One document matched: draft-ietf-enum-pstn-01.txt
Differences from draft-ietf-enum-pstn-00.txt
ENUM Working Group J. Livingood
Internet-Draft Comcast Cable Communications
Expires: June 4, 2006 R. Shockey
NeuStar
December 2005
IANA Registration for an Enumservice
Containing PSTN Signaling Information
draft-ietf-enum-pstn-01
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Copyright (C) The Internet Society (2005).
Abstract
This document registers the Enumservice “pstn” and subtype “tel”
using the URI scheme ‘tel:’, as well as the subtype “sip” using the
URI scheme ‘sip’ as per the IANA registration process defined in the
ENUM specification, RFC 3761. This data is used to facilitate the
routing of telephone calls in those countries where Number
Portability exists.
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Table of Contents
1. Terminology....................................................2
2. Introduction...................................................2
3. Distribution of Data...........................................4
4. Record Conflict Resolution.....................................4
5. ENUM Service Registration for PSTN.............................4
6. Examples.......................................................5
6.1 Example of a Ported Number, Using a ‘tel’ URI Scheme.......5
6.2 Example of a Ported Number, Using a ‘sip’ URI Scheme.......5
6.3 Example of a Non-Ported Number, Using a ‘tel’ URI Scheme...6
6.4 Example of a Non-Ported Number, Using a ‘sip’ URI Scheme...6
6.5 Example Using a Regular Expression.........................6
7. Implementation Recommendations.................................7
8. Example of E2U+pstn in Call Processing.........................7
8.1 Dialed Number Not Available On-Net.........................7
8.2 Dialed Number Available On-Net and on the PSTN.............7
9. Security Considerations........................................8
10. IANA Considerations...........................................9
11. Acknowledgements..............................................9
12. References....................................................9
12.1 Normative References......................................9
12.2 Informative References...................................10
Authors’ Addresses...............................................10
Intellectual Property and Copyright Statements...................11
1. Terminology
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 BCP 14, RFC-2119 [1].
2. Introduction
ENUM (E.164 Number Mapping, RFC 3761 [1]) is a system that transforms
E.164 numbers (The International Public Telecommunication Number
Plan, ITU-T Recommendation E.164 [2]) into domain names and then uses
DNS (Domain Name System, RFC 1034 [3]) delegation through NS records
and NAPTR records (Dynamic Delegation Discovery System (DDDS) Part
Three: The Domain Name System (DNS) Database, RFC 3403 [4]) to look
up what services are available for a specific domain name.
This document registers Enumservices according to the guidelines
given in RFC 3761 [1] to be used for provisioning in the services
field of a NAPTR [4] resource record to indicate the types of
functionality associated with an end point and/or telephone number.
The registration is defined within the DDDS (Dynamic Delegation
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Discovery System [4][5][6][7][8]) hierarchy, for use with the "E2U"
DDDS Application defined in RFC 3761.
Number Portability allows telephone subscribers to keep their
telephone numbers when they change service provider, move to a new
location, or change the subscribed services [14]. In many counties,
such as the United States and Canada, the functions of naming and
addressing on the PSTN have been abstracted. In the case of a ported
number, the dialed number is not directly routable on the PSTN and
must be translated into a routing number for call completion. Other
numbers, which are not ported, and which can be routed directly on
the PSTN based on the dialed number, are typically assigned to
carriers and other entities in large blocks or pools. This non-
ported numbering information is distributed in a variety of methods
and formats around the world.
The following Enumservice is registered with this document: "pstn" to
indicate PSTN routing data, including number portability data, non-
ported telephone number data (individually or in number blocks), and
other PSTN-oriented data that is associated with E.164 telephone
numbers. The purpose of this Enumservice is to describe information
about telephone numbers which cannot be used on the public Internet
or a private/peered Internet Protocol (IP) network. Thus, these are
numbers which are only reachable via the traditional Public Switched
Telephone Network (PSTN).
This Enumservice could enable carriers, as well as other service
providers and users, to place ported, pooled, and blocks of numbers
and their associated PSTN contact information, into ENUM databases,
using standardized, non-proprietary methods. This, in turn, could
enable such parties to consolidate all telephone number lookups in
their networks into a single ENUM lookup, thereby simplifying call
routing and network operations, which would then result in either an
on-net, or IP-based response, or off-net, PSTN-based response. It is
conceivable that being able to query for this information in ENUM
could significantly reduce or eliminate the need for these parties to
maintain traditional, SS7/TCAP/SIGTRAN-based query gateways,
applications, and protocols in their networks.
The service parameters defined in RFC 3761 dictate that a "type" and
a "subtype" should be specified. Within this set of specifications
the convention is assumed that the "type" (being the more generic
term) defines the service and the "subtype" defines the URI scheme.
When only one URI scheme is associated with a given service, it
should be assumed that an additional URI scheme to be used with this
service may be added at a later time. Thus, the subtype is needed to
identify the specific Enumservice intended.
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In this document, two URI schemes are specified. The first is
'tel:', as specified in RFC 3966 [9], and as further specified with
number portability data in draft-ietf-iptel-tel-np-07.txt [10]
(Internet-Draft New Parameters for the "tel" URI to Support Number
Portability, draft-ietf-iptel-tel-np-07.txt [10]). And since
software implementations using ‘tel’ URIs are somewhat limited, a
second URI scheme can be used, ‘sip:’, as specified in RFC 3261 [11].
3. Distribution of Data
The distribution of number portability data is often highly
restricted either by contract or regulation of a National Regulatory
Authority (NRA), therefore NAPTR records specified herein may or may
not be part of the e164.arpa DNS tree.
The NAPTR records described herein probably would not be part of the
e164.arpa DNS tree. Distribution of this NAPTR data would be either
(a) on a private basis (within a service provider’s internal network,
or on a private basis between one or more parties using a variety of
security mechanisms to prohibit general public access), (b) openly
available or, (c) distributed by the relevant number portability
organization or other industry organization, but possibly on a
national basis and subject to or in accordance with national
regulatory policy.
The authors believe that it is more likely that these records will be
distributed on a purely private basis. If such data was distributed
nationally, the national telephone numbering authority, or some other
regulatory body or numbering organization, may have jurisdiction.
Such a body may choose to restrict distribution of the data in such a
way that it may not pass over that country’s national borders. How
number portability data is collected and distributed is out of scope
of this document.
4. Record Conflict Resolution
It is likely that, in some cases, a query will return multiple
records. In this case, this could result in what is essentially an
on-net and off-net record. Thus, one record gives the associated
address on an IP network, while the other gives the associated
address on the PSTN. As with multiple records resulting from a
typical ENUM query of the e164.arpa tree, it is up to the application
using an ENUM resolver to determine which record(s) to use and which
record(s) to ignore. For example, such a resolver could be
configured to grant preference to the on-net record, or execute other
logic as required by the application.
5. ENUM Service Registration for PSTN
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Enumservice Name: "pstn"
Enumservice Type: "pstn"
Enumservice Subtypes: "tel", “SIP”
URI Schemes: 'tel:', ‘sip:’
Functional Specification:
These Enumservices indicate that the remote resource identified can
be addressed by the associated URI scheme in order to initiate a
telecommunication session, which may include two-way voice or other
communications, to the PSTN.
Security Considerations: See Section 9.
Intended Usage: COMMON
Authors:
Jason Livingood and Richard Shockey (for author contact detail see
Authors' Addresses section)
Any other information the author deems interesting:
None
6. Examples
The following sub-sections document several examples for illustrative
purposes. These examples shall in no way limit the various forms
that this Enumservice may take.
6.1 Example of a Ported Number, Using a ‘tel’ URI Scheme
$ORIGIN 3.1.8.7.1.8.9.5.1.2.1.e164.arpa.
NAPTR 10 100 "u" "E2U+pstn:tel"
"!^.*$!tel:+1-215-981-7813;rn=+1-215-555-1212;npdi!".
In this example, a Routing Number (rn) and a Number Portability Dip
Indicator (npdi) are used as shown in draft-ietf-iptel-tel-np-07.txt
[10] (Internet-Draft New Parameters for the "tel" URI to Support
Number Portability, draft-ietf-iptel-tel-np-07.txt [10]). The ‘npdi’
field is included in order to prevent subsequent lookups in legacy-
style PSTN databases.
6.2 Example of a Ported Number, Using a ‘sip’ URI Scheme
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$ORIGIN 3.1.8.7.1.8.9.5.1.2.1.e164.arpa.
NAPTR 10 100 "u" "E2U+pstn:sip"
"!^.*$!sip:+1-215-981-7813;rn=+1-215-555-
1212;npdi@gw.example.com;user=phone!".
In this example, a Routing Number (rn) and a Number Portability Dip
Indicator (npdi) are used as shown in draft-ietf-iptel-tel-np-07.txt
[10] (Internet-Draft New Parameters for the "tel" URI to Support
Number Portability, draft-ietf-iptel-tel-np-07.txt [10]). The ‘npdi’
field is included in order to prevent subsequent lookups in legacy-
style PSTN databases. The method of conversion from a tel to a SIP
URI is as demonstrated in RFC 3261, Section 19.1.6 [11], as well as
in , draft-ietf-iptel-tel-np-07.txt Section 6.3 [10].
6.3 Example of a Non-Ported Number, Using a ‘tel’ URI Scheme
$ORIGIN 3.1.8.7.1.8.9.5.1.2.1.e164.arpa.
NAPTR 10 100 "u" "E2U+pstn:tel"
"!^.*$!tel:+1-215-981-7813;npdi!".
In this example, a Number Portability Dip Indicator (npdi) is used
[10]. The ‘npdi’ field is included in order to prevent subsequent
lookups in legacy-style PSTN databases.
6.4 Example of a Non-Ported Number, Using a ‘sip’ URI Scheme
$ORIGIN 3.1.8.7.1.8.9.5.1.2.1.e164.arpa.
NAPTR 10 100 "u" "E2U+pstn:sip"
"!^.*$!sip:+1-215-981-7813;npdi@gw.example.com;user=phone!".
In this example, a Number Portability Dip Indicator (npdi) is used
[10]. The ‘npdi’ field is included in order to prevent subsequent
lookups in legacy-style PSTN databases. The method of conversion
from a tel to a SIP URI is as demonstrated in RFC 3261, Section
19.1.6 [11], as well as in , draft-ietf-iptel-tel-np-07.txt Section
6.3 [10].
6.5 Example Using a Regular Expression
$ORIGIN 3.1.8.7.1.8.9.5.1.2.1.e164.arpa.
NAPTR 10 100 "u" "E2U+pstn:tel"
"!^.*$!tel:\1;npdi!".
In this example, a regular expression replacement function is used to
reduce the size of the NAPTR record. The tel URI uses “\1” which
would dynamically create a record with the TN from the original NAPTR
query, in this case +1-215-981-7813.
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7. Implementation Recommendations
Software vendors consulted during development of this draft have
suggested that tel URIs may be easier and more efficient to use in
practice. In addition, they have indicated that this will result in
somewhat smaller NAPTR records which, when considering adding
hundreds of millions of these records to the DNS, could have a
substantial impact on the processing and storage requirements for
service providers or other entities making use of this Enumservice
type.
In addition, it is likely that both E2U+sip and E2U+pstn Enumservice
type records will be returned for a given query. Implementers should
take this into consideration and build logic into their applications
that can select appropriately from multiple records based on
business, network, or other rules.
It is also recommended that regular expressions be used, in order to
reduce the size of individual NAPTRs. This will have a significant
effect on the overall size of the data involved. Using the Section
6.5 example from above, this is 11 bytes per record. Based on an
estimated 200 million records, this equates to approximately 2.1GB of
data. In addition, where regular expressions are not used, the “-“
hyphen delimiters in the URIs in the above section are shown in order
to make the numbers in each example more readable. In practice,
however, including hyphens is not recommended as this also increases
the data storage requirements.
8. Example of E2U+pstn in Call Processing
This is an example of how a switch, proxy, or other calling
application may make use of this Enumservice type during the call
initiation process.
8.1 Dialed Number Not Available On-Net
a) A user, which is connected to a calling application, dials an
E.164 telephone number: 1-215-981-7813.
b) The calling application uses the dialed number to form a NAPTR
record: 3.1.8.7.1.8.9.5.1.2.1.e164.arpa.
c) The DNS finds an E2U+pstn:tel record and returns a tel URI for
processing by the calling application: tel:+1-215-981-
7813;npdi.
d) The calling application uses routing logic to determine which
media gateway is the closest to this number and routes the
call appropriately.
8.2 Dialed Number Available On-Net and on the PSTN
a) A user, which is connected to a calling application, dials an
E.164 telephone number: 1-215-981-7813.
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b) The calling application uses the dialed number to form a NAPTR
record: 3.1.8.7.1.8.9.5.1.2.1.e164.arpa.
c) The DNS finds both an E2U+pstn record, as well as an E2U+sip
record, since this number happens to be on the IP network of a
connected network.
d) The calling application prioritizes the on-net record first:
sip:+1-215-981-7813;npdi@gw.example.com;user=phone.
e) The calling application uses routing logic to determine which
proxy, router, session border controller, or other device to
use, and routes the call appropriately.
f) Should the IP call route fail for whatever reason, the calling
application may be able to utilize the E2U+pstn record to
invoke a fallback route to a media gateway that is connected
to the PSTN.
9. Security Considerations
DNS, as used by ENUM, is a global, distributed database. Thus any
information stored there is visible to anyone anonymously. While
this is not qualitatively different from publication in a Telephone
Directory, it does open or ease access to such data without any
indication that such data has been accessed or by whom it has been
accessed.
Such data harvesting by third parties is often used to generate lists
of targets for unsolicited information. Thus, a third party could
use this to generate a list that they can use to make unsolicited
"telemarketing" phone calls. Many countries have do-not-call
registries or other legal or regulatory mechanisms in place to deal
with such abuses.
Carriers, service providers, and other users may simply choose not to
publish such information in the public E164.ARPA tree, but may
instead simply publish this in their internal ENUM routing database
which is only able to be queried by trusted elements of their
network, such as softswitches and SIP proxy servers. They may also
choose to publish such information in a carrier-only branch of the
E164.ARPA tree, should one be created.
Although an E.164 telephone number does not appear to reveal as much
identity information about a user as a name in the format
sip:username@hostname or email:username@hostname, the information is
still publicly available, thus there is still the risk of unwanted
communication.
An analysis of threats specific to the dependence of ENUM on the DNS
and the applicability of DNSSEC [13] to this is provided in RFC 3761
[1]. A thorough analysis of threats to the DNS itself is covered in
RFC 3833 [14].
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10. IANA Considerations
This document registers the 'pstn' Enumservice and the subtype “tel”
and “SIP” under the Enumservice registry described in the IANA
considerations in RFC 3761. Details of this registration are
provided in sections 3 and 4 of this document.
11. Acknowledgements
The authors wish to thank Tom Creighton, Jason Gaedtke, Jaime
Jimenez, Chris Kennedy and Rich Woundy from Comcast Cable, Jonathan
Rosenberg from Cisco, Doug Ranalli and Bob Walter from NetNumber, and
James Yu from NeuStar, for their helpful discussion on this topic.
The authors also wish to thank the IETF’s ENUM Working Group for
helpful feedback in refining and developing this draft.
12. References
12.1 Normative References
[1] Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource
Identifiers (URI) Dynamic Delegation Discovery System (DDDS)
Application (ENUM)", RFC 3761, April 2004.
[2] ITU-T, "The International Public Telecommunication Number Plan",
Recommendation E.164, May 1997.
[3] Mockapetris, P., "DOMAIN NAMES - CONCEPTS AND FACILITIES", RFC
1034, November 1987.
[4] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Three: The Domain Name System (DNS) Database", RFC 3403, October
2002.
[5] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
One: The Comprehensive DDDS", RFC 3401, October 2002.
[6] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Two: The Algorithm", RFC 3402, October 2002.
[7] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Four: The Uniform Resource Identifiers (URI)", RFC 3404, October
2002.
[8] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Five: URI.ARPA Assignment Procedures", RFC 3405, October 2002.
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[9] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
December 2004.
[10] Yu, J., "New Parameters for the "tel" URI to Support Number
Portability", draft-ietf-iptel-tel-np-07, July 2005.
[11] Rosenberg, J., et al., “SIP: Session Initiation Protocol”, RFC
3261, June 2002.
12.2 Informative References
[12] Bradner, et al., "IANA Registration for Enumservices email, fax,
mms, ems and sms", draft-ietf-enum-msg-05.txt, May 2005.
[13] Arends, R. and et al., "Protocol Modifications for the DNS
Security Extensions", RFC 4035, March 2005.
[14] Atkins, D. and Austein, R., "Threat Analysis of the Domain Name
System (DNS)", RFC 3833, August 2004.
[15] Foster, M., McGarry, T., and Yu, J., "Number Portability in the
GSTN: An Overview", RFC 3482, February 2003.
[16] Peterson, J., "enumservice Registration for Session Initiation
Protocol (SIP) Addresses-of-Record”, RFC 3764, April 2004.
Authors’ Addresses
Jason Livingood
Comcast Cable Communications
1500 Market Street
Philadelphia, PA 19102
USA
Phone: +1-215-981-7813
Email: jason_livingood@cable.comcast.com
Richard Shockey
NeuStar
46000 Center Oak Plaza
Sterling, VA 20166
USA
Phone: +1-571-434-5651
Email: richard.shockey@neustar.biz
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