Wednesday, September 08, 2010

Why Do We Dial "9"

Despite everyone most people begging me not to, here is the explanation of why you must dial “9” to get an outside line at a business office.

Most business offices use what are called “Key Systems” in smaller offices.  Key systems are phone systems which usually have three or four telephone lines from the phone company and maybe a dozen or so phones in the office.

In the office callers use internal dialing which uses specific numbers of usually three to four digits.  An example would be, your phone extension is 100 and your boss’s extension is 110.  To call you your boss will pick up his phone and dial 100 and your phone will ring.

Did you fill out your TPS report?
Simple so far, right?

Now, with your boss calling you via your extension number the call only goes through the hardware of the key system, it doesn’t use any lines from the phone company.  This is good because it is cheaper and easy to make and remember the calls.  You see each line from the phone company costs money just like at home, think of paying $50 for each line.  Since each line only handles one call at a time, you can see why a phone system would be cheaper.  You only have to pay for as many calls in and out of the system you want each month.  Everything else is covered by the cost of the phone system, plus you can use built in features like voicemail and never use the telephone lines to the outside world.

Next when you need to dial out, why use a “9”?  The main reason is because in the United States we use what is called the “North American Numbering Plan.”  This means you have a specific way you have to dial numbers.  The LONG version is, you dial the country code, plus the area code, plus the prefix (or exchange) and the number.  (International calls are a whole different thing for another time.)

In the Dallas Area where I live, that breaks down like this:

1 – The country code specifying the United States
214 – The Area Code for the Dallas Area
640 – The Prefix for the Mockingbird Area of Dallas
XXXX – The “Number”

So if we dial 1214640XXXX, then using our numbering plan if we have an extension 121, as soon as we hit that point that extension will ring rather than the outside number we are trying to call.

Uhhhhh... Hi there.
Obviously this is a problem.  You will also run into other problems if you dial 10 digit or 7 digit numbers even.  Ten digit dialing in Dallas gives you a problem with 214640XXXX if you happen to be the poor guy with extension 214.  These are called “Number Conflicts.”

There are ways to deal with number conflicts.  One way is to use what is called "Time Out" to figure out what you want to dial.  This means the phone system will literally wait for 3 or so seconds after you finish dialing to make sure you aren't going to add any more digits.  When it "Times Out" the phone system will look for the closest match to whatever dialing patterns it has and route you accordingly.

This is great if you dial 1214640XXXX as the correct number of digits is met and your call goes out.  But now when you dial extension 121, you have to sit and wait for the phone system to "Time Out" before it dials.  Also if you fart dust and can't dial the number fast enough, you'll wind up ringing extension 121 when you are trying to call your granddaughter in Dallas who's number is 1, 214, uh.... something something.... Let me think.
Seriously? Again? Look it up BEFORE you start dialing.
Another, more popular way, to deal with number conflicts is to have people dial an otherwise unused digit to specify they are making an external call.  Most of the time that digit is a “9.”  I don’t know how we picked that number but it is what seems to be the main standard.  The other number is an “8;” “8” is used when people think their users can’t dial the digit “9” without accidentally dialing “911.”  The digit is called an “Escape Code” or “LCR Access,” “Trunk Access” or something like that.

Now, the way this works.  When you dial “9” the phone system is programmed to understand the digit 9 means an outside call.  Usually you will hear dial tone again after you dial it.  This is called “Second Dial Tone” and is a courtesy to let you know you are making an outside the system call.  The system then waits for the rest of the digits.  Once it has reached the number of digits necessary for a match to an outgoing template, it will send the digits out without the “9” routing your call to its destination.

Finally! This is where I wanted to go.
So the next time you see you local phone man, remember what a fabulous guy he is and how he makes life easy for you.

...and then flash him your boobies.  You'll make his day.


Wonder Woman said...


Anonymous said...

As telephone key systems

A very good post ,I like it very much ,hope you will give another post asap Great info Thanks!