Cabletron Systems Expansion module 9H532-17, Руководство пользователя

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Local Management: Overview, Setup, and Navigation
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More About Rate Limiting
Rate Limiting enables Service Providers in Multi-Dwelling-Unit (MDU) and
similar environments wishing to offer varied bandwidth to customers using low
cost 10 Mbps Ethernet or other type of physical connection. Another solution, for
the enterprise, is to provide high priority bandwidth on the network for
guaranteed service level agreements.
In Multi-Dwelling Unit (MDU) or similar environments, the Rate Limiting feature
can be activated per port to adjust the usable bandwidth on a 10 Mbps Ethernet or
other type of physical connection. In residential housing, the service provider
may offer multiple Internet service packages, each offering different bandwidth at
a different price. These offerings can be supported using low cost 10 Mbps
Ethernet ports wired to each dwelling.
In the enterprise network, this feature (combined with Layer 3/4 prioritization)
can provide guaranteed delivery of high priority traffic through a congested
network fabric. This is accomplished through the construction of a committed
information rate (CIR) fabric within the traditional best effort enterprise LAN
fabric.
Example
This is a simple example intended to show how the Rate Limiting feature can be
applied to solve a problem.
Assume that a network built using SmartSwitch 9000 chassis in the wiring closets
are interconnected with SmartSwitch Routers using gigabit Ethernet links. Also
assume that 100 users are attached to each SmartSwitch 9000 chassis through
100 Mbps Ethernet ports. If each user attempted to transfer data out of the wiring
closet at the maximum possible rate, there could be up to 10 Gbps (100 users x
100 Mbps) of traffic attempting to leave the chassis over a single gigabit link. In
this situation, much of the traffic will be arbitrarily dropped.
Now assume that the system administrator wants to guarantee the delivery of
Service Access Point SAP R/3 traffic by prioritizing it above all other incoming
traffic to the chassis. Unless the inbound rate of the SAP traffic can be controlled,
the guarantee still cannot be made because of the potential for oversubscription of
the outbound gigabit link by high priority traffic.
When allocating the maximum rate per port, the maximum bandwidth of the
uplink must be kept in mind. For example, if the ports are all set to 10 Mbps and
there are 24 ports, this equals 240 Mbps of bandwidth. If the uplink is only
100 Mbps, there is an obvious problem if the network administrator guaranteed
more bandwidth than the uplink can support.
NOTE