Emergency Service Identifiers draft-ietf-ecrit-service-urn-01

1
Emergency Service Identifiersdraft-ietf-ecrit-ser
vice-urn-01

• Henning Schulzrinne
• Columbia University
• hgs_at_cs.columbia.edu

2
Open Issues

• Identifying the call post-resolution
• Server resolution

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UA recognition UA resolution
location information
mapping
mapping may recurse
DHCP LLDP-MED
9-1-1 (dial string)
leonianj.gov
INVITE sippsap_at_leonianj.gov To
urnservicesos Accept-Contact
sip.service"urnservicesos" ltlocationgt
INVITE sippsap_at_leonianj.gov To
urnservicesos Accept-Contact
sip.service"urnservicesos" ltlocationgt
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UA recognition proxy resolution
mapping
9-1-1
provider.com
INVITE urnservicesos To urnservicesos Accept-
Contact sip.service"urnservicesos" ltlocatio
ngt
INVITE sippsap_at_leonianj.gov To
urnservicesos Accept-Contact
sip.service"urnservicesos" ltlocationgt
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UA recognition proxy resolution(proxy location
determination)
mapping
9-1-1
provider.com
INVITE sippsap_at_leonianj.gov To
urnservicesos Location ltlocationgt Accept-Contac
t sip.service"urnservicesos"
INVITE urnservicesos To urnservicesos Accept-
Contact sip.service"urnservicesos"
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Proxy recognition proxy resolution
mapping
9-1-1
provider.com
INVITE sippsap_at_leonianj.gov To
sip911_at_provider.comuserphone Location
ltlocationgt Accept-Contact sip.service"urnserv
icesos"
INVITE sip911_at_provider.comuserphone To
sip911_at_provider.comuserphone
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Problems with approach

• No authentication ? call alice_at_yahoo.com, mark as
  emergency call ? get free call
• assumes that IP calls are charged
• unlikely that providers will just gateway to
  E.164 PSAP numbers
• if mapping done by outbound proxy, next entity
  will be PSAP URL anyway
• no home routing for emergency services! (visited
  service in IMS)
• ? only problem for UA rec/res
• thus, could we punt?

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Call identification alternatives

• only trust Accept-Contact from same trust domain
• see P-Asserted-Identity model (RFC 3325) ?
  brittle
• or use Identity model ? signed by outbound proxy
• unfortunately, not covered by
• doesnt help with UA rec/res model!
• creating a new header likely to have similar
  issues
• re-do mapping and ensure that URL matches
• server can learn list of legal URLs after a
  while
• can fail if mapping is dynamic (advertisement
  changes)
• then just replaces URL
• forces each outbound proxy to do mapping

• check external source that URL is indeed a PSAP
• use draft-ietf-sipping-certs for destination URL,
  but would need to have a role-based cert this is
  a bona-fide PSAP
• easy to posit, harder to deploy globally
• can incur significant delay
• but only needed when theres service
  differentiation
• new TLD for PSAPs only ?

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Resolution DDDS

• (Most) URNs have a resolution mechanism ? DDDS
• Extract service part, e.g., sos.fire
• Get domain D from local source
• DHCP ? ISP as service provider
• domain part of AOR ? VSP as service provider
• SIP configuration
• Resolve NAPTR record for D example.com.
• order pref flags service regexp
  replacement
• IN NAPTR 50 50 "u" "LOSTD2T"
• "!urnservice(.)!http//example.com/map/\1
  !i" .

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Summary

• Only two (known) open issues
• marking ? can be separated, if needed
• DDDS ? needs NAPTR expert advice