from
Communications News March, 1999
Teleport
Communications Group, Inc. (TCG) provides local telephone service
in 65 major markets nationwide. When the company began implementing
ISDN services in 1997, it wanted a solution to remotely monitor
and test ISDN circuits before connecting customers to the network.
The company also wanted the capability of remotely duplicating customer
applications to rapidly resolve problems.
To
meet these objectives, TCG had to be able to test a circuit using
real traffic before it went on line. Sergio Santiago, the company's
ISDN product manager, says, "Other local carriers dispatch technicians
first and troubleshoot after. TCG wanted a way to test the circuit
with real digital signals and the ability to accurately simulate
an individual customer's traffic. We needed to be able to do complete
end-to-end testing from the network management center (NMC). We
wanted to be sure that when we connected ISDN customers, they had
a working line. Also, if they had problems, we wanted to rapidly
isolate the cause and get them back on line quickly without the
delay of dispatching service personnel to the site."
TCG
selected the TSI-1567 ISDN Test Unit (ITU), from Telesync, Inc.
of Norcross, GA, to handle the testing requirements. The ITU can
place and receive calls and combines the features of a protocol
analyzer and multichannel bit error rate test set (BERTS) in a single
unit. It provides a dial-up means of automatically looping back
or generating BERT patterns on any of the 23 DS-0 B channels in
an ISDN PRI DS-1 stream. The TSI-1567 ITU is used to troubleshoot
BONDed calls, switched digital services, and translation tables
in switches.
One
ITU is located in every switch location. As new switches are brought
on line, they are immediately outfitted with an ITU. In this way,
the ITU can be used to turn up PRI service to the customer, as well
as provide a maintenance and troubleshooting tool when required.
A
dial-up modem is used to access the RS-232 port of the ITU. Local
operations personnel, as well as the NMC personnel, can dial into
any ITU in the network of switches to monitor or test any PRI application.
Accessing
the ITU, the operation and maintenance personnel can emulate the
end user's applications and determine in a matter of minutes whether
the problem lies within the network or at the customer's equipment.
"Although located at the switch, the ITU can test both the local
loop and the customer interface," Santiago says.
The
network switch is translated to route the incoming calls assigned
to the ITU into the DS-1 applied to the unit. The switch translations
that affect the ITU can be changed to mirror a customer's PRI application,
giving the operations personnel the capability to exactly emulate
the customer's application at the Layer 2 and 3 level, namely, call
setup and network control.
Upon
receiving a trouble call from a customer, the NMC personnel dial
up the switch ITU in the city where the trouble is reported. The
test format is built on the display screen of the workstation and
a call is placed to the customer's application. Layer 1, 2, and
3 information is scanned using the ITU's overview, L1, L2, and L3
screens. The log screen will show the messages transmitted and received
by the switch from the customer's application on the D channel.
The
method of sectionalization--the determination of "trouble in or
out"--takes approximately 20 seconds, the length of time it takes
to place a call. If the call is successful, the speed of the call
(56K or 64K) is determined, as well as whether it is voice or data,
and, most importantly, the destination of the call. By changing
the translations of the ITU to match those of the customer, including
trunk routing and long-distance carrier selection and routing index,
the technician can place the same call as the customer into the
network and to the far-end destination. In this instance, the overview
and log formats will be most helpful in analyzing a failure, if
one occurs.
To
date, network call failures are typically of two types. One is calls
made utilizing a long-distance carrier whose networks are not end-to-end
64K. The other is calls routed through tandem switching arrangements
and meet-point trunking locations that do not have sufficient trunking
capacity to accept the ISDN traffic loads. A call can be placed
into the network at 64K, but there is no guarantee that it will
complete at 64K.
As
more and more carriers upgrade their networks to 64K clear-channel
capability, the problem of placing and receiving 64K calls should
disappear.
TCG's
monitoring/testing strategy was designed in cooperation with Odyssey
Solutions, Inc. "TCG has taken a proactive approach to providing
quality customer service by implementing a maintenance strategy
before it introduced its primary rate ISDN service offerings," says
Warren Schmitt, Odyssey's chief technology officer. "This will provide
significant benefits for its ISDN customers."
**Note:
The TSI-1567 has been replaced by the TSI-1569
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