service
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... 2].
These emerging standards have opened up the possibility of a broad
and dramatic decentralization of the provisioning of telephone
services so they can be under the user's control.
Many Internet telephony ...
...
Many Internet telephony services can, and should, be implemented
entirely on end devices. Multi-party calls, for instance, or call
...
... Multi-party calls, for instance, or call
waiting alert tones, or camp-on services, depend heavily on end-
system state and on the specific content of media streams ...
... media streams,
information which often is only available to the end system. A
variety of services, however -- those involving user location, call
distribution, behavior when end systems are busy, and the like -- are
independent of a particular end device, or need to be operational
...
... independent of a particular end device, or need to be operational
even when an end device is unavailable. These services are still best
located in a network device, rather than in an end system.
...
... services have been created only by
service providers. Service creation typically involved using
proprietary or restricted tools ...
... created only by
service providers. Service creation typically involved using
proprietary or restricted tools, and there was little range ...
... Internet
environment, however, this changes. Global connectivity and open
protocols allow end users or third parties to design and implement
new or customized services, and to deploy and modify their services
dynamically without requiring a service provider ...
... protocols allow end users or third parties to design and implement
new or customized services, and to deploy and modify their services
dynamically without requiring a service provider to act as an
...
... services, and to deploy and modify their services
dynamically without requiring a service provider to act as an
intermediary.
...
... environment for Internet telephony, we need a standardized, safe way
for these new service creators to describe the desired behavior of
network servers.
...
... terminals and other endpoints. The gatekeeper may also
provide other services to the endpoints such as bandwidth
...
... script: A particular instance of a CPL, describing a particular
set of services desired.
end system: A device from which and to which calls are
...
... Example services ...
... To motivate the subsequent discussion, this section gives some
specific examples of services which we want users to be able to
create programmatically. Note that some of these examples are
...
... o Script creation by end user
In the most direct approach for creating a service with a CPL,
an end user simply creates ...
... CPL,
an end user simply creates a script describing their service.
He or she simply decides what service he or she wants,
...
... creates a script describing their service.
He or she simply decides what service he or she wants,
describes it using a CPL script, and then uploads it to a
...
... language, it can also be used
to allow third parties to create or customize services for
clients. These scripts can then be run on servers owned by the
...
... clients. These scripts can then be run on servers owned by the
end user or the user's service provider.
o Administrator ...
... administrators to create
simple services or describe policy for servers they control.
If a server is implementing CPL services ...
... services or describe policy for servers they control.
If a server is implementing CPL services in any case, extending
the service architecture to allow administrators ...
... CPL services in any case, extending
the service architecture to allow administrators as well as
users to create ...
... o Web middleware
Finally, there have been a number of proposals for service
creation or customization using web interfaces. A CPL ...
... create a CPL script on behalf of a user, and the
telephony server could then implement the services without
either component having to be aware of the specifics of the
other.
...
... signalling information may have bypassed them. This architectural
limitation implies a number of restrictions on how some services can
be implemented. For instance, a network system cannot reliably know
...
... associated with; while scripts associated with user addresses are
probably the most useful for most services, there is no reason that a
script could not be associated with any other type of address as
...
... customize which department the user wishes to be found at, for
instance, whereas a script at the departmental server could be used
for more fine-grained location customization. Some services, such as
filtering out unwanted calls, could be located at either server. See
...
... register themselves with; this may be through manual configuration,
or through automated means such as the Service Location Protocol [7].
It has been proposed that automated means of locating such servers
...
... claim to solve it, but the problem is not any worse for CPL scripts
than for any other means of deploying services.
Another class ...
... The ITU's IN series describe, on an abstract level, service creation
environments [6]. These describe services ...
... service creation
environments [6]. These describe services in a traditional circuit-
switched telephone network ...
... arranged in a directed acyclic graph. Many vendors of IN services use
modified and extended versions of this for their proprietary service ...
... services use
modified and extended versions of this for their proprietary service
creation environments.
...
... low-level interface, and would not be
appropriate for services written by non-trusted users.
The paper "Programming Internet Telephony ...
...
The paper "Programming Internet Telephony Services" [10] discusses
the similarities and contrasts between SIP ...
... execution environment, but are still necessary to allow some standard
services to be implemented. (This list is not exhaustive.)
o Pattern-matching
...
... Date/time information
Users may wish to condition some services (e.g., call
forwarding, call distribution) on the current time of day, day
of the week, etc.
...
... Guttman, E., Perkins, C., Veizades, J. and M. Day, "Service Location Protocol, Version 2", RFC 2608, June 1999. ...
... J. Rosenberg, J. Lennox, and H. Schulzrinne, "Programming internet telephony services," Technical Report CUCS-010-99, Columbia University, New York, New York, Mar. 1999. ...