ecrit                                                           B. Rosen
Internet-Draft                                                   NeuStar
Intended status: Standards Track                         January 5, 2009
Expires: July 9, 2009


 Requirements for handling abandoned calls and premature disconnects in
                    emergency calls on the Internet
            draft-rosen-ecrit-premature-disconnect-rqmts-02

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Abstract

   The -phonebcp draft currently requires endpoints to disable sending a



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   BYE on an emergency call.  Insufficient justification and lack of
   attention to the entire problem has caused comment on that section of
   the document.  This document attempts to define the problem and the
   requirements to controlling disconnect on emergency calls.


Table of Contents

   1.  Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Premature disconnect  . . . . . . . . . . . . . . . . . . . 3
     1.2.  Abandoned Call  . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements for Premature Disconnect . . . . . . . . . . . . . 4
   3.  Requirements for Abandoned Call . . . . . . . . . . . . . . . . 5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
   7.  Informative References  . . . . . . . . . . . . . . . . . . . . 6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6

































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1.  Problem Statement

   [I-D.ietf-ecrit-phonebcp] currently disallows sending of BYE by the
   calling UA.  This requirement has generated a request for additional
   capability, and has also caused some to question why it is needed,
   and how the mechanisms interact with current and future emergency
   call systems.  There are two aspects of handing emergency calls that
   give rise to the discussion.

1.1.  Premature disconnect

   Occasionally, when on an emergency call, a caller hangs up the call
   before the call taker is finished acquiring enough information.
   Emergency calls are stressful, and mistakes are inevitablely made.  A
   mechanism is needed to re-establish communication between the caller
   and the call taker when this happens.  The PSTN has a feature
   available, "Called Party Hold" (CPH) which is used in some
   jurisdictions to meet this requirement.  If the user hangs up When
   CPH is engaged, the call is not torn down, but instead is maintained
   despite the "on hook" condition.  The call taker may also have a
   mechanism (called "Ringback" which is different than call-back) to
   ring the user's telephone.  If the handset is picked up, since the
   call is still active and resources maintained, the caller and the
   call taker are readily reconnected.  Called Party Hold is a feature
   that has long been available in wireline networks, but is not
   currently implemented in wireless networks.  Some jurisdictions are
   desirous of maintaining their current PSAP call disconnect control
   capability, while other jurisdictions would like to regain access to
   those capabilities.  Still, in other jurisdictions, the function may
   not be needed or desired, even in jurisdictions that want to have the
   feature, it may not be desirable in all circumstances.  For example,
   if the call is queued due to congestion, it is undesirable to hold up
   the call and user initiated disconnect should be permitted.

1.2.  Abandoned Call

   It is not uncommon for an emergency call to be cancelled before it
   reaches a call taker.  Abandoned, in this context, means that the
   call is terminated before a call taker answers it.  While it can be
   that the user is fully aware that the call is being cancelled, and
   considers the cancellation the most appropriate solution, abandoned
   calls are problematic to PSAPs because they don't know why the call
   was abandoned.  Unfortunately, what looks like an abandoned call can
   be a more serious circumstance such as a hostage situation.  In some
   jurisdictions, the PSAP dispatches a police unit to all logged
   abandoned calls.  In such jurisdictions, dispatching resources could
   be avoided for true inadvertent calling if the call went through, and
   the call taker was able to assess the actual situation.  Other



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   jurisdictions do not have the resources and may not respond to
   abandoned calls at all.  As with premature disconnect, application of
   the function depends on conditions.  For example, in a mass calling
   event, an Interactive Media Response unit may be used to answer
   calls.  Abandoning a call answered by a machine may be appropriate.
   Even if jurisdictions respond to abandoned calls by dispatching
   emergency personnel in normal situations, they may not in this
   situation.

   There is always a period of time after a call is initiated by a
   caller before there is any reasonable possibility to determine that a
   call is abandoned.  Since the appication of special handling for
   abandoned call is dependent on conditions, there is an implication
   that some form of negotiating is needed between the UAS and the UAC
   to invoke any kind of abandoned call processing.  This in turn
   implies that if the call is abandoned before the signaling
   negotiation completes, no special handling should be provided.
   Accordingly, an abandoned call is defined as a call which is
   attempted to be disconnected prior to the UAS answering, but after
   any signaling that would enable the feature is completed.

   Retaining the connection is extremely important when there is no
   callback information (e.g., uninitialized phone) or the caller has
   call termination features active (such as call forwarding, do not
   disturb) and the PSAP is unable to reconnect via callback.


2.  Requirements for Premature Disconnect

   In the following discussion the entities are the humans who take part
   in the call.
   PD-1  Some times, when a caller attempts to disconnect from an
      established emergency call, s/he may find that disconnection
      appears not to work
     Rationale:  Some callers attempt to disconnect before the call
      taker has enough information to provide help.
   PD-2  When a caller attempts to disconnect, the call taker gets an
      indication of such an attempt.  If the device has a mechanical
      "hook switch" or similar mechanism that cannot be locked out, and
      the user picks up the handset, the call taker gets an indication
      of that action.
     Rationale:  Knowledge of the caller action gives valuable
      information to the call taker which may influence how the call
      will be managed going forward.







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   PD-4  When PD-1 is enforced, the call taker must be able to cause
      alerting to the caller which has attempted to prematurely
      disconnect from the emergency call.
     Rationale:  The caller believes they have disconnected.  The
      ability to alert is needed to encourage the caller to reconnect.
   PD-5  When PD-1 is enforced,the caller must not be able to place
      another call until the PSAP allows the call to be released.  This
      requirement is not intended to imply a user inteface with multiple
      lines accessible independently is locked to the single line that
      placed the emergency call.  As mistakes can be made, an override
      mechanism invoked by the caller must be be feasible.  The
      implementation must fail safely such that the phone cannot be
      locked and unable to call for help.
     Rationale:  Priority must be given to the call taker until such
      time she/he determines the call can be terminated.
   PD-6  If the user responds to the alerting (PD-4), the caller and the
      call taker must be able to converse roughly immediately.  "Roughly
      immediately" is in human terms: the time from when the caller
      reacts to the alerting, initialting reconnect, and the time the
      call taker can resume conversing, and is perhaps a second.
     Rationale:  If the user responds, caller re-answers.
   PD-7  Control of premature disconnect is not needed in all
      jurisdictions.  It must be possible for the PSAP to not invoke the
      function and allow premature disconnect to terminate the call as
      if no special features were present.
     Rationale:  Whether the function is enabled is a call-by-call
      decision and takes into account the jurisdiction practice and
      conditions at the PSAP for the call.


3.  Requirements for Abandoned Call

   In the following discussion the entities are the humans who take part
   in the call.
   AC-1  Where enabled, an emergency call, once "dialed" by the caller,
      completes even if the caller attempts to abandon it.  Normal
      mechanisms used by the caller to disconnect appear to be disabled.
     Rationale:  Call takers cannot distinguish between calls which are
      appropriately abandoned and calls that need response but were cut
      short.  Controls to limit abandonment are needed for those
      jurisdictions who would otherwise respond to all abandoned calls.
   AC-2  The user may note that in some circumstances, a disconnect
      request initiated very quickly after initiation does succeed.
     Rationale:  Disallowing call abandonment early minimizes the
      chances of abandoned calls, but since the conditions at the call
      taker have to be considered before the mechanism can be invoked.





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   AC-3  The user may note that some times, the disconnect works.  This
      may depend on where s/he is calling from, or other conditions.
      For example, disconnect may work if the call is placed during a
      mass calling event.
     Rationale:  Whether the function is enabled is a call-by-call
      decision and takes into account the jurisdiction practice and
      conditions at the PSAP for the call. .


4.  IANA Considerations

   There are no IANA Considerations for this document


5.  Security Considerations

   If these features can be enabled by entities other than PSAPs, the
   entity may gain more control over the end device.  Failures of
   various kinds may prohibit callers from being able to disconnect.


6.  Acknowledgments

   Thanks to Guy Caron, Theresa Reese, John Hearty, Ric Atkins, Anand
   Akundi and other members of the NENA i2.5 working group for their
   comments and suggestions on this draft.


7.  Informative References

   [I-D.ietf-ecrit-phonebcp]
              Rosen, B. and J. Polk, "Best Current Practice for
              Communications Services in support of Emergency  Calling",
              draft-ietf-ecrit-phonebcp-06 (work in progress),
              November 2008.


Author's Address

   Brian Rosen
   NeuStar
   470 Conrad Dr.
   Mars, PA  16046
   US

   Phone: +1 724 382 1051
   Email: br@brianrosen.net




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