GarrettCom 6K16V manual Packet Prioritization, 802.1p QOS, Frame Buffering and Flow Control

Magnum 6K16V Managed Fiber Switch Installation and User Guide (06/04)

The 1000Mb Gigabit fiber-port modules on the Magnum 6K16V are normally set (factory default) to operate in full-duplex mode for best fiber distance and performance. The 1000Mbps SC fiber-optic module on the Gigabit -SX and Gigabit-LX transceivers are compatible with the IEEE 802.3z Gigabit standards.

There are two LEDs mounted on each Gigabit port module. The Gigabit fiber port is fixed at 1000Mbps speed full-duplex mode at all times and has LEDs that indicate LK (Link status) and ACT (receiving activity) on that port when lit.

2.2.6Packet Prioritization, 802.1p QOS

Quality of Service means providing consistent predictable data delivery to

users from datagram paths that go all across a network. As a LAN device, the Magnum 6K16V can do its part to prevent any QOS degradation while it is handling Ethernet traffic through its ports and buffers.

The Magnum 6K16V 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 (R2) supports two 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.

2.2.7Frame Buffering and Flow Control

Magnum 6K16V’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

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