RFC 7406
Extensions to the Emergency Services Architecture for Dealing With Unauthenticated and Unauthorized Devices
Extensions to the Emergency Services Architecture for Dealing With Unauthenticated and Unauthorized Devices ✨
okay bestie, this is the title block tea 🍵
- RFC number: 7406 🎀
- Stream: Internet Engineering Task Force (IETF)
- Category: Informational
- ISSN: 2070-1721
- Date: December 2014
- Authors: H. Schulzrinne (Columbia University), S. McCann (BlackBerry Ltd), G. Bajko (MediaTek), H. Tschofenig, and D. Kroeselberg (Siemens Corporate Technology)
- Obsoletes / Updates: this header doesn't list anything it obsoletes or updates 🦋
Abstract 🌸
This doc gives a problem statement, introduces the terminology, and describes an extension to the base IETF emergency services architecture. It's for cases where an emergency caller isn't authenticated, has no identifiable service provider, or has no remaining credit to pay for network access. Main character energy for emergency calls 📞✨
Status of This Memo 💜
This document is not an Internet Standards Track specification; it is published for informational purposes.
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/rfc7406.
Copyright Notice 🔥
Copyright (c) 2014 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 🧚
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Use-Case Categories . . . . . . . . . . . . . . . . . . . . . 5
4. ZBP Considerations . . . . . . . . . . . . . . . . . . . . . 12
5. NASP Considerations . . . . . . . . . . . . . . . . . . . . . 12
5.1. End-Host Profile . . . . . . . . . . . . . . . . . . . . 15
5.1.1. LoST Server Discovery . . . . . . . . . . . . . . . . 15
5.1.2. ESRP Discovery . . . . . . . . . . . . . . . . . . . 15
5.1.3. Location Determination and Location Configuration . . 15
5.1.4. Emergency Call Identification . . . . . . . . . . . . 15
5.1.5. SIP Emergency Call Signaling . . . . . . . . . . . . 15
5.1.6. Media . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1.7. Testing . . . . . . . . . . . . . . . . . . . . . . . 16
5.2. IAP/ISP Profile . . . . . . . . . . . . . . . . . . . . . 16
5.2.1. ESRP Discovery . . . . . . . . . . . . . . . . . . . 16
5.2.2. Location Determination and Location Configuration . . 16
5.3. ESRP Profile . . . . . . . . . . . . . . . . . . . . . . 16
5.3.1. Emergency Call Routing . . . . . . . . . . . . . . . 16
5.3.2. Emergency Call Identification . . . . . . . . . . . . 16
5.3.3. SIP Emergency Call Signaling . . . . . . . . . . . . 17
6. Lower-Layer Considerations for NAA Case . . . . . . . . . . . 17
6.1. Link-Layer Emergency Indication . . . . . . . . . . . . . 18
6.2. Securing Network Attachment in NAA Cases . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 20
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.1. Normative References . . . . . . . . . . . . . . . . . . 21
8.2. Informative References . . . . . . . . . . . . . . . . . 22
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 251. Introduction 📞
Calling the police, the fire department, or an ambulance in an emergency is one of the core, most-loved things a phone does 🚨💖. As phone calls move from circuit-switched telephony to Internet telephony, users rightfully expect that this core function keeps working at least as well as it did with the older tech. New devices and services are popping up that could be used to ask for help. They aren't traditional phones, and people are increasingly expecting them to place emergency calls 🙈.
Roughly speaking, the IETF emergency services architecture (see [RFC6881] and [RFC6443]) splits up the work of handling emergency calls between three players. First, there's the access network, which is the Internet Access Provider (IAP) or ISP. Then there's the application service provider (ASP), which may be a VoIP service provider (VSP). Last, there's the provider of emergency signaling services, the emergency service network (ESN). The access network may provide location information to end systems, but it does not have to provide any ASP signaling functionality. The emergency caller can reach the ESN either directly or through the ASP's outbound proxy. Any of the three parties can provide the mapping from location to the Public Safety Answering Point (PSAP) URI by offering Location-to-Service Translation (LoST) [RFC5222] services 🗺️.
In general, a set of automated configuration mechanisms lets a device work across a variety of architectures without the user needing to know who provides location, mapping services, or call routing. However, if emergency calling is supposed to work when the calling device lacks access network authorization or doesn't have an ASP, one or more of the providers may need to offer extra services and functions 🎀.
In all cases, the end device has to be able to perform a LoST lookup and otherwise conduct the emergency call the same way it would when the three exceptional conditions discussed below don't apply 💅.
We distinguish among three conditions:
- No Access Authentication (NAA): In the NAA case, the emergency caller doesn't possess valid credentials for the access network. This includes the case where the access network allows pay-per-use, as is common for wireless hotspots, but there's not enough time to enter the credit card details and other registration information required for access. It also covers all cases where either no credentials are available at all or the available credentials don't work for the given IAP/ISP. As a result, the NAA case basically combines the No ASP (NASP) and zero-balance ASP (ZBP) cases below, but at the IAP/ISP level. Support for emergency call handling in the NAA case is subject to the local policy of the ISP. Such policy may vary substantially between ISPs and typically depends on external factors that are not under the ISP's control 🌍.
- No ASP (NASP): The caller doesn't have an ASP at the time of the call. This can happen when the caller either doesn't possess any valid subscription for a reachable ASP, or does possess a valid subscription but none of the ASPs are reachable through the ISP.
Note: The interoperability need is increased with this scenario, since the client software used by the emergency caller must be compatible with the protocols and extensions deployed by the ESN. ⚠️
- Zero-balance ASP (ZBP): In the case of a zero-balance ASP, the ASP can authenticate the caller, but the caller isn't authorized to use ASP services, e.g., because the contract has expired or the prepaid account for the customer has been depleted 💸.
These three cases are not mutually exclusive. A caller in need of help may, for example, be both in an NAA and NASP situation, as explained in more detail in Figure 1. Depending on local policy and regulations, it may not be possible to place emergency calls in the NAA case. Unless local regulations require user identification, it should always be possible to place calls in the NASP case, with minimal impact on the ISP. Unless the ESN requires that all calls traverse a known set of Voice Service Providers (VSPs), it is technically possible to let a caller place an emergency call in the ZBP case. We discuss each case in more detail in Section 3 🧠.
Some of the functionality provided in this document is already available in the Public Switched Telephone Network (PSTN). Consequently, there's real-world experience to learn from, and not all of it is positive 😬. For example, the functionality of calls without Subscriber Identity Modules (SIMs) in today's cellular system has led to a fair amount of hoax or test calls in certain countries.
This causes overload situations at PSAPs, which is considered harmful to the overall availability and reliability of emergency services 🚫.
As an example, the Federal Office of Communications (OFCOM, Switzerland) provided statistics about emergency (112) calls in Switzerland from Jan. 1997 to Nov. 2001. Switzerland did not offer SIM-less emergency calls except for almost a month in July 2000, when a significant increase in hoax and test calls was reported. As a consequence, the functionality was disabled again. More details can be found in the panel presentations of the 3rd Standards Development Organization (SDO) Emergency Services Workshop [esw07]. 🇨🇭
2. Terminology 💜
In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in [RFC2119].
This document reuses terminology from [RFC5687] and [RFC5012], namely Internet Access Provider (IAP), Internet Service Provider (ISP), Application Service Provider (ASP), Voice Service Provider (VSP), Emergency Service Routing Proxy (ESRP), Public Safety Answering Point (PSAP), Location Configuration Server (LCS), (emergency) service dial string, and (emergency) service identifier 🎀✨
3. Use-Case Categories ✨
okay so bestie, picture this 🎀 an end host is NOT attached to the network, and the user is starting to place an emergency call 🚨. Here's what the device has to do, in order, no cap 💅
Link-Layer Attachment 🔌: Some networks have added support for unauthenticated emergency access, and others advertise that they can do it using layer beacons (multicast or broadcast announcements) 📡. The end host finds out about these unauthenticated emergency services capabilities from either the link layer type or the advertisement. Then it uses the link-layer-specific network attachment procedures for unauthenticated network access to actually get on the network 🦋
Pre-emergency Service Configuration ⚙️: Once the link-layer attachment is done, the end host picks up basic configuration info using DHCP from the ISP 🌸 Then it uses a Location Configuration Protocol (LCP) to grab location information 📍 After that, the LoST protocol [RFC5222] comes in to figure out the relevant emergency numbers and get the PSAP URI for that location. Iconic teamwork 👑
Emergency Call 📞: When someone needs help, a user dials an emergency number, and the SIP User Agent (UA) kicks off the emergency call procedures by talking to the PSAP. Main character moment 💖
Figure 1 is giving full flowchart energy 🧚 It lays out the basic logic for network entry when you're requesting an emergency service, and it shows how the three conditions above connect to each other ✨
+-----Y
|Start|
`...../
|
| Are credentials
| for network attachment
| available?
|
NO v YES
+----------------------------+
| |
| |
V v
.............. ................
| Idle: Wait | |Execute |
| for ES Call| |LLA Procedures|
| Initiation | "--------------'
"------------' |
Is | +---------->O
emergency | | | Is ASP
service | NO +-----Y | | configured?
network +--->| End | | +---------------+
attachment| `...../ | YES | | NO
possible? | | | |
v | v v
+------------+ | +------------+ +------------+
| Execute | | | Execute | | Execute |
| NAA |--------+ | Phone BCP | | NASP |
| Procedures | | Procedures | | Procedures |
+------------+ +------------+ +------------+
Authorization for| |
making an | |
emergency call | |
with the ASP/VSP?| |
+--------------+ v
| NO | YES +-----Y
| | | Done|
v v `...../
+------------+ +------------+
| Execute | | Execute |
| ZBP | | Phone BCP |
| Procedures | | Procedures |
+------------+ +------------+
| |
| |
v v
+-----Y +-----Y
| Done| | Done|
`...../ `...../
Abbreviations:
LLA: Link-Layer Attachment
ES: Emergency Services
Figure 1: Flow Diagram: NAA, ZBP, and NSAP ScenariosAbbreviations, quick recap 🤓
- LLA: Link-Layer Attachment
- ES: Emergency Services
The diagrams below zoom in on the most important steps for the three cases 🔍 Here's the first one:
+-----Y
|Start|
`...../
|
| No
| credentials
| for network access
| available
v
..............
| Idle: Wait |
| for ES Call|
| Initiation |
"------------'
|
|
|
v
--
// --
/ --
// Is --
/ emergency --
| service | NO +--------+
| network |------>| Call |
| attachment | Failed |
\ possible? / `......../
\ //
\\ //
\ //
\--/
|
| YES
|
|
v
+------------+
| Execute |
| NAA |
| Procedures |
+------------+
|
| Network
| attachment
| in progress
v
/--\ Continue
| | with
| | application-layer
\--/ interaction
Figure 2: Flow Diagram: NAA ScenarioNext up, the ZBP scenario 🦋
+-----+
+------------|Start|-----------------+
| `...../ |
v v
+------------+ +----------------+
| NAA | | Regular |
| Procedures | | Network Access |
+------------+ | Procedures |
| +----------------+
| |
| |
----------------o--------------------+
|
|
|
|
Network
Attachment
Completed
|
|
|
|
v
+------------+ +---------+
| ASP | NO | See |
| Configured?|----->| main |
+------------+ | diagram |
| `........./
|
| YES
|
v
//----
/ --
// --
/ - +---------+
| Authorization| YES | See |
| for making |------>| main |
| ES call | | diagram |
\ with / `........./
\ VSP/ASP? //
\\ //
\ //
\--/
|
| NO
|
|
v
+------------+
| Execute |
| ZBP |
| Procedures |
+------------+
|
| Call
| in progress
|
v
+--------+
| Call |
Success|
`......../
Figure 3: Flow Diagram: ZBP ScenarioAnd last but not least, the NASP scenario 💅
+-----+
+------------|Start|-----------------+
| `...../ |
v v
+------------+ +----------------+
| NAA | | Regular |
| Procedures | | Network Access |
+------------+ | Procedures |
| +----------------+
| |
| |
----------------o--------------------+
|
|
|
|
Network
Attachment
Completed
|
|
|
|
v
+------------+ +---------+
| ASP | YES | See |
| Configured?|----->| main |
+------------+ | diagram |
| `........./
|
| NO
|
v
+------------+
| Execute |
| NASP |
| Procedures |
+------------+
|
| Call
| in progress
|
v
+--------+
| Call |
| Success|
`......../
Figure 4: Flow Diagram: NASP ScenarioWhere to find the procedure details 🗺️ The NAA procedures are described in Section 6. The ZBP procedures are described in Section 4. The NASP procedures are described in Section 5. The Phone BCP procedures are described in [RFC6881]. And the LLA procedures? Not covered in this document, since they depend on whichever link-layer technology is in use 🌈
4. ZBP Considerations 🎀
okay so ZBP covers every case where an ASP knows who the subscriber is, but they just aren't authorized to use the regular ASP services 💅 Think empty prepaid accounts, barred accounts, roaming and mobility restrictions, or literally any other condition the ASP's policy sets 😭
Now the emergency part 🚨 Local regulation might say emergency calls can't go through without successful service authorization. But in some regulatory regimes it may be possible to let emergency calls continue even when authorization fails ✨ To tell an emergency call apart from a regular one, an ASP can check the service URN [RFC5031] used in call setup 🔍 So the ZBP case only affects the ASP, not anyone else 💖
Letting a call through despite authorization failures could be an opportunity for abuse 💀 The ASP may choose to verify the destination of emergency calls and only allow calls to certain preconfigured entities (e.g., local PSAPs) 🏫 Section 7 gets way more into this topic 🧠
An ASP without a regulatory requirement to authorize emergency calls can deny emergency call setup 🙅♀️ When an ASP doesn't authorize an emergency call, the caller may be able to fall back to NASP procedures 🔁
5. NASP Considerations 🌸
okay let's walk through an emergency call step by step using Figure 5 🦋
- First up, the devices attach to the network, as shown in step (1). This step is outside the scope of this section.
- Once the link-layer network attachment is done, the end host gets its basic IP configuration from the ISP using DHCP, as shown in step (2).
- When the end host has configured its IP address, it starts talking to the discovered LCS at the ISP, as shown in step (3). In certain deployments, the ISP may need to interact with the IAP. That protocol exchange is shown in step (4).
- Once location information is obtained, the end host triggers the LoST protocol to get the address of the ESRP/PSAP. This is shown in step (5).
- In step (6), the SIP UA sends a SIP INVITE request to the indicated ESRP. The INVITE message contains all the necessary parameters required by Section 5.1.5.
- The ESRP receives the INVITE and processes it according to the description in Section 5.3.3.
- The ESRP routes the call to the PSAP, as shown in step (8), and may interact with a LoST server first to figure out the route.
- The PSAP evaluates the initial INVITE and aims to complete the call setup.
- Finally, once call setup is complete, media traffic can be exchanged between the PSAP and the SIP UA. ✨
For brevity, the end-to-end SIP and media exchange between the PSAP and SIP UA is not shown in Figure 5.
+-------+
| PSAP |
| |
+-------+
^
| (8)
|
+----------+(7) +----------+
| LoST |<-->| ESRP |
| Server | | |
+----------+ +----------+
^ ^
+----------------+----------------|--------------+
| ISP | | |
|+----------+ | | +----------+|
|| LCS-ISP | (3)| | | DHCP ||
|| |<-+ | | | Server ||
|+----------+ | | | +----------+|
+-------^------+-+----------------|-----------^--+
+-------|------+-+----------------|-----------|--+
| IAP | (4) | |(5) | | |
| V | | | | |
|+----------+ | | | | |
|| LCS-IAP | | | +--------+ | | |
|| | | | | Link- | |(6) | |
|+----------+ | | | Layer | | | |
| | | | Device | | (2)| |
| | | +--------+ | | |
| | | ^ | | |
| | | | | | |
+--------------+-|-------|--------|-----------|--+
| | | | |
| | (1)| | |
| | | | |
| | | +----+ |
| | v | |
| | +----------+ |
| +->| End |<-------------+
+___>| Host |
+----------+
Figure 5: Architectural OverviewNote: Figure 5 doesn't show who operates the ESRP and the LoST server. Lots of deployment options exist 🌈
5.1. End-Host Profile 📱
5.1.1. LoST Server Discovery
The end host MUST discover a LoST server [RFC5222] using DHCP [RFC5223], unless a LoST server has already been provisioned some other way 🫶
5.1.2. ESRP Discovery
The end host MUST discover the ESRP using the LoST protocol [RFC5222], unless an ESRP has been provisioned using other means 🗺️
5.1.3. Location Determination and Location Configuration
The end host MUST support location acquisition and the LCPs described in Section 6.5 of [RFC6881]. The descriptions in Sections 6.5 and 6.6 of [RFC6881] about how the device and the Location Information Server (LIS) interact apply to this document 📍
The SIP UA in the end host MUST attach available location information in a Presence Information Data Format Location Object (PIDF-LO) [RFC4119] when making an emergency call. When building the PIDF-LO, the guidelines in the PIDF-LO profile [RFC5491] MUST be followed. For civic location information, the format defined in [RFC5139] MUST be supported 💅
5.1.4. Emergency Call Identification
To work out which calls are emergency calls, some entity needs to map a user-entered dial string into this URN scheme. A user may "dial" 1-1-2, 9-1-1, etc., but the call would be sent to urn:service:sos. This mapping SHOULD be performed at the endpoint device 📞
End hosts MUST use the Service URN mechanism [RFC5031] to mark calls as emergency calls for their home emergency dial string 🚑
5.1.5. SIP Emergency Call Signaling
SIP signaling capabilities [RFC3261] are REQUIRED for end hosts 📨
The initial SIP signaling method is an INVITE. The SIP INVITE request MUST be constructed according to the requirements in Section 9.2 of [RFC6881] 💌
To enable callbacks, SIP UAs SHOULD place a globally routable URI in a Contact header field 🔁
5.1.6. Media
Endpoints MUST comply with the media requirements for endpoints placing an emergency call, as described in Section 14 of [RFC6881] 🎙️
5.1.7. Testing
The description in Section 15 of [RFC6881] is fully applicable to this document 🧪
5.2. IAP/ISP Profile 🏢
5.2.1. ESRP Discovery
An ISP MUST provision a DHCP server with information about LoST servers [RFC5223]. An ISP operator may choose to run a LoST server itself or outsource it to other parties 🛠️
5.2.2. Location Determination and Location Configuration
The ISP is responsible for location determination and exposes this information to the endpoints via location configuration protocols. The considerations described in [RFC6444] are applicable to this document 🧭
The ISP MUST support one of the LCPs described in Section 6.5 of [RFC6881]. The descriptions in Sections 6.5 and 6.6 of [RFC6881] about how the end device and the LIS interact apply to this document 🤝
The interaction between the LIS at the ISP and the IAP is often proprietary, but the description in [LIS] may be relevant to the reader 👀
5.3. ESRP Profile 🏛️
5.3.1. Emergency Call Routing
The ESRP continues to route the emergency call to the PSAP responsible for the physical location of the end host. This may require further interactions with LoST servers, but it depends on the specific deployment 🗺️
5.3.2. Emergency Call Identification
The ESRP MUST understand the Service URN mechanism [RFC5031] (i.e., the 'urn:service:sos' tree) 🔍
5.3.3. SIP Emergency Call Signaling
SIP signaling capabilities [RFC3261] are REQUIRED for the ESRP. The ESRP MUST process the messages sent by the client, according to Section 5.1.5 📬
Furthermore, if a PSAP wants to support NASP calls, then it MUST NOT restrict incoming calls to a particular set of ASPs. that's a big deal, bestie 🌈
6. Lower-Layer Considerations for NAA Case 🌐
Some networks have added support for unauthenticated emergency access, while others have advertised these capabilities using layer beacons. The end host learns about these unauthenticated emergency services either from the link-layer type or from an advertisement 📡
It's important to highlight that the NAA case is inherently a Layer 2 problem. The general form of the solution is to provide an "emergency only" access type, with appropriate limits or monitoring to prevent abuse 🔒 The described mechanisms are informative in nature, since their relationship to the IETF emergency services architecture is only indirect. It runs through some protocols developed within the IETF (e.g., EAP and EAP methods) that require extensions to support this functionality 🧩
This section discusses different methods to indicate an emergency service request as part of network attachment. It gives some general considerations and recommendations that aren't specific to any access technology 🦋
To do network attachment and get access to the resources provided by an IAP/ISP, the end host uses access technology-specific network attachment procedures, including network detection and selection, authentication, and authorization. For initial network attachment of an emergency service requester, how the emergency indication is given to the IAP/ISP is specific to the access technology. However, a number of general approaches can be identified 💫
- Link-layer emergency indication: The end host provides an indication, e.g., an emergency parameter or flag, as part of the link-layer signaling for initial network attachment. Examples include an emergency bit signaled in the IEEE 802.16-2009 wireless link. In IEEE 802.11 WLAN [IEEE802.11], an emergency support indicator allows the station (i.e., the end host in this context) to download before association to a Network Access Identifier (NAI), which it can use to request server-side authentication only for an IEEE 802.1X network 📶
- Higher-layer emergency indication: Typically, the emergency indication is provided in the network access authentication procedure. The emergency caller's end host provides an indication as part of the access authentication exchanges. Authentication via the EAP [RFC3748] is of particular relevance here. Examples are the EAP NAI decoration used in Worldwide Interoperability for Microwave Access (WiMAX) networks and the modification of the authentication exchange in IEEE 802.11 [nwgstg3] 🔐
6.1. Link-Layer Emergency Indication
okay so link-layer emergency indications are lowkey the dream for getting an emergency request noticed super early in network attachment, like before anything else even happens 🚨✨ the catch is that end hosts supporting these methods isn't something you can count on being everywhere 🥺
No general recommendations are given in the scope of this memo, and there are a few reasons for that 💅:
- It depends on the specific access technology 🛜
- It depends on the specific access network architecture 🏗️ Access authorization and policy decisions usually happen at different layers of the protocol stack, and in different entities than the ones that terminate the link-layer signaling. So link-layer indications have to be passed along and translated between the different layers and entities involved. The right methods are specific to the actual architecture of the IAP/ISP network 🧩
- Combining emergency indications with the actual network attachment procedure (the part doing authentication and authorization) is giving main character energy 👑 The emergency indication can be taken into account directly by the authentication and authorization server that owns the policy for granting access to network resources. That means there's no direct dependency on the access network architecture, which would otherwise have to handle merging link-layer indications into the authentication, authorization, and policy decision process 🙌
- EAP signaling happens at a fairly early stage of network attachment, so it's likely to match most requirements for prioritizing emergency signaling 💖 But it doesn't cover the early stages of link-layer activity in the network attachment process 🙈 Conflicts might come up, for example when filtering is based on Media Access Control (MAC) in entities that terminate link-layer signaling in the network (like a base station 📡). In normal operation, EAP-related information is only recognized in the Network Access Server (NAS). Any entity sitting between the end host and the NAS should not be expected to understand or parse EAP messages 🫠
- An emergency indication can be given by forming a specific NAI that's used as the identity in EAP-based authentication for network entry 🪪✨
6.2. Securing Network Attachment in NAA Cases
For network attachment in NAA cases, it may make sense to secure the link-layer connection between the device and the IAP/ISP 🔐 This is especially true for wireless access, with examples being access based on IEEE 802.11 or IEEE 802.16. The latter even mandates secured communication across the wireless link for all IAP/ISP networks based on [nwgstg3] 😤
So for network attachment that's by default based on EAP authentication, it's desirable for NAA network attachment to also use a key-generating EAP method. That kind of method provides a Master Session Key (MSK) to the authenticator, which bootstraps further key derivation for protecting the wireless link 🗝️💜
To match the above, the following approaches can be identified 🦋:
- Server-Only Authentication: The device of the emergency service requester performs an EAP method with the IAP/ISP EAP server, and only the server side gets authenticated. An example of this is EAP-TLS [RFC5216]. This gives the device user a certain level of assurance about the IAP/ISP 🫶 It requires the device to be provisioned with appropriate trusted root certificates so it can verify the server certificate of the EAP server (unless this step is explicitly skipped in the device in case of an emergency service request). This method is used to give devices without existing credentials access to an IEEE 802.1X network. The details are incorporated in the IEEE 802.11-2012 specification [IEEE802.11] 📘
- Null Authentication: In one case (e.g., WiMAX), an EAP method is performed, but no credentials specific to the server, the device, or the subscription are used as part of the authentication exchange 🫥 An example would be an EAP-TLS exchange using the
TLS_DH_anon(anonymous) ciphersuite. Alternatively, a publicly available static key for emergency access could be used. In that latter case, the device would need to be provisioned with the appropriate emergency key for the IAP/ISP in advance 🔑 In another case (e.g., IEEE 802.11), no EAP method is used, so empty frames are transported during the over-the-air IEEE 802.1X exchange. In this case, the authentication state machine completes with no cryptographic keys being exchanged 🌸 - Device Authentication: This case extends the server-only authentication case 🚀 If the device is configured with a device certificate, and the IAP/ISP EAP server can rely on a trusted root that allows the EAP server to verify the device certificate, then at least the device identity (e.g., the MAC address) can be authenticated by the IAP/ISP in NAA cases. An example is WiMAX devices that ship with device certificates issued under the global WiMAX device public-key infrastructure 🏷️ To make unauthenticated emergency calls (if the IAP/ISP allows it), such devices perform network attachment based on EAP-TLS with client authentication based on the device certificate 🧚
7. Security Considerations 🔒
The security threats discussed in [RFC5069] are applicable to this document. Bestie, please pay attention to this part 🥹
The NASP and NAA cases introduce new vulnerabilities, since the PSAP operator will typically have no information about the identity of the caller via the signaling path 😭 Today, in countries where this functionality is used for Global System for Mobile Communications (GSM) networks, this has led to a significant amount of misuse 💀
In the context of NAA, the IAP and the ISP will probably want to make sure that the claimed emergency caller really is placing an emergency call, and not using the network for other purposes while acting fraudulently by skipping any authentication, authorization, and accounting procedures 🚫 By restricting the unauthenticated emergency caller's access to the LoST server and the PSAP URI, traffic can be restricted to only emergency calls 🎀 This can be accomplished with traffic separation. However, the details (e.g., for using filtering) depend on the deployed ISP architecture and are beyond the scope of this document 🙃
We only illustrate a possible model 🧩 If the ISP runs its own (caching) LoST server, the ISP would maintain an access control list populated with IP-address information obtained from LoST responses (in the mappings). These URIs would either be URIs for contacting further LoST servers or PSAP URIs. It may be necessary to translate domain names returned in LoST responses to IP addresses. Since the media destination addresses are not predictable, the ISP also has to provide a SIP outbound proxy so that it can determine the media addresses and add those to the filter list 📝
For the ZBP case, the additional aspect of fraud has to be considered 🚨 Unless the emergency call traverses a PSTN gateway or the ASP charges for IP-to-IP calls, there is little potential for fraud. If the ASP also operates the LoST server, the outbound proxy MAY restrict outbound calls to the SIP URIs returned by the LoST server. It is NOT RECOMMENDED to rely on a fixed list of SIP URIs, as that list may change 🙅♀️
RFC 6280 [RFC6280] discusses security vulnerabilities caused by an adversary faking location information and thereby lying about the actual location of the emergency caller 👀 These threats may be less problematic in the context of an unauthenticated emergency, when location information can be verified by the ISP to fall within a specific geographical area 🌍
8. References 📚
8.1. Normative References
- [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997,
http://www.rfc-editor.org/info/rfc2119. 💖 - [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002,
http://www.rfc-editor.org/info/rfc3261. 📞 - [RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object Format", RFC 4119, December 2005,
http://www.rfc-editor.org/info/rfc4119. 🗺️ - [RFC5031] Schulzrinne, H., "A Uniform Resource Name (URN) for Emergency and Other Well-Known Services", RFC 5031, January 2008,
http://www.rfc-editor.org/info/rfc5031. 🆘 - [RFC5139] Thomson, M. and J. Winterbottom, "Revised Civic Location Format for Presence Information Data Format Location Object (PIDF-LO)", RFC 5139, February 2008,
http://www.rfc-editor.org/info/rfc5139. 🏠 - [RFC5222] Hardie, T., Newton, A., Schulzrinne, H., and H. Tschofenig, "LoST: A Location-to-Service Translation Protocol", RFC 5222, August 2008,
http://www.rfc-editor.org/info/rfc5222. 🧭 - [RFC5223] Schulzrinne, H., Polk, J., and H. Tschofenig, "Discovering Location-to-Service Translation (LoST) Servers Using the Dynamic Host Configuration Protocol (DHCP)", RFC 5223, August 2008,
http://www.rfc-editor.org/info/rfc5223. 🔎 - [RFC5491] Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV Presence Information Data Format Location Object (PIDF-LO) Usage Clarification, Considerations, and Recommendations", RFC 5491, March 2009,
http://www.rfc-editor.org/info/rfc5491. ✨ - [RFC6881] Rosen, B. and J. Polk, "Best Current Practice for Communications Services in Support of Emergency Calling", BCP 181, RFC 6881, March 2013,
http://www.rfc-editor.org/info/rfc6881. 🌈
8.2. Informative References 📚
okay so these are the "good to know" refs, bestie. you don't have to read them to implement the thing, but they're the receipts 💅
[IEEE802.11] IEEE, "IEEE Standard for Information Technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications", IEEE Std 802.11-2012, March 2012, <http://standards.ieee.org/about/get/802/802.11.html>. 📶
[LIS] Winterbottom, J. and S. Norreys, "LIS to LIS Protocol Requirements", Work in Progress, draft-winterbottom-geopriv-lis2lis-req-01, November 2007. 🌸
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004, <http://www.rfc-editor.org/info/rfc3748>. 🔐
[RFC5012] Schulzrinne, H. and R. Marshall, "Requirements for Emergency Context Resolution with Internet Technologies", RFC 5012, January 2008, <http://www.rfc-editor.org/info/rfc5012>. 🚨
[RFC5069] Taylor, T., Tschofenig, H., Schulzrinne, H., and M. Shanmugam, "Security Threats and Requirements for Emergency Call Marking and Mapping", RFC 5069, January 2008, <http://www.rfc-editor.org/info/rfc5069>. 🛡️
[RFC5216] Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS Authentication Protocol", RFC 5216, March 2008, <http://www.rfc-editor.org/info/rfc5216>. 🎀
[RFC5687] Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7 Location Configuration Protocol: Problem Statement and Requirements", RFC 5687, March 2010, <http://www.rfc-editor.org/info/rfc5687>. 📍
[RFC6280] Barnes, R., Lepinski, M., Cooper, A., Morris, J., Tschofenig, H., and H. Schulzrinne, "An Architecture for Location and Location Privacy in Internet Applications", BCP 160, RFC 6280, July 2011, <http://www.rfc-editor.org/info/rfc6280>. 🗺️
[RFC6443] Rosen, B., Schulzrinne, H., Polk, J., and A. Newton, "Framework for Emergency Calling Using Internet Multimedia", RFC 6443, December 2011, <http://www.rfc-editor.org/info/rfc6443>. 📞
[RFC6444] Schulzrinne, H., Liess, L., Tschofenig, H., Stark, B., and A. Kuett, "Location Hiding: Problem Statement and Requirements", RFC 6444, January 2012, <http://www.rfc-editor.org/info/rfc6444>. 🙈
[esw07] "3rd Standards Development Organziations (SDO) Emergency Services Workshop", October 30th - November 1st 2007, <http://www.emergency-services-coordination.info/2007Nov/>. 🗓️
[nwgstg3] WiMAX Forum, "WiMAX Forum Network Architecture - Detailed Protocols and Procedures Base Specification", Stage-3 WMF-T33-001-R022V02, April 2014, <http://resources.wimaxforum.org/sites/wimaxforum.org/files/technical_document/2014/05/WMF-T33-001-R022v02_Network-Stage3-Base.pdf>. 📡
Acknowledgments 🫶
okay the thank-yous 🥹 parts of this doc are derived from [RFC6881], and the folks at the 2nd and 3rd SDO Emergency Services Workshop gave super helpful input, so big love to them 💜
we also owe a huge thank you to Richard Barnes, Marc Linsner, James Polk, Brian Rosen, and Martin Thomson for their feedback at the IETF#80 Emergency Context Resolution with Internet Technology (ECRIT) meeting 🌈
and then Martin Thomson and Bernard Aboba did a detailed document review ahead of the 81st IETF meeting, which is literally the most thorough bestie behaviour ever 🔥 Alexey Melnikov was the General Area (Gen-Art) reviewer 🧚 a bunch of changes happened after the AD review by Richard Barnes too ✨
last but not least, Spencer Dawkins, Stephen Farrell, Joel Jaeggli, Barry Leiba, Ted Lemon, and Pete Resnick all gave IESG review comments 👑 the whole squad showed up 😭
Authors' Addresses 📮
here's where to find the authors, iykyk 🦋
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
United States
Phone: +1 212 939 7004
EMail: hgs+ecrit@cs.columbia.edu
URI: http://www.cs.columbia.edu
Stephen McCann
BlackBerry Ltd
200 Bath Road
Slough, Berks SL1 3XE
United Kingdom
Phone: +44 1753 667099
EMail: smccann@blackberry.com
URI: http://www.blackberry.com
Gabor Bajko
MediaTek
EMail: gabor.bajko@mediatek.com
Hannes Tschofenig
Hall in Tirol 6060
Austria
EMail: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
Dirk Kroeselberg
Siemens Corporate Technology
Otto-Hahn-Ring 6
Munich 81739
Germany
EMail: dirk.kroeselberg@siemens.comand that's a wrap on RFC 7406, bestie!! 🌈💖✨
📦 where this page comes from
- ietf: rfc7406 2014-12
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms