Request for Comments: 6739
Category: Experimental
ISSN: 2070-1721
Columbia University
H. Tschofenig
Nokia Siemens Networks
October 2012
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Synchronizing Service Boundaries and <mapping> Elements Based on the
Location-to-Service Translation (LoST) Protocol
Abstract
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The Location-to-Service Translation (LoST) protocol is an XML-based protocol for mapping service identifiers and geodetic or civic location information to service URIs and service boundaries. In particular, it can be used to determine the location-appropriate Public Safety Answering Point (PSAP) for emergency services.
The <mapping> element in the LoST protocol specification encapsulates information about service boundaries and circumscribes the region within which all locations map to the same service Uniform Resource Identifier (URI) or set of URIs for a given service.
This document defines an XML protocol to exchange these mappings between two nodes. This mechanism is designed for the exchange of authoritative <mapping> elements between two entities. Exchanging cached <mapping> elements, i.e., non-authoritative elements, is possible but not envisioned. Even though the <mapping> element format is reused from the LoST specification, the mechanism in this document can be used without the LoST protocol.
Status of This Memo
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This document is not an Internet Standards Track specification; it is published for examination, experimental implementation, and evaluation.
This document defines an Experimental Protocol for the Internet community. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6739.
Copyright Notice
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Copyright © 2012 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
Table of Contents
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. A Motivating Example . . . . . . . . . . . . . . . . . . . . . 4 4. Querying for Mappings with a <getMappingsRequest>/<getMappingsResponse> Exchange . . . . . 9 4.1. Behavior of the LoST Sync Destination . . . . . . . . . . 9 4.2. Behavior of the LoST Sync Source . . . . . . . . . . . . . 10 4.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 10 5. Pushing Mappings via <pushMappings> and <pushMappingsResponse> . . . . . . . . . . . . . . . . . . . . 12 5.1. Behavior of the LoST Sync Source . . . . . . . . . . . . . 12 5.2. Behavior of the LoST Sync Destination . . . . . . . . . . 13 5.3. Example . . . . . . . . . . . . . . . . . . . . . . . . . 14 6. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 16 7. RELAX NG . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 8. Operational Considerations . . . . . . . . . . . . . . . . . . 19 9. Security Considerations . . . . . . . . . . . . . . . . . . . 20 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 10.1. Media Type Registration . . . . . . . . . . . . . . . . . 21 10.2. LoST Sync RELAX NG Schema Registration . . . . . . . . . . 22 10.3. LoST Synchronization Namespace Registration . . . . . . . 22 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24 12.1. Normative References . . . . . . . . . . . . . . . . . . . 24 12.2. Informative References . . . . . . . . . . . . . . . . . . 24
1. Introduction
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Since the early days of emergency services, there has been a desire to route emergency calls to Public Safety Answering Points (PSAPs) that are nearest to the location of the emergency caller. For this purpose each PSAP discloses one or more service boundaries so that this information can be used to select the appropriate PSAP and to route the call to it. RFC 5222 [RFC5222] defines this data structure in the following way:
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A service boundary circumscribes the region within which all locations map to the same service URI or set of URIs for a given service. A service boundary may consist of several non-contiguous geometric shapes.
RFC 5222 [RFC5222] also specifies the data structure itself as the <mapping> element.
This document reuses this existing data structure and defines an XML- based protocol to exchange authoritative service boundaries between two entities, namely, the LoST Sync source and the LoST Sync destination. This protocol can be used whether or not the LoST protocol is used for querying for service boundary information.
The rest of the document is structured as follows. Section 3 starts with an example usage of the LoST protocol. In Sections 4, 5, 6, and 7, we describe the protocol semantics, transport considerations, and the schema. Finally, we conclude with operational, security, and IANA considerations in Sections 8, 9, and 10.
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2. Terminology
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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 RFC 2119 [RFC2119].
This document reuses terminology introduced by the mapping architecture document [RFC5582], such as 'coverage region', 'forest guide', 'mapping', and 'authoritative mapping server'. This document also uses the term 'ESRP', defined in [RFC5012].
Throughout this document, we use the terms 'LoST Sync source' and 'LoST Sync destination' to denote the protocol endpoints of the exchange. The protocol is referred to as 'LoST Sync' within the text.
3. A Motivating Example
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The LoST Sync mechanism can, for example, be used in the LoST architecture, as specified in [RFC5582]. There, LoST servers cooperate to provide an ubiquitous, globally scalable, and resilient mapping service. In the LoST mapping architecture, LoST servers can peer, i.e., have an ongoing data exchange relationship. Peering relationships are set up manually, based on local policies. A LoST server may peer with any number of other LoST servers. Forest guides peer with other forest guides; authoritative mapping servers peer with forest guides and other authoritative servers, either in the same cluster or above or below them in the tree. Authoritative mapping servers push coverage regions "up" the tree, i.e., from child nodes to parent nodes. The child informs the parent of the geospatial or civic region that it covers for a specific service.
Consider a hypothetical deployment of LoST in two countries, for example, Austria and Finland. Austria, in our example, runs three authoritative mapping servers labeled as 'East', 'West', and 'Vienna', where the former two cover the entire country except for Vienna, which is covered by a separate LoST server. There may be other caching LoST servers run by ISPs, universities, and Voice Service Providers (VSPs), but they are not relevant for this illustration. Finland, on the other hand, decided to only deploy a single LoST server that also acts as a forest guide. For this simplistic illustration, we assume that only one service is available, namely 'urn:service:sos' since otherwise the number of stored mappings would have to be multiplied by the number of used services.
Figure 1 shows the example deployment.
+---LoST-Sync-->\\ //<--LoST-Sync----+ | ----- | | | \/ \/ ----- ----- // \\ // \\ / \ / \ | Forest | | Forest | | Guide | | Guide | | Austria | | Finland \ / \ / +--------->\\ //<--------+ \\ // | ----- | ----- | /\ | | LoST | LoST //------\\ Sync LoST Sync |Co-Located| | Sync | | LoST | \/ | \/ | Server | //----\\ \/ //----\\ \\------// | LoST | //----\\ | LoST | | Server | | LoST | | Server | | 'East' | | Server | |'Vienna'| \\----// | 'West' | \\----// \\----//
Figure 1: LoST Deployment Example
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The nodes are configured as follows:
Forest Guide Austria: This forest guide contains mappings for the three authoritative mapping servers (East, West, and Vienna) describing the area for which they are responsible. Note that each mapping contains a service URN, and these mappings point to LoST servers rather than to PSAPs or Emergency Services Routing Proxies (ESRPs). LoST Server 'East': This LoST server contains all the mappings to PSAPs covering the eastern part of the country.-
Additionally, the LoST server aggregates all the information it has and provides an abstracted view towards the forest guide indicating that it is responsible for a certain area (for a given service and for a given location profile). For our example, the structure of a mapping is shown below:
<mapping xmlns="urn:ietf:params:xml:ns:lost1" xmlns:gml="http://www.opengis.net/gml" expires="2009-01-01T01:44:33Z" lastUpdated="2009-12-01T01:00:00Z" source="east-austria.lost-example.com" sourceId="e8b05a41d8d1415b80f2cdbb96ccf109"> <displayName xml:lang="en">LoST Server 'East'</displayName> <service>urn:service:sos</service> <serviceBoundary profile="geodetic-2d"> <gml:Polygon srsName="urn:ogc:def::crs:EPSG::4326"> <gml:exterior> <gml:LinearRing> <gml:pos> ... </gml:pos> ..... list of coordinates for boundary of LoST server 'East' <gml:pos> ... </gml:pos> </gml:LinearRing> </gml:exterior> </gml:Polygon> </serviceBoundary> <uri/> </mapping>-
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Figure 2: Forest Guide Austria Mapping XML Snippet
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Note that the XML code snippet in Figure 2 serves illustrative purposes only and does not validate. As can be seen in this example, the <uri> element is absent, and the 'source' attribute identifies the LoST server, namely "east-austria.lost- example.com".
The mapping shown above is what is the LoST server "east- austria.lost-example.com" provides to the Austrian forest guide.
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LoST Server 'West': This LoST server contains all the mappings to PSAPs covering the western half of the country. LoST Server 'Vienna': This LoST server contains all the mappings to PSAPs for the city of Vienna. Forest Guide Finland: In our example, we assume that Finland deploys a single ESRP for the entire country as their IP-based emergency services solution. There is only a single LoST server, and it is co-located with the forest guide, as shown in Figure 1. The mapping data this forest guide (FG) then distributes via LoST Sync is shown in Figure 3. <mapping xmlns="urn:ietf:params:xml:ns:lost1" expires="2007-01-01T01:44:33Z" lastUpdated="2006-11-01T01:00:00Z" source="finland.lost-example.com" sourceId="7e3f40b098c711dbb6060800200c9a66"> <displayName xml:lang="en">Finland ESRP</displayName> <service>urn:service:sos</service> <serviceBoundary profile="civic"> <civicAddress xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"> <country>FI</country> </civicAddress> </serviceBoundary> <uri/> </mapping>-
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Figure 3: Forest Guide Finland Mapping XML Snippet
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An example mapping stored at the co-located LoST server is shown in Figure 4.
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<mapping xmlns="urn:ietf:params:xml:ns:lost1" expires="2007-01-01T01:44:33Z" lastUpdated="2006-11-01T01:00:00Z" source="finland.lost-example.com" sourceId="7e3f40b098c711dbb6060800200c9a66"> <displayName xml:lang="en">Finland ESRP</displayName> <service>urn:service:sos</service> <serviceBoundary profile="civic"> <civicAddress xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"> <country>FI</country> </civicAddress> </serviceBoundary> <uri>sip:esrp@finland-example.com</uri> <uri>xmpp:esrp@finland-example.com</uri> <serviceNumber>112</serviceNumber> </mapping>-
Figure 4: Forest Guide Finland / Co-Located LoST Server Mapping
XML Snippet
The LoST Sync mechanism described in this document can be run between the two forest guides. That way, the three mappings stored in the FG Austria are sent to the FG Finland, and a single mapping in the FG Finland is sent to the FG Austria. Additionally, the three Austrian LoST servers could utilize LoST Sync to inform the Austrian FG about their boundaries. These three authoritative mapping servers in
Austria would be responsible for maintaining their own mapping information. Since the amount of data being exchanged is small and the expected rate of change is low, the nodes are configured to always exchange all their mapping information whenever a change happens.
This document defines two types of exchanges, which are best described by the exchange between two nodes as shown in Figures 5 and 6. The protocol exchange always runs between a LoST Sync source and a LoST Sync destination. Node A in the examples of Figures 5 and 6 has mappings that Node B is going to retrieve. Node A acts as the source for the data and Node B is the destination.
The <getMappingsRequest> request allows a LoST Sync source to request mappings from a LoST Sync destination.
+---------+ +---------+ | Node B | | Node A | | acting | | acting | | as | | as | | LoST | | LoST | | Sync | | Sync | | Dest. | | Source | +---------+ +---------+ | | | | | | | <getMappingsRequest> | |----------------------------->| | | | <getMappingsResponse> | |<-----------------------------| | | | | | |Figure 5: Querying for Mappings with a <getMappingsRequest> Message
Note that in the exchange illustrated in Figure 5, Node B is issuing the first request and plays the role of the HTTPS client, and Node A plays the role of the HTTPS server.
In Figure 6, the <pushMappingsRequest> exchange allows a LoST Sync source to push mappings to a LoST Sync destination. In this example, we assume that Node A has been configured maintain state about the mappings it had pushed to Node B.
This document does not define a publish/subscribe mechanism. Such a mechanism would allow Node B to tell Node A what mappings it is interested in. This document also does not define a mechanism for nodes to find out to which other entities mappings have to be pushed.
+---------+ +---------+ | Node A | | Node B | | acting | | acting | | as | | as | | LoST | | LoST | | Sync | | Sync | | Source | | Dest. | +---------+ +---------+ | | | | | | | <pushMappingsRequest> | |----------------------------->| | | | <pushMappingsResponse> | |<-----------------------------| | | | | | |-
Figure 6: Pushing Mappings with a <pushMappingsRequest> Message
Node A issuing the first request in Figure 6 plays the role of the HTTPS client, and Node B plays the role of the HTTPS server.
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4. Querying for Mappings with a <getMappingsRequest>/
<getMappingsResponse> Exchange
4.1. Behavior of the LoST Sync Destination
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A LoST Sync destination has two ways to retrieve <mapping> elements from a LoST Sync source.
- When the Lost Sync destination does not have any mappings, it submits an empty <getMappingsRequest> message, as shown in Figure 7. This indicates that it wishes to retrieve all mappings from the LoST Sync source. Note that the request does not propagate further to other nodes.
- In case a LoST Sync destination node has already obtained mappings in previous exchanges, then it may want to check whether these mappings have been updated in the meanwhile. The policy regarding when to poll for updated mapping information is outside the scope of this document. The <getMappingsRequest> message with one or more <exists> child element(s) allows the source to only return mappings that are missing at the destination or have been updated.
After issuing the <getMappingsRequest> message, the LoST Sync destination waits for the <getMappingsResponse> message. In case of a successful response, the LoST Sync destination stores the received mappings and determines which mappings to update.
4.2. Behavior of the LoST Sync Source
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When a LoST Sync source receives an empty <getMappingsRequest> message, then all locally available mappings MUST be returned.
When a LoST Sync source receives a <getMappingsRequest> message with one or more <exists> child element(s), then it MUST consult with the local mapping database to determine whether any of the mappings of the client is stale and whether there are mappings locally that the client does not yet have. The former can be determined by finding mappings corresponding to the 'source' and 'sourceID' attributes where a mapping with a more recent 'lastUpdated' date exists.
Processing a <getMappingsRequest> message MAY lead to a successful response in the form of a <getMappingsResponse> or an <errors> message. Only the <badRequest>, <forbidden>, <internalError>, and <serverTimeout> errors, defined in [RFC5222], are used by this specification. Neither the <redirect> nor the <warnings> messages are reused by this message.
4.3. Examples
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The first example shows an empty <getMappingsRequest> message that would retrieve all locally stored mappings at the LoST Sync source.
<?xml version="1.0" encoding="UTF-8"?> <getMappingsRequest xmlns="urn:ietf:params:xml:ns:lostsync1"/>
Figure 7: Example of Empty <getMappingsRequest> Message
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A further example request is shown in Figure 8, and the corresponding response is depicted in Figure 9. In this example, the <getMappingsRequest> element contains information about the mapping that is locally available to the client inside the
<mapping-fingerprint> element (with source="authoritative.bar.example", sourceId="7e3f40b098c711dbb6060800200c9a66", and lastUpdated="2006- 11-01T01:00:00Z"). The query asks for mappings that are more recent than the available one as well as any missing mapping.
<?xml version="1.0" encoding="UTF-8"?> <getMappingsRequest xmlns="urn:ietf:params:xml:ns:lostsync1"> <exists> <mapping-fingerprint source="authoritative.bar.example" sourceId="7e3f40b098c711dbb6060800200c9a66" lastUpdated="2006-11-01T01:00:00Z"> </mapping-fingerprint> </exists> </getMappingsRequest>
Figure 8: Example <getMappingsRequest> Message
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The response to the above request is shown in Figure 9. A more recent mapping was available with the identification of source="authoritative.bar.example" and sourceId="7e3f40b098c711dbb6060800200c9a66". Only one missing mapping, with source "authoritative.foo.example", was found and returned.
<?xml version="1.0" encoding="UTF-8"?> <sync:getMappingsResponse
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xmlns:sync="urn:ietf:params:xml:ns:lostsync1" xmlns="urn:ietf:params:xml:ns:lost1" xmlns:gml="http://www.opengis.net/gml">
<mapping source="authoritative.bar.example" sourceId="7e3f40b098c711dbb6060800200c9a66" lastUpdated="2008-11-26T01:00:00Z" expires="2009-12-26T01:00:00Z"> <displayName xml:lang="en">Leonia Police Department </displayName> <service>urn:service:sos.police</service> <serviceBoundary profile="urn:ietf:params:lost:location-profile:basic-civic"> <civicAddress xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"> <country>US</country> <A1>NJ</A1> <A3>Leonia</A3> <PC>07605</PC> </civicAddress> </serviceBoundary> <uri>sip:police@leonianj2.example.org</uri> <serviceNumber>911</serviceNumber> </mapping> <mapping expires="2009-01-01T01:44:33Z" lastUpdated="2008-11-01T01:00:00Z" source="authoritative.foo.example" sourceId="7e3f40b098c711dbb606011111111111"> <displayName xml:lang="en">New York City Police Department </displayName> <service>urn:service:sos.police</service> <serviceBoundary profile="geodetic-2d"> <gml:Polygon srsName="urn:ogc:def::crs:EPSG::4326"> <gml:exterior> <gml:LinearRing> <gml:pos>37.775 -122.4194</gml:pos> <gml:pos>37.555 -122.4194</gml:pos> <gml:pos>37.555 -122.4264</gml:pos> <gml:pos>37.775 -122.4264</gml:pos> <gml:pos>37.775 -122.4194</gml:pos> </gml:LinearRing> </gml:exterior> </gml:Polygon> </serviceBoundary> <uri>sip:nypd@example.com</uri> <uri>xmpp:nypd@example.com</uri> <serviceNumber>911</serviceNumber> </mapping> </sync:getMappingsResponse> -
Figure 9: Example <getMappingsResponse> Message
5. Pushing Mappings via <pushMappings> and <pushMappingsResponse>
5.1. Behavior of the LoST Sync Source
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When a LoST Sync source obtains new information that is of interest to its peers, it may push the new mappings to its peers. Configuration settings at both peers decide whether this functionality is used and what mappings are pushed to which other peers. New mappings may arrive through various means, such as a manual addition to the local mapping database, or through the interaction with other entities. Deleting mappings may also trigger a protocol interaction.
The LoST Sync source SHOULD keep track of which LoST Sync destination it has pushed <mapping> elements to. If it does not keep state information, then it always has to push the complete data set. As discussed in Section 5.1 of [RFC5222], <mapping> elements are identified by the 'source', 'sourceID', and 'lastUpdated' attributes. A mapping is considered the same if these three attributes match.
A <pushMappings> request sent by a LoST Sync source MUST contain one or more <mapping> elements.
To delete a mapping, the content of the mapping is left empty, i.e., the <mapping> element only contains the 'source', 'sourceID', 'lastUpdated', and 'expires' attributes. Figure 10 shows an example request where the mapping with the source="nj.us.example", sourceId="123", lastUpdated="2008-11-01T01:00:00Z", and expires="2008-11-01T01:00:00Z" is requested to be deleted. Note that the 'expires' attribute is required per the schema definition but will be ignored in processing the request on the receiving side. A sync source may want to delete the mapping from its internal mapping database but has to remember the peers to which it has distributed this update unless it has other ways to ensure that databases do not get out of sync.
5.2. Behavior of the LoST Sync Destination
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When a LoST Sync destination receives a <pushMappingsRequest> message, then the cache with the existing mappings is inspected to determine whether the received mapping should lead to an update of an already existing mapping, should create a new mapping in the cache, or should be discarded.
If a newly received mapping has a more recent time in its 'lastUpdated' attribute, it MUST update an existing mapping that has matching 'source' and 'sourceID' attributes.
If the received mapping does not match with any existing mapping based on the 'source' and 'sourceId', then it MUST be added to the local cache as an independent mapping.
If a <pushMappingsRequest> message with an empty <mapping> element is received, then a corresponding mapping has to be determined based on the 'source' and the 'sourceID'.
If no mapping can be identified, then an <errors> response MUST be returned that contains the <notDeleted> child element. The <notDeleted> element MAY contain a 'message' attribute with an error description used for debugging purposes. The <notDeleted> element MUST contain the <mapping> element(s) that caused the error.
The response to a <pushMappingsRequest> request is a <pushMappingsResponse> message. With this specification, a successful response message returns no additional elements, whereas an <errors> response is returned in the response message if the request failed. Only the <badRequest>, <forbidden>, <internalError>, or <serverTimeout> errors defined in Section 13.1 of [RFC5222] are used. The <redirect> and <warnings> messages are not used for this query/response.
If the set of nodes that are synchronizing their data does not form a tree, it is possible that the same information arrives through several other nodes. This is unavoidable but generally only imposes a modest overhead. (It would be possible to create a spanning tree in the same fashion as IP multicast, but the complexity does not seem warranted, given the relatively low volume of data.)
5.3. Example
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An example is shown in Figure 10. Imagine a LoST node that obtained two new mappings identified as follows:
- source="authoritative.example" sourceId="7e3f40b098c711dbb6060800200c9a66" lastUpdated="2008-11-26T01:00:00Z"
- source="authoritative.example" sourceId="7e3f40b098c711dbb606011111111111" lastUpdated="2008-11-01T01:00:00Z"
These two mappings have to be added to the peer's mapping database.
Additionally, the following mapping has to be deleted:
- source="nj.us.example" sourceId="123" lastUpdated="2008-11-01T01:00:00Z"
<?xml version="1.0" encoding="UTF-8"?> <sync:pushMappings
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xmlns:sync="urn:ietf:params:xml:ns:lostsync1" xmlns="urn:ietf:params:xml:ns:lost1" xmlns:gml="http://www.opengis.net/gml">
<mapping source="authoritative.example" sourceId="7e3f40b098c711dbb6060800200c9a66" lastUpdated="2008-11-26T01:00:00Z" expires="2009-12-26T01:00:00Z"> <displayName xml:lang="en">Leonia Police Department </displayName> <service>urn:service:sos.police</service> <serviceBoundary profile="urn:ietf:params:lost:location-profile:basic-civic"> <civicAddress xmlns="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"> <country>US</country> <A1>NJ</A1> <A3>Leonia</A3> <PC>07605</PC> </civicAddress> </serviceBoundary> <uri>sip:police@leonianj.example.org</uri> <serviceNumber>911</serviceNumber> </mapping> <mapping expires="2009-01-01T01:44:33Z" lastUpdated="2008-11-01T01:00:00Z" source="authoritative.example" sourceId="7e3f40b098c711dbb606011111111111"> <displayName xml:lang="en">New York City Police Department </displayName> <service>urn:service:sos.police</service> <serviceBoundary profile="geodetic-2d"> <gml:Polygon srsName="urn:ogc:def::crs:EPSG::4326"> <gml:exterior> <gml:LinearRing> <gml:pos>37.775 -122.4194</gml:pos> <gml:pos>37.555 -122.4194</gml:pos> <gml:pos>37.555 -122.4264</gml:pos> <gml:pos>37.775 -122.4264</gml:pos> <gml:pos>37.775 -122.4194</gml:pos> </gml:LinearRing> </gml:exterior> </gml:Polygon> </serviceBoundary> <uri>sip:nypd@example.com</uri> <uri>xmpp:nypd@example.com</uri> <serviceNumber>911</serviceNumber> </mapping>-
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<mapping source="nj.us.example"
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sourceId="123"
lastUpdated="2008-11-01T01:00:00Z" expires="2008-11-01T01:00:00Z"/>
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</sync:pushMappings>
Figure 10: Example <pushMappingsRequest> Message
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In response, the peer performs the necessary operations and updates its mapping database. In particular, it will check whether the other peer is authorized to perform the update and whether the elements and attributes contain values that it understands. In our example, a positive response is returned as shown in Figure 11.
<?xml version="1.0" encoding="UTF-8"?> <pushMappingsResponse xmlns="urn:ietf:params:xml:ns:lostsync1" />
Figure 11: Example <pushMappingsResponse>
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In case a mapping could not be deleted as requested, the following error response might be returned instead.
<?xml version="1.0" encoding="UTF-8"?> <errors xmlns="urn:ietf:params:xml:ns:lost1"
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xmlns:sync="urn:ietf:params:xml:ns:lostsync1" source="nodeA.example.com">
<sync:notDeleted
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message="Could not delete the indicated mapping." xml:lang="en">
<mapping source="nj.us.example" sourceId="123" lastUpdated="2008-11-01T01:00:00Z" expires="2008-11-01T01:00:00Z"/> </sync:notDeleted> </errors> -
Figure 12: Example <errors> Message
6. Transport
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LoST Sync needs an underlying protocol transport mechanism to carry requests and responses. This document uses HTTPS as a transport to exchange XML documents. No fallback to HTTP is provided.
When using HTTP over Transport Layer Security (TLS) [RFC2818], LoST Sync messages use the POST method. Requests MUST use the Cache- Control response directive "no-cache".
All LoST Sync responses, including those indicating a LoST warning or error, are carried in 2xx responses, typically 200 (OK). 3xx, 4xx, and 5xx HTTP response codes indicate that the request itself failed or was redirected; these responses do not contain any LoST Sync XML elements.
7. RELAX NG
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Note: In order to avoid copying pattern definitions from the LoST Regular Language for XML Next Generation (RELAX NG) schema [RFC5222] to this document, we include it as "lost.rng" (XML syntax) in the RELAX NG schema below.
<?xml version="1.0" encoding="utf-8"?>
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<grammar ns="urn:ietf:params:xml:ns:lostsync1" xmlns="http://relaxng.org/ns/structure/1.0" xmlns:a="http://relaxng.org/ns/compatibility/annotations/1.0" datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
<include href="lost.rng"/> <start combine="choice"> <a:documentation> Location-to-Service Translation (LoST) Synchronization Protocol</a:documentation> <choice> <ref name="pushMappings"/> <ref name="pushMappingsResponse"/> <ref name="getMappingsRequest"/> <ref name="getMappingsResponse"/> </choice> </start>-
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<define name="pushMappings">
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<element name="pushMappings">
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<oneOrMore> <ref name="mapping"/> </oneOrMore> <ref name="extensionPoint"/> </element> </define> <define name="pushMappingsResponse"> <element name="pushMappingsResponse"> <ref name="extensionPoint"/> </element> </define> <define name="getMappingsRequest"> <element name="getMappingsRequest"> <choice> <ref name="exists"></ref> <ref name="extensionPoint"/> </choice> </element> </define> <define name="exists"> <element name="exists"> <oneOrMore> <element name="mapping-fingerprint"> <attribute name="source"> <data type="token"/> </attribute> <attribute name="sourceId"> <data type="token"/> </attribute> <attribute name="lastUpdated"> <data type="dateTime"/> </attribute> <ref name="extensionPoint"/> </element> </oneOrMore> </element> </define> <define name="getMappingsResponse"> <element name="getMappingsResponse"> <oneOrMore> <ref name="mapping"/> </oneOrMore> <ref name="extensionPoint"/> </element> </define> <!-- error messages --> <define name="notDeleted"> <element name="notDeleted"> <ref name="basicException"/> <oneOrMore> <ref name="mapping"/> </oneOrMore> </element> </define> </grammar> -
8. Operational Considerations
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It is important to avoid loops when more than two LoST servers use the mechanism described in this document. The example shown in Figure 13 with three LoST servers A, B, and C (each of them acts as a sync source and a sync destination) illustrates the challenge in more detail. A and B synchronize data between each other; the same is true for A and C, and B and C, respectively.
A -------- B \ / \ / \ / \ / C
Figure 13: Synchronization Configuration Example
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Now, imagine that server A adds a new mapping. This mapping is uniquely identified by the combination of "source", "sourceid", and "last updated". Assume that A wants to push this new mapping to B and C. When B obtains this new mapping, it determines that it has to distribute it to its peer C. C also needs to distribute the mapping to its peer B. If the original mapping with the "source", "sourceid", and "last updated" is not modified by either B or C, then these two servers would recognize that they already possess the mapping and can ignore the update.
Implementations MUST NOT modify mappings they receive. An entity acting maliciously would, however, intentionally modify mappings or inject bogus mappings. To avoid the possibility of an untrustworthy member claiming a coverage region for which it is not authorized, authoritative mapping servers MUST sign mappings they distribute using an XML digital signature [W3C.REC-xmldsig-core-20020212]. A recipient MUST verify that the signing entity is indeed authorized to speak for that region. In many cases, this will require an out-of- band agreement to be in place to agree on specific entities to take on this role. Determining who can speak for a particular region is inherently difficult unless there is a small set of authorizing entities that participants in the mapping architecture can trust. Receiving systems should be particularly suspicious if an existing coverage region is replaced by a new one that contains a different value in the <uri> element. When mappings are digitally signed, they cannot be modified by intermediate LoST servers.
9. Security Considerations
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This document defines a protocol for exchange of authoritative mapping information between two entities. Hence, the protocol operations described in this document require authentication of neighboring nodes.
The LoST Sync client and servers MUST implement TLS and use TLS. Which version(s) ought to be implemented will vary over time and depend on the widespread deployment and known security vulnerabilities at the time of implementation. At the time of this writing, TLS version 1.2 [RFC5246] is the most recent version but has very limited actual deployment and might not be readily available in implementation tool kits. TLS version 1.0 [RFC2246] is the most widely deployed version and will give the broadest interoperability.
Mutual authentication between the LoST Sync source and the LoST Sync destination is not necessarily required in all deployments unless an emergency service authority wants to enforce access control prior to the distribution of their <mapping> elements. This may, for example, be the case when certain emergency services networks distribute internal mappings that are not meant for public distribution.
An additional threat is caused by compromised or misconfigured LoST servers. A denial of service could be the consequence of an injected mapping. If the mapping data contains a URL that does not exist, then emergency services for the indicated area are not reachable. If all mapping data contains URLs that point to a single PSAP (rather than a large number of PSAPs), then this PSAP is likely to experience overload conditions. If the mapping data contains a URL that points to a server controlled by the adversary itself, then it might impersonate PSAPs.
Section 8 discusses this security threat and mandates signed mappings. For unusual changes to the mapping database, approval by a system administrator of the emergency services infrastructure (or a similar expert) may be required before any mappings are installed.
10. IANA Considerations
10.1. Media Type Registration
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This specification requests the registration of a new media type according to the procedures of RFC 4288 [RFC4288] and guidelines in RFC 3023 [RFC3023].
Type name: application Subtype name: lostsync+xml Required parameters: none Optional parameters: charset
Encoding considerations: Identical to those of "application/xml" as described in [RFC3023], Section 3.2. Security considerations: This content type is designed to carry LoST Synchronization protocol payloads, and the security considerations section of RFC 6739 is applicable. In addition, as this media type uses the "+xml" convention, it shares the same security considerations as described in [RFC3023], Section 10. Interoperability considerations: None Published specification: RFC 6739 Applications that use this media type: Emergency and Location-based SystemsAdditional information:
Magic number(s): None File extension(s): .lostsyncxml Macintosh file type code(s): 'TEXT'Person & email address to contact for further information:
Hannes Tschofenig <Hannes.Tschofenig@gmx.net> Intended usage: LIMITED USE Restrictions on usage: None Author: Hannes Tschofenig <Hannes.Tschofenig@gmx.net>
Change controller:
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This specification is a work item of the IETF ECRIT working group, with mailing list address <ecrit@ietf.org>.
Change controller:
The IESG <iesg@ietf.org>
10.2. LoST Sync RELAX NG Schema Registration
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The schema defined in this document has been registered under the XML schema registry at http://www.iana.org/assignments/xml-registry/schema.html URI: urn:ietf:params:xml:schema:lostsync1 Registrant Contact: IETF ECRIT Working Group, Hannes Tschofenig (Hannes.Tschofenig@gmx.net). RELAX NG Schema: The RELAX NG schema that has been registered is contained in Section 7.
10.3. LoST Synchronization Namespace Registration
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The namespace defined in this document has been registered under the XML namespace registry at http://www.iana.org/assignments/xml-registry/ns.html URI: urn:ietf:params:xml:ns:lostsync1 Registrant Contact: IETF ECRIT Working Group, Hannes Tschofenig (Hannes.Tschofenig@gmx.net).XML:
BEGIN <?xml version="1.0"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN" "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="content-type" content="text/html;charset=iso-8859-1"/> <title>LoST Synchronization Namespace</title> </head> <body> <h1>Namespace for LoST server synchronization</h1> <h2>urn:ietf:params:xml:ns:lostsync1</h2> <p>See <a href="[URL of published RFC]">RFC 6739 </a>.</p> </body> </html> END
11. Acknowledgments
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Robins George, Cullen Jennings, Karl Heinz Wolf, Richard Barnes, Mayutan Arumaithurai, Alexander Mayrhofer, and Andrew Newton provided helpful input. Jari Urpalainen assisted with the RELAX NG schema. We would also like to thank our document shepherd Roger Marshall for his help with the document.
We would like to particularly thank Andrew Newton for his timely and valuable review of the XML-related content.
We would like to thank Robert Sparks, Barry Leiba, Stephen Farrell, Brian Haberman, Pete Resnick, and Sean Turner for their AD reviews. We would also like to thank Bjoern Hoehrmann for his media type review, Julian Reschke and Martin Duerst for their applications area reviews, and Wassim Haddad for his Gen-ART review.
12. References
12.1. Normative References
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types", RFC 3023, January 2001. [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", BCP 13, RFC 4288, December 2005. [RFC5222] Hardie, T., Newton, A., Schulzrinne, H., and H. Tschofenig, "LoST: A Location-to-Service Translation Protocol", RFC 5222, August 2008. [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008.
[W3C.REC-xmldsig-core-20020212]
Eastlake, D., Reagle, J., Solo, D., Hirsch, F., and T. Roessler, "XML-Signature Syntax and Processing", World Wide Web Consortium, Second Edition, REC-xmldsig-core- 20020212, June 2008.
12.2. Informative References
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[RFC5012] Schulzrinne, H. and R. Marshall, "Requirements for Emergency Context Resolution with Internet Technologies", RFC 5012, January 2008. [RFC5582] Schulzrinne, H., "Location-to-URL Mapping Architecture and Framework", RFC 5582, September 2009.
Authors' Addresses
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Henning Schulzrinne Columbia University Department of Computer Science 450 Computer Science Building New York, NY 10027 USA Phone: +1 212 939 7004 EMail: hgs+ecrit@cs.columbia.edu URI: http://www.cs.columbia.edu
Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
FinlandPhone: +358 (50) 4871445 EMail: Hannes.Tschofenig@gmx.net URI: http://www.tschofenig.priv.at