How It Works; Derived Rates - Cisco WS C4224V 8FXS - 200Mbps Ethernet Switch Software Configuration Manual

Frame Relay Traffic Shaping

How It Works

Derived Rates

Catalyst 4224 Access Gateway Switch Software Configuration Guide
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Using FRTS, you can configure rate enforcement to either the CIR or some other
defined value such as the excess information rate on a per-VC basis. The ability
to allow the transmission speed used by the router to be controlled by criteria
other than line speed provides a mechanism for sharing media by multiple VCs.
You can allocate bandwidth to each VC, creating a virtual time-division
multiplexing (TDM) network.
You can also define PQ, CQ, and WFQ at the VC or subinterface level. Using
these queueing methods allows for finer granularity in the prioritization and
queueing of traffic, providing more control over the traffic flow on an individual
VC. If you combine CQ with the per-VC queueing and rate enforcement
capabilities, you enable Frame Relay VCs to carry multiple traffic types such as
IP, SNA, and Internetwork Packet Exchange (IPX) with bandwidth guaranteed for
each traffic type.
Using information contained in the BECN-tagged packets received from the
network, FRTS can also dynamically throttle traffic. With BECN-based
throttling, packets are held in the buffers of the router to reduce the data flow from
the router into the Frame Relay network. The throttling is done on a per-VC basis
and the transmission rate is adjusted based on the number of BECN-tagged
packets received.
With the Cisco FRTS feature, you can integrate ATM ForeSight closed-loop
congestion control to actively adapt to downstream congestion conditions.
In Frame Relay networks, BECNs and FECNs indicate congestion. BECN and
FECN are specified by bits within a Frame Relay frame.
FECNs are generated when data is sent out a congested interface; they indicate to
a DTE device that congestion was encountered. Traffic is marked with BECN if
the queue for the opposite direction is deep enough to trigger FECNs at the current
time.
BECNs notify the sender to decrease the transmission rate. If the traffic is
one-way only (such as multicast traffic), there is no reverse traffic with BECNs
to notify the sender to slow down. Thus, when a DTE device receives an FECN,
it first determines if it is sending any data in return. If it is sending return data,
Chapter 10 Traffic Shaping
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