Internet DRAFT - draft-gundavelli-dispatch-e911-wifi
draft-gundavelli-dispatch-e911-wifi
DISPATCH S. Gundavelli
Internet-Draft M. Grayson
Intended status: Standards Track Cisco
Expires: 14 September 2023 13 March 2023
Emergency 911 Services over Wi-Fi
draft-gundavelli-dispatch-e911-wifi-00.txt
Abstract
Proposed is an approach for supporting emergency 911 services over
IEEE 802.11 based Wi-Fi access networks. This approach leverages the
legal framework and the building blocks of the OpenRoaming federation
for extending emergency 911 calling support to already deployed tens
of thousands of OpenRoaming Wi-Fi hotspots. The proposal addresses
the key issues in emergency calling, around discovery and
authentication to access network supporting emergency services,
emergency access credentials, location determination of the emergency
caller, and delivering emergency voice service configuration to the
device and call routing.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 14 September 2023.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
2.1. Conventions . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Key Service Requirements . . . . . . . . . . . . . . . . . . 7
5. Access Network Location . . . . . . . . . . . . . . . . . . . 7
6. WLAN Network Identification and Selection . . . . . . . . . . 8
7. Legal and Regulatory Requirements . . . . . . . . . . . . . . 8
8. Authentication on the emergency RCOI WLAN . . . . . . . . . . 9
9. Authentication using the sos.fcc-authorized.org realm . . . . 9
10. Emergency CSCF operation for end-users using
sos.fcc-authorized.org credentials . . . . . . . . . . . 9
11. Emergency calling by OpenRoaming subscribers on MNOs . . . . 10
12. Call Flows . . . . . . . . . . . . . . . . . . . . . . . . . 10
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
14. Security Considerations . . . . . . . . . . . . . . . . . . . 14
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
16.1. Normative References . . . . . . . . . . . . . . . . . . 14
16.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
The Federal Communications Commission's (FCC) Communications
Security, Reliability, and Interoperability Council (CSRIC) is
drafting a report to Congress regarding use of Wi-Fi technology to
access emergency 911 services when there is no mobile coverage. The
report will likely detail non-proprietary standards that can support
911 services over IEEE 802.11 based Wi-Fi access technology.
Additional commentary suggests that legal and regulatory changes may
be needed to address liability, privacy, and security concerns
associated with providing public access to 911 over Wi-Fi.
The study looked at the technical feasibility and cost of:
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* making telecommunications service provider-owned Wi-Fi access
points, and other communications technologies operating on
unlicensed spectrum, available to the general public for access to
9-1-1 services, without requiring any login credentials, during
times of emergency when mobile service is unavailable;
* the provision by non-telecommunications service provider-owned Wi-
Fi access points of public access to 9-1-1 services during times
of emergency when mobile service is unavailable; and
* ther alternative means of providing the public with access to
9-1-1 services during times of emergency when mobile service is
unavailable."
We have reviewed these requirements and proposed an approach
leveraging the OpenRoaming federation of Wi-Fi access providers and
Identity Providers for supporting emergency 911 services over
unlicensed Wi-Fi access.
2. Conventions and Terminology
2.1. Conventions
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].
2.2. Terminology
All the mobility terms used in this document are to be interpreted as
defined in the IETF and 3GPP specifications. For convenience, the
definitions for some of the terms are provided below.
Subscription Permanent Identifier (SUPI))
A globally unique 5G Subscription Permanent Identifier (SUPI) is
allocated to each subscriber in the 5G System. The SUPI value is
provisioned in USIM and UDM/UDR function in 5G Core. The
structure of SUPI and its privacy is specified [TS23501]
OpenRoaming (OR)
A federation that provides the framework for connecting
unprecedented footprint of millions of Wi-Fi hotspots with
identity providers.
Identity Provider (IDP)
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An entity that manages identity credentials and policies for
devices and provides authentications services.
Access Network Provider (ANP)
An entity providing internet connectivity services.
Passpoint Profile
Passpoint is a Wi-Fi Alliance (WFA) protocol that enables mobile
devices to discover and authenticate to Wi-Fi hotspots that
provide internet access. Profile includes the user's credentials
and the access network identifiers.
Roaming Consortium Identifier (RCOI)
It is a 3-octet, or a 5-octet value carried in the 802.11 beacon
information element (IE). It is also sent in the ANQP messages.
RCOI identifies the groups or identity providers that are
supported by the network.
Connectivity Location Function (CLF)
It maintains mappings between the endpoint's dynamically assigned
IP address and its physical location. An enhanced CLF maintains
the mapping between the devices' access point identifier (BSSID)
and the physical location.
Public Safety Answering Point (PSAP)
A PSAP is a facility where emergency calls are received under the
responsibility of a public authority.
Route Determination Function (RDF)
It resolves a physical location, either a civic address or a geo-
spatial address to the serving PSAP.
E-CSCF
Enhanced Call Session Control Function. It takes the requests
from P-CSCF (Proxy CSCF) and routes the emergency sessions to the
PSAP based on CLF and RDF queries.
3. Overview
Following are the key aspects in this approach:
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IDP
+==================================+
| IDP: sos.fcc-authorized.org |
| +---+ +------+ |
| |CLF|--------------|E-CSCF| |
| +---+ CLF Query +------+ |
| | for Location | |----><PSAP>
| +---+ +------+ |
| |AAA| |P-CSCF| |
| +---+ +------+ |
+==================================+
. : .
/|\ : /|\
| : |
_----_ | : |
_( Open )_ | : |
----( Roaming )............: |
(_ _) | : |
'----' | : |
| _-----_ |
| _( )_ | P-Access-Network-Info
RADIUS | ( Access )- | SIP Header (RFC 3455)
Attributes | -(_Network)- | and RFC 7315 Defined
(BSSID, Civic-Loc | '-----' | 3GPP Header for carrying
SLT) | | | BSSID and/or SLT
| | |
\|/ | |
. +----+ |
| AP | |
+----+ |
: |
: \|/
+========+
| Device |
+========+
Figure 1: Technical Architecture
There will be a designated Identity Provider (IDP) and designated
emergency calling services for supporting emergency 911 service. The
AAA server in the IDP supports the realm "@sos.fcc-authorized.org"
and the policies for E-911-RCOI (i.e., an E911-specific HotSpot2.0
Roaming Consortium or RCOI). There will also be dedicated P/E-CSCF
(Proxy/Emergency Call Services Control Function) for supporting
emergency calling services. DNS servers for the realm will be
configured to enable ANPs to dynamically discover the designated
IDP's AAA servers.
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The devices are pre-configured with a HotSpot2.0/Passpoint profile,
which includes the emergency RCOI (E-911-RCOI), and a common
identity, e.g., anonymous@sos.fcc-athorized.org. Device eco-systems
vendors can pre-configure this profile into every device at the time
of manufacturing or push an updated profile using established
carrier-bundle based provisioning. This anonymous profile will be
common for all devices. This allows the device to discover Wi-Fi
access networks that support emergency 911 services. Furthermore,
the SIP User Agent in the mobile device will be able to use P/E-CSCF
configuration obtained from the Wi-Fi access network.
Wi-Fi access networks that are part of the OpenRoaming federation and
willing to support emergency 911 services will configure the
emergency RCOI on their WLAN equipment. WLAN OEM suppliers can
augment existing OpenRoaming provisioning interfaces with emergency
RCOI settings. These networks allow any devices without access
credentials to connect to the network for emergency calling. The Wi-
Fi access network will recover the realm from the identity and use
DNS system to discover the designated IDP's AAA servers.
OpenRoaming already requires access networks to provide their Civic
Location and/or Geo-spatial coordinates in the IDP signaling
messages. The location information may be manually configured or can
be obtained from a reliable source. The device will also be able to
discover emergency voice services (CSCF) and the related
configuration from the access network or from a cloud entity. This
allows device to be able to use the emergency e911 services when
connected to access networks that are not part of the OpenRoaming
federation. NOTE that this assumes that the device has basic
internet connectivity and can initiate emergency calls without
requiring emergency calling support from the access network. The
device can include location elements, obtained either from the access
network or from a cloud function, and include them in the SIP
signaling using the Geolocation header fields defined in RFC 6442.
The E-CSCF function will retrieve the location elements from the
signaling messages from the device.
For supporting the architecture based on this approach, we need the
following updates to the WBA OpenRoaming architecture. Cisco has
discussed such change request with WBA that includes:
* enhancement to WBA OpenRoaming technical framework to include use
of emergency RCOI.
* enhancements to OpenRoaming templated legal terms for access
network providers on use of emergency RCOI and associated
requirements, e.g., related to use of existing defined RFC 5580
location attributes.
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* updates to WBA WRIX offered-service VSA to include new string for
"openroaming-emergency" service definition.
* definition of policies required to be enforced by ANP when filter-
id attribute mirrors the "openroaming-emergency" tag.
4. Key Service Requirements
Emergency service considerations for supporting this emergency 911
service.
An emergency call handling service shall be designated to handle Wi-
Fi-enabled 9-1-1 calls, along with an IDP function for the realm
e.g., "sos.fcc-authorized.org", where an existing MNO cannot (non-
provisioned device or MNO core is unavailable). This should consider
third-party providers such as IDPaaS/MNO/Voice Service Providers to
host these services.
Broadband service providers and HotSpot venue operators shall provide
the Civic-Location and or the Geo-spatial coordinates of the venue,
and the emergency voice service configuration to the device in the IP
address configuration procedures.
Consumer devices should be pre-configured by OEMs or through
established carrier-bundle based provisioning with a HotSpot2.0/
Passpoint profile, including the emergency RCOI (E-911-RCOI) and a
common identity such as "anonymous@sos.fcc-authorized.org.".
5. Access Network Location
Location of the caller is a key element in the emergency-service
workflow. Emergency response centers must be able to determine the
location of the caller before service is dispatched. A caller may be
too young, frightened or confused to provide the location of
emergency, therefore automatic location determination by PSAP is an
essential requirement.
The device making the emergency call must be able to obtain the Civic
and/or Geo-spatial coordinates for inclusion in SIP Registration
messages. Reliance on GPS is not an option for most indoor
environments.
The WLANs supporting emergency 911 services should be capable of
providing the Civic Location or the Geo-Spatial coordinates of the
caller, or of the access point. An OpenRoaming access point must be
manually configured with the Civic and/or the Geo-Spatial coordinates
or able to derive location through other means. For example, an
access point operating in 6 GHz Standard Power mode is required to
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include its geo-location in the spectrum grant requests sent to the
AFC. In some environments, the access point can learn the location
information from a connected ethernet switch, or from a broadband
service provider network. Furthermore, any access points supporting
indoor localization services will be able to meet the location
requirement.
It is proposed to re-use the definition of location signaling in
OpenRoaming, enabling the access point to provide the Civic address
and/or the Geo-spatial coordinates of the device or of the access
point to the IDP for CLF population. A confidence-level indicator is
also optionally included in the reported location-data, based on RFC
7459 considerations. This parameter is indicative of the
uncertainity and the confidence level of the reported location.
6. WLAN Network Identification and Selection
The OpenRoaming federation makes extensive use of Passpoint specified
Roaming Consortium Organization Identifiers (RCOIs) for defining
polices that are supported by particular access network providers
(ANPs) and those policies supported by individual identity providers
(IDPs). The supported RCOIs are provisioned in WLAN equipment by the
ANPs and configured in the Passpoint profile of devices managed by
IDPs. Only when there is a match of RCOIs between WLAN and Passpoint
profile will an authentication exchange be triggered. It is proposed
to define the use of an emergency-RCOI for use in the systems to
support E911 only service.
7. Legal and Regulatory Requirements
The OpenRoaming federation has a foundation in a legal framework,
whereby the Wireless Broadband Alliance (WBA) as the federation's
policy authority is responsible for defining the framework under
which the federation operates. WBA defines the privacy policy that
providers are required to comply with as well as end-user terms and
conditions. In addition, WBA defines the legal templated terms that
are used between OpenRoaming brokers and OpenRoaming providers,
defining immutable terms that all OpenRoaming providers need to agree
to. Finally, WBA agrees legal terms directly with OpenRoaming
brokers, including terms that require OpenRoaming brokers to use the
WBA templated terms in their agreements with providers. It is
proposed that these legal agreements be amended with terms that cover
operation of E911 service and allow provisions to indemnify ANPs
against any liabilities resulting from e911 call failures.
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8. Authentication on the emergency RCOI WLAN
The requirements include being able to support emergency calls for
users without valid credentials to fully authenticate to the WLAN, in
this case a credential that has been issued by a specific OpenRoaming
IDP designated to support users without a full credential. 3GPP has
defined an approach that uses a 3GPP defined vendor specific EAP
method called EAP-3GPP-LimitedService for supporting devices without
credentials. However, this vendor specific EAP method is not widely
supported. Instead, this use-case leverages the well supported EAP-
TTLS method with a common set of credentials used by all users
wanting to access on the emergency-RCOI WLAN. The EAP-Identity shall
be specified as anonymous@sos.fcc-authorized.org with common
credentials being used in the inner method.
9. Authentication using the sos.fcc-authorized.org realm
OpenRoaming dynamically discovers the signaling peers used to
authenticate end-users using DNS. The same approaches are re-used by
ANPs to discover the signaling systems used to support the EAP-server
for the sos.fcc-authorized.org realm. The EAP-server will use the
common credentials to authenticate users without valid OpenRoaming
credentials onto the WLAN. OpenRoaming defines the RADIUS messages
exchanged between ANP and IDP. These include the "offered-service"
vendor specific attribute as well as RFC 5580 defined location
attributes. It is proposed to define a new value for the offered
service, e.g., "openroaming-emergency" to unambiguously indicate that
the authentication has come from a WLAN configured with the emergency
RCOI.
10. Emergency CSCF operation for end-users using sos.fcc-authorized.org
credentials
Whereas 3GPP defines the E-CSCF as always operating in the access
network, in this use-case the E-CSCF is a common function that can be
leveraged by all OpenRoaming ANPs that have configured the emergency-
RCOI. This means that the E-CSCF isn't coupled to the access network
by which it can recover network provided location information.
Instead, in this use-case we leverage the existing OpenRoaming
specifications that define the signaling of civic and geo-spatial
location in the RADIUS exchange between ANP and IDP. Unlike in
cellular networks, users on WLAN systems will frequently be allocated
private IP addresses. This IP address information can be included in
the RADIUS exchange between ANP and IDP, but because it will
frequently represent a private address, it cannot be used to uniquely
identify a user. Instead, it is proposed to enhance the Connectivity
Location Function (CLF) to allow querying based on Basic Service Set
ID (BSSID) which represents the MAC address of the WLAN radio
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interface that is serving a user, and optionally a Secure Location
Tag (SLT) which the WLAN system will deliver it to the device. The
BSSID and/or the SLT will be included in the P-ANI SIP header sent by
the device as well as being included in the ANP to IDP RADIUS
signaling. It's proposed that the definition of the IDP hosting the
sos.fcc-authorized.org realm includes support for enhanced CLF
capability that enables the IDP to be queried by an E-CSCF based on
BSSID and/or SLT. The IDP can then match the BSSID and/or SLT with
that received in RADIUS messages originated from individual ANPs and
return the corresponding location information to the E-CSCF.
11. Emergency calling by OpenRoaming subscribers on MNOs
End users who have been provisioned with a full OpenRoaming profile
will successfully authenticate onto the OpenRoaming ANP using their
standard profile and standard OpenRoaming RCOI. As an OpenRoaming
IDP, the MNO is able to similarly match the civic-location and/or
geospatial location of authentication requests with the BSSID and/or
the SLT signaled by the ANP. The MNO operating the CSCF is able to
recover the BSSID and/or the SLT from the P-ANI header and determine
the location of their own users.
12. Call Flows
+---+ +---+ +----+ +---+ +---+ +----+ +----+
|Dev| |AP | |DHCP| |DNS| |AAA| |P/E | |PSAP|
+---+ +---+ +----+ +---+ +---+ |CSCF| +----+
| | | | | +----+ |
| | | | | | |
<1> <2> | | <3> | |
| | | | | | |
|<---<4>-->| | | | | |
|<---<5>-->| | | | | |
|<---<6>-->| | | | | |
| |<----------<7>-------->| | | |
| |<----------<8>------------------->| | |
| | <9> | | | |
|<-----------<10>------| | | | |
| | | | | | |
| <11> | | <12> | |
| | | | | | |
|---<13>-->|----------------<14>------------->| | |
|<--------------------------<15>------------->| | |
|<---------|<---------------<16>--------------| | |
|<---<17>->| | | | | |
| | | | <18> | |
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|<--------------------------<19>--------------|-------->| |
| | | | |<--<20>--| |
| | | | | <21> |
|<----------------------------------------------------->|<-<22>->|
1. Passpoint Profile with Emergency-RCOI,
ananonymous@sos.fcc-authorized.org.
2. Advertises E-RCOI on that BSSID, Civic & Geo-Location Attributes
configured on the AP.
3. IDP & Voice Services for Emergency Calling. Possibly managed by FCC
or WBA. Manages policies for E-RCOI\nand "sos.fcc.org" identities.
4. 802.11u with RCOI in Beacon IE
5. Attach to SSID matching the E-RCOI
6. Authentication Exchange (No credential validation)
7. Realm Lookup (sos.fcc.org) / IDP Discovery
8. TLS Tunnel Setup, Authentication ID federated issued certs
9. Generates location tag (SLT) based\non device indoor positioning, or
location configuration of the AP
10. Delivery of SLT from AN over ANQP/AssocResp/DHCP/IPv6 ND
11. BSSID + SLT (optional) + Location Attributes sent to IDP in the
below RADIUS message exchange
12. E-CSCF FQDN and Emergency\nCalling numbers sent to AN in the below
RADIUS message exchange
13. EAP-ID/Resp / 802.1x
14. EAP over RADUIUS (TLS)
15. EAP-TTLS with well-known credentials
16. EAP-Success
17. Delivers IMS Configuration over 802.11, DHCP, or IPv6 ND
18. Updates the local CLF to include BSSID and/or SLT to Location
Mapping
19. SIP UA Registration includes BSSID and SLT (optional) in the P-ANI
Header
20. CLF Query for Location Check using BSSID and/or SLT
21. Determination of PSAP based on query to RDF
22. Emergency Call Routed to PSAP with location
Figure 2: Emergency e911 Services over Wi-Fi Access
Following is some additional text explaining above interactions.
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* The device is pre-configured with the emergency passpoint profile,
which includes the emergency RCOI, and a common identity,
"anonymous@sos.fcc.org". This allows the device to discover
access networks that support emergency 911 services.
* An 802.11 access network supporting EAP-based authentication
method and is part of the OpenRoaming federation is either
configured with the Civic-Location and/or the Geo Spatial
coordinates of the access point or has the ability to derive
location coordinates through other means.
* The access network for supporting emergency 911 services will
advertise the emergency RCOI in the 802.11 Beacon messages, and
furthermore will respond to any ANQP queries on the supported
services.
* A device that is in coverage of a WLAN but without any valid
conventional access-network credentials may use the UI interaction
to trigger the selection of the profile containing the emergency
RCOI. The end user's selection of an emergency calling
application, or interaction with the default phone application
(e.g., by selecting the emergency call option in the UI or by
dialing an emergency phone number) may trigger the selection of
the Passport profile with the emergency RCOI, resulting in the
device performing a network-attach for emergency-call access.
* The device will use the default identity, "anonymous@sos.fcc.org"
from passpoint profile in the initial authentication message
exchange, allowing the access network to discover the AAA server /
IDP for EAP authentication.
* The access network using the realm portion of the identity,
"sos.fcc.org." will perform a DNS lookup the AAA server for the
IDP supporting the emergency RCOI and the realm.
* The access network and the AAA server will establish a secure TLS
tunnel for securing the 802.1x/EAP traffic between the device and
the IDP. The authentication of the peers will be based on the
OpenRoaming federation issued X.509 certificates.
* The device will complete the EAP authentication using the common
credentials from the emergency passpoint profile. The 802.1x/EAP
messages are tunneled as RADIUS messages between the access point
and the AAA server.
* The access point will generate secure location tag (SLT) for the
device. The SLT will be delivered to the device over one of the
protocols (ANQP/802.11/DHCP/IPv6 ND). SLT is a tag representative
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of the device' location. In another variation, SLT can be a
composite object composed of a signed location by the access
network or a cloud function, along with the identifiers of the
signing entity. Functions such as E-CSCF will be able to verify
the location by verifying the signature of the signing entity.
* The access point includes the BSSID of the access point in the
Calling-Station-Id attribute (RFC 2865) and/or the SLT in a new
attribute to be defined.
* The access point will also include the attributes for carrying the
Civic Location and/or the Geo-Spatial coordinates of the access
point (RFC 5580).
* The AAA server will send the IMS configuration (E-CSCF FQDN)
supporting emergency call routing services to the access point.
* A success EAP transaction between the device and the AAA server
will result in the AAA server sending EAP-SUCCESS to the device.
* The AAA server will update the local CLF function with the
location of the access point, using BSSID and/or the SLT as
location identifiers.
* The access point delivers the IMS configuration to the client over
one of the interfaces (802.11/ANQP/DHCP/IPv6 ND). ANP will apply
policies which limits the usage of the network over emergency RCOI
only for emergency calling. Furthermore, the ANP will apply QoS
policies on the emergency session for ensuring the call meets the
SLA defined for the emergency service. ANP will prioritize
traffic and sessions on emergency RCOI over other RCOIs.
* The IMS client in the device performs registration with the
emergency IMS system. The UA inserts the P-Access-Network-Info
header field in the SIP message using the 3GPP 24.229 defined
fields. It contains the BSSID of the access point (access-
type="IEEE-802.11", wlan-node-id="BSSID", and optionally a secure-
location-tag=SLT). A new parameter, "secure-location-tag" will be
defined.
* The E-CSCF function uses the BSSID and/or the SLT from the P-ANI
header for determination of the device's location. It queries the
CLF for retrieving the Civic and/or the Geo-spatial coordinates of
the access point. The E-CSCF function may query the RDF function
for the PSAP destination address.
* The E-CSCF will route the emergency call to the nearest PSAP.
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13. IANA Considerations
This document does not requires any IANA actions.
14. Security Considerations
network access identifier [RFC7542]
A rogue user or a compromised device may potentially trigger a volume
of emergency calls, including calls spoofing the caller's real
location. The value set for the field, "i-wlan-node-id" in the PANI
header can potentially be a false BSSID which maps to a different
location in the CLF database.
In this use-case, we eliminate this threat with the use of SLT
(Secure Location Tag) that the network will generate dynamically and
will provide it to the device for inclusion in emergency call
signaling.
A trusted OpenRoaming access network signals the same location tag
along with the civic and/or geo-spatial coordinates to the IDP. The
CSCF function will retrieve the SLT from the call signaling from the
device and will look up the civic location and/or geo-spatial
coordinates of the device by querying the CLF database populated by
the IDP. SLT serves as an index to the real-location and the
generated tag is valid for a short duration, thereby eliminating any
replay attacks.
A rogue user or a compromised device may also initiate a volume of
emergency calls, including a valid caller's location. This threat is
not a new threat and exists even in today's emergency services
supported over wireline and cellular architectures.
15. Acknowledgements
We had many discussions with the members of FCC CSRIC 8 WG and that
feedback greatly us greatly in developing this proposal.
16. References
16.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
Gundavelli & Grayson Expires 14 September 2023 [Page 14]
Internet-Draft Emergency 911 Services March 2023
[RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542,
DOI 10.17487/RFC7542, May 2015,
<https://www.rfc-editor.org/info/rfc7542>.
16.2. Informative References
[TS23501] 23.501, 3. T., "Numbering, addressing and identification",
2021.
Authors' Addresses
Sri Gundavelli
Cisco
170 West Tasman Drive
San Jose, CA 95134
United States of America
Email: sgundave@cisco.com
Mark Grayson
Cisco
11 New Square Park
Bedfont Lakes
United Kingdom
Email: mgrayson@cisco.com
Gundavelli & Grayson Expires 14 September 2023 [Page 15]
