Specifications

ES1008 Operating Manual Page 4
each 100Mbps port and a proper link (LK lit) must be made with the device at the other end of the cable in order for
the LK LEDs to provide valid indications of operating conditions.
2.2 10/100 Dual-speed Switched Ports, RJ45 (Copper)
All ES1008 models have 8 10/100Mbps dual speed switch
ports. The 10/100Mbps switched ports are independently N-way
auto-negotiating (as a default setting), for operation at 10 or
100Mbps in full- or half-duplex mode. They independently move to
half-duplex mode at 10 Mbps or at 100Mbps speed if the device at the other end of the twisted pair cable is half-
duplex or is not an auto-negotiating device.
There are three LED’s for each port. The LK/Act (Link/Activity) steady ON for Link with no traffic and blinking
indicates port is receiving and transmitting. The Speed LED indicates operation at 100Mbps speed when ON and at
10 Mbps speed when OFF (when auto-negotiation is not disabled). The F/H LED is ON to indicate full-duplex
operation and OFF to indicate half-duplex mode. A twisted pair cable must be connected into each RJ45
10/100Mbps port and a proper Link (LK lit) must be made with the device at the other end of the cable in order for
the LEDs to provide valid indications of operating conditions.
Port #1 is equipped with a Media Dependent Interface-Crossover (MDI-X) push-button switch to simplify
cascaded or uplink connections.
2.3 Frame Buffering and Latency
All ES1008 models are store-and-forward switches. 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 a valid
length and have the correct CRC, i.e. 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 connected Ethernet segments. 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 allows
more bandwidth to be available for good packets when the traffic load is greatest.
To minimize the possibility of dropping frames on congested ports, each ES1008 switch dynamically allocates
buffer space from a 1Mbps 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 ES1008 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, the ES1008 switches are
constantly adapting internally to provide maximum network performance with the least dropped packets.
When the ES1008 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 sequence occurs in a fraction of a second and is
transparent to an observer.
Another feature implemented in ES1008 switches 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
1 2 3 4 5 6 7 8
POWER
ERROR
L/A
SPEED
F/H
UPLINK
= X