1. Auto Switch/SPID Detection Many of the newer ISDN adapters will automatically detect the central office switch/SPID configuration on their own. Purchasing an ISDN adapter with this capability is a good idea. Here is how it works:

   The central office switch talks to your ISDN adapter by using special messages called a protocol. Different central office switches use slightly different messages. A smart ISDN adapter can tell by looking at some of those messages what kind of central office switch it's talking to. Clever eh? The other thing a smart ISDN adapter can do is guess the SPIDS. In order to accomplish this it needs to know the phone number(s) of the ISDN line.

   If you have already guessed that a SPID is just a phone number with some extra junk attached, you're correct!

2. Data Compression Some ISDN adapters will compress data like a modem. This feature is mostly found in the bridge/router products. Be sure both ends of the connection are able to compress, and use the same compression algorithm. Unlike modems, ISDN adapters don't necessarily use the same compression methods.

3. Protocols Protocols are the things that are used to carry your data across the ISDN. As with data compression, both ends of the ISDN connection must use the same protocol. Buffer has asked that I list the most popular protocols used over ISDN so here they are:
   1. V.110
      Protocols that are seldom used are sometimes called "legacy protocols". V.110 is an ISDN legacy protocol.

   2. V.120
      Another legacy ISDN protocol.

   3. Asynchronous To Synchronous PPP Conversion
      This is part of the PPP (Point To Point) Protocol. It is taken from RFC 1662, ("Buffer is that the most recent RFC?"). It gets used because ISDN adapters like to talk to each other using HDLC ("You really don't want to know what HDLC is...Honestly.") which uses synchronous framing of the protocols data. PC's like to use asynchronous framing out their serial or COM ports when they talk to an ISDN adapter, so some ISDN adapters will convert the asynchronous PPP from PC into the synchronous PPP that the ISDN adapters like.

   4. Bonding (About Bonding)
      There are many protocols around that will "bond" the two ISDN B-channel's together into a single one. Bonding and Buffer go way back, let him tell you all about it.

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