SIP-Based Emergency Notification System

1
SIP-Based Emergency Notification System

• Knarig Arabshian
• IRT Laboratory
• Columbia University
• December 5, 2001

2
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

3
What are Emergency Notification Systems?

• 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

4
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

5
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

6
Using SIP for Emergency Notification

• 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

7
SIP-based Emergency Notification System

• Subscribe/Notify methods
• SIP Authentication
• Network Architecture

8
Subscribe/Notify

• 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

9
Subscribe/Notify

• SIP message will have SUBSCRIBE or NOTIFY in
  the method section of the SIP request.
• The SUBSCRIBE request
• 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

10
Subscribe/Notify

• 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 Call-ID
  but different CSeq number
• To unsubscribe, it sends a SUBSCRIBE message with
  the Expires field set to zero

11
Subscribe/Notify

• 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

12
Subscribe/Notify

• 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

13
Emergency Notification Process
Send Notify to UAC
UAC
UAS
Send 200 Confirmation response to UAS
14
Alert Process
Process message body of NOTIFY request
SOUND ALERT!!
UAC
15
SIP-based Emergency Notification System

• Subscribe/Notify methods
• SIP Authentication
• Network Architecture

16
SIP Authentication

• 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 securitytransmits username and
  password in plain sight
• Digest better choiceuses more name-value pairs

17
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

18
Third Party Provides Credentials

• 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

19
Third Party Provides Credentials

• 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

20
Third Party Provides Credentials

• 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

21
Emergency Notification Server Provides Credentials

• Each emergency notification server has a
  pre-established 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

22
Emergency Notification Server Provides Credentials

• 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

23
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 WWW-Authenticate message
UAS confirms with a NOTIFY response message
24
SIP-based Emergency Notification System

• Subscribe/Notify methods
• SIP Authentication
• Network Architecture

25
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

26
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

27
Hierarchy of Emergency Notification Server in the
United States
USA
AL
AK
WY
Abbeville
Montgomery
28
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

29
Benefits in using SIP for Emergency Notification

• Use on Different Applications and Devices
• Internet telephony, multimedia applications,
  instant messaging and others
• 3G cell phones, PDAs, home PCs and telephones

30
Benefits in using SIP for Emergency Notification

• 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

31
Benefits in using SIP for Emergency Notification

• 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.

32
Benefits in using SIP for Emergency Notification

• 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

33
Benefits in using SIP for Emergency Notification

• 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

34
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