Paradyne BitStorm 2400, Руководство пользователя

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1. BitStorm 2400 Overview
2400-A2-GB20-10 December 2002
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EtherLoop
EtherLoop, like Ethernet, is a “burst-mode” technology – it transmits only when
there is information to send. In contrast, conventional copper access technologies
maintain constant signal, regardless of whether or not there is information to send.
Because EtherLoop is not always transmitting, it has the opportunity to “listen” to
the loop. Each EtherLoop-based modem has built-in Spectrum Manager™. This
innovative feature measures the spectral environment of the loop, analyzes the
results, and identifies potential interference. Because EtherLoop is agile in
frequency, the modem can adjust its frequency away from the interference source.
Based on this unique patented capability, EtherLoop can be deployed without
restriction in accordance with ANSI T1.417 Spectrum Management standard.
Data Rate Limiting
Data Rate Limiting allows service providers to offer various levels of service to
subscribers. Each discreet level of service translates into an
upstream/downstream maximum data rate (MDR) and maximum burst (MB)
values. Service levels can be offered in units of 64 kbps steps of upstream or
downstream bandwidth.
Maximum upstream/downstream burst limits shall be provisioned as the maximum
number of bytes that may be transmitted in a burst of traffic before the rate limiting
will take effect. Maximum burst size should typically be some multiple of the
respective MDR value. Example: A user who has a downstream MDR of 512 kbps
could be allowed a maximum burst size of 192 kbps (MB = 3 * MDR/second). The
aggregate upstream and downstream MDRs should not exceed the actual
bandwidth available on the EtherLoop circuit. SNMP traps may be set to monitor
EtherLoop line rates that fall below specified rate limit.
Token Bucket
Data Rate Limiting is set up using SNMP software, such as StormTracker EMS. It
is implemented by a Token Bucket mechanism on the transmit scheduler. The
Token Bucket will be a counter representing the number of “in policy” bytes of data
that may be transmitted. Tokens will be added to the bucket at the rate of MDR/8
per second.
The Token Bucket will have a maximum value (size) equal to the MB parameter.
Tokens will be added to the bucket until the point that the MB value has been
reached. Once the bucket is “full” the refresh tokens will overflow and not
accumulate in the bucket.
Frames will be admitted to the transmit queue only if there are enough tokens
available in the bucket based on the byte length of the frame to be transmitted.
Tokens will be removed from the bucket as frames are passed to the output queue.
“Out of Policy” frames (frames for which there are insufficient tokens available)
arriving at the transmit process will be dropped.