Table of Contents
Advertisement
Magnum 10KG Managed Switch Installation and User Guide
Packet Prioritization, 802.1p QOS
4.4
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 10KG can do its part to prevent any QOS degradation while it is handling
Ethernet traffic through its ports and internal switch buffers.
The Magnum 10KG 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.
4.5
Frame Buffering
Magnum 10KG'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
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 is that more bandwidth is available for good packets when the traffic load is
greatest.
When the Magnum 10KG 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 it packets to cause "flow control". This tells the sending devices to temporarily
stop sending traffic, which allows the traffic to catch-up 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 Magnum 10KG 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 more frames from
entering by forcing a collision signal on all receiving half-duplex ports in order to stop
incoming traffic.
www GarrettCom com
.
.
30
07/12
Hide quick links:
Advertisement
Table of Contents
