Specifications

D-Link xStack Switch Series: Meeting the Need at the Edge of the Network 14
D-Link Systems, Inc.
October 2004
xStack Technology Overview
The D-Link xStack technology provides an innovative new method for collectively utilizing the
capabilities of a stack of switches. Individual switches intelligently join to create a single
switching unit. Configuration and routing information is shared by every switch in the stack,
creating a single switching unit. Switches can be added and deleted from a working stack without
affecting performance.
The Stack Interconnect Functionality
D-Link xStack Technology unites up to twelve individual D-Link xStack switches into a single
logical unit, using special stack interconnect cables and stacking software. The stack behaves as
a single switching unit that is managed by a master switch elected from one of the member
switches. The master switch automatically creates and updates all the switching and optional
routing tables. A working stack can accept new members or delete old ones with minor service
interruption.
Bidirectional Flow—Fail-Safe Ring-Stacking
A key differentiator for xStack Switches is their resilient stacking feature. xStack Switches can
stack up to 12 units with a cascade stacking design, assuring continuous uptime even if a single
switch in the stack should fail. A loop-back or cascade cable is used to seamlessly connect the
entire stack to provide no single point of failure. In the unlikely event of a switch failure, traffic
performance is maintained at 20Gbps on the immediate units on either direction of the failed unit
via a ‘wrapping’ method; the remaining units in the stack continue to send traffic bi-directionally
at full bandwidth capability of 40Gbps per switch. When a break is detected in a cable, the traffic
immediately loops back across the single remaining 20Gbps path to continue forwarding.
Whenever a frame is ready for transmission onto the path, a calculation is made to see which
path has the most available bandwidth. The entire frame is then copied onto this half of the path.
Traffic is serviced depending upon its class of service (CoS) or differentiated services code point
(DSCP) designation. Low latency traffic is given priority.
1. Number of units in a stack may vary depending of xStack model