5, according to one study [4]. Further, the distributed
bandwidth provides a resource for the operator to provision a higher burst data
rate for a customer than the nominal sustained data rate that the customer is allowed.
This is controlled via the token-bucket rate-limiting algorithm, in which the operator can
provision a customer with a burst size (in bytes) for which data can be sent and received
at up to the line rate (e.g., 38 Mbps down, 30 Mbps up) and with a maximum sustained
rate that applies to the long-term average for transmissions.
Layer 2 Virtual Private Networks
As part of the Business Services over DOCSIS family of specifications [2], CableLabs
has developed a specification detailing a feature package that enables standardized
configuration and management of Layer 2 virtual private networks (L2VPNs) that
overlay the cable data network. These L2VPNs can coexist easily with other broadband
data service offerings including residential broadband data service and VoIP telephony.
This optional extension to standard DOCSIS equipment contains requirements on the
CM and CMTS that ensure isolation of L2VPNs from one another as well as from the
traditional (non-L2VPN) data customer traffic.
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