The Services in the PSTN/IN Requesting InTernet Services (SPIRITS) 
Working Group addresses how services supported by IP network entities 
can be started from IN (Intelligent Network) requests, as well as the 
protocol arrangements through which PSTN (Public Switched Telephone 
Network) can request actions to be carried out in the IP network in 
response to events (IN Triggers) occurring within the PSTN/IN.  SPIRITS 
concerns architecture and protocols for secure transport of IN trigger 
information (requests for actions, as well as plain event 
notifications, 
including parameters) from PSTN/IN to the IP network, and optional 
responses from the IP network back to the PSTN/IN.

The SPIRITS architecture includes, but not limited to, three 
potentially
independent entities:

 - the SPIRITS client

 - the SPIRITS server

 - the PSTN/IN requesting system

The SPIRITS client is the entity that requests notification or some 
actions to be performed in the IP network.  The SPIRITS server is the 
entity that receives notifications or requests from the PSTN/IN and 
returns optional responses back to the PSTN/IN, while initiating 
execution of the services requested in the IP domain.  The SPIRITS 
server and PSTN/IN requesting sytem both reside in the IP domain, with 
PSTN/IN entity on the boundary between the IP and PSTN/IN networks.  
The 
presence of three independent parties implies a requirement to support 
complex trust models. Accordingly, the security architecture must 
support limited trust between the parties.

The parameters passed in any SPIRITS Service request are limited
to information available from PSTN/IN entities. An example of such a
service is Internet Call Waiting: on an incoming PSTN call, an IP node
is notified of the call and can then carry out some actions. Definition 
of any information or data within the PSTN is the responsibility of the 
ITU-T and so is out of scope for SPIRITS.

The target of this working group is to describe building blocks for 
PSTN-IP services that start from PSTN/IN requests, and not to 
standardize the PSTN-IP services themselves.  The WG will focus on an 
event-oriented design, rather than a service-oriented design.  Specific 
services to be considered initially as examples are: (1) Incoming Call 
Notification (Internet Call Waiting); (2) Internet Caller-Id Delivery; 
and (3) Internet Call Forwarding and "Follow Me".

SPIRITS will:

o Produce an Informational RFC that describes current practices
  for supporting the services in question.

o Produce an Informational RFC on the overall architecture of 
  SPIRITS-type services.

o Develop a Standards Track RFC that specifies a protocol by
  which PSTN Intelligent Network Service Nodes (or any other
  node that implements the Service Control Function) can
  request services of IP hosts, and which can return status
  indications to the PSTN/IN.

o Consider security and privacy issues relating to providing
  functions of SPIRITS type. In particular, understand any
  threats posed by this technology and address them in the
  proposed standard.
 
o Develop a standards track RFC for a SPIRITS MIB to support the
  service management protocol between Internet applications and the
  PSTN/IN Service Management System.  The MIB is to conform to SNMP
  standards.

SPIRITS will collaborate with other IETF WG's working on similar issues
and having expertise in PSTN/IP interworking (IPTEL, MMUSIC, PINT, 
SIP).
SPIRITS will also establish communication with other relevant standard
bodies (ITU-T SG11).