WHY ISDN

WHY ISDN
INSTEAD
OF ANALOG

KINDS OF ISDN
EQUIPMENT

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Data Compression

Protocols

Bonding

Buffer
Does Bonding
(story)

Voice Features

FAX Machines
and Modems

TO CONNECT
2 THE NET

BUFFER DELIVERS
THE MAIL

SETTING UP
YOUR OWN INTRANET

Buffer had his ISDN Adapter completely apart on the floor, along with a hot glue gun. There was glue everywhere!

I yelled, "Buffer what the heck are you doing?"

"I am going to do Bonding"

"Why is that, Buffer?"

Buffer concentrated on his mess and proceeded to explain that by bonding the two B, or Bearer Channels in an ISDN they could act like one and go twice as fast.

"O-kay," I said, scratching my head. "That sounds like a potentially good idea, but before you glue your paws together there, why don't we have a little chat."Buffer agreed, mostly because he was out of glue, I think. Buffer went to clean up.

"Now, I'll start by telling everyone that unlike an analog line, an ISDN phone line has two separate channels that can be used at the same time, just as if they were two regular phone lines. The phone company folks call these Bearer Channels or B-channels, for short, because they can bear calls. The two B-channels are separate and distinct within the same wire, not unlike a television cable that carries multiple TV channels on the same wire. If you could talk very fast, then it might be possible that a single phone line couldn't carry (or bear) all the information. So, if you had *two* phone lines, and a little magic, you could split up your fast talking, and send one word down one phone line, while sending another word down the other phone line. The "magic" would bond the words back together at the other end and reconstruct the original conversation from the two separate channels of words.

Below are methods of bonding the two B-channels together in an ISDN. All of them will work. All of them work *differently*. The important thing to remember is, if you want to do bonding ("Buffer are you listening?") both ends of the call(s) have to use the *same* method.

1. 1. Bonding (The Protocol) Public *Static bandwidth allocation *No overhead to payload

2. 2. MP (RFC 1717) Public *Static bandwidth allocation *Some overhead to payload

3. 3. MP+ (Enhanced RFC 1717) Proprietary *Dynamic bandwidth allocation *Some overhead to payload

4. 4. BACP (Bandwidth Allocation and Control Protocol) Public *Dynamic bandwidth allocation *Some overhead to payload

Buffer emerged from the bathroom walking on three legs, his right front paw stuck to his ear.

"I've got myself stuck together."

"Humm... you do appear to have a problem." I reached for the solvent. As i began removing the various globs of glue from my dog, I began explaining one of the other important features of bonding called Bandwidth Allocation/Deallocation. This is a way of selectively adding or removing more bandwidth from a call, thereby glueing or unglueing the B-channels as necessary.

"Hold still, won't you Buffer!"

"Yelp!"

"Dang! I got some fur with that one!"

"Yelp!"

What would be good for the bonding on Buffer's ISDN adapter is if he could add and subtract B-channels whenever he needed one. Let me give an example. Suppose Buffer's surfing cyberspace, and I need to call him from my cell phone, or FAX him. Now, if Buffer's surfing with *both* the B-channels when my call comes in to his ISDN Adapter, it would be really cool if the phone/FAX connected to Buffer's ISDN Adapter rang, telling Buffer he had a new incoming call. When Buffer answered the call, his ISDN Adapter would "knock down" one of those B-channels so he could talk to me, then add it back after I hung up. That's called Dynamic Bandwidth Allocation.

It makes Buffer's ISDN adapter more useful. Without Dynamic Bandwidth Allocation we must allocate a fixed number of B-channels for the entire call. So when I call Buffer I get a busy signal. I think you can see why Dynamic Allocation/Deallocation is the better way.

"Now if i could just get Buffer to answer the phone when I call..." "Could you have used any more glue, Buffer? It's all over your head!"

Which reminds me--there is one other thing you need to know about bonding, and that's called Overhead. Most bonding protocols require overhead. This means that they take away a little of your available B-channel(s) in order to be able to glue and unglue them together. This can be important if you are trying to use your ISDN Adapter together with a codec of some kind, to send pure audio or video.

"There Buffer, you're all cleaned up and ready for another adventure in cyberspace."

"Bark!"

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