WATERS NETWORK SYSTEMS
ProSwitch-Xtreme Operating Manual
Page 3
Thermal design enables the ProSwitch-Xtreme to be used in uncontrolled temperature applications.
The ProSwitch-Xtreme’s advanced thermal packaging with rugged 18-gauge high steel enclosures used as a
heat sink is designed specifically for temperatures in sensitive applications such as portable classroom trailers,
roadside traffic data collection and control stations, underground vaults or mines, high temperature industrial plant
locations, ceiling locations in warehouses, and military field operations sites.
MTBF over 15 years, per Bellcore calculation method
for MTBF details.
2.1
Fiber Port, SC Connectors
The Fast Ethernet fiber switched ports on the ProSwitch-Xtreme operate at fixed 100Mbps speed and full-
duplex mode for the best performance. The ProSwitch-Xtreme’s fiber ports are factory-built as either multimode or
singlemode SC connectors. A yellow label on the fiber port connector will indicate if it is singlemode, otherwise it is a
multimode port. Each of the 100Mbps fiber ports are switched and perform as a domain, providing a high bandwidth
backbone connection and supporting long (up to 20km singlemode) fiber cable distances for installation versatility.
On ProSwitch-Xtreme units, there are three LED’s for each of the RJ45 switched ports. The F/H indicates full-
duplex when ON; and half-duplex when it is OFF. One (LK/ACT) is steady ON to indicate LINK, and blinking indicates
the port is transmitting/receiving. The 10/100 LED is ON for 100Mbps and OFF for 10Mbps (when LINK is made).
For fiber ports, the LEDs are the same except no F/H (and 10Mbps is not available).
A device must be connected to the other end of a port’s cable and a proper link (LK lit) must be made with the
device at the other end of the cable in order for each LINK LED to provide a valid indication of operating conditions.
2.2
Frame Buffering and Latency
The ProSwitch-Xtreme is a store-and-forward switch. Each frame (or packet) is 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 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, 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 ProSwitch-Xtreme 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 ProSwitch-Xtreme 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, the ProSwitch-Xtremes are constantly
adapting internally to provide maximum network performance with the least dropped packets.
When the ProSwitch-Xtreme 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 sequence occurs in a small fraction of a second
and is transparent to an observer.
Another feature implemented in the ProSwitch-Xtreme is a collision-based flow-control mechanism (when
operating at half-duplex only). When the switch detects that its free buffer queue space is low, the switch prevents
more frames from entering by forcing a collision signal on all receiving RJ45 half-duplex ports in order to stop
incoming traffic.
The latency (the time the frame spends in the switch before it is sent along or forwarded to its destination) of
the ProSwitch-Xtreme varies with the port-speed types, and the length of the frame is a variable, as it is with all store-
and-forward switches. For 10Mbps-to-10Mbps or 10Mbps-to-100Mbps or 100Mbps-to-10Mbps forwarding, the latency
is 15 microseconds plus the packet time at 10Mbps. For 100Mbps-to-100Mbps forwarding, the latency is 5
microseconds plus the packet time at 100Mbps.
