Requirements for handling abandoned calls and premature disconnects in emergency calls on the Internet
draft-rosen-ecrit-premature-disconnect-rqmts-00

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Abstract

The -phonebcp draft currently requires endpoints to disable sending a 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
    1.1.  Premature disconnect
    1.2.  Abandoned Call
2.  Requirements for Premature Disconnect
3.  Requirements for Abandoned Call
4.  IANA Considerations
5.  Security Considerations
6.  Acknowledgments
7.  Informative References
§  Author's Address
§  Intellectual Property and Copyright Statements

1.  Problem Statement

[I‑D.ietf‑ecrit‑phonebcp] (Rosen, B. and J. Polk, “Best Current Practice for Communications Services in support of Emergency Calling,” January 2010.) 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 easily 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" which is used in some jurisdictions to meet this requirement. When CPH is engaged, if the user hangs up, the call is not torn down, but instead is maintained despite the "on hook" condition. The call taker has 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 the current PSAP call disconnect control capability, while other jurisdictions would like to gain access to those capabilities. Still, in other jurisdictions, the function may not be needed or desired.

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 the 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, dispatch could be avoided for true inadvertent calling if the call went through, and the call taker was able to assess the actual situation. Other jurisdictions do not have the resources and may not respond to abandoned calls at all. Sometimes, 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.

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 callback.

2.  Requirements for Premature Disconnect

PD-1

It must be possible to have the PSAP rapidly re-establish communications with a caller that attempts to prematurely disconnect from the call.

Rationale:

Time is paramount when handling emergency calls. Keeping resources active and available until the call taker determines the call can be terminated saves valuable time.

PD-2

It must be possible for the PSAP to know when the user has attempted to prematurely disconnect

Rationale:

Knowledge of the device state (and caller action) gives valuable information to the call taker which may influence how the call will be managed going forward.

PD-3

Reconnecting the caller must work reasonably reliably under congestion conditions.

Rationale:

PSAPs require robust mechanisms to perform their tasks.

PD-4

When PD-1 is enforced, the PSAP must be able to cause alerting at an endpoint which has attempted to prematurely disconnect from the emergency call

Rationale:

The user believes they have disconnected. The ability to alert is needed to encourage the user 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.

Rationale:

Priority must be given to the PSAP until such time the call taker determines the call can be terminated.

PD-6

All Media and signaling streams flowing between the caller and call taker must be maintained to the extent needed for rapid reconnection.

Rationale:

Media and signaling resources must be available as soon as the user re-answers.

PD-7

Control of premature disconnect is not needed in all jurisdictions. It must be possible to not invoke the function and allow premature disconnect to terminate the call as if no special features were present.

Rationale:

This reflects the current situation.

3.  Requirements for Abandoned Call

AC-1

It must be possible for the PSAP, or the network that serves it, to have abandoned calls complete and stay connected.

Rationale:

PSAPs 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 PSAPs who would otherwise respond to all abandoned calls.

AC-2

AC-1 shall be applied at the earliest possible time in the call establishment process.

Rationale:

Disallowing call abandonment early minimizes the chances of abandoned calls.

AC-3

Control of abandoned call is not needed in all jurisdictions. It must be possible to not invoke the function and allow calls to be abandoned as if no special features were present. Enabling or disabling must be dynamic, so that it can be enforced or not depending on requirements at the PSAP.

Rationale:

This reflects the current situation.

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 and other members of the NENA i2.5 working group for their comments and suggestions on this draft.

7. Informative References

Author's Address

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