information from receiver  601 , executing instructions stored in memory  603 , reading data from and writing data into memory  603 , executing the tasks described below and with respect to  FIG. 8 , and transmitting information to transmitter  604 . In some alternative embodiments of the present invention, processor  602  might be a special-purpose processor. In either case, it will be clear to those skilled in the art, after reading this specification, how to make and use processor  602 . 
     Memory  603  stores the instructions and data used by processor  602 . Memory  603  might be any combination of dynamic random-access memory (RAM), flash memory, disk drive memory, and so forth. It will be clear to those skilled in the art, after reading this specification, how to make and use memory  603 . 
     Transmitter  604  is part of a network interface that receives information from processor  602  and is capable of transmitting signals that encode this information to other client endpoints in the same private domain, as well as signals to one or more of server data-processing systems  203 - 1  through  203 -N via network  201 , in well-known fashion. It will be clear to those skilled in the art, after reading this specification, how to make and use transmitter  604 . 
     Keypad  605  accepts input signals from the user, and display  606  presents displayable signals to the user, both in well-known fashion. 
       FIG. 7  depicts the salient components of server data-processing system  203 - n  in accordance with the illustrative embodiment of the present invention. Server  203 - n  comprises receiver  701 , processor  702 , memory  703 , and transmitter  704 , interconnected as shown. 
     Receiver  701  is part of a network interface that receives signals from client endpoints (e.g., endpoint  202 - m , etc.) via network  201  and forwards the information encoded in the signals to processor  702 , in well-known fashion. It will be clear to those skilled in the art, after reading this specification, how to make and use receiver  701 . 
     Processor  702  is a general-purpose processor that is capable of receiving information from receiver  701 , executing instructions stored in memory  703 , reading data from and writing data into memory  703 , executing the tasks described below and with respect to  FIG. 9 , and transmitting information to transmitter  704 . In some alternative embodiments of the present invention, processor  702  might be a special-purpose processor. In either case, it will be clear to those skilled in the art, after reading this specification, how to make and use processor  702 . 
     Memory  703  stores the instructions and data used by processor  702 . Memory  703  might be any combination of dynamic random-access memory (RAM), flash memory, disk drive memory, and so forth. It will be clear to those skilled in the art, after reading this specification, how to make and use memory  703 . 
     Transmitter  704  is part of a network interface that receives information from processor  702  and transmits signals that encode this information to client endpoints (e.g., endpoint  202 - m , etc.) via network  201 , in well-known fashion. It will be clear to those skilled in the art, after reading this specification, how to make and use transmitter  704 . 
       FIGS. 8 and 9  depict flowcharts of salient tasks that involve informing a client endpoint that is subscribing to a telecommunications feature about where the feature is being handled (e.g., at another client endpoint  202 - m , at server  203 - n , etc.). In particular, the tasks in  FIG. 8  constitute a first technique, in which the subscribing endpoint first queries other endpoints in the same private domain about one or more capabilities, such as the ability to provide a feature, and then receives a report on where those capabilities can be found. The tasks in  FIG. 9  constitute a second technique in which server  203 - n  informs the subscribing endpoint about where the feature can be found. As those who are skilled in the art will appreciate, some of the tasks that appear in  FIG. 8  or  9  can be performed in parallel or in a different order than that depicted. Moreover, those who are skilled in the art will further appreciate that in some embodiments of the present invention, only the tasks in  FIG. 8  are performed, while in some other embodiments only the tasks in  FIG. 9  are performed, while in still some other embodiments some or all of the tasks in both  FIGS. 8 and 9  are performed. 
       FIG. 8  depicts a flowchart of the salient tasks that are executed by client endpoint  202 - m , in accordance with the illustrative embodiment of the present invention. The depicted tasks involve informing a first client endpoint about where one or more capabilities are being handled, including features that the first client endpoint might subscribe to. The tasks are associated with communication among one or more of client endpoints  202 - 1  through  202 -M and, optionally, with server  203 - n . For pedagogical purposes, the tasks associated with  FIG. 8  are described below as being executed by endpoint  202 - 1 . 
     At task  801 , endpoint  202 - 1  transmits a registration message to a registrar server, which for pedagogical purposes is server  203 - 2 . Referring to  FIG. 5 , endpoint  202 - 1  transmits the message via endpoint  202 - 2 , which handles at least some of the communication with server  203 - 2  as an agent of endpoint  202 - 1 . In some alternative embodiments, endpoint  202 - 1  is able to transmit at least the registration message to server  203 - 2  without the assistance of any other endpoint. 
     At task  802 , in response to having sent the registration message, endpoint  202 - 1  receives a plurality of contact addresses of endpoints (e.g., in a list, etc.) that are associated with the user of private domain  520 . The plurality of contact addresses essentially identifies member endpoints of domain  520  to endpoint  202 - 1 . 
     At task  803 , endpoint  202 - 1  transmits a first message to a second endpoint (e.g., endpoint  202 - 2 , endpoint  202 - 3 , etc.) based on that second endpoint having been identified by a first contact address in the plurality of contact addresses. The first message inquires about one or more capabilities that might be present in the plurality of endpoints. Capabilities that might be present at one or more endpoints include, but are not limited to, the following:
         i. the ability to communicate in a particular manner (e.g., at a specific level of service, via a specific protocol, in a specific format, etc.);   ii. the ability to process or store information in a particular manner;   iii. the ability to present information to an endpoint user in a particular manner; and   iv. the ability to provide a particular telecommunications feature to another endpoint or endpoints.
 
The inquiry might refer to specific capabilities, or the inquiry might be a general request to report back on whatever capabilities are supported. In some alternative embodiments, endpoint  202 - 1  also transmits a capabilities inquiry message to one or more additional endpoints identified by the plurality of contact addresses.
       

     At task  804 , endpoint  202 - 1  receives a second message from one of the members of the plurality of endpoints, wherein the second message comprises a report on one or more capabilities queried about at task  803 . In some embodiments, the member endpoint that reports the capabilities might be the same as the endpoint to which the inquiry was sent, while in some other embodiments the member endpoint that reports the capabilities might be different than the queried endpoint. Furthermore, report messages might be received from more than one endpoint. For example, endpoint  202 - 3  might indicate that it has voice-handling capabilities, and endpoint  202 - 5  might indicate that it has instant messaging capabilities. As another example, endpoint  202 - 2  (i.e., the super peer) might indicate that endpoint  202 - 3  has voice-handling capabilities and endpoint  202 - 5  has instant messaging capabilities. Based on the available capabilities, the querying endpoint can determine the best endpoint or subset of endpoints to handle a particular feature on behalf of the querying endpoint. 
     In accordance with the illustrative embodiment, each queried endpoint determines which capabilities to advertise to endpoint  202 - 1  as being available. In some alternative embodiments, endpoint  202 - 1  instead determines which capabilities it can use out of the reported capabilities, while in some other alternative embodiment yet another endpoint (e.g., super-peer endpoint  202 - 2 , etc.) determines which capabilities endpoint  202 - 1  can use. This determination is based on one or more considerations that include, but are not limited to, the following:
         i. attributes in the private domain, such as the physical proximity of endpoints to each other or the quality-of-service levels that are available for communication;   ii. the identity of the querying endpoint;   iii. other attributes of the querying endpoint, such as one or more capabilities of the endpoint;   iv. attributes of other endpoints;   v. the relationship of two or more endpoints; and   vi. the telecommunications feature that will be subscribed to by the querying endpoint.       

     At task  805 , endpoint  202 - 1  checks whether a particular telecommunications feature is available at an endpoint in domain  520  or at a server, based on one or more capabilities reports that endpoint  202 - 1  received from other endpoints at task  804 . If the feature of interest is to be handled by an endpoint, task execution proceeds to task  806 . Otherwise, if the feature of interest is to be handled by a server, task execution proceeds to task  807 . 
     At task  806 , endpoint  202 - 1  transmits a subscribe message to the client endpoint that is handling the feature being subscribed to (i.e., a designated endpoint), in which the message indicates the feature. In some other embodiments, endpoint  202 - 1  transmits the message to a different member client endpoint in domain  520  than the one that handles the feature, which then processes the subscribe message. Task execution then ends. 
     At task  807 , endpoint  202 - 1  transmits a subscribe message to server  203 - n , in which the message indicates the feature that is being subscribed to. The subscribe process then continues in well-known fashion. Task execution then ends. 
       FIG. 9  depicts a flowchart of the salient tasks that are executed by server data-processing system  203 - n , in accordance with the illustrative embodiment of the present invention. The depicted tasks involve server  203 - n  informing a first client endpoint about where a particular feature is being handled that the first client endpoint is subscribing to. The tasks are associated with communication between one or more client endpoints  202 - m  and server  203 - n . For pedagogical purposes, the tasks associated with  FIG. 9  are described below as being executed by server  203 - 1 , which receives a message from endpoint  202 - 1 . 
     At task  901 , server  203 - 1  receives a subscribe message from client endpoint  202 - 1  that is attempting to subscribe to a particular telecommunications feature. The subscribe message indicates the feature or features to which endpoint  202 - 1  is attempting to subscribe. In some alternative embodiments, server  203 - 1  receives a subscribe message instead from a different member client endpoint of endpoint  202 - 1 &#39;s private domain, which message indicates that endpoint  202 - 1  is attempting to subscribe to a specified feature or features. This might be the case when, for example, a super-peer endpoint is handling the subscribe-related communications between the private domain and server  203 - 1 . 
     At task  902 , server  203 - 1  then determines whether the feature being subscribed to is to be handled by the server itself (or another server such as server  203 - 2 ) or by a designated client endpoint that belongs to the same private domain as endpoint  202 - 1 . This determination is based on one or more considerations that include, but are not limited to, the following:
         vii. the feature itself;   viii. one or more rules that are configured for a business, such as rules that are based on what defines a private domain;   ix. attributes that define a private domain, such as the physical proximity of endpoints to each other;   x. the identity of the endpoint that is attempting to subscribe;   xi. other attributes of the endpoint, such as one or more capabilities of the endpoint; and   xii. attributes of the server itself, such as the current resource utilization of the server.
 
For example, some features are to be always be handled by the server, while other features by an endpoint in the private domain. As a second example, if the determination is based on a rule that involves the bandwidth allocation of a communication channel, a subscribing endpoint that can efficiently communicate with other endpoints in the domain can be redirected to another endpoint in the domain for the feature, while a subscribing endpoint that cannot efficiently communicate with the other endpoints can be directed to the server. As a third example, if the subscribing endpoint is incapable of accessing the feature at another endpoint, the subscribing endpoint can be directed to the server. And as a fourth example, the server might choose to redirect subscribing endpoints to their own private domain only when the current resource utilization at the server rises above a predetermined level.
       

     A variety of telecommunications features can be handled by a designated client endpoint as an agent of the other endpoints in a private domain, instead of being handled by the server. One example of such a feature is a SIP event package, as is known in the art, such as conferencing. Another example of such a feature is the monitoring of device presence, which in a centralized server architecture can result in too much message traffic being offered to the server. Device presence is the low-level state of an individual client device, such as whether the device is on or off. In accordance with the illustrative embodiment, the designated client endpoint can track each device&#39;s presence and then aggregate the presence information to present an overall indication of user availability to server  203 - 1 . As yet another example of a reallocated feature, the designated endpoint can handle media such as voice messaging, instant messaging, and so forth. A more specific example of media handling is call recording, in which a user wants to record a new call. Instead of using mixing resources on the centralized server, one or more endpoints in the private domain bridge on and share the responsibilities for recording and storage of the media. As those who are skilled in the art will appreciate, other telecommunications features than those mentioned in the examples can be handled by a designated client endpoint instead of being handled by the server. 
     The designated client endpoint, which for pedagogical purposes is endpoint  202 - 2 , can be designated in any of a variety of ways as the endpoint to handle the telecommunications feature being subscribed to. The endpoints in the private domain can elect endpoint  202 - 2  or server  203 - 1  can select endpoint  202 - 2  to handle a particular feature. Furthermore, the super-peer endpoint in the illustrative embodiment is also the designated endpoint that handles a feature for its domain; however, as those who are skilled in the art will appreciate in some alternative embodiments, a non-super peer endpoint can handle a feature, or at least a feature that does not require communicating with the servers. And finally, where there are multiple features that are reallocated to the private domain, a first designated endpoint can handle a first feature, a second designated endpoint can handle a second feature, and so forth. 
     At task  903 , server  203 - 1  checks whether the telecommunications feature being subscribed to is to be handled by a designated client endpoint. If the feature is to be handled by a designated client endpoint, then task execution proceeds to task  904 . If not, task execution proceeds to task  906 . 
     At task  904 , server  203 - 1  optionally initiates a call to the designated client endpoint (i.e., endpoint  202 - 2 ), instructing the designated endpoint to assume the handling of the telecommunications feature being subscribed to. This occurs when the designated client endpoint is not already in a state in which it is ready to handle the feature. 
     At task  905 , server  203 - 1  transmits a redirecting message to endpoint  202 - 1  that indicates that the feature being subscribed to is being handled by an endpoint in endpoint  202 - 1 &#39;s private domain. In the illustrative embodiment, the message indicates the particular endpoint that is handling the feature (i.e., endpoint  202 - 2 ). In some alternative embodiments, the message merely indicates that the feature is being handled in the private domain—in which case, it is up to endpoint  202 - 1  to determine the particular endpoint that is handling the feature. 
     Although in the illustrative embodiment server  203 - 1  transmits the message to the subscribing endpoint, in some alternative embodiments server  203 - 1  transmits the message to a different endpoint or endpoints in the private domain (e.g., designated endpoint  202 - 2 , etc.). In this case, it is up to the endpoint that receives the message to inform the subscribing endpoint, which might be indicated in the message or which might need to be determined by the endpoint that receives the message. 
     After server  203 - 1  executes task  905 , task execution proceeds back to task  901 . 
     At task  906 , server  203 - 1  transmits a response to endpoint  202 - 1  that the endpoint has been subscribed to the feature, which is being handled by the server itself. Task execution then proceeds back to task  901 . 
     It is to be understood that the above-described embodiments are merely illustrative of the present invention and that many variations of the above-described embodiments can be devised by those skilled in the art without departing from the scope of the invention. For example, in this Specification, numerous specific details are provided in order to provide a thorough description and understanding of the illustrative embodiments of the present invention. Those skilled in the art will recognize, however, that the invention can be practiced without one or more of those details, or with other methods, materials, components, etc. 
     Furthermore, in some instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the illustrative embodiments. It is understood that the various embodiments shown in the Figures are illustrative, and are not necessarily drawn to scale. Reference throughout the specification to “one embodiment” or “an embodiment” or “some embodiments” means that a particular feature, structure, material, or characteristic described in connection with the embodiment(s) is included in at least one embodiment of the present invention, but not necessarily all embodiments. Consequently, the appearances of the phrase “in one embodiment,” “in an embodiment,” or “in some embodiments” in various places throughout the Specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments. It is therefore intended that such variations be included within the scope of the following claims and their equivalents.