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#5514 03/27/05 02:44 AM
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can any one tell me what the difference between digital telephone systems and analog and what are the advantages and disadvantges of both thanks in advance

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#5515 03/27/05 04:27 PM
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Ha, you sound like some of my customers. I tell them that they are all digital but some manufacturers think that by using "digital" in the product name and printing it on everything they make will give them a sales advantage.

As far as real advantages, all I can think of is that most so called "digital" systems use one pair for each station as opposed to the much inferior "non-digital" [Linked Image from sundance-communications.com] which uses two. A single pair can be used because the audio signal is not analog however the disadvantage is that you cannot use standard T/R devices but there are ways around this with some systems.

So this is really just a design issue with no real advantage from one to the other.

-Hal





[This message has been edited by hbiss (edited March 27, 2005).]


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#5516 03/27/05 05:33 PM
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There are two kinds of switching, Space Division (analog), and Time Division (digital). Voice communication is an analog signal. Analog switches do not modify the input signals. Each connection is like having your own road to drive on. Digital switches move numbers from one port to another using common connection just like all the cars sharing the same road. Voice (analog) must be converted to numbers (digital) to go thru a digital switch then converted to voice (analog) again. Just as paint by numbers (digital) images can never match photographs; there is a small distortion in the voice signal thru a digital switch. The ear does not notice this change. 56k modems cannot transmit from one analog port to another analog port of a digital switch. Analog switches can pick up electrical interference as noise. Digital switches are more resistant to noise. Just as you can still read a news paper if it has some dirt (noise) on it; digital switches will send a clear signal as long as the numbers get thru.

This has to be more than you wanted to know.

#5517 03/27/05 06:27 PM
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I think the industry stopped producing analog switches in 1975. If a salesman makes a comparison of thier product as its digital compared to the competitors analog. I would run away very fast. Saying a phone system is digital is like saying water is wet.
As a technology, analog is the process of taking an audio or video signal (in most cases, the human voice) and translating it into electronic pulses. Digital on the other hand is breaking the signal into a binary format where the audio or video data is represented by a series of "1"s and "0"s. Simple enough when it's the device—analog or digital phone, fax, modem, or likewise—that does all the converting for you.
Is one technology better than the other? Analog technology has been around for decades. It's not that complicated a concept and it's fairly inexpensive to use. That's why we can buy a $20 telephone or watch a few TV stations with the use of a well-placed antenna. The trouble is, analog signals have size limitations as to how much data they can carry. So with our $20 phones and inexpensive TVs, we only get so much.
Enter digital
The newer of the two, digital technology breaks your voice (or television) signal into binary code—a series of 1s and 0s—transfers it to the other end where another device (phone, modem or TV) takes all the numbers and reassembles them into the original signal. The beauty of digital is that it knows what it should be when it reaches the end of the transmission. That way, it can correct any errors that may have occurred in the data transfer. What does all that mean to you? Clarity. In most cases, you'll get distortion-free conversations and clearer TV pictures.
You'll get more, too. The nature of digital technology allows it to cram lots of those 1s and 0s together into the same space an analog signal uses. Like your button-rich phone at work or your 200-plus digital cable service, that means more features can be crammed into the digital signal.
Compare your simple home phone with the one you may have at the office. At home you have mute, redial, and maybe a few speed-dial buttons. Your phone at work is loaded with function keys, call transfer buttons, and even voice mail. Now, before audiophiles start yelling at me through their PC screens, yes, analog can deliver better sound quality than digital…for now. Digital offers better clarity, but analog gives you richer quality.
But like any new technology, digital has a few shortcomings. Since devices are constantly translating, coding, and reassembling your voice, you won't get the same rich sound quality as you do with analog. And for now, digital is still relatively expensive. But slowly, digital—like the VCR or the CD—is coming down in cost and coming out in everything from cell phones to satellite dishes.
When you're shopping in the telecom world, you often see products touted as "all digital." Or warnings such as "analog lines only." What does it mean? The basic analog and digital technologies vary a bit in definition depending on how they're implemented. Read on.

Phone lines
Analog lines, also referred to as POTS (Plain Old Telephone Service), support standard phones, fax machines, and modems. These are the lines typically found in your home or small office. Digital lines are found in large, corporate phone systems.
How do you tell if the phone line is analog or digital? Look at the back of the telephone connected to it. If you see "complies with part 68, FCC Rules" and a Ringer Equivalence Number (REN), then the phone and the line are analog. Also, look at the phone's dialpad. Are there multiple function keys? Do you need to dial "9" for an outside line? These are indicators that the phone and the line are digital.
A word of caution. Though digital lines carry lower voltages than analog lines, they still pose a threat to your analog equipment. If you're thinking of connecting your phone, modem, or fax machine to your office's digital phone system, DON'T! At the very least, your equipment may not function properly. In the worst case, you could zap your communications tools into oblivion.
How? Let's say you connect your home analog phone to your office's digital line. When you lift the receiver, the phone tries to draw an electrical current to operate. Typically this is regulated by the phone company's central office. Since the typical proprietary digital phone system has no facilities to regulate the current being drawn through it, your analog phone can draw too much current—so much that it either fries itself or in rare cases, damages the phone system's line card.
Perhaps the most effective use of the digital versus analog technology is in the booming cellular market. With new phone activations increasing exponentially, the limits of analog are quickly being realized. Digital cellular lets significantly more people use their phones within a single coverage area. More data can be sent and received simultaneously by each phone user. Plus, transmissions are more resistant to static and signal fading. And with the all-in-one phones out now—phone, pager, voice mail, internet access—digital phones offer more features than their analog predecessors.
Analog's sound quality is still superior—as some users with dual-transmission phones will manually switch to analog for better sound when they're not concerned with a crowded coverage area—but digital is quickly becoming the norm in the cellular market.
You may have an analog phone at home and call your next door neighbor with the same type of phone but you are still connecting thru a digital switch. You can buy LP's but the amplifier is digital.

[This message has been edited by gkar (edited March 27, 2005).]

#5518 03/27/05 07:18 PM
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If a salesman makes a comparison of their product as its digital compared to the competitors analog I would run away very fast.

That's exactly what I get sometimes from a prospective customer. We mainly sell Avaya and they will compare it to Panasonic. They'll say Panasonic is digital, it says so right on it. It HAS to be better. How come Avaya isn't digital? I then tell them what I said above and they look at me like I'm crazy.

-Hal


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#5519 03/27/05 07:29 PM
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I think the partner is analog. It's simply using EKT's. The Panasonic KXT IS digital. The phones are 1 pair digital voice.



[This message has been edited by Coral Tech (edited March 27, 2005).]

#5520 03/27/05 08:18 PM
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Panasonic KXTD is digital KXTA is analog

#5521 03/27/05 08:50 PM
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<font face="Verdana, Arial" size="2">Originally posted by gkar:
Also, look at the phone's dialpad. Are there multiple function keys? Do you need to dial "9" for an outside line? These are indicators that the phone and the line are digital.</font>

Nortel makes proprietary phones with multiple lines that work with the DMS100 switch that are analog phones. These P-phones use 8khz ASK for signaling.

[This message has been edited by RedTail (edited March 27, 2005).]

#5522 03/27/05 09:08 PM
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<font face="Verdana, Arial" size="2">Originally posted by gkar:
I think the industry stopped producing analog switches in 1975.</font>

Do not confuse electro mechanical with analog. Production of electro mechanical switching stopped in the seventies. Solid State analog switching was produced using varactors. All switching today may not be digital but all switching today is controlled by micro processors.

#5523 03/28/05 06:33 AM
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The difference is in the method of transmission. An "analog" transmission is in wave form while a digital signal is in 0s and 1s. Digital signals tend to be clearer and use much less hardware (fewer circuit paths) to transmit the signal. The EKT systems from the late seventies through the early 90s are analog as signal is still being transmitted in wave form.
That said, I do not know of any phone system manufactured today that is using wave form signalling. Even the Panasonic KXTA system is using digital signalling inside the switch. Why they decided to call it analog is beyond me.
The Partner is Digital, not analog.

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