ETSI TS 103 698 V1.1.1 (2020-12)

Emergency Communications (EMTEL); Lightweight Messaging Protocol for Emergency Service Accessibility (LMPE)

DTS/EMTEL-00050

General Information

• Status: Not Published
• Technical Committee: EMTEL - Emergency Communications
• Current Stage: 12 - Completion
• Due Date: 18-Dec-2020
• Completion Date: 17-Dec-2020

Standards Content (Sample)

TECHNICAL SPECIFICATION
Emergency Communications (EMTEL);
Lightweight Messaging Protocol for
Emergency Service Accessibility (LMPE)

2 ETSI TS 103 698 V1.1.1 (2020-12)

Reference
DTS/EMTEL-00050
Keywords
chat, decentralized identifier, emergency
services, location, SSL/TLS certificates
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3 ETSI TS 103 698 V1.1.1 (2020-12)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 5
Executive summary . 5
Introduction . 6
1 Scope . 7
2 References . 7
2.1 Normative references . 7
2.2 Informative references . 8
3 Definition of terms, symbols and abbreviations . 8
3.1 Terms . 8
3.2 Symbols . 8
3.3 Abbreviations . 9
4 General . 10
4.1 Overview . 10
4.2 Architecture . 10
4.3 Mandatory Interfaces . 11
4.4 Optional Interfaces . 12
5 Entities . 12
5.1 Border Control Function (BCF) . 12
5.1.1 Overview . 12
5.1.2 Mandatory Interfaces . 12
5.1.3 Optional Interfaces . 13
5.2 Emergency Service Routing Proxy (ESRP) . 13
5.2.1 Overview . 13
5.2.2 Mandatory Interfaces . 13
5.2.3 Optional Interfaces . 14
5.3 Emergency Call Routing Function (ECRF) . 14
5.3.1 Overview . 14
5.3.2 Mandatory Interfaces . 14
5.3.3 Optional Interfaces . 14
5.4 Public Safety Answering Point (PSAP). 14
5.4.1 Overview . 14
5.4.2 Mandatory Interfaces . 14
5.4.3 Optional Interfaces . 15
5.5 Location Information Server (LIS) . 15
5.5.1 Overview . 15
5.5.2 Mandatory Interfaces . 15
5.5.3 Optional Interfaces . 15
5.5.4 Location Representation . 16
5.6 Chat Application (APP) . 16
5.6.1 Overview . 16
5.6.2 Mandatory Interfaces . 16
5.6.3 Optional Interfaces . 16
5.6.4 Location Representation . 16
6 Interfaces . 17
6.1 Signalling . 17
6.1.1 SIP Transport (SIP-1) . 17
6.1.2 SIP Session (SIP-2) . 17
6.1.2.1 Overview . 17
6.1.2.2 SIP Methods . 17
6.1.2.3 Required SIP Headers . 17
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4 ETSI TS 103 698 V1.1.1 (2020-12)
6.1.2.4 Accepted SIP Headers . 18
6.1.2.5 Resource Priority . 19
6.1.2.6 History-Info and Reason . 19
6.1.2.7 Call-Info . 19
6.1.2.8 SIP Message Bodies . 20
6.1.2.9 SIP Element Overload . 20
6.1.2.10 Test Call . 21
6.1.2.11 Decentralised Identifier (DID) . 21
6.2 Instant Messaging (IM-2) . 22
6.2.1 Overview . 22
6.2.2 Session Mode Initiation . 22
6.2.3 Session Mode Chat . 23
6.2.4 Session Mode Termination . 24
6.2.5 Keep-Alive Messages . 24
6.2.6 Transfer . 25
6.2.7 Redirect . 26
6.3 Chat Transfer (HTTP-3) . 28
6.3.1 Overview . 28
6.3.2 Transfer Negotiation . 28
6.3.3 Transfer Execution . 29
6.3.4 Message Sequence Chart . 29
Annex A (normative): JSON Schema . 33
A.1 ChatTransferNegotiationRequest . 33
A.2 ChatTransferNegotiationResponse . 33
A.3 ChatTransferExecutionRequest . 34
A.4 ChatTransferExecutionResponse . 34
A.5 Message Type Definition . 35
Annex B (informative): Organizational Descriptions . 36
B.0 General . 36
B.1 Certificate Authority. 36
B.2 National, and Regional Authorities . 36
B.3 Public Safety Computer Emergency Response Team (CERT) . 36
B.4 ETSI Protocol Naming and Numbering Service (PNNS) . 36
B.5 Emergency Call Service Authorities . 36
Annex C (informative): Parameter Registries . 38
C.0 General . 38
Annex D (informative): Use Case Examples . 39
D.0 General . 39
D.1 National/Regional . 39
D.2 International/Roaming . 40
D.3 Smart IoT Devices And Chatbots . 41
History . 42

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5 ETSI TS 103 698 V1.1.1 (2020-12)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Trademarks
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ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
Foreword
This Technical Specification (TS) has been produced by ETSI Special Committee Emergency Communications
(EMTEL).
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Executive summary
Lightweight Messaging Protocol for Emergency Service accessibility (LMPE) extends a SIP SIMPLE based messaging
service with session mode and facilities to redirect or transfer a chat. The mechanisms introduced in the present
document differ from existing solutions like MSRP in a sense that no media plane is required. This reduces the
functionality to chat, but requires less deployment effort and complexity (e.g. no intermediate services or relays in case
of NAT), especially in a roaming use case. In addition, to further reduce complexity, the identification of a user is
carried out via a device identifier only, such as a mobile phone number as with comparable chat services. In summary, it
simplifies the implementation and thus can be used in simple mobile applications or even smart IoT devices and
chatbots, which for example send or respond to messages automatically.
The referred baseline specification (ETSI TS 103 479 [1]) already defines page mode messaging suitable for a single
message exchange or a series of short messages similar to paging or SMS on a mobile device. Routing and mapping
mechanisms (defined in ETSI TS 103 479 [1]) to determine the proper control room, are based on location information.
Therefore a single message exchange is not practicable as caller location may change and lead to messages being routed
to a different control room. The present document defines specific message types to group messages into sessions with
routing and mapping only required at setup time. In addition the same principles are used to support supplementary
services like chat redirect and transfer. Each mechanism is transparent to ETSI TS 103 479 [1] core services and
requires only minor modifications to the PSAP interface.
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6 ETSI TS 103 698 V1.1.1 (2020-12)
Introduction
Emergency communications services are primarily voice only, along with a marginal share of data and multimedia used
by Public Safety Answering Points (PSAPs). Improving access to emergency services for citizens, especially for the
deaf and hard of hearing, requires PSAPs and people in need to handle new modes of communications such as text.
Messenger services are widespread and well known to the public and currently, the present document defines extension
to support a comparable messenger service to access emergency control rooms by leveraging the new architecture
introduced in ETSI TS 103 479 [1]. The main purpose of the extensions is to enable a simplified chat session mode
combined with means to redirect or transfer a chat session. Furthermore the specification allows a lightweight
implementation of a messenger application for emergency chat or bot services. The fact that besides a signalling plane,
no further media sessions are required, supports a straight integration with firewalls or, in general, network security
technologies.
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7 ETSI TS 103 698 V1.1.1 (2020-12)
1 Scope
The purpose of the present document is to describe a lightweight session based emergency chat protocol that extends
the base messaging functionality as defined in ETSI TS 103 479 [1]. The messaging service is based only on methods of
the SIP signalling plane and interworks with Border Control Function, Emergency Service Routing Proxy, Emergency
Call Routing Function, Public Safety Answering Point, the Location Information Server. It is important to emphasize
that the introduced feature is an alternative to MSRP, real-time text or, in general, total conversation and not a
replacement.
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long-term validity.
Referenced documents which are not found to be publicly available in the expected location might be found at
https://docbox.etsi.org/Reference.
The following referenced documents are necessary for the application of the present document.
[1] ETSI TS 103 479: "Emergency Communications (EMTEL); Core elements for network
independent access to emergency services".
[2] IETF RFC 2046: "Multipurpose Internet Mail Extensions (MIME) Part Two: MediaTypes ", Freed
N. and Borenstein, N., November 1996.
[3] IETF RFC 3261: "SIP: Session Initiation Protocol", Rosenberg, J., Schulzrinne, H., Camarillo, G.,
Johnston, A., Peterson, J., Sparks, R., Handley, M. and Schooler, E. June 2002.
[4] IETF RFC 3325: "Private Extensions to the Session Initiation Protocol (SIP) for Asserted Identity
Within Trusted Networks", Jennings, C., Peterson, J. and Watson, M., November 2002.
[5] IETF RFC 3326: "The Reason Header Field for the Session Initiation Protocol (SIP)", Oran, D.
and Camarillo, G., December 2002.
[6] IETF RFC 3428: "Session Initiation Protocol (SIP) Extension for Instant Messaging", Campbell,
B., Rosenberg, J., Schulzrinne, H., Huitema, C. and Gurle, D., December 2002.
[7] IETF RFC 3841: " Caller Preferences for the Session Initiation Protocol (SIP)"," Rosenberg, J.,
Schulzrinne, H. and Kyzivat, P., August 2004.
[8] IETF RFC 4119: "A Presence-Based GEOPRIV Location Object Format", Peterson, J., December
2005.
[9] IETF RFC 4244: "An Extension to the Session Initiation Protocol (SIP) for Request History
Information", Barnes, M., November 2005.
[10] IETF RFC 4412: "Communications Resource Priority for the Session Initiation Protocol (SIP)",
Schulzrinne, H. and Polk, J., February 2006.
[11] IETF RFC 4566: "SDP: Session Description Protocol", Handley, M., Jacobson, V. and Perkins, C.,
July 2006.
[12] IETF RFC 5031: "A Uniform Resource Name (URN) for Emergency and Other Well-Known
Services", Schulzrinne, H., January 2008.
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8 ETSI TS 103 698 V1.1.1 (2020-12)
[13] IETF RFC 5621: "Message Body Handling in the Session Initiation Protocol (SIP)", Camarillo, G.,
September 2009.
[14] IETF RFC 6442: "Location Conveyance for the Session Initiation Protocol", Polk, J., Rosen, B.
and Peterson, J., December 2011.
[15] IETF RFC 6881: "Best Current Practice for Communications Services in Support of Emergency
Calling", Rosen, B. and Polk, J. March 2013.
[16] IETF RFC 7135: "Registering a SIP Resource Priority Header Field Namespace for Local
Emergency Communications", Polk, J. May 2014.
[17] IETF RFC 8446: "The Transport Layer Security (TLS) Protocol Version 1.3", V Rescorla, E.,
August 2018.
[18] W3C: "Decentralized Identifiers (DIDs) v1.0 Core Data Model and representations", Working
Draft 08 November 2020.
NOTE: Available at https://www.w3.org/TR/did-core/.
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long-term validity.
The following referenced documents are not necessary for the application of the present document, but they assist the
user with regard to a particular subject area.
[i.1] EENA, Version 1.1, March 2013: "Next Generation 112 Long Term Definition".
NOTE: Available at https://eena.org/knowledge-hub/documents/ng112-long-term-definition-standard-for-
emergency-services/.
[i.2] EENA Version 1.05, March 2016: "Public Safety Digital Transformation The Internet of Things
(IoT) and Emergency Services".
NOTE: Available at https://eena.org/document/the-internet-of-things-and-emergency-services/.
[i.3] W3C Recommendation, November 2019: "Verifiable Credentials Data Model 1.0".
NOTE: Available at https://www.w3.org/TR/vc-data-model/#ecosystem-overview.
3 Definition of terms, symbols and abbreviations
3.1 Terms
Void.
3.2 Symbols
Void.
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9 ETSI TS 103 698 V1.1.1 (2020-12)
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
AP Application Provider
BCF Border Control Function
BGP Border Gateway Protocol
CA Certification Authority
CAP Common Alerting Protocol
CERT Computer Emergency Response Team
CR Carriage Return
DID Decentralised Identifier
DLT Distributed Ledger Technology
ECRF Emergency Call Routing Function
ESInet Emergency Services IP network
ESRF Emergency Service Routing Function
ESRP Emergency Service Routing Proxy
ETSI European Telecommunications Standards Institute
FG Forest Guide
GIS Geographic Information System
HELD HTTP Enabled Location Delivery
HTTP Hypertext Transfer Protocol
HTTPS Hypertext Transfer Protocol Secure
IETF Internet Engineering Task Force
IF Interface
IM Instant Messaging
IoT Internet of Things
IP Internet Protocol
IT Information Technology
JSON JavaScript® Object Notation
LF Line Feed
LIS Location Information Server
LMPE Lightweight Messaging Protocol for Emergency Service accessibility
LO Location Object
LOST Location to Service Translation
LTD Long-term Definition
MSD Minimum Set of Data
MSRP Message Session Relay Protocol
NAT Network Address Translation
P-A-I P-Asserted-Identity
PIDF Presence Information Data Format
PIDF-LO Presence Information Data Format - Location Object
PNNS Protocol Naming and Numbering Service
PSAP Public Safety Answering Point
RCS Rich Communication Services
RFC Request For Comment
SDP Session Description Protocol
SIP Session Initiation Protocol
SMS Short Message Service
TCP Transmission Control Protocol
TLS Transport Layer Security
TR (ETSI) Technical Report
TS (ETSI) Technical Specification
UDP User Datagram Protocol
URI Uniform Resource Identifier
URN Uniform Resource Name
UTF Unicode Transformation Format
WGS84 World Geodetic System 1984
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10 ETSI TS 103 698 V1.1.1 (2020-12)
4 General
4.1 Overview
Per ETSI TS 103 479 [1] emergency calls are routed by the ESRF to the ESRP via a BCF. Depending on national PSAP
models the ESRP may then forward directly to the appropriate PSAP as explained in NG112 LTD [i.1] . The same
mechanism applies to instant messaging in a non-session mode. The present document defines certain extensions to
interfaces and introduces a mobile application (APP) interface to support a session based chat application. Figure 1
illustrates a high level functional architecture, where specific Application Provider (AP) services are used to manage the
application (AP BE) or to interconnect with an ESInet (SIP PROXY). Chat messages addressed to public emergency
service SIP URI or service URN are forwarded to a BCF and routed within the ESInet utilizing a geodetic location
determined by the mobile application (typically via sensor fusion).

Figure 1: High level functional architecture
The present document specifies only the signalling interface between APP, PSAP and other core services required to
setup a session based chat. The following architecture introduces functional elements that comprise an IP only
environment. Such elements provide security measures (BCF), emergency call routing (ESRP), mapping PSAP
boundaries to SIP URIs (ECRF), a mobile application (APP) and chat processing equipment (PSAP).
4.2 Architecture
The definition of core elements and interfaces supporting a Lightweight Messaging Protocol for Emergency Service
accessibility (LMPE) is based on the core concept introduced in ETSI TS 103 479 [1]. LMPE utilizes IP technology and
requires public and private managed, and routed IP networks. The present document introduces new interfaces between
the functional elements APP and PSAP (dashed-line boxes in Figure 2), and refers to functional elements with their
internal and external interfaces as defined in ETSI TS 103 479 [1]; listed below:
• Border Control Function (BCF);
• Emergency Call Routing Function (ECRF);
• Chat Application (APP);
• Public Safety Answering Point (PSAP);
• Emergency Services Routing Proxy (ESRP); and
• Location Information Service (LIS).
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11 ETSI TS 103 698 V1.1.1 (2020-12)

Figure 2: Core elements
4.3 Mandatory Interfaces
Mandatory interfaces are either referenced (ETSI TS 103 479 [1]), or introduced by the present document to define
simple chat capabilities of an APP and ESInet core elements. Figure 3 shows interfaces as listed in the following:
• SIP-1, SIP-2: Interface between APP, BCF, ESRP and PSAP elements that defines SIP transport and
signalling capabilities.
• LOST-1, LOST-2: Interface between ESRP and ECRF elements that defines LoST signalling capabilities.
• HELD-1, HELD-2: Interface between ESRP or PSAP and LIS elements that defines location dereference and
HELD signalling capabilities.
• IM-2: APP and PSAP chat handling capabilities to support instant messaging.

Figure 3: Considered mandatory interfaces
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12 ETSI TS 103 698 V1.1.1 (2020-12)
4.4 Optional Interfaces
In addition, optional interfaces as defined in to ETSI TS 103 479 [1], are referenced by the current document to extend
mandatory capabilities. Figure 4 shows interfaces as listed in the following:
• HTTP-2: Interface between BCF and PSAP elements that defines domain specific web service capabilities.
• HTTP-3: Interface between PSAP elements that defines domain specific web service capabilities.
• LOST-1: Interface between APP and ECRF elements that defines LoST signalling capabilities.
• HELD-1: Interface between APP and LIS elements that defines HELD signalling capabilities.

Figure 4: Considered optional interfaces
5 Entities
5.1 Border Control Function (BCF)
5.1.1 Overview
A BCF is the entry point (point-of-interconnect) to the ESInet infrastructure where all traffic from external networks
transits. General procedures and interfaces are specified in ETSI TS 103 479 [1].
5.1.2 Mandatory Interfaces
To be compliant with the procedures in the present document, a BCF shall support:
1) the SIP-1 interface as specified in ETSI TS 103 479 [1], clause 6.1.1;
2) the SIP-2 interface as specified in ETSI TS 103 479 [1], clause 6.1.2.
Figure 5 shows mandatory interfaces and neighbouring entities.
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13 ETSI TS 103 698 V1.1.1 (2020-12)

Figure 5: BCF mandatory interfaces
5.1.3 Optional Interfaces
In addition to all mandatory interfaces, a BCF may support any other specific interface as listed in ETSI
TS 103 479 [1]:
1) the HTTP-2 interface as specified in ETSI TS 103 479 [1], clause 6.2.2;
Figure 6 shows optional interfaces and neighbouring entities.

Figure 6: BCF optional interfaces
5.2 Emergency Service Routing Proxy (ESRP)
5.2.1 Overview
The Emergency Service Routing Proxy (ESRP) is the base routing function for emergency chat. General procedures and
interfaces are specified in ETSI TS 103 479 [1].
5.2.2 Mandatory Interfaces
To be compliant with the procedures in the present document, an ESRP shall support:
1) the SIP-1 interface as specified in ETSI TS 103 479 [1], clause 6.1.1;
2) the SIP-2 interface as specified in ETSI TS 103 479 [1], clause 6.1.2;
3) the LOST-1 interface as specified in ETSI TS 103 479 [1], clause 6.4.1;
4) the LOST-2 interface as specified in ETSI TS 103 479 [1], clause 6.4.2;
5) the HELD-1 interface as specified in ETSI TS 103 479 [1], clause 6.5.1;
6) the HELD-2 interface as specified in ETSI TS 103 479 [1], clause 6.5.2.
Figure 7 shows mandatory interfaces and neighbouring entities.

Figure 7: ESRP mandatory interfaces
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14 ETSI TS 103 698 V1.1.1 (2020-12)
5.2.3 Optional Interfaces
In addition to all mandatory interfaces, an ESRP may support any other specific interface as listed in ETSI
TS 103 479 [1].
5.3 Emergency Call Routing Function (ECRF)
5.3.1 Overview
The Emergency Call Routing Function (ECRF) is the base mapping function for emergency chat. General procedures
and interfaces are specified in ETSI TS 103 479 [1].
5.3.2 Mandatory Interfaces
To be compliant with the procedures in the present document, an ECRF shall support:
1) the LOST-1 interface as specified in ETSI TS 103 479 [1], clause 6.4.1;
2) the LOST-2 interface as specified in ETSI TS 103 479 [1], clause 6.4.2.
Figure 8 shows mandatory interfaces and neighbouring entities.

Figure 8: ECRF mandatory interfaces
5.3.3 Optional Interfaces
In addition to all mandatory interfaces, an ECRF may support any other specific interface as listed in ETSI
TS 103 479 [1].
5.4 Public Safety Answering Point (PSAP)
5.4.1 Overview
A PSAP is a service, typically composed of more than one functional element. The functional elements that make up a
PSAP are out of scope of the present document. The PSAP implements the LMPE interface including the chat
capability as specified in the present document.
5.4.2 Mandatory Interfaces
To be compliant with the procedures in the present document, a PSAP shall support:
1) the SIP-1 interface as specified in ETSI TS 103 479 [1], clause 6.1.1;
2) the SIP-2 interface as specified in ETSI TS 103 479 [1], clause 6.1.2;
3) the HELD-2 interface as specified in ETSI TS 103 479 [1], clause 6.5.2;
4) the IM-2 interface as specified in clause 6.2.
Figure 9 shows mandatory interfaces and neighbouring entities.
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15 ETSI TS 103 698 V1.1.1 (2020-12)

Figure 9: PSAP mandatory interfaces
5.4.3 Optional Interfaces
In addition to all mandatory interfaces, a PSAP may support any other specific interface as listed in ETSI
TS 103 479 [1] and below.
1) the HTTP-2 interface as specified in ETSI TS 103 479 [1], clause 6.2.2;
2) the HTTP-3 interface as specified in clause 6.3.
Figure 10 shows optional interfaces and neighbouring entities.

Figure 10: PSAP optional interfaces
5.5 Location Information Server (LIS)
5.5.1 Overview
Location is fundamental to the operation of the emergency services, and the generic functional entity that provides
location is a Location Information Server (LIS) as specified in ETSI TS 103 479 [1].
5.5.2 Mandatory Interfaces
To be compliant with the procedures in the present document, a LIS shall support:
1) the HELD-1 interface as specified in ETSI TS 103 479 [1], clause 6.5.1;
2) the HELD-2 interface as specified in ETSI TS 103 479 [1], clause 6.5.2.
Figure 11 shows mandatory interfaces and neighbouring entities.

Figure 11: LIS mandatory interfaces
5.5.3 Optional Interfaces
In addition to all mandatory interfaces, a LIS may support any other specific interface as listed in ETSI TS 103 479 [1].
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16 ETSI TS 103 698 V1.1.1 (2020-12)
5.5.4 Location Representation
Location is represented by content in a PIDF-LO document (IETF RFC 4119 [8]). All geodetic data shall use WGS84
as the datum. The representation of the location object within the PIDF document shall utilize the tuple element as
defined in IETF RFC 4119 [8].
5.6 Chat Application (APP)
5.6.1 Overview
The APP implements the LMPE interface including the chat capability as specified in the present document. Other
backend services required by the APP are out of scope of the present document.
5.6.2 Mandatory Interfaces
To be compliant with the procedures in the present document, an APP shall support:
1) the SIP-1 interface as specified in ETSI TS 103 479 [1], clause 6.1.1;
2) the SIP-2 interface as specified in ETSI TS 103 479 [1], clause 6.1.2;
3) the IM-2 interface as specified in clause 6.2.
Figure 12 shows mandatory interfaces and neighbouring entities.

Figure 12: LIS mandatory interfaces
5.6.3 Optional Interfaces
In addition to all mandatory interfaces, an APP may support any other specific interface as listed in ETSI
TS 103 479 [1] and below.
1) the LOST-1 interface as specified in ETSI TS 103 479 [1], clause 6.4.1;
2) the HELD-1 interface as specified in ETSI TS 103 479 [1], clause 6.5.1.
Figure 13 shows optional interfaces and neighbouring entities.

Figure 13: APP optional interfaces
5.6.4 Location Representation
Location is represented by content in a PIDF-LO document (IETF RFC 4119 [8]). All geodetic data shall use WGS84 as
the datum. The representation of the location object within the PIDF document shall utilize the tuple element as
defined in IETF RFC 4119 [8].
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17 ETSI TS 103 698 V1.1.1 (2020-12)
6 Interfaces
6.1 Signalling
6.1.1 SIP Transport (SIP-1)
SIP signalling within the ESInet shall be TCP with TLS as defined in IETF RFC 8446 [17]. When a TLS connection
already exists, either peering entity shall reuse that TLS connection for all SIP messages within a chat (refer to
clause 6.2.3) by utilizing a proper session timeout of at least 3 minutes. Fallback to UDP is allowed. However
emergency call messages have many large elements, for example a PIDF-LO, and are more likely to be fragmented
when carried in UDP. Fragmentation and reassembly shall be supported by all ESInet elements. If TLS establishment
fails, fallback to transport protocols without TLS is allowed.
If fallback with TLS occurs, additional security weaknesses should be considered, and implementations should be
prepared to deal with the security risks when TLS protection is not available. Known attacks on incomplete
fragmentation/reassembly implementations are another concern, which should be addressed by all elements in the
ESInet. Persistent TLS connections between elements that frequently exchange SIP transactions should be deployed.
TLS implementations shall support mutual authentication (using at least RSA-1024), which implies both ends have an
X.509 certificate available to the other party. How a certificate is created and issued by a Certificate Authority (CA) is
out of scope of the present document.
6.1.2 SIP Session (SIP-2)
6.1.2.1 Overview
The call interface is SIP (as defined in IETF RFC 3261 [3]). All chat messages presented to the ESInet shall be SIP
signalled as specified in ETSI TS 103 479 [1], clause 6.7.
6.1.2.2 SIP Methods
MESSAGE:
The MESSAGE method, an extension to SIP, allows the transfer of Instant Messages and is also used to carry a
Common Alerting Protocol (CAP) message. Since the MESSAGE request is an extension to SIP, it inherits all the
request routing and security features of that protocol. MESSAGE requests carry the content in the form of MIME body
parts. MESSAGE requests do not themselves initiate a SIP dialog or session.
MESSAGE requests may be sent in the context of a dialog or session initiated by some other SIP request (such as
INVITE), for example in a multi-media call or text messaging session. For more information on MESSAGE please refer
to IETF RFC 3428 [6]. Non-human-associated calls are sent using MESSAGE requests outside of a session. Text
messages or instant messages may be sent using MESSAGE within a session (in which case an interactive associated
stream of such messages is established) or outside a session (in which case a set of disconnected stand-alone messages
are sent). MESSAGE is part of the SIP/SIMPLE presence and messaging system.
6.1.2.3 Required SIP Headers
Table 1 shows the SIP header fields required in the MESSAGE methods, recalling that the Request-URI will contain
urn:service:sos or a sub-service of it as defined in IETF RFC 6881 [15], section 5.
ETSI
18 ETSI TS 103 698 V1.1.1 (2020-12)
Table 1: Required SIP Headers
Header Defined In See section (or Notes
Field/Request IETF RFC 6881 [15])
Request-URI IETF RFC 3261 [3], ED62 1. "urn:service:sos" or a subservice of it
section 8.1.1.1
To IETF RFC 3261 [3], ED62 2. Usually sip:112 or "urn:service:sos"
sections 8.1.1.2 & 20.39
From IETF RFC 3261 [3], ED62 3. Content cannot be trusted unless protected by an
sections 8.1.1.3 & 20.20 Identity header
Via IETF RFC 3261 [3], Occurs multiple times, once for each SIP element in
sections 8.1.1.7 & 20.42 the path
CSeq IETF RFC 3261 [3], Defines the order of transactions in a session
sections 8.1.1.5 & 20.16
Call-ID IETF RFC 3261 [3], This is the SIP call id
sections 8.1.1.4 & 20.8
Call-Info IETF RFC 3261 [3], May contain Additional Data, Call and Incident
sections 8.1.1.10 & 20.9 Tracking IDs
Content-Length IETF RFC 3261 [3],
section 20.14
Content-Type IETF RFC 3261 [3], Used, for example, in IETF RFC 4119 [8] and
sections 8.2.3 & 20.15 IETF RFC 4566 [11]
Geolocation IETF RFC 6442 [14] ED62 8.
Geolocation- IETF RFC 6442 [14] ED62 8. Specifies if the Geolocation header field can be used
Routing for routing
History-Info IETF RFC
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