Riverstone Networks WICT1-12 - Manual (Page 611)

Riverstone Networks RS Switch Router User Guide Release 8.0 30-7
WAN Configuration Frame Relay Overview
Congestion Management
One of the most important features of configuring the RS to ensure Quality of Service is the obvious advantage gained
when you are able to avoid network congestion. The following topics touch on a few of the most prominent aspects of
congestion avoidance when configuring the RS.
Random Early Discard (RED)
Random Early Discard (RED) allows network operators to manage traffic during periods of congestion based on
policies. RED works with TCP to provide fair reductions in traffic proportional to the bandwidth being used. Weighted
Random Early Discard (WRED) works with IP Precedence or priority, as defined in the
qos
configuration command
line, to provide preferential traffic handling for higher-priority traffic.
The CLI commands related to RED in both the Frame Relay and PPP protocol environments allow you to set maximum
and minimum threshold values for each of the low-, medium-, and high-priority categories of WAN traffic.
Adaptive Shaping
Adaptive shaping implements the congestion-sensitive rate adjustment function and has the following characteristics:
• No blocking of data flow under normal condition if the traffic rate is below Bc+Be.
• Reduction to a lower CIR upon detection of network congestion.
• Progressive return to the negotiated information transfer rate upon congestion abatement.
The CLI command related to adaptive shaping allows you to set threshold values for triggering the adaptive shaping
function.
30.3 FRAME RELAY OVERVIEW
Frame relay interfaces are commonly used in a WAN to link several remote routers together via a single central switch.
This eliminates the need to have direct connections between all of the remote members of a complex network, such as
a host of corporate satellite offices. The advantage that Frame Relay offers to this type of geographic layout is the
ability to switch packet data across the interfaces of different types of devices like switch-routers and bridges, for
example.
Frame Relay employs the use of Virtual Circuits (VCs) when handling multiple logical data connections over a single
physical link between different pieces of network equipment. The Frame Relay environment, by nature, deals with
these connections quite well through its extremely efficient use of precious (sometimes scarce) bandwidth.
You can set up frame relay ports on your RS with the commands described in the Riverstone RS Switch Router
Command Line Interface Reference Manual.
30.3.1 Virtual Circuits
Think of a Virtual Circuit (VC) as a “virtual interface” (sometimes referred to as “sub-interfaces”) over which Frame
Relay traffic travels. Frame Relay interfaces on the RS use one or more VCs to establish bidirectional, end-to-end
connections with remote end points throughout the WAN. For example, you can connect a series of multi-protocol
routers in various locations using a Frame Relay network.