ES-CUTP and ES-FUTP Manual
Page 5
2.4
Fiber port, ST or SC Connector for the ES-FUTP-8
100Mbps Fiber port:
ST
SC
The Fast Ethernet fiber switched port on the ES-FUTP-8 is set to operate at fixed 100Mbps for
guaranteed high performance. The fiber port is factory-built as either a multi-mode ST, SC, or MTRJ
connector. The 100Mbps fiber port will run at 100Mbps at all times with manually selected full- and half-
duplex capability. The 100Mbps fiber port is a switched port and performs as a domain, providing a high
bandwidth backbone connection (no media converter is required!).
The fiber port has an “F - H” user-selectable manual switch. When set in the “F” position, it
forces full-duplex mode. When set in the “H” position, it forces half-duplex mode, still at 100Mbps speed.
On the ES family of switches, there are three LED’s for the switched ports. One (LK/ACT) is
steady ON to indicate LINK, blinking indicates the port is transmitting and receiving. The SPEED LED is
ON for 100Mbps and OFF for 10Mbps (when LINK is made). The F/H indicates full duplex when ON,
when it is OFF, operation is half duplex.
A fiber cable must be connected to the 100Mbps port and a proper link (LK lit) must be made
with the device at the other end of the cable in order for these LEDs to provide valid indications of
operating conditions.
2.5
Frame Buffering and Latency
Waters’ ES switches are store-and-forward, with each frame (or packet) loaded into the switch’s
memory and inspected before forwarding can occur. This technique ensures that all forwarded frames
are of a valid length and have the correct CRC, i.e., are good packets. This eliminates the propagation
of bad packets, enabling all of the available bandwidth to be used for valid information.
While other switching technologies such as "cut-through" or "express" impose minimal frame
latency, they will also permit bad frames to propagate out to the Ethernet segments connected. The
"cut-through" technique permits collision fragment frames, which are a result of late collisions, to be
forwarded to add to the network traffic. Since there is no way to filter frames with a bad CRC (the entire
frame must be present in order for CRC to be calculated), the result of indiscriminate cut-through
forwarding is greater traffic congestion, especially at peak activity. Since collisions and bad packets are
more likely when traffic is heavy, the result of store-and-forward operation is that more bandwidth is
available for good packets when the traffic load is greatest.
To minimize the possibility of dropping frames on congested ports, each ES switch dynamically
allocates buffer space from a 1MB memory pool, ensuring that heavily used ports receive very large
buffer space for packet storage. (Many other switches have their packet buffer storage space divided
evenly across all ports, resulting in a small, fixed number of packets to be stored per port. When the
port buffer fills up, dropped packets result.) This dynamic buffer allocation provides the capability for the
maximum resources of the switch to be applied to all traffic loads, even when the traffic activity is
unbalanced across the ports. Since the traffic on an operating network is constantly varying in packet
density per port and in aggregate density, Waters’ ES switches are constantly adapting internally to
provide maximum network performance with the least dropped packets.
When the switch detects that its free buffer queue space is low, the switch sends industry
standard (full-duplex only) PAUSE packets out to the devices sending packets to cause “flow control”.
This tells the sending devices to temporarily stop sending traffic, which allows a traffic catch-up to occur
without dropping packets. Then, normal packet buffering and processing resumes. This flow-control
Tx Rx
F
H
= X
UPLINK
Tx Rx
F
H
= X
UPLINK
F
H
