Enterasys Networks 2E253 Manual Do Utilizador

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.

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.

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 SmartSwitch 6000 chassis in each wiring closet and 
interconnected with SmartSwitch Routers using Gigabit Ethernet links. Also, assume that 100 
users are attached to each SmartSwitch 6000 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.)

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.