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What is an E1 Frame ?
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Originally the E1 frame
was developed to connect PABX systems carrying 30 PCM
encoded voice channels together with associated
signalling. The PCM digitisation rate is 8000
samples/second x 8 bits/sample, or 64Kbps. The signalling
for all 30 channels takes a further 64Kbps. The aggregate
of 31 channels represents a data rate of 64Kbps x 31 or
1984Kbps. Because the E1 framing rate is also 64Kbps, the
operating rate of the E1 carrier is 2.048Mbps.
The E1 frame consists of 32 timeslots, each one byte long.
Synchronisation is achieved using the framing information
in timeslot 0. The other 31 timeslots are available for
use, each giving an effective data rate of 64Kbps.
Using a E1 multiplexer companies can integrate the transmission
of voice, data and video between locations, routing this
mixture of data onto a common E1 transmission line.
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Can I use more than four Nx64 channels on one E1 link ?
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Yes ! An Echo can
have four Nx64 channels fitted, but additional Echos may
be daisy-chained (concatenated) together using the
D&I port, adding extra channels as required.
The Envoy supports up to 14 data channels without the need for
concatenation.
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I have installed a Drop and Insert multiplexer between a PABX and the
link, but I now sometimes hear clicking and calls are
occasionally being dropped. When I take the multiplexers out it
works fine.
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There are two possible causes:
a) Incorrect Clock Master
The clocking may be set incorrectly. In any E1 system, one of
the units must provide the master clock. Before the Echos
were installed, it would have been one of the PABXs. It
is CRUCIAL that the Echo which is connected directly to
the MASTER CLOCK PABX be set to THROUGH
clock. The other Echo should be set to LOOP
clock.
When using an Elink 4 in Drop and Insert mode, both units must be set to
Clock Source: Drop.
b) Incorrect SYNC mode (searching for CRC4 sync)
If the Echos are set to CRC4 synchronisation on
the D&I ports, but the PABXs are not set for CRC4,
the Echo’s will remain in CRC4 HUNT
mode. This will pass calls OK for a while, but after a
period of not finding full synchronisation, SYNC will be
abandoned and re-started. Echo software version 1.05 and
above will show a MAJOR ALARM by default if the units are
in CRC4 HUNT mode.
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When I pick up a phone, the corresponding phone rings but no
voice goes through.
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You have probably not set the correct timeslot for drop and
insert (D&I). Check the PABX documentation as to which timeslots
it is programmed to use and then set the multiplexer accordingly.
PABXs
use timeslot 16 exclusively for signalling information.
This means you must set timeslot 16 for drop and insert
D&I (even if you are using ADPCM). Once this is set
all signalling information will go through and thus the
corresponding phone will ring even if the correct voice
channel has not been configured.
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My PABX system uses the additional (SA) bits in the E1 frame
for communication. Can these bits be passed
transparently ?
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Normally the Echo uses the
SA bits in timeslot 0 for communicating with the remote
Echo so that you can configure both multiplexers from the
same location. Some PABXs also use the SA bits for
communication and can therefore become confused if Echos
are introduced. Since Echo software version V1.05, you
can make the SA bits transparent so that connected PABXs
can use the SA bits exclusively for themselves without
interruption. This feature can be turned on or off as
required so that you can configure or monitor the remote
Echo at any time if required.
The Elink 4 can be configured to use any timeslot (or none) for
management though we recomend using Timeslot 0 if the SA bits are
not otherwise being used.
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Can I send FAX or modem calls through an Echo ?
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The Echo does not
affect the communication of PCM data between PABXs,
therefore FAX and modem calls will pass through as
before.
When using the ADPCM compressor, the speed of the FAX or modem
may be reduced due to the ADPCM algorithm.
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How many events are stored in the Echo event log ?
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The Echo event
log stores up to 960 events in a non-volatile 'ring
buffer', i.e. when the event log is full, the oldest
events get overwritten first. This information is stored
even if power is interrupted. The event log records
events such as synchronisation loss or power interruption
together with a time stamp to aid fault finding. The
event log can of course be reset when required.
The statistics display records the E1 link statistics history
for the last 24 hours broken into 15 minute intervals.
The statistics show any data errors which may have
occurred on the line.
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