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Switch Overview SmartStack STS16-20D/STS16-20R Token Ring Switches Installation and User Guide
CrossLink Connections
Two or more Token-Ring ports can be configured to comprise a CrossLink.
A CrossLink is a collection of identical parallel links between two switches or
between a switch and an end node, aggregated to appear as one single link of the
aggregate capacity. The traffic distribution mechanism attempts to balance the load
on the individual links. If one of the links in a CrossLink fails, the traffic is
automatically moved from this link and distributed among the other links, thus
providing active resilience.
The CrossLink ports on a STS16-20x switch can be used to connect to another
STS16-20x switch, or a server with multiple RapidFire adapters using ClearServer
for Token-Ring. (Please note that ClearServer for Token-Ring is supported on
selected models of RapidFire adapters only. For details, refer to the ClearServer for
LAN product information.)
The CrossLinks provide load distribution as well as resilience. In normal operation,
the traffic is distributed on the physical ports of the CrossLink according to the
frame MAC addresses. This ensures the sequence of a flow. Should a link fail or
otherwise become inoperative, the switch dynamically redistributes the traffic to
the remaining links. The CrossLink remains in operation as long as there is at least
one link in operation. If a failed link is restored, traffic is once more redistributed
to make use of the restored link.
A CrossLink is in many ways operating as one single link. For example, the
spanning tree protocol will only have one port entity covering all ports in the
CrossLink. The ports will all have the same operating state. As for VLAN and CRF
configuration, the CrossLink is also seen as one link. Configuration changes apply
to all links in the CrossLink.
On the STS16-20/RM/STS16-20FRM switch, CrossLinks can also be configured
on the High-Speed Token-Ring ports of the SSIM-R2-02/SSIM-R8-02 High Speed
Token Ring SmartStack modules or on the Fast Ethernet ports of the SSIM-H2-02
Fast Ethernet -Translational Switch SmartStack module. CrossLinks on Fast
Ethernet ports can only consist of two ports available on the same SSIM-H2-02 Fast
Ethernet -Translational Switch SmartStack module.
The CrossLink concept is designed to be compatible with the coming Link
Aggregation standard, IEEE 802.3ad.
On SmartStack STS16-20D only the network ports 17–20 will allow CrossLinks.
On this switch you can achieve up to 128 Mbps using four ports. On the SmartStack
STS16-20R up to 256 Mbps can be achieved, using eight ports.
The STS16-20/RM/STS16-20FRM switch allows up to eight CrossLinks, each
consisting of up to eight Token-Ring links.