Thread Subject: Re: teitac-telecom, PSTN Reference
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From: Gregg Vanderheiden
Date: Fri, Mar 30 2007 8:50 AM
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It is important however to note that the world is not divided into PSTN and
I would suggest that we think of Telecom in 3 categories
1) Public Analog phone systems (PSTN)
- only 1 channel which is for voice
- can't transmit data except as tones
2) Public IP/SIP phone system (emerging - SIP / IP)
- public IP Phone network
- currently just uses the Internet (for
public system. Other networks are used for private.)
- shouldn't be transmitting data via tones.
Data (including text) can and should be transmitted as data.
- supports multiple parallel channels in
both directions (voice, text, and video)
3) All other non-public phone systems that either do or do not connect
to the public system(s)
Some examples of #3 would include
- Cellular phone systems (the link from phone to PSTN only)
- phone systems run by Cable Companies (from house to PSTN or
WHY DIVIDED IN THREE
I divide it into these three because they have very different
characteristics and need different rules.
- what works in 1 won't work well in 2.
- What works in 2 doesn't work in 1.
So the requirements must be different between these two.
#3 is internal and controlled by each system. Also use a wide variety of
- shouldn't regulate these except where they interface with users or the
- internally, we should keep hands off for HOW. Just talk
about what they should be capable of.
- So we should say WHAT they (#3 technologies) should do but NOT HOW they
should do it.
#1 and #2 however are not controlled by any one party.
o They are not even controlled by any one industry.
o So we need to specify not only WHAT but ALSO HOW they implement
some things or there will be no interoperability.
o They can do other things in ADDITION to the required formats. But
they MUST support the required format or there is no guarantee of
interoperability. And market forces cannot enforce or cause
interoperability as has been so often shown.
Gregg C Vanderheiden Ph.D.
> -----Original Message-----
> From: = EMAIL ADDRESS REMOVED =
> [mailto: = EMAIL ADDRESS REMOVED = ] On Behalf Of
> Michaelis, Paul R. (Paul)
> Sent: Monday, March 26, 2007 10:28 AM
> To: TEITAC Telecommunications Subcommittee
> Subject: Re: [teitac-telecom] teitac-telecom, PSTN Reference
> Quoting from the web page you cited:
> "Public Switched Telephone Network communications (PSTN,
> T.70) The collection of interconnected systems operated by
> the various telephone companies and administrations (telcos
> and PTTs) around the world. Also known as the Plain Old
> Telephone System (POTS) in contrast to xDSL and ISDN (not to
> mention other forms of PANS)."
> Note that this definition seems to say that services such as ISDN are
> *not* considered to be PSTN. Presumably, this would also
> mean that digital telephones, operating behind a PBX, are not
> PSTN. These phones are not IP either. This would mean that
> the proposal to classify equipment as either PSTN or IP will
> leave an entire category of telecom equipment without an obvious home.
> A reason why I am passionate about this issue is that I've
> wasted a tremendous amount of time over the past seven years,
> arguing with people
> -- including people in my own company -- about how to
> interpret the Section 508 requirements. "This requirement
> means this!" "No, it means that!!!" As part of the Section
> 508 refresh, we need to write unambiguous requirements that
> cannot be misinterpreted. Without that, contract officers
> will continue to buy whatever the heck they want,
> manufacturers will continue to sell inaccessible solutions to
> the government, and the likelihood that my company will let
> me build anything else will be close to nil.
> Getting back to the use of "PSTN" to describe non-IP phones,
> my fear is that some people who are looking for an excuse to
> avoid investing in accessibility -- including people in my
> own company -- will claim that ISDN and digital phones behind
> a PBX are exempt because they don't fall into either
> category. During the next seven years, I want to spend more
> time building solutions, and less time arguing about whether
> they ought to be built.
> -- Paul Michaelis
> -----Original Message-----
> From: Jasionowski, Tony [mailto: = EMAIL ADDRESS REMOVED = ]
> Sent: Monday, March 26, 2007 7:42 AM
> To: = EMAIL ADDRESS REMOVED =
> Subject: [teitac-telecom] teitac-telecom, PSTN Reference
> "wired analog and wired non-IP digital" seems odd considering
> we also have "cordless analog and digital". I suggest we
> stick with PSTN for now unless someone can propose acceptable
> alternative term. FYI, anyone can easily find the definition
> of PSTN at several web sites including:
> Therefore, PSTN may not be so confusing after all.
> Tony Jasionowski
> Message: 1
> Date: Sat, 24 Mar 2007 17:41:44 -0600
> From: "Michaelis, Paul R. (Paul)" < = EMAIL ADDRESS REMOVED = >
> Subject: Re: [teitac-telecom] Telecommunications Working Group- Draft
> 1 Template for 508 in WORD
> To: "TEITAC Telecommunications Subcommittee"
> < = EMAIL ADDRESS REMOVED = >
> Cc: = EMAIL ADDRESS REMOVED = , Creagan Tim
> < = EMAIL ADDRESS REMOVED = >
> < = EMAIL ADDRESS REMOVED = .
> Content-Type: text/plain; charset="us-ascii"
> Regarding the reference to "PSTN" versus "IP" in many of the
> proposed requirements, I agree that IP telephones should be
> treated differently but am concerned that describing the
> non-IP systems as "PSTN" will create a lot of confusion.
> The "PSTN" is the Public Switched Telephone Network. If
> asked to describe a PSTN telephony endpoint, I imagine that
> most telecom specialists would say it was an analog device
> that complies with the FCC regulations that govern
> residential telephones. If we use this definition, I can't
> remember the last time I've seen a government procurement of
> telecom equipment that falls into this category.
> There are at least three different categories of non-IP wired
> telephones in common use today:
> Residential analog. (This is what most folks would classify
> as a "PSTN
> Enterprise analog. (The distinction between these phones and
> residential analog sets is that the enterprise sets connect
> to the PSTN via a PBX or switch that is owned by the
> enterprise. An important electrical distinction is that,
> unlike enterprise analog telephones, residential telephones
> are required to do "automatic loop length compensation" to
> account for distance-related differences in electrical
> resistance and capacitance in the line between the phone and
> the associated central office. Another important distinction
> is that many enterprise analog solutions are actually hybrid
> analog/digital sets.
> The audio stream is carried as traditional analog,
> supplemented by digital signaling that, for example, controls
> the phone's display.)
> Enterprise digital. (This is what is purchased in the vast
> majority of non-IP wired telephony procurements by the
> government. All audio transmissions entering or leaving the
> phone are digitally encoded, typically using the G.711
> algorithm that I described in a previous message. Signaling
> and call control is also digital, typically using protocols
> that are proprietary to the individual manufacturers.)
> Wired residential analog systems, wired enterprise analog
> systems, and wired enterprise digital systems are able to
> transmit Baudot TTY signals with 100% reliability. IP
> telephony is different.
> Depending on network characteristics, the mechanisms that are
> used in order to transport voice signals within IP networks
> are not always suitable for transporting Baudot TTY tones.
> Common sources of impairment include packet loss and the use
> of voice-optimized audio compression algorithms, such as
> G.729. For this reason, a traditional TTY device used in
> conjunction with an IP phone (for example, via an acoustic
> coupler) is not always going to be reliable.
> The good news is that, although not yet in common use, there
> are international standards that describe how to transport
> text and Baudot tones reliably on IP networks. In general,
> these techniques do not use the same audio encoding and
> transmission mechanisms that are used for voice. I agree
> completely that the availability of these techniques, coupled
> with the inherent unreliability of Baudot TTY transmissions
> via the "voice channels" of IP telephone networks, makes it
> essential that we treat IP telephony as a special case in the
> Section 508 refresh.
> Getting back to the original topic of my message... We need
> a term other than PSTN to describe non-IP wired telephony.
> Ideally, it should be a term or description that would make
> sense to someone who is not knowledgeable about telephone
> engineering. To start the ball rolling, I suggest "wired
> analog and wired non-IP digital" as a substitute for PSTN.
> (I deliberately use the word "wired" because wireless devices
> have special characteristics that may need to be addressed
> -- Paul Michaelis
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