rfc2995.txt

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            |              |            |                         |
        +---+---+      +---+---+                                  |
        |  IP   |      |  SSP  |                                  |
        +-------+      +---+---+                        +-------------+
                           |                   +---+    |  (UAC/UAS)  |
                       +---+---+              ||   ||   |    ICW      |
             |---------|  LEX  |--------------  + +     |Client System|
           +---+       +-------+               +++++----+-------------+
          ||   ||                             (callee)
            + +                           ICW Subscriber's Phone and PC
           +++++
         (caller)

                INAP : Intelligent Network Application Protocol
                PINT : PSTN/Internet Interworking Protocol
                SL   : Service Logic
                UAS  : User Agent Server
                UAC  : User Agent Client

     Figure 1: Network Architecture of the Korea Telecom ICW Service






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3.3. Network Entities

3.3.1. SSP

   The SSP performs the Service Switching Function (SSF) and Call
   Control Function (CCF).  When detecting that the called party is busy
   (T_Busy), the SSP sends a query to the SCP and processes the call
   under the control of the SCP.

3.3.2. SCP

   The SCP performs the Service Control Function (SCF) and Service Data
   Function (SDF).  It, when queried, instructs the SSP to process the
   call based on the service logic.  In the case of the ICW service, the
   service logic ultimately governs the notification of a waiting call
   to an online ICW subscriber and the disposition of the call.  In
   addition, the SCP performs the Service Control Gateway Function
   (SCGF) for protocol inter-working between the PSTN/IN and Internet.
   It translates the SIP message from the ICW Server to the service
   control interface message and vise versa.  The SCGF is an IP end
   point and behaves as a UAS (User Agent server) or UAC (User Agent
   client).

3.3.3. IP

   The IP contains Service Resource Function (SRF).  It, when necessary,
   plays announcements to the calling party during the ICW service
   before/after receiving the response from the ICW subscriber and
   records the calling party number or voice message from the calling
   party when the call is forwarded to the Voice Mail System (VMS).

3.3.4. ICW Server System

   The ICW Server system serves as a SIP proxy or a redirect server for
   message routing between the ICW Client and SCGF.  The ICW Server is
   also responsible for managing the ICW Clients that are connected to
   it.  When an ICW Client (subscriber) sends a registration request for
   the ICW service, the ICW Server relays that request to the SCP, waits
   for the result of authorization from the SCP, and registers the
   authorized subscriber in its data base.  In addition, the ICW Server
   monitors the connection status of the registered ICW Clients.  As
   soon as a client deactivates the ICW service or terminates the
   Internet connection, the ICW Server detects the status change and
   deactivates the ICW service for the client.  Finally, the ICW Server
   manages profiles for each ICW subscribers as well as logs all the
   call processing results.





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3.3.5. ICW Client System

   The ICW Client System is an application program running on the
   subscriber's PC.  Launched as soon as the subscriber powers on the
   PC, it monitors the Internet connection status of the PC (or
   subscriber).  Upon the subscriber's connection to the Internet, the
   ICW Client sends a REGISTRATION request to the SCGF via the ICW
   Server and then eventually to the SCP.  In this capacity, the ICW
   Client acts as a UAC to the SCGF, which acts as a UAS.  Thereafter it
   notifies the ICW Server periodically of the connection status of the
   subscriber.

   The ICW Client is also responsible for popping up a dialog box on the
   subscriber's PC to announce an incoming call.  The dialog box
   displays the number and name of calling party, calling time, and the
   call processing options (including Accept, Reject, Forward to another
   number or VMS).  After the subscriber selects the option, the ICW
   Client sends it to the SCP.  In this capacity, the ICW Client acts as
   a UAS.

   Depending on the pre-defined ICW Service Profile, the ICW Client may
   screen the incoming call before notifying the subscriber.

   The ICW Client manages the ICW Service Profile, which contains the
   following fields:

   o  Subscriber Information (including, Name, Directory Number,
      Password)

   o  Service Status (Activation/De-activation)

   o  Automatic Call Processing Method

    + Call Processing Method on No Answer (Reject/Forward/VMS) - The
      call is automatically handled by the method if the subscriber
      doesn't respond after a pre-defined period of time.

    + Do Not Disturb Mode (On/Off) - When this is set on, the subscriber
      won't be notified of the incoming calls.

    + Call Processing Method on Do Not Disturb (Reject/Forward/VMS)

    + Call Processing List by Calling Party Numbers
      (Accept/Reject/Forward/VMS) - Calls originated from a number on
      the list are handled by the associated call processing method.

   o  The ICW Client records the call processing method and the result
      for each incoming call in a log file on the subscriber's PC.  The



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      call record in the call log contains the following information:

   - Calling Time
   - Calling Party Number
   - Calling Party Name (optional)
   - Call Processing Method (Accept/Reject/Forward/Forward to VMS)
   - Result (Success/Fail)

3.3.6. Firewall

   Packet Filtering Firewall Systems are between the ICW server and
   clients as well as between the SCGF and ICW server for accessing the
   Korea Telecom IN Nodes.

3.4. Network Interfaces

   o  The SCF-SDF, SCF-SSF, and SCF-SRF interfaces are the same as
      existing PSTN IN Interfaces based on the KT INAP CS-1.

   o  The SCGF-SCF interface relays requests either from the IN or the
      Internet and is implemented based on the internal API of the SCP.

   o  The SCGF-ICW Server and ICW Server-ICW Client interfaces are
      implemented based on the PINT Service Protocol V.1.  We adopted
      UAS-Proxy-UAC relationships as shown in Figure 2.

           +---------+        +-------------+        +---------+
           |(UAC/UAS)|PINT 1.0|   (Proxy)   |PINT 1.0|(UAC/UAS)|
           |         |--------|     ICW     |--------|   ICW   |
           |  SCGF   |        |    Server   |        |  Client |
           +---------+        +-------------+        +---------+

                  Figure 2: PINT Protocol Architecture

3.5. Protocols

3.5.1. Intelligent Network Application Part Protocol (INAP)

   The SCP, SSP, and IP support the KT INAP V1.0, which is based on
   ITU-T INAP CS-1 with the incorporation of two INAP CS-2 messages [PRM
   (PromptAndReceiveMessage) and EM (EraseMessage)] for recording the
   voice message.

3.5.2. PINT Protocol

   The ICW service uses the PINT Service Protocol 1.0 [1] for
   communications between the SCP and the ICW Server System, and between
   the ICW Server System and the ICW Client System.  Developed in the



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   IETF PINT Working Group for invoking telephone services from an IP
   network, the PINT Service Protocol 1.0 specifies a set of
   enhancements to SIP 2.0 and SDP.

   Summarized below are the elements of the PINT Service Protocol 1.0
   relevant to the Korea Telecom ICW implementation:

      o REGISTER

      The REGISTER method is used to inform the SCP of the connection
      status of an ICW subscriber.  With this method, the ICW Client
      sends to the ICW Server the IP address (of the PC) and phone
      number of the subscriber when the subscriber is first connected to
      the Internet.  The ICW server relays the information to the SCP,
      which updates the data base (if the subscriber is authorized), and
      in the end sends a registration acknowledgment to the ICW Server
      and then the Client.  After the subscriber is connected to the
      Internet, the ICW Client sends a REGISTER request to the ICW
      Server periodically at a pre-defined interval (e.g., 20 seconds)
      to indicate its connection status.  The request is not relayed to
      the SCP.  The ICW Server only checks if it is from the authorized
      subscriber.  Finally, when the subscriber terminates the Internet
      connection, the Client sends the last REGISTER request to the SCP
      via the ICW Server.  If the REGISTER request does not arrive
      during the pre-defined interval, the ICW Server can also detect
      the change of the connection status of the ICW Client.

      o INVITE

      The SCP uses the INVITE method to notify the ICW Client, via the
      ICW Server, of an incoming call.

      o ACK

      Both the SCP and the ICW Server use the ACK method to confirm the
      receipt of the final responses to their requests.

      o BYE

      The BYE method terminates a service session.  In addition to this
      original usage, we use the value (success or failure) of the
      Subject header to indicate the result of the desired disposition
      of an incoming call in the PSTN.








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      o CANCEL

      When the calling party releases the call before the called party
      responds, the SCP sends a CANCEL request to the ICW Client to
      cancel the INVITE request that it sent previously.

      o OPTION

      This method is not used in the KT implementation.

      o Responses

      The SCP responds to a REGISTER request with one of the status
      codes and associated comments below:

      . 100 Trying: Trying
      . 200 OK: Registered

      The ICW Client responds to an INVITE request with one of the
      status codes and associated comments below:

      . 100 Trying: Trying
      . 200 OK: Accept the Call
      . 303 see other: Forward the Call to Another Number
      . 380 alternative service: Forward the Call to the VMS
      . 603 decline: Reject the Call

3.6.  Example Scenarios

3.6.1. ICW Service Subscription

   Access to the Korea Telecom ICW service is by subscription.  Here
   Korea Telecom serves as both the PSTN operator and IN-based ICW
   service provider.  Note that the subscription data need to be loaded
   onto the relevant SSPs, including the local ones that may not be
   operated by Korea Telecom.

3.6.2. ICW Client Installation

   An ICW subscriber should install the ICW Client program in his or her
   PC.  The ICW Client is automatically activated to run as a daemon
   process when the subscriber's PC is turned on.  The Client monitors
   the Internet connection status of the subscriber.








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