ecrit B. Rosen
Internet-Draft NeuStar
Intended status: Standards Track J. Polk
Expires: August 28, 2008 Cisco Systems
February 25, 2008
Best Current Practice for Communications Services in support of
Emergency Calling
draft-ietf-ecrit-phonebcp-04
Status of this Memo
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
The IETF and other standards organization have efforts targeted at
standardizing various aspects of placing emergency calls on IP
networks. This memo describes best current practice on how devices,
networks and services should use such standards to make emergency
calls.
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview of how emergency calls are placed . . . . . . . . . . 3
4. Which devices and services should support emergency calls . . 4
5. Identifying an emergency call . . . . . . . . . . . . . . . . 4
6. Location and its role in an emergency call . . . . . . . . . . 5
6.1. Types of location information . . . . . . . . . . . . . . 5
6.2. Location Determination . . . . . . . . . . . . . . . . . . 5
6.2.1. User-entered location information . . . . . . . . . . 6
6.2.2. Access network "wire database" location
information . . . . . . . . . . . . . . . . . . . . . 6
6.2.3. End-system measured location information . . . . . . . 6
6.2.4. Network-measured location information . . . . . . . . 6
6.3. Who adds location, endpoint or proxy . . . . . . . . . . . 7
6.4. Location and references to location . . . . . . . . . . . 7
6.5. End system location configuration . . . . . . . . . . . . 7
6.6. When location should be configured . . . . . . . . . . . . 8
6.7. Conveying location in SIP . . . . . . . . . . . . . . . . 9
6.8. Location updates . . . . . . . . . . . . . . . . . . . . . 10
6.9. Multiple locations . . . . . . . . . . . . . . . . . . . . 10
6.10. Location validation . . . . . . . . . . . . . . . . . . . 11
6.11. Default location . . . . . . . . . . . . . . . . . . . . . 11
6.12. Other location considerations . . . . . . . . . . . . . . 11
7. LIS and LoST Discovery . . . . . . . . . . . . . . . . . . . . 11
8. Routing the call to the PSAP . . . . . . . . . . . . . . . . . 12
9. Signaling of emergency calls . . . . . . . . . . . . . . . . . 13
9.1. Use of TLS . . . . . . . . . . . . . . . . . . . . . . . . 13
9.2. SIP signaling requirements for User Agents . . . . . . . . 13
9.3. SIP signaling requirements for proxy servers . . . . . . . 15
10. Call backs . . . . . . . . . . . . . . . . . . . . . . . . . . 15
11. Mid-call behavior . . . . . . . . . . . . . . . . . . . . . . 16
12. Call termination . . . . . . . . . . . . . . . . . . . . . . . 16
13. Disabling of features . . . . . . . . . . . . . . . . . . . . 16
14. Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
15. Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
16. Security Considerations . . . . . . . . . . . . . . . . . . . 18
17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
18. Normative References . . . . . . . . . . . . . . . . . . . . . 19
Appendix A. BCP Requirements Sorted by Responsible Party . . . . 24
A.1. Requirements of End Devices . . . . . . . . . . . . . . . 24
A.2. Requirements of Service Providers . . . . . . . . . . . . 32
A.3. Requirements of Access Network . . . . . . . . . . . . . . 37
A.4. Requirements of Intermediate Devices . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 42
Intellectual Property and Copyright Statements . . . . . . . . . . 43
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1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
This document uses terms from [RFC3261],
[I-D.ietf-ecrit-requirements] and [I-D.ietf-ecrit-framework].
2. Introduction
This document describes how access networks, SIP user agents, proxy
servers and PSAPs support emergency calling, as outlined in
[I-D.ietf-ecrit-framework], which is designed to complement the
present document in section headings, numbering and content. This
BCP succinctly describes the requirements of end devicesand
applications (requirements prefaced by "ED-"), access networks
(requirements prefaced by "AN-", service providers (requirements
prefaced by "SP-") and PSAPs to achieve globally interoperable
emergency calling on the Internet.
This document also defines requirements for "Intermediate" devices
which exist between end devices or applications and the access
network. For example, a home router is an "Intermediate" device.
Reporting location on an emergency call (see Section 6 may depend on
the ability of such intermediate devices to meet the requirements
prefaced by "INT-".
3. Overview of how emergency calls are placed
An emergency call can be distinguished (Section 5) from any other
call by a unique Service URN[I-D.ietf-ecrit-service-urn], which is
placed in the call set-up signaling when a home or visited emergency
dial string is detected. Because emergency services are local to
specific geographic regions, a caller must obtain his location
(Section 6) prior to making emergency calls. To get this location,
either a form of measuring (e.g., GPS) (Section 6.2.3) device
location in the endpoint is deployed, or the endpoint is configured
(Section 6.5) with its location from the access network's Location
Information Server (LIS). The location is conveyed (Section 6.7) in
the SIP signaling with the call. The call is routed (Section 8)
based on location using the LoST protocol [I-D.ietf-ecrit-lost],
which maps a location to a set of PSAP URIs. Each URI resolves to a
PSAP or an Emergency Services Routing Proxy (ESRP), which serves a
group of PSAPs. The call arrives at the PSAP with the location
included in the SIP INVITE request.
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4. Which devices and services should support emergency calls
ED-1 A device or application SHOULD support emergency calling if a
user could reasonably expect to be able to place a call for help with
the device.
SP-1 If a device or application expects to be able to place a call
for help, the service provider that supports it MUST facilitate
emergency calling.
ED-2 Devices that create media sessions and exchange audio, video
and/or text, and have the capability to establish sessions to a wide
variety of addresses, and communicate over private IP networks or the
Internet, SHOULD support emergency calls.
5. Identifying an emergency call
ED-3 Endpoints SHOULD recognize dial strings of emergency calls. If
the service provider always knows the location of the device, then
the service provider could recognize them.
SP-2 Proxy servers SHOULD recognize emergency dial string if for some
reason the endpoint does not recognize them. This cannot be relied
upon by the device if the service provider cannot always determine
the location of the device.
ED-4/SP-3 Emergency calls MUST be marked with a Service URN in the
Request-URI of the INVITE.
ED-5/SP-4 Local dial strings MUST be recognized.
ED-6/SP-5 Home dial strings MAY be recognized.
ED-7/SP-6 Local emergency dial strings SHOULD be determined from LoST
[I-D.ietf-ecrit-lost].
ED-8 Endpoints which do not recognize emergency dial strings SHOULD
send dial strings as per [RFC4967].
SP-7 Proxy Servers MUST recognize emergency dial strings represented
by [RFC4967] and SHOULD recognize emergency dial strings represented
by a tel URI [RFC3966].
SP-8 Service providers MAY provide home dial strings by configuration
[I-D.ietf-sipping-config-framework].
ED-9 Endpoints SHOULD be able to have home dial strings provisioned
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by configuration.
ED-10 Devices SHOULD NOT have one button emergency calling
initiation.
ED-11/SP-9 All emergency services specified in
[I-D.ietf-ecrit-service-urn] MUST be recognized.
6. Location and its role in an emergency call
Handling location for emergency calling usually involves several
steps to process and multiple elements are involved. In Internet
emergency calling, where the endpoint is located is "determined"
using a variety of measurement or wiretracing methods. Endpoints may
be "configured" with their own location by the access network. In
some circumstances, a proxy server may insert location into the
signaling on behalf of the endpoint. The location is "mapped" to the
URI to send the call to, and the location is "conveyed" to the PSAP
(and other elements) in the signaling. Likewise, we employ Location
Configuration Protocols, the Location-to-Service Mapping Protocol,
and Location Conveyance Protocols for these functions. The Location-
to-Service Translation protocol [I-D.ietf-ecrit-lost] is the Location
Mapping Protocol defined by the IETF.
6.1. Types of location information
There are several forms of location. In IETF protocols, civic and
geospatial (geo) forms are both supported. The civic forms include
both postal and jurisdictional fields. A cell tower/sector can be
represented as a point (geo or civic) or polygon. Other forms of
location representation must be mapped into either a geo or civic for
use in emergency calls.
ED-12/INT-1/SP-10 Endpoints, Intermediate Devices and Service
Providers MUST be prepared to handle location represented in either
civic or geo form.
ED-13/INT-2/SP-11/AN-1 Elements MUST NOT convert (civic to geo or geo
to civic) from the form of location the determination mechanism
supplied.
6.2. Location Determination
ED-14/INT-3/AN-2 Any suitable location determination mechanism MAY be
used.
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6.2.1. User-entered location information
ED-15/INT-4/AN-3 Devices, intermediate Devices and/or access networks
SHOULD support a manual method to "override" the location the access
network determines. Where a civic form of location is provided, all
fields in the PIDF-LO [RFC4119] and [RFC5139] MUST be able to be
specified.
6.2.2. Access network "wire database" location information
AN-4 Access networks supporting copper, fiber or other hard wired IP
packet service SHOULD support location configuration. If the network
does not support location configuration, it MUST require every device
that connects to the network to support end system measured location.
AN-5/INT-5 Access networks and intermediate devices providing wire
database location information SHOULD provide interior location data
(building, floor, room, cubicle) where possible. It is RECOMMENDED
that interior location be provided when spaces exceed approximately
650 square meters.
AN-6/INT-6 Access networks and intermediate devices (including
enterprise networks) which support intermediate range wireless
connections (typically 100m or less of range) and which do not
support a more accurate location determination mechanism such as
triangulation, MUST support location configuration where the location
of the access point is reflected as the location of the clients of
that access point. Where the access network provides location
configuration, intermediate devices MUST either be transparent to it,
or provide an interconnected client for the supported configuration
mechanism and a server for a configuration protocol supported by end
devices upstream of the intermediate device
6.2.3. End-system measured location information
ED-16/INT-7 Devices MAY support end-system measured location.
Uncertainty of less than 100 m with 95% confidence SHOULD be
available for dispatch.
ED-17/INT-8/AN-7 Devices that support endpoint measuring of location
MUST have at least a coarse location capability (typically <1km
accuracy when not location hiding) at all times for routing of calls.
This mechanism MAY be a service provided by the access network.
6.2.4. Network-measured location information
AN-8 Access networks MAY provide network-measured location
determination. Wireless access network which do not support network
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measured location MUST require that all devices connected to the
network have end-system measured location. Uncertainty of less than
100 m with 95% confidence SHOULD be available for dispatch.
AN-9 Access networks that provide network measured location MUST have
at least a coarse location (typically <1km when not location hiding)
capability at all times for routing of calls.
AN-10 Access networks with range of <10 meters MUST provide a
location to mobile devices connected to it. The location provided
SHOULD be that of the access point location unless a more accurate
mechanism is provided.
6.3. Who adds location, endpoint or proxy
ED-18/INT-9 Endpoints SHOULD do configure their own location.
SP-12 Proxies MAY provide location on behalf of devices if:
o The proxy has a relationship with all access networks the device
could connect to, and the relationship allows it to obtain
location.
o The proxy has an identifier, such as an IP address, that can be
used by the access network to determine the location of the
endpoint, even in the presence of NAT and VPN tunnels that may
obscure the identifier between the access network and the service
provider.
ED-19/INT-10/SP-13 Where proxies provide location on behalf of
endpoints, the the service provider MUST ensure that either the end
device is provided with the local dial strings for its current
location (where the end device recognizes dial strings), or the
service provider proxy MUST detect the appropriate local dial strings
at the time of the call.
6.4. Location and references to location
ED-20/INT-11 Devices SHOULD be able to accept and forward location by
value or by reference. An end device that receives location by
reference (and does not also get the corresponding value) MUST be
able to perform a dereference operation to obtain a value.
6.5. End system location configuration
ED-21/INT-12 Devices MUST support all of: DHCP location options
[RFC4676] and [RFC3825], HELD
[I-D.ietf-geopriv-http-location-delivery] and LLDP-MED [LLDP-MED].
AN-11/INT-13 The access network MUST support at least one of: DHCP
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location options, HELD or LLDP-MED.
AN-12/INT-14 Where a router is employed between a LAN and WAN in a
small (less than approximately 650 square meters) area, the router
MUST be transparent to the location provided by the WAN to the LAN.
This may mean the router must obtain location as a client from the
WAN, and supply an LCP server to the LAN with the location it
obtains. Where the area is larger, the LAN MUST have a location
configuration mechanism meeting this BCP.
ED-22/INT-15 Endpoints SHOULD try all LCPs supported by the device in
any order or in parallel. The first one that succeeds in supplying
location can be used.
AN-13/INT-16 Access networks that support more than one LCP MUST
reply with the same location information (within the limits of the
data format for the specific LCP) for all LCPs it supports.
ED-23/INT-17/SP-14 When HELD is the LCP, the request MUST specify a
value of "emergencyRouting" for the "responseTime" parameter and use
the resulting location for routing. If a value for dispatch location
will be sent, another request with the "responseTime" parameter set
to "emergencyDispatch" must be completed, with the result sent for
dispatch purposes.
ED-24 Where the operating system supporting application programs
which need location for emergency calls does not allow access to
Layer 2 and Layer 3 functions necessary for a client application to
use DHCP location options and/or LLDP-MED, the operating system MUST
provide a published API conforming to ED-12 through ED-21 and ED-21
through ED-31. It is RECOMMENDED that all operating systems provide
such an API.
6.6. When location should be configured
ED-25/INT-18 Endpoints SHOULD obtain location immediately after
obtaining local network configuration information.When HELD is the
LCP the client MUST support a random back-off period (between 30
seconds and 300 seconds) for re-trying the HELD query, when no
response is received.
ED-26/INT-19 If the device is configured to use DHCP for
bootstrapping, it MUST include both options for location acquisition
(civic and geodetic), the option for LIS discovery, and the option
for LoST discovery as defined in [RFC4676], [RFC3825],
[I-D.thomson-geopriv-lis-discovery] and
[I-D.ietf-ecrit-dhc-lost-discovery].
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ED-27/INT-20 If the device sends a DHCP INFORM message, it MUST
include both options for location acquisition (civic and geodetic),
the option for LIS discovery, and the option for LoST discovery as
defined in [RFC4676], [RFC3825], [I-D.thomson-geopriv-lis-discovery]
and [I-D.ietf-ecrit-dhc-lost-discovery].
ED-28/INT-21 To minimize the effects of VPNs that do not allow split
tunneling VPNs, location configuration SHOULD be attempted before
such tunnels are established.
ED-29/INT-22 Software which uses LCPs SHOULD locate and use the
actual hardware network interface rather than a VPN tunnel interface
to direct LCP requests to the LIS in the actual access network.
AN-14 Network administrators MUST take care in assigning IP addresses
such that VPN address assignments can be distinguished from local
devices (by subnet choice, for example), and LISs SHOULD NOT attempt
to provide location to addresses that arrive via VPN connections
unless it can accurately determine the location for such addresses.
AN-15 Placement of NAT devices where an LCP uses IP address for an
identifier SHOULD consider the effect of the NAT on the LCP. The
address used to query the LIS MUST be able to correctly identify the
record in the LIS representing the location of the querying device
ED-30/INT-23 For devices which are not expected to roam, refreshing
location on the order of once per day is RECOMMENDED.
ED-31/INT-24 For devices which roam, refresh of location information
SHOULD be more frequent, with the frequency related to the mobility
of the device and the ability of the access network to support the
refresh operation. If the device can detect that it has moved, for
example when it changes access points, the device SHOULD refresh its
location.
ED-32/INT-25/AN-16 It is RECOMMENDED that location determination not
take longer than 250 ms to obtain routing location and systems SHOULD
be designed such that the typical response is under 100 ms. However,
as much as 3 seconds to obtain routing location MAY be tolerated if
location accuracy can be substantially improved over what can be
obtained in 250 ms.
6.7. Conveying location in SIP
ED-33/SP-15 Location sent between SIP elements MUST be conveyed using
[I-D.ietf-sip-location-conveyance].
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6.8. Location updates
ED-34/AN-17 Where the absolute location or the accuracy of location
of the endpoint may change between the time the call is received at
the PSAP and the time dispatch is completed, location update
mechanisms MUST be provided.
ED-35/AN-18 Mobile devices MUST be provided with a mechanism to get
repeated location updates to track the motion of the device during
the complete processing of the call.
ED-36/AN-19 The LIS SHOULD provide a location reference which permits
a subscription with appropriate filtering.
ED-37/AN-20 For calls sent with location-by-reference, with a SIP or
SIPS scheme, the server resolving the reference MUST support a
SUBSCRIBE [RFC3265] to the presence event [RFC3856]. For other
location-by-reference schemes, the PSAP will have to repeatedly
dereference the URI to determine if the device moved.
ED-38 If location was sent by value, and the endpoint gets updated
location, it MUST send the updated location to the PSAP via a SIP re-
INVITE or UPDATE request. Such updates SHOULD be limited to no more
than one update every 10 seconds.
6.9. Multiple locations
ED-39 If a UA has more than one location available to it, it MUST
choose one location to route the call towards the PSAP.
SP-16 If a proxy inserts location on behalf of an endpoint, and it
has multiple locations available for the endpoint it MUST choose one
location to use to route the call towards the PSAP.
SP-17 If a proxy is attempting to insert location but the UA conveyed
a location to it, the proxy MUST use the UA's location for routing
and MUST convey that location towards the PSAP. It MAY also include
what it believes the location to be in a separate Geolocation header.
SP-18 All location objects received by a proxy MUST be delivered to
the PSAP.
ED-40/SP-19 Location objects MUST contain information about the
method by which the location was determined, such as GPS, manually
entered, or based on access network topology included in a PIDF- LO
"method" element. In addition, the source of the location
information MUST be included in a PIDF-LO "provided-by" element.
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ED-41/SP-20 The "used-for-routing" parameter MUST be set to the
location that was used to query LoST.
6.10. Location validation
AN-21 A LIS should perform location validation of civic locations via
LoST before entering a location in its database.
ED-42 Endpoints SHOULD validate civic locations when they receive
them from their LCP. Validation SHOULD be performed in conjunction
with the LoST route query to minimize load on the LoST server.
6.11. Default location
AN-22 When the access network cannot determine the actual location of
the caller, it MUST supply a default location. The default SHOULD be
chosen to be as close to the probable location of the device as the
network can determine. See [I-D.ietf-ecrit-framework]
SP-21 Proxies handling emergency calls MUST insert a default location
if the call does not contain a location and the proxy does not have a
method for obtaining a better location.
AN-23/SP-22 Default locations MUST be marked with method=Default and
the proxy MUST be identfied in provided-by element of the PIDF-LO.
6.12. Other location considerations
ED-43 If the LCP does not return location in the form of a PIDF-LO
[RFC4119], the endpoint MUST map the location information it receives
from the configuration protocol to a PIDF-LO.
ED-44/AN-24 To prevent against spoofing of the DHCP server, elements
implementing DHCP for location configuration SHOULD use although the
difficulty in providing appropriate credentials is significant.
[RFC3118].
ED-45 S/MIME MUST NOT be used to encrypt the SIP Geolocation header
or bodies.
ED-46/SP-23 TLS MUST be used to protect location (but see
Section 9.1). IPSEC [RFC2401] is an acceptable alternative.
7. LIS and LoST Discovery
ED-47 Endpoints MUST support one or more mechanisms that allow them
to determine their public IP address. Examples include ICE
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[I-D.ietf-mmusic-ice] and HTTP get.
ED-48 Endpoints MUST support LIS discovery as described in
[I-D.thomson-geopriv-lis-discovery], and the LoST discovery as
described in [I-D.ietf-ecrit-dhc-lost-discovery].
ED-49 The device MUST have a configurable default LoST server
parameter. If the device is provided by or managed by service
provider, it is expected that the service provider will configure
this option.
8. Routing the call to the PSAP
ED-50 Endpoints who obtain their own location SHOULD perform LoST
mapping to the PSAP URI.
ED-51 Mapping SHOULD be performed at boot time and whenever location
changes beyond the service boundary obtained from a prior LoST
mapping operation or the time-to-live value of that response has
expired. The value MUST be cached for possible later use.
ED-52 The endpoint MUST attempt to update its location at the time of
an emergency call. If it cannot obtain a new location quickly (see
Section 6), it MUST use the cached value.
ED-53 The endpoint SHOULD attempt to update the LoST mapping at the
time of an emergency call. If it cannot obtain a new mapping
quickly, it MUST use the cached value if it has one.
SP-24 Networks MUST be designed so that at least one proxy in the
outbound path can recognize emergency calls with a Request URI of the
service URN in the "sos" tree. An endpoint places a service URN in
the Request URI to indicate that the endpoint understood the call was
an emergency call. A proxy that processes such a call looks for the
presence of a SIP Route header field with a URI of a PSAP. Absence
of such a Route header indicates the UAC was unable to invoke LoST
and the proxy MUST perform the LoST mapping and insert a Route header
field with the URI obtained.
SP-25 To deal with old user agents that predate this specification
and with UAs that do not have access to their own location data, a
proxy that recognizes a call as an emergency call that is not marked
as such (see Section 5) MUST also perform this mapping, with the best
location it has available for the endpoint. The resulting PSAP URI
would be placed in a Route header with the service URN in the Request
URI.
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SP-26 Proxy servers performing mapping SHOULD use location obtained
from the access network for the mapping. If no location is
available, a default location (see Section 6.11) MUST be supplied.
SP-27 A proxy server which attempts mapping and fails to get a
mapping MUST provide a default mapping. A suitable default mapping
would be the mapping obtained previously for the default location
appropriate for the caller.
ED-54/SP-28 [RFC3261] and [RFC3263] procedures MUST be used to route
an emergency call towards the PSAP's URI.
ED-55 Initial INVITES MUST provide an Offer [RFC3264].
9. Signaling of emergency calls
ED-56 Best Current Practice for SIP user agents [RFC4504] including
handling of audio, video and real-time text [RFC4103] SHOULD be
applied. This memo can be considered as an addition to [RFC4504] for
endpoints.
9.1. Use of TLS
ED-57/SP-29 TLS MUST be specified when attempting to signal an
emergency call with SIP per [I-D.ietf-sip-sips]. IPSEC [RFC2401] is
an acceptable alternative.
ED-58/SP-30 If TLS session establishment fails, the call MUST be
retried without TLS.
ED-59/SP-31 [I-D.ietf-sip-outbound] is RECOMMENDED to maintain
persistent TLS connections between elements.
ED-60/AN-25 TLS MUST be specified when attempting to retrieve
location (configuration or dereferencing) with HELD. The use of
[RFC4507] is RECOMMENDED to minimise the time to establish TLS
sessions.
ED-61/AN-26 If TLS session establishment fails, the location
retrieveal MUST be retried without TLS.
9.2. SIP signaling requirements for User Agents
ED-62 The initial SIP signaling method is an INVITE request:
1. The Request URI SHOULD be the service URN in the "sos" tree, If
the device cannot interpert local dial strings, the Request-URI
SHOULD be a dial string URI [RFC4967] with the dialed digits.
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2. The To header SHOULD be a service URN in the "sos" tree. If the
device cannot do interpret local dial strings, the To: SHOULD be
a dial string URI with the dialed digits.
3. The From header MUST be present and SHOULD be the AoR of the
caller.
4. A Via header MUST be present.
5. A Route header SHOULD be present with a PSAP URI obtained from
LoST (see Section 8) and the loose route parameter. If the
device does not interpet dial plans, or was unable to obtain a
route from a LoST serverr, no Route header will be present.
6. A Contact header MUST be present which MUST be globally
routable, for example a GRUU [I-D.ietf-sip-gruu], to permit an
immediate call-back to the specific device which placed the
emergency call.
7. Other headers MAY be included as per normal SIP behavior.
8. A Supported header MUST be included with the 'geolocation'
option tag [I-D.ietf-sip-location-conveyance], unless the device
does not understand the concept of SIP location.
9. If a device understands the SIP location conveyance
[I-D.ietf-sip-location-conveyance] extension and has its
location available, it MUST include location either by-value,
by-reference or both.
10. If a device understands the SIP Location Conveyance extension
and has its location unavailable or unknown to that device, it
MUST include a Supported header with a "geolocation" option tag,
and MUST NOT include a Geolocation header, and not include a
PIDF-LO message body.
11. If a device understands the SIP Location Conveyance extension
and supports LoST [I-D.ietf-ecrit-lost], the Geolocation "used-
for-routing" header parameter MUST be added to the corresponding
URI in the Geolocation header.
12. A normal SDP offer SHOULD be included in the INVITE. If voice
is supported the offer MUST include the G.711 codec, see
Section 14.
13. If the device includes location-by-value, the UA MUST support
multipart message bodies, since SDP will likely be also in the
INVITE.
14. A UAC SHOULD include a "inserted-by=endpoint" header parameter
on all Geolocation headers . This informs downstream elements
which device entered the location at this URI (either cid-URL or
location-by-reference URI).
15. SIP Caller Preferences [RFC3841] MAY be used to signal how the
PSAP should handle the call. For example, a language preference
expressed in an Accept-Language header may be used as a hint to
cause the PSAP to route the call to a call taker who speaks the
requested language. SIP Caller Preferences may also be used to
indicate a need to invoke a relay service for communication with
people with disabilities in the call.
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9.3. SIP signaling requirements for proxy servers
SP-32 SIP Proxy servers processing emergency calls:
1. If the proxy does interprets dial plans on behalf of user agents,
the proxy MUST look for the local emergency dial string at the
location of the end device and MAY look for the home dial string.
If it finds it, the proxy MUST:
* Insert a Geolocation header as above. Location-by-reference
MUST be used because proxies must not insert bodies.
* Include the Geolocation "inserted-by=server" and "used-for-
routing" parameters.
* Map the location to a PSAP URI using LoST.
* Add a Route header with the PSAP URI.
* Replace the Request-URI (which was the dial string) with the
service URN appropriate for the emergency dial string.
* Route the call using normal SIP routing mechanisms.
2. If the proxy recognizes the service URN in the Request URI, and
does not find a Route header with a PSAP URI, it MUST run LoST
routing. If a location was provided (which should be the case),
the proxy uses that location to query LoST. The proxy may have
to dereference a location by reference to get a value. If a
location is not present, and the proxy can query a LIS which has
the location of the UA it MUST do so. If no location is present,
and the proxy does not have access to a LIS which could provide
location, the proxy MUST supply a default location (See
Section 6.11). The location (in the signaling, obtained from a
LIS, or default) MUST be used in a query to LoST with the service
URN received with the call. The resulting URI MUST be placed in
a Route header added to the call.
3. The "inserted-by=" parameter in any Geolocation: header received
on the call MUST NOT be modified or deleted in transit.
4. The proxy SHOULD NOT modify any parameters in Geolocation headers
received in the call. It MAY add a Geolocation header. Such an
additional location SHOULD NOT be used for routing; the location
provided by the UA should be used.
5. Either a P-Asserted-Identity [RFC3325] or an Identity header
[RFC4474], or both, MUST be included to identify the sender.
10. Call backs
SP-33 Unitialized devices, like any device MUST have a globally
routable URI in a Contact: header.
SP-34 Unitialized devices SHOULD have a persistent URI in a
P-Asserted-Identity: header if there is some way to assign such an
identifier to the device.
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11. Mid-call behavior
ED-63/SP-35 During the course of an emergency call, devices and
proxies MUST support REFER transactions and the Referred-by: header
[RFC3515].
ED-64/SP-36 User agents and proxies MUST support Session Timer
[RFC4028] to guard against session corruption.
12. Call termination
ED-65 UACs with an active emergency call (i.e. SIP Dialog) MUST NOT
generate a BYE request (or equivalent for other non-SIP signaling).
The PSAP must be the only entity that can terminate a call. If the
user "hangs up" an emergency call, the device should alert the user,
and if the user responds by attempting to pick up the call, the
device MUST reconnect the caller to the PSAP.
ED-66 There can be a case where the session signaling path is lost,
and the user agent does not receive the BYE. If the call is hung up,
and the session timer (if implemented) expires, the call MAY be
declared lost. If in the interval, an incoming call is received from
the domain of the PSAP, the device MUST drop the old call and alert
for the (new) incoming call. Dropping of the old call MUST only
occur if the user is attempting to hang up; the domain of an incoming
call can only be determined from the From header, which is not
reliable, and could be spoofed. Dropping an active call by a new
call with a spoofed From: would be a DoS attack.
13. Disabling of features
ED-67/SP-37 User Agents and proxys MUST disable outgoing call
features such as
o Call Waiting
o Call Transfer
o Three Way Call
o Flash hold
o Outbound Call Blocking
when an emergency call is established. Also see ED-72 in Section 14.
ED-68/SP-38 The emergency dialstrings SHOULD NOT be permitted in Call
Forward numbers or speed dial lists.
ED-69/SP-39 The User Agent and Proxies SHOULD disable the following
incoming call features on call backs from the PSAP:
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o Call Waiting
o Do Not Disturb
o Call Forward (all kinds)
ED-70 Call backs SHOULD be determined by retaining the domain of the
PSAP which answers an outgoing emergency call and instantiating a
timer which starts when the call is terminated. If a call is
received from the same domain and within the timer period, sent to
the Contact: or AoR used in the emergency call, it should be assumed
to be a call back. The suggested timer period is 5 minutes.
14. Media
ED-71 Endpoints MUST send and receive media streams on RTP [RFC3550].
ED-72 Normal SIP offer/answer [RFC3264] negotiations MUST be used to
agree on the media streams to be used.
ED-73 Endpoints supporting voice MUST support G.711 A law (and mu Law
if they could be used in North America) encoded voice as described in
[RFC3551]. It is desirable to include wideband codecs such as AMR-WB
in the offer.
ED-74 Silence suppression (Voice Activity Detection methods) MUST NOT
be used on emergency calls. PSAP call takers sometimes get
information on what is happening in the background to determine how
to process the call.
ED-75 Endpoints supporting IM MUST support both [RFC3428] and
[RFC4975].
ED-76 Endpoints supporting real-time text MUST use [RFC4103]. The
expectations for emergency service support for the real-time text
medium, described in [I-D.ietf-sipping-toip], Section 7.1 SHOULD be
fulfilled.
ED-77 Endpoints supporting video MUST support H.264 per [RFC3984].
15. Testing
ED-78 INVITE requests to a service URN ending in ".test" indicates a
request for an automated test. For example,
"urn:service.sos.fire.test". As in standard SIP, a 200 (OK) response
indicates that the address was recognized and a 404 (Not found) that
it was not. A 486 (Busy Here) MUST be returned if the test service
is busy, and a 488 (Not Acceptable Here) MUST be returned if the PSAP
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does not support the test mechanism.
ED-79 In its response to the test, the PSAP MAY include a text body
(text/plain) indicating the identity of the PSAP, the requested
service, and the location reported with the call. For the latter,
the PSAP SHOULD return location-by-value even if the original
location delivered with the test was by-reference. If the location-
by-reference was supplied, and the dereference requires credentials,
the PSAP SHOULD use credentials supplied by the LIS for test
purposes. This alerts the LIS that the dereference is not for an
actual emergency call and location hiding techniques, if they are
being used, may be employed for this dereference. The response MAY
include the connected identity of the PSAP per
[I-D.ietf-sip-connected-identity].
ED-80 A PSAP accepting a test call SHOULD accept a media loopback
test [I-D.ietf-mmusic-media-loopback] and SHOULD support the "rtp-
pkt-loopback" and "rtp-start-loopback" options. The user agent would
specify a loopback attribute of "loopback-source", the PSAP being the
mirror. User Agents should expect the PSAP to loop back no more than
3 packets of each media type accepted (which limits the duration of
the test), after which the PSAP would normally send BYE.
ED-81 User agents SHOULD perform a full call test, including media
loopback, after a disconnect and subsequent change in IP address not
due to a reboot. After an initial test, a full test SHOULD be
repeated approximately every 30 days with a random interval.
ED-82 User agents MUST NOT place a test call immediately after
booting. If the IP address changes after booting, the UA should wait
a random amount of time (in perhaps a 30 minute period, sufficient
for any avalanche restart to complete) and then test.
ED-83 PSAPs MAY refuse repeated requests for test from the same
device in a short period of time. Any refusal is signaled with a 486
or 488 response.
16. Security Considerations
Security considerations for emergency calling have been documented in
[I-D.ietf-ecrit-security-threats], and [I-D.barnes-geopriv-lo-sec].
17. Acknowledgements
Work group members participating in the creation and review of this
document include include Hannes Tschofenig, Ted Hardie, Marc Linsner,
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Roger Marshall, Stu Goldman, Shida Schubert, James Winterbottom,
Barbara Stark, Richard Barnes and Peter Blatherwick.
18. Normative References
[I-D.barnes-geopriv-lo-sec]
Barnes, R., Lepinski, M., Tschofenig, H., and H.
Schulzrinne, "Security Requirements for the Geopriv
Location System", draft-barnes-geopriv-lo-sec-02 (work in
progress), February 2008.
[I-D.ietf-ecrit-dhc-lost-discovery]
Schulzrinne, H., "A Dynamic Host Configuration Protocol
(DHCP) based Location-to-Service Translation Protocol
(LoST) Discovery Procedure",
draft-ietf-ecrit-dhc-lost-discovery-02 (work in progress),
July 2007.
[I-D.ietf-ecrit-framework]
Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
"Framework for Emergency Calling using Internet
Multimedia", draft-ietf-ecrit-framework-04 (work in
progress), November 2007.
[I-D.ietf-ecrit-lost]
Hardie, T., Newton, A., Schulzrinne, H., and H.
Tschofenig, "LoST: A Location-to-Service Translation
Protocol", draft-ietf-ecrit-lost-07 (work in progress),
February 2008.
[I-D.ietf-ecrit-requirements]
Schulzrinne, H. and R. Marshall, "Requirements for
Emergency Context Resolution with Internet Technologies",
draft-ietf-ecrit-requirements-13 (work in progress),
March 2007.
[I-D.ietf-ecrit-security-threats]
Taylor, T., "Security Threats and Requirements for
Emergency Call Marking and Mapping",
draft-ietf-ecrit-security-threats-05 (work in progress),
August 2007.
[I-D.ietf-ecrit-service-urn]
Schulzrinne, H., "A Uniform Resource Name (URN) for
Emergency and Other Well-Known Services",
draft-ietf-ecrit-service-urn-07 (work in progress),
August 2007.
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[I-D.ietf-geopriv-http-location-delivery]
Barnes, M., Winterbottom, J., Thomson, M., and B. Stark,
"HTTP Enabled Location Delivery (HELD)",
draft-ietf-geopriv-http-location-delivery-05 (work in
progress), February 2008.
[I-D.ietf-geopriv-pdif-lo-profile]
Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
PIDF-LO Usage Clarification, Considerations and
Recommendations", draft-ietf-geopriv-pdif-lo-profile-11
(work in progress), February 2008.
[I-D.ietf-mmusic-ice]
Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols",
draft-ietf-mmusic-ice-19 (work in progress), October 2007.
[I-D.ietf-mmusic-media-loopback]
Hedayat, K., "An Extension to the Session Description
Protocol (SDP) for Media Loopback",
draft-ietf-mmusic-media-loopback-07 (work in progress),
November 2007.
[I-D.ietf-sip-connected-identity]
Elwell, J., "Connected Identity in the Session Initiation
Protocol (SIP)", draft-ietf-sip-connected-identity-05
(work in progress), February 2007.
[I-D.ietf-sip-gruu]
Rosenberg, J., "Obtaining and Using Globally Routable User
Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-15 (work in progress),
October 2007.
[I-D.ietf-sip-location-conveyance]
Polk, J. and B. Rosen, "Location Conveyance for the
Session Initiation Protocol",
draft-ietf-sip-location-conveyance-09 (work in progress),
November 2007.
[I-D.ietf-sip-outbound]
Jennings, C. and R. Mahy, "Managing Client Initiated
Connections in the Session Initiation Protocol (SIP)",
draft-ietf-sip-outbound-11 (work in progress),
November 2007.
[I-D.ietf-sip-sips]
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Audet, F., "The use of the SIPS URI Scheme in the Session
Initiation Protocol (SIP)", draft-ietf-sip-sips-08 (work
in progress), February 2008.
[I-D.ietf-sipping-config-framework]
Channabasappa, S., "A Framework for Session Initiation
Protocol User Agent Profile Delivery",
draft-ietf-sipping-config-framework-15 (work in progress),
February 2008.
[I-D.ietf-sipping-toip]
Wijk, A. and G. Gybels, "Framework for real-time text over
IP using the Session Initiation Protocol (SIP)",
draft-ietf-sipping-toip-08 (work in progress),
October 2007.
[I-D.thomson-geopriv-lis-discovery]
Thomson, M. and J. Winterbottom, "Discovering the Local
Location Information Server (LIS)",
draft-thomson-geopriv-lis-discovery-03 (work in progress),
September 2007.
[LLDP] IEEE, "IEEE802.1ab Station and Media Access Control",
Dec 2004.
[LLDP-MED]
TIA, "ANSI/TIA-1057 Link Layer Discovery Protocol - Media
Endpoint Discovery".
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option",
RFC 3046, January 2001.
[RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP
Messages", RFC 3118, June 2001.
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[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation
Protocol (SIP): Locating SIP Servers", RFC 3263,
June 2002.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
June 2002.
[RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific
Event Notification", RFC 3265, June 2002.
[RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
Extensions to the Session Initiation Protocol (SIP) for
Asserted Identity within Trusted Networks", RFC 3325,
November 2002.
[RFC3428] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C.,
and D. Gurle, "Session Initiation Protocol (SIP) Extension
for Instant Messaging", RFC 3428, December 2002.
[RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", STD 65, RFC 3551,
July 2003.
[RFC3825] Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host
Configuration Protocol Option for Coordinate-based
Location Configuration Information", RFC 3825, July 2004.
[RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, August 2004.
[RFC3856] Rosenberg, J., "A Presence Event Package for the Session
Initiation Protocol (SIP)", RFC 3856, August 2004.
[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers",
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RFC 3966, December 2004.
[RFC3984] Wenger, S., Hannuksela, M., Stockhammer, T., Westerlund,
M., and D. Singer, "RTP Payload Format for H.264 Video",
RFC 3984, February 2005.
[RFC4028] Donovan, S. and J. Rosenberg, "Session Timers in the
Session Initiation Protocol (SIP)", RFC 4028, April 2005.
[RFC4103] Hellstrom, G. and P. Jones, "RTP Payload for Text
Conversation", RFC 4103, June 2005.
[RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005.
[RFC4190] Carlberg, K., Brown, I., and C. Beard, "Framework for
Supporting Emergency Telecommunications Service (ETS) in
IP Telephony", RFC 4190, November 2005.
[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474, August 2006.
[RFC4504] Sinnreich, H., Lass, S., and C. Stredicke, "SIP Telephony
Device Requirements and Configuration", RFC 4504,
May 2006.
[RFC4507] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 4507, May 2006.
[RFC4676] Schulzrinne, H., "Dynamic Host Configuration Protocol
(DHCPv4 and DHCPv6) Option for Civic Addresses
Configuration Information", RFC 4676, October 2006.
[RFC4967] Rosen, B., "Dial String Parameter for the Session
Initiation Protocol Uniform Resource Identifier",
RFC 4967, July 2007.
[RFC4975] Campbell, B., Mahy, R., and C. Jennings, "The Message
Session Relay Protocol (MSRP)", RFC 4975, September 2007.
[RFC5139] Thomson, M. and J. Winterbottom, "Revised Civic Location
Format for Presence Information Data Format Location
Object (PIDF-LO)", RFC 5139, February 2008.
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Appendix A. BCP Requirements Sorted by Responsible Party
A.1. Requirements of End Devices
ED-1 A device or application SHOULD support emergency calling if a
user could reasonably expect to be able to place a call for help with
the device.
ED-2 Devices that create media sessions and exchange audio, video
and/or text, and have the capability to establish sessions to a wide
variety of addresses, and communicate over private IP networks or the
Internet, SHOULD support emergency calls.
ED-3 Endpoints SHOULD recognize dial strings of emergency calls. If
the service provider always knows the location of the device, then
the service provider could recognize them.
ED-4 Emergency calls MUST be marked with a Service URN in the
Request-URI of the INVITE.
ED-5 Local dial strings MUST be recognized.
ED-6 Home dial strings MAY be recognized.
ED-7 Local emergency dial strings SHOULD be determined from LoST
[I-D.ietf-ecrit-lost].
ED-8 Endpoints which do not recognize emergency dial strings SHOULD
send dial strings as per [RFC4967].
ED-9 Endpoints SHOULD be able to have home dial strings provisioned
by configuration.
ED-10 Devices SHOULD NOT have one button emergency calling
initiation.
ED-11 All emergency services specified in
[I-D.ietf-ecrit-service-urn] MUST be recognized.
ED-12 Endpoints, Intermediate Devices and Service Providers MUST be
prepared to handle location represented in either civic or geo form.
ED-13 Elements MUST NOT convert (civic to geo or geo to civic) from
the form of location the determination mechanism supplied.
ED-14 Any suitable location determination mechanism MAY be used.
ED-15 Devices, intermediate Devices and/or access networks SHOULD
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support a manual method to "override" the location the access network
determines. Where a civic form of location is provided, all fields
in the PIDF-LO [RFC4119] and [RFC5139] MUST be able to be specified.
ED-16 Devices MAY support end-system measured location. Uncertainty
of less than 100 m with 95% confidence SHOULD be available for
dispatch.
ED-17 Devices that support endpoint measuring of location MUST have
at least a coarse location capability (typically <1km accuracy when
not location hiding) at all times for routing of calls. This
mechanism MAY be a service provided by the access network.
ED-18 Endpoints SHOULD do configure their own location.
ED-19 Where proxies provide location on behalf of endpoints, the the
service provider MUST ensure that either the end device is provided
with the local dial strings for its current location (where the end
device recognizes dial strings), or the service provider proxy MUST
detect the appropriate local dial strings at the time of the call.
ED-20 Devices SHOULD be able to accept and forward location by value
or by reference. An end device that receives location by reference
(and does not also get the corresponding value) MUST be able to
perform a dereference operation to obtain a value.
ED-21 Devices MUST support all of: DHCP location options [RFC4676]
and [RFC3825], HELD [I-D.ietf-geopriv-http-location-delivery] and
LLDP-MED [LLDP-MED].
ED-22 Endpoints SHOULD try all LCPs supported by the device in any
order or in parallel. The first one that succeeds in supplying
location can be used.
ED-23 When HELD is the LCP, the request MUST specify a value of
"emergencyRouting" for the "responseTime" parameter and use the
resulting location for routing. If a value for dispatch location
will be sent, another request with the "responseTime" parameter set
to "emergencyDispatch" must be completed, with the result sent for
dispatch purposes.
ED-24 Where the operating system supporting application programs
which need location for emergency calls does not allow access to
Layer 2 and Layer 3 functions necessary for a client application to
use DHCP location options and/or LLDP-MED, the operating system MUST
provide a published API conforming to ED-12 through ED-18 and ED-21
through ED-27. It is RECOMMENDED that all operating systems provide
such an API.
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ED-25 Endpoints SHOULD obtain location immediately after obtaining
local network configuration information.When HELD is the LCP the
client MUST support a random back-off period (between 30 seconds and
300 seconds) for re-trying the HELD query, when no response is
received.
ED-26 If the device is configured to use DHCP for bootstrapping, it
MUST include both options for location acquisition (civic and
geodetic), the option for LIS discovery, and the option for LoST
discovery as defined in [RFC4676], [RFC3825],
[I-D.thomson-geopriv-lis-discovery] and
[I-D.ietf-ecrit-dhc-lost-discovery].
ED-27 If the device sends a DHCP INFORM message, it MUST include both
options for location acquisition (civic and geodetic), the option for
LIS discovery, and the option for LoST discovery as defined in
[RFC4676], [RFC3825], [I-D.thomson-geopriv-lis-discovery] and
[I-D.ietf-ecrit-dhc-lost-discovery].
ED-28 To minimize the effects of VPNs that do not allow split
tunneling VPNs, location configuration SHOULD be attempted before
such tunnels are established.
ED-29 Software which uses LCPs SHOULD locate and use the actual
hardware network interface rather than a VPN tunnel interface to
direct LCP requests to the LIS in the actual access network.
ED-30 For devices which are not expected to roam, refreshing location
on the order of once per day is RECOMMENDED.
ED-31 For devices which roam, refresh of location information SHOULD
be more frequent, with the frequency related to the mobility of the
device and the ability of the access network to support the refresh
operation. If the device can detect that it has moved, for example
when it changes access points, the device SHOULD refresh its
location.
ED-32 It is RECOMMENDED that location determination not take longer
than 250 ms to obtain routing location and systems SHOULD be designed
such that the typical response is under 100 ms. However, as much as
3 seconds to obtain routing location MAY be tolerated if location
accuracy can be substantially improved over what can be obtained in
250 ms.
ED-33 Location sent between SIP elements MUST be conveyed using
[I-D.ietf-sip-location-conveyance].
ED-34 Where the absolute location or the accuracy of location of the
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endpoint may change between the time the call is received at the PSAP
and the time dispatch is completed, location update mechanisms MUST
be provided.
ED-35 Mobile devices MUST be provided with a mechanism to get
repeated location updates to track the motion of the device during
the complete processing of the call.
ED-36 The LIS SHOULD provide a location reference which permits a
subscription with appropriate filtering.
ED-37 For calls sent with location-by-reference, with a SIP or SIPS
scheme, the server resolving the reference MUST support a SUBSCRIBE
[RFC3265] to the presence event [RFC3856]. For other location-by-
reference schemes, the PSAP will have to repeatedly dereference the
URI to determine if the device moved.
ED-38 If location was sent by value, and the endpoint gets updated
location, it MUST send the updated location to the PSAP via a SIP re-
INVITE or UPDATE request. Such updates SHOULD be limited to no more
than one update every 10 seconds.
ED-39 If a UA has more than one location available to it, it MUST
choose one location to route the call towards the PSAP.
ED-40 Location objects MUST contain information about the method by
which the location was determined, such as GPS, manually entered, or
based on access network topology included in a PIDF- LO "method"
element. In addition, the source of the location information MUST be
included in a PIDF-LO "provided-by" element.
ED-41 The "used-for-routing" parameter MUST be set to the location
that was used to query LoST.
ED-42 Endpoints SHOULD validate civic locations when they receive
them from their LCP. Validation SHOULD be performed in conjunction
with the LoST route query to minimize load on the LoST server.
ED-43 If the LCP does not return location in the form of a PIDF-LO
[RFC4119], the endpoint MUST map the location information it receives
from the configuration protocol to a PIDF-LO.
ED-44 To prevent against spoofing of the DHCP server, elements
implementing DHCP for location configuration SHOULD use although the
difficulty in providing appropriate credentials is significant.
[RFC3118].
ED-45 S/MIME MUST NOT be used to encrypt the SIP Geolocation header
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or bodies.
ED-46 TLS MUST be used to protect location (but see Section 9.1).
IPSEC [RFC2401] is an acceptable alternative.
ED-47 Endpoints MUST support one or more mechanisms that allow them
to determine their public IP address. Examples include ICE
[I-D.ietf-mmusic-ice] and HTTP get.
ED-48 Endpoints MUST support LIS discovery as described in
[I-D.thomson-geopriv-lis-discovery], and the LoST discovery as
described in [I-D.ietf-ecrit-dhc-lost-discovery].
ED-49 The device MUST have a configurable default LoST server
parameter. If the device is provided by or managed by service
provider, it is expected that the service provider will configure
this option.
ED-50 Endpoints who obtain their own location SHOULD perform LoST
mapping to the PSAP URI.
ED-51 Mapping SHOULD be performed at boot time and whenever location
changes beyond the service boundary obtained from a prior LoST
mapping operation or the time-to-live value of that response has
expired. The value MUST be cached for possible later use.
ED-52 The endpoint MUST attempt to update its location at the time of
an emergency call. If it cannot obtain a new location quickly (see
Section 6), it MUST use the cached value.
ED-53 The endpoint SHOULD attempt to update the LoST mapping at the
time of an emergency call. If it cannot obtain a new mapping
quickly, it MUST use the cached value if it has one.
ED-54 [RFC3261] and [RFC3263] procedures MUST be used to route an
emergency call towards the PSAP's URI.
ED-55 Initial INVITES MUST provide an Offer [RFC3264].
ED-56 Best Current Practice for SIP user agents [RFC4504] including
handling of audio, video and real-time text [RFC4103] SHOULD be
applied. This memo can be considered as an addition to [RFC4504] for
endpoints.
ED-57 TLS MUST be specified when attempting to signal an emergency
call with SIP per [I-D.ietf-sip-sips]. IPSEC [RFC2401] is an
acceptable alternative.
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ED-58 If TLS session establishment fails, the call MUST be retried
without TLS.
ED-59 [I-D.ietf-sip-outbound] is RECOMMENDED to maintain persistent
TLS connections between elements.
ED-60 TLS MUST be specified when attempting to retrieve location
(configuration or dereferencing) with HELD. The use of [RFC4507] is
RECOMMENDED to minimise the time to establish TLS sessions.
ED-61 If TLS session establishment fails, the location retrieveal
MUST be retried without TLS.
ED-62 The initial SIP signaling method is an INVITE request:
1. The Request URI SHOULD be the service URN in the "sos" tree, If
the device cannot interpert local dial strings, the Request-URI
SHOULD be a dial string URI [RFC4967] with the dialed digits.
2. The To header SHOULD be a service URN in the "sos" tree. If the
device cannot do interpret local dial strings, the To: SHOULD be
a dial string URI with the dialed digits.
3. The From header MUST be present and SHOULD be the AoR of the
caller.
4. A Via header MUST be present.
5. A Route header SHOULD be present with a PSAP URI obtained from
LoST (see Section 8) and the loose route parameter. If the
device does not interpet dial plans, or was unable to obtain a
route from a LoST serverr, no Route header will be present.
6. A Contact header MUST be present which MUST be globally
routable, for example a GRUU [I-D.ietf-sip-gruu], to permit an
immediate call-back to the specific device which placed the
emergency call.
7. Other headers MAY be included as per normal SIP behavior.
8. A Supported header MUST be included with the 'geolocation'
option tag [I-D.ietf-sip-location-conveyance], unless the device
does not understand the concept of SIP location.
9. If a device understands the SIP location conveyance
[I-D.ietf-sip-location-conveyance] extension and has its
location available, it MUST include location either by-value,
by-reference or both.
10. If a device understands the SIP Location Conveyance extension
and has its location unavailable or unknown to that device, it
MUST include a Supported header with a "geolocation" option tag,
and MUST NOT include a Geolocation header, and not include a
PIDF-LO message body.
11. If a device understands the SIP Location Conveyance extension
and supports LoST [I-D.ietf-ecrit-lost], the Geolocation "used-
for-routing" header parameter MUST be added to the corresponding
URI in the Geolocation header.
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12. A normal SDP offer SHOULD be included in the INVITE. If voice
is supported the offer MUST include the G.711 codec, see
Section 14.
13. If the device includes location-by-value, the UA MUST support
multipart message bodies, since SDP will likely be also in the
INVITE.
14. A UAC SHOULD include a "inserted-by=endpoint" header parameter
on all Geolocation headers . This informs downstream elements
which device entered the location at this URI (either cid-URL or
location-by-reference URI).
15. SIP Caller Preferences [RFC3841] MAY be used to signal how the
PSAP should handle the call. For example, a language preference
expressed in an Accept-Language header may be used as a hint to
cause the PSAP to route the call to a call taker who speaks the
requested language. SIP Caller Preferences may also be used to
indicate a need to invoke a relay service for communication with
people with disabilities in the call.
ED-63 During the course of an emergency call, devices and proxies
MUST support REFER transactions and the Referred-by: header
[RFC3515].
ED-64 User agents and proxies MUST support Session Timer [RFC4028] to
guard against session corruption.
ED-65 UACs with an active emergency call (i.e. SIP Dialog) MUST NOT
generate a BYE request (or equivalent for other non-SIP signaling).
The PSAP must be the only entity that can terminate a call. If the
user "hangs up" an emergency call, the device should alert the user,
and if the user responds by attempting to pick up the call, the
device MUST reconnect the caller to the PSAP.
ED-66 There can be a case where the session signaling path is lost,
and the user agent does not receive the BYE. If the call is hung up,
and the session timer (if implemented) expires, the call MAY be
declared lost. If in the interval, an incoming call is received from
the domain of the PSAP, the device MUST drop the old call and alert
for the (new) incoming call. Dropping of the old call MUST only
occur if the user is attempting to hang up; the domain of an incoming
call can only be determined from the From header, which is not
reliable, and could be spoofed. Dropping an active call by a new
call with a spoofed From: would be a DoS attack.
ED-67 User Agents and proxys MUST disable outgoing call features such
as
o Call Waiting
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o Call Transfer
o Three Way Call
o Flash hold
o Outbound Call Blocking
when an emergency call is established. Also see ED-72 in Section 14.
ED-68 The emergency dialstrings SHOULD NOT be permitted in Call
Forward numbers or speed dial lists.
ED-69 The User Agent and Proxies SHOULD disable the following
incoming call features on call backs from the PSAP:
o Call Waiting
o Do Not Disturb
o Call Forward (all kinds)
ED-70 Call backs SHOULD be determined by retaining the domain of the
PSAP which answers an outgoing emergency call and instantiating a
timer which starts when the call is terminated. If a call is
received from the same domain and within the timer period, sent to
the Contact: or AoR used in the emergency call, it should be assumed
to be a call back. The suggested timer period is 5 minutes.
ED-71 Endpoints MUST send and receive media streams on RTP [RFC3550].
ED-72 Normal SIP offer/answer [RFC3264] negotiations MUST be used to
agree on the media streams to be used.
ED-73 Endpoints supporting voice MUST support G.711 A law (and mu Law
if they could be used in North America) encoded voice as described in
[RFC3551]. It is desirable to include wideband codecs such as AMR-WB
in the offer.
ED-74 Silence suppression (Voice Activity Detection methods) MUST NOT
be used on emergency calls. PSAP call takers sometimes get
information on what is happening in the background to determine how
to process the call.
ED-75 Endpoints supporting IM MUST support both [RFC3428] and
[RFC4975].
ED-76 Endpoints supporting real-time text MUST use [RFC4103]. The
expectations for emergency service support for the real-time text
medium, described in [I-D.ietf-sipping-toip], Section 7.1 SHOULD be
fulfilled.
ED-77 Endpoints supporting video MUST support H.264 per [RFC3984].
ED-78 INVITE requests to a service URN ending in ".test" indicates a
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request for an automated test. For example,
"urn:service.sos.fire.test". As in standard SIP, a 200 (OK) response
indicates that the address was recognized and a 404 (Not found) that
it was not. A 486 (Busy Here) MUST be returned if the test service
is busy, and a 488 (Not Acceptable Here) MUST be returned if the PSAP
does not support the test mechanism.
ED-79 In its response to the test, the PSAP MAY include a text body
(text/plain) indicating the identity of the PSAP, the requested
service, and the location reported with the call. For the latter,
the PSAP SHOULD return location-by-value even if the original
location delivered with the test was by-reference. If the location-
by-reference was supplied, and the dereference requires credentials,
the PSAP SHOULD use credentials supplied by the LIS for test
purposes. This alerts the LIS that the dereference is not for an
actual emergency call and location hiding techniques, if they are
being used, may be employed for this dereference. The response MAY
include the connected identity of the PSAP per
[I-D.ietf-sip-connected-identity].
ED-80 A PSAP accepting a test call SHOULD accept a media loopback
test [I-D.ietf-mmusic-media-loopback] and SHOULD support the "rtp-
pkt-loopback" and "rtp-start-loopback" options. The user agent would
specify a loopback attribute of "loopback-source", the PSAP being the
mirror. User Agents should expect the PSAP to loop back no more than
3 packets of each media type accepted (which limits the duration of
the test), after which the PSAP would normally send BYE.
ED-81 User agents SHOULD perform a full call test, including media
loopback, after a disconnect and subsequent change in IP address not
due to a reboot. After an initial test, a full test SHOULD be
repeated approximately every 30 days with a random interval.
ED-82 User agents MUST NOT place a test call immediately after
booting. If the IP address changes after booting, the UA should wait
a random amount of time (in perhaps a 30 minute period, sufficient
for any avalanche restart to complete) and then test.
ED-83 PSAPs MAY refuse repeated requests for test from the same
device in a short period of time. Any refusal is signaled with a 486
or 488 response.
A.2. Requirements of Service Providers
SP-1 If a device or application expects to be able to place a call
for help, the service provider that supports it MUST facilitate
emergency calling.
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SP-2 Proxy servers SHOULD recognize emergency dial string if for some
reason the endpoint does not recognize them. This cannot be relied
upon by the device if the service provider cannot always determine
the location of the device.
SP-3 Emergency calls MUST be marked with a Service URN in the
Request-URI of the INVITE.
SP-4 Local dial strings MUST be recognized.
SP-5 Home dial strings MAY be recognized.
SP-6 Local emergency dial strings SHOULD be determined from LoST
[I-D.ietf-ecrit-lost].
SP-7 Proxy Servers MUST recognize emergency dial strings represented
by [RFC4967] and SHOULD recognize emergency dial strings represented
by a tel URI [RFC3966].
SP-8 Service providers MAY provide home dial strings by configuration
[I-D.ietf-sipping-config-framework].
SP-9 All emergency services specified in [I-D.ietf-ecrit-service-urn]
MUST be recognized.
SP-10 Endpoints, Intermediate Devices and Service Providers MUST be
prepared to handle location represented in either civic or geo form.
SP-11 Elements MUST NOT convert (civic to geo or geo to civic) from
the form of location the determination mechanism supplied.
SP-12 Proxies MAY provide location on behalf of devices if:
o The proxy has a relationship with all access networks the device
could connect to, and the relationship allows it to obtain
location.
o The proxy has an identifier, such as an IP address, that can be
used by the access network to determine the location of the
endpoint, even in the presence of NAT and VPN tunnels that may
obscure the identifier between the access network and the service
provider.
SP-13 Where proxies provide location on behalf of endpoints, the the
service provider MUST ensure that either the end device is provided
with the local dial strings for its current location (where the end
device recognizes dial strings), or the service provider proxy MUST
detect the appropriate local dial strings at the time of the call.
SP-14 When HELD is the LCP, the request MUST specify a value of
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"emergencyRouting" for the "responseTime" parameter and use the
resulting location for routing. If a value for dispatch location
will be sent, another request with the "responseTime" parameter set
to "emergencyDispatch" must be completed, with the result sent for
dispatch purposes.
SP-15 Location sent between SIP elements MUST be conveyed using
[I-D.ietf-sip-location-conveyance].
SP-16 If a proxy inserts location on behalf of an endpoint, and it
has multiple locations available for the endpoint it MUST choose one
location to use to route the call towards the PSAP.
SP-17 If a proxy is attempting to insert location but the UA conveyed
a location to it, the proxy MUST use the UA's location for routing
and MUST convey that location towards the PSAP. It MAY also include
what it believes the location to be in a separate Geolocation header.
SP-18 All location objects received by a proxy MUST be delivered to
the PSAP.
SP-19 Location objects MUST contain information about the method by
which the location was determined, such as GPS, manually entered, or
based on access network topology included in a PIDF- LO "method"
element. In addition, the source of the location information MUST be
included in a PIDF-LO "provided-by" element.
SP-20 The "used-for-routing" parameter MUST be set to the location
that was used to query LoST.
SP-21 Proxies handling emergency calls MUST insert a default location
if the call does not contain a location and the proxy does not have a
method for obtaining a better location.
SP-22 Default locations MUST be marked with method=Default and the
proxy MUST be identfied in provided-by element of the PIDF-LO.
SP-23 TLS MUST be used to protect location (but see Section 9.1).
IPSEC [RFC2401] is an acceptable alternative.
SP-24 Networks MUST be designed so that at least one proxy in the
outbound path can recognize emergency calls with a Request URI of the
service URN in the "sos" tree. An endpoint places a service URN in
the Request URI to indicate that the endpoint understood the call was
an emergency call. A proxy that processes such a call looks for the
presence of a SIP Route header field with a URI of a PSAP. Absence
of such a Route header indicates the UAC was unable to invoke LoST
and the proxy MUST perform the LoST mapping and insert a Route header
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field with the URI obtained.
SP-25 To deal with old user agents that predate this specification
and with UAs that do not have access to their own location data, a
proxy that recognizes a call as an emergency call that is not marked
as such (see Section 5) MUST also perform this mapping, with the best
location it has available for the endpoint. The resulting PSAP URI
would be placed in a Route header with the service URN in the Request
URI.
SP-26 Proxy servers performing mapping SHOULD use location obtained
from the access network for the mapping. If no location is
available, a default location (see Section 6.11) MUST be supplied.
SP-27 A proxy server which attempts mapping and fails to get a
mapping MUST provide a default mapping. A suitable default mapping
would be the mapping obtained previously for the default location
appropriate for the caller.
SP-28 [RFC3261] and [RFC3263] procedures MUST be used to route an
emergency call towards the PSAP's URI.
SP-29 TLS MUST be specified when attempting to signal an emergency
call with SIP per [I-D.ietf-sip-sips]. IPSEC [RFC2401] is an
acceptable alternative.
SP-30 If TLS session establishment fails, the call MUST be retried
without TLS.
SP-31 [I-D.ietf-sip-outbound] is RECOMMENDED to maintain persistent
TLS connections between elements.
SP-32 SIP Proxy servers processing emergency calls:
1. If the proxy does interprets dial plans on behalf of user agents,
the proxy MUST look for the local emergency dial string at the
location of the end device and MAY look for the home dial string.
If it finds it, the proxy MUST:
* Insert a Geolocation header as above. Location-by-reference
MUST be used because proxies must not insert bodies.
* Include the Geolocation "inserted-by=server" and "used-for-
routing" parameters.
* Map the location to a PSAP URI using LoST.
* Add a Route header with the PSAP URI.
* Replace the Request-URI (which was the dial string) with the
service URN appropriate for the emergency dial string.
* Route the call using normal SIP routing mechanisms.
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2. If the proxy recognizes the service URN in the Request URI, and
does not find a Route header with a PSAP URI, it MUST run LoST
routing. If a location was provided (which should be the case),
the proxy uses that location to query LoST. The proxy may have
to dereference a location by reference to get a value. If a
location is not present, and the proxy can query a LIS which has
the location of the UA it MUST do so. If no location is present,
and the proxy does not have access to a LIS which could provide
location, the proxy MUST supply a default location (See
Section 6.11). The location (in the signaling, obtained from a
LIS, or default) MUST be used in a query to LoST with the service
URN received with the call. The resulting URI MUST be placed in
a Route header added to the call.
3. The "inserted-by=" parameter in any Geolocation: header received
on the call MUST NOT be modified or deleted in transit.
4. The proxy SHOULD NOT modify any parameters in Geolocation headers
received in the call. It MAY add a Geolocation header. Such an
additional location SHOULD NOT be used for routing; the location
provided by the UA should be used.
5. Either a P-Asserted-Identity [RFC3325] or an Identity header
[RFC4474], or both, MUST be included to identify the sender.
SP-33 Unitialized devices, like any device MUST have a globally
routable URI in a Contact: header.
SP-34 Unitialized devices SHOULD have a persistent URI in a
P-Asserted-Identity: header if there is some way to assign such an
identifier to the device.
SP-35 During the course of an emergency call, devices and proxies
MUST support REFER transactions and the Referred-by: header
[RFC3515].
SP-36 User agents and proxies MUST support Session Timer [RFC4028] to
guard against session corruption.
SP-37 User Agents and proxys MUST disable outgoing call features such
as
o Call Waiting
o Call Transfer
o Three Way Call
o Flash hold
o Outbound Call Blocking
when an emergency call is established. Also see ED-72 in Section 14.
SP-38 The emergency dialstrings SHOULD NOT be permitted in Call
Forward numbers or speed dial lists.
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SP-39 The User Agent and Proxies SHOULD disable the following
incoming call features on call backs from the PSAP:
o Call Waiting
o Do Not Disturb
o Call Forward (all kinds)
A.3. Requirements of Access Network
AN-1 Elements MUST NOT convert (civic to geo or geo to civic) from
the form of location the determination mechanism supplied.
AN-2 Any suitable location determination mechanism MAY be used.
AN-3 Devices, intermediate Devices and/or access networks SHOULD
support a manual method to "override" the location the access network
determines. Where a civic form of location is provided, all fields
in the PIDF-LO [RFC4119] and [RFC5139] MUST be able to be specified.
AN-4 Access networks supporting copper, fiber or other hard wired IP
packet service SHOULD support location configuration. If the network
does not support location configuration, it MUST require every device
that connects to the network to support end system measured location.
AN-5 Access networks and intermediate devices providing wire database
location information SHOULD provide interior location data (building,
floor, room, cubicle) where possible. It is RECOMMENDED that
interior location be provided when spaces exceed approximately 650
square meters.
AN-6 Access networks and intermediate devices (including enterprise
networks) which support intermediate range wireless connections
(typically 100m or less of range) and which do not support a more
accurate location determination mechanism such as triangulation, MUST
support location configuration where the location of the access point
is reflected as the location of the clients of that access point.
Where the access network provides location configuration,
intermediate devices MUST either be transparent to it, or provide an
interconnected client for the supported configuration mechanism and a
server for a configuration protocol supported by end devices upstream
of the intermediate device
AN-7 Devices that support endpoint measuring of location MUST have at
least a coarse location capability (typically <1km accuracy when not
location hiding) at all times for routing of calls. This mechanism
MAY be a service provided by the access network.
AN-8 Access networks MAY provide network-measured location
determination. Wireless access network which do not support network
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measured location MUST require that all devices connected to the
network have end-system measured location. Uncertainty of less than
100 m with 95% confidence SHOULD be available for dispatch.
AN-9 Access networks that provide network measured location MUST have
at least a coarse location (typically <1km when not location hiding)
capability at all times for routing of calls.
AN-10 Access networks with range of <10 meters MUST provide a
location to mobile devices connected to it. The location provided
SHOULD be that of the access point location unless a more accurate
mechanism is provided.
AN-11 The access network MUST support at least one of: DHCP location
options, HELD or LLDP-MED.
AN-12 Where a router is employed between a LAN and WAN in a small
(less than approximately 650 square meters) area, the router MUST be
transparent to the location provided by the WAN to the LAN. This may
mean the router must obtain location as a client from the WAN, and
supply an LCP server to the LAN with the location it obtains. Where
the area is larger, the LAN MUST have a location configuration
mechanism meeting this BCP.
AN-13 Access networks that support more than one LCP MUST reply with
the same location information (within the limits of the data format
for the specific LCP) for all LCPs it supports.
AN-14 Network administrators MUST take care in assigning IP addresses
such that VPN address assignments can be distinguished from local
devices (by subnet choice, for example), and LISs SHOULD NOT attempt
to provide location to addresses that arrive via VPN connections
unless it can accurately determine the location for such addresses.
AN-15 Placement of NAT devices where an LCP uses IP address for an
identifier SHOULD consider the effect of the NAT on the LCP. The
address used to query the LIS MUST be able to correctly identify the
record in the LIS representing the location of the querying device
AN-16 It is RECOMMENDED that location determination not take longer
than 250 ms to obtain routing location and systems SHOULD be designed
such that the typical response is under 100 ms. However, as much as
3 seconds to obtain routing location MAY be tolerated if location
accuracy can be substantially improved over what can be obtained in
250 ms.
AN-17 Where the absolute location or the accuracy of location of the
endpoint may change between the time the call is received at the PSAP
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and the time dispatch is completed, location update mechanisms MUST
be provided.
AN-18 Mobile devices MUST be provided with a mechanism to get
repeated location updates to track the motion of the device during
the complete processing of the call.
AN-19 The LIS SHOULD provide a location reference which permits a
subscription with appropriate filtering.
AN-20 For calls sent with location-by-reference, with a SIP or SIPS
scheme, the server resolving the reference MUST support a SUBSCRIBE
[RFC3265] to the presence event [RFC3856]. For other location-by-
reference schemes, the PSAP will have to repeatedly dereference the
URI to determine if the device moved.
AN-21 A LIS should perform location validation of civic locations via
LoST before entering a location in its database.
AN-22 When the access network cannot determine the actual location of
the caller, it MUST supply a default location. The default SHOULD be
chosen to be as close to the probable location of the device as the
network can determine. See [I-D.ietf-ecrit-framework]
AN-23 Default locations MUST be marked with method=Default and the
proxy MUST be identfied in provided-by element of the PIDF-LO.
AN-24 To prevent against spoofing of the DHCP server, elements
implementing DHCP for location configuration SHOULD use although the
difficulty in providing appropriate credentials is significant.
[RFC3118].
AN-25 TLS MUST be specified when attempting to retrieve location
(configuration or dereferencing) with HELD. The use of [RFC4507] is
RECOMMENDED to minimise the time to establish TLS sessions.
AN-26 If TLS session establishment fails, the location retrieveal
MUST be retried without TLS.
A.4. Requirements of Intermediate Devices
INT-1 Endpoints, Intermediate Devices and Service Providers MUST be
prepared to handle location represented in either civic or geo form.
INT-2 Elements MUST NOT convert (civic to geo or geo to civic) from
the form of location the determination mechanism supplied.
INT-3 Any suitable location determination mechanism MAY be used.
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INT-4 Devices, intermediate Devices and/or access networks SHOULD
support a manual method to "override" the location the access network
determines. Where a civic form of location is provided, all fields
in the PIDF-LO [RFC4119] and [RFC5139] MUST be able to be specified.
INT-5 Access networks and intermediate devices providing wire
database location information SHOULD provide interior location data
(building, floor, room, cubicle) where possible. It is RECOMMENDED
that interior location be provided when spaces exceed approximately
650 square meters.
INT-6 Access networks and intermediate devices (including enterprise
networks) which support intermediate range wireless connections
(typically 100m or less of range) and which do not support a more
accurate location determination mechanism such as triangulation, MUST
support location configuration where the location of the access point
is reflected as the location of the clients of that access point.
Where the access network provides location configuration,
intermediate devices MUST either be transparent to it, or provide an
interconnected client for the supported configuration mechanism and a
server for a configuration protocol supported by end devices upstream
of the intermediate device
INT-7 Devices MAY support end-system measured location. Uncertainty
of less than 100 m with 95% confidence SHOULD be available for
dispatch.
INT-8 Devices that support endpoint measuring of location MUST have
at least a coarse location capability (typically <1km accuracy when
not location hiding) at all times for routing of calls. This
mechanism MAY be a service provided by the access network.
INT-9 Endpoints SHOULD do configure their own location.
INT-10 Where proxies provide location on behalf of endpoints, the the
service provider MUST ensure that either the end device is provided
with the local dial strings for its current location (where the end
device recognizes dial strings), or the service provider proxy MUST
detect the appropriate local dial strings at the time of the call.
INT-11 Devices SHOULD be able to accept and forward location by value
or by reference. An end device that receives location by reference
(and does not also get the corresponding value) MUST be able to
perform a dereference operation to obtain a value.
INT-12 Devices MUST support all of: DHCP location options [RFC4676]
and [RFC3825], HELD [I-D.ietf-geopriv-http-location-delivery] and
LLDP-MED [LLDP-MED].
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INT-13 The access network MUST support at least one of: DHCP location
options, HELD or LLDP-MED.
INT-14 Where a router is employed between a LAN and WAN in a small
(less than approximately 650 square meters) area, the router MUST be
transparent to the location provided by the WAN to the LAN. This may
mean the router must obtain location as a client from the WAN, and
supply an LCP server to the LAN with the location it obtains. Where
the area is larger, the LAN MUST have a location configuration
mechanism meeting this BCP.
INT-15 Endpoints SHOULD try all LCPs supported by the device in any
order or in parallel. The first one that succeeds in supplying
location can be used.
INT-16 Access networks that support more than one LCP MUST reply with
the same location information (within the limits of the data format
for the specific LCP) for all LCPs it supports.
INT-17 When HELD is the LCP, the request MUST specify a value of
"emergencyRouting" for the "responseTime" parameter and use the
resulting location for routing. If a value for dispatch location
will be sent, another request with the "responseTime" parameter set
to "emergencyDispatch" must be completed, with the result sent for
dispatch purposes.
INT-18 Endpoints SHOULD obtain location immediately after obtaining
local network configuration information.When HELD is the LCP the
client MUST support a random back-off period (between 30 seconds and
300 seconds) for re-trying the HELD query, when no response is
received.
INT-19 If the device is configured to use DHCP for bootstrapping, it
MUST include both options for location acquisition (civic and
geodetic), the option for LIS discovery, and the option for LoST
discovery as defined in [RFC4676], [RFC3825],
[I-D.thomson-geopriv-lis-discovery] and
[I-D.ietf-ecrit-dhc-lost-discovery].
INT-20 If the device sends a DHCP INFORM message, it MUST include
both options for location acquisition (civic and geodetic), the
option for LIS discovery, and the option for LoST discovery as
defined in [RFC4676], [RFC3825], [I-D.thomson-geopriv-lis-discovery]
and [I-D.ietf-ecrit-dhc-lost-discovery].
INT-21 To minimize the effects of VPNs that do not allow split
tunneling VPNs, location configuration SHOULD be attempted before
such tunnels are established.
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INT-22 Software which uses LCPs SHOULD locate and use the actual
hardware network interface rather than a VPN tunnel interface to
direct LCP requests to the LIS in the actual access network.
INT-23 For devices which are not expected to roam, refreshing
location on the order of once per day is RECOMMENDED.
INT-24 For devices which roam, refresh of location information SHOULD
be more frequent, with the frequency related to the mobility of the
device and the ability of the access network to support the refresh
operation. If the device can detect that it has moved, for example
when it changes access points, the device SHOULD refresh its
location.
INT-25 It is RECOMMENDED that location determination not take longer
than 250 ms to obtain routing location and systems SHOULD be designed
such that the typical response is under 100 ms. However, as much as
3 seconds to obtain routing location MAY be tolerated if location
accuracy can be substantially improved over what can be obtained in
250 ms.
Authors' Addresses
Brian Rosen
NeuStar
470 Conrad Dr.
Mars, PA 16046
US
Phone: +1 724 382 1051
Email: br@brianrosen.net
James Polk
Cisco Systems
3913 Treemont Circle
Colleyville, TX 76034
US
Phone: +1-817-271-3552
Email: jmpolk@cisco.com
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