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Tributary Testing
Individual 2048 kbit/s tributaries within 8488 kbit/s signals can be
tested to ensure correct functioning of multiplexes.
Unstructured
Where the structures on digital links do not conform to the usual
ITU-T Recommendations, for example inter-computer links, they
can be tested using an unframed format.
DATA INTERFACE TESTING
All commonly used data interfaces are provided as standard to give a
comprehensive data test capability together with primary and second
order PCM rate testing. Thus PCM and data circuits and equipment
can be tested with one compact, fully integrated test instrument.
Data test interfaces provided are RS-232, X.21, RS-449 (V.36), V.35
(2851), codirectional and contradirectional (2850B and 2851). DTE
is standard, DCE optional, EUROCOM D/1 is optionally available for
European military network applications.
Modes
Both synchronous and asynchronous modes are possible with a wide
range of standard and user programmable data rates, so that traditional
data interface testing can be addressed together with modern
digital data services at 64 kbit/s, n x 64 kbit/s and other rates.
REMOTE LOOPBACK
Remote loop activation and deactivation is provided for the RS-232
test interface according to ITU-T Recommendation V.54 by means of
control lines. This facilitates testing of data circuits automatically
without the need for manual intervention.
STRUCTURED DATA OPTION
The Structured Data option for 2850B/S and 2851/S provides comprehensive
X.50, 6+2 and reiterated structured data test capability
through Co/Contradirectional, V.11 and TTL data interfaces, and
within a 2048 kbit/s digital signal.
Channel rates
As well as the standard sub-channel rates up to 19.2 kbit/s additional
rates of 14.4, and 48 kbit/s are provided. It is also possible for the user
to programme other rates for special applications.
Out-of-service testing
Out-of-service testing can be used for error performance testing of
structured data sub-channels out to subscribers' equipment as well as
checking functionality of multiplex equipment. The equipment can
be stressed by injecting errors into framing bits. Alarms and housekeeping
bits can also be exercised to complete this flexible test capability.
Test access can be directly at 64 kbit/s or via a 64 kbit/s channel within
a 2 Mbit/s signal.
Remote loop activation is provided according to national requirements
to facilitate testing out to subscribers' equipment.
In-service testing
Two types of in-service testing can be performed, in-service monitoring
and drop and insert testing.
In-service monitoring
An X.50 or reiterated data signal can be monitored directly at
64 kbit/s or via a 64 kbit/s channel of a 2 Mbit/s signal.
For 64 kbit/s signals via V.11 or Co/Contradirectional interfaces connection
can be made across the line in high impedance mode (bridging).
For 2 Mbit/s signals monitor and bridging modes are available.
Various parameters can be monitored during in-service testing
including framing errors and housekeeping and alarm bits. Where
test patterns are being carried within selected sub-channels these can
also be monitored for errors.
X.50 Drop and Insert Testing
Drop and insert testing can be performed directly at 64 kbit/s or on
64 kbit/s channels within 2 Mbit/s signals.
For 64 kbit/s signals via V.11 or Co/Contradirectional interfaces the
X.50 signal is looped through and an X.50 sub-channel replaced by a
test pattern. A second 64 kbit/s receiver is provided to enable monitoring
of the return signal for test pattern errors.
For 2 Mbit/s signals an X.50 signal can be looped through on a selected
channel and at the same time performing drop and insert on an
X.50 sub-channel.
These are the normal drop and insert modes that will be used in-traffic
for 64 kbit/s and 2 Mbit/s signals. Other configurations can be
adopted for special applications for mixed 2 Mbit/s and
64 kbit/s connections.
FLEXIBLE ERROR MEASUREMENTS
Where appropriate, 2850B and 2851 have the ability to detect, simultaneously,
Code Errors, Framing Errors, Pattern Errors and CRC
Errors. Further measurements are then made on a selected error
type, including error distribution.
Error Distribution/Histogram
The results are displayed in the form of a histogram with accumulation
over 72 hours, and a maximum resolution of 1 minute. Other
events such as sync loss are also stored on the histogram. All stored
results are tagged with time and date, so that a comprehensive record
of long term measurements is available to assist in fault localization.
A permanent record of results can also be obtained by printing a text
equivalent or a facsimile of the histogram subsequent to the test. In
addition the instrument can be programmed to Autoprint selected
parameters on event or at timed intervals.
G.821 and G.921 Measurements with Histograms
Where availability measurements are being made on 64 kbit/s channels,
results in G.821 format will be provided, while for higher rates
Annex D of G.821 is applied. In addition up to 100 day histograms are
provided for each of the G.821 parameters with automatic recognition
of exceeding daily limits, defined by circuit grade and length for
G.821, or circuit classification for G.921. Alternatively user defined
limits can be entered directly. Where short tests are required histograms
can be selected up to 25, 50 or 100 hours with a resolution of
15, 30 or 60 minutes.
G.826 and M.2100 Measurements
G.826 extends measurements to 2 Mbit/s and above, while M.2100
adds other events such as alarms which contribute towards G.821 and
G.826 measurements.
RESIDUAL BIT ERROR RATE
Assessment of background error performance is useful in systems
subject to periodic degraded performance, such as radio or satellite
systems. This measurement is a long term error rate ignoring severe
