Subject: [Enum] draft-loughney-enum-roaming-00.txt

From: James Yu <[email-masked]>
Date: Mon, 6 Nov 2000 15:39:54 -0600

It has been quiet on this particular I-D.  At the last ENUM meeting, some
people commented that ENUM was not appropriate for the cellular roaming use.
This is to clarify why ENUM can be used between two cellular/PCS networks.

When a roamer appears in the visited cellular network, it registers itself
using its International Mobile Station Identity (IMSI).  I'll use a simple
case by assuming that Temporary Mobile Station Identity (TMSI) is not
involved.  This IMSI (E.212 recommendation) is first converted to a mobile
global title described in E.214  recommendation by the Visitor Location
Register (VLR).  The SS7 networks uses the E.214 number in the Signaling
System Number 7 (SS7) Signaling Connection Control Part (SCCP) Called Party
Address parameter to perform global title translations (GTTs) and
eventually reaches the Home Location Register (HLR) of the roamer.  In the
Mobile Application Part (MAP) layer (e.g., GSM MAP), an E.164 number
identifier called VLRID is present that tells the HLR to use that VLRID to
route the response back (the VLRID is also in the SCCP Calling Party Address
parameter of the 1st message from the VLR to the HLR.  The key point is that
the first message uses an E.214 number (actually it is very similar to an
E.164 number) but the subsequent messages all use E.164 numbers (VLRID and
HLRID) to transport SS7 messages between the HLR and VLR.  

Since ENUM deals with E.164 numbers only, "ROAM" service in this I-D  allows
the cellular nodes to allocate the HLR or VLR associated with a roamer.
The resolution of E.214 numbers (or directly using the E.212 numbers) may
require another ENUM-like process (e.g., e214.arpa).  There are certainly
ways that can avoid the use of ENUM.  But here we are discussing how ENUM
can be used.  The HLRID and VLRID can be E.164 numbers not assigned to the
end users.  This is what I called 'network-related service" in the
draft-pfautz-yu-enum-adm.00.txt, "ENUM Administrative Process in the U.S.A."
One reason that GTT is used in SS7 message transport is because the message
routing in many cases involve two cellular networks in different countries.
A SS7 point code in U.K. cannot be used directly by a SS7 node in France to
send a SS7 message to.   IP will change that because IP is global.  This is
just one example of use of ENUM.  Another example is to identify the message
center that serves a particular cellular subscriber when there is a short
message destined towards that subscriber.  In this example, the E.164 number
is assigned to an cellular subscriber; however, the service that uses ENUM
is again a "network-related service."

John and I would like to hear from you to see whether they is any problem to
move this I-D forward.  Thanks.

James Yu
Principal Technical Industry Liaison
NeuStar Inc.
1120 Vermont Avenue, NW,
Suite 550
Washington, D.C. 20005
USA
+1-202-533-2814 (B)
+1-202-285-8326 (Mobile)
+1-202-533-2976 (Fax)
[email-masked]
http://www.neustar.com

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