B+B SmartWorx IE-MultiWay User Manual page 27

Egress Traffic
Shaping
OSI Level Used in
Calculations
(Open Systems
Interconnect -
referring to the seven
layers for TCP/IP)
Unit Rate Control
Enable/Disable
*OSI NOTE: The Bandwidth Limit functions can be adjusted to only count the Layer 1, 2, or
3 portions of the physical line rate. Layer 1 is used to relate Bandwidth to the physical line
rate where a 100BaseT Ethernet line can carry a MAX bandwidth of 100Mbps. Layer 2 may
be more useful when the Ethernet Frame may be carried over several different physical
protocols such as SONET or SDH. Only the bandwidth required by the Ethernet frame is
counted, making this a more consistent number over different protocols. Layer 3 counting
could be used when a relationship to the actual customer data or line payload is required. If
a 10 Mbps customer file needs to be sent in one second, then a minimum bandwidth limit of
10Mbps would need to use Layer 3 counting to allow this.
It must be noted that only Layer 1 counting is not affected by the size of the Ethernet frame.
At 64 -yte Ethernet frames, the MAX bandwidth the line can support at Layer 2 is only
76.2% of the line rate. This maximum falls to 54.8% of the line rate when counting is further
limited by only counting Layer 3 payload data.
Actively controls the transmitter and hard limits the
maximum frame rate that can be sent. Frames can be
delayed in the internal buffers of the unit, waiting their turn
to be sent. If the internal buffers are full, excess traffic will
be dropped. The Unit Rate Control can be used to alleviate
this.
Choose Layer 1, 2 or 3 for the counter, this will determine
how my bytes from the Ethernet frame are to be included in
the calculations.
Layer 1: Preamble + DA to CRC + IFG
Layer 2:
Frames DA to CRC
Layer 3:
Frames DA to CRC – 18
(- 4 if frame is tagged)
Explanations:
Preamble: 8 bytes
DA:
EtherNet Destination Address
CRC: EtherNet Checksum
IFG: 12 bytes
Allows the end user to globally configure all Bandwidth
settings when enabling Unit Rate Control (Flow Control). If
the END device connected to the port also has Flow
Control enabled, this ensures packets will not be dropped.
27
-MultiWay
IE