Overview
Introduction 1-5
1.1.9 Traffic Rate Limiting
The Rate Limiting feature enables the SmartSwitch device to have control over traffic rates on a
per-port, per-priority basis. The network administrator can configure a rate limit (from 100 kbps to
1 Gbps) for a given port with an associated list of IEEE 802.1p priorities (which can include one,
some, or all of the eight priority levels defined in 802.1p). Each rate limit is specified as an
inbound or an outbound limit. The combined rate of all traffic on the port that matches the listed
priorities cannot exceed the programmed limit. If the rate exceeds the defined limit, frames are
dropped until the rate falls below the limit.
Administrators can configure up to four rate limit rules per port; however, each rule must not
include conflicting 802.1p priority values. In order to control traffic inbound and outbound on the
same port, two rate limit rules must be configured (one inbound and one outbound). Since the rate
limiting operation occurs after the processing of the multi-layer classification rules, the two
features can be combined to provide application-aware rate limiting.
For more information about the application of rate limiting, refer to SmartSwitch Series 2E253,
2H252, 2H253, and 2H258 Local Management User’s Guide.
1.1.10 Flow Control
Flow control is a method of managing the flow of frames between two devices. It ensures that a
transmitting device does not overwhelm a receiving device with data. This is accomplished by the
transmitting device pausing its transmission while the receiving device processes the frames
already received.
The 2E253-49R supports the following two types of flow control:
•Frame based 802.3x
•Back pressure
Frame based 802.3x flow control is supported on all Ethernet ports operating in the full duplex
mode. Flow control can be enabled or disabled on a port-by-port basis.
Back pressure flow control is supported on all Ethernet ports operating in the standard mode of
operation. Flow control can be enabled or disabled on a port-by-port basis.
NOTE This rate limiting function is not supported on ports connected to SmartTrunk ports.