Transcript SIP-Based Emergency Notification System

SIP-Based Emergency
Notification System
Knarig Arabshian
IRT Laboratory
Columbia University
December 5, 2001
Overview
What is an Emergency Notification System?
 Current Emergency Notification Systems
 Using SIP for an Emergency Notification
System
 Benefits in using SIP for Emergency
Notification
 Conclusion and Future work

What are Emergency Notification
Systems?
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Allow government officials to notify a community
of an emergency and precautionary measures that
must be taken
Different emergency situations and alert methods
 Fire Alarms
 Earthquake or chemical spills indicated by
sirens
 Notifying public of terrorist attacks via
radio/TV broadcasting
Current Emergency Notification
Systems

Emergency Alert System (EAS)
 Controlled by the government and used
mostly for wide area emergency
notification
 Specifies how and when state and local
governments provide emergency
instruction to the public
Current Emergency Notification
Systems

Localized Emergency Alerting Systems
 Reverse 911, Community Alert Network
notifies local officials or companies that
subscribe to a network
 Subscriptions include preferences regarding:
 Geographical location of notification
 Types of emergency alerts
 Alert methods
Using SIP for Emergency
Notification
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It is likely that traditional modes of
communication will be augmented by Internet
telephones and applications in the near future
We need to have Emergency Notification Systems
established on the Internet
SIP is an application-layer signaling protocol
which can be used for event notification
SIP-based Emergency
Notification System
Subscribe/Notify methods
 SIP Authentication
 Network Architecture

Subscribe/Notify
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SIP clients can subscribe to a remote SIP server
and request notification from it
In case of an event, remote server will alert the
client that an event has occurred
User Agent Client (UAC) represents the institution
that subscribes for emergency notification
User Agent Server (UAS) is the institution that
issues notifications during an emergency
Subscribe/Notify

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SIP message will have “SUBSCRIBE or
“NOTIFY” in the method section of the SIP
request.
The SUBSCRIBE request
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Resembles that of a SIP INVITE
Must have one “Event” header in the header field which
will specify the type of event it is subscribing to.
Must also contain an “Expires” header which defines
the duration of the subscription
Subscribe/Notify
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If the UAC wants to subscribe to multiple events,
then it must send multiple SUBSCRIBE messages,
with distinct Call-IDs, to the UAS and indicate
each Event it is subscribing to
If the Subscription has expired, then it sends
another SUBSCRIBE message with the same CallID but different CSeq number
To unsubscribe, it sends a SUBSCRIBE message
with the ”Expires” field set to zero
Subscribe/Notify
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Can contain optional message body in
SUBSCRIBE request
 Further details of notification such as methods
of alerting (sirens, IM Messages, telephone calls)
 Standardized grammar to automate the
processing of the SUBSCRIBE request in the
UAS
If message body is not present then UAC will
expect the default method of alert
Subscribe/Notify
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NOTIFY Message Request
 The “Event” header will indicate the type
of emergency notification it is
 The message body of the NOTIFY
message will include specific instructions
on the alert methods
Emergency Notification Process
Send Notify to UAC
UAC
UAS
Send 200 Confirmation
response to UAS
Alert Process
UAC
SIP-based Emergency
Notification System
Subscribe/Notify methods
 SIP Authentication
 Network Architecture

SIP Authentication
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UAS must verify that UAC is an authorized
official capable of handling emergency alerts
UAC must also authenticate the veracity of the
emergency alerts sent by the UAS to prevent false
alarms
Two authentication schemes
 Basic: weak security—transmits username and
password in plain sight
 Digest: better choice—uses more name-value
pairs
SIP Authentication
Subscriber must be aware of all the local
emergency alerting agencies in its area
 Someone has to provide this information
 Third party
 Emergency notification server
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Third Party Provides Credentials
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Third party operates directory server with
information about a local area
Monitored and maintained by government officials
who recognize UACs and UASs as valid
institutions
UACs and UASs subscribe to the directory server
indicating alerts they request or support
Maps UACs to local UASs
Third Party Provides Credentials
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Lightweight Directory Access Protocol (LDAP)
can be used to obtain information from local
directory server
Government officials managing the directory
server
 Provide certificates to local UACs and UASs
which establish them as valid institutions for
community alerting
 Create and distribute passwords to the UACs
and their matching UASs
Third Party Provides Credentials
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This method is scalable and works well for large
number of UACs and UASs
Not the preferred method for this system since
there are only a limited number of agencies within
a community who are authorized by the
government to provide and receive emergency
notification
Separate directory server needlessly complicates
the system
Emergency Notification Server
Provides Credentials
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Each emergency notification server has a preestablished list of authorized government officials
in its area
It sends either postal mail or encrypted e-mail to
them indicating
 Their password is if they wanted to subscribe
 Types of emergency notifications the server
supports
Emergency Notification Server
Provides Credentials
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UAC sends a SUBSCRIBE message to the UAS directly
UAC receives a 401 WWW-Authenticate message in
response
UAC responds with its encrypted password in the
Authorization header
UAS verifies the password and adds the subscriber as a
registered user in its database
UAS sends a confirmation NOTIFY message to the UAC
UAC adds the UAS to its database of emergency
notification servers
UAC sends an encrypted concatenation
of username and password in the
Authorization header
UAC sends a SUBSCRIBE
message to UAS
UAC
UAS
UAS responds with WWWAuthenticate message
UAS confirms with a NOTIFY
response message
SIP-based Emergency
Notification System
Subscribe/Notify methods
 SIP Authentication
 Network Architecture
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Network Architecture
Hierarchical network structure provides
good scalability and facilitates the
breakdown of geographical location
 Main emergency notification server at the
root serves all the states in the USA
 Each state has a server that serves its cities
and so on
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Network Architecture
Within the hierarchical tree, children of the
same parent should have directory listings
of each other
 This is beneficial because the number of
government officials within a community
will not be very high
 Saves time and resources in a critical
emergency situation
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Hierarchy of Emergency Notification
Server in the United States
USA
AL
Abbeville
Montgomery
AK
WY
Network Architecture
Directory listing maintained by each server
should map a server to an IP address
 Server names are stored in a database using
their geographical location names as keys
 Child nodes must subscribe to their parent
node servers and siblings must subscribe to
each other
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Benefits in using SIP for
Emergency Notification
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Use on Different Applications and Devices
 Internet telephony, multimedia
applications, instant messaging and
others
 3G cell phones, PDAs, home PCs and
telephones
Benefits in using SIP for
Emergency Notification
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More Information
 SIP message can carry a lot of
information which can give a detailed
description of the emergency event
 Single message can have multilingual
content and receiver of the message can
choose a language
Benefits in using SIP for
Emergency Notification
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Automated Action
 SIP message body automates subscription and
notification process
 UAC subscribes to UAS with following
preferences in message body: fire, sound alarm
bells
 In case of a fire, UAS sends a NOTIFY to the
UAC with its message body containing
information which will invoke sounding of
alarm bells.
Benefits in using SIP for
Emergency Notification
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Lower Resource Consumption
 SIP will be running over the Internet which is a
much faster medium than PSTN
 Example of a local network connected with a
T1 (1.5Mb/s) line
 50 subscribers/line
 200 Kb/message
 7.49 subscribers/second/T1 line
 Compare this with PSTN (56 Kb/s) line which
yields 0.28 subscribers/second/PSTN line.
 T1 reaches 27 times more subscribers/sec/line
Benefits in using SIP for
Emergency Notification
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Complementary to Current EAS System
 SIP-based emergency systems can be
integrated with radio/TV broadcasting to
provide emergency notifications via the
Internet as well
Conclusion and Future Work
Using SIP SUBSCRIBE/NOTIFY messages
we can develop an Internet-based
emergency notification system
 Extend sipc to develop a flashing lights
demo
 Use SOAP (Simple Object Access Protocol)
within the NOTIFY message body to
automate alert process
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