providing emergency services in internet telephony henning schulzrinne and knarig arabshian...
Post on 20-Dec-2015
214 views
TRANSCRIPT
Providing Emergency Providing Emergency Services in Internet Services in Internet
TelephonyTelephony
Henning Schulzrinne and Knarig Arabshian
Department of Computer ScienceColumbia University
{hgs,knarig}@cs.columbia.eduFebruary 25, 2003
OverviewOverview
Basics of SIP (Session Initiation Protocol)
Emergency notification using SIP Details of notification architecture Benefits Conclusions
Using SIP for Emergency NotificationUsing 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
What is SIP?What is SIP? The Session Initiation Protocol (SIP) is a signaling protocol
used for establishing sessions in an IP network. SIP is part of the IETF standards and is modeled upon other
Internet protocols such as SMTP (Simple Mail Transfer Protocol for e-mail) and HTTP (Hypertext Transfer Protocol for www)
SIP is also being used in Microsoft Messenger in Windows XP
A session could be a simple two-way telephone call or it could be a collaborative multi-media conference session.
Different services are possible Internet telephony Instant Messaging with buddy lists Event notification Device control
What is SIP?What is SIP? Two Components within SIP: User Agent and
the SIP Network Server. User Agent is the end system component
for the call The User agent can be both a User Agent
Client (UAC) and a User Agent Server (UAS) The client element initiates the calls and
the server element answers the calls. SIP Server is the network device that
handles the signaling associated with multiple calls.
What is SIP?What is SIP? Main function of the SIP servers is to provide
name resolution and user location Caller is unlikely to know the IP address or
host name of the called party since the caller will dial a an email-like address or a telephone number associated with the called party.
A SIP proxy server receives requests, determines where to send these, and passes them onto the next server (using next hop routing principals).
The SIP Server component has three forms: the SIP stateful proxy server, the SIP stateless proxy server and the SIP re-direct server.
What is SIP?What is SIP? Difference between a stateful and stateless proxy server:
stateful proxy server remembers the incoming requests it receives, along with the responses it sends back and the outgoing requests it sends on. It can fork requests to try multiple user locations and then send the best response back (call is received at multiple places)
A stateless proxy server forgets all information once it has sent on a request..
Stateless Proxy servers are most likely to be the fast, backbone of the SIP infrastructure
Stateful proxy servers are probably the local devices close to the User Agents, controlling domains of users and becoming the prime platform for the application services.
What is SIP?What is SIP?
A re-direct server receives requests, but instead of passing these onto the next server it responds to the caller indicating the address for the called user.
The caller then contacts the callee at the next server directly.
home.com
office.com alice
bobm2.home.com
Basic call setupBasic call setup E-mail like identifier: <sip:[email protected]> Alice’s phone registers with home.com Bob dials [email protected]; Phone does DNS
Registrar
REGISTER home.com SIP/2.0To: sip:[email protected]: sip:[email protected]…
DNS lookup sip.udp.home.com
Resolve to pc4.home.com
pc4.home.com
home.com
office.com
alice
bobm2.home.com
Basic call setupBasic call setup
Phone sends INVITE; acts as User Agent Client Server can proxy the call to current location
INVITE sip:[email protected] …To: sip:[email protected]: “Bob” <sip:[email protected]>…c=IN IP4 128.59.19.60m=audio 8000 RTP/AVP 0 5 8
User agent client
INVITE sip:[email protected] …
To: sip:[email protected]: “Bob”
<sip:[email protected]>…
Proxy
home.com
office.com alice
bobm2.home.com
Basic call setupBasic call setup Alice’s phone rings; acts as a User Agent Server When Alice picks up, call is accepted and bob’s
phone sends ACK to complete the setup
pc4.home.com
SIP/2.0 180 Ringing
ProxyUser agent
server
SIP/2.0 200 OK…c=IN IP4 135.180.144.32m=audio 9000 RTP/AVP 0 8
home.com
office.comalice
bob
Basic call setupBasic call setup Encoded audio packets sent over RTP
home.com
office.comalice
bob
Basic call setupBasic call setup When either party hangs up BYE is sent
BYE sip:[email protected]
SIP-based Emergency SIP-based Emergency NotificationNotification
Besides VoIP, SIP also supports SUBSCRIBE/NOTIFY methods for event notifications
Clients will subscribe to servers for emergency notification
Servers will notify clients of particular emergency situation
Subscribe/NotifySubscribe/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
Subscribe/NotifySubscribe/Notify If the Subscriber wants to subscribe to
multiple events, then it must send multiple SUBSCRIBE messages, with distinct Call-IDs, to the Notifier and indicate each Event it is subscribing to
If the Subscription has expired, then it sends another SUBSCRIBE message
To unsubscribe, it sends a SUBSCRIBE message with the ”Expires” field set to zero
Subscribe/NotifySubscribe/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 Notification Server
If message body is not present then Subscriber will expect the default method of alert
Subscribe/NotifySubscribe/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
In our implementation, we use SOAP (Simple Object Access Protocol) for remote procedure calls
CLIENT(SUBSCRIBER)
SUBSCRIBE sip:[email protected] SIP/2.0Event: emergencyExpires: 86400 From: sip:[email protected]: sip:[email protected]
SERVER(NOTIFIER)SIP/2.0 202 Accepted
From: sip:[email protected]: 86400
NOTIFY sip:[email protected] SIP/2.0Event: emergencyTo: sip:[email protected]: sip:[email protected]<soap:body> <m:emergency> <type>fire</type> <material>wood</material> <alarms>2</alarms> </m:emergency></soap>
What is SOAP (Simple Object What is SOAP (Simple Object Access Protocol) ?Access Protocol) ? Lightweight XML-based protocol used
for exchange of messages in a decentralized, distributed environment
Facilitates interoperability in a platform-independent manner
Used for Remote Procedure Calls W3C note defines the use of SOAP with
XML as payload and HTTP as transport, but other transport protocols can be used such as SMTP and SIP.
SOAP and SIP Emergency SOAP and SIP Emergency NotificationNotification
Send a NOTIFY message with SOAP payload
Body of the SOAP message will invoke a remote procedure relevant to the particular emergency event
Use XML Schema to specify different emergency events handled and parameters needed
XML SchemaXML Schema<?xml version="1.0" ?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:complexType name="EmergencyType"> <xs:sequence> <xs:element name="Fire" type="Fire"/> <xs:element name="Earthquake" type="Earthquake"/> </xs:sequence> </xs:complexType> <xs:complexType name="Fire"> <xs:sequence> <xs:element name=“materials" type="string"/> <xs:element name=“alarms" type=“decimal"/>
</xs:sequence> </xs:complexType> <xs:complexType name="Earthquake"> <xs:sequence> <xs:element name="location" type="string"/> <xs:element name="scale" type="decimal"/> </xs:sequence> </xs:complexType> </xs:schema>
Why Soap?Why Soap? SOAP is a scalable and widely used
wiring protocol Can use XML Schemas to configure
notification parameters Although still not an industry
standard and needs fine-tuning, using SIP and SOAP for emergency notification is simple and effective
Wide remote system interoperability
Columbia SIP user agent Columbia SIP user agent (sipc)(sipc) Media
Audio, video, text, white board Screen sharing Shared web browsing
Advanced Presence, instant messaging Conference control Emergency notification and handling Device control
Columbia SIP user agent Columbia SIP user agent (sipc)(sipc)
Calls 911 by connecting to the
local PSAP
Receive emergency notification
alerts from various event servers that user has
subscribed to
Invoke Emergency
Services
Detailed overview of Detailed overview of architecturearchitecture
2) Generic emergency address:
[email protected] is added to sipc
Fire
[email protected] Notification server (sipd)
3) Sipc contacts notification server and gets list of
emergency events user can subscribe to
4) User subscribes to event it
wants to be notified of
1) Event generators publish their events to notification server
5) Sipc gets XML schema reference from notification server that will generate a form which queries for the
event’s properties. Sipc then updates its subscription to the notification server with
the filtered expressions
Detailed overview of Detailed overview of architecturearchitecture
3)Sipc will process SOAP body and invoke the
procedure call—such as flashing of lights
Fire
[email protected] server (sipd)
2) Sipd will process parameters of the fire and send a NOTIFY to
sipcincluding SOAP body
1) Fire occurs and event generator notifies
sipd
Example of Notification: Flashing of Example of Notification: Flashing of LightsLights
serial port
lamp
X10 device
•Emergency event notification invokes multiple calls of the SIP “DO” method
•This causes the lamp (connected to the PC by an X10 device) to flash
DO sip:[email protected] SIP/2.0…..<Control><Action>turn lamp on</Action></Control>
Alerting HierarchyAlerting Hierarchy
United States
Federal Govt.
Alabama AlaskaNew Jersey
Wisconsin Wyoming
NJ StateGovt.
Atlantic Bergen
NOTIFYSUBSCRIBE
SIP AuthenticationSIP Authentication
Notifier must verify that Subscriber is an authorized official capable of handling emergency alerts
Subscriber must also authenticate the veracity of the emergency alerts sent by the Notifier to prevent false alarms
SIP AuthenticationSIP 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
Third Party Provides CredentialsThird Party Provides Credentials
Third party operates directory server with information about a local area
Monitored and maintained by government officials who recognize Notification Servers and Subscribers as valid institutions
Subsribers and Notifiers subscribe to the directory server indicating alerts they request or support
Maps Subscribers to local Notifiers
Third Party Provides CredentialsThird 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 Subsribers
and Notifiers which establish them as valid institutions for community alerting
Create and distribute passwords to the Subscribers and their matching Notifiers
Third Party Provides CredentialsThird Party Provides Credentials
This method is scalable and works well for large number of Subscribers and Notifiers
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 Emergency Notification Server Provides CredentialsProvides 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
BenefitsBenefits Device Neutrality
There are likely to be range of SIP-based end systems, ranging from IP telephones, 3G wireless handsets, IM/presence software to embedded devices.
Thus, the emergency alert system can migrate to new devices, without having to explicitly be extended to handle them.
More Information and Automated Action Video conferencing, text messaging Device control which causes flashing lights
and aides the hearing-impaired
BenefitsBenefits Lower resource consumption
A one-minute alert call consumes about 480 kbytes (one way), while an alert notification is likely to be at most a few hundred bytes long.
The same bandwidth can reach approximately1,000 times as many people in the same time period.
Integration with current systems It would be straightforward to feed EAS (Emergency
Alert System) and EDIS (emergency digital information system) into the SIP emergency alert system.
BenefitsBenefits Out-of-area notification
Current notification systems assume that only those in close physical proximity of the emergency event need to know about the event.
SIP-based systems address cases where the recipient of the information is currently away, but still needs to be alerted.
Examples: owners of summer cottages need to be aware of impending
storms so that they can summon appropriate assistance or have their property checked on.
Those at work may need to know about conditions affecting their home.
Conclusion and Future Conclusion and Future WorkWork
SIP gives opportunity to enhance existing emergency services by creating more functional, robust and flexible systems
Next generation devices will be interoperable with SIP
Using SIP SUBSCRIBE/NOTIFY messages we can develop an Internet-based emergency notification system
Future/Ongoing work includes extending sipc features: Creating an E-911 system Creating a generic event notification server
