Magnum P62-Series Hardened Switches | Installation and User Guide (12/02) |
To minimize the possibility of dropping frames on congested ports, each Magnum P62- Series Hardened Switch dynamically allocates buffer space from an 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 Magnum P62-Series unit 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 Magnum P62-Series Hardened Switches are constantly adapting internally to provide maximum network performance with the least dropped packets.
When the P62-Series 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 small fraction of a second and is transparent to an observer. See Section 4.6 for additional details.
Another feature implemented in Magnum P62-Series Hardened Ethernet 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 Hardened Switch prevents more frames from entering by forcing a collision signal on all receiving RJ-45 half-duplex ports in order to stop incoming traffic.
The latency (the time the frame spends in the Hardened Switch before it is sent along or forwarded to its destination) of the P62-Series Hardened Ethernet Switch varies with the port- speed types, and 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 10Mb. For 100Mb-to-100Mb forwarding, the latency is 5 microseconds plus the packet time at 100Mb.
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