+---Location Request---+
                            |         (2)          |
                        +---V---+                  |
                        |  LIS  |                  |
                        +----+--+             +----+----+
                             |                |         |
                             +----Location--->|  Soft   |
 +--------+                          (3)      | Switch  |
 | Caller |------Call Initiation------------> |         |   
 +--------+          (1)                      +-+-^---+-+
                 +-------------+                | |   |
                 | LoST Server |<-Find Service--+ |   |        
                 +------+------+     (4)          |   |  
                        |                         |   |
                        +----------Service--------+   |
                                    (5)               |
                          +-----------+               |
                          | ESRP/PSAP |<------Call----+
                          +-----------+       (6)            
                                            

Figure 2: Softswitch-Centric Calling Model

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 [RFC7216] to acquire the serving domain name and then using [RFC5986] 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 [RFC6881] for example, the LIS validates civic locations using a location validation procedure based on the LoST protocol [RFC5222]. 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 [RFC6881] 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.

4. Mechanism

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 Section 3.

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 SHALL support returning URIs for urn:service:sos

A LIS that does understand the routing request element but can’t obtain any routing information for the end-device's location SHALL only return location information.

A LIS that understands the routing request element but not the specified service URN, returns the routing URIs for the urn:service:sos service.

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.

The LoST Protocol [RFC5222] 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.

5. HELD Schema Extension

This section describes the schema extension to HELD.

<?xml version="1.0"?>
<xs:schema
  targetNamespace="urn:ietf:params:xml:ns:geopriv:held:ri"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:ri="urn:ietf:params:xml:ns:geopriv:held:ri"
  xmlns:xml="http://www.w3.org/XML/1998/namespace"
  elementFormDefault="qualified" attributeFormDefault="unqualified">

  <xs:element name="requestRoutingInformation">
     <xs:complexType name="empty">
        <xs:attribute name="service" type="xs:anyUri”
     	    use="optional" default="urn:service:sos"/>
     </xs:complexType>
  </xs:element>
  
  <xs:complexType name="service">
     <xs:complexContent>
       <xs:restriction base="xs:anyType">
       	  <xs:sequence>
       	     <xs:element name="dest" type="xs:anyURI"
       	          maxOccurs="unbounded"/>
       	     <xs:any namespace="##other" processContents="lax"
                    minOccurs="0" maxOccurs="unbounded"/>
       	  </xs:sequence>
       	  <xs:attribute name="serviceUri" type="xs:anyURI"
       	                use="required"/>
       </xs:restriction>
     </xs:complexContent>
  </xs:complexType>
    
  <xs:element name="routingInformation" type="ri:riType"/>
     <xs:complexType name="riType">
       <xs:complexContent>
         <xs:restriction base="xs:anyType">
          <xs:sequence>
            <xs:element name="service" type="ri:service"/>
            <xs:any namespace="##other" processContents="lax"
                    minOccurs="0" maxOccurs="unbounded"/>
          </xs:sequence>
          <xs:anyAttribute namespace="##any" processContents="lax"/>
        </xs:restriction>
      </xs:complexContent>
     </xs:complexType>

</xs:schema>

6. Examples

Figure 3 illustrates a <locationRequest> example that contains IP flow information in the request.

<locationRequest xmlns="urn:ietf:params:xml:ns:geopriv:held"
		 responseTime="emergencyRouting">
	
	<requestRoutingInformation
	    xmlns=”urn:ietf:params:xml:ns:geopriv:held:ri"/>

	<flow xmlns="urn:ietf:params:xml:ns:geopriv:held:flow"
	      layer4="tcp" layer3="ipv4">
	   <src>
	      <address>192.168.1.1</address>
	      <port>1024</port>
	   </src>
	   <dst>
	      <address>10.0.0.1</address>
	      <port>80</port>
	   </dst>
	</flow>
</locationRequest>

<locationResponse xmlns="urn:ietf:params:xml:ns:geopriv:held">
      <locationUriSet expires="2006-01-01T13:00:00.0Z">
	<locationURI>
		https://ls.example.com:9768/357yc6s64ceyoiuy5ax3o
	</locationURI>
        <locationURI>
		sip:9769+357yc6s64ceyoiuy5ax3o@ls.example.com
        </locationURI>
      </locationUriSet>
      
      <routingInformation
          xmlns="urn:ietf:params:xml:ns:geopriv:held:ri">
        <service serviceUri="urn:service:sos">
          <dest>sip:112@example.com</dest>
          <dest>sips:112@example.com</dest>
          <dest>xmpp:112@example.com</dest>
        </service>
      </routingInformation>
      
   </locationResponse>

BEGIN
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  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
  <head>
    <title>HELD Routing Information Extensions</title>
  </head>
  <body>
   <h1>Additional Element for HELD Routing Information</h1>
   <h2>urn:ietf:params:xml:ns:geopriv:held:ri</h2>
   [[NOTE TO IANA/RFC-EDITOR: Please update RFC URL and replace XXXX
     with the RFC number for this specification.]]
   <p>See <a href="[[RFC URL]]">RFCXXXX</a>.</p>
  </body>
 </html>
END