Network Working Group L. Slutsman, Editor Request for Comments: 3136 AT&T Labs Category: Informational I. Faynberg H. Lu M. Weissman Lucent Technologies June 2001 The SPIRITS Architecture Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2001). All Rights Reserved.
AbstractThis document describes the architecture for supporting SPIRITS services, which are those originating in the PSTN (Public Switched Telephone Network)and necessitating the interactions between the PSTN and the Internet. (Internet Call Waiting, Internet Caller-ID Delivery, and Internet Call Forwarding are examples of SPIRIT services.) Specifically, it defines the components constituting the architecture and the interfaces between the components. Section 2 describes example SPIRITS services from the end-user point of view; + Section 3 describes the SPIRITS architecture;
1]. Typical ways for handling a call include: + Accept the incoming call over the PSTN by terminating the Internet connection. (As switching cannot be done immediately, the caller may hear an opening announcement followed by the "ringing" tone.) + Forward the incoming call to another telephone number. The subscriber will remain connected to the Internet, while the caller will hear an announcement indicating the call is being forwarded and eventually be connected to the new destination number. + Accept the incoming call by voice over IP. The subscriber will answer the incoming call via the already established Internet connection. (The proposed SPIRITS architecture, however, does not reflect this feature.) + Redirect the incoming call to voice mail. The subscriber will remain connected to the Internet, while the caller will hear an announcement inviting him (or her) to leave a message. + Play a pre-recorded message to the calling party and disconnect the call. The subscriber will remain connected to the Internet. + Reject the incoming call. The subscriber will remain connected to the Internet, while the caller will hear an announcement rejecting the call. The subscriber may specify the call treatment on the fly when notified of an incoming call. Alternatively, the subscriber may specify a priori a general treatment for all calls (e.g., re-directed to voice mail) or call treatments tailored to the origination numbers. As a result, when a call comes in, the subscriber won't be presented the call but can examine afterwards the treatment and outcome of the call from the log that is kept for all the calls
processed during the ICW service. Typical information recorded in the log includes the incoming call date and time, calling party number, calling party name, and call disposition. Section 2.1. Otherwise, the subscriber's IP host serves as an auxiliary device of the telephone to which the call is first sent. Section 2.1. Otherwise, the subscriber's IP host serves as an auxiliary device of the telephone to which the call is first sent. Figure 1 of the Appendix depicts the SPIRITS architecture, which includes the following entities: 1. Service Control Function (SCF) , which executes service logic, interacts with the entities in the IP domain (e.g., the SPIRITS Gateway and PINT Server) through the SPIRITS Client, and instructs the switches on how to complete a call. Physically, the SCF may be located in either stand-alone general-purpose computers called Service Control Points (SCPs) or specialized pieces of equipment called Service Nodes (SNs) . 2. Service Switching Function (SSF) , which normally resides in a switch and is responsible for the recognition of Intelligent Network (IN) triggers and interactions with the SCF. 3. SPIRITS Client, which is responsible for receiving PSTN requests from the SCF as well as sending responses back. It may be co- located with the SCF. If not, it communicates with the SCF over the D interface.
4. PINT Server, which receives PINT requests from the PINT Client and relays them to the PSTN for execution over the E interface. 5. SPIRITS Gateway, which is co-located with the PINT Server or PINT Gateway (or both when they are co-located as assumed here for simplicity) and serves as an intermediary between the SPIRITS Server and SPRITS Client via the B and C interfaces, respectively. 6. PINT Client, which resides in the subscriber's IP host and is responsible for initiating PINT requests, which are sent to the PINT server over the A interface. 7. SPIRITS Server, which terminates PSTN requests and is responsible for all interactions (e.g., incoming call notification and relaying the call treatment) between the subscriber and the SPIRITS Gateway. The rest of the Section describes the interfaces between the entities in detail. Section 2). In addition, this interface may be used for service subscription.
The SCF "transforms" the user's disposition into appropriate actions, such as playing an announcement to the caller, and resuming the suspended call processing in the SSP. Figure 1 demonstrates, there are two distinct communications interfaces, B and C. The B interface is, in general, across the public Internet and is thus most vulnerable to security attacks resulting in theft or denial of service. The C interface, on the other hand is likely to be implemented across a service provider's intranet, where the security measures should be applied at the discretion of the service provider. Even then, because at least one IP host (the PINT gateway) is connected to the Internet, special measures (e.g., installation of firewalls, although this particular measure alone may be insufficient) need to be taken to protect the interface C and the rest of the network from security attacks. The assumption that the PINT Client and SPIRITS server are co- located, dictates that the security considerations for the A and B interfaces are exactly the same. Detailed security requirements and solutions for interface A (and, consequently, B) can be found in RFC 2848 . In addition, security requirements are listed in the companion SPIRITS Protocol Requirements RFC.
 Lu, H., Editor, Faynberg, I., Voelker, J., Weissman, M., Zhang, W., Rhim, S., Hwang, J., Ago, S., Moeenuddin, S., Hadvani, S., Nyckelgard, S., Yoakum, J. and L. Robart, "Pre-SPIRITS Implementations of PSTN-Initiated Services", RFC 2995, November 2000.  Faynberg, I., L. Gabuzda, M. Kaplan, and N.Shah, "The Intelligent Network Standards: Their Application to Services", McGraw-Hill, 1997.  Petrack, S. and L. Conroy, "The PINT Service Protocol: Extensions to SIP and SDP for IP Access to Telephone Call Services", RFC 2848, June 2000.
...................... +----------------+ . . | +------------+ | . +------------+ . | | | | A . | | . | | PINT Client|********************|PINT Server/|******** | | | | . Gateway | * | +------------+ | . +------------+ . * | | . . * | Subscriber's | . . * | | . . * | IP Host | . . * | | . +------------+ . * | +------------+ | . | SPIRITS | . * | | SPIRITS | | B . | Gateway | . * | | Server |********************| | . * E | | | | . +------------+ . * | +------------+ | . * . * +----------------+ . * . * ...........*.......... * //-------\\ * * /// \\\ * * | Subscriber's | * C * | Telephone | * * \\\ /// * * \\ -------// * * * * * * * * ++++++++++++++++++++++++++ PSTN ++++++++++++++++++++++++++ * * * * * * * +------------------+ * * Line | SPIRITS Client | * * | | * +--------------------+ +---+----- D ---------+-*+ | | INAP/SS7 | | |Service Switching ************Service Control Function | | Function | | | | | +-------------------------+ | | | | +--------------------+ Figure 1: SPIRITS Architecture
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