The general ECRIT calling models described in and require a local LoST server or network of forest guides in order to determine the address of the PSAP in the best position to handle a call. Networks of forest guides have not eventuated and while PSAPs are moving towards IP networks, LoST server deployment is not ubiquitous. Some regions and countries have expressed reluctance to deploy LoST servers making aspects of the current ECRIT architecture hard to realize. Evolving architectures in Europe to address regulatory requirements, such as , couple location and routing information in the access network whilst using a softswitch-centric approach to emergency call processing. This document describes adding an extension to the HELD protocol so that a location information server can provide emergency routing information in the absence of a LoST server or network of forest guides.

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 . The terms LIS, ESRP, VSP and PSAP are used as defined in . The term "Access Network Provider" is used as defined in and incompasses both the Internet Access Provider (IAP) and Internet Service Provider (ISP).

The Internet emergency calling architecture specified in describes two main models for emergency call processing. The first is a device-centric model, where a device obtains location information using a location configuration protocol, such a HELD , and then proceeds to determine the address of the next hop closer to the local PSAP using LoST . shows this model in a simplified form.

| VSP | (5) +-------+ ]]> The second approach is a softswitch-centric model, where a device initiates an emergency call and the serving softswitch detects that the call is an emergency and initiates retrieving the caller's location from a Location Information Server (LIS) using HELD with identity extensions and then determining the route to the local PSAP using LoST . shows the high-level protocol interactions.

| Soft | +--------+ (3) | Switch | | Caller |------Call Initiation------------> | | +--------+ (1) +-+-^---+-+ +-------------+ | | | | LoST Server |<-Find Service--+ | | +------+------+ (4) | | | | | +----------Service--------+ | (5) | +-----------+ | | ESRP/PSAP |<------Call----+ +-----------+ (6) ]]> In the softswitch-centric model when a VSP receives an emergency call it performs two tasks. The first task is to determine the correct LIS to ask for location information, this is done using a combination of reverse DNS lookup described in to acquire the serving domain name and then using to determine the LIS URI. Once the location is obtained from the LIS, the VSP determines the LoST server associated with the domain serving the caller and queries it for the correct PSAP address. LoST server discovery is a domain based activity, similar to the LIS discovery technique. However, unlike the LIS that is a domain bound service, a LoST server is a geographically bound service. This means that for a domain that spans multiple geographic regions the LoST server determined may not be able to provide a route to the necessary PSAP. When this occurs, the contacted LoST server invokes the help of other LoST servers and this requires the deployment of forest guides. At the time of writing, several countries have expressed a reluctance to deploy public LoST servers. In countries amenable to the use of LoST and forest guides no public forest guides have been deployed. There appears little interest from the public sector in establishing a global forest guide network. These issues pose threats to both the device-centric and the softswitch-centric calling approaches in terms of them operating everywhere. The device-centric and softswitch-centric calling models both involve the notion of a LIS bound to the serving access network. In many cases the LIS already knows the destination PSAP URI for any given location. In for example, the LIS validates civic locations using a location validation procedure based on the LoST protocol . The LoST validation request is similar to a LoST routing request and provides the LIS with the same PSAP routing information that a routing request would. In other cases, the LIS knows the correct PSAP for a given location at provisioning time, or the access network might always route to the same emergency provider. Irrespective of the way in which the LIS learns the PSAP URI for a location, the LIS will, in a great many cases, already have this information. This document specifies an extension to the HELD protocol so that emergency routing information can be requested from the LIS at the same time that location information is requested. The document updates by requiring devices and softswitches that understand this specification to always request routing information to avoid the risk of query failure where no LoST server or forest guide network is deployed.

The LoST Protocol defines a <mapping> element that describes a service region and associated service URLs. Reusing this element from LoST to provide the routing URIs was considered. However, this would have meant that several of the mandatory components in the <mapping> element would have had to contain ambiguous or misleading values. Specifically, the "source" attribute is required to contain a LoST application unique string for the authoritative server. However, in the situations described in this specification there may not be an authoritative LoST server, so any value put into this attribute would be misleading. In addition to this, routing information received in the manner described in this specification should not be cached by the receiver, so detailing when the routing information expires or was last updated is irrelevant.

The mechanism consists of adding an element to the HELD locationRequest and an element to the locationResponse. The request element indicates that the requestor wants the LIS to provide routing information based on the location of the end-device. If the routing request is sent with no attribute then URIs for urn:service:sos are returned. If the requestor wants routing information for a specific service then they may include an optional service URN. If a service is specified, and the LIS does not understand the requested service then URIs for urn:service:sos are returned. If the LIS understands the routing request and has routing information for the location then it includes the information in a routingInformation element returned in the locationResponse. How the LIS obtains this information is left to implementation, one possible option is that the LIS acquires it from a LoST server, other possibilities are described in . A LIS that does not understand the routing request element ignores it and returns location as normal. A LIS that does support the routing request element MUST support returning URIs for urn:service:sos and any regionally defined sub-services while following the URN traversal rules defined in . A LIS that does understand the routing request element but can't obtain any routing information for the end-device's location MUST only return location information. A LIS that understands the routing request element but not the specified service URN, MUST follow the URN traversal rules defined in . A LIS that receives a request for emergency routing information that it understands MUST return the correct emergency routing information if it has or is able to acquire the routing information for the location of the target device. The routing information in the location response consists of a service element identified by a service name. The service name is a urn and might contain a general emergency service urn such as urn:service:sos or might contain a specific service urn depending on what was requested and what the LIS is able to provide. A list of one or more service destinations is provided for the service name. Each destination is expressed as a URI and each URI scheme should only appear once in this list. The routing URIs are intended to be used at the time they are received. To avoid any risks of using stale routing URIs the values MUST NOT be cached by the receiving entity.

This section describes the schema extension to HELD.

]]>

illustrates a <locationRequest> example that contains IP flow information in the request.

192.168.1.1

1024

10.0.0.1

80 ]]> illustrates the <locationResponse> message containing two location URIs: a HTTPS and a SIP URI. Additionally, the response contains routing information.

https://ls.example.com:9768/357yc6s64ceyoiuy5ax3o sip:9769+357yc6s64ceyoiuy5ax3o@ls.example.com sip:112@example.com sips:112@example.com xmpp:112@example.com ]]>

This document makes no changes that require privacy considerations beyond those already described in . It does however extend those described in . describes the issues surrounding Layer 7 location configuration protocols, which this document makes no specific changes to. extends HELD beyond a simple LCP by enabling authorized third-parties to acquire location information and describes the issues in Section 4. The HELD Routing extension supports returning URIs that represent specific services operating in the Target's vicinity. This represents additional information about the Target, as a consequence it is recommended that this option only be used when a location URI is returned by the LIS.

This document imposes no additional security considerations beyond those already described in and .

This document calls for IANA to register a new XML namespace, as per the guidelines in . urn:ietf:params:xml:ns:geopriv:held:ri IETF, ECRIT working group (ecrit@ietf.org), James Winterbottom (a.james.winterbottom@gmail.com).

HELD Routing Information Extensions

Additional Element for HELD Routing Information

urn:ietf:params:xml:ns:geopriv:held:ri

[[NOTE TO IANA/RFC-EDITOR: Please update RFC URL and replace XXXX with the RFC number for this specification.]]

See RFCXXXX.

END ]]>

This section registers an XML schema as per the procedures in . urn:ietf:params:xml:schema:geopriv:held:ri IETF, ECRIT working group, (ecrit@ietf.org), James Winterbottom (a.james.winterbottom@gmail.com). The XML for this schema can be found as the entirety of of this document.

We would like to thank Wilfried Lange for sharing his views with us. We would also like to thank Bruno Chatras for his early review comments and Keith Drage ofr his more detailed review. Thanks to Roger Marshall and Randy Gellens for their helpful suggestions.