Requirements and Architecture for Emergency Calling draft-schulzrinne-sipping-emergency-arch draft-schulzrinne-sipping-emergency-req

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Requirements and Architecture for Emergency
Callingdraft-schulzrinne-sipping-emergency-archd
raft-schulzrinne-sipping-emergency-req

• Henning Schulzrinne
• Columbia University

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Big picture

• Get citizen emergency call to emergency call
  center (Public Safety Answering Point) PSAP
• Not emergency coordination (see IEPREP)
• Not just VoIP, but also video, text, data,
• Not green field incremental deployment
• Architectures
• trunk replacement (last hop only)
• VoIP to traditional PSAP
• end-to-end VoIP

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Traditional Emergency Calling

• Basic 911 just route to local PSAP
• based on local switch
• no location delivery
• Enhanced 911 route location delivery (90?)
• multiple PSAPs per PSTN switch
• multiple switches per PSAP
• location delivered out-of-band via caller number
• Phase I wireless (70)
• call delivery based on cell tower and face
• no location delivery
• Phase II wireless (30)
• call delivery based on geo address
• geo location delivery to PSAP

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Core problems

• PSTN approximate routing often works
• same switch
• based on cell tower
• based on caller number
• PSTN relatively few, regionally-limited telecom
  providers (carriers)
• IP carrier bobs-bakery.com
• IP no such approximations (usually)
• application layer (e.g., SIP) has no clue as to
  location
• L1L3 may know about location (at least
  approximately), but dont know about emergency
  calls

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Three stages to VoIP 911
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Location-based call routing UA knows its
location
GPS
INVITE sipssos_at_
48 49' N 2 29' E
outbound proxy server
DHCP
48 49' N 2 29' E ? Paris fire department
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Requirements Emergency identifier

• A1 Universal
• elements in call path need to recognize emergency
  call for special handling
• cannot use traditional numbers too many,
  changing, conflicts with non-emergency numbers
• A2 Local
• users need to be able to dial the local emergency
  number (112, 911) even if device was bought
  non-locally

• A3 Recognizable
• proxies and other elements need to recognize
  emergency calls
• location insertion, security, routing
• A4 Minimal configuration
• A5 Secure configuration

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Requirements caller location

• L1 Multiple location providers
• end system network
• L2 Civic and geographic
• precise geo not always available (e.g., within
  building)
• Room 345, 3rd floor more useful than 125
  above sea level
• provide both if generated
• allow for in-path translations (geocoding)
• L3 Location-source identification
• L4 Ascertain validity of location information
• could be combined with call testing
• existing system MSAG (street and address range)

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Requirements Identifying the correct PSAP

• Decentralized routing
• cannot have a global PSAP-level directory
• must respect current political and organizational
  hierarchies (and rivalries)
• I1 Correct PSAP
• I2 Early routing

• I3 Choice of PSAPs
• local vs. public
• I4 Assuring PSAP identity
• I5 Traceable resolution

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Requirements identifying the correct PSAP

• I6 Assuring directory identity
• I7 Query response integrity
• I8 Assuring directory update integrity

• I9 Call setup latency
• I10 Multiple directories
• no global or nationwide database
• but delegation ok

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Requirements identifying the correct PSAP

• I11 Referral
• I12 Multiple query protocols
• I13 Robustness
• work as long as PSAP itself is reachable
• I14 Incrementally deployable
• I15 Testable
• check if call reaches right PSAP without tying up
  PSAP call taker resources

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Caller identity

• C1 Allow (but not mandate) caller identification
• C2 Privacy override
• cant rely on user to manually enable delivery of
  location information
• user may not be aware of device operation
• e.g., phone in hotel or when visiting friend

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Requirements Call setup

• S1 authentication override
• place emergency call even if not subscribed to
  service
• S2 mid-call features
• disable transfer or hold
• S3 testable
• all aspects, including media path (NATs!)
• S4 integrity
• signaling media

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Elements configuration

• Location-dependent configuration of available
  emergency numbers
• e.g., 911 in North America, 112 in Europe
• Can use SIP configuration mechanisms, but may not
  be available or correspond to number boundary

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Architecture Elements Identification

• Use sipsos_at_home-domain
• Similar to conventions for URIs (RFC xxx)
• Can be handled at multiple locations in call path
• If all else fails, users home domain does
  routing
• can be tested ahead of time
• no need to rely on borrowed device or hotel proxy

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Architecture routing

• Can take place at
• UAC
• outbound proxy
• home domain
• May be done at multiple levels
• UAC routes to country-level emergency call proxy
• country-level proxy routes to state/province,
  etc.
• parts of path may be hidden behind firewall

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Routing core requirements

• Both civic and geo coordinates
• conversion from civic to geo may introduce errors
• need to check validity of civic addresses
• thus, need to map both point-in-polygon and
  hierarchical strings
• Delegation
• service boundaries follow arcane political maps
• mapping updates must be done at local level
• Scaling
• global directory
• Caching
• cant go to root directory for each call
• must work even if routing machinery is
  temporarily unavailable
• Reliable
• WAN-scale automated replication

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Routing proposals

• DNS
• map civic to labels
• e.g., 313.westview-ave.leonia.bergen.nj.us.sos.arp
  a
• store (by reference) geo boundaries
• TRIP
• similar notion of hierarchical resolution, but
  not based on numbers
• not clear that dynamic updates are particularly
  useful here
• IRIS
• XML-based query protocol used for domain name
  registrar information, but easily generalizable
• would need to deal with referrals
• uses SRV for redundancy
• LDAP

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Open issues

• Is this the right modularity?
• location conveyance, call identification,
  routing, configuration
• What existing protocols are suitable for
  location-based lookups?
• Worry about existing SIP devices?
• do not recognize emergency calls
• cannot query directory service

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Open issues directory

• Multiple directory operators for each geographic
  area?
• Is location? PSAP mapping public or secret?
• i.e., only high-level routing exposed
• e.g., all calls for US go to one SIP address
• hard to do testing with secret data
• likely to be supportable by most directory
  solutions

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A note on timing

• Hardest problem is call routing
• but may only implemented be relatively few
  systems (proxies)
• or, at least, can be implemented in proxies only
• But need to solve call identification real soon
  now (somewhere)
• needs to be implemented in end devices
• very useful even for I2, not just I3
• e.g., needed for authorizing location disclosure
• SIP-specific could be solved in SIPPING