ENUM Working Group A. Gallant
Internet Draft Comsat Corporation
Expires: January 6, 2001 July 7, 2000
The Number Portability Supplement to ITU-T Recommendation E.164
<draft-ietf-enum-e164s2-np-00.txt>
Status of this Memo
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1. Abstract
This document contains a text version of the Number Portability
Supplement (11/98) to ITU-T Recommendation E.164 (The international
public telecommunication numbering plan, 05/97) [2]. That
Supplement [3] defined terminology for number portability within an
E.164 numbering scheme; identified formats, call flows,
architectures, and routing approaches for some methods; and gave
examples of some processes needed to implement number portability.
A January 2000 workshop on IP-Telecomms interworking (focused on
numbering, naming, addressing, and routing) identified issues to be
addressed by the IETF and/or the ITU [4]. This Supplement was noted
as a document related to a joint IETF/ITU issue on E.164 number
portability. A text version was posted on the ITU's web site in
March 2000 and notified to the itu+ietf and enum mailing lists.
This Internet Draft is being submitted to support work of the ENUM
(Telephone Number Mapping) Working Group on impacts of local number
portability on a DNS-based architecture and protocols for mapping a
telephone number to a set of attributes (e.g., URLs) [5].
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2. Convention used in this document
"e164s2" below flags the section numbering from the ITU original.
3. Table of Contents
Status of this Memo . . . . . . . . . . . . . . . . . . . . . . . 1
1. Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Convention Used in this Document . . . . . . . . . . . . . . . 2
3. Table of Contents . . . . . . . . . . . . . . . . . . . . . . 2
4. Text Version of the Number Portability Supplement . . . . . . 3
(e164s2) 1 Scope . . . . . . . . . . . . . . . . . . . . . . . . 3
(e164s2) 2 References . . . . . . . . . . . . . . . . . . . . . . 3
(e164s2) 3 Definitions and abbreviations . . . . . . . . . . . . 3
(e164s2) 4 E.164 number structures . . . . . . . . . . . . . . . 6
(e164s2) 4.1 International public telecommunication number for
geographic areas . . . . . . . . . . . . . . . . . . 7
(e164s2) 4.2 International public telecommunication number for
global services . . . . . . . . . . . . . . . . . . 7
(e164s2) 4.3 International public telecommunication number for
networks . . . . . . . . . . . . . . . . . . . . . . 8
(e164s2) 5 Number portability types . . . . . . . . . . . . . . . 8
(e164s2) 6 Generic implementation of number portability . . . . . 11
(e164s2) 7 Entities addressed by routing . . . . . . . . . . . . 12
(e164s2) 8 Number portability mechanisms . . . . . . . . . . . . 13
(e164s2) 8.1 Assumptions . . . . . . . . . . . . . . . . . . . . 13
(e164s2) 8.2 General description . . . . . . . . . . . . . . . . 13
(e164s2) 9 Types of addresses and numbers _ within networks and
across network boundaries . . . . . . . . . . . . . . 18
(e164s2) 9.1 Concatenated address . . . . . . . . . . . . . . . . 19
(e164s2) 9.2 Separated addresses . . . . . . . . . . . . . . . . 21
(e164s2) 9.3 RN only . . . . . . . . . . . . . . . . . . . . . . 22
(e164s2) 9.4 Only DN (normally across network boundaries) . . . . 22
(e164s2) 10 Combinations of addressing types, addressed entities
and mechanisms: general signalling requirements . . . 23
(e164s2) 11 Examples of locations of number portability
database(s) within networks . . . . . . . . . . . . . 24
(e164s2) 12 Administrative processes . . . . . . . . . . . . . . 25
5. Front Matter from the ITU-T Published Version . . . . . . . . 26
6. Security Considerations . . . . . . . . . . . . . . . . . . . 27
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
9. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 28
10. Full Copyright Statement . . . . . . . . . . . . . . . . . . 28
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4. Text Version of the Number Portability Supplement
This section contains the text of the Rec. E.164 Supplement on
Number Portability. It also contains text versions of all figures
and tables. The front matter of the ITU-T published version is
found in Section 6 of this document.
--------------------------------------------------------------------
SUPPLEMENT 2 to Recommendation E.164 (The international
public telecommunication numbering plan)
Number Portability
(Geneva, 1998)
(e164s2) 1 Scope
This Supplement defines standard terminology for a common
understanding of the different aspects of number portability within
an E.164 numbering scheme. It identifies numbering and addressing
formats, call flows, network architectures and routing approaches
that will provide alternative methods of implementation. It also
proposes some examples of the administrative and operational
processes required for the successful implementation of number
portability.
(e164s2) 2 References
- ITU-T Recommendation E.164 (1997), The international public
telecommunication numbering plan.
(e164s2) 3 Definitions and abbreviations
(e164s2) 3.1 Definitions
The following definitions and terms used in this Supplement are to
be used within the context of number portability.
(e164s2) 3.1.1 address (taken from E.164): A string or combination
of decimal digits, symbols and additional information which
identifies the specific termination point(s) of a connection in a
public network(s) or, where applicable, in interconnected private
network(s).
(e164s2) 3.1.2 directory number: See end user's number.
(e164s2) 3.1.3 donor network/exchange: The initial
network/exchange where a number was located before ever being
ported.
(e164s2) 3.1.4 donor service provider: The service provider from
whom the number was initially ported.
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(e164s2) 3.1.5 end user's number: The E.164 number used by the
calling party to establish a call to the end user. This number is
also used for presentation services like Calling Line Identification
(CLI) and Connected Line Identification Presentation (COLP).
The end user's number is equivalent to a directory number.
(e164s2) 3.1.6 Geographic Number (GN): An E.164 number which
corresponds to a discrete geographic area.
(e164s2) 3.1.7 location portability: The ability of an end user to
retain the same E.164 international public telecommunication number
when moving from one location to another.
(e164s2) 3.1.8 network operator: An entity that operates a network
in order to route calls.
(e164s2) 3.1.9 Non-Geographic Number (NGN): An E.164 number which
has no geographic significance.
(e164s2) 3.1.10 numbering plan: A numbering plan specifies the
format and structure of the numbers used within that plan. It
typically consists of decimal digits segmented into groups in order
to identify specific elements used for identification, routing and
charging capabilities, e.g. within E.164 to identify countries,
national destinations and subscribers.
A numbering plan does not include prefixes, suffixes and additional
information required to complete a call.
The national numbering plan is the national implementation of the
E.164 numbering plan.
(e164s2) 3.1.11 originating network/exchange: The network/exchange
serving a calling end user.
(e164s2) 3.1.12 portable number: An entire E.164 number identified
by an appropriate authority which is subject to number portability.
(e164s2) 3.1.13 ported number: An end user's E.164 number that has
been subject to number portability.
(e164s2) 3.1.14 recipient network/exchange: The network/exchange
where a number is located after being ported. [Footnote: The
recipient exchange may consist of a central processor and both co-
located and remote concentrator units. The routing number may
identify either this whole ensemble or a specific concentrator (in
which case the ensemble may use several different routing numbers).]
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(e164s2) 3.1.15 recipient service provider: The service provider to
whom the number is ported.
(e164s2) 3.1.16 routing number: A number that is derived and used
by the network to route the call towards a ported number.
Four types of entities can be indicated by routing numbers as
follows:
- Recipient network: The routing number identifies the network
where the customer is now located. Therefore the routing process
will need additional information (i.e. DN) to be completed.
- Recipient exchange: The routing number identifies the exchange
where the customer is now located. Therefore the routing process
within the recipient exchange will need additional information (i.e.
DN) to be completed.
- Point of interconnection: The routing number identifies an
interface to the next network in the routing process. Therefore the
routing process will need additional information (i.e. DN) to be
completed.
- Network termination point: The routing number identifies the
subscriber/access line/service. The ported customer identified by
the RN is unique. Therefore the routing process in terms of number
portability can be completed without any additional information.
(e164s2) 3.1.17 serving network(s)/exchange(s): The
network(s)/exchange(s) that determines the status of a number in an
environment capable of supporting number portability and, if
necessary, obtains the routing information for ported numbers. The
functionality to provide these capabilities may reside in either the
originating, donor, recipient or transit network/exchange or in some
combination.
(e164s2) 3.1.18 service number: A non-geographic E.164 number
allocated to a specific category of services.
(e164s2) 3.1.19 service portability: The ability of an end user to
retain the same E.164 international public telecommunication number
when changing from one type of service to another.
(e164s2) 3.1.20 service provider: An entity that offers services to
users involving the use of network resources.
(e164s2) 3.1.21 service provider portability: The ability of an end
user to retain the same E.164 international public telecommunication
number when changing from one service provider to another.
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(e164s2) 3.1.22 service provider portability for geographic
numbers: The ability of an end user to retain the same geographic
E.164 international public telecommunication number when changing
from one service provider to another without changing their location
and without changing the nature of the service offered.
(e164s2) 3.1.23 service provider portability for non-geographic
numbers: The ability of an end user to retain the same non-
geographic E.164 international public telecommunications number when
changing from one service provider to another without changing the
nature of the service offered.
(e164s2) 3.1.24 transit network(s)/exchange(s): A network/exchange
between two networks.
(e164s2) 3.2 Abbreviations
CCBS Completion of Calls to Busy Subscriber
DDI Direct-Dialling-In
DN Directory Number
GNP Geographic Number Portability
IN Intelligent Network
MSN Multiple Subscriber Number
NGNP Non-Geographic Number Portability
RN Routing Number
SP Service Provider
(e164s2) 4 E.164 number structures
This clause identifies three different structures for the
international public telecommunication number:
- international public telecommunication number for geographic
areas;
- international public telecommunication number for global
services;
- international public telecommunication number for networks.
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(e164s2) 4.1 International public telecommunication number for
geographic areas
+-------------+ +-----------------+ +---------------------+
| CC | | NDC | | SN |
+-------------+ +-----------------+ +---------------------+
| | | |
|1 to 3 digits| | Max (15-n) digits |
| | | |
| |<-----National (significant) number----->|
| |
|<---------------------Max 15 digits--------------------->|
| |
|<--------International public telecommunication--------->|
| number for geographic areas |
CC Country Code for geographic areas
NDC National Destination Code (optional)
SN Subscriber Number
n Number of digits in the country code
NOTE - National and international prefixes are not part of
the international public telecommunication number for
geographic areas.
Figure 1 - International public telecommunication
number structure for geographic areas
(e164s2) 4.2 International public telecommunication number
for global services
+-------------+ +-----------------------------------------+
| CC | | GSN |
+-------------+ +-----------------------------------------+
| | | |
| 3 digits | |<-------------Max 12 digits------------->|
| | | |
|<---------------------Max 15 digits--------------------->|
| |
|<--------International public telecommunication--------->|
| number for global services |
CC Country Code for global services
GSN Global Subscriber Number
NOTE - National and international prefixes are not
considered to be part of the international public
telecommunication number for global services.
Figure 2 - International public telecommunication
number structure for global services
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(e164s2) 4.3 International public telecommunication number for
networks
+-------------+ +-----------------+ +---------------------+
| CC | | IC | | SN |
+-------------+ +-----------------+ +---------------------+
| | | | | |
| 3 digits | | 1 to 4 digits | | Max (12-x) digits |
| | | |
| |<-------------Max 12 digits------------->|
| |
|<---------------------Max 15 digits--------------------->|
| |
|<--------International public telecommunication--------->|
| number for networks |
CC Country Code for networks
IC Identification Code
SN Subscriber Number
x Number of digits in Identification Code (IC)
NOTE - National and international prefixes are not part of
the international public telecommunication number for
networks.
Figure 3 - International public telecommunication
number structure for networks
(e164s2) 5 Number portability types
An E.164 number is classified into the following three types
of country codes:
1) beginning with CC for geographic areas;
2) beginning with CC for global services; and
3) beginning with CC for networks.
The following tables provide an overview of the applicability of
each type of portability, when considered against the three number
types.
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Table 1 - Service provider portability
+---------------------------------------------------------+
| Scope | | |
|-----------| | |
|CC type | Between CC domains | Within CC domains |
| (Note 1) | | |
|-----------+-----------+----------+-----------+----------|
|Geographic |Porting |Standards |Porting |Standards |
| |not |not |applicable |not |
| |applicable |required | |required |
| | | | | (Note 4) |
|-----------+-----------+----------+-----------+----------|
|Global |Porting |Standards |Porting |Standards |
|Services |not |not |applicable |not |
| |applicable |required | |required |
| | | | | (Note 2) |
|-----------+-----------+----------+-----------+----------|
|Network |Porting |Standards |Network |Network |
| (Note 3) |not |not |operator |operator |
| |applicable |required |matter |matter |
+---------------------------------------------------------+
Table 2 - Service portability
+---------------------------------------------------------+
| Scope | | |
|-----------| | |
|CC type | Between CC domains | Within CC domains |
| (Note 1) | | |
|-----------+-----------+----------+-----------+----------|
|Geographic |Porting |Standards |Porting |Standards |
| |not |not |applicable |not |
| |applicable |required | |required |
| | | | | (Note 4) |
|-----------+-----------+----------+-----------+----------|
|Global |Porting |Standards |Porting |Standards |
|Services |not |not |not |not |
| |applicable |required |applicable |required |
|-----------+-----------+----------+-----------+----------|
|Network |Porting |Standards |Network |Network |
| (Note 3) |not |not |operator |operator |
| |applicable |required |matter |matter |
+---------------------------------------------------------+
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Table 3 - Location portability
+---------------------------------------------------------+
| Scope | | |
|-----------| | |
|CC type | Between CC domains | Within CC domains |
| (Note 1) | | |
|-----------+-----------+----------+-----------+----------|
|Geographic |Porting |Standards |Porting |Standards |
| |not |not |applicable |not |
| |applicable |required | |required |
| | | | | (Note 4) |
|-----------+-----------+----------+-----------+----------|
|Global |Porting |Standards |Porting |Standards |
|Services |not |not |applicable |not |
| |applicable |required | (Note 5) |required |
|-----------+-----------+----------+-----------+----------|
|Network |Porting |Standards |Network |Network |
| (Note 3) |not |not |operator |operator |
| |applicable |required |matter |matter |
+---------------------------------------------------------+
Notes to Tables 1, 2 and 3:
NOTE 1 - Portability not supported between CC types.
NOTE 2 - Requires international agreement(s) and infrastructure to
support number portability (e.g. UIFN).
NOTE 3 - Includes the CC + IC digits required to uniquely identify
the network.
NOTE 4 - International standardization not required but could be of
use.
NOTE 5 - These resources are "non-geographic" therefore location
portability is inherent.
NOTE 6 - For purposes of Tables 1, 2 and 3, "Standards" means ITU-T
Recommendations.
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(e164s2) 6 Generic implementation of number portability
The following general routing scheme is assumed as the routing model
for calls routed to a ported customer.
incoming call
|
1st step of the |
routing process, |
based on dialled digits |
|
+---------------------------+ +--------------------+
| Serving Network | | | Transit Network |
| v | | (optional) |
| +-+ | | |
| | | |-------------------+ |
| Serving Exchange +-+ | | | |
+---------------------------+ +---------------|----+
|
2nd step of the |
routing process, |
based on routing number |
v
+---------------------------+
| Recipient Network | |
| v |
| +-+ |
| | | |
| Recipient Exchange +-+ |
+---------------------------+
|
|
+---+
customer with | |
ported number | |
+---+
NOTE - The serving network may be the originating network
and/or the donor or a transit network.
Figure 4 - Conceptual framework for incoming calls
NOTE 1 - The caller sets up the call by dialling the end user's
number which in this case is a ported number. The end user's number
is enough to initiate the routing process. Furthermore, number
portability, by definition, implies that the callers should continue
to dial the same end user's number and nothing more to set up a call
to a ported customer.
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NOTE 2 - The routing process is split into two consecutive main
steps:
a) Normal routing based on end user's number towards a serving
exchange:
As a 1st step in the routing process, the originating network routes
the call up to a serving exchange clearly identified by the analysis
of a certain number of leading digits of the end user's number.
b) Routing to customer's interface based on routing number(s)
obtained by this serving exchange:
It should be noted that this step might be subdivided into sub-steps
(e.g. the serving exchange could provide information to route to a
database - within the recipient network or accessed by the recipient
network - which provides subsequent routing information identifying
the recipient exchange, information used for a subsequent sub- step
in the routing process).
NOTE 3 - If only the recipient network is identified, then it is the
responsibility of the recipient network to terminate the call at the
recipient exchange.
NOTE 4 - The internal routing process in the recipient exchange
shall unambiguously determine the called customer's interface and
complete the call taking into account the supplementary services
activated.
NOTE 5 - If a number is ported subsequently from service provider
No. 1 to service provider No. 2, then to service provider No. 3,
etc. this will change the routing number but not the routing
principles.
(e164s2) 7 Entities addressed by routing
Entities which need to be addressed by a Routing Number (RN) in one
or more routing solutions are identified in this clause.
According to the structure of the routing number, one or a
combination of several of the following entities should be
addressable:
- A recipient network: In this option, the routing number
identifies the network where the customer is now located. Therefore
the routing process will need additional information (i.e. DN) to be
completed.
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- A Point of Interconnection (POI): In this option, the routing
number identifies an interface to the next network in the routing
process. Therefore the routing process will need additional
information (i.e. DN) to be completed.
- Recipient exchange: In this option, the routing number
identifies the exchange where the customer is now located. Therefore
the routing process within the recipient exchange will need an
additional information (i.e. DN) to be completed.
- Network Termination Point (NTP): In this option, the routing
number identifies the subscriber/access line/service. The ported
customer identified by the RN is unique. Therefore the routing
process, in terms of number portability, can be completed without
any additional information.
(e164s2) 8 Number portability mechanisms
(e164s2) 8.1 Assumptions
The following document internal assumptions that have been made:
a) that Calling Line Identification (CLI) is required to be
transported, with display information, unchanged to recipient
network;
b) that Connected Line Identification (COLI) is required to be
transported, with display information, unchanged to originating
network;
c) that initial routing arrangements have been defined and
implemented prior to the introduction of routing based on a routing
number;
d) that number portability is not allowed to influence the carrier
selection function;
e) that an NP solution shall not influence functions in PBXs.
(e164s2) 8.2 General description
(e164s2) 8.2.1 Call rerouted from donor network by use of onward
routing principles
The first step/solution discussed for number portability is often
that the donor network maintains the portability information, i.e.
the complete address to both recipient network and exchange, for
ported-out numbers and reroutes incoming calls to ported-out numbers
onward towards the recipient network according to onward routing
principles outlined in Figure 5.
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Originating Transit Donor
Network Network(s)(A) Network
+-------+ +-------+ +-------+
| | IAM | | IAM | +--+|
+-->| |------>| |------>| |DB||.....
| | | | | | +--+| .
| +-------+ +-------+ +-------+ .
| | | .
Calling a1)IAM | |b)IAM .
Subscriber +---------+ | .
| | Called
| | Subscriber
v v ^
+-------+ +-------+ |
| |a2)IAM | | |
| |------>| |----+
| | | |
+-------+ +-------+
Transit Recipient
Network(s)(B) Network
Figure 5 - Call rerouting to recipient network by
onward routing principles from donor network
In Figure 5, the donor network receives an incoming call. It then
detects that the called number has been ported-out to another
network and makes a DB query to retrieve a routing number. It
thereafter reroutes the call onward towards the recipient network
using retrieved routing information.
Please note that the transit network(s) are optional, i.e. direct
interconnections connections between originating network and donor
network might exist and the same also between donor network and
recipient network. Note also that the transit network(s) A and B can
be the same depending on network structure and call case.
(e164s2) 8.2.2 Call rerouted by dropback principles from donor
network
One possible enhancement of the previously described onward routing
solution, is that the donor network initiates the rerouting of the
call towards the recipient network according to "dropback"
principles outlined in Figure 6. Also, in this scenario, only the
donor network maintains NP information, i.e. the complete address to
both recipient network and exchange, for ported-out numbers.
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Originating Transit Donor
Network Network(s)(A) Network
+-------+ +-------+ +-------+
| | IAM | | IAM | +--+|
+-->| |------>| |......>| |DB||.....
| | | | |<......| +--+| .
| +-------+ +-------+ Dropb.+-------+ .
| | | .
Calling a1)IAM| | b)IAM .
Subscriber | +---------+ .
| | Called
| | Subscriber
----> v v ^
Lasting +-------+ +-------+ |
relation | |a2)IAM | | |
....> | |------>| |----+
Temporary | | | |
relation +-------+ +-------+
Transit Recipient
Network(s)(B) Network
Figure 6 - Dropback with rerouting information and
onward rerouting performed by a transit network
The option b) is valid when direct interconnection exists between
transit network A and recipient network.
A further evolution is that the dropback indication is sent back to
the originating network. This is mainly of interest if the
originating network has direct interconnections to other networks
than the transit network used in the call attempt to the donor
network.
The dropback indication is also passed through to the originating
network if either the transit network A has no "dropback" capability
or determines that the preceding network has "dropback" capability.
The originating network, at reception of the release, reroutes the
call towards recipient network.
Please note that the transit networks are optional (i.e. direct
connections between originating network and donor network might
exist) but might exist [case a1) and a2)] between the onward routing
(transit or originating) network and recipient network.
When carrier selection is valid for the call, the originating
network reuses the carrier selection information after reception of
dropback indication. It could be debated if a selected carrier (e.g.
TN A) is allowed/recommended to transport the dropback to
originating network, but it has no option if it has no redirect on
"dropback" capability.
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(e164s2) 8.2.3 Call rerouting initiated by "Query on Release
(QoR)" principles from donor network
A similar case as the previously described "dropback" principle is
when the preceding network to donor initiates NP actions, i.e. an NP
DB query, at reception of a release message. This case is often
referred to as "Query on Release (QoR)".
In Figure 7, the donor network receives an incoming call. It then
detects that the called number has been ported out to another
network. It then determines that one of the preceding networks has
QoR capability by looking at received signalling information. It
thereafter releases the call with a special indication telling that
called number is ported out. The transit network then traps the
release, determines that preceding network has no QoR capability,
makes an NP database query and reroutes the call onward towards the
recipient network. In this scenario the transit network has access
to an NP DB with the complete address to the recipient network, at
least for ported-out numbers.
Options a1) and a2), in Figure 7, are valid when transit network A
either has no direct interconnection to recipient network or when
overflow traffic is placed via transit network B.
Originating Transit Donor
Network Network(s)(A) Network
+-------+ +-------+ +-------+
| | IAM | +--+| IAM | |
+-->| |------>| |DB||......>| |.....
| | | | +--+|<......| | .
| +-------+ +-------+ REL +-------+ .
| | | .
Calling a1)IAM| | b)IAM .
Subscriber | +---------+ .
| | Called
| | Subscriber
----> v v ^
Lasting +-------+ +-------+ |
relation | |a2)IAM | | |
....> | |------>| |----+
Temporary | | | |
relation +-------+ +-------+
Transit Recipient
Network(s)(B) Network
Figure 7 - Query on Release by transit network
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The option b), in Figure 7, is valid when direct interconnection
exists between transit network A and recipient network.
Please note in this case that the DB query might take place also in
the originating network, i.e. that the DB could also exist in the
originating network.
That is what may occur if either the transit network A has no QoR
query capability or determines that the preceding network has QoR
capability. It therefore lets the release pass through to
originating network. The originating network, at reception of the
release, queries its NP database and reroutes the call towards
recipient network. In this scenario the originating network has
access to an NP DB with the complete address to both recipient
network and exchange, at least for ported-out numbers.
Sending back the release message to the originating network is also
of interest if the originating network has direct connections to
networks other than the transit network currently used.
When carrier selection is valid for the call, the originating
network reuses the carrier selection information after querying NP
DB. It could be debated if a selected carrier is allowed/recommended
to transport the release message to originating network, but it has
no option if it has no redirect on QoR capability.
(e164s2) 8.2.4 Routing initiated by "All call query" principles
In the scenario shown in Figure 8, the originating network has
access to an NP DB with the complete address to the recipient
exchange, at least for ported-out numbers. This implies that only
one NP DB look-up needs to be performed to complete the call.
Note however, that more than one DB look-up may be required if there
is not sufficient information to route to the recipient exchange.
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Originating Transit Donor
Network Network Network
+-------+ +-------+ +-------+
| +--+|a1)IAM | | | |
+-->| |DB||------>| | | |.....
| | +--+| | | | | .
| +-------+ +-------+ +-------+ .
| | | .
Calling | | a2)IAM .
Subscriber +---------+ +---------+ .
| | Called
| | Subscriber
----> | v ^
Lasting | b)IAM +-------+ |
relation +------------->| | |
....> | |----+
Temporary | |
relation +-------+
Recipient
Network
Figure 8 - All call query by originating network
As can be seen in Figure 8, the donor network is not involved in the
call set-up at all, however optionally the transit network [see
cases a1) and a2) above] might be transiting the call to the
recipient network.
Alternatively, a transit network, rather than the originating
network, could perform the NP DB look-up.
(e164s2) 9 Types of addresses and numbers - within networks
and across network boundaries
With service provider portability it may no longer be possible to
use an end user's number, dialled by the calling party, to route the
call to the customer. If a customer changes service provider, a
Routing Number (RN) is needed to be able to route the call. The
routing information may have one of the following:
- concatenated address (see 9.1);
- separated address (see 9.2);
- RN only, i.e. a plain network address, suppressed E.164 number
(see 9.3);
- DN only, i.e. a plain E.164 number (see 9.4).
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(e164s2) 9.1 Concatenated address
(e164s2) 9.1.1 Description
In this type of address, two numbers are concatenated in the same
signalling field (the called party number) which is used to route
the call (Figure 9).
+-----------------------+-----------------------+
| RN | DN |
+-----------------------+-----------------------+
Figure 9 - Showing a concatenated address
RN is a routing number prefixed for a routing purpose. The length of
RN may vary from country to country.
If some non-ported numbers have DN leading digits identical to the
RN, this may imply a signalling field exists which indicates
"Routing information for a ported number"; otherwise, the routing
would be ambiguous.
The RN could take one of the following values:
Case 1: RN represents the first digits of a number block usually
handled by the addressed entity to which the call has to be routed.
In this case, specific information carried by the signalling
protocol is needed to indicate that it is a call to a ported number.
Case 2: One or more of the first digits of the RN are digits not
used as first digits in the national numbering plan used to indicate
that the call is to a ported number. The value of the digits could
be between 0 and 9 (spare in the national numbering plan). The rest
of the RN identifies the addressed entity to which the call has to
be routed and is used for this purpose.
Case 3: This case is similar to case 2, but the first (or first
two) digit(s) of the RN field is (are) one of the hexadecimal values
nationally spare in the Signalling System No. 7. RN is used to route
the call to the addressed entity.
(e164s2) 9.1.2 Brief analysis
Case 1
Pros:
This solution does not waste any numbering resource since the RN
value is formed by the first digits of the number block usually
handled by the addressed entity.
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This solution does not need a specific addressing scheme (for
identifying the addressed exchange) and can be accommodated in the
existing signalling.
Cons:
This solution requires the use of a specific identifier to qualify
the routing number as an address used for a ported call which
requires special treatment. The routing mechanisms in exchanges have
to be adapted to be able to provide this special treatment. As there
is a constraint on the maximum length of the complete concatenated
address, the numbering space available for RN may be insufficient;
limitations can be present on the maximum numbers of digits being
supported by the signalling system and the exchanges in the
different networks involved.
Case 2
Pros:
As for case 1, this solution can also be accommodated in the
existing signalling. In opposition to case 1, this solution does not
require any additional information to qualify the call as a ported
call since one of the first digits of the routing number is
dedicated to ported calls.
Cons:
This solution makes use of a part of the national numbering scheme.
To be able to handle the prefix, routing mechanisms in the exchanges
will have to be changed. As there is a constraint on the maximum
length of the complete concatenated address, the numbering space
available for RN may be insufficient.
Case 3
Pros:
This solution does not waste any resource from the national
numbering plan since the first digit(s) is (are) hexadecimal.
[Footnote: That is, one of the 6 values A, B, C, D, E or F.] The
advantages are similar to those already mentioned for case 2.
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Cons:
The drawbacks are similar to those already mentioned for case 2.
However, since this solution makes use of hexadecimal character(s),
it requires changes (e.g. in signalling systems, switches and
support systems). Although the solution does not require any
resources from the national numbering plan, it does take up
numbering resources (it uses a spare value from the Signalling
System No. 7).
(e164s2) 9.2 Separated addresses
(e164s2) 9.2.1 Description
In this address type, the routing number and the directory number
are carried in two different fields in the signalling messages
(Figure 10). The address identifying the destination of the ported
call, routing number, is used to route the call. The DN is carried
transparently in a separate signalling parameter and is only used at
the called side to complete the call.
+-----------------------+
| RN |
+-----------------------+
+-----------------------+
| DN |
+-----------------------+
Figure 10 - Showing a separated address
(e164s2) 9.2.2 Brief analysis
Pros:
The routing number can either be an E.164 number or a non- E.164
number. In either case the routing number should be in the same
format as the national numbering plan. Since the called number and
routing number are carried in separate signalling parameters, the
possibility for mis-routing is minimized. If non-E.164 numbers are
used, all numbers from the national numbering plan can be used as
routing numbers. If E.164 numbers are used, numbers within the
national numbering plans must be identified and assigned only for
routing purposes. As opposed to prefix solutions, no special
treatment of routing numbers need to be provided by the routing
mechanisms of the exchange.
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Cons:
Such a separated address solution requires, by definition, that
signalling systems used are able to carry both RN and DN in separate
signalling parameters.
(e164s2) 9.3 RN only
(e164s2) 9.3.1 Description
In this case the routing number is the only information being sent
between exchanges/networks (Figure 11). The directory number, E.164
number, is not sent between exchanges but is translated into a
routing number. The routing number must point out the access line to
which the called party is connected as no other method is available.
+-----------------------+
| RN |
+-----------------------+
Figure 11 - Showing a routing number only
(e164s2) 9.3.2 Brief analysis
Pros:
The advantages of this addressing method are that it is
internationally available today because the RNs are E.164 numbers
and that it does not require any changes in the signalling systems.
Cons:
To be able to provide information regarding the DN, in services like
COLP, a second query in the recipient exchange (or in the last
transit exchange) is needed. This solution can waste numbering
resources (depending on the solution).
(e164s2) 9.4 Only DN (normally across network boundaries)
(e164s2) 9.4.1 Description
In this case the directory number is the only information that is
being sent between networks.
+-----------------------+
| DN |
+-----------------------+
Figure 12 - Showing a directory number only
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(e164s2) 9.4.2 Brief analysis
Pros:
It is not mandatory to introduce RN transfer between networks, i.e.
this solution does not affect existing network interfaces. It allows
different addressing options of different operators to work
together. Operators will have to transport routing information with
ported calls inside their networks, regardless of which number
portability solution is chosen. There are multiple options to
transport this routing information. Separation or concatenation of
routing information and directory number is the main characteristic.
Internal routing is not dependent on information given by other
networks (no network interdependence).
Cons:
Use of this addressing method requires the use of "all call query
all networks" architecture at the network interface.
(e164s2) 10 Combinations of addressing types, addressed
entities and mechanisms: general signalling requirements
The previous clauses above have identified that there are three
components that must be determined in any implementation of service
provider number portability:
1) the entity addressed by the routing number;
2) the method of transporting the routing number;
3) the architecture used to determine the routing number.
Addressed entity: Assuming a routing number is utilized (see below),
there are four possible entities that can be identified by the
routing number:
1) network termination point;
2) recipient exchange;
3) recipient network;
4) point of interconnection.
Transport of routing number: There are four transport methods
described:
1) concatenated;
2) separated;
3) no routing number used;
4) routing number only.
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Architectures: There are four architectures described:
1) onward routing;
2) dropback;
3) query on release;
4) all call query.
With the exception of the "No routing number used/routing number
only" transport mechanisms, the three components are independent of
one another, allowing a multitude of theoretically possible
solutions by combining the components. For example, an
implementation could consist of:
- Routing number identifies the recipient exchange, is transported
concatenated with dialled digits and is derived using an onward
routing architecture.
Or, an alternate implementation could be:
- Routing number identifies the recipient network, is transported
in a separate field to the dialled digits and is derived using an
all call query architecture.
The various combinations provide flexibility of implementation to
take into account economical and technical parameters of each
individual situation. For this reason this Supplement does not
recommend one solution over another.
(e164s2) 11 Examples of locations of number portability
database(s) within networks
(e164s2) 11.1 General description
Depending on the evolutionary level in a particular network, the NP
database will be located in different places of the network or
possibly even external to the network. The following principles of
NP data storing have been identified, described and evaluated:
a) exchange-based (distributed) solutions;
b) exchange external (centralized) solutions.
The following options for NP data query places have been identified,
described and evaluated:
1) originating local exchange;
2) gateway exchange(s);
3) transit or gateway exchange(s);
4) donor local exchange(s).
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Regardless of data storing place, the exchange/network can act
according to different NP principles, e.g. onward routing the call,
dropping back the rerouting information or even acting as a database
and responding a query with rerouting information.
(e164s2) 12 Administrative processes
In establishing number portability, processes that underpin its
introduction and management are a key requirement. The following
list provides top level guidance on specific areas of activity and
the steps that need to be covered.
Process activity Steps to be covered
Service Initial contact between operators
establishment Planning stage
Implementation planning
Network implementation and testing
Service Introduction of a new switch
maintenance Introduction of a new numbering block
Number change
New routing number
Service Request
ordering Validation
Scheduling
Contingency plans
Hours
Subsequent portability
Change of account name
Reasons for rejection
Installation
Cancellation
Fault and repair
handling
Directory number Directory entries
information Operator assistance
Emergency service
Number plan administration
Law enforcement agencies
Billing
--------------------------------------------------------------------
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5. Front Matter from the ITU-T Published Version
This section contains sections from the front matter of the ITU-T
published version of Supplement 2 to Rec. E.164, including the
Source, the Foreword, the note on "ROA," the text on intellectual
property rights, and the copyright notice. They are provided here
for information and reference. The text here was valid at the time
of publication, but there may have been revisions since then.
5.1 Source (from the ITU-T published version)
Supplement 2 to ITU-T Recommendation E.164 was prepared by ITU-T
Study Group 2 (1997-2000) and was approved under the WTSC Resolution
No. 5 procedure on the 9th of November 1998.
5.2 FOREWORD (from the ITU-T published version)
ITU (International Telecommunication Union) is the United Nations
Specialized Agency in the field of telecommunications. The ITU
Telecommunication Standardization Sector (ITU-T) is a permanent
organ of the ITU. The ITU-T is responsible for studying technical,
operating and tariff questions and issuing Recommendations on them
with a view to standardizing telecommunications on a worldwide
basis.
The World Telecommunication Standardization Conference (WTSC), which
meets every four years, establishes the topics for study by the
ITU-T Study Groups which, in their turn, produce Recommendations on
these topics.
The approval of Recommendations by the Members of the ITU-T is
covered by the procedure laid down in WTSC Resolution No. 1.
In some areas of information technology which fall within ITU-T's
purview, the necessary standards are prepared on a collaborative
basis with ISO and IEC.
5.3 NOTE (from the ITU-T published version)
In this Recommendation the term "recognized operating agency" (ROA)
includes any individual, company, corporation or governmental
organization that operates a public correspondence service. The
terms "Administration," "ROA" and "public correspondence" are
defined in the "Constitution of the ITU (Geneva, 1992).
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5.4 INTELLECTUAL PROPERTY RIGHTS (from the ITU-T published version)
The ITU draws attention to the possibility that the practice or
implementation of this Recommendation may involve the use of a
claimed Intellectual Property Right. The ITU takes no position
concerning the evidence, validity or applicability of claimed
Intellectual Property Rights, whether asserted by ITU members or
others outside of the Recommendation development process.
As of the date of approval of this Recommendation, the ITU had not
received notice of intellectual property, protected by patents,
which may be required to implement this Recommendation. However,
implementors are cautioned that this may not represent the latest
information and are therefore strongly urged to consult the TSB
patent database.
5.5 Copyright Notice (from E.164 Supp. 2, ITU-T published version)
(c) ITU 1999
All rights reserved. No part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical,
including photocopying and microfilm, without permission in writing
from the ITU.
6. Security Considerations
None.
7. References
1 Bradner, S., "The Internet Standards Process -- Revision 3",
BCP 9, RFC 2026, October 1996.
2 ITU-T Recommendation E.164 (05/97), "The international public
telecommunication numbering plan".
3 Supplement 2 (11/98) to ITU-T Recommendation E.164 (05/97),
"Supplement 2: Number Portability".
4 "Report of the IP-Telecoms Interworking Workshop (Numbering,
Naming, Addressing and Routing), ITU, Geneva 25-27 January 2000",
http://www.itu.int/ITU-T/ip-telecoms/ip-telecoms.htm, last
modified 2000-03-20.
5 "Telephone Number Mapping (enum)", last modified 03-Jul-00,
http://www.ietf.org/html.charters/enum-charter.html.
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8. Acknowledgments
I would like to thank the ITU TSB (Telecommunication Standardization
Bureau), and Mr. John Tar in particular, for helping to make the
text of Supplement 2 to E.164 freely available on the ITU web site.
9. Author's Address
Andrew Gallant
Comsat Corporation
6560 Rock Spring Drive
Bethesda, MD 20817 USA
Phone: +1 301 214 3264
Fax: +1 301 214 7226
Email: andrew.gallant@comsat.com
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