Cabletron Systems STS16-20D, STS16-20R manual Transmission Priority Queues, ClearSession Support

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Transmission Priority Queues

To address the needs of delay-sensitive data, such as multimedia, the Token Ring ports of the SmartStack STS16-20D/STS16-20R have two transmit queues, a high- priority queue and a low-priority queue.

The queue for a frame is determined by the value of the priority field in the frame control (FC) byte. If FC priority is above a configurable level (default 3), the frame is put into the high-priority queue. If an output port becomes congested, you can dynamically configure the port to transmit all frames at high priority regardless of the FC byte contents.

ClearSession Support

The SmartStack STS16-20RM switch family support the ClearSession high availability and network redundancy features.

ClearSession is a framework for mission critical networks. It prevents session loss by providing a network failure recovery time of, typically, less than three seconds. ClearSession consists of a several product features. Some of these, ClearServer, CrossLinks and Dynamic Source Route Recovery, are supported by the CSmartStack STS16-20RM switch family. These features provide the following functionality:

ClearServer. Token-Ring ClearServer for LAN, allow multiple adapters to be treated as one virtual adapter in the server, thus allowing multiple connections between a server and the backbone switch or switches. During normal operation the traffic is distributed on the links. The SmartStack STS16-20RM switch familysupport ClearServer for LAN to be used on servers connected to the switch.

CrossLinks. Any Token-Ring link or dedicated Token-Ring link between SmartStack STS16-20RM family switches may be expanded to a CrossLink. A CrossLink is an aggregation of two to eight identical parallel links, working as one link of the aggregate capacity, providing protection from physical link failure. Should one of the links fail, the traffic is redistributed among the remaining operational links.

Dynamic Source Route Recovery. DSRR is a feature that enables two or more SmartStack STS16-20RM family switches performing source route bridging between a shared-media access ring and a common backbone ring to function as backup for each other. Should one of the switches fail or lose connectivity to one of the access rings, the other switch immediately takes over and bridges source- routed traffic marked with the failed path. DSRR protects source-routed traffic to and from shared access segments, such as user rings, with redundant connections to two Token-Ring switches. Traffic to and from such rings that is non-source- routed relies on the spanning tree.

SmartStack STS16-20D/STS16-20R Token Ring Switches Installation and User Guide Switch Overview