ZyXEL Communications SAM1316-22, User Manual

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Chapter 14 xDSL Profiles Setup
SAM1316-22 User’s Guide
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at time B. If the next cell arrives earlier than time C, it is discarded or tagged for
not complying with the TAT. Time C is calculated based on the CDVT or BT.
Figure 54 TAT, CDVT and BT in Traffic Shaping
14.6 Upstream Policing
Upstream policing is an agreement between the carrier and the subscriber to
regulate the average rate and fluctuations of data transmission coming from the
subscriber's device to the SAM1316-22.
Note: Upstream policing controls incoming (upstream) traffic, not outgoing
(downstream).
The ATM traffic classes and parameters are identical with downstream shaping.
Upstream policing can control the upstream incoming traffic rate on specific PVCs.
Upstream ATM cell traffic that violates the policing profile will be discarded. Traffic
shaping must also be enabled on the subscriber's device in order to use upstream
policing. If a subscriber attempts to enlarge his device's PVC shaping parameters
in order to get more upstream traffic bandwidth, it will violate the SAM1316-22's
upstream policing profile and the traffic will be discarded. Operators can use this
feature to prevent subscribers from changing their device settings.
Note: Traffic shaping must also be enabled on the subscriber's device in order to use
upstream policing.
Note that since the SAM1316-22 uses ATM QoS, if the subscriber device's
upstream shaping rate is larger than the SAM1316-22's upstream policing rate,
some ATM cells will be discarded. In the worst case, none of the Ethernet packets
from the CPE will be able to be reassembled from AAL5, so no packets from the
subscriber's device can be received by the SAM1316-22.
The upstream policing feature can be enabled/disabled per PVC. No matter which
ATM traffic class is used for the PVC's upstream traffic (CBR, VBR, or UBR), the
SAM1316-22 will drop any upstream traffic that violates the specified ATM VC
profile.