Magnum 10ETS / 10XTS Installation and User Guide
06/12
34
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General information -
Auto-negotiation per-port for 802.3u-compliant switches occurs when:
-- the devices at both ends of the cable are capable of operation at either
10Mb or 100Mb speed and/or in full- or half-duplex mode, and can
send/receive auto-negotiation pulses, and . . .
-- the second of the two connected devices is powered up*, i.e., when
LINK is established for a port, or
-- the LINK is re-established on a port after being lost temporarily.
•
NOTE
–
Some NIC cards only auto-negotiate when the computer system
that they are part of is powered up. These are exceptions to the “negotiate at
LINK – enabled” rule above, but may be occasionally encountered.
When operating in 100Mb half-duplex mode, cable distances and hop-counts
may be limited within that collision domain. The Path Delay Value (PDV) bit-times must
account for all devices and cable lengths within that domain. For Magnum 10ETS/XTS
Fast Ethernet switched ports operating at 100Mb half-duplex, the bit time delay is 50BT.
4.3
Packet Prioritization, 802.1p QOS
Quality of Service (QOS) means providing consistent predictable data delivery
to users from datagram paths that go all across a network. As a LAN device, the
Magnum 10ETS/XTS can do its part to prevent any QOS degradation while it is handling
Ethernet traffic through its ports and internal switch buffers.
The Magnum 10ETS/XTS switching hardware supports the IEEE 802.1p
standard, and fulfills its role in support of QOS, giving packet processing priority to
priority-tagged packets according to the 802.1p standard. In addition to hardware
support for QOS, the MNS software supports four priority queues that can be shared
across the eight levels of defined packet priorities for application-specific priority control
by the user through software configuration settings.
4.4 Frame
Buffering
Magnum 10ETS/XTS’s 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 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 which add to the network
traffic. Since there is no way to filter frames with a bad CRC (the entire frame must be