Instruction manual

MULTILINK MC-E10 & MC-E100 CONVERTER SWITCH
MULTILINK ML2400 ETHERNET COMMUNICATIONS SWITCH – INSTRUCTION MANUAL 7
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 Multilink MC-E10
& MC-E100 Converter dynamically allocates buffer space from 128Kb 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 Multilink MC-E10 & Multilink MC-E100 units 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 Multilink MC-E10 & MC-E100 Converters 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, it 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 Multilink MC-E10 & Multilink MC-E100 Series Converters 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, it prevents more frames from
entering by forcing a collision signal on all receiving half-duplex ports in order to stop
incoming traffic.
The latency (the time the frame spends in the Converter before it is sent along or
forwarded to its destination) of the Multilink MC-E10 & Multilink MC-E100 Converter varies
with the port-speed types. The length of the frame is a variable here as it is with all store-
and-forward switches. For 10 Mb-to-10 Mb or 10 Mb-to-100Mb or 100Mb-to-10 Mb
forwarding, the latency is 15 microseconds plus the packet time at 10 Mb. For 100Mb-to-
100Mb forwarding, the latency is 5 microseconds plus the packet time at 100Mb.