Internet DRAFT - draft-barnes-atoca-meta
draft-barnes-atoca-meta
ATOCA M. Lepinski
Internet-Draft BBN Technologies
Intended status: Informational K. Seo
Expires: January 16, 2013 BBN Technologes
R. Barnes
BBN Technologies
July 15, 2012
Alert Metadata Protocol (AMP)
draft-barnes-atoca-meta-03.txt
Abstract
This document specifies a set of mechanisms that devices on an IP
network can use to discover an alert metadata server able to provide
information about local emergency alert services. Additionally, this
document provides a protocol that devices on an IP network can use to
retrieve local information from an alert metadata server about
sources of emergency alerts and register contact information for
receipt of alerts.
Please send feedback to the atoca@ietf.org mailing list.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 16, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Open Questions . . . . . . . . . . . . . . . . . . . . . . 4
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Server Discovery . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Discovery using Access Network Domain Name . . . . . . . . 5
3.1.1. NAPTR Record Format . . . . . . . . . . . . . . . . . 6
3.1.2. Client Processing . . . . . . . . . . . . . . . . . . 7
3.2. Discovery using LoST . . . . . . . . . . . . . . . . . . . 7
3.2.1. LoST Server Discovery . . . . . . . . . . . . . . . . 7
3.2.2. Client Processing . . . . . . . . . . . . . . . . . . 7
4. AMP Protocol . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Message Format . . . . . . . . . . . . . . . . . . . . . . 8
4.1.1. Advertisement . . . . . . . . . . . . . . . . . . . . 8
4.1.2. Registration . . . . . . . . . . . . . . . . . . . . . 9
4.1.3. Refer . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1.4. Alert . . . . . . . . . . . . . . . . . . . . . . . . 11
4.2. AMP Sessions . . . . . . . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
5.1. AMP Message Type Registry . . . . . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
In order for clients to securely receive alerts, both endpoints and
servers may need a certain amount of configuration. Clients need to
know the identities of trusted alerting authorities so that they can
reject false alerts. In some environments, servers need to gather
location and contact information for end clients to support alert
targeting and delivery, for example client location, language
preferences, or device capabilities.
In this context, alert delivery proceeds in three phases. First, a
client device connects to a network where alerts are provided and
discovers a local alert metadata server. Second, the device
discovers an alert metadata server, downloads information about local
alert servers, and (optionally) registers some information about
itself. Third, an alert server delivers an alert to the client.
These roles are illustrated in Figure 1. This document addresses the
first two phases (discovery and configuration), and provides one
possible channel for alert delivery.
+-------------------+
| AMP Discovery |
+-(1) AMP Srv. URI--| (DHCP, DNS, LoST) |
| +-------------------+
|
|
|
|
V
+--------+ +-------------------+
| AMP |--(2) AMP Reg.-->| AMP |
| Client |<-(2) AMP Adv.---| Server |
+--------+ +-------------------+
^
|
|
|
|
| +-------------------+
+-(3) Alert Msg.----| Alert Server |
+-------------------+
Figure 1: AMP alert configuration
This document addresses this problem in two parts. First, we
describe the process by which a client discovers an AMP server for a
local network or for a location of interest. Second, we define a
simple protocol that the client can use to interact with the server
to download metadata, register state, and receive alerts.
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1.1. Open Questions
The current version of this draft specifies transport security (i.e.,
TLS) as the only mechanism for providing security for AMP messages.
However, this document could also specify as an option the use the
mechanisms defined by of the JOSE working group to provide object
security for the JSON bodies on a per-message basis (independent of
the underlying transport).
The current version of this draft specifies only a WebSocket
transport for AMP messages. However, as an alternative this document
could also specify an option to use HTTP as a transport for AMP
messages.
2. Definitions
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].
The following entities are important in the AMP protocol:
Client: An end-user device interested in receiving alerts. The
device may be connected to a local network in the area covered by
alerts, or may be remote.
Alert Metadata Server: A server that maintains information about
clients and information about how alerts are delivered within some
scope (e.g., within a jurisdiction).
Alert Server: A server that delivers emergency alerts to clients.
Alerting Authority: An entity that is authorized to originate alerts
in a given context (e.g., a jurisdiction)
In a given deployment, the Alert Metadata Server and the Alert Server
may be the same server, but this is not necessarily the case.
3. Server Discovery
In this section we describe two mechanisms for clients to discover
alert metadata servers. The first mechanism enables a client to rely
upon its ISP or access network to provide a reference to an
appropriate alert metadata server. Many alerting scenarios are local
(e.g., natural disasters) and ISPs are often well-positioned to
gather information on their local environment. Therefore, it can be
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useful for an ISP to provide information about local alerting
resources to clients. Likewise, clients should be able to discover
information advertised by their local networks. This first
mechanism, is based on the discovery procedure described in RFC 5986
[RFC5986]. It relies on a DHCP option specifying the Access Network
Domain Name, and a U-NAPTR resolution that uses the Access Network
Domain Name to obtain the name of the alert metadata server.
The second mechanism enables a client to discover an alert metadata
server with information about alerts relevant to a particular
location. This may be the client's own location, or some other
location of interest. This mechanism may be used either in cases
where the client's ISP does not provide explicit support for
emergency alerting, or in cases where the client is interested in
receiving alerts for some region that does not include the client's
current location. This mechanism makes use of the LoST protocol
[RFC5222], and its corresponding discovery mechanism [RFC5223].
Client implementations SHOULD support both discovery using the Access
Network Domain Name (Section 3.1) and discovery based using LoST
(Section 3.2). Additionally, client implementations SHOULD support
out-of-band discovery by allowing a user to specify a static URI for
an appropriate alert metadata server.
3.1. Discovery using Access Network Domain Name
The mechanism presented here is based on the discovery procedure
described in RFC 5986 [RFC5986]. It relies on the DHCP option for
Access Network Domain Name, which is specified in RFC 5986 for both
DHCPv4 and DHCPv6. IP networks that support emergency alerting
SHOULD provide the Access Network Domain Name option to devices on
network that are configured via DHCP. This option provides to the
device a domain name that is suitable for service discovery within
the access network.. This domain is used as input to the U-NAPTR
resolution process for alert server discovery.
In addition to providing the Access Network Domain Name to devices
via DHCP, an IP network that supports emergency alerting SHOULD
provision DNS records to support a U-NAPTR lookup for AMP Server
discovery. U-NAPTR [RFC4848] is a Dynamic Delegation Discovery
Service (DDDS) profile that produces a URI (in this case, the URI for
the appropriate AMP alert server). Section 3.1.1 specifies the
format of the DNS NAPTR record used for this discovery, and Section
3.1,2 provides processing instructions for the client device
performing the discovery.
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3.1.1. NAPTR Record Format
U-NAPTR resolution for an alert server takes a domain name as input
and produces a URI that identifies the alert server. This process
also requires an Application Service tag and an Application Protocol
tag, which differentiate NAPTR records for alert server discovery
from other records for that domain. Section 5.1 defines an
Application Service tag of "AMP", which is used to identify the AMP
alert server that is appropriate for use by devices in a given
domain. The Application Protocol tags "ws", and "wss" are used to
identify alert servers that support the WebSocket protocol and its
secure variant. The NAPTR records in the following example
demonstrate the use of the Application Service and Protocol tags.
Iterative NAPTR resolution is used to delegate responsibility for the
alert server from "zonea.example.net." and "zoneb.example.net." to
"outsource.example.com."
zonea.example.net.
;; order pref flags
IN NAPTR 100 10 "" "AMP:wss" ( ; service
"" ; regex
outsource.example.com. ; replacement
)
zoneb.example.net.
;; order pref flags
IN NAPTR 100 10 "" "AMP:wss" ( ; service
"" ; regex
outsource.example.com. ; replacement
)
outsource.example.com.
;; order pref flags
IN NAPTR 100 10 "u" "AMP:wss" ( ; service
"!.*!wss://alerts.example.org:80/!" ; regex
. ; replacement
)
Figure 1: Sample AMP NAPTR Records
U-NAPTR resolution might produce multiple results from each iteration
of the algorithm. Order and preference values in the NAPTR record
determine which value is chosen. A Device MAY attempt to use
alternative choices if the first choice is not successful. An WSS
URI for an alert server that is a product of U-NAPTR MUST be
authenticated using the domain name method described in Section 3.1
of RFC 6455 [RFC6455]. The domain name that is used in this
authentication is the one extracted from the URI, not the one that
was input to the U-NAPTR resolution process.
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3.1.2. Client Processing
In order to discover an appropriate alert server, a client device
must first obtain a domain name for the local access network. The
client device first attempts to obtain configuration information via
DHCP. If the DHCP configuration contains the Access Network Domain
Name option, then the client uses the domain name in this option as
the domain name for the local access network. Once the client has
the domain name of the local access network, it uses this domain name
to make a U-NAPTR query [RFC4848] for the Application Service AMP in
this domain.
If the DHCP configuration does not contain the Access Network Domain
Name option, then the client MUST follow the process described in
[I-D.ietf-geopriv-res-gw-lis-discovery] to search the reverse DNS
tree for a U-NAPTR record based on the client's IP address.
3.2. Discovery using LoST
The mechanism presented here is based on the Location to Service
Translation protocol (LoST) [RFC5222]. This protocol enables a
client to query with an arbitrary location (either its own location
or an alternative location of interest) and obtain the URI for an
alert metadata server that is able to provide information for alerts
relevant to the given location.
3.2.1. LoST Server Discovery
In order to utilize LoST to discovery an alert metadata server, the
client must first obtain the address or URI of a LoST server.
Implementations supporting LoST-based discovery of alert metadata
servers MUST also support DHCP-based LoST discovery as specified in
RFC 5223 [RFC5223]. Implementations MAY provide an interface whereby
a user can directly configure a static LoST server URI or IP address,
but MUST prefer a discovered LoST server to a configured one.
3.2.2. Client Processing
To discover an alert metadata server for a given geography, a client
makes a LoST <findservice> request. The client populates the
<service> element of this request with the URN
"urn:service:alert-info", the URN specifying the alert metadata
service. The client populates the <location> element of the request
with a location for which the client is interested in receiving
emergency alerts. (This may be the client's own location, or may be
an alternate location of interest to the client.)
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4. AMP Protocol
The Alert Metadata Protocol (AMP) consists of a set of messages
encoded as JSON objects [RFC4627] exchanged over the WebSocket
protocol [[WebSocket]]. In this section we describe the format of
each AMP message type, and the overall flow of an AMP session.
4.1. Message Format
Each AMP message is a JSON object containing a "type" and other
fields that depend on the message type. An AMP object MUST contain
the following field:
"type": REQUIRED Token. The type of AMP message encoded in this
object.
This document defines four values of the "type" field, corresponding
to the four different alert types:
"advertisement": A message describing local alert servers and
authorities
"registration": A message registering client data with the server
"refer": A message referring the client to another AMP server
"alert": An emergency alert
Future documents may define additional message types.
Implementations MUST ignore any AMP message with an unknown type, or
any unknown field in an AMP message.
4.1.1. Advertisement
Advertisement messages are sent from servers to clients. These
messages allow servers to notify clients about local alert
authorities and local alert servers. This information enables the
client to determine whether future alerts are valid, regardless of
the protocol mechanism used to transport the alert. An advertisement
message can contain the following fields:
"token": OPTIONAL String. This field is an opaque string that the
server uses to identify the client on subsequent requests.
"contacts": REQUIRED Array of String. This field is an array of
strings, where each string contains a URI from which local alerts
may be sourced. This array MUST NOT have length zero.
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"certs": OPTIONAL Array of String. This field is an array of
strings, where each string contains an X.509 certificate for a
local authority. Each certificate is encoded with DER and
base64url encoded [[BASE64]]. These certificates are used to
validate local alerts signed by the given alert authority.
"public_keys": OPTIONAL Array of String. This field is an array of
strings, where each string contains Subject Public Key Information
(SPKI) for a local authority, encoded in DER and base64url
encoded. These are the public keys used to validate alerts signed
by the given alert authority.
"hash_values": OPTIONAL Array of String. This field is an array of
hash values that are used in ESCAPE verification, base64url
encoded.
"ttl": REQUIRED Number. This field is a positive integer that
indicates the length of time (in seconds) for which this
advertisement is valid. If the client does not receive a new
advertisement message from the server before the ttl indicates
that the advertisement is stale, then the client should attempt to
obtain a new advertisement message by sending a registration
message to the server.
An advertisement message MUST contain either a "certs" field or a
"public_keys" field.
The "token" field MUST be present except when the server does not
maintain state for clients. If the server sets the "token" field,
then the values it uses MUST be chosen to minimize the possibility
that one client will be able to guess another's token, since that
would allow one client to change or delete another client's
registered state. One algorithm for generating these tokens would be
to compute the HMAC of another client identifier (e.g., an IP address
and timestamp) using a secret key known only to the AMP server.
4.1.2. Registration
Registration messages are sent from clients to servers. They are
used by the clients to register with a server in order to receive
future alerts of the proper type and format (e.g., language). The
same message is also used to update existing registration information
or to request deletion of existing registration information. Note
that for location information, the Registration makes use of the
PIDF-LO format, which is defined in [RFC4119]. Registration messages
contain the following fields:
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"token": REQUIRED String. An opaque a string that identifies the
client. Once a client has received an advertisement message from
a server, it SHOULD copy the token from that message into all
future registration messages to that server, so that the server
can distinguish between new registrations and updates to existing
registrations.
"contacts": OPTIONAL Array of String. This field is an array of
strings, where each string contains a URI that can be used contact
the client. If this field is included, but the array is empty,
then the the server MUST delete any existing registration
information for this client.
"location": OPTIONAL String. This field is a string containing a
"geopriv" element from a PIDF-LO, base64url encoded.
"language": OPTIONAL String. This field is a string containing the
language in which the client wishes to receive alerts, in the
format defined by RFC 5646 [RFC5646].
If a server receives a new registration message from a previously
registered client (i.e., a registration message containing a token
that the server has previously sent in an advertisement message),
then the server should replace the existing registration information
for that client with the information contained in the new
registration message. If the server receives a registration message
containing only the token field, then the server should delete any
existing registration information associated with this client.
4.1.3. Refer
Refer messages are sent from servers to clients. These messages
allow servers to notify clients of a different AMP server that the
client should contact. For example, if an AMP server receives a
registration message indicating a location outside its jurisdiction,
it might send a refer message that refers the client to an
appropriate server for the client's current location. A refer
message must contain the following fields:
"to": REQUIRED String. The URI of the AMP server to which the
client is being referred.
Upon receiving a Refer message, a client SHOULD send establish a new
AMP session with the AMP server indicated in the "to" field of the
refer message.
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4.1.4. Alert
Alert messages are sent from servers to client. These messages are
one mechanism for distributing local alerts. (Other mechanisms for
transporting local alerts include LEAP [I-D.barnes-atoca-delivery].)
Alerts sent using an AMP alert message are encoded using ESCAPE
[I-D.barnes-atoca-escape], then base64url encoded. An Alert message
contains the following fields:
"alert_data": REQUIRED String. An ESCAPE-encoded, base64url-encoded
alert message.
The procedure for validating ESCAPE-encoded alert messages can be
found in [I-D.barnes-atoca-escape]
4.2. AMP Sessions
An AMP session is a WebSocket connection over which AMP messages are
conveyed. The first goal of an AMP session is to inform a client
about local alerting resources (alerting configuration information),
but the client may maintain a long-lived AMP session in order to
provide updated status (e.g., location or contact changes) as well as
to get updated configuration information over time.
The client initiates an AMP session by establishing a WebSocket
connection to the AMP server. The client sends the first message,
providing a Registration message with relevant information.
The AMP Server MUST respond with an Advertisement message containing
local alert information immediately upon the establishment of a
session. If the initial Registration contained a "token" value, then
the "token" field in the Advertisement MUST be either empty or equal
to the registered token value.
Once the initial handshake is complete, either side may send a
message at any time. When a message is received, the action taken
depends on the type of message:
o Client receives Refer: The client SHOULD close the current AMP
session and initiate a new AMP session with the server indicated
in the "to" field of the message. If the client received a token
in the first session, then it SHOULD include that token in the
initial Registration for the new session.
o Client receives Advertisement: The client MUST replace its local
alert configuration information with the contents of the
Advertisement. If the "token" field is present, then the client
MUST update its token.
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o Client receives Alert: The client MUST decode the encoded
"alert_data" element and process the resulting ESCAPE message
according to the ESCAPE validation rules. If the alert is valid,
the client renders it to the user.
o Server receives Registration: The server MUST replace its current
state for the client with the state in the message.
* If the "token" field is present, the server MUST verify that it
matches a token that it has assigned in an Advertisement
message in this session; if not, then this message MUST be
ignored.
* If the Registration message contains only the "type" field,
then the server MUST delete any state associated with this
session.
* If the location of the client has moved out of the server's
coverage area, then the server MUST close the connection. If
the responsible AMP server for the client's new location is
known, then the server SHOULD send a Refer message before
closing the connection.
If either side receives a message sent in the incorrect direction, it
MUST ignore it. For the server, this includes Advertisement, Refer,
and Alert messages. For the client, Registration messages.
Servers SHOULD maintain information about AMP servers covering
neighboring jurisdictions and their respective coverage areas. That
way, the server can issue a Refer message to the client as soon as
the client reports that it has left the coverage area. This will
help ensure that the client always has up-to-date alerting
configuration information, without the client having to repeatedly
perform AMP discovery.
5. IANA Considerations
This document requires several registrations by IANA into existing
registries, and creates a new registry of AMP message codes.
[[ TODO: Register the URN: "urn:service:alert-info" ]]
[[ TODO: Register NAPTR service tag "AMP" and application protocols
"http", "https" ]]
[[ TODO: Register media type application/amp+json ]]
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5.1. AMP Message Type Registry
IANA is requested to create a new registry of AMP Message Types.
This registry contains two fields, the name of the name of the
registered message type, and a specification pointer containing a
reference to the document that defines the registered message type.
IANA is requested to populate this new registry with the following
four entries:
Message Type Name Specification Pointer
+--------------------------------+--------------------------------+
| Registration | draft-barnes-atoca-meta |
| Advertisement | draft-barnes-atoca-meta |
| Refer | draft-barnes-atoca-meta |
| Alert | draft-barnes-atoca-meta |
+--------------------------------+--------------------------------+
6. Security Considerations
[Author's Note: The Security Considerations will be fleshed out in
more detail in the next version of this document.]
The AMP protocol contains contact and location information for a
device which for many devices will consist of private information
regarding the user of the device. Therefore, confidentiality
protection should be used when the registration request contains
private information.
The modification of AMP messages can cause client devices to accept
false alerts (in the case where the advertisement is modified) or to
receive alerts for the improper location (if the registration is
modified). Therefore, integrity protection should be applied to AMP
messages.
The AMP protocol runs over HTTP. Therefore, the use of HTTP over TLS
can provide confidentiality and integrity protection for AMP
messages.
Alert server discovery makes use of NAPTR. Standard security
considerations involving the use of NAPTR apply. DNSSEC SHOULD be
used to protect the DNS responses provided during the discovery
procedure.
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7. Acknowledgements
The authors would like to thank Derrick Kong for help in creating the
JSON schema for the AMP protocol.
8. References
8.1. Normative References
[I-D.barnes-atoca-escape]
Barnes, R., "Encoding of Secure Common Alert Protocol
Entities (ESCAPE)", draft-barnes-atoca-escape-00 (work in
progress), October 2011.
[I-D.ietf-geopriv-res-gw-lis-discovery]
Thomson, M. and R. Bellis, "Location Information Server
(LIS) Discovery using IP address and Reverse DNS",
draft-ietf-geopriv-res-gw-lis-discovery-03 (work in
progress), March 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005.
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[RFC4848] Daigle, L., "Domain-Based Application Service Location
Using URIs and the Dynamic Delegation Discovery Service
(DDDS)", RFC 4848, April 2007.
[RFC5222] Hardie, T., Newton, A., Schulzrinne, H., and H.
Tschofenig, "LoST: A Location-to-Service Translation
Protocol", RFC 5222, August 2008.
[RFC5646] Phillips, A. and M. Davis, "Tags for Identifying
Languages", BCP 47, RFC 5646, September 2009.
[RFC5986] Thomson, M. and J. Winterbottom, "Discovering the Local
Location Information Server (LIS)", RFC 5986,
September 2010.
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[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, December 2011.
8.2. Informative References
[I-D.barnes-atoca-delivery]
Barnes, R., "Lightweight Emergency Alerting Protocol
(LEAP)", draft-barnes-atoca-delivery-01 (work in
progress), October 2011.
[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.
Authors' Addresses
Matt Lepinski
BBN Technologies
10 Moulton St
Cambridge, MA 02138
US
Phone: +1 617 873 5939
Email: mlepinski@bbn.com
Karen Seo
BBN Technologes
10 Moulton St
Cambridge, MA 02138
US
Phone: +1 617 873 3152
Email: kseo@bbn.com
Richard Barnes
BBN Technologies
9861 Broken Land Parkway
Columbia, MD 21046
US
Phone: +1 410 290 6169
Email: rbarnes@bbn.com
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