One document matched: draft-rosen-ecrit-premature-disconnect-rqmts-02.txt
Differences from draft-rosen-ecrit-premature-disconnect-rqmts-01.txt
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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