[VL2006] - 78: VoIP in Tough Neighborhoods--the Payphone Idea.

Wed May 5 10:21:48 EDT 2010

VL on VoIP <www.viewsletter.com>

*The VoIP Payphone Idea
*

By William Flanagan

Remember the public phone booth by the side of the road? Plain Old 
Telephone Service (analog technology POTS lines) worked pretty well 
without environmental controls. Cell phones have almost eliminated phone 
booths, but we still have work environments in tough neighborhoods like 
power substations, pit heads at mines, and remote railway switch 
points.  Multi-tenant building with no air conditioning in the wiring 
closets qualify as harsh, too.

Moving from circuit switching to IP introduces three key concerns.

   1. Power for active routers/switches where passive copper loops
      needed none.
   2. Cooling for that electronic equipment.
   3. Extending Ethernet LANs to match the reach of analog phone lines.

Sales literature for VoIP equipment typically shows high-end phones on 
executive desks or in business call centers.  The assumption is that the 
user and the wiring closet enjoy a controlled "office" environment.  It 
ain't necessarily so when the phone system extends beyond the office.

Electrical power is seldom a problem.  The utilities will drop a feed if 
you're willing to pay.  For low-power equipment you can deploy a solar 
panel and a storage battery to run through the night, or a fuel cell.  
Low drain reduces the cost of power infrastructure.

There are items that boast of low power.  Snom says its model 300 IP 
handset <http://www.snom.com/en/products/ip-phones/snom-300-ip-phone/> 
is the lowest, at 1.7 to 2.7 watts.  Encore Networks has a ruggedized 
router <http://encorenetworks.com/click_ds_BANDIT_2.htm> that draws only 
7 W.  That's a total of less than 1 amp at 12 V for voice and data 
connectivity.  These days, wherever voice is wanted there's almost 
always a need for data as well, so it's best to budget for both.

With power that low, the need for cooling may disappear.  Encore's 
router is hardened to operate in ambient temperatures from -40 to 85 C 
(-40 to 193 F)--and that's not a typo, that's the IEEE 1613 standard 
<http://ieeexplore.ieee.org/Xplore/login.jsp?reload=true&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F8014%2F28253%2F01263435.pdf%3Farnumber%3D1263435&authDecision=-203>.  
Phones to cover that range are "less common": most phone are 4 to 40 C 
(40 to 104 F). Cisco's 6901 IP phone 
<http://www.cisco.com/en/US/prod/collateral/voicesw/ps6788/phones/ps10326/data_sheet_c78-584412.html>, 
relatively low power at 3.11 W, is rated for -5 to 45 C (23 to 113 F). 
An interesting exception is a ruggedized 
<http://www.ctiusa.com/electronic_systems/enviroxtreme.html> adaptation 
of the Cisco 7961 IP phone that's "dust proof,"  but it needs a heater 
for the LCD when it's cold.

In a migration from a legacy switch to VoIP, we can assume a copper loop 
is in place, perhaps even a 4-wire cable capable of T-1 transmission.  
Old copper is not much good for native Ethernet, as in 10 Mbit/s LAN, 
but well-proven technologies (ISDN BRI or PRI, DSU/CSU, or DSL) can push 
IP and Ethernet over legacy cable for more than a mile.   These digital 
services from a local exchange carrier (LEC) typically cost more than 
the existing POTS line, but enterprise versions of the hardware are 
available if you have the right of way or own the cable.  As an 
alternative, Encore's router offers an internal cellular radio (for a 
data service) in addition to a CSU (one can back up the other for higher 
availability).

VoIP payphones don't look like a hot item with LECs in the US.  More 
likely the technology will find use in private networks, for control 
functions (think SCADA protocol) and voice connections on sprawling 
infrastructure such as power lines, pipe lines, and railroads.  To find 
IP versions of real payphones look on the WWWeb--not at the side of your 
road.

__

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