E3Switch DS3 Operating information manual - page 12
Chapter 5: Operating Modes and Configuration
Chapter 5: Operating Modes and Configuration
Telecom
There are several, low-level configuration settings for telecom ports:
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CRC-length (16bit, 32bit, or none)
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Scrambling (on or off)
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Rate (typically full rather than a sub-rate or fractional rate)
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E3 vs DS3
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cable length (for long DS3 runs only)
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M13 vs C-Bit (for DS3 only)
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Circuit ID message (for C-Bit only)
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Transmit clock source
Use a “DS3” configuration setting typically for North America, Japan, and South Korea; otherwise, “E3”
speed.
Incorrect WAN settings will typically manifest in the errored-packet counts shown at the HTTP
management screen of the converter.
The cable length setting will transmit a slightly stronger signal on long DS3 coax runs. The M13/C-Bit
setting sets the AIC bit in DS3 frames to either 0 or 1. This bit is typically ignored by the DS3 carrier;
however DS3 carrier equipment set to auto-sense the incoming DS3 framing type will need this setting to be
correct.
Clock Source
The transmit clock source is typically “local” for both units. Certain DS3/E3 carrier equipment or optical
converters require the same transmit clock in each direction; this may manifest itself as frame-slip errors. In
such a case, set one unit to “loop” clock source. In very rare cases the carrier DS3/E3 equipment will
generate the clock for the entire path, and each unit should be set to “loop”. Setting both units to “loop” is
typically inappropriate and can result in transmission failure if a master clock is not being generated by
carrier equipment. Without a master clock, two units set in “loop” mode will wander to an unspecified
clock speed, which is unlikely to meet DS3/E3 specifications.
Dual-channel DS3/E3 units allow Port 2 transmit clock speed to be derived from incoming Port 1 clock
speed. This is an uncommon configuration requirement and should typically be avoided.
In the event of incoming clock loss, the transmit clock will automatically switch to a locally generated
DS3/E3 clock source.
The receive clock speeds are shown at the bottom of the unit's HTTP management statistics page to assist
timing diagnosis.
DS3 Circuit ID PMDL
DS3 Path Maintenance Data Link (PMDL) identification messages associated with C-Bit framed DS3 links
can be received and transmitted if desired. Circuit ID messages convey human-readable, configurable,
physical location information of the DS3 source equipment. These messages are transmitted in the C-Bits
of the frame and do not decrease bandwidth available for data. PMDL Circuit ID messages facilitate
confirmation of the data source when presented with a pair of unlabeled BNC cables.
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