1 Implementation of IMS-based S-CSCF with Presence Service Jenq-Muh Hsu and Yi-Han Lin National Chung Cheng University Department of Computer Science & Information Engineering

2 Outline Motivation Related Work System Design System Implementation Conclusion Future Work

3 Motivation (1/2) Service integration can be crucial for adoption of a personalized lifestyle A user may be reachable through multiple communication forms Voice, , Video, or Instant Messaging 3GPP’s IP multimedia subsystem (IMS) towards the provision of multimedia applications Rapid and efficient the development of innovative multimedia services for convergent networks

4 Motivation (2/2) The presence service is viewed as an indispensable feature for these next-generation services A positive effect on a service operator’s business by helping to generate new revenue and reduce churn Facilitating communications among communities of interest, such as groups of friends, colleagues working on the same projects, and families Numerous new services are currently being designed to take advantage of this feature E.g., push-to-talk (PTT) and instant messaging (IM)

5 Related Work Session Initiation Protocol SIP-based Presence service Four entities are based on 3GPP and IETF definitions Presence service issue

6 Session Initiation Protocol SIP defined in RFC 3261 Application-level text-based signaling protocol For initiating, managing and terminating multimedia sessions with two or more end users SIP is HTTP-like, “Request-Response” Common SIP methods REGISTER, INVITE, ACK,BYE, CANCEL, OPTIONS SIP extensions SUBSCRIBE and NOTIFY, PUBLISH, INFO, REFER …

2xx UACUAS Proxy server Registrar server Location server Proxy server REGISTER INVITE 3xx Redirect server INVITE 2xx REGISTER INVITE 1xx ACK 1xxACK INVITE 1xx ACK Response Status Code Informational Success Redirection Client-Error Server-Error Global-Failure 1xx 2xx 3xx 4xx 5xx 6xx

8 SIP-based Presence service Four components in SIP presence service Principal User supported by presence service and the owner of presentity Presentity Represent the principal’s ability and willingness to communicate and rules on how information can be accessed Watcher An entity subscribes to or that requests information from a presentity Presence server A network entity is responsible for managing presence information

9 Call Flow of SIP-based Presence Presence server Authorized watcher Notify watcher of current state Notify watcher of state change PresentityWatcher SUBSCRIBE 200 OK NOTIFY 200 OK PUBLISH NOTIFY 200 OK Publisher authorization Watcher subscribes to a particular event (i.e., contact) Status update Notifications are sent to all subscribed watchers

10 Presence service issue (1/2) Using distributed presence information in converged networks lacks for efficient querying and resource management Such presence-based services exploit the joint presence information of a SIP entity requesting a service and a SIP resource providing a service The collective presence information is distributed across multiple presence servers

11 Presence service issue (2/2) Propose an integral management of presence information scheme Each end user can obtain the latest buddies’ presence information from the centralized presence server via a request of subscription Design a centralized presence server to facilitate the management of presence information Personal information of subscribers, VoIP sessions, and Instant Messaging services in converged networks Implementation based on the well-known open source: SER (SIP Express Router)

12 System Design To support an integral management of presence information scheme PA (Presence Agent) Module Deployment PA (Presence Agent) Module Architecture Events of SUBSCRIBE and NOTIFY messages - subscription of presence information Event of PUBLISH message - collection of presence information Event of UNSUBSCRIBE message - unsubscription of presence information

13 Presentity Subscriber Presence Agent (PA) Module Subscribed Principal Watcher Local proxy Local proxy Internet SIP Express Router MySQL presentity Table subscriber Table watcherinfo Table REGISTER 200 OK SUBSCRIBE 401 Unauthorized RESPONSE 202 Accepted SUBSCRIBE NOTIFY 200 OK PUBLISH 200 OK UNSUBSCRIBE 200 OK NOTIFY 200 OK UNSUBSCRIBE 200 OK location Table User Current Presence User Current Presence User Current Presence User Current Presence User Presence Change User Presence Change PUBLISH 200 OK Management of Presence Information Scheme

14 PA Module Deployment (1/2) User Agent (Kphone 4.2) has following functionalities After registration, an initial PUBLISH message is issued Make subscription between the buddies in order to fetch someone’s presence information Whenever user status change occurs, a triggered delivery of publishing with the latest presence information An additional support to cancel subscriptions for the existing contacts and someone’s presence information becomes unavailable

15 PA Module Deployment (2/2) PA (Presence Agent) module uses following process On taking publishing from UAs to keep the up-to- date presence information After the approval of subscriptions, a notification with watcher information is dispatched to the specified UA In the receipt of UNSUBSCRIBE message the status of presentity entity is set to CLOSED

16 PA Module Architecture Presence Agent (PA) Module Presence Agent (PA) Module Watcher Subscribed Principal Presentity Presence protocol SIP / SIMPLE Presence Server (SER Core) Presence Server (SER Core) MySQL presentity Table subscriber Table watcherinfo Table Watcher information PUBLISH NOTIFY SUBSCRIBE

17 existing_subscription Presence Agent (PA) Presence Agent (PA) Message Method = SUBSCRIBE MySQL db_query MySQL db_reply (200) handle_subscription db_insert db_reply (200) 200 OK Message Method = NOTIFY Watcher watcherinfo Table presentity Table existing_subscription Presence Agent (PA) Presence Agent (PA) Message Method = SUBSCRIBE MySQL db_query MySQL db_reply (404)t_reply (481) add_presentity db_insert db_reply (200) t_reply (202) Subscriber presentity Table Events of SUBSCRIBE and NOTIFY messages

18 Event of PUBLISH message handle_publish Presence Agent (PA) Presence Agent (PA) Message Method = PUBLISH MySQL db_update MySQL db_reply (200) watcher_exists db_query db_reply (200) Subscribed Principal watcherinfo Table presentity Table db_reply (200) Watcher NOTIFY 200 OK

19 Event of UNSUBSCRIBE message existing_subscription Presence Agent (PA) Presence Agent (PA) Message Method = UNSUBSCRIBE MySQL db_query MySQL db_reply (200) free_subscription db_del db_reply (200) Watcher watcherinfo Table presentity Table

20 System Implementation - Subscription & Status update

21 System Implementation - Cancel subscription (Unsubscription)

22 Conclusion We propose an integral management of presence information scheme By this way, every network resource and user situation can be represented by the presence service We implement a SIP-based, centralized presence server Flexible integration with existing networks and applications to create new or enhanced services and solutions E.g., Push-To-Talk over Cellular (PoC) service, video call, and video conference

23 Future Work Making a study of presence-based admission control mechanism for 4G core networks High user-perceived quality, adaptive applications and adaptation-supportive network entities To improve quality of video reception allowing UA to automatically adapt itself when network topology changes To coordinate the resource demand and supply Integrating Context-aware capability To achieve Quality of Service and resource efficiency in a multi-user context