by Joe Blaschka, Jr., P.E.
It seems as though there is no rest for the weary. While weare still knee deep in wire-
less issues, another issue crops up that is going to createproblems. This issue is number
portability. Number portability means different things todifferent people. To the PCS
community, number portability can mean being able to use onenumber to reach a person
anywhere; to others it means being able to use your telephonenumber no matter where
you go, sort of a telephone number for life. To the CompetitiveLocal Exchange Carriers
(CLECs), sometimes called Competitive Access Providers (CAPs),providing it means
being able to compete against the dominant Local Exchange Carrier(LEC), and, in the
future, other CLECs, by having customers retain their telephonenumbers regardless of
who is providing dial-tone. (This battle has already been foughton the 800 number
battlefield with number portability in place now.) If you are aCLEC and a bank has the
telephone 555-BANK, you will be at a significant competitivedisadvantage if the bank
has to change their number. You can see why this is a big issuefor competitive
providers.
Today, in many places this is handled by using Remote CallForwarding (RCF) at the
terminating office. The call is processed as follows:
1. A customer dials the bank’s number: 360-555-BANK.
2. The call is routed through the network the same way any normalcall is through
the Public Switched Telephone Network (PSTN).
3. At the terminating end office for the bank’s NXX, the office”sees” that the call
must be routed (forwarded) to another phantom number that”belongs” to the
CLEC. The bank is likely not aware of this phantom number.
4. The call is routed to the forwarded number through the PSTN tothe CLEC
switch.
5. The bank’s phone system is alerted of an incoming call.
This approach has a couple of significant problems.
1. There are often feature restrictions on numbers/lines thathave been RCF’d (e.g.,
sometimes 3-way calling does not work).
2. This approach uses two telephone numbers, which are in shortsupply.
What happens when the bank dials 9-1-1? Well, usually the10-digit phantom number is
displayed. If the CLEC has put their numbers in the 9-1-1 database, the correct address
will show up on the ANI/ALI screen. However, when the call-takerrequests a confir-
mation of the caller’s telephone number, there will be a problembecause the phantom
number will be displayed but the caller will give the”bank’s” number of 555-2265. This
will likely cause some problem at the PSAP and may generate a”trouble ticket.” On the
positive side, if the call is a hangup call, the call-taker candial the phantom number and
still reach the bank. This is because the phantom number is adialable legitimate network
telephone number.
A new approach is being proposed to help resolve some of theseproblems but it may
create a bigger problem for E9-1-1. This new approach usescapabilities being proposed
for the Advanced Intelligent Network (AIN). Figure 2 is a diagramof how this might
work. Central to this concept is a break between what is known asthe Customer Net-
work Address (CNA) and the Network Node Address (NNA). Today (forthe most part),
these numbers are the same. The number of your home is not onlyassigned to you but
also represents the terminal address of the telephone line toyour house. This new con-
cept breaks this hard physical relationship and replaces it witha relationship in a data
base.
While at first glance this does not seem to be much differentthan the RCF version dis-
cussed before, the differences are significant. A call would beprocessed as follows:
1. A customer dials the bank’s CNA 555-BANK. This generates anAIN “trigger” in
the originating office, which in turn queries a data base for theNNA.
2. The call is now routed through the PSTN to the CLEC based onthe NNA.
The key here is that all network routing is based on NNAs, whichare not dialable
directly from a customer’s location. In fact, an NNA could beused as a CNA because
the only relationship between a CNA and an NNA is thatestablished in the data base.
Theoretically, NNAs might not even need to conform to theexisting North American
number plan as long as they are consistent within the network.
Now comes the problem for a 9-1-1 call. When the caller dials9-1-1, what will be
displayed at the PSAP? If the NNA is displayed, this could beused to look up the
address associated with the NNA, assuming it is in the data base.However, the PSAP
could not call the caller back because the NNA would not bedialable by the PSAP.
What would likely happen if an attempt is made to dial the NNA isthat it would be
considered a CNA by the originating office and routed to whoknows what NNA. Need-
less to say, this could cause significant problems for 9-1-1.
This approach also causes problems for the service known as”Caller-ID.” However,
Caller-ID is not generated in the network the same way E9-1-1 ANIis generated. Any
fix for Caller-ID may not fix the problem for E9-1-1.
This is another example of how changes in the telephone networkwill continue to cause
problems for 9-1-1 until the 9-1-1 systems are part of themainline telephone network.
We will be fighting battles constantly until Public Safetyrealizes they cannot fight the
battle against technology and the marketplace. 9-1-1 needs to bepart of the solution and
not a constant problem to be solved. “Eternal vigilance isthe price of freedom.” Public
Safety must be eternally vigilant to keep their system free fromthe tyranny of
obsolescence.
Joe Blaschka, Jr., P.E., started Adcomm Engineering Company inWoodinville, WA, 15
years ago and is its president. He has worked in thetelecommunications engineering
field for over 20 years. He is active in NENA’s PCS/PCN efforts.Mr. Blaschka received
his BSEE from Seattle University and is active in variousprofessional engineering and
public safety organizations.