Telos ZephyrExpress user manual Dealing with The Phone Company, Switch carriers

ISDN TIP!

If you want to temporarily switch carriers, try prefixing the call with these numbers:

commercials remind us for voice calls, you can choose an ISDN long-distance company on a per-call basis by prefixing the number with the “1010-xxx” carrier code.

iYou must dial the full number, including the 1 or 011 + country code, following the 1010- xxx numbers.

			1010-222 for MCI	1010-288 for AT&T	1010-333 for Sprint
			AT&T can be unfriendly to ISDN, and at times will block 1010 access for that service. You
			may have to contact them before dialing their access code.
			Some long-distance carriers ÑÊnot the big three ÑÊcanÕt handle ISDN at all. For the lat-
			est information check the section in the Appendix ÒISDN, BRI, ZephyrExpress, and YouÓ.
	Some long-distance connections are limited to 56kbps/channel. This limitation is be-
t	coming more rare. There is no certain way to know in advance. In addition, some carri -
	ers may work at 64Kbps and not 56Kbps. So, you may need to try both or temporarily
	switch carriers.
			DEEP TECH NOTE!
			This limitation arises from a quirk of the older telephone infrastructure. The channel
			banks that have been widely employed in the long-distance network have a native
			64kbps capability, but “rob” the low order PCM bit on every sixth frame in order to
			convey supervision information (on-hook/off-hook and dial pulses).
			As new telephone plant is built for clear 64kbps transmission and a technology called
			“Signaling System 7” is deployed to allow the various elements of the phone network
			to communicate without using the robbed bits, this limitation will disappear. The
			European network has universal full 64kbps capability.
		ZephyrExpress provides standard rate adaptation (officially known as ‘CCITT V.110’)
	from 56 to 64 kbps and vice versa when required. Bitrate adaptation happens automati-
	cally within the system depending upon the rate selected by the calling party. Since
	ZephyrExpress can’t communicate at two rates simultaneously, it ignores rate adaptation
	information on any second incoming call.

HOW TO ORDER ISDN

Dealing with The Phone Company

As is often the case when we broadcasters interface with the phone people, the lines of communication on ISDN can get a little tangled. Face it: we are not the usual customer.

The first order of business is to find someone who knows what ISDN is. While your usual account agent will be the normal entry point, you may be talking to a number of phone people before you find one who understands your needs. Some of the regional

ISDN 7-7