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Henning Schulzrinne Columbia University

Requirements and Architecture for Emergency Calling draft-schulzrinne-sipping-emergency-arch draft-schulzrinne-sipping-emergency-req. Henning Schulzrinne Columbia University. Big picture. Get citizen emergency call to emergency call center (Public Safety Answering Point) = PSAP

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Henning Schulzrinne Columbia University

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  1. Requirements and Architecture for Emergency Callingdraft-schulzrinne-sipping-emergency-archdraft-schulzrinne-sipping-emergency-req Henning Schulzrinne Columbia University ECRIT

  2. 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 ECRIT

  3. 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 ECRIT

  4. 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 • L1—L3 may know about location (at least approximately), but don’t know about emergency calls ECRIT

  5. Three stages to VoIP 911 ECRIT

  6. Location-based call routing – UA knows its location GPS INVITE sips:sos@ 48° 49' N 2° 29' E outbound proxy server DHCP 48° 49' N 2° 29' E  Paris fire department ECRIT

  7. 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 Requirements: Emergency identifier ECRIT

  8. 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) ECRIT

  9. 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 Requirements: Identifying the correct PSAP ECRIT

  10. 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 Requirements: identifying the correct PSAP ECRIT

  11. 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 ECRIT

  12. Caller identity • C1: Allow (but not mandate) caller identification • C2: Privacy override • can’t 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 ECRIT

  13. 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 ECRIT

  14. 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 ECRIT

  15. Architecture Elements: Identification • Use sip:sos@home-domain • Similar to conventions for URIs (RFC xxx) • Can be handled at multiple locations in call path • If all else fails, user’s home domain does routing • can be tested ahead of time • no need to rely on borrowed device or hotel proxy ECRIT

  16. 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 ECRIT

  17. 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 • can’t go to root directory for each call • must work even if routing machinery is temporarily unavailable • Reliable • WAN-scale automated replication ECRIT

  18. Routing proposals • DNS • map civic to labels • e.g., 313.westview-ave.leonia.bergen.nj.us.sos.arpa • 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 ECRIT

  19. 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 ECRIT

  20. 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 ECRIT

  21. 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 ECRIT

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