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Rate Limiting Configuration Screen
9.8.3
More About Rate Limiting
Rate Limiting enables Service Providers in Multi-Dwelling-Unit (MDU) and similar environments
to offer varied bandwidth to customers using low cost Ethernet connections. Another solution for
the enterprise, is to provide high priority bandwidth on the network for guaranteed service level
agreements.
NOTE: 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.
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 was built using a 6C105 chassis in each closet and interconnected with
Enterasys Networks switch routers using Gigabit Ethernet links. Also, assume that 100 users are
attached to each 6C105 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 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 inbound gigabit link by high priority traffic.)
9-44
802.1p Configuration Menu Screens
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