Wireless and VoIP Services as Carrier of Last Resort?

The shift continues for the traditional telecommunications companies away from copper based voice and DSL data services to wireless and fiber. One of the road blocks that appears to be loosening are the  Carrier of Last Resort (COLR) rules for carriers.

COLR rules are currently set at the state level (not the Federal Communications Commission) and regulate that every American has access to telephones service along with other utilities like electricity and water. A number of states have either passed legislation or are considering legislation that would end traditional landline rules and allow these services to be replaced by wireless (cell) or Voice over Internet Protocol (VoIP) services. Bills have emerged in Mississippi, Kentucky, New Jersey and California. Ohio's Senate Bill 271 is a good example of legislation currently being reviewed by lawmakers to cut traditional landline services. 

Opponents to these changes argue landline elimination could increase phone bills, reduce quality of service and impact 911 service. AARP Ohio State Director Bill Sundenmeyer is quoted in a recent post at Community Broadband Networks saying:

... besides preserving social contact, land-line phones are needed to protect seniors' health and safety. For instance, some seniors use the phone line to transmit routine health information from equipment in their home to their doctor's office.They can make an evaluation of a person's heart and how's it working, of their lungs, etc. That information would be very difficult to transmit over a cell phone.

There's more. Even though the FCC has stayed out of COLR regulations, leaving them to individual states, AT&T submitted a letter to the FCC back in August asking the FCC to effectively reclassify the public switched telephone network as an "information service", effectively removing all PSTN regulations and obligations. What does this mean? I think Bruce Kushnick describes it pretty well over at the Huff Post Tech Blog:

This means that almost all of the remaining wires, networks or even the obligation to offer services over those wires and networks are all removed -- as much of this infrastructure is classified as "telecommunications". The Public Switched Telephone Networks, the utility, would suddenly be reclassified as an information service. Sayonara any telco rules, regulations and oh yes, your rights. Your service breaks... tough. Prices go up and there's no direct competition -- too bad. Networks weren't upgraded -- so what. Net Neutrality? Neutered.

I'm not sure where you live but I'm in a relatively rural area of a fairly populated state. I've only got one wireless provider option at my home unless I climb up to the very peak of my roof where I can usually catch one bar of another provider. After the 2011 Halloween snowstorm cell service was out for almost a week at my home while landline service did not go down. 

Wireless service is great when it works. Wireless as carrier of last resort - someday yes but not just yet. AT&T has opened a window and the FCC now has an opportunity to step up and put a logical transitional process in place. 

Wavelength Division Multiplexing (WDM)

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.

Digital Multiplexing - Statistical Time Division Multiplexing

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).

Digital Multiplexing - Time Division Multiplexing

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.

Analog or Frequency Multiplexing

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

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 Basic Telephone Set Fundamental Functions

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:

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). 
2. To provide the telephone company with the number the caller wishes to call.
3. To provide a way for the telephone company to indicate that a call is coming in or ringing.
4. 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.

More Telephone History (1878-1918)

A couple of weeks ago I pulled a piece out of a book I wrote about ten years ago titled Introduction to Telecommunications Networks. In that post I described the first year in the development of telephone technology. As a follow-up to that post, here's some of the major technical breakthroughs that happened between 1878 and 1918.

1878
Bell sets up the first operator switching exchange and at the same time, Western Union Telegraph Company (http://www.westernunion.com) decided to use its existing national telegraph wire network to set up its own telephone company. Bell quickly sued Western Union and Western Union settled out of court, selling its network to Bell.

Henry Hummings in England gets a British patent for a variable resistance telephone transmitter that used finely ground carbon. The carbon transmitter solved many of the early problems Bell had trying to use liquid and electromagnetic transmitters. The carbon transmitter also used a voice cone attached to a diaphragm.

The diaphragm, which was attached to a conductor, vibrated with sound waves and caused the closed container of ground carbon to compress and uncompress changing resistance in the same way the liquid transmitters did.

1885
American Telephone and Telegraph Company (http://www.att.com) was formed to provide long distance telephone service, connecting small Bell regional telephone franchises.

AT&T buys Henry Hummings’ ground carbon variable resistance telephone transmitter patent rights.

1886
Thomas Edison modified Henry Hummings’ finely ground carbon transmitter by using larger carbon granules. The larger granules created more current paths with sound wave compression and therefore allowed more current to flow in conjunction with the compression. The larger granules also did not pack as tightly over time like the finely ground carbon in Hummings’ transmitter. When they did pack, usually lightly hitting the transmitter on a hard surface would loosen them up.

1899
AT&T reorganizes, assuming the business and property of American Bell and becomes the parent company of the Bell System.

1908
Siemens (http://www.siemens.com) first tests dialtone on the public switched telephone network in a German city.

1918
AT&T patents an anti-sidetone solution for telephone receiver and transmitters. This technology allowed talkers to more easily adjust their voice volume when speaking into the telephone transmitter.

I'll continue with more history in a later post.

The First Year Of The Telephone

About ten years ago I wrote a book titled Introduction to Telecommunications Networks. About half the book described how the now rapidly disappearing public switched telephone network (PSTN) worked. I haven't picked up the book in a while but a recent flip through has certainly brought back some memories. I thought it would be interesting to take a look at some of the history. Here's how it all started.

1876
Alexander Graham Bell and Elisha Gray, another inventor competing with Bell, are both scrambling to get their voice transmission inventions patented.
 
February 14, 1876
On this day Alexander Graham Bell’s father in law, attorney Gardiner Hubbard, delivered a patent application from Bell to the U.S. Patent for a device that transmits voice frequencies across wires.

Approximately three hours later on the same day Elisha Gray filed a caveat (a formal notice of an invention Gray hoped to patent) with the U.S. Patent Office describing a device that also transmitted voice frequencies across wires.

March 10, 1876
Alexander Graham Bell and Thomas A. Watson demonstrate a working telephone system but not without controversy. When Bell’s original patent and Gray’s caveat, both filed on February 14, were reviewed it was determined the device Bell described would not have worked while Gray’s would have. It was speculated that Bell had copied parts of Gray’s design. In Gray’s caveat he had detailed the use of a variable resistance transmitter which was used to produce a transmitter signal robust enough for the receiver to hear. Bell had been struggling to solve this same problem. In Bell’s patent application he made what appeared to be a last minute handwritten notation about the use of a variable resistance transmitter. People speculated that Bell had found out about Gray’s caveat and learned of Gray’s use of a variable resistance transmitter and, at the last minute before filing, Bell made a note on the patent application about using the new transmitter.

The variable resistance transmitter demonstrated by Bell on March 10, 1876 used a voice cone attached to a diaphragm. Also attached to the diaphragm was a wire that was emersed in a metal container of acidic solution.

The user talked into the voice cone, voice sound waves caused the diaphragm to vibrate and the wire moved up and down in the acidic solution. As the wire moved up and down in the solution the resistance between the wire and the metal container changed causing the DC current to vary in proportion to the variation in sound waves.

The controversy between Bell and Gray lead to years of litigation to the level of the United States Supreme Court where a split decision gave Bell the patent for the telephone entitled Improvements in Telegraphy.

It took a little over a year for Bell to acquire and convince his wealthy father-in-law, Gardinar Hubbard, to finance the Bell Telephone Company and fund the building of the voice network infrastructure.

It's interesting to look back at the legal back and forth between Bell and Gray. It reminds me a lot of what we're seeing between Mark Zuckerberg and Facebook, the Winklevoss Twins, Wayne Chang,  Paul Ceglia.... and others.

Is Faking Caller ID Illegal in the United States?

It used to be pretty easy to fake a caller ID in the U.S. I remember doing it years ago in one of my classes, calling my cell phone from another line using my own cell number as a spoofed caller ID. I could make it look like I was calling myself - kind of creepy if you did not know what was going on. I was using one of the services on the web - I won't post any links or names of companies here that offer /offered these services. Most of them shut their services down but you can still find thier sites on the web if you do some creative searching.

Is it illegal in the United States? Yes.

One year ago today, on February 23, 2010, the Senate passed a bill called the Truth in Caller ID Act of 2009 (S:30). It then went to the House of Representatives and was passed. Both the Senate and the House passed it by Unanimous Consent.

A couple months ago on December 22, 2010, President Obama signed it so it is now a law, currently illegal to cause any caller identification service to knowingly transmit misleading or inaccurate caller identification information with the intent to defraud, cause harm, or wrongfully obtain anything of value.

The law includes VoIP services like Skype and has an exemption allowing users to block their caller ID if they want to. In addition, law enforcement is exempt.

I've already been asked - Was Wisconsin Governor Scott Walker's prank call caller ID spoofed? I have no idea.

Why the Public Switched Telephone Network Is Sunsetting

In my last post, titled Verizon No Longer Concerned With Telephones Connected With Wires, I described an interview Ivan Seidenberg, chief executive of Verizon Communications, did at a Goldman Sachs investor conference on Thursday. In the inteview Seidenberg described how, by using the decentralized structure of the Internet rather than the traditional design of phone systems, Verizon had a new opportunity to cut costs sharply.

This summer I spent some time reading Martin Sauter's excellent new book Beyond 3G, Bringing Networks, Terminals and the Web Together. In the book Martin describes the movement in the wireless/cellular world away from circuit-switched telephony technologies like 2G, 2.5G (EDGE) and even 3G to 4G based technologies like LTE and WiMAX.

What does wireless technology have to do with copper wires? Like these wireless technologies, the Public Switched Telephone Network (PSTN) uses circuit-switched telephony technology designed around voice. Even DSL (a technology basically designed to extend the life of the copper wire based network by a few years) is a circuit-switched service - Internet based traffic goes to the Internet and voice traffic goes - you guessed it - right to the PSTN.

Circuit-switch based networks have made a lot of sense for the past 100 years or so. They work well for voice calls because by nature they are deterministic. If a circuit is available a connection is made. If a circuit is not available the call attempt gets rejected and the customer gets some kind of message back from the busy switch. Once a connection is made (phone-to-phone) the connection is also deterministic - each call is independent and cannot influence any other calls. A great design for voice communications - whether it be with copper wires or over wireless frequencies.

The problem with these circuit-switch based networks though is they were designed for voice. Sauter argues correctly that when networks are designed for specific applications, there is no separation between the network and the applications which ultimately prevents evolution. In addition, tight integration of applications and networks also prevents the evolution of an application because changing the applications also requires changes to the network itself. The PSTN basically cannot evolve beyond where it is now - it's been tweaked-up to the point where it cannot be tweaked-up any more.

Internet (TCP/IP based) technologies work using exactly the opposite approach. A neutral transport layer carries packets and any kind of application (voice, video, data, etc) can efficiently send high and low volumes of data through the network. For applications the connection process is transparent - the device operating system establishes an Internet connection before the application is even launched. The network and any applications running that use the network are independent of each other.

Verizon Wireless, AT&T, Sprint, etc are all moving to non-circuit-switched IP based 4G technologies like WiMAX and LTE to handle voice, video and data traffic. It is inevitable that Verizon's landline division (along with other landline carriers) move in this same direction.