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Archive      18 Dec 2006                 #56


by William Flanagan

We assume voice service will be there all the time.  Pick up the phone, there's dial
tone.  Dial a number, it's ringing within seconds.  It's taken over 100 years of
practice and refinement to achieve that status of "presumed perfect" using circuit
switching in the Private Branch Exchange (PBX).

Can you do that for packet switched voice in less than ten years?

Turns out, you can.  But it takes much care--and probably some outside help.  Just as
you rely on a telephone carrier for the CO service, and an interconnect or VAR for
telephone CPE, there will probably be similar providers of the best VoIP service.

Note that "service" was deliberate.  Hardware and software alone won't reach the high level of availability for VoIP that we enjoy for TDM telephony.  There is necessarily a human component--somebody has to tend to the machinery in the closet (or data center).  Many LEC employees have a rather limited view of the service they offer, perhaps as little as dial tone, though they own and operate the largest machine ever created--the Public Switched Telephone Network.

Admittedly, the Internet carries more bits, but it isn't as pervasive as the PSTN--yet.

Will VoIP make the Internet the clear winner of the Largest Machine Award?  No, because the most reliable voice services (the kind we all want and all businesses can pay for) will be on managed IP networks, not the generic Internet.  Under direct management of the voice services provider, an IP network protected from the spam and malware of the Internet can be as good as Marketing will let the techies make it--easily exceeding five 9's.

The next link in the HA chain for VoIP is local access.  That's relatively easy as T-1
lines have an excellent history.  Back up the leased line with DSL, WiMAX, or cable
modem and most customers will feel very confident they will have acceptable availability for phone service.

Routing VIP calls, offering directories, and providing the other functions related to
telephony (voice mail, multiple line appearances, and the other 500 features on major PBXs) relies on servers that support the call routing software.  Here we have some interesting options, but little in the way of standards.

Sun Microsystems has offered High Availability platforms to the telecoms industry for many years.  One VoIP vendor to take advantage of that platform is Natural Convergence, Ottawa.  Their business model for their call-processing product brings out the main features described above:
-- Carrier-oriented, where they sell to companies (local exchange carriers or VoIP-only carriers) dedicated to maintaining a hosted VoIP service that functions at all times.
-- On a dedicated IP network;  all the carriers using Natural Convergence call
processing install dedicated access (usually T-1 or E-1, but also DSL or fiber) between each customer and the IP network.  Often all IP addresses are private, non-routable, to protect the phone system from Internet attacks and eliminate the problem of providing a good firewall.  These days, such a private IP network is relatively easy to set up as a VPN on an MPLS network.

Deployed in redundant pairs, Sun Netra 240 servers can be managed to provide better than 99.999% uptime--including all maintenance such as software upgrades, patches, and hardware repairs--to over 10,000 users.  One server carries the full load if the other fails or is taken down for maintenance.  The switch-over is glitchless--users don't notice.

That leaves the last, and often the least, component of the VoIP system:  the LAN.  LANs don't have as good a reputation for availability as the phone system.  That will have to change significantly to make VoIP viable in large organizations.  Won't happen this week.  Natural Convergence is working to avoid the LAN reliability problem by avoiding the larger, multi-layer LANs.  Targeting the small to medium business sector, they find relatively simple LANs with a flat topology:  a good router and a few switches to provide power over Ethernet to the phones.

So is the effort to set up HA servers, dedicated IP networks, and reliable local access
and LANs justified by HA IP phones?  In a word, no.  Why bother when the old cross-bar in the basement is still dishing up reliable dial tone?

We want to bother because of additional services.  I've used VoIP, and found the SIP
"forking" of calls quite useful.  That is, an incoming call can ring on multiple phones,
the first of which to answer gets the call.  Natural Convergence has gone one better,
with a feature that "twins" a line appearance on a VoIP desk set with a cell phone.  If
a call is answered on the cell phone, the user can go into his office and pick up the
same call on the land line (where the button shows the line is in use).  Saves air time
at the cellular rates, you don't have to give out your cell phone number, and it works
on an IP phone anywhere.

The other feature I'm looking forward to is a single voice mail box for the land line
and cell phone--especially if it's always available.

"Flanagan Consulting" and "ViewsLetter" are Service Marks of W. A. Flanagan, Inc.

Flanagan Consulting
W. A. Flanagan, Inc.
45472 Holiday Drive, #3
Sterling, VA 20166
Ph:  +1.703.242.8381
Fx:  +1.703.242.8391
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