Cabletron Systems SmartSwitch manual Frame Relay Overview, Virtual Circuits, Adaptive Shaping

Chapter 22: WAN Configuration Guide

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.

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 SSR with the commands described in Chapter 15: “frame-relay Commands” in the SmartSwitch Router Command Line Interface Reference Manual.

Virtual Circuits

You can 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 SSR 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.

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