Abstract:
The present invention discloses a system and method for stateless publish/subscribe messaging using SIP that provides SIP with similar functionality to JMS™-based publish/subscribe messaging, thereby allowing client applications that require both SIP and JMS™ messaging to be implemented using SIP only.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to computer-based messaging in general, and more particularly to publish/subscribe messaging of stateless information using the Session Initiation Protocol (SIP). 
         [0003]    2. Related Art 
         [0004]    In classic publish/subscribe messaging systems, such as those modeled by the Java™ Message Service™ (JMS™) Application Programming Interface (API), a computer-based subscriber client application subscribes to a topic, where the subscription is managed by a messaging server. A publisher application then publishes messages to the topic by sending them to the messaging server, which then sends the messages to subscriber clients that subscribed to the topic. Such topics might include, for example, basketball, with basketball articles and game scores being published to the topic and sent to its subscribers. JMS™ supports durable subscriptions where published messages are stored for a subscriber when the subscription is not active, with the stored messages being sent to the subscriber when the subscription becomes active again (i.e., the subscriber resumes the subscription). 
         [0005]    Publish/subscribe messaging systems which use the Session Initiation Protocol (SIP) differ from classic publish/subscribe messaging systems, mainly in that in the SIP publish/subscribe model the client subscribes to the state of an entity rather than to a topic, where the state of the entity is published to and managed by a presence server. In SIP, a published event reflects a change in the state of an entity, which change is noted by the presence server. SIP does not support durable subscriptions, as past publications of an entity&#39;s previous states are not stored, an only the current state of an entity is transferred to a subscriber. 
         [0006]    Client applications that use both JMS™ and SIP services currently require a separate engine for each. This has several drawbacks, including: 
         [0007]    Requiring the implementation of two heavy messaging infrastructures at the server, each with its overhead of installation, administration, high availability and scalability requirements, etc.; 
         [0008]    Requiring the client application to be implemented with two different sets of APIs and protocols; 
         [0009]    Large client applications, which pose a problem for mobile clients with limited memory and CPU capacity; and 
         [0010]    Duplicative authentication and authorization against both the SIP and the JMS™ servers. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention discloses a system and method for stateless publish/subscribe messaging using Session Initiation Protocol (SIP) that provides SIP with similar functionality to JMS™-based publish/subscribe messaging, thereby allowing client applications that require both SIP and JMS™ messaging to be implemented using SIP only. 
         [0012]    A first aspect of the invention provides a system for stateless publish/subscribe messaging using Session Initiation Protocol (SIP), the system comprising: an SIP server configured to manage a subscription regarding an entity; and an SIP publisher configured to publish a message regarding said entity to said SIP server. 
         [0013]    A second aspect of the invention provides a method for stateless publish/subscribe messaging using Session Initiation Protocol (SIP), the method comprising: receiving an SIP subscription message initiating a subscription for published messages relating to a stateless entity; receiving a published message relating to said entity; and forwarding said message to an SIP subscriber associated with said subscription without updating a state table to indicate a state of said entity. 
         [0014]    A third aspect of the invention provides a program product stored on a computer-readable medium, which when executed, enables statelsess publish/subscribe messaging using Session Initiation Protocol (SIP), the program product comprising: program code for receiving a Session Initiation Protocol (SIP) subscription message initiating a subscription for published messages relating to a stateless entity; program code for receiving a published message relating to said entity; and program code for forwarding said message to a SIP subscriber associated with said subscription without updating a state table to indicate a state of said entity. 
         [0015]    A fourth aspect of the invention provides a method for deploying an application for enabling stateless publish/subscribe messaging using Session Initiation Protocol (SIP), comprising: providing a computer infrastructure being operable to: receive an SIP subscription message initiating a subscription for published messages relating to a stateless entity; receive a published message relating to said entity; and forward said message to a SIP subscriber associated with said subscription without updating a state table to indicate a state of said entity. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the appended drawings in which: 
           [0017]      FIG. 1A , is a simplified conceptual illustration of a system for stateless publish/subscribe messaging using SIP, constructed and operative in accordance with a preferred embodiment of the present invention; 
           [0018]      FIG. 1B  is a simplified flowchart illustration of an exemplary method of operation of the system of  FIG. 1A , operative in accordance with a preferred embodiment of the present invention; 
           [0019]      FIG. 2A  is a simplified flowchart illustration of a method for providing durable SIP subscriptions, operative in accordance with a preferred embodiment of the present invention; and 
           [0020]      FIG. 2B  is a simplified flowchart illustration of a method for publishing durable SIP subscriptions, operative in accordance with a preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Reference is now made to  FIG. 1A , which is a simplified conceptual illustration of a system for stateless publish/subscribe messaging using SIP, constructed and operative in accordance with a preferred embodiment of the present invention, and additionally to  FIG. 1B , which is a simplified flowchart illustration of an exemplary method of operation of the system of  FIG. 1A , operative in accordance with a preferred embodiment of the present invention. In the system and method of  FIGS. 1A and 1B , an SIP subscriber client  100 , such as may reside on a computing platform  102  such as a personal computer or a cellular telephone, submits a subscription to an SIP server  104 , such as an SIP presence server, for information regarding an entity  106 , such as a basketball news topic. In order to distinguish from the stateful SIP “presentity,” the term “entity” is used herein to indicate that SIP entities as implemented in the context of the present invention may be “stateless,” in that messages that are published for stateless entities are not intended to indicate a current entity state, and include, as such, “stateless” information. An SIP publisher  108 , such as may reside on a computing platform  110  submits publications associated with entity  106  to server  104 . Whereas in classic SIP applications such a subscription is for stateful information regarding the current state of an entity which is maintained by server  104  in a state table  112  (e.g., status is online, offline, busy, etc., where the entity is, for example, a cellular telephone subscriber), in accordance with the present invention the subscription may be for stateless information, such as a basketball game score published in connection with entity  106 , being the basketball news topic in the present example. This may be accomplished by publisher  108  using a standard SIP PUBLISH message with the EXPIRES header field set to a predetermined value, such as zero, a non-zero value, or a value exceeding a predefined maximum value. Server  104  may in turn be configured to recognize the predetermined value of the EXPIRES header field as identifying a publication of stateless information regarding entity  106 , and not including stateful information that is to be maintained as such by server  104 . Server  104  thus forwards such publications to subscriber  100  without updating state table  112 , as the publication is of stateless information. Alternatively, a separate header field may be used to identify the PUBLISH message as carrying stateless information, instead of using the EXPIRES field. Server  104  may then be configured to identify this field as such. 
         [0022]    The system of  FIG. 1A  may be used to provide content-based subscriptions, where subscribers may define filtering criteria and receive messages that match their criteria. Content-based filtering is enabled by associating an event schema with a message. An event schema, which is sometimes referred to as a message schema, defines the type of the information contained in a message, with the system of  FIG. 1A  preferably supporting multiple event schemas. For example, the schema for sports news may define a news item as containing the following attributes: title, sports (e.g., basketball, football, etc.) league, teams mentioned, individual players mentioned and item body. Server  104  may support content-based subscriptions for stateless messages using standard SIP subscriptions. Subscriber  100  may submit a SIP subscription for entity  106 , such as basketball news topic, and include filtering criteria such as [league=“NB36”] and [players INCLUDE “Michael Jordan”]. Server  104  preferably checks filtering criteria for messages published in connection with entity  106 , forwarding only those messages that meet the criteria to subscriber  100 . 
         [0023]    Reference is now made to  FIG. 2A , which is a simplified flowchart illustration of a method for providing durable SIP subscriptions, operative in accordance with a preferred embodiment of the present invention, and additionally to  FIG. 2B , which is a simplified flowchart illustration of a method for publishing for durable SIP subscriptions, operative in accordance with a preferred embodiment of the present invention. In the method of  FIGS. 2A and 2B , which may be implemented by the system of  FIG. 1A , support for durable subscriptions may be provided by server  104  upon receiving a request from subscriber  100  for a durable subscription. Such a request may be conveyed as part of the subscription by using a field to indicate whether or not the subscription is a durable subscription. Server  104  may in turn be configured to recognize whether or not a subscription is a durable subscription, storing published messages intended for subscriber  100  while subscriber  100  is not active, and forwarding stored messages to subscriber  100  when subscriber  100  again becomes active and resumes the subscription. Whereas in JMS™ “not active” typically refers to a connection to a JMS™ server that is severed, in accordance with the present invention a subscriber is considered to be “not active” with regard to an SIP session when the client fails to acknowledge the receipt of a NOTIFY message. Server  104  may retain the messages until subscriber  100  acknowledges receipt of the messages, or until the subscription expires. If additional messages associated with entity  106  are published while subscriber  100  is not active, server  104  preferably stores the messages and does not attempt to send the messages to subscriber  100 . Subscriber  100  may again become active by resuming the subscription, such as by sending a SUBSCRIBE message for entity  106 . If subscriber  100  resumes the subscription before it expires, server  104  preferably sends all the stored messages that were stored to subscriber  100 . The stored messages may be sent one by one using NOTIFY messages. Preferably, only after subscriber  100  acknowledges the receipt of the NOTIFY message is the message removed from the buffer of messages waiting to be sent to subscriber  100 . 
         [0024]    Since SIP allows subscriptions to have distant expiration dates, a time limit may be placed on the life of a durable subscription, such as to avoid overflow of stored messages at server  104 . For example, whereas the SIP protocol definition does not put any limit on the expiration period, server  104  may be configured to have a limit on the expiration of durable subscriptions. 
         [0025]    It is appreciated that the present invention will allow SIP applications to implement publish/subscribe messaging for stateless events at the server while supporting durable subscriptions. 
         [0026]    It is appreciated that one or more of the steps of any of the methods described herein may be omitted or carried out in a different order than that shown, without departing from the true spirit and scope of the invention. 
         [0027]    While the methods and apparatus disclosed herein may or may not have been described with reference to specific computer hardware or software, it is appreciated that the methods and apparatus described herein may be readily implemented in computer hardware or software using conventional techniques. 
         [0028]    While the present invention has been described with reference to one or more specific embodiments, the description is intended to be illustrative of the invention as a whole and is not to be construed as limiting the invention to the embodiments shown. It is appreciated that various modifications may occur to those skilled in the art that, while not specifically shown herein, are nevertheless within the true spirit and scope of the invention.