Hx1-Hx2 Manual-1.4.1 - Telos

A8 | appendix 1
Glare – On a POTS line an incoming call is signaled by periodically applying an AC ring
voltage to the line. Since there is a semi random period before the ring, and pauses between
rings, it is possible to seize a line which is “about to ring” (and answer a call) when attempting to
place an outgoing call. When this scenario happens it is called glare. Glare is much less likely if
Ground Start or ISDN trunks are used. See also Ground Start Trunk.
GR-303 - See SLC-96.
Grade of service- This is simply the ratio of calls blocked to total calls in a decimal form.
Therefore, a grade of service of P.08 would represent 8% blocking. Telephone tariffs regulate
the acceptable average grade of service which must be provided on public networks. See also
Blocking.
Ground Start Trunk – A type of telephone trunk where the request to make an outgoing call
(i.e. request for dial tone) is made by briefly grounding the Tip conductor. Many PBX system
use ground start trunks as they are less prone to glare than Loop start trunks. Ground start lines
are sometimes used with equipment designed for Loop Start lines. This may or may not work -
generally it serves to prevent outgoing calls while incoming calls work normally. Telcos may call
these “ground start lines”. See Loop Start Trunk. See also Glare.
GTD-5 - The GTD-5 EAX (General Telephone Digital Number 5 Electronic Automatic
Exchange) is the Class 5 telephone switch developed by GTE Automatic Electric Laboratories.
This digital central office telephone circuit switching system is used in the former GTE service
areas and by many smaller telecommunications service providers. It does not support ISDN.
HDSL - High-Data-Rate Digital Subscriber Line. HDSL delivers 1.544 Mbps of bandwidth
each way over two copper twisted pairs. Because HDSL provides T1 speed, telephone companies
have been using HDSL to provision local access to T1 services whenever possible. The
operating range of HDSL is limited to 12,000 feet, so repeaters can be installed to extend the
service. HDSL requires two twisted pairs, so it is deployed primarily for PBX network connections,
digital loop carrier systems, interexchange POPs, Internet servers, and private data
networks. DC voltage used to power the network Interface Unit (NIU) is “phantomed” between
the two pairs. See NIU.
Hunt group- A group of telephone channels configured so that if the first is busy (engaged) the
call goes to the next channel, if that channel is busy it goes to the next channel, etc. Hunt groups
may hunt from the highest to the lowest, the lowest to the highest, or on some other arbitrary
pattern. But the order of hunting will usually be fixed, beginning with one channel and working
through (“hunting”) until an unused channel is found. The term may have originated back in
the old manual switchboard days when the operator literally hunted for an unused jack to plug
a cord into. This arrangement is very common in business scenarios where a single incoming
number (the Listed Directory Number) is given to the public, but multiple incoming channels
are supported. See also LDN.
Hybrid – A device which converts from a two-wire signal such as POTS lines (or a 2-wire
intercom) to a four-wire system (separate send and receive paths) such as used in the pro-audio
world. While this task is theoretically quite simple, the fact the impedance of most phone lines
varies widely across frequency complicates matters. The Telos 10 telephone system was the first
practical DSP based hybrid and applied the then brand-new technology to this problem.
IEC -1) Inter-exchange Carrier. “Long Distance” carrier. Handles Interlata and interstate calls.
Most often referred to as IXC.
IEC - 2) International Electrotechnical Committee. A European standards body best known for
the power plug now used throughout the world for AC power cords for use on office equipment
and computers.