Internet Draft James Yu
Document: <draft-yu-tel-url-00.txt> NeuStar, Inc.
Category: Informational July 2000
Extensions to the "tel" and "fax" URLs to Support Number Portability
<draft-yu-tel-url-00.txt>
Status of this Memo
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<draft-yu-tel-url-00> Informational-Expiration on January 2001 1
Extension to the "tel" and "fax" URLs to Support NP July 2000
1. Abstract
Number portability (NP) allows the telephone subscribers to keep
their telephone numbers when they change service provider, move to a
new location, or change the subscribed services. The NP
implementations in many countries presently support service provider
portability for geographic numbers and non-geographical numbers. It
has been identified that NP has impacts on several works-in-progress
at the IETF. One of the impacts is to carry the NP related
information in the SIP INVITE message. This document proposed the
extensions to the "tel" and "fax" Uniform Resource Locators (URLs)
to support NP so that they can be used to carry the NP related
information in the Session Initiation Protocol (SIP) Request-URI.
2. Introduction
This document proposes the extensions to the "tel" and "fax" Uniform
Resource Locators (URLs) for supporting number portability (NP).
[NP] provides an overview of the NP in the GSTN and points out the
impacts of NP in several works-in-progress at the IETF Working
Groups. One of the impacts is to be able to carry the NP related
information in the Session Initiation Protocol (SIP) INVITE message.
The NP related information includes the dialed directory number, a
routing number and an indicator that indicates whether a query to
the Number Portability Database (NPDB) has been performed. The
routing number allows the network, either the Global Switched
Telephone Network (GSTN) or the IP-based network, to route the call
to the network or switch that currently serves the dialed called
party number that has ported out of the donor network. The NPDB dip
indicator informs the network entities downstream towards the
terminating network (e.g., the network that currently serves the
called party number) that NPDB dip has been performed; therefore,
there is no need to dip the NPDB again. The dialed called party
number is needed at the terminating switch so that the call can be
terminated to a correct line card. If the routing number only
points to the terminating network, the called party number would be
used for another NPDB query to retrieve another routing number that
is typically a network-specific routing number for routing the call
to the terminating switch.
3. SIP Request-URI
The SIP INVITE message contains a "Request-URI" element that is used
by the SIP servers for making routing decisions. As indicated in
[SIP], SIP servers may support Request-URIs with schemes other than
"SIP," for example, the "tel" URI scheme. [TEL] specifies the URL
schemes "tel," "fax" and "modem" for specifying the location of a
terminal in the phone network and the connection types (modes of
operation) that can be used to connect to that entity. By examining
the SIP URL and "tel" URL, it seems that the "tel" URL is a better
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Extension to the "tel" and "fax" URLs to Support NP July 2000
place to carry the NP related information. Since the "fax" URL may
be used for fax calls, both the "tel" and "fax" URLs need to be
enhanced to support NP.
4. Proposed extensions to the "tel" RUL Scheme
The following shows the extensions to the "tel" URL. Only the
impacted items/lines are shown below.
global-phone-number = (no change)
(no change)
(no change)
*1(number-portability)
local-phone-number = (no change)
(no change)
(no change)
(no change)
future-extension) *1(number-portability)
number-portability = ";" routing-number *1(";" npdb-dip-indicator)
routing-number = rn-tag "=" *1("+") rn-ident
rn-tag = "rn"
rn-ident = *15(hex excluding "F")
npdi-dip-indicator = npdi-tag "=" npdi-ident
npdi-tag = "npdi"
npdi-ident = "yes" / "no"
It is assumed that national routing number may appear with other
global-phone-number information and international routing number may
appear with other local-phone-number information. The routing
number digit can be any hexadecimal digit except the digit "F."
The routing number and the NPDB dip indicator can appear at most
once if present. The routing number can contain hexadecimal digits
from 0 to E. When the routing number is present, the NPDB dip
indicator may or may not be present. This is because that the
routing number may be present independent of NP. When the "npdi"
parameter is not present, it indicates that either NPDB dip has not
been performed (equivalent to npdi=no) or NP is not relevant. If a
SIP server is set to perform the NPDB queries and if a received
INVITE message does not contain "yes" in the "npdi" parameter, it
will perform the NPDB query. The NPDB query is outside the scope of
this document. The routing number received in the response (plus
the "+" and the country code when necessary) will replace the
routing number in the "rn" parameter if present or will be used by
the new "rn" parameter if "rn" parameter is not present. The "npdi"
parameter will be set to "yes" in this case. The routing number can
be a global routing number (e.g., with "+" and the country code) or
a local (e.g., network-specific) routing number. When the "rn"
parameter is present, it must be used for making routing decisions
(e.g., against the TRIP routing tables)[TRIP]. If the "rn"
parameter is not present, the telephone number right after "tel:" is
used as the routing number.
<draft-yu-tel-url-00> Informational - Expiration in January 2001 3
Extension to the "tel" and "fax" URLs to Support NP July 2000
It is possible that interworking between SIP and Signaling System
No. 7 (SS7) Integrated Services Digital Network User Part (ISUP) is
required at the border between the Global Switched Telephone Network
(GSTN) and the IP-based network. For SIP to GSTN interworking and
depending on the ISUP support of NP, the information in the "tel"
URL will be mapped/carried in the proper ISUP parameters. For
example, for the GSTN in the U.S., the routing number in the "rn"
parameter is carried in the ISUP Called Party Number Parameter. The
phone number after "tel:" is carried in the ISUP Generic Address
Parameter. Only national numbers are carried (e.g., without the "+"
and the country code) in the ISUP parameter. The "npdi" parameter
that contains "yes" cause the Forward Call Indicator parameter to be
properly set to indicate that NPDB has been dipped. If the
terminating GSTN supports concatenated routing number and directory
number (e.g., in Europe), then the routing number and the phone
number are concatenated and put in the ISUP Called Party Number
parameter. The NOA value will be set according the terminating
GSTN's NP standards.
For GSTN to IP interworking, when the ISUP signaling contains the NP
related information, the NP related information is mapped to the
"tel" URL. This happens for domestic calls where the originating
GSTN has performed the NPDB query, or for international calls that
have arrived at the terminating country's GSTN where that GSTN has
performed the NPDB query. It is assumed that the GSTN routes the
call via the IP-based network to the terminating switch or network
in the same country, and SIP and ISUP interworking is involved. For
the GSTN in the U.S., the interworking is straightforward. The
indication in the ISUP Forward Call Indicator parameter that NPDB
dip has been performed will set "npdi" to "yes," the number in the
Called Party Number parameter plus the "+" and the country code, if
a global routing number, is carried in the "rn" parameter, and
called party number in the Generic Address Parameter plus the "+"
and the country code, if a global phone number, appears after
"tel:". For GSTN that supports concatenated routing number and
directory number (e.g., in Europe), the IP entity that performs the
interworking needs to know the routing number used by the GSTN so
that the routing number and the directory number in the concatenated
format in the ISUP Called Party Number parameter can be separate out
and transported in the "rn" parameter and after "tel:" by adding the
"+" and the country code to them if they are global routing number
and phone numbers.
5. Proposed extension to the "fax" URL Scheme
The following shows the extensions to the "fax" URL. Only the
impacted items/lines are shown below.
fax-global-phone = (no change)
(no change)
(no change)
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Extension to the "tel" and "fax" URLs to Support NP July 2000
future extension) *1(number-portability)
fax-local-phone = (no change)
(no change)
(no change)
(no change)
future-extension) *1(number-portability)
number-portability = ";" routing-number *1(";" npdb-dip-indicator)
routing-number = rn-tag "=" *1("+") rn-ident
rn-tag = "rn"
rn-ident = *15(hex excluding "F")
npdi-dip-indicator = npdi-tag "=" npdi-ident
npdi-tag = "npdi"
npdi-ident = "yes" / "no"
The same discussions in Section 5 also apply to this section.
6. Examples
To simply the example and to focus on the "tel" URL in the Request-
URI, only the Request-Line of a complete SIP INVITE message is
shown. A SIP server receives an INVITE message as shown below where
+1-202-533-1234 is the dialed called party number and has been
ported out of the donor network.
INVITE tel:+1-202-533-1234 SIP/2.0
Assume that this SIP server is set to perform the NPDB query. Since
this INVITE message does not contain the "npdi" parameter, this SIP
server will perform a NPDB query. After receiving a response back
from a NPDB, it formulates the following SIP INVITE message:
INVITE tel:+1-202-533-1234;rn=+1-202-544-0000;npdi=yes SIP/2.0
This SIP server then uses the "rn" parameter to make the routing
decisions (e.g., using the routing number in the "rn" parameter to
check against the TRIP tables to determine the terminating GSTN
gateway).
If the dialed called party number +1-202-533-1234 is not ported and
the dialed called party number can be used as the routing number,
the outbound SIP INVITE message may look like
INVITE tel:+1-202-533-1234;rn=+1-202-533-1234;npdi=yes SIP/2.0
or
INVITE tel:+1-202-533-1234;npdi=yes SIP/2.0
The concept is that "rn," if present, is used for making routing
decisions, and the phone number after "tel:" is used if "rn" is not
present.
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Extension to the "tel" and "fax" URLs to Support NP July 2000
7. Conclusion
This Internet Draft proposes extensions to the "tel" and "fax" URLs
described in [TEL] to allow the SIP to carry the NP related
information in the "tel" and "fax" URLs. If agreed, it is proposed
to incorporate the proposed extensions in the next revision of
RFC2806.
REFERENCES
[NP] M. Foster, T. McGarry and J. Yu, "Number Portability in the
GSTN: An Overview," draft-foster-e164-gstn-np-01.txt, July
2000.
[TEL] A. Vaha-Sipila, "URLs for Telephone Calls," RFC 2806, April
2000.
[SIP] M. Handley, H. Schulzrinne, E. Schooler and J. Rosenberg,
"SIP: Session Initiation Protocol," draft--ietf-sip-
rfc2543bis-00.ps, May 2000.
[TRIP] J. Rosenberg, H. Salama and M. Squire, draft-ietf-iptel-trip-
02.txt, "Telephony Routing Information Protocol (TRIP)," May
2000.
Acknowledgement
The author would like to thank Jonathan Rosenberg and Henning
Schulzrinne for the discussion of SIP support of NP.
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