Chapter 26 xDSL Statistics
VMG3926-B10A User’s Guide
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Traffic Type
This displays the type of traffic the DSL port is sending and receiving.
Inactive
displays if
the DSL port is not currently sending or receiving traffic.
Link Uptime
This displays how long the port has been running (or connected) since the last time it was
started.
xDSL Port Details
Upstream
These are the statistics for the traffic direction going out from the port to the service
provider.
Downstream
These are the statistics for the traffic direction coming into the port from the service
provider.
Line Rate
These are the data transfer rates at which the port is sending and receiving data.
Actual Net Data
Rate
These are the rates at which the port is sending and receiving the payload data without
transport layer protocol headers and traffic.
Trellis Coding
This displays whether or not the port is using Trellis coding for traffic it is sending and
receiving. Trellis coding helps to reduce the noise in ADSL transmissions. Trellis may reduce
throughput but it makes the connection more stable.
SNR Margin
This is the upstream and downstream Signal-to-Noise Ratio margin (in dB). A DMT sub-
carrier’s SNR is the ratio between the received signal power and the received noise power.
The signal-to-noise ratio margin is the maximum that the received noise power could
increase with the system still being able to meet its transmission targets.
Actual Delay
This is the upstream and downstream interleave delay. It is the wait (in milliseconds) that
determines the size of a single block of data to be interleaved (assembled) and then
transmitted. Interleave delay is used when transmission error correction (Reed- Solomon)
is necessary due to a less than ideal telephone line. The bigger the delay, the bigger the
data block size, allowing better error correction to be performed.
Transmit Power
This is the upstream and downstream far end actual aggregate transmit power (in dBm).
Upstream is how much power the port is using to transmit to the service provider.
Downstream is how much port the service provider is using to transmit to the port.
Receive Power
Upstream is how much power the service provider is receiving from the port. Downstream
is how much power the port is receiving from the service provider.
Actual INP
Sudden spikes in the line’s level of external noise (impulse noise) can cause errors and
result in lost packets. This could especially impact the quality of multimedia traffic such as
voice or video. Impulse noise protection (INP) provides a buffer to allow for correction of
errors caused by error correction to deal with this. The number of DMT (Discrete Multi-
Tone) symbols shows the level of impulse noise protection for the upstream and
downstream traffic. A higher symbol value provides higher error correction capability, but it
causes overhead and higher delay which may increase error rates in received multimedia
data.
Total Attenuation
This is the upstream and downstream line attenuation, measured in decibels (dB). This
attenuation is the difference between the power transmitted at the near-end and the power
received at the far-end. Attenuation is affected by the channel characteristics (wire gauge,
quality, condition and length of the physical line).
Attainable Net
Data Rate
These are the highest theoretically possible transfer rates at which the port could send and
receive payload data without transport layer protocol headers and traffic.
xDSL Counters
Downstream
These are the statistics for the traffic direction coming into the port from the service
provider.
Upstream
These are the statistics for the traffic direction going out from the port to the service
provider.
FEC
This is the number of Far End Corrected blocks.
CRC
This is the number of Cyclic Redundancy Checks.
Table 106
Status > xDSL Statistics (continued)
LABEL
DESCRIPTION
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