Telos ZephyrExpress user manual Directory Numbers DNs, Long-Distance Digital Connectivity

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DEEP TECH NOTE!

SPIDs were designed to let telephone switches support different feature requirements by sensing the different identifier of each device on a BRI circuit. For example, mul- tibutton phones could retain functions when moving from line to line. (In this case, the line number would probably not be used as the SPID.) This lets a variety of different types of equipment, with different service requirements, share a single circuit.

None of this matters with our application, but we must enter the SPIDs nevertheless.

CURIOSITY NOTE!

There is hope that SPID difficulties will become a thing of the past. For one thing, the Telcos are beginning to standardize on area code + phone number + 0101 for SPIDs on National ISDN lines.

Standards for future versions of National ISDN will include automatic SPID assign- ment and selection, and non-initializing terminals which could operate basic functions without a SPID at all.

We’re monitoring these developments carefully, and at some point may be able to support these features — if they become available — in a ZephyrExpress software upgrade.

Directory Numbers (DNs)

Directory Numbers, or DNs for short, are the 7 digit telephone numbers assigned to the ISDN line (or what you’d typically find in a telephone directory). You may be assigned one or two, depending upon the line configuration. In the case where you have two ac- tive ISDN B channels, you will usually have two DNs (but not always). However, the “physical” channels are independent from the “logical” numbers. A call coming in on

ithe second number will be assigned the first physical B channel, if it is not already occu- pied. Therefore, there must be some way for the Zephyr to sort out which call goes to which channel/line. The DN is used for this function.ISDN TIP!You don’t need to enter DNs if they’re already contained as a seven-digit string

within your SPIDs. When DNs are required, only the seven digits — not the area code

— should be entered.

When a call rings in, it contains set-up information which includes the DN that was di- aled by the originating caller. The last seven digits are matched with the DNs pro- grammed into the Zephyr and the proper assignment is made. Therefore, problems with Directory Numbers will virtually always result in trouble receiving calls.

Long-Distance Digital Connectivity

Long-distance connectivity via ISDN is routinely available in most parts of the USA from the “big-three” carriers: AT&T, Sprint, and MCI. Connectivity between any two given points is somewhat variable. The default long-distance carrier may be chosen at the time you order the line, just as with traditional voice lines. Also, just as endless television

7-6 ISDN