2.5.2 Basic Level of Interoperability for SIP Services (bliss)

NOTE: This charter is a snapshot of the 75th IETF Meeting in Stockholm, Sweden. It may now be out-of-date.

Last Modified: 2009-09-25


Shida Schubert <shida@ntt-at.com>
Scott Lawrence <scott.lawrence@nortel.com>

Real-time Applications and Infrastructure Area Director(s):

Robert Sparks <rjsparks@nostrum.com>
Cullen Jennings <fluffy@cisco.com>

* The Real-time Applications and Infrastructure Area Directors were seated during the IETF 65.

Real-time Applications and Infrastructure Area Advisor:

Robert Sparks <rjsparks@nostrum.com>

Technical Advisor(s):

Jonathan Rosenberg <jdrosen@cisco.com>

Mailing Lists:

General Discussion: bliss@ietf.org
To Subscribe: https://www.ietf.org/mailman/listinfo/bliss
Archive: http://www.ietf.org/mail-archive/web/bliss

Description of Working Group:

The focus of the group is to facilitate effective feature
interoperability for features sharing common functional primitives
utilizing SIP in heterogeneous network environments as noted below.

SIP's approach to supporting more advanced features and applications
has been to specify a number of primitive operations, including refer,
dialog replacement and joining, and event packages, and then to allow
those primitives to be combined in many ways to realize different
features. This approach avoids the need for standardized definitions of
a feature, which can severely limit innovation and broad

While this approach brings great flexibility and generality, it
complicates interoperability. Without any kind of standardized
definition of a particular feature, each implementation creates its
own definition and corresponding set of call flows and primitives used
to realize this feature. In practice, this has resulted in a poor
track record for interoperability for more advanced features which
make assumptions on supported SIP extensions and behaviors from other

The problem is exacerbated by the desire for these features to work
across many types of SIP endpoints, including SIP hardphones,
softphones, and gateways to the PSTN and other VoIP networks including
non-centralized environments, and for the desire to work across domain
boundaries and to interwork with the PSTN, when applicable.

The focus will not be on rigorous definition of what the specific
feature is and exactly how it works. Rather, the focus will be on
documenting the variations that exist in the wild sharing common
interop problems, figuring out a minimum baseline requirement for a UA
and servers (minimum set of primitives etc.), defining minimum levels
of functionality and functional primitives required to realize a broad
class of related features, and on interoperating with other elements
which might implement one of those features in different ways.

The BLISS working group will coordinate closely with the SIP and
SIPPING working groups. Like SIPPING, its role is to focus on
applications of  the SIP protocol and not on core extensions to SIP
itself. The difference between SIPPING and BLISS, is that BLISS is
focused on a particular type of SIP application - call features, and
in particular, advanced call features requiring non-trivial call
control. SIP applications such as configuration, presence, SIP
extensions for IM, and session policy are clearly out of scope for
BLISS and remain the sole province of SIPPING. Of course, any features
considered by BLISS will support the full range of multimedia
supported by SIP - audio, video, text, messaging, and so on.

The BLISS working group will focus on resolving interpretability issues
on four functional primitives as an initial milestone. Summary for each
of the functional primitives are as follows.

A "Problem Statement" document will also be charted as the first
deliverable of this working group. This document will describe the
problem this working group is trying to address, the criteria to be
met for items to be accepted and a template for documenting a draft
for this working group.

Line Sharing

Description: this covers the functionality required for multiple UA
instances to be able to see and utilize sessions made to/from either
one. It covers a range of features including:

* multiple call appearances
* call suspend/resume
* retrieve
* conference across appearances


Description: this covers functionality required to move calls from
one instance to another without pre-arranged knowledge of the set of
instances on which the call is to be shared. Basically a dynamic
version of line sharing in a sense.  It would cover features including:

* park
* parked retrieval
* directed park
* directed pickup

Automated Handling

Description: this covers functionality required for a user to
indicate, asynchronously from the time of a call, what the handling of
a future call should be. It covers the rules on who implements the
processing and how it is signaled. Covers features including:


Call Queuing

Description: this covers functionality required to queue a call when
the callee is not available, handling of a queue and notifying when
callee is ready to receive a call. Covers features including:


Guiding principles for this working group work will include:

- Identify functional primitives with interoperability issues, based
on an analysis of variations of features sharing same or similar
functional primitives within heterogeneous network(s). Provide a clear
description of any interoperability problems that are identified by
documenting the variations that exist in the wild for features that is
already implemented.

- Document minimum baseline requirements relevant to the functional
requirements for addressing the interoperability issue.  Criteria to
* who is responsible for invoking?
* who is responsible for implementing?
* how does the functional primitive interact with multiple media types?
* how does the functional primitive work between administrative

- Initiate analysis of the pros and cons of key approaches to
addressing the requirements.

- Where the requirements can be satisfied within the capabilities of
the current standards, produce BCPs [and appropriate call-flows] to
document the best approach.

- Where normal event packages or SIP uri parameter is all what's
needed to prevent interoperability issues, appropriate extensions and
its usage would be defined and documented.

- Where extensions to standards are required beyond what's mentioned
above, bring the analysis, requirements and need for new extensions to
the appropriate working group (SIP, SIPPING or SIMPLE).

- As in the SIPPING charter, the security of all the deliverables
will be of special importance.

*Deliverable may attempt to...
1. Define a single approach to solve the problem.
2. Allow variations but mandate support for more than one mechanism.
3. Demonstrate that interoperability is possible even when entities
provide the feature with the functional primitive differently.

Goals and Milestones:

Apr 2008  Submit Problem Statement to the IESG as Informational RFC
Apr 2008  Submit Automated Handling to the IESG as BCP
Aug 2008  Submit Parking to the IESG as BCP
Aug 2008  Submit Call Queing to the IESG as BCP
Oct 2008  Submit Line Sharing to the IESG as BCP


  • draft-ietf-bliss-ach-analysis-05.txt
  • draft-ietf-bliss-call-completion-04.txt
  • draft-ietf-bliss-shared-appearances-03.txt
  • draft-ietf-bliss-call-park-extension-01.txt

    No Request For Comments

    Meeting Minutes


    Shared Line Appearance
    Call Completion
    Alert-Info URNs