Subject: [Iptel] Do we need CPL extensions?

From: Xiaotao Wu <[email-masked]>
Date: Fri, 21 Mar 2003 15:09:49 -0500 (EST)

Dear all,

I am thinking the following reasons should be valid for defining CPL
extensions:

    The CPL specification has many carefully designed elements, such as
    time-switch, string-switch and location modifier. It can be an
    ideal language for designing light-weight telecommunication services.

    However, there are very limited operations defined in the CPL
    specification. Currently, only three signalling operations
    defined, namely proxy, redirect and reject. It makes CPL can only
    perform very limited functionalities on a proxy/redirect server.

    We consider CPL is designed for Internet telephony systems, and it
    should take the benefits of what Internet telephony systems can offer.
    One of such benefits is the ability to provide presence information
    and instant message. And this benefit can bring many novel services.
    For example, a proxy server co-located with a presence agent can base
    on user's presence status to make call decision. To handle presence
    information will definitely need to extend the current specification.

    The other thing that Internet telephony systems are different from the
    traditional telephony systems is that in Internet telephony systems,
    end systems can have more and more functions. No doubt to say that
    Internet telephony end systems can perform simple call processing
    services. And in fact, many SIP phones have already had services in
    the phone. For end systems, the very basic functions are to make
    outgoing call and accept incoming call. Thus, for end system services,
    the 'make outgoin call' and 'accept incoming call' should be defined
    as signaling operations. We consider CPL-like language is suitable for
    end system services because it's XML based with simentatic meanings of
    the tags; it's simple -- uses a tree like structure for call decision
    making; it's safe. So, for end system services, it's also necessary to
    have CPL extensions.

    Some other things also need to extend the current CPL specification.
    For example, we would expect some services to base on a user's physical
    location (e.g., in a cinema, automatically reject the call) to perform
    call decisions. Thus, we may need a location-switch for such kind of
    services.

    So, I think we should define the following CPL extensions:

    1. CPL extensions for presence information handling (highest priority)
    2. CPL extensions for end system services
    3. CPL extensions for location-switch

Thanks!

-Xiaotao

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Name      : Xiaotao Wu
Email     : [email-masked], [email-masked]
Homepage  : http://www.cs.columbia.edu/~xiaotaow
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