Gordon's Information and Communications Technologies (ICT) Blog

RIP Chris Kalaveras - Killed By Alleged Drunk Driver

2012-01-23T18:08:00.000-05:00

Back in October of 2009 at The National Science Foundation ATE 2009 Principal Investigators Conference in Washington, DC I had the chance to talk on camera with DeAnza College students Chris Kalaveras and Paul Nguyen.

Students that attend the conference spend three days in a variety of seminars, demonstrating and sharing their work with other colleges. These students are the best of the best - it's a competitive and thorough process involving nomination by a professor and selection by a committee in Washington.

Chris and Paul were nominated and selected. At the conference they displayed and demonstrated how they were taking donated computers, fixing them up and donating them to DeAnza students. Couple of impressive young guys doing great stuff.

On Thursday Chris was killed riding his motorcycle. The driver of the car involved in the accident has been booked on felony DUI charges. Here's the obituary from the Mercury News in San Jose.

The Santa Clara County Coroner on Friday identified the motorcyclist who died Thursday (January 19, 2012) evening after a collision with an alleged drunken driver as 25-year-old Christopher Kalaveras of Santa Clara.
Santa Clara police identified the driver as Aaron Keith Taylor, who was booked into jail on felony DUI charges.
Police said the motorcycle and another vehicle collided in a residential neighborhood near Francis and Santa Maria avenues, east of Lawrence Expressway, at 8:45 p.m. Santa Clara paramedics pronounced Kalaveras dead about 10 minutes later.
Police said it was not immediately clear if other factors, such as a slick road, could have contributed to the crash.

Chris was a great kid doing great things and on track to do even greater things. Such a sad and unnecessary loss. If you get wasted - stay off the road.

In Protest of SOPA and PIPA 1/18/12

2012-01-17T21:25:00.000-05:00

Like many others, I personally and strongly oppose SOPA (Stop Online Piracy Act), also known as House Bill 3261 and the Senate version PIPA (Protect Intellectual Property Act) or S. 968.

Supporters believe the bills, if made law, would expand the ability of U.S. law enforcement and copyright holders to fight online trafficking in copyrighted intellectual property and counterfeit goods.

Opponents, like myself, believe that they violate the First Amendment, is Internet censorship, will cripple the Internet, and threaten whistle-blowing and other free speech actions.

Here's a statement from Google - like many businesses, entrepreneurs and web users, we oppose these bills because there are smart, targeted ways to shut down foreign rogue websites without asking American companies to censor the Internet

I encourage you to form your own opinion. If you do agree with Google, Wikipedia and thousands of other companies, tech activists, entrepreneurs and myself - contact your congressman to tell them you're against the bills, either by calling their office, writing a letter, or sending a prepared message through http://americancensorship.org/

Verizon Buying "Netflix like" URLs

2012-01-17T11:52:00.000-05:00

Back from a couple of great conferences in San Francisco and Frisco, Texas - great content, college faculty, admins and staff from around the country doing some amazing work! I get jealous - there are so many great career choices and opportunities for technology students at community colleges!

It's nice to be home though and get back on more of a regular schedule. I've been watching and talking about a few things at the conferences - one of the biggest things is video, especially in the mobile space. It's hot and it's growing - Morgan Stanley reports that approximately half of all mobile traffic today is video and this is expected to grow to 70% in the next four years.

With the rollout of Internet Protocol (IP)-based 4G services like LTE and the move to smart phones, providers are looking for something to replace revenue specifically from SMS (text messaging designed for cell phones). With the conversion to an all IP infrastructure and smart mobile devices, SMS (and text plans) will be rapidly replaced with free IP-based smart phone services like Apple's iChat.

About a month ago there were rumors going around about Verizon moving into the online video space. What's lacking when it comes to a company like Verizon offering video? The stuff Netflix is doing - content, streaming technology and subscription plans. So there were also rumors last month that Verizon was considering a bid for Netflix.

Where's it at today? It's still just rumors but Fusible did report that Verizon registered four new domain names on January 12:

http://whois.domaintools.com/verizoninstantvideo.com
http://whois.domaintools.com/verizoninstantmovies.com
http://whois.domaintools.com/verizoninstantmusic.com
http://whois.domaintools.com/verizoninstanttv.com

It will be interesting to watch where this goes.

Back From Vacation!

2012-01-04T13:35:00.000-05:00

We had a really nice ten day break and now it's back to reality.

I'm out on San Francisco now for our fourth National and Mid-Pacific ICT Centers Winter Conference. This conference runs January 5-6 and features excellent presentations from ICT industry and ICT education representatives. Even in this period of high unemployment, quality ICT education leads to quality ICT employment, and that has a positive impact on the economy – at many levels. We're sharing quality ICT education information, resources and practices, improving ICT education, helping people find good ICT jobs and improving our current economy. I'd like to thank the City College of San Francisco, Microsoft and San Francisco State University for all the work involved in setting up and running this conference.

We leave San Francisco on Saturday morning, flying to Dallas for the Winter Working Connections Conference we are co-sponsoring with the Convergence Technology Center at Collin College. We'll have two fast-paced networking opportunities and conference presentations followed by two days of an in-depth faculty institute at the Collin College Preston Ridge Campus in Frisco, TX.

Great cutting edge content, good people and always lots of fun!

Facebook Friends and Frenemies Report - Why We Add and Remove

2011-12-19T14:57:00.002-05:00

There's a new Facebook research report from Nielsen McKinsey's NM Incite titled Friends & Frenemies: Why We Add and Remove Facebook Friends that's pretty interesting. The report looks at the factors that help Facebook users decide whether they want to add someone as a friend or remove an existing person the their friend list. Here's a few details:

Knowing someone in real life is the top reason cited for friend-ing someone (82%)
Offensive comments are the main reason someone gets the boot (55%)

Additional report details suggests that real world interactions drive online friendships. Meanwhile, sales-oriented and depressing comments help drive friend removals. Facebook etiquette also plays a role, with updating too often, too little or having too many friends a consideration for some Facebook users.

Regarding gender, the report research indicates that men are more likely to use social media for careers/networking and dating – while women use social media for a creative outlet, to get coupons/promos or to give positive feedback. More men add friends based on business networks or physical attractiveness and women are more likely to friend based on knowing someone in real life or remove them due to offensive comments.

Here's an interesting infographic from the report.

What's a T3 Line?

2011-12-15T14:21:00.000-05:00

In my last post I described what a T1, also called a DS-1, line was. Most of us have also heard the "T3 Line" term used. Let's take a look at what a T3 or DS-3 line is.

DS-2 Signal
Before we can describe a DS-3 line, let's first take a look at a DS-2. In that last post we figured out how each DS-1 signal (T1 line or circuit) carries a bit rate of 1.544 Mbps. Four 1.544 Mbps digital DS-1 signals are multiplexed into one DS-2 signal. If we have 4 DS-1 signals per DS-2 signal and each DS-1 signal is 1.544 Mbps we can calculate:

Adding overhead consisting of timing and synchronization bits brings the DS-2 bit rate to 6.312 Mbps.

DS-2 Formation

DS-3 Signal

Each DS-2 signal carries a bit rate of 6.312 Mbps. Seven 6.312 Mbps digital DS-2 signals are multiplexed into one DS-3 signal. If we have 7 DS-2 signals per DS-3 signal and each DS-2 signal is 6.312 Mbps we can calculate:

Adding overhead consisting of timing and synchronization bits brings the DS-3 bit rate to 44.736 Mbps.

And..... 44.736 Mbps.... that's a T-3 line!

T1 Lines - What They Are

2011-12-06T18:28:00.001-05:00

Most of us have heard about "T1" lines. We know they are some kind of (expensive) communications line you can get from one of the telephone companies. It turns out T1's are part of the Digital Signal (DS) Level System.

Back in August, I wrote a post titled More on CODECs: Quantization + Sampling Rate = A PCM Wave. In that post I described how a piece of an analog signal is quantized and companded and then given an 8 bit binary code in a process referred to as encoding. From that post, we know to convert an analog signal to a digital signal the analog signal is sampled 8000 times per second and, after matching the instantaneous voltage sample level to one of 256 discrete levels, an 8 bit code is generated for each sample. If we multiply the sample rate by the bit code we get:

(8000 samples/second)(8 bits/sample) = 64,000 bits per second (bps)

So we can say a single analog voice channel, after conversion from analog to digital, requires 64Kbps of digital bandwidth. This 64Kbps is referred to as Digital Signal Level 0 (DS-0) and is the basic building block or channel for the existing digitally multiplexed T carrier system in the United States and the digital E carrier system used in Europe.

Voice calls are digitally multiplexed using either time division multiplexing or statistical time division multiplexing. Calls are grouped in a way similar to frequency division multiplexing. Let’s look at how this is done.

Digroups or DS-1 signals

Individual analog voice call channels converted to digital and require a bit rate of 64 Kbps each. 24 64 Kbps digital voice channels are multiplexed into digroups or DS-1 signals. If we have 24 DS-0 signals per DS-1 signal and each channel is 64 Kbps we can calculate:

Adding overhead consisting of timing and synchronization bits brings the DS-1 bit rate to 1.544 Mbps - that's a T1!

DS-1 Formation

DS-1 Overhead

We’ve described the process of encoding where an analog signal is sampled 8000 times per second, quantized into one of 256 discrete signal levels, companded it is then given an 8 bit binary code. After a single analog signal sample has been encoded it is multiplexed, with 24 other encoded 8 bit sample signals. This generates a 192 bit (8 bits/sample signal × 24 sample signals) sequence for the 24 sample signals. A process called framing then adds one framing bit to create a 193 bit frame.

DS-1 With Overhead

The framing bits are used to keep the receiving device in synch with the frames it is receiving. Every twelve frames are grouped into a masterframe, also referred to as a superframe. Included within each masterframe is a twelve bit frame pattern from the 12 grouped 193 bit frames This twelve bit frame pattern carries a bit pattern of 000110111001 and repeats itself with each masterframe.

Masterframe

This masterframe bit pattern is used for synchronization.

Remember each channel is sampled 8000 times per second so a single frame represents one eight-thousandth of 24 individual channels or telephone calls. We can also say that, in one second a DS-1 signal transmits 8000 193 bit frames. We can use these numbers to calculate the true DS-1 bit rate which includes both data and overhead (framing) bits:

Each DS-1 signal carries a bit rate of 1.544 Mbps and.... that's a T1!

Carrier IQ - are You Being Tracked?

2011-12-02T11:46:00.001-05:00

Last month, security researcher Trevor Eckhart published a report accusing CarrierIQ of installing malware on more than 140 million devices worldwide. Eckhart also published a video showing CIQ's software secretly running in the background and monitoring a variety of handset activity on an HTC device including key presses, browsing history, SMS logs, and location data. If you have not seen it, here's Part 2 of Trevor's video:

Yesterday Senator Al Franken from Minnesota "reached out" to AT&T, HTC, Samsung, and Sprint Nextel after they acknowledged their use of Carrier IQ’s diagnostic software to request that they explain (within the next 12 days) what they do with the information they receive from the software.
Also yesterday, Carrier IQ released a statement saying:

We measure and summarize performance of the device to assist Operators in delivering better service. While a few individuals have identified that there is a great deal of information available to the Carrier IQ software inside the handset, our software does not record, store or transmit the contents of SMS messages, email, photographs, audio or video. For example, we understand whether an SMS was sent accurately, but do not record or transmit the content of the SMS. We know which applications are draining your battery, but do not capture the screen.

In addition, the following updates have been posted by The Huffington Post:

Grant Paul, a well-known iPhone hacker who goes by the screenname "chpwn",wrote on his blog that Apple has included Carrier IQ on the iPhone, but the software's default is disabled.

Want to find out if your phone is secretly tracking you? Check out our comprehensive list of the devices and carriers known to use Carrier IQ.

Who And Why I Follow Back on Twitter

2011-11-26T09:47:00.001-05:00

Catching up on some work this morning and going through new people that started following me over the past two weeks. I've got my account setup so I get email notification when someone follows me and I look at each one, determining whether I want to follow back. Out of the 302 new followers I picked up in the past couple of weeks, I followed back only 27 this morning. That's only 8.95% and it is pretty typical.

Here's how I personally sort this stuff out:

When someone follows my feed I've got Twitter setup to send me an email notification.
I've got my email client (Thunderbird) setup to automatically move those Twitter email notifications to a separate Twitter folder. When I have some time (like this morning) I go through the notifications, determining whether I want to follow back. Here's my follow-back determination procedure:

1. I've got Thunderbird setup to preview email. The first thing I look for is a name (a person) attached to the account. If I don't know your organization and there is no name listed, I'm probably not going to follow back. Some details:

I try and only follow back those with similar interests, these interests can be both work and hobby related. If you are a business, organization, academic institution or individual involved in Science, Technology Engineering or Math (STEM) I'm definitely following you back. I'll also follow you back if you are focused on one of my hobbies - for example - saltwater flyfishing.
Sorry but religion and politics are always a do not follow back red flag for me. I know many use Twitter and other social media for this kind of stuff and I don't have a problem with that. It's just not what I personally use it for.

2. If I like what I see in the email preview I'll click the link to your feed and take a look at the last 5 or so posts. If it is junk - spam, any hint of profanity, etc. Done - I'm not following you. The best chance for a follow back is if you have something posted I'm interested in. Maybe it is a short description with a link to an interesting post on the web. If it is something I really like and retweet it, you are definitely getting a follow back.

3. There are some exceptions and I typically follow back the following:

Local businesses (not based on religion or politics). This includes my favorite Pizza shop in Western Massachusetts.
Known organizations, like the National Science Foundation (of course!)
Some celebrities - how could you not follow back someone like Weird Al Yankovic?
Old friends and sometimes friends of friends if I can sort the connections out.

4. Once I start following you - if I do see any spam, profanity, religion, politics I'm un-following you. I also occasionally go in and cull the list of people I follow and this is the kind of stuff I'm looking for.

So..... back to my experience today - only 27 follow backs out of 302 new followers..... 8.95%. Yes - there is a lot of junk out there but..... mixed in with the junk there is a lot of good stuff.

You can follow me on Twitter at www.twitter.com/gsnyder

Wavelength Division Multiplexing (WDM)

2011-11-24T08:08:00.000-05:00

In my last legacy Public Switched Telephone Network (PSTN) post I covered Statistical Time Division Multiplexing (STDM). In this post let's take a look at Wavelength Division Multiplexing (WDM and DWDM) methods.

As bandwidth requirements continue to grow for both the legacy Public Switched Telephone Network and the emerged Internet/IP network most of the high bandwidth backbone transmission is being done with fiber optics and a method called Wavelength Division Multiplexing or WDM. WDM functions very similarly to Frequency Division Multiplexing (FDM). With FDM different frequencies represent different communications channels with transmission done on copper or microwaves. WDM uses wavelength instead of frequency to differentiate the different communications channels.

Wavelength

Light is sinusoidal in nature and wavelength, represented by the Greek letter lambda (λ) is a distance measurement usually expressed in meters. Wavelength is defined as the distance in meters of one sinusoidal cycle.

Wavelength Measurement

Wavelength indicates the color of light. For example, the human eye can see light ranging in frequency from approximately 380 nm (dark violet) to approximately 765 nm (red). WDM multiplexers use wavelength, or color, of light to combine signal channels onto a single piece of optical fiber. Each WDM signal is separated by wavelength “guardbands” to protect from signal crossover. One of WDM’s biggest advantages is that it allows incoming high bandwidth signal carriers that have already been multiplexed to be multiplexed together again and transmitted long distances over one piece of fiber.

Wavelength Division Multiplexing

In addition to WDM systems engineers have developed even higher capacity Dense Wavelength Division Multiplexing (DWDM) systems. Just this past week, Cisco and US Signal announced the successful completion of the first 100 Gigabit (100G) coherent DWDM trial. As backbone bandwidth requirements continue to grow these WDM and DWDM systems are significantly reducing long haul bandwidth bottlenecks.

Podcast - Why We Are Not Google: Lessons from a Library Web site Usability Study

2011-11-23T10:39:00.000-05:00

Back in September I had the chance to interview Troy Swanson, an Associate Professor / Teaching and Learning Librarian at Moraine Valley Community College in Palos Hills, IL. In the interview we discussed a paper he published with Public Service Librarian Jeremy Green, also at Moraine Valley Community College. Here's the abstract from that paper published at Elsevier's ScienceDirect.

In the Fall of 2009, the Moraine Valley Community College Library, using guidelines developed by Jakob Nielsen, conducted a usability study to determine how students were using the library Web site and to inform the redesign of the Web site. The authors found that Moraine Valley's current gateway design was a more effective access point to library resources than a mock-up site which incorporated a central-search box on the site homepage. This finding stands in contrast to the observed trends of library Web site design that emphasizes a “Googlized” search.

Troy and Jeremy's findings are very interesting, especially if you are managing/modifying an existing site or are considering creating one.

You can listen here:

Here's the links Troy refers to in the podcast:

The Next Level (Blockbuster article)by James Surowiecki

http://www.newyorker.com/talk/financial/2010/10/18/101018ta_talk_surowiecki

useit.com: Jakob Nielsen's Website

http://www.useit.com/

The Googlization of Everything (book review)

http://www.googlizationofeverything.com/

Why We Are Not Google: Lessons from a Library Web site Usability Study

http://www.sciencedirect.com/science/article/pii/S0099133311000280

*******

If you have iTunes installed you can listen to and subscribe to our podcasts by clicking here.

Digital Multiplexing - Statistical Time Division Multiplexing

2011-11-16T10:10:00.001-05:00

In my last legacy Public Switched Telephone Network (PSTN) post I covered Time Division Multiplexing (TDM). I described how TDM works and why it does not efficiently use bandwidth. In this post let's take a look at Statistical Time Division Multiplexing (STDM or STATDM or STAT MUX), a much more efficient way to multiplex.

A Statistical Time Division Multiplexer (STDM or STATDM or STAT MUX) does not assign specific time slots for each device. An STDM adds an address field to each time slot in the frame and does not transmit empty frames. Only devices that require time slots get them.

STDM uses dynamic time slot lengths that are variable. Communicating devices that are very active will be assigned greater time slot lengths than devices that are less active. If a device is idle, it will not receive any time slots. For periods where there is much activity STDMs have buffer memory for temporary data storage.

STDM Multiplexing

Each STDM transmission carries channel identifier information. Channel identifier information includes source device address and a count of the number of data characters that belong to the listed source address. Channel identifiers are extra and considered overhead and are not data. To reduce the cost of channel identifier overhead it makes sense to group large numbers of characters for each channel together.

In my next legacy PSTN post I'll cover Wavelength Division Multiplexing (WDM).

Broadband Divide Continues

2011-11-14T17:43:00.001-05:00

Earlier this week, the Department of Commerce's Economics and Statistics Administration (ESA) and the National Telecommunications and Information Administration (NTIA) released a study titled Exploring the Digital Nation: Computer and Internet Use at Home. The study analyzed 54,000 households using 2010 census data. Here's some details from a blog post at speedmatters.org:

68 % of households used broadband in 2010.

Broadband adoption rates are slower that mobile.

Households with lower incomes and less education, as well as Blacks, Hispanics, people with disabilities, and rural residents, were less likely to have Internet service at home.

Seventy percent of urban households had broadband at home, compared to 57 percent of rural households.

Less than half (43 percent) of households with annual incomes below $25,000 had broadband access at home, while 93 percent of households with incomes exceeding $100,000 had broadband.

Here's more from the study report:

As of October 2010, more than 68 percent of households used broadband Internetaccess service, up from 64 percent one year earlier. Approximately80 percent of households had at least one Internet user, either at home or elsewhere.

Cable modem (32 percent) and DSL (23 percent) ranked as the most commonly usedbroadband technologies. Other technologies, including mobilebroadband, fiber optics, and satellite services, accounted for a small, but growing, segment of households with broadband Internet access service.

2000s – continued to decline from five percent in October 2009 to three percent one year later.

Over three-fourths (77 percent) of households had a computer – the principal means by which households access the Internet – compared with 62 percent in 2003. Low computer use correlates with low broadband adoption rates.

Broadband Internet adoption, as well as computer use, varied across demographic and geographic groups. Lower income families, people with less education, those with disabilities, Blacks, Hispanics, and rural residents generally lagged the national average in both broadband adoption and computer use. For example, home broadband adoption and computer use stood at only 16 percent and 27 percent, respectively, among rural households headed by a Black householder without a high school diploma. Also, households with school-age children exhibited higher broadband adoption and computer use rates than other households.

The differences in socio-economic attributes do not entirely explain why some groups lagged in adoption. Broadband Internet adoption disparities decrease when regression analysis holds constant certain household characteristics, such as income, education, race, ethnicity, foreign-born status, household composition, disability status, or geographic location. For example, the gap with respect to broadband Internet adoption associated with disabilities decreases from 29 to six percentage points when controlling for income, education, age, and other attributes.

The most important reasons households without broadband Internet or dial-up service gave for not subscribing were: (1) lack of need or interest (47 percent); (2) lack of affordability (24 percent); and (3) inadequate computer (15 percent).

Households reporting affordability as the major barrier to subscribing to broadband service cited both the fixed cost of purchasing a computer and the recurring monthly subscription costs as important factors. Our analysis of the expanded CPS data suggests that work, school, public libraries, and someone else’s house were all popular alternatives for Internet access among those with no home broadband Internet access service. Not surprisingly, individuals with no home broadband Internet access service relied on locations such as public libraries (20 percent) or other people’s houses (12 percent) more frequently than those who used broadband Internet access service at home.

The study also describes the $7 billion Recovery Act funding directed towards broadband in the U.S. Be sure to check out the complete study document linked here.

Digital Multiplexing - Time Division Multiplexing

2011-11-11T19:01:00.001-05:00

In my last legacy Public Switched Telephone Network (PSTN) post I covered analog or frequency multiplexing. Frequency division multiplexing is now considered obsolete technology on the telecommunications network. Analog signals are more sensitive to noise and other signals which can cause problems along the transmission path. They have been replaced with digital multiplexers.

Digital signals are combined or multiplexed typically using one of two techniques; Time Division Multiplexing (TDM) and Statistical Time Division Multiplexing (STDM). Let's cover TDM in this post.

Time Division Multiplexing allows multiple devices to communicate over the same circuit by assigning time slots for each device on the line. Devices communicating using TDM are typically placed in groups that are multiples of 4.

Each device is assigned a time slot where the TDM will accept an 8 bit character from the device. A TDM frame is then built and transmitted over the circuit. Another TDM on the other end of the circuit de-multiplexes the frame.

TDM Framing

TDM’s tend to waste time slots because a time slot is allocated for each device regardless of whether that device has anything to send. For example, in a TDM system if only two of four devices want to send and use frame space, the other two devices will not have anything to send.

TDM Framing Showing Wasted Slots

They do not require frame space but their time slot is still allocated and will be transmitted as empty frames. This is not an efficient use of bandwidth.

In my next legacy PSTN post, I'll cover statistical time division multiplexing (STDM), a much more efficient way to use bandwidth.

Verizon FiOS Buildout Essentially Done, Fixed LTE Coming

2011-10-27T07:23:00.000-04:00

In a quarterly earnings conference call last Friday Verizon confirmed a couple of things I've been saying here for the past couple of years. The FiOS build out is basically done for now and Verizon Wireless will be offerring a fixed LTE option in direct competition with the landlind side of the business.

Here's an interesting Q&A from the VZ - Q3 2011 Verizon Communications Inc Earnings Conference Call held on October 21, as posted at DSL Reports:

Citigroup Analyst: Is there any thought of taking that non-FiOS bundle of presumably LTE broadband LTE voice,what about taking that more nationally and making that more of a national product for you versus just maybe an out of FiOS region but in territory Verizon product?

Fran Shammo: Well, we are. And you're going to see that come in the fourth quarter with the -- what we now call the Cantenna which is not a commercial name obviously, but it's the antenna that we actually trialed with DIRECTV, which was extremely successful. And again, the benefit of this antenna is it operates the spectrum extremely efficiently. So if you look at a MiFi card or a dongle, this is very, very efficient, way above those two devices which is why it's critical to have that bundle with that Cantenna. So when we launch that you're going to see us go nationally with that type of an offer.

Analog or Frequency Multiplexing

2011-10-25T09:18:00.000-04:00

In this post I continue discussing some of the different legacy technologies used by the Public Switched Telephone Network (PSTN). Today let's take a dive into analog or frequency multiplexing.

Analog or frequency multiplexing is now an obsolete technology in the U.S. telecommunications industry. It was used up until the early 1990’s by long-distance carriers like AT&T and MCI and is still used today in other countries. The concept of channel banks was developed for analog multiplexing and this concept is still used today for other types of multiplexing. To multiplex calls each call was given a narrow range of frequency in the available bandwidth. We know all voice call channels occupy the same frequency range – approximately 4000 Hz if we include individual call guardbands. If we want to combine a group of voice calls and separate them by frequency we must translate the frequency of these individual call channels using a process called Single Sideband, Suppressed Carrier Modulation. This technique allowed 10,800 individual voice call channels to be combined and transmitted over one coaxial copper pair. Let’s look at how it was done.

Groups

Individual voice call channels are placed into groups of 12. If we have 12 channels per group and each channel is 4000 Hz we can calculate:

This 48KHz is placed in the frequency range of 60 – 108 KHz.

Single Group Formation

Supergroups

Individual groups are placed into supergroups of 5 and each supergroup contains 60 individual voice channels. If we have 5 groups and each group is 48 KHz we can calculate:

This 240KHz is placed in the frequency range of 312 – 552 KHz.

Supergroup Formation

Mastergroups

Individual supergroups are placed into mastergroups of 10 and each mastergroup contains 600 individual voice channels. If we have 10 supergroups and each supergroup is 240 KHz we can calculate:

This 2.40MHz is placed in the frequency range of 564 – 2.964 MHz.

Mastergroup Formation

Jumbogroups

Individual mastergroups are placed into jumbogroups of 6 and each jumbogroup contains 3600 individual voice channels. If we have 6 mastergroups and each mastergroup is 2.4 MHz we can calculate:

This 14.4 MHz is placed in the frequency range of 3.084 – 17.484 MHz.

Jumbogroup Formation

Jumbogroup Multiplex

The final multiplexing step involves combining individual jumbogroups which are placed into jumbogroup multiplexes of 3. Each jumbogroup multiplex contains 10,800 individual voice channels. I'm still amazed - 10,800 calls on one piece of coaxial cable!

Frequency multiplexing is now considered obsolete technology on the telecommunications network. Analog signals are more sensitive to noise and other signals which can cause problems along the transmission path. Those long coaxial cables make pretty good antennas. They have been replaced with digital multiplexers. In my next legacy PSTN post I'll cover how digital multiplexing works.

reference: Introduction to Telecommunications Networks by Gordon F Snyder Jr, 2002

Multiplexing - A Brief Introduction

2011-10-23T10:11:00.000-04:00

In this post I continue discussing some of the different legacy technologies used by the Public Switched Telephone Network (PSTN). Today let's take a quick look at what multiplexing is.

Before the invention of the telephone both Alexander Graham Bell and Thomas Edison were experimenting with ways to transmit more than one telegraph signal at a time over a single wire. They both realized this was a critical piece if any communications network was to grow in the number of users.

Multiplexing

There are three ways to multiplex or combine multiple signals on the telephone network. They are analog or frequency multiplexing, digital multiplexing and wavelength division multiplexing. I'll dig pretty deep into each in upcoming legacy posts.

The SLC-96

2011-10-20T14:42:00.000-04:00

In this post I continue discussing some of the different legacy technologies used by the Public Switched Telephone Network (PSTN). Today let's take a look at how the PSTN designed and tuned for voice communications started to change in the late 1970's with something called an SLC-96 (pronounced "Slick 96").

It's still not economical even today to run fiber into every home but Local Exchange Carriers like Verizon and AT&T have been working to replace portions of the local loop with fiber by running fiber out from the CO into a Remote Terminal (RT) pedestal box in the field called a Multiple Subscriber Line (or Loop) Carrier System or SLC-96. Each SLC-96 takes 96 64 Kbps analog voice or modem signals, converts them to digital and then multiplexes them at the Remote Terminal. The Remote Terminal is connected to a Central Office Terminal (COT) using 5 T1 (DS-1) lines.

SLC-96 Field Pedestal Configuration

Four of these T1 lines are used to carry the 96 digitized voice channels (1 T1 line = 24 digitized voice channels so 4 T1’s are required to transmit 96 voice channels). The fifth T1 line is used for protective switching and is a backup if one of the four fails.

In my next legacy PSTN post I'll start covering multiplexing.

Hybrid-Terrestrial-Satellite Networks?

2011-10-16T09:51:00.001-04:00

That's what Charlie Ergen at Dish Networks is putting together and it makes sense. Ergen's a former professional blackjack player billionaire currently transforming Dish to a wireless mobile video company. An October 17-23, 2011 Business Week Companies & Industries piece titled Charlie Ergen Wants To Beam You Everything does a nice job summarizing where Ergen is taking Dish. Here's some details.

Dish has spent over $5 billion this year on acquisitions of companies in bankruptcy. Here's three of the biggest:

Blockbuster video chain - video content
EchoStar set-top box maker - IP-based end device connectivity
Hughes Communications - satellite Internet service provider

Ergen moved fast with the Blockbuster acquisition, rolling out a Blockbuster branded movie streaming service to Dish customers last month.

What's next? Ergen currently has a $1.9 billion offer on the books for Hulu which is currently owned by News Corp., Walt Disney and Comcast. Picking up Hulu would give Dish rights to more than one million paying subscribers.

Dish also has pending deals to pick up DBSD North America and TerreStar Networks. These two companies also own wireless spectrum which could be the real prize and an indication of things to come. What the company really needs is more wireless. Access to an existing broad wireless network (DBSD and TerreStar will not be enough) is coming so watch for Ergen to go after a provider (maybe Sprint?) or maybe cut a deal with one of the other providers (Verizon Wireless or AT&T?).

What about competition from companies like Netflix? Peter M. Hoffman from GHL is quoted in that Business Week piece "What Charlie's done is put together content and distribution. Netflix still has to rely on someone else's distribution to deliver its content."

Adding that wireless broadband piece (that Ergen needs for video delivery) could turn Dish into a viable broadband alternative to telcos like Verizon and cable companies like Time Warner. What really excites me is the access Dish could offer rural areas where there is currently not good broadband options.

New UMass President and Massachusetts Green High Performance Computing Center

2011-10-11T16:10:00.001-04:00

I've written in the past about high performance computing in Western Massachusetts.

I had the opportunity today to visit the Massachusetts Green High Performance Computing Center (MGHPCC) in Holyoke, MA. A small group of us toured the Center with new University of Massachusetts President Robert Caret.
As a UMass Amherst grad (Class of 1979) I have to admit it was pretty cool to be among the group to introduce Dr Caret to High Performance Computing in the Pioneer Valley. I'd like to thank MGHPCC Executive Director John Goodhue for the invite to this special event. Here's a few pics I snapped during the tour.

Mass Green High Perf Computing Center, a set on Flickr.

Go UMass! Go MGHPCC!

A Few Additional Telephone System Features

2011-10-07T09:37:00.000-04:00

In this post I continue to describe the legacy Public Switched Telephone Network (PSTN), looking at a few other common telephone system features we are all used to having and relying on. These are additional handset signals and PIC. I would also want to include Caller ID here but I've already covered how it works in a previous post.

Some Common Handset Signals

We are all used to hearing these additional common signals coming from our telephone.

Line Busy Signal - 480 Hz and 630 Hz tones on for .5 seconds and off for .5 seconds, then repeats.

Block Signal - 480 Hz and 620 Hz tones on for .2 seconds and off for .3 seconds, then repeats. This signal is often referred to as fast busy.

Off-Hook - 1400 Hz, 2060 Hz, 2450 Hz and 2600 Hz tones on for .1 seconds and off for .1 seconds, then repeats with a duration of 40 seconds. This signal is designed to be heard from across a room and is very loud.

Preferred Interexchange Carrier (PIC)

Since the 1976 MCI ruling AT&T has been required to open the long distance market to other long distance providers. Prior to this, all long distance traffic in the United States was handled by AT&T and users would just dial a “1” to connect to an AT&T long distance trunk. As other long distance carriers entered the market, AT&T had a big advantage. Customers were already used to dialing a “1” for long distance and placing a long distance call to anywhere in the United States involved dialing a minimum number of numbers. – only 11. This included “1”, the area code, and the 7 digit number. Customers that wanted to used other long distance carriers had to dial 25 numbers to make a long distance call. These calls required an 800 number be called initially (11 numbers), a 4 number personal identification number (PIN), the area code, and the 7 digit number.

In 1987 a method called Feature Group D was implemented to automatically pass calls to the customers preferred long distance carrier using something called a Preferred Interexchange Carrier (PIC) number. Customers are required to select a preferred carrier and the preferred carrier information is added to the local switch database the customer is connected to.

Feature Group D also allows a customer to bypass the preferred PIC by dialing a 101XXXX number and use another long distance carrier. These 101XXXX are commonly referred to as dial-around service numbers.

RIP Steve Jobs

2011-10-05T20:56:00.000-04:00

“.. almost everything – all external expectations, all pride, all fear of embarrassment or failure - these things just fall away in the face of death, leaving only what is truly important. Remembering that you are going to die is the best way I know to avoid the trap of thinking you have something to lose. You are already naked. There is no reason not to follow your heart.”

Steve Jobs

1955 - 2011
Rest In Peace

Telephone Set Function 4. To convert voice frequencies to electrical signals that can be transmitted

2011-09-30T09:51:00.000-04:00

In my last few legacy Public Switched Telephone Network (PSTN) posts, I covered pulse or rotary dial service, dual tone multi frequency (DTMF) dialing service and what makes a telephone ring. In this post let's look at microphones and speakers.

A telephone converts voice frequencies to electrical signals and electrical signals back to voice frequencies using basic microphone transmitter and speaker theory and application.

Transmitters

A telephone transmitter is built into the handset of the phone and is responsible for converting sound waves into electrical signals that can be transmitted.

Telephone Carbon Granule Transmitter

Carbon granule transmitters are still common in wired home phones. Sound travels in waves that are actually variations in air pressure. Some of these waves enter the mouthpiece and cause a diaphragm in the transmitter microphone to vibrate back and forth. These vibrations put either more or less pressure on carbon granules in the base of the microphone. If more pressure is applied, the granules pack more tightly and conduct electricity more efficiently. Inversely, in between the waves the granules unpack and do not conduct as well. Voltage is applied across the electrical contacts and the varying amounts of resistance caused by the carbon granules in the microphone cause varying amounts of current to flow. This current variation is an electrical representation of the sound waves (voice=analog signal) entering the microphone.

In addition to carbon granule transmitters many modern telephones use dynamic transmitters that function by moving a coil of wire inside a magnetic field to produce an electrical current in response to soundwaves or electret transmitters, also known as condenser microphones, which use a capacitor for a transducer and generally contain an amplifier circuit.

Receivers

The telephone handset receiver is just a simple speaker. It performs the opposite function of the transmitter in that it takes the incoming electrical signal and converts it to sound waves that can be heard by the listener.

Simple Speaker Diagram

The incoming electrical signal flows through a magnetic coil in the speaker. The magnetic field surrounding the coil changes in conjunction with the changing current flowing through the coil. This changing magnetic field causes a cone in the speaker to vibrate. These vibrations create air pressure waves forming sound.

In my next legacy PSTN post I'll describe how some additional telephone features work.

Early Fall Walk Around the STCC Technology Park

2011-09-28T12:18:00.001-04:00

I took a quick walk at lunch time today around the STCC Technology Park. The Tech Park is part of Springfield Technical Community College and located directly across the street from the main campus. Our NSF funded National Center for Information and Communications Technologies is located in the Scibelli Enterprise Center building in the Tech Park. Lots of cool technology going on in the Tech Park - things like photovoltaics, electric cars and of course Information Technology and Communications! Here's some of the pics I took today.

gordonfsnyder's photostream on Flickr.

A great place to locate a business and work!

Telephone Set Function 3 - To provide a way for the telephone company to indicate that a call is coming in or ringing

2011-09-25T11:12:00.000-04:00

In my last two legacy Public Switched Telephone Network (PSTN) posts I covered pulse or rotary dial service along with dual tone multi frequency (DTMF) dialing service. In this post let's look at what makes a telephone ring.

When the user begins dialing the phone each sequenced number is stored in the central office computerized switch at the Local Exchange Carrier (LEC) Central Office (CO) and analyzed. The first three digits determine if the call is local or long distance. If the call is local, the switch determines if it can complete the call itself or the call needs to be forwarded to another local LEC CO that handles that telephone number. If the call is long distance, the call needs to be forwarded to the customer's long distance carrier.

Once the call destination is determined a switch on the receiving end sends a repeating 90 Vrms 20 Hz ringing signal (on for 2 seconds with a 4 second pause) called a ring or alerting signal to the receiving phone causing it to ring.

Ring or Alerting Signal

Notice the ringing signal has an inaudible frequency of 20 Hz - this is why different phones can have different ring styles.

At the same time, a ring back signal that is a mix of 440Hz and 480Hz is sent back to the caller. This signal is on for 2 seconds and off for 4 seconds and indicates that the phone being dialed is ringing. When the receiver picks up the handset the telephone goes off-hook. The switch hook on the receiving phone closes, current flows and the CO switches turn off the ringing signals.

Facebook Will Need Its Own Operating System

2011-09-21T19:59:00.000-04:00

Gabby came home today for a little while and she had her Chromebook with her. If you haven't seen one yet - it's a pretty cool little notebook running Google's Chrome operating system. It boots up in about three seconds and has a battery that lasts over 8 hours. Everything is stored in the cloud so everything is accessible with a web connection. Pretty nice for a first generation device.

It got me thinking - Facebook does not have a mobile operating system (or any operating system for that matter). Apple does, Microsoft does and Google now has more than one. Poking around on the web I found an interesting report from ABI Research titled Mobile Social Networking. Here's some quotes from that report:

The number of people accessing social networks from mobile phones will exceed 550 million in 2011, and that figure will more than triple to over 1.7 billion by the end of 2016.

For Facebook, the growing importance of mobile is both an opportunity and a serious strategic challenge. On one hand, mobile allows the world’s leading social network to engage with millions of new consumers, but on the other hand its ability to make money from mobile users remains untested.

Senior analyst Aapo Markkanen is also quoted in the report saying, "A huge problem for Facebook is that while on the web it is a platform, on mobile it’s just another application. To strengthen its hand in the short term we expect Facebook to aggressively take advantage of HTML5, but in the longer term it should absolutely become a mobile operating system of its own."

Facebook is lagging. Google+ is tied in very tightly with Android and Chrome already. Twitter is going to be built into Apple's iOS 5. Practice director Dan Shey is also quoted saying, “The interesting aspect in Apple’s and Twitter’s partnership is how it can provide iPhone users with a verifiable social identity for websites and apps. That gives developers a lot of scope to innovate in areas such as authentication, personalization and advertising. It’s a hint of things to come.”

Rural Broadband - Holland, Massachusetts

2011-09-14T13:54:00.000-04:00

The Springfield (MA) Sunday Republican runs a Q&A piece every week titled Just Ask. this past Sunday a woman who lives in Holland, MA posted a pretty interesting question. Before we get to the question though, let's take a quick look at Holland (source Wikipedia). According to the United States Census Bureau:

The town has a total area of 13.1 square miles (33.9 km²), of which, 12.4 square miles (32.1 km²) of it is land and 0.7 square miles (1.8 km²) of it (5.34%) is water.
As of the census of 2000, there were 2,407 people, 898 households, and 668 families residing in the town. The population density was 194.2 people per square mile (75.0/km²). There were 1,317 housing units at an average density of 106.3 per square mile (41.0/km²).
The median income for a household in the town was $52,073, and the median income for a family was $57,024.
Holland has it's own elementary school but is considering merging its elementary school with the town of Wales. Holland students attend Tantasqua Regional Junior High School (grades 7-8) and Tantasqua Regional High School in Sturbridge.

A typical rural New England town that can be compared to likely hundreds of other rural communities across the U.S. Now for the newspaper reader question.

Question: Is it true that Verizon Communications does not have fiberoptics in my home area, Holland, and that there are no plans to install same? What I have now is a dial-up modem with Verizon, and it is very slow. It takes 10 full minutes for me to access my checking account online, after four screen changes. I understand the need for security, but this is ridiculous. I’m a teacher and need to cover a lot of ground on the Internet in a single day. At such snail speeds, I’m limited to very few online tasks like collecting emails. Over the past three years I have made numerous calls to Verizon service to ask if I could sign-up for high-speed Internet service, and the answer was always “no.”
In this year of speed-of-light communications, do I have any other options?
– Kathleen McGrory, Holland

And the answer from reporter Jim Kinney:

Answer: While it is true Verizon does not offer DSL service for people in your area of Holland, there are other options available. Cox Communications, Holland’s cable provider, does offer provide high-speed Internet in this area. Since you sent us this inquiry, we understand you signed up with Cox’s Broadband service and can now quickly access your checkbook online. Welcome to the 21st century, Kathleen.
Verizon spokesman Philip G. Santoro said, “There just aren’t enough customers there (for Verizon) to justify the expense.” He suggested people like you contact their local cable operator. He also pointed out that there is a third option, and that is Verizon Wireless’ 3G coverage, which would provide high-speed Internet through cell phone coverage.

Many small rural towns in the U.S. do not have any option except dial-up. It is upsetting to read the Verizon spokesman's honest answer regarding high speed landline based service in Holland. Nothing against Verizon - it's the frustrating reality of situations across our country. From a business perspective it does not make sense for a traditional telephone company to offer high-speed data service in a town like Holland. With current data caps in place from Verizon Wireless and other providers I don't see 3G (or upcoming 4G) services as a competitive alternative.

Holland residents are fortunate they do have a cable option. Many similar communities in our country are stuck with dial-up as their only option.

9/14/11 at 7:28 PM

This comment came in from retired Cable Executive Steven Solomon via Google+.

Gordon, I would add this comment to your post. What is often invisible to the public is the real demographics of a community like Holland. I know about this first hand. I helped negotiate the cable TV franchise with the town on the part of the predecessor provider to Cox, Continental Cablevision.

As of 1994, of the 2,400 or so residents of the town, only about 600 homeowners lived in their homes all year round. The rest kept their residences as vacation or second homes. This put the full-time residents at a great disadvantage in getting broadband by landline of any sort.

Putting in broadband plant at about $20G a mile is not a reasonable business proposition for the private sector if the company is relying only on the margin earned from Internet (which now competes with phone and cable TV). Thus, I don't see any alternative to the private sector stepping in with the 21st century equivalent of rural electrification.

Memories of September 11, 2001

2011-09-09T08:39:00.001-04:00

I first published this three years ago.

I was walking into the office when our technician told me a plane had hit one of the towers - he said "they think it was a small plane" and I did not think too much about it. 20 minutes or so later I was in a meeting and the same tech came in saying it was an airliner. We all left the meeting and turned on a small television in our lab. I also made sure I had a computer close by so I could watch email.......

At the time we were running a national listserv for a large group of community college faculty and administrators involved in a Working Connections grant with Microsoft and the American Association of Community Colleges (AACC). I've pulled out a few emails that came to the list. Here's one of the first from Mete at Borough of Manhattan Community College (BMCC):

11:50 AM, 9/11/01

It is chaos here, but everybody at BMCC is OK. We are closed for the day and the roads/subways to in/out of Manhattan are blocked. I am in Brooklyn (home) now and the sky is dark from smoke/ash/soot. I have a feeling it is going to take a long time to recover from this one.
Hope all is well with everyone around the country,

Mete

BMCC is on Chambers Street, next to ground zero and a college building was damaged from the attack. Mete was on the subway on his way in when the attack started and I believe he walked home to Brooklyn.

Here's a reply message from Lynn at the AACC in Washington, DC::

12:05AM, 9/11/01
We are ok here, but our office is closing so people can try to get home. The smoke from the Pentagon is visible from our 4th floor conference room. Most of the federal offices have now closed, a couple of subway stations near the Pentagon are closed, the streets are crowded with people driving and walking home from downtown offices, and cars with sirens go by every 5 minutes or so. Folks who live near Capitol Hill are sticking around the office until things calm down in that part of town.

Lynn

A flurry of emails went back and forth during the day from people all around the coutry. We were all worried, frustrated and upset about the attacks and our friends in New York, Washington and Pennsylvania. Here's a sample of the response from Paula at Richland College in Dallas:

11:50AM, 9/11/01
Thank you both for taking the time to provide us with an update of your safety. Our prayers are with you and all Americans during this tragedy. As in other states, thousands are donating blood. A major sports arena in Dallas has been setup as a blood donation facility. Churches are conducting special services. Please assist us to remain informed as to organizations/drives that are established that will provide direct support.

Paula

This came from Chris at the Fashion Institute of Technology (FIT) in New York City a few days later:

10:50AM, 9/14/01
FIT is safe and sound and open for business but few classes are running normally. It is hard to describe the experience of walking south on Manhattan's avenues and seeing a column of smoke where the World Trade Towers should be. When the wind shifts, the smell of the fire comes to Chelsea with a light dusting of the cement that is ankle deep a few blocks away.

We are glad to hear that all are well at BMCC and in Washington.

Chris

Here's a followup from Mete that was also sent on September 14:

12:36AM, 9/14/01

The building that we (CIS) dept was suppose to move this Sept., (but did not because of delays) is quite damaged. They are using our main building as command/triage/morgue center. We will be closed until the end of next week. The cleanup is going very slowly and there is very limited access to downtown Manhattan.

The subways are not running and all the outer borough are choked with traffic with people bringing their cars and parking them as close to Manhattan as possible. The air quality is bad, there is possibility that some more buildings (including our own that was next to a collapsed building) may come down aggravating the situation.

There are a number people that I know, with families, that perished in the bombings (we were going go to a 10th bday party this weekend, but the mother is missing - what do we do now ??) from my daughter's school and our neighborhood. But they are defiant, and most of the businesses try to operate as usual with a backdrop of surrealism...

Thanks for all of your e-mails and good wishes. We appreciate it and find comfort in them.

Mete

Hundreds of emails went back and forth over the next few weeks on the listserv. I've saved them all.

Greplin - Search All Your Data In One Place Immediately

2011-09-08T18:16:00.000-04:00

I recently started using a new search utility called Greplin. Greplin, co-founded by 20 year old Israeli Daniel Gross, lets users enter credentials to their Gmail, Facebook, Twitter, Tumblr, LinkedIn, etc accounts and then builds a custom search engine that will search through content in each allowed application.

Most of us have got information coming at us from multiple sources (email, Facebook, Twitter, etc) and it's often difficult to remember where an important piece of information came from and is located. That's exactly what happened to Goss a few years ago - he was on his way to a party and was trying to find the address. He could not remember what app the invitation came in on and spent a while flipping through different apps on his smartphone before he found it. Instead of just complaining about it, Goss decided it was time to build a search engine that could be customized to search individual user content across apps.

Greplin has a “freemium” or free service along with an enhanced version that will search business apps like Salesforce for $5 per month or $50 per year. There are smartphone versions and a very nice plugin for the Chrome browser. Check it out.

Tropical storm Irene and The Connecticut River

2011-09-02T19:10:00.000-04:00

This was my first week back from vacation and it was a busy one both inside and outside the office. Tropical Storm Irene came through last weekend and the flooding after really did some terrible damage and continues to impact people's lives from North Carolina to Maine..

Much of the rain that fell north of us from Irene eventually ended up flowing down the Connecticut River that separates Vermont and New Hampshire and splits Massachusetts and Connecticut. I drive by the Holyoke Dam every day going to and returning from work and took a few minutes to shoot some video on August 30, the day the river crested. I have never seen the river this high and this powerful. This was shot on the bridge connecting Holyoke and South Hadley Falls.

I could not believe the debris along with the color of the water.

Telephone Set Function 2. To provide the telephone company with the number the caller wishes to call - Part 2

2011-09-01T11:10:00.000-04:00

In my last legacy Public Switched Telephone Network (PSTN) post I covered pulse or rotary dial service. Let's look at dual tone multi frequency (DTMF) dialing service in this post.

The most commonly used method for inputting a number in the US and Europe is now the dual-tone-multifrequency (DTMF) signaling method. DTMF telephones are also commonly known as Touchtone telephones. These phones also use numerical keypads but offer an even faster way to signal the number to call by sending tones on the telephone line. The DTMF phone uses a 12-button keypad. When a button is pressed on the keypad an electric contact is closed and two oscillators generate two tones at specific frequencies.

Telephone DTMF Keypad

These tones combine to form one sound to the listener, just like when two different musical notes on an instrument are played at exactly the same time. The combined tones are a signal for the button that was pressed on the keypad. The frequencies used are illustrated in the keypad diagram. For example, notice when the number 8 is pressed the frequencies 852 Hz and 1336 Hz are combined to form the number 8 tone.

For the central office to accept tones from a caller, the tones must be at least 50 milliseconds long and also be separated by a 50 millisecond pause. DTMF phones offer much more rapid dialing of numbers than rotary pulse methods with the average phone number taking 10 to 15 times less time to dial using a Touchtone phone. Not only are Touchtone phones faster, they are also more reliable because they do not depend on as many moving parts as a rotary phone.

In my next legacy PSTN post, I'll describe how a telephone is made to ring.

Community Colleges - The Jobless Solution

2011-08-31T11:38:00.000-04:00

The August 24, 2011 issue of Business Week has an upsetting article titled The Slow Disappearance of the American Working Man. Here's some details from the piece:

The portion of men holding a job—any job, full- or part-time—fell to 63.5 percent in July—hovering stubbornly near the low point of 63.3 percent it reached in December 2009.
These are the lowest numbers in statistics going back to 1948.
Among the critical category of prime working-age men between 25 and 54, only 81.2 percent held jobs, a barely noticeable improvement from its low point last year—and still well below the depths of the 1982-83 recession, when employment among prime-age men never dropped below 85 percent.
In 1969 95 percent of men in their prime working years had a job.
Median wages for men between 30 and 50 dropped 27 percent—to $33,000 a year— from 1969 to 2009, putting them back at their earnings capacity of the 1950s.
Both men and women have confronted job losses in the weak economy. In July, 68.9 percent of women aged 25-54 had jobs, vs. 72.8 percent in January 2008.
Unemployed men are now more likely than women to be among the long-term jobless.

The piece goes on to discuss how women (who currently account for 57% of jobs in the U.S.) have made up the majority of college students over the past 30 years and fit better into our data-driven economy. However, women continue to earn about 16 percent less than men and struggle against gender discrimination and career interruptions.

All this going on while, at the same time, we've got companies struggling to hire workers with the right skills.

President Obama will layout a new jobs plan shortly after Labor Day and community colleges must be a major part of the solution. They are the perfect place for long-term jobless women and men to go and get the education and training needed for stable and well-paying careers.

If you are out of work and feel you have no prospects well..... you are 100% wrong. There is a ton of opportunity at your local community college. The fall semester has either just started or is starting soon. There is time right now to get yourself on track. The American Association of Community Colleges has a great interactive community college finder on their website - click here to link.

Study: iPhones, Backups and Toilets

2011-08-29T09:23:00.001-04:00

Retrevo.com's got an interesting new Gadgetology study titled iPhones, Backups and Toilets, What's the Connection?

The study focuses on cell phone security and who is the most unprepared. Here's some highlights:

39% of Android owners haven't done anything to prevent someone from misusing data on their cell phone if it were lost or stolen (compared to 30% of BlackBerry owners and 26% of iPhone owners).
Only 32% of Android owners think their cell phones can get malware and 27% don't know.
36% of iPhone owners think their cell phone can get malware and 30% don't know.
If they lost their cell phone today, only 18% of Android owners would use a recovery service to get their cell phone. back, compared to 28% of BlackBerry owners and 37% of iPhone owners. 39% of Android owners don't know how they would get their cell phones back, compared with 31% of BlackBerry owners and 26% of iPhone owners.
BlackBerry (62%) and iPhone (61%) owners are the most likely to have password protection on their cell phone, compared to Android owners (only 49%).

Retrevo also asked: Have any of the following ever happened to you or someone you know?

36% of people said they had, or knew someone who has "Dropped a cell phone in a toilet".
31% of people said they had, or knew someone who has "Had a cell phone fall in a pool, lake or other body of water".
44% of people said they had, or knew someone who has "Dropped a cell phone on the floor and had it break".
30% of people said they had, or knew someone who has "Spilled coffee or other liquid on a cell phone".

Telephone Set Function 2. To provide the telephone company with the number the caller wishes to call - Part 1

2011-08-22T19:34:00.001-04:00

In this post I continue legacy Public Switched Telephone Network (PSTN) technology coverage.

There are two methods currently used to provide numbers to the telephone company, pulse or rotary dial service and dual tone multi frequency dialing. Let's look at pulse or rotary dial service in this post.

In the past, when a handset was lifted, the caller did not hear dialtone, the caller heard an operator asking for the number the caller wanted to dial. As the number of telephones grew, telephone companies projected that hundreds of thousands of new operators would be needed so rotary dials were added to telephones.

Rotary dials were invented to eliminate operators and use dial pulsing to automate the switching required to get from a caller to a receiver. The rotary dial generates pulses on the local loop by opening and closing an electrical switch when the dial is rotated and released. Each pulse opens the loop and interrupts the local loop current flow of 20 - 120mA resulting in a series of current pulses on the local loop. This process is referred to as out-pulsing and pulses are generated at a rate of ten pulses per second. Each pulse is actually an interruption in current flow on the loop and is .05s with a .05s pause between pulses. Each number on the dial corresponds to the number of pulses produced for that number. For example, dialing the number 4 produces four pulses as indicated in the figure below and takes a total of .4 seconds (8 x ,05 seconds = ,4 seconds). As you can see, rotary dialers are slow when compared to modern telephones today.

Telephone Rotary Dial Timing Diagram of the Number “4”

Example

How long does it take to dial the single number "9" on a mechanical rotary phone?

Solution

Dialing the number "9" produces:

.05s pulse, .05s pause, 05s pulse, .05s pause, 05s pulse, .05s pause, .05s pulse, .05s pause, 05s pulse, .05s pause, 05s pulse, .05s pause, .05s pulse, .05s pause, 05s pulse, .05s pause, 05s pulse, .05s pause

.05 seconds x 18 = .9 seconds

As telephone manufacturing technology developed the rotary dials were replaced on many phones with a push-button keypad. These keypads use an electronic circuit to generate the pulses, not a mechanical rotary dial. Since people can punch numbers very rapidly and pulse signals still must be .05s long and be separated by .05s pauses, this type of dial is equipped with a buffer that stores numbers as they are keyed. The buffer then out-pulses the numbers with the proper timing intervals. You may also have noticed a telephone "digital" keypad number sequence is opposite that of a calculator. This was done purposely to slow people down when dialing on pulse generators.

Pulse generation phones still work on the Public Switched Telephone Network (PSTN). It's amazing the telephone companies still support these now almost obsolete phones! In my next telephone technology post I'll cover dual tone multi frequency dialing.

Verizon Strike To End On Tuesday

2011-08-20T19:39:00.002-04:00

It looks like the strike will be over Tuesday, at least for now. The Communication Workers of America (CWA) and the International Brotherhood of Electrical Workers (IBEW) have agreed to go back while they continue negotiations. Here's a quote from the Pittsburg Business Times published at 6:24 PM today.

"We have reached agreement with Verizon on how bargaining will proceed and how it will be restructured," said a joint statement released Saturday afternoon by the Communications Workers of America and the International Brotherhood of Electrical Workers . "The major issues remain to be discussed, but overall, issues now are focused and narrowed."

The two unions and the company will continue to negotiate the sticky points as listed by William Huber, president of IBEW Local 827 in New Jersey:

Verizon wants to tie pay increases to performance review.

Verizon wants the union workers to contribute to health-plan premiums.

Verizon wants to freeze pensions at the end of this year.

Verizon wants to eliminate the sickness and death program

Verizon wants to cut the sickness disability benefits from 52 to 26 weeks.

45,000 workers will return to work under the contract that expired on August 6. At this time, there is no specific deadline for a new contract.

Verizon Strike Goes On

2011-08-19T08:07:00.010-04:00

The strike continues. Here's some interesting details pulled from a Steven Greenhouse New York Times piece published on August 14:

Verizon says its unionized workers average $70,000 a year before overtime and $91,000 with overtime. But union officials say only a small percentage of workers earn that much with overtime, an amount they say would require hundreds of hours of it.
Company officials note that the average U.S. worker earns $23 an hour, translating to $48,000 a year for a full-time worker.
Union officials say Verizon's proposed health insurance changes would cost some workers $6,800 more each year, and its overall proposals would cost workers $20,000 on average each year.
In addition to the health insurance changes, Verizon has called for a pension freeze, reduction of sick days and elimination of all job security provisions -- a proposal workers fear will lead to far more layoffs and outsourcing, especially of call center workers.

Doug Anderson, a Verizon technician for 15 years is quoted in the piece:

"What we make is just a living wage in the New York area. On what I earn, my family can't even afford to live where I work -- Westchester County (NY). And on what we earn, it's hard to send a child through college."

The estimated median household income for Westchester County, New York in 2009 was $77,189 and the mean price for a detached house was $776,277.

Dialtone Generation

2011-08-18T19:58:00.001-04:00

In my last telephone set post I described what happens when a telephone handset is picked up. Here's a diagram showing that process.

Dialtone Generation

Dialtone is a signal formed by the simultaneous transmission of a 330 Hz tone and a 440 Hz tone. After the first number is dialed by the caller the dial-tone generator is shut off.

Quick Thoughts on Google Acquiring Motorola

2011-08-15T21:19:00.003-04:00

Here's some quick thoughts on today's Google Motorola announcement:

It's been done before - Microsoft cut a similar deal earlier this year with hardware manufacturer Nokia.
Google is looking to further follow Apple's vertical integration strategy - basically creating device hardware and operating systems.
Motorola has been struggling. The company is a goldmine of patents and technology. Merge Google's software,marketing and innovation with Motorola's hardware engineering and some really good things should start happening. Good for consumers.
There's been a lot of legal/patent back and forth with Android and this has slowed development. The Motorola deal should smooth some of the legal issues out. Good for consumers.
Google's Larry Page said today that Google will keep Motorola and Google as separate businesses and will continue to keep the Android operating system as an open platform for other hardware suppliers. This is an interesting strategy - will a hybrid closed/open strategy work? Even with questions - I still believe this is good for consumers.
Other Android device hardware manufacturers including Samsung, Huawei and HTC are going to have to adjust to this. This may not be good for consumers in the short term.
I've got a Motorola broadband cable modem in my house. Google has done some experimenting with Google TV. Combine the two and we could see some interesting and innovative content coming into our homes soon. This could be really good for consumers.

The acquisition requires both U.S. and European Union approvals and should be completed around the end of this year.

The Basic Telephone Set Fundamental Functions

2011-08-12T19:05:00.003-04:00

With my recent posts on the Public Switched Telephone Network (PSTN) I've been getting some email questions and suggested posts. I've received a few questions on telephones (what I would call end user devices) so I thought I'd take a few posts to describe how a basic telephone works.

The basic telephone set connected to the telephone network we are all very comfortable with using, has 4 basic functions:

To provide a signal to the telephone company that a call is to be made (off-hook) or a call is complete (on-hook).
To provide the telephone company with the number the caller wishes to call.
To provide a way for the telephone company to indicate that a call is coming in or ringing.
To convert voice frequencies to electrical signals that can be transmitted at the transmitter and convert those electrical signals back to voice frequencies at the receiver.

The Federal Communications Commission (FCC) has set standards for the above features and all manufacturers selling telephones in this country must match these standards or the phone will not work properly. In addition many modern telephones also come with features like speed dial, redial, memory, caller ID, voice mail, etc. These are all additional features that are not necessary to make or receive calls.

Let's look at Telephone Set Function 1: To provide a signal to the telephone company that a call is to be made (off-hook) or a call is complete (on-hook).

The switchhook gets its name from the old telephones that had a hook on the side. On modern phones the switchhook is a button that is depressed when the handset is put on the cradle of the telephone.

According to telephone company specifications individual telephone set DC resistance should be 200 Ω but in reality most telephones range between 150 and 1000 Ω of DC resistance. When a user picks up a connected telephone handset to make a call the switchhooks in the figure below (S1 and S2) close (off-hook condition) and the local loop circuit is complete.

When a handset is picked up, a DC current ranging between 20 and 120 mA flows on the pair of wires connecting the telephone to the CO. This current flow causes a relay coil to magnetize and it's contacts close.

In the CO current flows through a relay coil attached to the local loop wire pair. The coil energizes, it’s contacts close and the CO switch knows a phone is off hook somewhere. A line feeder in the CO switch looks for the off-hook signal, finds it and sets up a connection. In the CO switch a dial-tone generator is connected to the line so the caller knows they can dial a number.

I'll cover dial-tone generation (and why cell phones don't use dial-tone) in my next post.

Q&A: Wireless Data Caps And Other Wireless Stuff

2011-08-08T07:55:00.003-04:00

I started working on this post on Friday with the intention of posting today. It seems even more appropriate today with the Verizon strike starting over the weekend......

I've had the chance to speak at four or five conferences over the past few months or so on emerging broadband technologies and services. A good chunk of one of these presentations always covers wireless technologies with a focus on 4G (WiMax and LTE) upgrades. One thing I can count on are questions from the audience about wireless data caps. With Verizon Wireless halting their all you can eat plan on July 6th, these questions have become even more frequent. Here's some of those questions and my answers:

Question: Why are the wireless providers doing this?

Answers:

Expensive to maintain landline divisions of the big providers (AT&T and Verizon), still comprise approximately half of their business. In comparison, wireless is less expensive to install and maintain.
Average wireless subscriber voice plan revenue has dropped from $50 per month in 2005 to approximately $33 today. Wireless voice plans have become commoditized.
Smartphones with expensive data plans have allowed the wireless providers to replace the loss in voice revenue.
These same smartphones have put incredible demand on wireless bandwidth, wireless spectrum and fiber backhaul connecting cell towers. 4G technologies operate at approximately 10 times the rate of 3G and will continue to challenge the providers when it comes to capacity needs.
A recent Business Week article refers to cellular upgrades by the major providers in the U.S. as "Money Pits". In 2010 the telcos cost of capital exceeded their return on invested capital - which may mean they're throwing good money after bad.

Question: My students, my own kids, grandkids, etc are constantly texting. Hasn't text messaging provided some nice revenue for the wireless providers?

Answers:

comScore reports 69.6 percent of U.S. mobile subscribers used text messaging on their mobile devices in 2010.
The same Business Week piece referenced above estimates text messaging represents 16% of Verizon Wireless revenue and contributes as much as 40% to total profit. AT&T numbers are likely similar.
Text messaging was designed for voice phones - basically phones that do not have alphabet keyboards. You don't see too many of those around anymore. Smartphones have more capabilities and options.
The problem is, with a smartphone you don't need a text plan from a wireless provider to send text messages. Smartphone users can send and receive unlimited text messages using free apps like Skype, Google Voice, TextNow and GroupMe using the smartphone's data connectivity. Using many of these apps users can also text from there computers at work, laptops, iPads etc as long as they have an Internet connection.
Apple will be releasing a new messaging feature called iMessage and the next version of Microsoft Windows Phone will integrate texting with Facebook chat. Both of these services will also bypass the wireless texting technology.
Text message revenues are going to drop rapidly as users move to apps that run on smartphones.
Capping data is one way wireless providers will try to recover some of this revenue. There is a bit of a flaw in this strategy though - the average text message (unless pictures are attached) uses very small amounts of data bandwidth.

Question: 4G services are fast and a monthly 5GB cap is not going to last long. Are you concerned?

Answers:

Right now I'm a little concerned. For example, I'm on an unlimited data plan now from AT&T and I'll keep that as long as I can. Even though I never come close to 5GB per month, if I were to end up switching, I'd go with a provider that does not cap bandwidth. I would not lock into a long term capped data plan with any provider.
Right now Sprint is still offering unlimited data plans - the big two (AT&amp;amp;amp;T and Verizon) are not. If you are concerned about caps I would take a close look at Sprint.
In places where I do use my phone for data I would estimate over 50% of the time I'm in a location where I have secure WiFi access. As long as I've got the WiFi radio on I'm not using wireless (3G/4G) bandwidth.
I live in a small town that only has a couple of gas stations. The price per gallon is always high. The next town over has a number of gas stations in a relatively small area and price per gallon competition is fierce. When one drops their price the others follow almost instantly. Competition is good. Right now AT&T and Verizon have agreed to implement caps. If one of them cracks or another alternative provider comes along (Google, Microsoft or who knows who?) with unlimited service at a competitive price they'll all have to drop their caps fast to prevent customer churn.

Over the long term, I'm not really worried about data caps.

Verizon Strike - Could Be A Long One

2011-08-07T20:34:00.014-04:00

I'll front this post by saying my Dad worked for AT&T as a technician for about 30 years, retiring right around divestiture. I was only 11 but remember the long strike (over 100 days) in 1968 like it was yesterday. I've also been teaching telecommunications classes to NYNEX, Bell Atlantic and now Verizon technicians since 1995 as part of the Verizon NextStep program, I've had hundreds of Verizon technicians in my classes and have always been impressed.

Verizon is actually two separate companies when it comes to unionization. There is the landline side - what most of us would call the traditional telephone company. 45,000 Verizon landline employees are unionized and represented by the Communications Workers of America (CWA) and the International Brotherhood of Electrical Workers (IBEW). These employees are on the east coast, ranging from D.C. north to Massachusetts. Verizon Wireless is non-union and has coverage across the United States.

It's no secret the landline business is in decline and the company is currently focused on building out the wireless business. Here's the sticky points as listed by William Huber, president of IBEW Local 827 in New Jersey:

Verizon wants to tie pay increases to performance review.

Verizon wants the union workers to contribute to health-plan premiums.

Verizon wants to freeze pensions at the end of this year.

Verizon wants to eliminate the sickness and death program

Verizon wants to cut the sickness disability benefits from 52 to 26 weeks.

I've always been impressed with the work ethic of the technicians, starting with my Dad who went about 19 years without taking a sick day. I see the same level of work and family commitment I saw in my Dad in today's Verizon technicians.

I do think this strike could rival my Dad's long 1968 strike in length. Hope I'm wrong.

Update 8/8/11 at 6:39 AM

Here's a piece of an interesting email I got from one of the technicians I had in class a while ago:

"We were told for the last year that Ivan was stepping down as CEO after the contract was done. When the news came out a couple weeks ago that he was stepping down a week before the contract expired, we should have known that was not good. We always received decent contracts from Ivan. From what I hear the company would not back down on any of their demands, even late Saturday, I also heard the union had agreed to pay some towards healthcare."

Ivan Seidenberg worked his way up in the company the old school way, starting as a cable splicer (he was in the union) out of high school. Lowell McAdam, the new President and Chief Executive Officer of Verizon, came up a different path.

More on CODECs: Quantization + Sampling Rate = A PCM Wave

2011-08-03T21:18:00.015-04:00

In my last post I started writing about about CODECs and how they are used in a communications system to convert analog signals to digital signals on one end and, on the other end, convert a digital signal back to an analog signal. I discussed sampling rates and the Nyquist Sampling Theorem. It turns out there's more to generating the Pulse Code Modulated (PCM) wave shown in that last post.

Quantization is used along with the sampling rate to generate a PCM wave. The instantaneous voltage value of an analog signal is quantized into 2⁸ (256) discrete signal levels. With each sample the signal is instantaneously measured and adjusted to match one of the 256 discrete voltage levels.

PCM Wave Generation (note: not to scale)

Since quantization adjusts voltage levels to match one of 256 discrete voltage levels it is easy to see that there will be some signal distortion. This distortion is known as quantizing noise and is greater for low amplitude signals than high amplitude signals. A technique called companding is used to compress and divide the lower amplitude signals into more voltage levels and provide more signal detail at the lower voltage amplitudes. In North America and Japan, this is done using an algorithm called the μ-law. Other countries in the world use the A-law algorithm so conversion is required when calls are made between countries using different algorithms.

Once a piece of an analog signal has been quantized and companded it is then given an 8 bit binary code. This process is referred to as encoding.

After a single analog signal has been encoded it is multiplexed, or combined, with 24 other encoded 8 bit signals. This generates a 192 bit (8×24) sequence for the 24 signals. A process called framing then adds one framing bit to create a 193 bit frame. The framing bits are used to keep the receiving device in synchronization with the frames it is receiving and follow a 12 frame pattern that is repeated with each 12 frames. This sampling rate has determined the Digital Signal (DS) Level System I'll cover here in a future post.

Analog to Digital (and Digital to Analog) with CODECs

2011-08-02T21:41:00.027-04:00

In this post I continue to discuss the (rapidly disappearing) Public Switched Telephone Network (PSTN).
CODECs are used to convert analog signals to digital signals on one end and, on the other end, convert a digital signal back to an analog signal.

CODEC Conversions

CODECs use a method called Pulse Code Modulation (PCM) to convert the analog signals to digital bit streams. PCM uses a technique called sampling to obtain instantaneous voltage values at specific times in the analog signal cycle. This sample generates a Pulse Amplitude Modulated (PAM) signal.

PAM Signal Generation

The diagram above shows an analog signal multiplied with a digital pulse train instantaneous point by instantaneous point with the result being a PAM wave representation of the analog waveform. The digital pulse train determines the sampling rate and it is easy to see if the analog signal is not sampled enough, the analog signal will not be properly represented by the PAM signal.

In 1924 while working for AT&T Henry Nyquist studied this sampling technique and developed the Nyquist Sampling Theorem. This theorem states that an analog signal can be uniquely reconstructed, without error, from samples taken at equal time intervals if the sampling rate is equal to, or greater than, twice the highest frequency component in the analog signal or:

Sampling Rate = 2(BW)

Example

The Public Switched Telephone Network (PSTN) has a bandwidth of approximately 3300 Hz. Using the Nyquist Sampling Theorem calculate the minimal sampling rate of the PSTN.

Solution:

Sampling Rate = 2(BW) = 2(3300 Hz) = 6600 Samples per Second

This means, for minimal analog to digital conversion, an analog voice telephone line must be sampled minimally 6600 samples per second. Sampling at a rate of less than 6600 samples per second will not reproduce the signal properly. Sampling rates of greater than 6600 samples per second will produce more detail. Designers of the voice network used Nyquist’s Sampling Theorem to determine the proper sampling rate. They knew they could not sample under the 6600 samples per second rate and also knew going over the 6600 samples per second rate would produce higher quality. A PCM sampling rate of 8000 samples per second was selected.

In my next post I'll discuss Quantization, which is used along with the sampling rate to generate a PCM wave.

Analog Signals Beyond the Local Loop

2011-07-24T22:37:00.001-04:00

Analog transmission works fine for voice transmission on the local loop and the existing copper pairs coming into our homes will exist in some parts of the United States for a number of years. Several companies have been working towards converting the copper twisted pair local loop to fiber. In addition several cable television companies are now offering dial tone to their customers.

Let’s continue our focus on the telcos and look at what happens to our analog voice transmission when it gets to the telephone company Central Office (CO).

Local Loop and CO

Our analog voice signal is converted to a digital signal by a device called a CODEC (short for Coder/Decoder) and is then multiplexed, or combined, with other converted analog signals coming from other telephones or analog modems being served by the same CO. Once multiplexed, the calls are then sent out of the CO along their way on a higher bandwidth transmission medium such as fiber or microwave.

I'll write about CODECs in my next post and multiplexing in a future post.

Locking In To An LTE Provider

2011-07-21T11:20:00.000-04:00

Amrisa Bhagwandin has an interesting post over at goingLTE.com titled Verizon Reserving Its Phones for Its Own Network?

In the post, Amrisa speculates that Verizon Wireless is designing its phones so they will only run on the Verizon Wireless network. Bhagwandin also speculates AT&T may end up doing the same. Here's some of the technical details:

The Verizon Wireless and AT&T 4G Long Term Evolution (LTE) networks run on different frequency bands:

AT&T runs in the 704-746 Mega Hertz (MHz) band

Verizon Wireless runs in the 746-787 MHz band

There is some slight overlap between the two bands but there is not enough overlap for devices to run on each others networks. It's also important to remember the 4G conversion is not going to be like throwing a switch. Tower antennas will be gradually updated from 3G to 4G. This means 4G phones have both 3G and 4G radios in them - the 4G radio is used when 4G service is available and the 3G radio is used when 4G service is not available. This fallback also causes a problem. In locations where 4G service is not available, Verizon phones will fall back on the Verizon wireless CDMA 3G network and AT&T phones will fall back on the AT&T HSPA/GSM 3G network.

And..... it gets even more complicated - both Verizon Wireless and AT&T both own spectrum through MetroPCS and Bhagwandin thinks we'll see both companies setting up sales through MetroPCS to try and lock customers into their networks . In addition, we may see similar deals being made with Lightsquared and Cricket since both of these companies are developing their own 4G networks.

I'm in wait-and-see mode right now and not going to lock into any new long term wireless contracts until I get a better idea of how it is all going to shake out.

Mike Elgan On Why He's Loving Google+

2011-07-18T09:28:00.013-04:00

This is a great Google+ post from tech writer Mike Elgan. Mike is in the middle of a Google+ experiment he's calling his Google+ Diet. He's using Google+ for all of his online communication and has stopped using Facebook, Twitter, Foursquare, e-mail and several other services. Here's Mike's July 15 Google+ public post summarizing what he's experienced on the Google+ Diet so far:

Here's what I love about Google+ in general and the Google+ Diet in particular:

Instead of saying, "I'm going to write a blog post now," or "I'm going to send an e-mail" or "I think I'll tweet something" you simply say what you have to say, then decide who you're going to say it to.

If you address it to "Public," it's a blog post.

If you address it to "Your Circles" it's a tweet.

If you address it to your "My Customers" Circle it's a business newsletter.

If you address it to a single person, it can be a letter to your mother.

I'd say this is pretty revolutionary.

I haven't personally ditched any of my other social media yet but I do find myself going to Google+ more and using Facebook and Twitter less frequently.

You can follow Mike's Google+ Diet experiment here. My Google+ public stream is linked here.

Bridged Taps - More On The Local Loop

2011-07-15T12:47:00.003-04:00

A bridged tap is an unterminated wire pair that sits in parallel to the main wire pair. Ideally, the local loop is a continuous wire point-to-point connection. At one time, the local loops were all setup this way but, with the growth of neighborhoods, new unused wire pairs got added. Typically, extra pairs are included though not initially used when cable is run down a street. When a new house is built, or a line is added, a phone company technician taps into one of the unused pairs. The technician typically does not cut the pair, the wires are just “tapped,” leaving the unterminated ends running down the street. This way, if the line is no longer needed, a technician can come out, remove the tap and still use the pair for another customer farther down the street. This leaves a bridged tap with the tap point being where the technician spliced into the wire pair on the street.

Bridged Tap Example

Bridged taps can create an impairment to the transmission system. A signal on the loop moves down the un-terminated cable and will reflect back to the main pair affecting the main signal. A bridged tap will typically not be noticed at voice transmission frequencies because the wavelength of voice frequencies is always greater than the line length. All that is experienced is a slight increase in attenuation due to added capacitive load which is usually so small it is not detected by the human ear.

However, when it comes to Digital Subscriber Line (DSL) technologies, bridged taps can cause major data communications problems and frequently require cleaning up by telecom technicians. I'll discuss how DSL technologies work in a future post.

Loading Coils - More On The Local Loop

2011-07-14T08:00:00.007-04:00

Early in the development of the telephone system infrastructure designers realized our everyday speech lies in between 125 Hz and 8 KHz with most voice centered between 400 and 600 Hz. With more studies designers realized that humans can recognize and interpret voice if they stayed within this frequency range. Voice frequencies below 200 Hz and above 2 KHz play very little role in voice recognition.

Frequency Range Diagram

Since the early 1900’s the infrastructure has been tuned to match these frequency requirements using devices called loading coils.

Both George Campbell at AT&T and Michael Pupin at Columbia University were working in 1899 on wire pair mutual capacitance problem. Both realized that, by adding a lump series inductance called a loading coil, resonance could be used to cancel the effects of shunt capacitive reactance and increase signal strength over long local loops. Michael Pupin ended up getting the patent and by late 1899 loading coils were being installed in the field on copper wire pairs longer than 3 miles.

Western Electric 25 Pair Loading Coil Cable Case (circa 1977)
[and.... circa 1977 is the cable case, not me!]

Loading coils are a simple lump series inductance that produce an effect called loading. Loading increases the series inductance of the loop and effectively makes the loop a low pass filter, increasing the impedance of the line which drops signal attenuation. A typical 26 gauge local loop pair is loaded with a 26H88 loading coil. The letter H designates a coil that is added every 6000 feet, 26 represents 26 gauge wire and 88 indicates the inductance of the coil is 88 mH. This loading makes the loop perform as a low pass filter and cuts the frequency off sharply at around 3.4KHz. Loading coils work great for the low bandwidth requirements of voice but causes problems when you want to transmit data at higher bandwidths over these same wires.

Loaded and Unloaded Loss

At voice frequencies, the cutoff frequency (f_C) for a transmission line can be approximated as follows:

where: L = Loading Coil Inductance

D = Distance in miles btwn loading coils

C = capacitance per mile

Example 1

Calculate the cutoff frequency and sketch the frequency response curve for a local 3 mile loop using 26H88 loading coils spaced every 6000 feet.

Solution:

                                                               L = 88mH
                                                  D = 6000 feet ≈ 1 mile
                                                  C = .083 μF/mile

Notice using this formula total loop distance is not used in the calculation – only distance between coils is required.

In addition to H (6000 ft) load coil spacing, there are also B (3000 ft) spacing and D (4500 ft) spacing loading coils. By changing coil spacing along with coil inductance the loop cutoff frequency can be adjusted or tuned to the proper value. Let's look at another example.

Example 2

22mH loading coils are spaced every 3000 ft on a local loop. Calculate the cutoff frequency.

Solution:

                                                                    L = 22mH
                                                      D = 3000 feet ≈ .5 miles
                                                      C = .083 μF/mile

Notice in this example by reducing the distance between coils and decreasing the individual coil inductance values, we can increase the cutoff frequency. There are three commonly used loading coils in the United States and the coil specifications are listed below:

Loading coils have been used over the last 100 years and are an excellent way to tune a local loop to voice frequencies between 300 and 3300 Hz. As carriers move to provide high bandwidth data services such as ADSL on the same local loop being used for voice the low pass filter characteristics of the loaded local loop provide significant bandwidth limitations. We can see frequencies above 4000 Hz on loaded loops are blocked. For this reason loading coils are being removed from the local loop.